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Old 04-08-2017, 09:22 PM   #1
Col.Kalashnikov
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Question Mysterious Fueling Symptoms, My 940 is a Pile.

Hey There,

I purchased a 93 944 Turbo(Autotragic) in the summer to mainly winter beat, I never really got it done for winter, but did get it on the road in February. I've been experiencing some silly issues with it since and I'm looking for some advice. I did **** with the car a bit, I put a reclocked 16t on 15G exhaust housing as the turbo on the car was kinda messed and I had one kicking around (Coming from whiteblocks)... I threw a boost gauge and wideband in as I was planning on raising the boost via ghetto MBC. I did **** around with injectors(Bosch Blues(Light blue)) (Using low impedance with a resistor bypass etc), but I've pulled everything back out because of a few issues I'm seeing as per wide band. (Stock injectors and resistor are back in). I put together a ****ty cat back and put a new cat on it. Performed general maintenance (timing belt, wp, vacuum lines, new fuel filter, etc), new pcv (car still has crank case pressure issues but thats another issue all together( rings as per leakdown :( )

Car had issues coming on to boost, car would start to go Rich, then Lean out then Rich. You would feel the car lose power and gain power when it went from Lean to rich. All the while the car idled/cruised pretty good bouncing between 14.3-15.2. These were the first issues i was trying to address.

I checked and repaired a significant amount of vacuum leaks including injector seals etc.
No change in symptoms, car still had silly lean spot while building boost.

I couldn't check fuel pressure at the time as I was waiting on a fitting to make my gauge work with the schraeder.

After exhausting all vaccuum leaks as per boost leak tester, I changed the MAF out for another MAF (016), but had the exact same symptoms.

Car would sometimes run pig rich randomly(11,10,12? at cruise/idle, then mysteriously shoot back to normal stoich).

Issues with the random rich running started to appear more frequently. I noticed extended cranks were required to get the car to fire sometimes. I decided to drop another CTS in. Car still had lean spots, behaved the same, wasn't expecting too much here. Did seem to fire up on first crank though. AFR's behaved as they usually did, huge lean spot in boost, otherwise ok. No CEL's this entire time, never any Codes to pull from either Fuel or Spark Computer.

Finally get fitting for fuel pressure test, check pressure, running at 36-40PSI at Idle, take vacuum line of FPR and it shoots up. Looks like everything is working ok so I slap the car back together. Drive it home last night and it starts running PIG rich consistently, can't cruise/idle, anything close to stoich, always running 10/11/12/13 AFR. This reading comes with symptoms of the car not running normally, so I figure, well it was the last thing I touched, and swap the FPR for a new one today just in case my messing with it screwed it up. By the time I put it in the car had decided to start running normally again. Car feels like it's idling smoother than it has, and feels great. Check Charcoal canister for any fuel, it's bone dry.

Go to leave shop again today, car's cold, running normal then starts running lean and hesitating, 16/17 AFR's and then shows that while cruising, usually mid temp. Then it starts getting PIG rich when warm again, 10,11,12 Cruising, WOT, Partial throttle, everywhere, car is just running Rich and then lean, then rich. Car seems to get pig rich whenever it bloody well pleases with no rhyme or reason.

Haven't changed O2 yet. -_-.

TL;DR, car had lean spots when boosting before going rich, now just runs pig rich or leans out whenever it wants.


Any ideas? Directions to go?
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Old 04-08-2017, 09:34 PM   #2
Shifted
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IAC valve OK?
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Old 04-08-2017, 10:00 PM   #3
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What types of tests could I run. I saw in the service history of the vehicle it's been replaced once. Would that affect AFR in all conditions?
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Old 04-08-2017, 11:49 PM   #4
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Airleaks, maf, ECT...
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Old 04-09-2017, 12:11 AM   #5
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Changed ECT, ran boost leak tests and soaped up stuff, ended up fixing a bunch of ****. Biggest issue is the fact that it's consistently running rich now. I'll run another boost leak test tomorrow. The intermittence is really strange though. it's like flipping a switch, all the sudden its good. I did change the ECT, and two different mafs show the exact same symptoms at the same time (tried swapping mafs while it was happening).

Thanks again for any/all advice.
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Old 04-09-2017, 06:25 AM   #6
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thermostat working OK? if it's stuck open maybe the coolant is staying too cold causing rich AFR.
any error codes in the OBD?
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Old 04-09-2017, 08:23 AM   #7
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Where's your feedback coming from? The wideband? I doubt it, because you mentioned not having changed the O2. That's where I'd look for a on/off mixture switch. What is OBD telling you? 113?
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Old 04-09-2017, 09:50 AM   #8
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How corroded are the connections on the maf plug?
At the coolant temp sensor plug? Reads properly back to the ecu when acting up?
02 switches properly when idling/cruising?



Any of those can cause some very strange symptoms even if individual components, basic engine health and potential air leaks are "fine" or verified to be basically good.
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Old 04-09-2017, 10:50 AM   #9
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Monitor injector pulse width.
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Old 04-09-2017, 10:57 PM   #10
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@Shifted, I took the IACV out today to check cleanliness (it was clean) and shook it(Turned back and forth) to see if it was free, it appeared to be by clunking noise inside unit, disconnecting had a noticeable impact on idle (started hunting), hooked it back up car idled fine, AFR's still sucked, until I changed o2.

@Janspeed, car does it always when it does it, cold, warm, hot, just decides to do it when it does it. Even if the thermostat was stuck wide open, I would expect AFR to normalize at operating temperature, with thermostat fully open. I haven't changed that yet though and might be something I will look into. Although now with a new o2 and ecu reset car is co-operating.

@cleanflametrap. Wideband UEGO AEM gauge. I changed the factory o2 today for NTK unit and reset ecu, car appears to be co-operating better for now.

@Kjetsonaplane, The connections seem ok. I'll inspect in further detail. At the coolant temp gauge it appeared to have been dielectric greased with some sort of green grease, I thought it was corrosion at first but it came right off when I cleaned the connector with Non-Chlorinated brake clean yesterday. No difference in operation. I read resistance today at the sensor, not at ECU yet, but it was reading about 262Ohms when it was hot and left sitting for a bit. I also tried removing connectors to various sensors to see if a noticeable difference appeared in AFR, only after I changed o2(It improved to 13ish without reset) (and then reset ECU) did my AFRS return to running stoich at Cruise/Idle. Still have the stupid lean spot in boost, unless i let the car go past 3500 and then build boost, it's fine then.

@ZVOLV, If it starts acting up again I'll get a multimeter I can monitor it with.


Changing o2 seemed to have biggest difference, waiting to see if car decides to be a dick again. Lean spot at start of boost remains, maybe just tune having trouble with the 16t? It's been there consistently, with and without my ghetto fabbed intake, with and without bigger injectors.

Thanks all, will keep posted.
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Old 07-14-2017, 06:04 PM   #11
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You ever figure this ish out? I'm dealing with some very similar stuff over here.
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