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1G Bad Intermittent misfire when warm, and warm starts

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1slw3sgte

Proven Member
31
8
Jul 3, 2020
Los Angeles, California
My 91 tsi randomly when warm gets a bad misfire as if it’s running on 2 cylinders, basically not drivable. When it happens also my wideband reads super rich (at 10.0).

After waiting for like 10-15 minutes for the car to cool off it will turn on and run fine until it wants to misfire again. I’ve replaced coil pack, spark plug wires, and power transistor but still have the issue. I’ve also took my injectors to get cleaned and tested and their good. No check engine light.

This issue has to be electrical because the car runs solid until that happens then have to wait for it to cool off, no overheating issues.
 
Despite everyone telling you that the proper way to fix this is to NOT keep replacing parts you guess might be at fault, you're still doing this? How do you expect people to try to help you if you're not following their advice?
 
I've only looked quickly at the first log but I have to ask what's up with your wideband? You tell DSMLink it's connected to the front O2 but DSMLink doesn't think so in the ECU Inputs tab but NBO2 isn't enabled on the NBO2 sim tab.

You have made a few changes to the fueling DA tables, do you have strong cases for each of them?
 
Despite everyone telling you that the proper way to fix this is to NOT keep replacing parts you guess might be at fault, you're still doing this? How do you expect people to try to help you if you're not following their advice?
I’m very sorry I was replacing parts its my fault. This problem started before I changed said parts I changed the narrowband o2 sensor before. Alternator battery are new like a year old and the coolant temp sensor is new aswell.
I've only looked quickly at the first log but I have to ask what's up with your wideband? You tell DSMLink it's connected to the front O2 but DSMLink doesn't think so in the ECU Inputs tab but NBO2 isn't enabled on the NBO2 sim tab.

You have made a few changes to the fueling DA tables, do you have strong cases for each of them?
I have the narrowband sensor still in the from o2, the wideband I have is not connected to the ecu. Do you mean the fuel table? They are 1200cc but you need to add your global fuel due to e85. The airflowsperrev go up a a whole lot always when it starts to misfire maybe that indicates something, also the timing goes down a whole lot aswell, as if it’s not advancing timing.
 
Spark plugs? The spark plug gap sets the maximum voltage seen by the coils and transistors. If the gap is excessive (worn or incorrectly gapped when installed as for 'pre-gapped' plugs that aren't for a turbo car) there's higher stress on the other parts and they may fail.

Pull the plugs, check the gaps, set them per the service manual -- that would be 0.028 on a 2G but 1G may be different. If this makes your problem better you also have a coil or transistor problem but if you now replace whatever is the failing part, it'll have a normal lifespan.
 
SD guys, I thought the MAP sensor got logged as Baro but in these logs it's flatlined @ 30.1 inHg. With all the reported problems with the Omni sensors lately and the spikes in AFRest and InjOn in these logs I wanted to make sure the MAP wasn't also spiking but I can't seem to see the real values.

IAT also seems to be flatlined and I would expect a little change as time goes on.

The log also shows why I don't like simulating the IPS. It misses the throttle opening on several blips.
 
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SD guys, I thought the MAP sensor got logged as Baro but in these logs it's flatlined @ 30.1 inHg. With all the reported problems with the Omni sensors lately and the spikes in AFRest and InjOn in these logs I wanted to make sure the MAP wasn't also spiking but I can't seem to see the real values.

IAT also seems to be flatlined and I would expect a little change as time goes on.

I log my MAP sensor with the Baro input, and "Baro" in my logs is always flatlined at 30.1 like his is. I don't know why. But he needs to pick "Omni Power 4-bar" in "Captured Values" to log his MAP. Then we would see it. I see mine as "LinBoost".

Something like that with his IAT. He needs to pick "GM IAT" in his Captured Values list to set it up. My IAT always logs as 77 deg also, but I actually don't have an IAT sensor. I'm looking at one of Marty's logs right now and he does have a GM IAT sensor. His logged IntTemp value is always 77 also. But you can find IAT in his Displayed Values list and that does give a varying number that looks real. I think his shows up as "IAT" rather than "GM IAT" because he actually named it "IAT" with the middle column on that page where you can give it your own name.
 
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Bump… So the issue I’m having happens randomly either cruising, or on start ups. When I turned over last time and started to do that problem I pulled off the plugs and all of them where wet with e85 and also the cylinders had Had in burnt fuel in it so the problem is that it either floods or the ignition acts up idk. I opened the ecu and no leaking capacitors and resodered some pins that where cracked, ecmlink rebuilt it by previous owner like 2 years ago. Still problem persists. Also a new issue has arised, at 1500 rpm and 2200rpm at those specific rpm the car goes lean, like lean spikes.
 
Make sure all your connectors are tightly fitting. I had a loose TPS connector that drove me insane. It did exactly what you are saying here.

I had this problem recently. It would only happen sometimes and then come and go, setting the P0300 random misfire. It would only happen with a load on the engine while driving. I replaced the plugs, wires, coils, PTU, CPS and cleaned the carbon out of my ignition switch (small voltage drop) and checked all voltages and signals of the ignition system on an oscilloscope; couldn't see anything wrong. Playing around under the hood I bumped the connector for my TPS with my hand. It felt a little loose, like I could wiggle it. I used two zip ties to firmly anchor it and went for a cruise. Haven't had the problem since. My guess is hitting bumps and engine vibration was probably sending intermittent TPS data to the ECU making it think the throttle was closed at times which would then turn off the injectors.

Could be other connectors too, such as PTU, injector, etc. These cars are dinosaurs and lots of things can be wrong with the connectors. Make sure the contacts are clean and bite tightly against the pins. They can be corroded or tension can be worn out. I ordered all new connectors for mine. Wasted too much time on a stupid problem that could have been easily prevented.
 
Confirmed by swapping out parts or voltage test?
From logging, it would jumpto 45.2psi random which is max for the Omni 4 bar setting. I put a gm 3 bar changed the setting on link and haven’t had the issue since.

Yes Omni 4 bar old logo not the new one, might buy the revised version later
 
From logging, it would jumpto 45.2psi random which is max for the Omni 4 bar setting. I put a gm 3 bar changed the setting on link and haven’t had the issue since.
Any other way this unit can be tested without the logging app? Pressure tester?
 
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