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I dare anyone to solve this...car runs either super rich or super lean

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YOOOO

15+ Year Contributor
117
0
Apr 18, 2008
Woodbridge, Virginia
To the point: Car was tuned on V2 by the best DSM tuner in the area. Car ran amazing for about 2 weeks, and then inexplicably started running either really rich or really lean at partial throttle depending on it's mood. It always runs rich in boost. Plugs and wires are new (NGK).


Since then I've:
-tested and fixed all boost leaks
-upgraded DSMlink from V2 to V3
-ditched the GM MAF w/translater and went speed density
-swapped igniters
-swapped CAS's
-swapped fuel pressure regulators
-checked the o ring on the fuel pump
-replaced the MPI/MFI relay
-swapped TPS sensors
-tried every possible trick with DSMlink (no codes are being thrown)

Nothing has helped it. It is impossible to get the injector cycle duties under control at partial throttle and idle (when it runs rich). Going to try swapping injectors from a friend next. What else should I try? I know some pretty damn knowledgeable DSM people, and none of them have ever seen anything like this. Car is a 95 with a 2.3L 6 bolt.
 
Last edited by a moderator:
just an idea. check your o2 sensor. might of went bad on you or is starting to.
 
just an idea. check your o2 sensor. might of went bad on you or is starting to.

O2 sensor was replaced less then 2 months go with OEM. It reads normal and is not throwing a code.

have you checked for any exhaust leaks? those can screw up your afr

It has a small leak after the o2. But that wouldn't explain why it runs eratically. If it was lean all the time or rich all the time that would be one thing, but it's either/or with no consistent variable.
 
do you have a fuel pressure gauge? Not a bad investment anyways. Wideband is going to give you significantly more accurate aft adjustments. narrowband is linear from about 14 to 15.5, ~0-1V respectively, where anything less than 14 or greater than 15.5 will have the same voltage out. wideband is linear across its whole range from 10-20, ~0-5V respectively.
 
The guys i work with are saying there is a sensor input not being seen by the ecu when it runs rich or lean and it is seeing the input then it runs rich or lean. If you can understand what I just said....
 
First of all, thank you for all the responses everyone

How's the turbo running?

Just fine, builds boost normally

Faulty coolant temp sensor... :thumb:

That would throw a code, also see below

read this: sd101 [ECMTuning - wiki]

you may want to try ignoring the coolant temp. sensor as i heard it can be buggy if you use the coolant temp. and iat for a/f.

Yep tried that currently the ecu is set to always run in open loop.

do you have a fuel pressure gauge? Not a bad investment anyways. Wideband is going to give you significantly more accurate aft adjustments. narrowband is linear from about 14 to 15.5, ~0-1V respectively, where anything less than 14 or greater than 15.5 will have the same voltage out. wideband is linear across its whole range from 10-20, ~0-5V respectively.

I do. It's set at 43 psi. I already swapped fuel pressure regulators from another car to make sure that wasn't the issue. Also yes I have a wideband, I have a 400+ awhp car with a built motor haha.

The guys i work with are saying there is a sensor input not being seen by the ecu when it runs rich or lean and it is seeing the input then it runs rich or lean. If you can understand what I just said....

haha I do...can you be more specific? what sensor or what input?

On my way now to swap injectors...we'll see how this goes
 
The ecu doesn't see the o2 sensor in open loop. Thats way every car co. is trying to get vehicles into closed loop faster.(to get better mps and low co and co2 counts) The ecu just goes by other inputs to make it run till it goes into closed loop. And/or preset tables the ecu has to run. So if the ecu is staying in open loop there is a senor that is keeping it there. ie coolant temp sensor. My temp sensor was getting grounded out by a clamp that got moved every so slightly and my gauge would shoot straight to hot. Even though I just started the car.
 
The ecu doesn't see the o2 sensor in open loop. Thats way every car co. is trying to get vehicles into closed loop faster.(to get better mps and low co and co2 counts) The ecu just goes by other inputs to make it run till it goes into closed loop. And/or preset tables the ecu has to run. So if the ecu is staying in open loop there is a senor that is keeping it there. ie coolant temp sensor. My temp sensor was getting grounded out by a clamp that got moved every so slightly and my gauge would shoot straight to hot. Even though I just started the car.

I see what your saying but that's not the problem. I have DSMlinkV3 and can put the ecu in open/closed loop as I choose and disable input from the coolant temp sensor. However I finally got it to run somewhat normally by disabling the o2 and putting it in permanent closed loop. Now the car just runs off the fuel map with no input from the o2. Of course this requires extensive time tuning and adjusting to get right so it's not finished. On a positive note though the car now responds normally to changes in the fuel map, while before it would not behave accordingly. Obviously this is not ideal, but at the very least the car now runs consistently. I still have no idea what the problem was though. It's hard for me to belive an OEM o2 sensor with 500 miles on it would go haywire and not throw a code or show any signs of failure and be the cause of the problem.
 
If you have no codes thrown, my guess is an intermittent wiring issue. Datalog all the sensor requirements for closed loop fuel trimming, my bet is that one of those sensors is causing the car to flip between open and closed loop or is feeding an intermittently degraded signal to the ECU.

Coolant temp between 51-228 degrees F.
TPS
Front O2 signal
 
Check your compression, check what your spark plugs look like. Could be bad. could be the plug wires (one may be stripped or worn from too much heat) check your 02 sensors as well.
 
so the problem was going on with the MAFT setup as well as speed density. Are any other things going on, anything at all. at what points is it rich/lean is it a specific rpm range, or is it whenever it wants to kind of deal.
 
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