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Discussion Starter · #1 ·
Had mostly resolved my FI issues last year except for that lingering bucking happening whenever the car was sitting still for a week unused. It will only stutter when under load and it would usually go away after a few hard accelerations once car was warmed up. Spark plugs were replaced late in the summer, which seemed to improve the run and reduced bucking. They were slightly fouled so I was thinking either the injectors could maybe be leaking when still or were a bit clogged up/lazy and once enough fuel was going through, it was making the issue go away...

I still had the original Bosch green/blue injectors from 1971 so I ordered a set of the equivalent Beck and Arnley ones. Made the swap and now the car has a slightly bouncy idle, whereas it did not before. On warm engine, loosening the idle screw under the intake opening helped somewhat but not much. Idle was still irregular even if RPM was going up. Even had some minor pinging when opening up the throttle on idle. Never had that. Is there something I should be adjusting with the new injectors in?

Tried a run around the street and the car was running terribly. Was bucking even worse than ever before. Pinging quite a lot under load too. Barely made it back. Double checked that all the injectors plug were well inserted (connected peg is slightly different on the beck n arlney so I made sure they were in. Tried with one fully off, car wouldn't even fire up, so I get that they are all firing...

Now back to the FuPu...Checked the fuel pressure, holds 20 psi with the pump switched on. And on idle was a steady 29-30 PSI. When opening throttle, it drops irregularly in the 24-26 range and bounce back up (assuming this is normal instantly after opening throttle?). Fuel filter has about 5k miles on it. As far as I know this is the original FuPu as well. Should I be repacing it?

Any way to check/reset the ECU unit knob to stock position? I had played a bit with it last year as I thought the car was running rich (fouled plugs). But it might have been caused by bad injectors?

Any idea on the FuPu behavious/testing or the beck and arnley injectors experience?
 

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Discussion Starter · #2 · (Edited)
Actually just took out again the plugs to verify, they are very black with a lot of soot... Cleaned them up. Runs nicer on idle, but after 20 mins idling, they are black again... Should I be changing the ECU adjustment on this finding? Where should the ECU idle mixture knob normally sit? Middle of the run?

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Discussion Starter · #3 ·
Oh well... So much for having a "volvo specialist" last year to adjust the TPS, while also providing them with the D-Jet service manual...
As I found out, the TPS lower contact was not even touching, leading to permanent enrichment I assume. Likely it was the cause for the fouled plugs, and causing over enrichment on acceleration. Strange that the issue would go away after a few hard acceleration (maybe after a while the plugs cleaned themselves enough to cope with the extra fuel?)

Maybe the old injector had obstruction/muck internally reducing the available fuel, making somewhat good use of the over enrichment...

I've temporarily adjusted the TPS so that the lower contact barely touches as per adjustment instructions in the manual. Will ensure tomorrow that the throttle stop is properly set up too. Hopefully this solves all bucking issues!

In the meantime, any insight on where the ECU rheostat knob should sit by default? middle?

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First off, I can't help you with the D jet controller adjustment screw because I sold my controller to a friend with a P 1800E as a back up for his in case it ever crapped out.

When you mentioned bouncy idle, my initial reaction was incorrectly set throttle switch. My 1971 142 service manual and the D jet Trouble Shooting guide differ slightly in the TPS set up. My service manual says
  • release lock nut on throttle stop screw and back screw out 2 turns
  • screw in stop screw until it just touches the stop on the throttle valve spindle.
  • turn screw in 1/4 to 1/2 turn and tighten lock nut (trouble shooting manual says 1 turn)
  • connect continuity tester between terminal 17 and 14 on TPS
  • loosen two screws holding the TPS in place and turn switch body clock wise as far as it will go - continuity should read open circuit / infinite ohms
  • slowly turn the switch body CCW until the tester reads closed circuit and then turn 1 deg more (1/2 mark on the scale on the upper attaching screw). Tighten the TPS mounting screws.
  • insert a 0.02" feeler gauge between the stop screw and the stop on the throttle valve spindle. This should open the throttle slightly and cause the continuity tester to go from closed to open. If not, you need to repeat the adjustment.

Make sure that your throttle cable is well lubricated because a sticking cable can screw this adjustment up.

After the TPS is set up, then you can set idle speed with the idle speed screw. You do this with a hot engine and you need to make sure that the auxiliary air regulator is closed (not leaking any air).

