SwedeSpeed - Volvo Performance Forum banner
1 - 19 of 19 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter · #1 ·
I hate to just throw parts at this thing, but I'm running out of good options... I appreciate any thoughtful input and sleuthing.

When car is warm about 1 of every 40 times coming to a stop, the idle drops below 500 and doesn't recover. Car gives a little shudder and gives up the ghost. Always starts right back up like nothing happened til the next 40th or so stop. This is my daughter's car, and this is not a safe scenario.

ETM's on these were crap, so that was my first stop. Cleaned it up and it seemed ok for awhile. Until it stalled again. So OK, the ETM is bad. I get another from a junkyard, clean it up and slap it on. OK for awhile. Until it stalled again. Took it back, got another, same thing. Yes, I know, they're used, but I'm trying to avoid the $500 for a new one [turbo model ETMs available aftermkt. Not so for N.A.]. Three bad in a row? Possible but not likely.

Complete tune up - fresh plugs, K&N air filter, gas treatment out the wazoo. No difference.

The only code it ever throws is P0420, Cat Efficiency Low, but I checked cat temp with laser thermo and it's a couple hundred degrees hotter on the output than the input, suggesting it's working. When I was swapping ETM's, those actually had a huge bearing on how persistent the P0420 was, one ETM causing it to trigger frequently, another hardly at all.

I have discovered that resetting the ECM [battery disconn'd for half hour or so] yields a fine coming to stop idle but it then degrades and goes back to dropping too low at stops. Am I clearing something that "builds up" afterwards?

Blew a benjamin on a local Volvo 'expert' who put it on his scanner and guessed it might could possibly be O2 sensors... To that end, I tested the upstream w VOM and at op temp it varied between .1 and about .7 VDC, about what you'd expect I think.

With my OBDII I've discovered that Short Term Fuel Trim at idle is way negative -- neg 15 to neg 25. BUT, at 2-2.5k RPM, it happily ranges between -3 to +3.

SO, I'm thinkin' something in that feedback loop is running it rich [big negative STFT] but can't figure out what. MAF was cleaned, Fuel Pressure running solidly 55 psi according to OBDII data, upstream seemed to test ok, no vacuum leaks I can find, runs in Closed Loop shortly after starting up.

Worse comes to worse I guess I'll change Fuel Pressure Sensor, MAF, the O2's, maybe spring for a new ETM... But heck, there's just something demeaning in having to resort to the blind-hog-and-acorn approach.

What am I missing here? Thanks in advance for the wealth of wisdom I anticipate to start rollin in...
 

·
Registered
Joined
·
256 Posts
While you should probably re-post in the right section, here's my $0.02. Keep in mind I am not an expert on your particular engine, this is just based on my general knowledge of modern engines.

My advice would be to be absolutely sure there are no vacuum leaks first. Do a smoke test on the intake system to be sure. The fact that fuel trim is adjusting to such extremes at idle (i.e. at max vacuum), but seems to be OK when up in the revs would suggest a vacuum leak.

Other than that, look at whatever else can have an effect on long term fuel trim and/or ignition advance, since your issues seem to go away temporarily after resetting the computer then progressively come back after accumulating some runtime data.

The next part I would try replacing would be the upstream O2 sensor. If it is giving inaccurate readings when in closed loop mode that could also cause long term fuel trim to adjust further and further from where it should be. Eventually resulting in stalling at idle. You said it "seems" to test ok, but if it obviously tested as bad, you would already have a DTC to tell you that. Also the catalyst inefficiency code indicates that the difference between the upstream and downstream O2 sensor readings is not what is expected, which could be the result of an inefficient cat, or an inaccurate reading from one of the two sensors. Since the downstream sensor is not looped into the fuel delivery system, that again would point at the upstream O2 sensor.

If the MAF were the problem I would expect it to throw a code since, on most modern engines, the MAF readings are constantly checked for ballpark accuracy by the ECU using MAP, IAT, and engine speed to back calculate MAF.

Not sure how the fuel system works on your particular engine, but if it has a vacuum modulated FPR, it might be worth replacing.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #3 ·
Sorry guys! After the 13th hour at work I tend to miss little things like the Year Range of the forum.

While you have my apologies for that, budleach, you also have my appreciation for the thoughtful response. This is a much deeper dive into the subject matter than my typical wrench-turning, and your input above helps in that education.

