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Non-Z related, but maybe you guys can help me out?


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No one else seems to know what's going on. Basically, here's the situation:

 

my daily driver's a neon r/t, with intake, mopar ECU, mopar street header, and an underdrive pulley. (Relevant mods, anyways). The header's collector gasket got cooked a little while ago, and I had it replaced. The guy who did my exhaust confirmed that my car didn't feel like it was running right. Pyrometer readings on my header pipes were reading 220* on cyl 1 and 4, and 320* on 2 and 3!

 

I know middle two cylinders run hotter, but 100* difference is a little much. The pre-cat O2 sensor from the header is immaculately clean, no deposits. The post-cat o2 sensor is somewhat burned with deposits. plugs are new, proper gap, and there are no exhaust leaks. The ECU isn't giving me any rich mixture failures.

 

I am thinking maybe the throttle position sensor, or bad injectors? Neither TPS nor injector failure show up on the OBD II codes when I do a test. Truthfully, the car gets beat on a lot, has seen track, etc. But I also do proper maintenance on it. Car goes to dealer for inspection in 2 weeks (theyre booked), under extended coverage.

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TP sensor tells computer what the throttle is doing and it responds evenly across the cylinders - I don't think that's it. I had a pyrometer in my Mustang for awhile and noticed that one side always ran cooler, did some swapping of wires and checking and figured it out - dribbling fuel injector! This was one cylinder on a bank of four and because of that the O2 changed the mixture on that side to compensate for the condition.

 

I'm not sure the above applies to you except that I KNOW a bad injector will change the temps. In my case the car seemed to run fine but the injector was likely dribbling. I'll put my money on a bad injector or maybe an injector driver in the ECU?

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That sounds like a likely explanation. I don't think ECU had anything changed on it, it's been in the car for over a year prior to this incident. Granted, I may not have known about it until I replaced the stock cast iron exhaust manifold with a header. It could very well be bad injectors. Thanks for the tip.

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  • 2 weeks later...

Update. Took the car into the dealer today, and the guy calls me back and tells me the car's perfectly fine within factory specs. I asked him about injectors, and he said it was fine because it didn't spit out any error messages from the ECU. What a numbnut!

 

I could've told him that myself, I can check my own error codes. I was thinking, since the cylinders 2 and 3 are running hotter, they are actually running richer, not leaner. The higher temp output is because the unburnt fuel is igniting in the header pipes, causing the gasket to cook. icon_sad.gif Tomorrow I'll swap injectors on cylinders 1 and 2 as a test and to a pyro reading on the header pipes off those cylinders. If the temps change, I have leaky injectors.

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