When you replace the injectors you should replace the O ring seals around the pintle (nose of the injector) because they will not reseal if they are more than a couple of years old. I use a little silicone grease to help the injector fit into the seal because they are pretty tight.

Ageing B20E/F intake manifolds can be pretty leaky. Air leaks into the manifold do not screw up the fuel mix; but, they make it impossible to set the idle speed correctly. On my B20E, I hooked up my shop vac in reverse to blow into the intake (clamp or block off the MAP sensor so you don't damage it). I then sprayed with a pump bottle of soapy water to find the leaks (all of them). The last leak I tracked down was around the spindle of the throttle plate.

Black spark plugs seems like a fuel mixture issue. How is your air filter? Check the coolant temperature sensor resistance. If the sensor is out of spec this may cause it to go into permanent enrichment warm up causing fouled spark plugs. Do the same with the intake air temperature sensor, although the errors in the intake air temperature measurement do not have the same drastic effect as the coolant sensor.

Fouled spark plugs can be caused by too much fuel pressure, not a lack of fuel pressure.

Check the wiring on all the sensors. On my 1971, the wiring to the sensors and some of the injectors had become hard and brittle and had broken off in places leading to intermittent shorts and mal operation. I had to cut back the engine fuel injection harness and replace a couple of feet of wire and re terminate the plugs.

I have had the BA injectors on my car since 2015 and have had no issue with them. The Bosch D jet plugs fit in them without issue. If you run out of things to check, remove the 4 injectors from the engine; but, leave them connected to the rail and the electrical connectors. Get 4 cups and put them under the injector tips to catch fuel. Turn the ignition on and let the fuel pump pressurize the system and check for drooling injectors.

If you are suffering from pinging, that seems more like an ignition timing issue. If this is a B20E you need to be running 91 octane fuel (R+M/2). Static ignition timing should be set at 10 deg BTDC. If you still suffer from pinging, try reducing the advance a little bit until it goes away. I find that the B20E is most prone to pinging around 2500 - 3500 RPM and about 3/4 throttle.

Your fuel pressure seems iffy. That might be the pump or it might be a dirty fuel filter or the fuel pressure regulator may be past its best before date. However, as long as your plugs are coming out fouled I would be less worried about a lack of fuel. Fix the spark plug fouling and if they are coming out too white then focus on fuel supply problems.

Have you adjusted your valve lash correctly? Don't try and set idle speed until both the lash and the ignition are correctly set.
 

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A lot of great ideas/things to check have been talked about. But have you cleaned and lubricated the points in the bottom of the distributor that control the injectors? For the adjustment screw on your ECU - that is only for idle mixture and does not do anything when the ECU thinks the car is not idling (glad you found a damaged throttle switch) I used to set that screw using an exhaust gas analyzer - to whatever the spec was (~1% co or hc maybe, it's been a long time ago !)

And I guess you have learned that the only person that will be able to fix your car is you - there are very few people with the knowledge (and the desire ) to fix a xx year old car -

If they have the knowledge they are like me and retired. (and still don't desire to fix something that old) If they don't have the knowledge - there are cars out there they make more money on so yours will be avoided (it's all about billed hours unfortunately)
 

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Discussion Starter · #6 · (Edited)
I did not mention, but my distributor was changed to a 123 ignition distributor quite a few years ago. Do you mean under the distributor cap where there is the rotor?

@142 Guy : The Beck and Arnley injectors do not appear to have pintle caps on them. I did use new matching set of seals on them (fat and small one on tip) when installing with a bit of dielectric lubicant. Should I have been moving the pintle caps from the old Bosch injectors?
 

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Discussion Starter · #7 ·
With regard to possible FuPu replacement. Noting that the 3 ports style on the 1971 is NLA. I see most vintage parts sites listing the Bosch #460900 as a replacement (looks like it is from the 240 cars?). Those being 2 ports, what is to be done with the third port hose? Can't seem to find any documentation on the conversion required to the two ports variant.

Those Bosch pumps seem decently priced. I figure it cannot be a bad thing to replace/retire the 51 year old Bosch three port unit...
 

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Dalsim;

...some disjointed notes after reading the thread, which I hope and expect you will be able apply...

