Persistant misfire issue

[nicknorth11]

Back-story: I was out doing some very easy driving when all of a sudden the car started missing. I was barely able to get it home, and it barely runs unless I give it continuous gas and keep the RPMs higher. Nothing was worked on prior to the drive. A log is posted at the bottom of this post.

Below is everything I have tried so far:

Spark:
Replaced plugs (gap is correct)
Tested wires with ohm meter: all were good
Removed all plug wires one at a time: no noticeable change
Replaced coil pack with known working one
Replaced ignitor (power transistor) with known working one
Disconnected Dynatek ignition box and tried stock setup
Tested spark by setting plugs next to screwdriver: all had great spark before and after all tests

Fuel:
Replaced injectors with stock, known working ones
Checked fuel pressure
Checked fuel filter
Checked all wiring going to the fuel pumps to ensure they weren't intermittently losing signal or power.Listened for injector "click" with screwdriver to ear: all were getting signal/working
Unhooked each injector individually to identify bad cylinder. Each one made the misfire significantly worse, and all were the same before and after.

Air:
GM MAS is reading appropriately on link
GM MAS has no debris inside

Electrical:
All settings in link are correct
Tested battery ground with ohm meter: good
Checked all relays and fuses
Replaced coolant temp sensor
ECU looks/smells good. Everything else on the car is working perfectly and link shows no issues.
Replaced cam angle sensor and crank position sensor

Engine:
Tested compression: 182, 182, 190, 186
Tested for boost leaks: held 20 (not ideal, but not bad enough to cause this problem)
Checked timing: it was dead on

What is left?

 

[ChrisMgst]

Are you on a 1g CAS?

 

[nicknorth11]

No. Stock configuration: 96 CAS.

 

[Talon64]

I am assuming you check transistor. Also you checked timing. Ignition with a timing light or the timing marks? You said ignitor there is fuel injector one and the transistor next to the coil pack.

 

[ChrisMgst]

I would post an idle log with anything, and everything being displayed.
Have you checked the power transistor?

 

[nicknorth11]

Yes, the ignition transistor (ignitor) was replaced. Mechanical timing was verified. I don't think timing advance needs to be verified since this happened while driving and it wouldn't just change. I haven't checked the injector resistor pack. Do those actually go bad? I'll post a log in the morning.

 

[TSiAWD666]

Did you verify the cas is working properly? While I use a different one on my 99 when it was failing I experienced missing and of course first tried everything you did before looking at it.

 

[nicknorth11]

Yes, as stated in the first post.

Log posted in original post.

 

[boost97gst]

Well, you didnt open this thread half-cocked, ill say that. You did just about everything.

The only thing i would try, and i know its looking good in link and all, is replace the gm maf with the stocker and set it back to stock in link. Thats about the only thing you havent tested at this point. Very thorough... I hope you find the problem soon

 

[nicknorth11]

Thanks. I don't have the stock setup, but I can try to locate one.

 

[tru-dsmer69]

Sounds like power transistor I had the same problem.. Check computer also...

 

[boost97gst]

Sounds like power transistor I had the same problem.. Check computer also...

When he says "ignitor" just read power transistor. As he explained, its already been swapped out. ECU is a long shot but cant rule it out yet.

 

[ChrisMgst]

How long have you had link?
Have you done a TPS adjust? Where you give it a full throttle swing? I see your offset is 11% but you didn't click it.
Also I see you have AEM WB in the rear yet it's not being captured in your log along with your RawLinWB.

 

[nicknorth11]

I've had link for about 7 years. TPS adjust was done a long time ago for a temporary fix, but is not needed now, hence the unchecked box. It is setup and working perfectly now. My wideband is being captured as "AEMWBGaugeR1" and is in the displayed values.

 

[SBstar]

I found an interesting thread on the link forums that somewhat sounds similar. Might have nothing to do with your issue but one more thing to check. They didn't do a very good job explaining exactly how the car was "running" with the issues, just that it was idling terribly, forcing them to rev to keep it going, but they did say the car was still driveable. Your wideband doesn't seem to be reading rich though.

