Still would help illuminate the situation knowing fuel trim values, at idle and on the highway. One other troubleshooting technique described on this forum is to run the engine in the dark and look for arcing all along the #1 wire path. I would examine the crank reluctor ring for any bent tabs out of alignment, just because it is easy and you have tried everything else. I thought you were going to swap the ECU as a final troubleshooting test.

 

Yeah I’ve replaced and cleaned the MAF a few times and I just recently replaced the fuel pump. So I think it’s gotta be ignition as it’s really just cyl 1. I’m also not throwing codes.

I’ve got a page set up on the Ultragauge to monitor fuel trims, but I can’t recall how to decipher the values. I also recently did up stream O2 sensors just as matter of service (NTK or whatever, not Bosch as seems to be the recommendation) as well and set up a page to monitor, but I don’t think that is my issue.

If the plugs don’t get it for me, I’ll probably run a can of Sea Foam in the tank again (I did the one into the intake a good while back as well). I’ve cleaned my idle control valve and even pulled the throttle body and cleaned it when I did a new heater plate.

Last will be coils and wires I guess.

I need to study how to read fuel trims again…

 

I’m kinda adding a bunch to what isn’t my thread, but I hope it will help someone as this forum has been invaluable to me during my D2 journey.

According to the UG manual, fuel trim is basically how long the injectors stay open based on a bunch of variables (O2 sensors, MAF input, ambient temp, coolant temp, engine load, and a few others). Negative values mean rich and positive values mean lean. And just to be clear, Cyl 1 is on Bank 1 in the values the UG presents. Short is what it’s doing in the immediate and Long is what it has been doing historically. I suspect this is part of what “Reseting Adaptive Values” in the Nanocom does.

So I’ll just monitor that for a bit and see what I should see…

 

I had a few minutes before my next call for work and went out and took a couple videos of fuel trim and O2 sensor values.

I think by and large I’m good.

I let it get to around 170F and this was a couple minutes after a stone cold start (sat overnight) and ambient is in the mid 80s.

https://photos.smugmug.com/Cars/Land..._1773-1280.mp4

https://photos.smugmug.com/Cars/Land..._1774-1280.mp4

Sorry, I don’t know how to embed videos from the photo hosting site I use.

 

Long Tall, LTFTs are nearly +18%. That's a lot. 25% is maximum. Factory default is near zero at sea level. So the ECU is needing to add a lot of fuel to achieve stoich. STFTs are taking away fuel when you open the throttle. So, likely means you have a bit of a vacuum leak (less vacuum when throttle is open, so less air leaking in, so less fuel required). Classic vacuum leak symptoms. Equal values on both banks is good. Equal values also means the vacuum leak is effecting both banks equally. O2 sensors are both modulating. That's also good and shows the system is still able to compensate properly.

So, I would check for vacuum leaks. For example, my truck had similar symptoms when I forgot to connect the manifold vacuum tube to the fuel pressure regulator. Maybe check all rubber/plastic tube connections to the intake manifold, as well as gasket joints and injector seals. Maybe #1 injector to manifold seal is leaking.

 

You are a rock star! I will say those LTFTs dropped when I drove it this evening and were closer to 10. And I’ve not been below 6k feet for a good while, but still I’d think it would be leaner not more rich at elevation.

But still, what makes you oh so right is that I buggered one of the intake connections and used RTV to sort it, and that was like 3+ years ago. I need to just order that part and replace, but I bet that’s it as just like you said, because under throttle I don’t get the stutter except right off idle.

As for Cyl 1, again, you could very well be correct and if the plugs don’t sort it along with the vacuum leak, I guess I get to pull the intake and do the injector seal dance.

Thanks!!!