...also, your ECU having the Idle CO adjustment knob means a late ('73?) D-Jet, but you should always state year and model and any deviations from stock setup when asking for help (I do see Ign changes, which when set to nominal should not affect of cause your issues).

Knob on (late) ECU only sets the mixture at Idle (so it is not the cause of what does sound like continuous rich running). I believe Green Book covers setting, which might need to be done with an exhaust gas analyzer...then again, when I went to my Dep of Mot Veh, to get my '73 ES inspected, the inspector (a former Volvo mechanic!) simply reached up and tweeked the knob saying (from memory) something like "...they ALL need to be set to two clicks off CCW"...I thought that was rather handy and fortuitous!!

I have not studied the early style TPS in as supergreat a detail as I have the later style, but electrically and functionally they are absolutely the SAME as far as the ECU goes, (only connectors to the outside world are inverted), but connector is keyed, so don't get distracted or confused by this (see: SW-EM D-Jet Idle Adjustment ). The info here is applicable: SW-EM D-Jet Idle Adjustment (17 [idle contact] MUST show continuity to 14 [ground/chassis] when Throttle is fully CW...if it does not, TPS adjustment is called for!) ...and in your picture, the "TPS lower [Idle] contact was not even touching [means the ECU NEVER knew it was at Idle!], leading to permanent enrichment I assume.(I'm not sure about that, because TPS does not do anything but inform ECU that it is at Idle, AND call for enrichment pulses when moving CCW...it does NOT inform ECU of absolute Throttle position, and so does NOTHING at steady Throttle position or when Throttle shaft is turning CW!...at steady Throttle pos, the Manif Press Sensor is the major mixture determining input to ECU!) ". I suggest you first assure TPS is functioning as expected using Ohm meter, then adjust its position on Throttleshaft per procedure...then you should be able to check that off your list, and move on to other troubleshooting...!

...the varying fuel pressure sounds suspicious, and reason for this needs to be ascertained and corrected! Rail pressure MUST remain constant at ALL times FuPu is powered, PERIOD! If you haven't changed FuFi, I'd change it, and inspect what(and how much) the old one has caught (often rust particles from Tank). See: SW-EM Bosch D-Jet Notes

I also agree with 142guy that increased rail pressure will cause a rich condition, but not lowered pressure, so that is due to something else (and Temp Sensor which makes the ECU think engine is still cold is often the cause).

I also recommend checking Injector volume and delivery...I like the safer method (no open fuel being squirted around at high pressure just looking for an ignition source!!) here: SW-EM Bosch D-Jet Notes

Good Hunting!
 

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I did not mention, but my distributor was changed to a 123 ignition distributor quite a few years ago. Do you mean under the distributor cap where there is the rotor?

@142 Guy : The Beck and Arnley injectors do not appear to have pintle caps on them. I did use new matching set of seals on them (fat and small one on tip) when installing with a bit of dielectric lubicant. Should I have been moving the pintle caps from the old Bosch injectors?
Don't move the caps over to the BA injectors. The BA injectors are a disc valve style injector. If you look carefully you will see that it has 3 (or is it 5??) little holes in the injector tip. The Bosch is the old style pintle valve and you can see the tip of the valve mechanism sticking out the end of the injector. I suspect that the plastic caps on the end of the Bosch injectors may be to prevent impact damage to the valve mechanism. The Bosch operate just fine without the caps. If you put the Bosch cap on the BA injector you will screw up the spray pattern from the 3 holes.

Interesting note, I flow tested both the Bosch and BA injectors to confirm the BA injectors were suitable replacements. Despite having 3 holes, the spray pattern of the BA injectors appeared identical to that of the Bosch injectors.
 

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Discussion Starter · #10 ·
Dalsim;

...some disjointed notes after reading the thread, which I hope and expect you will be able apply...

...also, your ECU having the Idle CO adjustment knob means a late ('73?) D-Jet, but you should always state year and model and any deviations from stock setup when asking for help (I do see Ign changes, which when set to nominal should not affect of cause your issues).

Knob on (late) ECU only sets the mixture at Idle (so it is not the cause of what does sound like continuous rich running). I believe Green Book covers setting, which might need to be done with an exhaust gas analyzer...then again, when I went to my Dep of Mot Veh, to get my '73 ES inspected, the inspector (a former Volvo mechanic!) simply reached up and tweeked the knob saying (from memory) something like "...they ALL need to be set to two clicks off CCW"...I thought that was rather handy and fortuitous!!

