Running like crap.

[luke_hkd]

My 1992 RT/TT has been running poorly off and on since I've known it. My brother and I have scanned it, and it doesn't fire on cylinder 6 and the engine light comes on almost every time it runs lately. This problem usually only occurs when the engine reaches operating temperature. It used to kind of clear up after running at highway speed for a while, and coolant temp has never been out of the ordinary. The code says injector circuit and also tps.
We know it isn't the ecu, because it runs my brother's 93 just fine. Could it be the tps? we can't switch tps s because 92 and 93 are different.
This is really bothering me, and I really need my car. I can't figure out why it would miss and why the tps would only be bad after running for a while. Anyone have any ideas or suggestions?
Any ideas would be very appreciated. Thanks a lot in advance.

[1993RT/TT]

Have any wise people ever had this issue? I've dug up several threads with these same symptoms but the threads always die before the resolution

[Jimvr4]

If #6 isn't firing have you determined whether it's a spark or fuel issue? There's a similar unresolved thread on the other site that appears to be a fuel issue on #4.

[Roybatty]

There are numerous things that can cause the 'running like crap.' But since you are getting codes...I would focus on that, as Jim mentions. Pull spark plug #6 and assess condition. I believe the code only tells you which bank, so you will need to check the rear bank IIRC, may as well check all while you are there anyway.

Plug condition will lead you to answers...is it soaked with fuel, no spark, could be anything in the 'fire' spark, plug, wire, coils, etc. How does the suspect plug look compared to others? If its less brown looking, could have a fuel issue in that cylinder...ie injectors, filter, fuel pump, regulator etc.

Stealth 316 - Spark Plug Change (http://www.stealth316.com/2-sparkchange.htm)

[Chris@Rvengeperformance]

I would replace the rear injector harness. It replaces all 3 rear injector wires and clips. About $25.00 from cherry hill mitsu.

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[Jimvr4]

I would replace the rear injector harness. It replaces all 3 rear injector wires and clips. About $25.00 from cherry hill mitsu.

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Not a bad suggestion but be sure to get the correct one as the NA and turbo cars use a different harness.

[1993RT/TT]

results: we just replaced the TPS and calibrated it with the datalogger. The car ran better than it had since june when it got really bad (couldn't drive 3 miles without the CEL coming on). Everything logged great and no issues. Turned it off and started it back up about 20 minutes later and it threw its codes 14 and 41 again, and its missing on cylinder 6(again). What is going on? I'm completely at a loss at this point and i don't know what to try next. It has something to do with the temperature of the engine compartment i know that for a FACT. Please help, thanks
Jake

[rawavr4]

Did you change the rear injector harness? Code 41 is the injector circuit.

[Mike-92RT]

maybe check the wiring to your injector harness?.. maybe #6 isn't plugged in properly?.. could also be a wiring issue.

pull #6 sparkplug, smell if fuel is getting to it, also check to see if the sparkplug is giving out spark.

[luke_hkd]

Spark plugs are great, so scratch that variable. Going out to inspect harness and replace injector 6 now. Have some spare injectors laying around so it's worth a try right?

Could engine heat cause injector failure like this? Before the car warms up, it runs great and doesn't miss. This conditional failure is what puzzles me. We thought we had it fixed during the test drive after the TPS replacement because it ran so strong. It even got pretty warm and the CEL didn't turn on and it didn't miss. Only upon restarting the engine after a few minutes did it start missing again. Then a few hours later we drove it again and it only ran good for about a mile before the CEL and missing returned.

So for now, I'm going to try injector. Then the injector harness I suppose. Others have had similar issues caused by ECU and TPS, both of which are known to be good in this instance.

Edit: Found out plug wires are serviceable but should be replaced soon. After changing the injector, nothing has changed. The harness looks just fine as well.

[1993RT/TT]

Did you change the rear injector harness? Code 41 is the injector circuit.

this code was thrown when my ecu was bad and when i had a bad injector. I think it comes on anytime there is an injector not working for whatever reason, not just because the harness is bad.

[rawavr4]

It came on for me once when I left an injector connector loose. But it doesnt hurt to change that harness anyway, especially on high mileage cars with old cracking wires.

[speedy25]

And speaking of old cracking wires....

Ignition coils are known to fail or be inconsistent just because of their age. If yours are originals, replacing all three is a good thing. I have had one test good on continuity but still be BAD and not fire both plugs so dont be fooled. I have yet to hear of an injector fail from age even though they are basically the same thing... coils of varnished wire.

-SP

[Roybatty]

OP...did this ever get resolved???

[1993RT/TT]

Yes, I took it to a dealer and injector 5 failed several tests. I replaced it and it hasn't repeated the issue since. I don't understand how or why a bad injector 5 would kill cylinder 6 but it did and the car runs well again.

edit: the dealer wanted $385 ($110/hr) to change a front injector that I did in about an hour