I was actually about to call around and find a smoke tester, as that was one thing I hadn't checked [ehh, I waved a small handful of incense sticks around the engine bay to see if the smoke was sucked in any particular direction, but it was far from a legit test]. I didn't have a lot of hope in a vac leak though, because I thought that would make it run lean, not rich (introducing too much air in the system) but maybe my logic is backward there.

Yes, from what I've seen, if it's an O2, it's the upstream, and on this vehicle it's accessible without being a midget with 3 elbows [that phrase may now be politically incorrect; my apologies to any offended].

I'll post this in the appropriate section, but thanks again budleach.
 

·
Super Moderator
Joined
·
8,734 Posts
Moved, merged, and cleaned. :thumbup:
 

·
Registered
Joined
·
515 Posts
The ETM were actually good from 2003 on. I also had the rpm drop at stop - no stall but getting quite low. Always cleaned the ETM flap and went fine - I did clean it near the hinges really well, inside too as far as I could reach. Also check the wires at the connector

May be something else, quite hard to say. Not sure about the front O2, at least it quite easy to undo on the NA www.youtube.com/watch?v=IKx3wIrtYh4

A few things I would try to test. The 2004 was the first year with water leaking on the CEM. Easy to see with a flashlight for any traces of water on the cover

May as well look at the grounds around the engine bay, top of each fender, and one smaller behind from the top of the engine near the exhust cam

Perhaps also check all thick red power cables at the fuse panel in the engine bay, at the battery..

These were also sensitive at the FPS and PEM
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #6 ·
Thanks Orange, good to know about the CEM, I'll check it for signs of moisture. I've cleaned all 3 throttle bodies I've had on it within an inch or their lives. Hadn't thought to check ETM wires but definitely can't hurt.

Did a smoke test yesterday. All was good except the backside of the air filter housing where the cover meets the base. Looks a bit like one or the other is slightly warped and not making a perfect seal. Did get some smoke there. I'll get that sorted and see if it helps.

Aside from the checks Orange mentions, I think my next stop is the upstream O2 sensor. Hey, even a blind hog can find an acorn now and then...
 

·
Registered
Joined
·
94 Posts
I am having similar problems - stalling - temperature dependent AND I think , fan problems .
On the oxygen sensors (for any vehicle), IMO, they are good for 100-200 K miles and should be renewed "every so often" . .
In an aspect, hilarious about the midget with articulated elbows .. I miss my old Saabs and old cars in general. So much simpler and easier to work on .
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #8 ·
Aw man, 'worm, don't get me started on the old Chevelle's and 911 Targa of my past. Beautiful to work on. I can't even identify a lot of the parts in a newer engine bay... But older wasn't always necessarily easier. Had a 70-something Fiat X-1/9. Handled like it was on rails but its mid-engine was where I became familiar with the midget description.

Changed the upstream O2 tonight. Still seems to be running way more negative on ST FT than it should. We'll see. If it's going to stall again it'll do it in the next few days.

Yes, I've read Temp could cause the stalling, at least the coolant temp sensor being fubar. Let me know if you get yours sorted and I'll do same!
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #10 ·
Hey man,

I've used my laptop software-base obdii and my buddy's higher-end Bosch scanner, but neither with the capability that I'm aware of to record. Now that you mention it, it would be notably helpful to see what all the players are doing when it goes belly-up and stalls.

After changing the upstream O2 a few days ago, it hasn't stalled yet, but has flirted with the 500-rpm level. It seems that during the final stages of deceleration, when it shifts from 3rd to 2nd, then 2nd to first, it 'lugs' the motor and drops rpm momentarily. (I would think it'd the the opposite, x-speed going into lower gear would INcrease rpm temporarily, but... that pursuit could be purely academic.)

While it hasn't stalled yet, it did throw the P0420 since the new upstream sensor install. SO, I'm ordering the downstream now and eliminate both O2's. I know there are varying opinions as to how involved the downstream is in the loop beyond triggering a CEL, but I just want to have them both changed.

The thing that's a real puzzler for me is why it idles so well at a stop following a disconnected-battery-induced reset but then over time idles rougher and rougher at stops until it's stalling regularly. Again, hasn't actually stalled since the O2 change, but... time will tell on that. Thanks man!
 