I have not studied the early style TPS in as supergreat a detail as I have the later style, but electrically and functionally they are absolutely the SAME as far as the ECU goes, (only connectors to the outside world are inverted), but connector is keyed, so don't get distracted or confused by this (see: SW-EM D-Jet Idle Adjustment ). The info here is applicable: SW-EM D-Jet Idle Adjustment (17 [idle contact] MUST show continuity to 14 [ground/chassis] when Throttle is fully CW...if it does not, TPS adjustment is called for!) ...and in your picture, the "TPS lower [Idle] contact was not even touching [means the ECU NEVER knew it was at Idle!], leading to permanent enrichment I assume.(I'm not sure about that, because TPS does not do anything but inform ECU that it is at Idle, AND call for enrichment pulses when moving CCW...it does NOT inform ECU of absolute Throttle position, and so does NOTHING a steady Throttle position or when Throttle shaft is turning CW!...at steady Throttle pos, the Manif Press Sensor is the major mixture determining input to ECU!) ". I suggest you first assure TPS is functioning as expected using Ohm meter, then adjust its position on Throttleshaft per procedure...then you should be able to check that off your list, and move on to other troubleshooting...!

...the varying fuel pressure sounds suspicious, and reason for this needs to be ascertained and corrected! Rail pressure MUST remain constant at ALL times FuPu is powered, PERIOD! If you haven't changed FuFi, I'd change it, and inspect what(and how much) the old one has caught (often rust particles from Tank). See: SW-EM Bosch D-Jet Notes

I also agree with 142guy that increased rail pressure will cause a rich condition, but not lowered pressure, so that is due to something else (and Temp Sensor which makes the ECU think engine is still cold is often the cause).

I also recommend checking Injector volume and delivery...I like the safer method (no open fuel being squirted around at high pressure just looking for an ignition source!!) here: SW-EM Bosch D-Jet Notes

Good Hunting!
- ECU should be original to the car, which is a 1971. I have never changed it in 20 years of ownership, and bought the car with 57k miles. I would assume it is original based on that. I can confirm it has the adjustment knob for idle. Annoying as in my province there is no emission testing requirement, so I do not have access to a CO tester. Google just floods me with home or work safety gas alarms when searching. Found a Gunson G4125 Gastester which seems to do that, but not available anywhere apparently. Any idea on what might do the trick to measure emission alternatively? I might be missing the proper search keyword for it.

- TPS I confirm as you noted that it was enriching the mixture permanently. I'm thinking this is indeed the cause for the fouling of plugs. Car was running well, except a bit high. Was not able to lower it to 900 without it dying. Was running quite well on idle, but only if set to 1200 or so. That was after turning the TPS body CW until there was continuity between 17 and 14. To fully adjust the TPS, I will need to source a replacement screw for the throttle stop. Hoping the local hardware store may have something with matching thread pattern. It took a lot of lubricant and care to remove without snapping it (thank god to that induction heater rod I bought last year!). Philips head pattern was also damaged. Likely from when whoever messed with it many years ago. Locking nut was rusted badly on the screw shank too. I hope this will fully sort the high idle and rich running condition screwing plugs up.

- As for the fuel pump, I'm thinking it cannot hurt to replace it, even just because of its age. It does not appear rusted outside, or leaking from anywhere. It it loud however whenever I have not used the car in a while. I'm thinking the motor in it is starting to stick/seize (just like my blower fan motor) on startup, and once it ran enough, it gets back its power or something... Any thoughts on what changes are needed to accomodate the 2 port-style FuPu when replacing? Is it just removing the "T" connection on the return line and basically plugging the return line into the tank return port direct? Agreed it is counterintuitive that fuel rail pressure would be linked to my plugs issues. But it might explain the hesitation when accelerating once going. Given at that point, the pump is more solicited than at idle. It might we providing enough fuel at idle, but under load, it is showing its age...
 

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With regard to possible FuPu replacement. Noting that the 3 ports style on the 1971 is NLA. I see most vintage parts sites listing the Bosch #460900 as a replacement (looks like it is from the 240 cars?). Those being 2 ports, what is to be done with the third port hose? Can't seem to find any documentation on the conversion required to the two ports variant.

