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Discussion Starter · #1 · (Edited)
OK, let me start by thanking those of you who have posted your trials and tribulations concerning this issue here. One recent cold morning, my car went from being a well behaved 2004 S60R with a stage I tune to a stuttering mess between 2,500 and 4,000 under full throttle after reaching full boost. Only took a little searching here to realize a lot of other people were chasing the same ghost I was.

From my own background as an engineer/mechanic and using the insight I found here I was escalating through all the typical checks. Changed the FPS, MAP, TCV and cleaned the MAF to no avail. I even got discouraged and put the car back to stock tune and gave it to our better volvo dealer here in the area to take a look at. After checking of my systems including potential problems like the throttle controller and VVT they were as baffled as I was. At this point I assumed a plumbing or intercooler leak, but after building a pressure tester and running things up to 20 psi I realized that wasn't the problem either.



At this point I knew I was in for some deep digging. While waiting for my datalogger from IPD I at least have a ScanGauge II so I started looking at the most suspect sensor that has not been changed and assumed to be ok, the MAF. I set my SG to monitor my air flow and started watching things.

I also did some calculations and tests to determine the airflow to rpm ratio for all boost levels right up to the stock tune's 15 psi. That's where I thought I found the problem. I assumed the stutter was the result of the ECU's parameter map assuming an over boost situation since my MAF readings during the stutter were indicating that the engine was processing more air than would be possible even if the boost levels were over 16 PSI even though the actual manifold boost was 13 PSI.
EDIT: Bad assumption, the high MAF readings were just the engine reaching peak volumetric efficiency

Now that the problem was whittled down I bought and modified a secure 25 torx to pull and more closely inspect and clean the MAF sensor. It looked clean, but fortunately while doing a lot of web research on MAF's I found a few different tech articles talking about MAFs going bad when the silicon potting compound seeps from the electronics enclosure onto the thin film sensor. And what I found upon close inspection of the film sensor was just that. I realized I had nothing to lose so I took a small, sharp screwdriver and removed what I could and gave it another cleaning.
Let me just say that the change was immediate and noticible, but unfortunately my sensor is still reading a little high so I can sometimes still get just a single hiccup on boost spikes now instead of the constant stuttering I had before. Tonight when I go home I'm gonna do a little more digging, this time with a sharp exacto knife to see if I can save the sensor I got instead of shelling out another $250 for a MAF in addition to the $400 I've already blown, lol.

Speaking of that, I have a slightly used MAP and TCV for sale that are good if anyone needs one or would like to buy some parts for swapping and diagnostics.

I'll be posting an update later tonight after messing with the MAF some more.



EDIT: Problem Ended Up Being A Bad Coil. Read whole thread for progression of the diagnostics.
 

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Re: Found The Cause Of My 3-4K RPM Full Throttle Stutter (StealthyS60R)

Does your problem go away after a few minutes?

I noticed that with my Stage I, less so with my Stage II, that I had all sorts of cold weather bucking and stuttering. I think it has to do with the cold IAT causing the tune to get overly aggressive and then abruptly dial back.

Goes away after a minute or two. And it can be very abrupt.
 

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Discussion Starter · #3 ·
It was even worse when I had the stage 1 tune running due to the higher boost pressures. You'd assume something was seriously FUBAR the problem was so severe.

Switching back to stock only slightly reduced the problem due to the reduced boost and flows.

The problem is more noticible during cold weather and due to the ECU being more boost happy due to the colder IATs.
 

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Re: Found The Cause Of My 3-4K RPM Full Throttle Stutter (StealthyS60R)

Quote, originally posted by StealthyS60R »
Now that the problem was whittled down I bought and modified a secure 25 torx to pull and more closely inspect and clean the MAF sensor. It looked clean, but fortunately while doing a lot of web research on MAF's I found a few different tech articles talking about MAFs going bad when the silicon potting compound seeps from the electronics enclosure onto the thin film sensor. And what I found upon close inspection of the film sensor was just that. I realized I had nothing to lose so I took a small, sharp screwdriver and removed what I could and gave it another cleaning.

If at all possible, please take pictures of what you see on/in your MAF and post them here so we will know what we're looking for. Thank you for the write-up!!! http://********************/smile/emcocktl.gif
 

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Discussion Starter · #5 ·
Re: Found The Cause Of My 3-4K RPM Full Throttle Stutter (TarP)

Sure thing. Unfortunately in an attempt to remove additional potting compound from around the MAF sensor element I accidentally broke it. Lets just say its way to fragile for such things but at least I can now tear the unit apart to better see what was most likely giving me the high flow readings.