The diaphragm for the fuel pressure regulator tore. Which in turn was pumping fuel through the diaphragm and out of the boost reference hole back into the intake. So it was essentially flooding the motor with unaccounted, pressurized fuel. We put a stock fuel pressure regulator back on the car and it runs like a champ. We rebuilt the Aeromotive regulator and stuck it on another car and it works like a champ again.

Also are you running the maft with a translator or the Link cable? Try another translator as it may be faulty?

Most of the suggestions I'm finding for you seem ridiculous in my mind, but I have nothing else to throw out as you've checked just about everything!

 

[nicknorth11]

Thanks Shane! I'm using the link cable. My regulator only has several thousand miles on it, but I guess it's possible. I really appreciate your help with this.

 

[Colt4G63 also]

It sure looks lean, and your injector test confirmed that you're getting spark in all four cylinders. How did you test fuel pressure? Was the car running? Did you check for flow coming out the return line? Did you check fuel flow under boost? Does it miss at idle? I see lean as hell under all conditions, and lean will feel like a miss or stumble. It sounds like you are barely pumping enough fuel to idle the engine. I would look more closely at the pump and strainer. Possibly reverse flush the pump if you find it lacking.

 

[nicknorth11]

It sure looks lean, and your injector test confirmed that you're getting spark in all four cylinders. How did you test fuel pressure? Was the car running? Did you check for flow coming out the return line? Did you check fuel flow under boost? Does it miss at idle? I see lean as hell under all conditions, and lean will feel like a miss or stumble. It sounds like you are barely pumping enough fuel to idle the engine. I would look more closely at the pump and strainer. Possibly reverse flush the pump if you find it lacking.

Not long ago, I put on a new exhaust that has a bad leak right before the wideband, so it's not accurate right now. The tune is fine, though. Fuel pressure was tested with the car off and at idle. I didn't check the return line for flow. The issue happens under all conditions, so checking flow under boost isn't necessary. I have two pumps, a walbro 255 in-tank and a bosch 044 inline. Both pumps are kicking on, and the filter is clean.

 

[Colt4G63 also]

If you say so. Is it supposed to never enter closed loop mode, or is that because the front O2 sensor reads lean so often?

 

[nicknorth11]

I'm not sure why it's not entering closed loop. I'd love to figure that one out. I plan to check fuel flow at the return, like you suggested. I'll also check some other things regarding fuel to make sure that's not my problem. Thanks a lot for the recommendations, I really appreciate the advice.

 

[ChrisMgst]

Your wideband isn't calibrated correctly. In your pin assignments you have it listed as aemgaugeR1 and on your displayed values it's listed as LinWideband. I'd get that gauge reading correctly. Pull your spark plugs lets have a look at them.
Why isn't the TPS adjust no longer needed?

 

[nicknorth11]

Your wideband isn't calibrated correctly. In your pin assignments you have it listed as aemgaugeR1 and on your displayed values it's listed as LinWideband. I'd get that gauge reading correctly. Pull your spark plugs lets have a look at them.
Why isn't the TPS adjust no longer needed?

How familiar are you with this stuff? My wideband is setup correctly. The pin assignment and displayed value are both aem...r1. It is off now due to an exhaust leak, but has been working correctly since installed. Secondly, I've pulled my plugs and replaced them, as stated in the original post. Lastly, TPS adjust isn't needed if the sensor is mechanically set correctly, which mine is.

 

[ChrisMgst]

In the log you posted your RawLinWB says "V", and your LinWideband says "1"
I did notice that your combined fuel trim stays at zero throughout the log.
I'm no expert on Link btw.

Someone who has viewed his log please chime in, and correct me if I'm wrong.
In his pin assignments does it say aemgaugeR1, and in his log does it say Linwideband?
In the log they don't show up as highlighted or being captured.
Now I'll mind mine. Good Luck

 

[MJBean420]

I just figured mine out. It was from a cracked valve guide on cylinder 2 giving a sporatic random misfire.

 

[ChrisMgst]

What injectors are you using? Your profile says 1450cc. While your log says different?