Those Bosch pumps seem decently priced. I figure it cannot be a bad thing to replace/retire the 51 year old Bosch three port unit...
My original Bosch fuel pump developed a leak in 2015; but, it still pumped fine. Not being keen on self immolation, I decided to replace it which was a painful experience. All of the common replacement in-line pumps require a bunch of plumbing bodges to get them to fit and the Airtex pump that VP Autoparts sold me only lasted about 3 -4 months. While trolling around for another replacement I came across the pump for the 1978 - 83 Nissan 280ZX, part # 17011-P7211

It is pretty much a drop in replacement for the later 2 port Bosch pump. The hose fitting sizes and arrangement and the pump diameter and length are identical to the Bosch pump. The only thing that is different is the wiring terminal arrangement - you can no longer use the original 2 pin plug.



It cost me $280 US in 2015 so it was not inexpensive. It is now significantly more expensive. Check around; but, these guys seem to have the lowest price and I think they are the firm that I purchased from in 2015.
OEM NEW 1978-1982 Nissan 200SX 280Z 280ZX Fuel Pump 17011-P7211 17011-P7211 | QuirkParts

Being a 2 port pump, it has an internal by-pass so you just need to block off the over flow line to the tank.

It is not inexpensive; but, being able to mount it in the stock position with no plumbing bodges was worth the extra money for me. Most of the replacement pumps are smaller diameter pumps and require rubber filler strips to hold the pump in the original bracket and they have problems staying put. The Nissan pump has worked reliably since 2015 and is nice and quiet.

I have heard that Nissan licensed (or copied) the Bosch components for the first fuel injection systems on the 280Z. If you look at the injectors and some of the other components they sure look like D jet so it's not s surprise that the pump is an almost exact fit.
 

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Dalsim;

"I'm thinking the motor in it is starting to stick/seize (just like my blower fan motor) on startup "
FuPu is a "wet pump" meaning fuel continuously runs through it cooling and "lubing", so it might be sluggish initially from fuel gum after a 20 year storage, but once going, fuel also serves to flush any gummage away...it also runs full bore at all times, pumping WAY more than called for at Idle.

Assure good electrical supply to Pump! Fuse 5 has been known to have a poor connection - all the way from slight R in series (clean those conical fuse contact areas to shiny metal, and treat with ACZP!), which would serve to drop SOME V, which FuPu would not get and therfore run slower/possibly sluggish, to fully OPEN such that FuPu does not run at all!!) Measure and check V... at Pump!...anything less than power buss V will certainly cause and explain a sluggish FuPu...sort this FIRST! Ref D-Jet Wiring for a '71: SW-EM Bosch D-Jet Notes ...so if your ECU has the Idle CO knob, which I believe only was on '73 possibly '72 ECUs, that suggests it has been changed, just as a sidenote...

...with VPReg regulating the Rail pressure and dumping any fuel beyond immediate demand back to the Tank...frankly, I don't think replacing the FuPu will buy you anything...my position is: If the pump is working (and not leaking, or doing anything else which might be a reason for replacing it), I would concentrate on the constant pressure requirement on the Rail...that is the main first requirement for a properly functioning D-Jet Sys! I'd plumb in a provision for checking Rail pressure (I've done this with an Oil Press Gauge...a bit "rustic" with it hanging out the back edge of the Hood, but just what you need during troubleshooting!...then there is NO question or doubt!...it allows monitoring and IMMEDIATE checking of the pressure under all driving and fuel demand conditions, including when intermittent symptoms occurred, which eliminated a lot of other unsubstantiated guessing!!).

Repeating: Rail pressure MUST remain constant at 28-30PSI (FPReg setting dependent), at ALL times FuPu is powered. PERIOD!

Good Hunting!
 

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Discussion Starter · #13 ·
Dalsim;

"I'm thinking the motor in it is starting to stick/seize (just like my blower fan motor) on startup "
FuPu is a "wet pump" meaning fuel continuously runs through it cooling and "lubing", so it might be sluggish initially from fuel gum after a 20 year storage, but once going, fuel also serves to flush any gummage away...it also runs full bore at all times, pumping WAY more than called for at Idle.