This first pic is the limited view you get down the sensor hole. Can't really see it in this pic but I could see where the sensor electronics emerged that there was potting compound creeping out and onto the sensor.



Upon opening the unit up you can get a better view of how the compound was creeping down the sensor element. My theory is that the compound was conducting away some extra heat from the leading edge of the sensor, leading it to think more air was passing by than there actually was at lower flow volumes. And this is after I was able to remove some of the compound this morning.



For those of you who don't know, the MAF is held in the flow tube by some 5 point torx like security screws. Grinding 3 prongs off a six point T-25 secure bit makes a good fitting solution though.



Before I got to this point I assumed my pressurized plumbing might have been leaking so to rule it out I even created my own device to pressure test my system.



Now that my MAF is toast I'll be stopping by the dealer in the morning to pick up a new unit. After so many other false starts I'll wait till after its in and tested to know if I can declare victory yet though.

 

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Discussion Starter · #6 ·
First off, let me say that limp home mode when you lose your MAF isn't very limp at all, lol. In fact the car ran and boosted great with no problems whatsoever on the way to the dealer this morning. The A/F meter showed it cruised a bit rich (about 13.5/1) above 2K RPM but in every other way it ran great with no stumbles, hiccups or stutter.

Put the new MAF in and was glad to see that that it was reading lower flows as I had assumed it should.

Sad to say that if I jump the throttle in the 2500-3500 range that the engine will still sometimes just miss a beat or two when the boost spikes in the high gears but it then just drops back a psi or two and runs well from that point on. I can see from the new MAF readings that this burp is still occuring for flow rates that appear above the assumed theoretical.

Has me wondering if I have some kind of tempermental leak on the pressure side. PCV or EGR perhaps?

I should be getting my datalogger in the next 24 hours so hopefully I will have some detailed data I can analyze soon to get a better idea of exactly why this blip is occuring.

So while the stutter is gone I don't like that I still hit hit some kind of obvious limiter.
 

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Discussion Starter · #7 ·
Re: (StealthyS60R)

Arrg! On the way home I almost thought the adaptives were adjusting to the new MAF since the car ran great and only hiccupped once or twice on my 21 mile commute.

My new MAF came with a couple nice plastic endcaps so I decided to mod one so I could pressure test the whole intake system. Still couldn't find any major leaks though. Including a pic below for inspiration to any fellow problem hunters out there.

Took it for a ride after putting it back together to see if anything is any different and it was back to stuttering badly. I'm starting to suspect the stock intercooler and/or its plumbing has a leak which only likes to open up under the right circumstances.

 

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Re: (StealthyS60R)

I know this is a "duh" suggestion, but have you considered reversing back to STOCK ECU program, and then perform an updated ECU "overwrite" program @ dealer with very latest code? Once that's done, re-read your new "stock" program ECU after sufficient adaptions (say 1-week of driving), and get an updated stage 1 tune that you have. That would be my #1 thing to do if I were you. Lots of updates to that ECU since 2004. I wonder aloud if this might solve your issue.
 

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Discussion Starter · #9 ·
Good suggestions, and yes I've done both.

Part of what the dealer did to try to correct the problem was reflash the ECU, even though I had set it back to stock tune before giving it to them to check out.

I've been working on this problem now for about 2 weeks, just haven't posted here about it till now though.
 

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Discussion Starter · #11 ·
Checked the TCV lines and upgraded to the IPD controller. Checked the wastegate diaphram and base opening pressure. Boost pressures when the system is not hiccuping are well maintained and corrolated to the last half of pedal travel as they should be.

At this point I'm just gonna double down and upgrade to a nice aftermarket intercooler system. No need to polish the turd that the stock system is.
 

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how about just cleaning the IC's and see what happens? I mean, it's fairly easy to take apart, an then just pour in some good ole fashioned gasoline to sort it out.. just make sure you completely clean it afterwards before you reinstall..
 

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Discussion Starter · #13 ·
Re: (vsigma)

Its not a case of the IC being dirty but instead a leak or leaks finally adding up to the point of throwing off the ECU map at low RPMs and high boost.