·
Registered
Joined
·
53 Posts
If your fuel trims are negative at idle, this means your computer is trying to take fuel away to get the mixture right meaning you are running too rich. If you had a vacuum leak your trims would go positive because more air would need more fuel to stay 14.7:1

I think a lot of idle A/F ratio issues (lean or rich) go away under load or higher RPM’s since the % contribution of the leak or problem is buried once a lot of fuel and air start flowing outside of idle.

Bad coolant temp sensor maybe perpetually telling your computer that the car is cold when it isn’t.....OR

You might have a leaking or malfunctioning fuel injector or overpressure? Does your car have a fuel pressure regulator? Thats my $.02

Downstream O2 sensor input isn’t used for fuel trims to my knowledge it only verifies function of the catalytic converter.

I’d never rely too much on any diagnosis without known history on O2 sensor age.

Wait.....can a turbo engine have a vacuum leak? I thought I remembered reading once that turbo air leaks are losing air out (like a balloon with a pinhole) not sucking air in since the whole system is under pressure. What’s the idle boost PSI for the engine at idle?
 

·
Registered
Joined
·
256 Posts
If your fuel trims are negative at idle, this means your computer is trying to take fuel away to get the mixture right meaning you are running too rich. If you had a vacuum leak your trims would go positive because more air would need more fuel to stay 14.7:1

I think a lot of idle A/F ratio issues (lean or rich) go away under load or higher RPM’s since the % contribution of the leak or problem is buried once a lot of fuel and air start flowing outside of idle.

Bad coolant temp sensor maybe perpetually telling your computer that the car is cold when it isn’t.....OR

You might have a leaking or malfunctioning fuel injector or overpressure? Does your car have a fuel pressure regulator? Thats my $.02

Downstream O2 sensor input isn’t used for fuel trims to my knowledge it only verifies function of the catalytic converter.

I’d never rely too much on any diagnosis without known history on O2 sensor age.

Wait.....can a turbo engine have a vacuum leak? I thought I remembered reading once that turbo air leaks are losing air out (like a balloon with a pinhole) not sucking air in since the whole system is under pressure. What’s the idle boost PSI for the engine at idle?
Turbo cars operate just like NA cars when under light load. They run in vacuum (below atmospheric pressure) when you're not requesting much power. They do indeed leak in the opposite direction when under boost though. So a vac leak on a turbo car would cause lean condition under idle/light load, no noticeable leak when MAP=Atmospheric pressure, and rich when under boost.

A vac leak is typically defined as a leak between the throttle body and the manifold/head interface. Since that is the only volume that can see a vacuum. It is the pumping action of the engine, working against the restriction of the throttle plate that creates a vacuum. In a turbo car, there is also all of the piping between the compressor outlet and the TB that is pressurized under boost. A leak in this piping would cause rich under load condition, but have very little vac leak (lean under idle) contribution. Technically a leak after the MAF could siphon in some extra unmetered air when not under boost, but the pressure differential between atmosphere and inside the boost piping when the engine is not under load is minimal. You would need a pretty significant opening, and a venturi shape in the intake piping to draw in a significant volume of air.

I agree with your line of thinking here though. Assuming vac/boost leak has been ruled out, If upstream O2 sensor doesn't fix it I would look next at the fuel delivery. Possibly an injector that is not fully closing? Could this be checked by doing a leak down test on fuel pressure in the rail after the car is turned off? Not sure how this fuel system works, but my old (2006) Saab had a on demand fuel pump with no fuel return line, it would maintain fuel pressure in the rail after the car was turned off.

Stuck injector seems like a bit if a long shot to me, since I personally have never had a fuel injector issue. But it might make sense with the symptoms. Of course if that were the case it would only be affecting one cylinder, which would probably be obvious when pulling all the spark plugs and inspecting them side by side.

Only other obvious culprit is MAF sensor but, at least in my experience, that has always thrown a code when it is failing.
 