Assure good electrical supply to Pump! Fuse 5 has been known to have a poor connection - all the way from slight R in series (clean those conical fuse contact areas to shiny metal, and treat with ACZP!), which would serve to drop SOME V, which FuPu would not get and therfore run slower/possibly sluggish, to fully OPEN such that FuPu does not run at all!!) Measure and check V... at Pump!...anything less than power buss V will certainly cause and explain a sluggish FuPu...sort this FIRST! Ref D-Jet Wiring for a '71: SW-EM Bosch D-Jet Notes ...so if your ECU has the Idle CO knob, which I believe only was on '73 possibly '72 ECUs, that suggests it has been changed, just as a sidenote...

...with VPReg regulating the Rail pressure and dumping any fuel beyond immediate demand back to the Tank...frankly, I don't think replacing the FuPu will buy you anything...my position is: If the pump is working (and not leaking, or doing anything else which might be a reason for replacing it), I would concentrate on the constant pressure requirement on the Rail...that is the main first requirement for a properly functioning D-Jet Sys! I'd plumb in a provision for checking Rail pressure (I've done this with an Oil Press Gauge...a bit "rustic" with it hanging out the back edge of the Hood, but just what you need during troubleshooting!...then there is NO question or doubt!...it allows monitoring and IMMEDIATE checking of the pressure under all driving and fuel demand conditions, including when intermittent symptoms occurred, which eliminated a lot of other unsubstantiated guessing!!).

Repeating: Rail pressure MUST remain constant at 28-30PSI (FPReg setting dependent), at ALL times FuPu is powered. PERIOD!

Good Hunting!
Definitely adding the voltage measure on the FuPu to the to do list. I did add in a gauge along the cold start valve when I adjusted the fuel pressure last year. With ignition on, but engne off, it stays on 20 psi. Engine on idle, the pressure is a steady 29-30 psi. When playing with the throttle cable, it is mostly steady, but drops to 24-ich range (if only for a split second as I turn the throttle valve). It corrects itself to 30 almost instantly. Are you saying it should not move at all ever, not even for a split second?
 

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...and in your picture, the "TPS lower [Idle] contact was not even touching [means the ECU NEVER knew it was at Idle!],

leading to permanent enrichment I assume.(I'm not sure about that, because TPS does not do anything but inform ECU that it is at Idle, AND call for enrichment pulses when moving CCW.
Wow - eagle eyed!

I have never examined the idle control circuit in the D jet controller in detail so I don't know exactly what it does other than the idle hunts if the contact is not closed. From superficial examination, the mixture adjustment screw is non functional when the throttle closed contact is not closed so Dalsim007 could twiddle the knob until the cows come home and there should be no effect on non idle fuel mix. I believe that the setting range of the adjustment screw is limited and can actually go lean or rich. As you imply, I don't think the non operation of the idle contact is the cause of the rich fuel mixture.

On some D jet versions including the 1971 Volvo implementation, the idle contact has a secondary function of fuel cut. If you completely close the throttle and the engine RPM is high the closed contact will cause the controller to initiate a fuel cut until the RPM drops to about 1000 RPM where it resumes fuel delivery. If the idle speed is permanently high (aux air valve problem or manifold air leak) this can get you into the weird area where the controller is shutting fuel off and then turning it back on repeatedly - severe hunting idle. Being an analog device I am sure that the RPM values are variable given component tolerances and ageing drift. However, I believe that the contact has to be closed for this to occur and since it appears that it was always open this should not have been the cause of the 'bouncy idle' originally described by Dalsim007. I believe that this fuel cut feature was deleted from some later controllers so it is a controller thing, not a TPS thing as I kind of implied.
 

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Definitely adding the voltage measure on the FuPu to the to do list. I did add in a gauge along the cold start valve when I adjusted the fuel pressure last year. With ignition on, but engne off, it stays on 20 psi. Engine on idle, the pressure is a steady 29-30 psi. When playing with the throttle cable, it is mostly steady, but drops to 24-ich range (if only for a split second as I turn the throttle valve). It corrects itself to 30 almost instantly. Are you saying it should not move at all ever, not even for a split second?
There is always a transient period when responding to a change in operating conditions. The fuel pressure regulator has to measure a pressure drop before it 'knows' that it has to correct the pressure. The question is how long is your split second? If you can set up to do Ron's oil pressure gauge style measurement (I have done this) with the gauge duct taped to the front vent cowl, go out and take a spin on the highway and do a full throttle test in 4th gear or over drive at around 3000 RPM. If the pressure stays at 30 psi with the pedal to the metal then the fuel pump is functioning correctly.