Stilll waiting for my datalogging option from IPD but from what I've been reading on my ScanGauge II it appears when the problem is at its worst I'm leaking out about 8 liters of air per second @ 13 PSI of boost. That may sound like a lot to some people but that rate of flow would take over 5 minutes to empty out a 10 gallon compressor. At full boost @ 2500 RPMs the motor should only be moving about 80 liters per second. It appears 10% excess flow is enough to make the ECU assume overboost and cut back power but not enough to throw a leak code.

Down here in florida in summertime its not unusual for the IATs to be in the 140s when its in the 90s and the A/C is on do to the primary intercooler being sandwitched between the radiator and A/C condensor.

Just as I held out till my old tube TV died before I bought my big flatscreen, I see this problem as an excellent reason to finally upgrade to a big aftermarket FMIC before the hot summer temps return.

 

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Re: (StealthyS60R)

just came across this thread and was wondering if you've solved anything yet? do you have a new IC in yet? if so did that make any difference? I've been having the exact same problem on my 98 for months except for the fact that mine only happens when the car experiences a change in lateral or veritcal G's (cresting hills, going through dips, or turning)
 

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Discussion Starter · #15 ·
Re: (95854turbo)

My appointment for the swap is later next week so I should have a solid answer in another week and a half.

Now that's I've been watching and milking the problem for a while I've also noticed that road conditions like bumps, crests and lateral G's have an effect on the problem. Temps too, like whether the A/C is running.

When I pressure tested the system I couldn't feel any leaks around the main pressure tubes so my educated guess is that the leak might be from one of the main intercooler's plastic endcaps. Since that's where its secured to the chassis I'm assuming that the loads and thermal expansion issues have variable effects on the leak there. Once I get it out of the car I'll certainly be looking to see if I can find it though it should hopefully be a moot point by then.

If not I'm going to be building a smoke machine to see if I can find any other leaks in the system.
 

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Discussion Starter · #16 ·
Re: (StealthyS60R)

Well, I finally got my datalogger option from IPD/MTE last weekend after several weeks of waiting and murphy's law raining supreme.

I've got to say I was very disappointed that the datalogger doesn't include critical data like fuel trim and timing so I'm still left wondering what exactly the ECU is doing during the stutter.

The stutter is cleary visible in the following TQ chart around the 3K RPM point. While the torque curve is usually pretty flat you can see a few of the paths falling off around that point during the stutter.



In the detail of one of the runs you can see the torque drop off and RPM loss starting between the 2350 and 2600 RPM range. From the graph above you can see that torque would normally plateau through this RPM range around 220 FT-LBs if not for the stutter. Boost and A/F is well maintained through this range so I'm still thinking my theory that a boost leak and torque limiter is to blame is the cause. Too bad I can't see timing with this thing to see if that is how the ECU is pulling back the power.



Dark Red - A/F Ratio
Light Red - Boost PSI
Orange - IAT/10
Blue - WTQ/10

The car is going in for its new intercooler on thursday so I should have some more information by this weekend.
 

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Re: (StealthyS60R)

Does your IC have a crack in the side tank(s)? Is that a leading theory?
 

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Discussion Starter · #18 ·
Re: (Short Circuit)

Yes, that's my leading theory since the severity of the problem varies greatly depending on things like hard turns, bumps in the road and ambient temps. Rapid pressure increases are also worse than slow gradual ones as well.

When I pressure tested the system I couldn't feel anything leaking out around the plumbing or connectors so I assume it has to be coming from somewhere I couldn't feel it.

Once the shop removes the old one I will be seriously looking it over to see if I can find the leak, assuming that's what it really is.

Years of running an aftermarket tune and snapping the throttle close could have certainly busted something open by now. The fact that it died on one of few freezing days we have in florida also adds to my suspicions since plastic is more brittle when its cold.
 

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Re: (StealthyS60R)

I have a Phuz FMIC, but would be curious on where the crack is - if indeed you find one. Post a pic for all to learn from.

Another reason to get aftermarket FMIC -or- to somehow insert rubber washers at all support points of the stock FMIC...

Keep us posted...
 

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Discussion Starter · #20 ·
Big time update to the thread. Upon the additional stress of trying to force a spark across higher boost of stage 1 one of my coils gave up the ghost.

Just got done doing a coil and plug swap to determine I got a bad coil.

This could be the cause of my stutter but I won't know till I change it out.

At least it got me motivated to do one hell of a tune up, lol.
 
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