·
Registered
Joined
·
256 Posts
Just did some quick googling and it looks like the 2.4 engine is a NA motor (no turbo). Also looks to be a no return style fuel delivery system, with no vac modulated FPR. Looks like just a fuel pressure sensor on the rail and a computer to modulate the pump to maintain pressure and flow rate.

https://www.youtube.com/watch?v=Cv7O8xHUiFc
 

·
Registered
Joined
·
306 Posts
Well, the pressure sensors are notorious for failure, will fail and run extremely rich sometimes causing the engine to stall or run rough. You've also got a fuel pump control module (PEM) that are prone to failure as well. Highly unlikely its a fuel pump - Typically they don't fail and create more pressure.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #15 ·
UPDATE: While I'm not quite ready to call it Mission Accomplished just yet, I changed the upstream O2 sensor almost 2 weeks ago and she hasn't stalled since. A few days after, it threw the P0420 Cat code, so I went ahead and ordered the downstream O2 and replaced it this weekend. I drove it yesterday with the scanner reading live, and once it warmed up, Trims were about where they should be. So with both fresh O2's, we'll see what happens in the next few weeks, but just say I am cautiously optimistic about the matter... Oh, and probably everyone in the world but me has always used PB Blaster, but I just discovered it in the course of the O2's, and I will not go without a can on the shelf from here on out.

Re: the fuel pressure, my diagnostic showed a pretty-much constant 55 psi, and despite varying values of reference when I tried to find it, seems to be in line. If O2's fail to prevent further stalling, I'll still replace the pressure sensor and start looking at leaking injector(s).

My thanks and appreciation to all who weighed in and contributed to preventing me from pulling out what hair I have left.
 

·
Registered
Joined
·
357 Posts
So the Engine Control Module was getting a signal from one or both of the defective Oxygen sensors indicating a rich mixture, when in fact the mixture was normal or possibly lean. The ECM then turned around and sent a signal to the Fuel Pump Module causing it to shut down the fuel pump. That is one scenario. The other scenario is that the ECM shut down the fuel injectors to lean the mixture, causing the engine to stall. The car can be mechanically sound, but if the electronic controls are defective, or the sensors are defective, it will not run well, or run at all.
 

·
Registered
Joined
·
53 Posts
So the Engine Control Module was getting a signal from one or both of the defective Oxygen sensors indicating a rich mixture, when in fact the mixture was normal or possibly lean. The ECM then turned around and sent a signal to the Fuel Pump Module causing it to shut down the fuel pump. That is one scenario. The other scenario is that the ECM shut down the fuel injectors to lean the mixture, causing the engine to stall. The car can be mechanically sound, but if the electronic controls are defective, or the sensors are defective, it will not run well, or run at all.
It seems like the programming would default back to some type of preset A/F tables vs. manipulating fuel system to the point of stalling the vehicle.......like how a car can run without a MAF. My understanding of O2 sensors is that their primary job is to improve efficiency. I’d imagine a car would still run even if you unplugged them.
 

·
Registered
Joined
·
357 Posts
The original poster was having a symptom that he interpreted to be lack of fuel leading to engine stall. He made some mechanical repairs including replacing the fuel pump, and the problem was not solved. Replacing both oxygen sensors seems to have eliminated the problem with engine stall. The car might run with no oxygen sensors, but not very well. I have never tried to operate a vehicle without a mass airflow sensor in place, so I can't comment on what the result might be.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #19 ·
The original poster was having a symptom that he interpreted to be lack of fuel leading to engine stall. He made some mechanical repairs including replacing the fuel pump, and the problem was not solved. Replacing both oxygen sensors seems to have eliminated the problem with engine stall. The car might run with no oxygen sensors, but not very well. I have never tried to operate a vehicle without a mass airflow sensor in place, so I can't comment on what the result might be.
For clarity, I didn't suspect either lack of fuel nor excess of, at least not initially. The problem seemed spot-on symptomatic of the issues that apparently only the earlier ETM's commonly had. I never replaced the fuel pump, as nothing indicated that was the issue. Once I saw such low fuel trims I suspected that it was just getting too much "go richer" data and too much fuel during a stop 'flooded' it out... There seems to be a laundry list of stuff that can cause ST and LT FT's to go out of whack; I started with the cheapest and easiest but quickly took the recommendations from this forum and did the O2's, which, so far, seem to have done the trick, thankfully.

Again, I appreciate all the thoughtful input from the forum on this. Now on to replacing the busted door handle on this plasticized machine. If it's not one thing, it's two more...
 
1 - 19 of 19 Posts
Top