If the fuel pressure regulator takes significantly more than a split second to respond to an increase in flow requirements it might be getting old; however, even the relatively new Nissan FPR on my 142 shows fuel pressure transients when operating conditions change.
 

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The ‘71 also has the idle adjustment knob on the ECU, my ‘71 is so equipped , and it’s the correct ECU for the year. I have a gunson ex gas analyzer that I used to set the idle mixture, bought from the UK. I’m not sure it makes much difference though. The biggest problems I had when I got the car and running rich were the coolant and air temp sensors, once I replaced those, and set the valve lash and TPS all is good. I also have the Beck Arnley injectors, they’ve been running fine since I installed them a 3-4 years ago. Possibly your fuel pressure regulator is dodgy? Possibly the comb in your tps has a worn, scored line and makes intermittent contact. I’ve read that the comb can be slightly repositioned to contact on an unworn surface , I’ve never had to do that though, so can’t offer any experience.
 

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Discussion Starter · #17 ·
Lucky that these older Volvos are all SAE. For once, they had the replacement screws I needed! Never happened when looking for the C30, S80 or S90! :D
New throttle stop screw and nut are in, new TPS locking screw are in too. I should receive a sec of gauge to measure that 0,5mm gap and conclude the TPS exploration tomorrow. Will try it all out on cleaned plugs and proprely reset TPS position.

@142 Guy: Yes the drop in the fuel pressure is very much a tiny half second thing. At any rate, I need to wrap up the evident enrichment issues before hunting for fuel pressure issues.

At all of you, you are such a previous source of knowledge! Can't express enough how much I appreciate your various tips and advice!
 

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Dalsim;

I read what Craig wrote about his ECU also having an Idle CO adjustment, and I'll believe it if he says it, but I just can't unremember what I heard from what I thought was a reliable source, that only the very last ECUs, so maybe '72 and '73 had them...some research of the gcp.se PNs should clarify this, but it seems to me it is really is not critical to locating and sorting the bigger issues here...

A strictly momentary drop in Rail pressure may/will occur as a result of a sudden high demand, when stomping on the Throttle, due to enrichment pulses drawing from the "Rail-Reservoir", but given the FuPu high output pressure (up to 60PSI) and volume, the FPReg better respond fast enough to bring it back up very quickly (in less than a second!)...if it doesn't, then an inline impedance to fuelflow may still be present (including all the way back to FuFi!)...I guess the way to find out and answer the question I would ask is if poor running or studder or sluggish accel still occur after pressure has recovered from that momentary minor drop (and minor is all I would expect it to be!!)...if the answer is yes, then Rail pressure is less of a suspect... Sidenote: Parts suppliers who have noted this transient rail pressure condition and offer super groovy replacement fuel rails (with increased volume), and maybe polished, which decreases these transients, are taking advantage of peoples neuroses...I would say those fall into the silicon breast enhancement category (don't do much but look nice!).

Craig: "Possibly the comb in your tps has a worn, scored line and makes intermittent contact." The comb contacts and interfacing circuit are brilliantly accommodating to wear, and immune to intermittent/multiple contact as a result of Bosch's excellent design practice! For fully detailed explanation, see: SW-EM D-Jet Idle Adjustment ...my recommendation is to keep the all the contacts of the TPS clean, well lubed with Deoxit, and when the Comb-contacts start exhibiting significant wear enough to bother me, just buy and [Carefully!!] install a replacement PCB.
See: SW-EM Bosch D-Jet Notes

Cheers
 

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Ron, I had cross referenced the ECU’s on Dr DJet, so given the source, hard to doubt. Agree that probably doesn’t have an impact on the current problem. But always good to “know what you have”.

Dalsim, are you sure the fuel is clean? No sediment in the tank and fuel filter doing it’s job? Would be worth a new, correct fuel filter: they’re different between the 70-71 and 72+. Also might be worth blowing out the fuel and return lines from front to back while disconnected. Do that outside. And how’s your ground strap from the bell housing to the frame rail? Worth cleaning those connections too, and some ACZP.
 
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