NCSUcherokee
NAXJA Forum User
- Location
- North Carolina
This problem goes back a few threads, so I might be forgetting some information, but I will try to make this description as robust as possible. I wanted to start a new thread, presenting the information in a different manner, maybe that will bring up some new ideas.
Vehicle: 1990 XJ
Engine:1988 4.0
I have not been able to get this engine to run since i swapped it in. I can nurse it to life and get it to idle fairly well, but beyond that it is pretty much DOA. I'll run down the symptoms
-Applying throttle causes popping and backfiring through the intake manifold; HOWEVER, moving the TPS to full open actually makes the idle smoother, but doesn't effect off-idle performance. It was my understanding that moving the TPS by itself would cause the engine to stumble and die.(This has me stumped)
-IAC/IAS whatever you like to call it, seems to have a detrimental effect on idle. Best engine results are obtained with the IAC unplugged. almost as if it is not letting enough air in for combustion. (To much fuel/not enough air?)
-Spark plugs were replaced when the engine was installed. They were covered in powdery carbon after running for only a couple of minutes. (This is what originally lead me to think it is a rich A/F or weak spark)
-Extremely hot exhaust, to much unburnt fuel leaving the CC. This actually melted the seat belt that was above the muffler.
The plugs, wires, cap and rotor were replaced when the engine was installed. An optima battery jumped to a running vehicle, and a replacement coil made no difference
The CPS ohms 225
TPS Voltage is variable from .56 to 4.77 and was swapped against an extra, yielding no change.
The map sensor volted out of spec so it was replaced. the line is undamaged.
O2 sensor was swapped against a working unit.
The CamPS/distributor was swapped/Indexed.
Grounds were cleaned.
Timing chain is still in correct position.
and after all that, the engine will still not rev above 7 or 800 RPM
Where else can i look for problems
Vehicle: 1990 XJ
Engine:1988 4.0
I have not been able to get this engine to run since i swapped it in. I can nurse it to life and get it to idle fairly well, but beyond that it is pretty much DOA. I'll run down the symptoms
-Applying throttle causes popping and backfiring through the intake manifold; HOWEVER, moving the TPS to full open actually makes the idle smoother, but doesn't effect off-idle performance. It was my understanding that moving the TPS by itself would cause the engine to stumble and die.(This has me stumped)
-IAC/IAS whatever you like to call it, seems to have a detrimental effect on idle. Best engine results are obtained with the IAC unplugged. almost as if it is not letting enough air in for combustion. (To much fuel/not enough air?)
-Spark plugs were replaced when the engine was installed. They were covered in powdery carbon after running for only a couple of minutes. (This is what originally lead me to think it is a rich A/F or weak spark)
-Extremely hot exhaust, to much unburnt fuel leaving the CC. This actually melted the seat belt that was above the muffler.
The plugs, wires, cap and rotor were replaced when the engine was installed. An optima battery jumped to a running vehicle, and a replacement coil made no difference
The CPS ohms 225
TPS Voltage is variable from .56 to 4.77 and was swapped against an extra, yielding no change.
The map sensor volted out of spec so it was replaced. the line is undamaged.
O2 sensor was swapped against a working unit.
The CamPS/distributor was swapped/Indexed.
Grounds were cleaned.
Timing chain is still in correct position.
and after all that, the engine will still not rev above 7 or 800 RPM
Where else can i look for problems
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