TPS or computer fried? - no start
#1
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TPS or computer fried? - no start
My XJ broke down on me, threw the parts cannon at it, ended up cleaning the C101 and it fired up. After getting the motor running i went back to readjust the TPS voltage, since i had removed and reinstalled it, so during my attempt to adjust the TPS voltage, backprobing with safety-pins, i think i shorted something.. the TPS or maybe the computer. It cranks and cranks, no start. I do still get 5vdc at the TPS. Thinking about just buying a computer off of ebay, i'm out of ideas.
#3
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
If you still have the 5-volts supply from the computer, then I doubt it's fried. Will it start if the TPS is unplugged? Still see good ground on the black wire ground wire to the connector? Do you have spark or injectors going?
#5
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I have good ground, it doesn't start with the TPS unplugged. It tries to start when spray a little throttle cleaner down the throttle. Perhaps the injectors aren't getting a signal.
#6
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Year: 1997
Model: Cherokee (XJ)
Engine: 4.0
My XJ broke down on me, threw the parts cannon at it, ended up cleaning the C101 and it fired up. After getting the motor running i went back to readjust the TPS voltage, since i had removed and reinstalled it, so during my attempt to adjust the TPS voltage, backprobing with safety-pins, i think i shorted something.. the TPS or maybe the computer. It cranks and cranks, no start. I do still get 5vdc at the TPS. Thinking about just buying a computer off of ebay, i'm out of ideas.
When you turn the key to the ON position, do your gauges move? If you leave the key on for 15 seconds or so and your needles don't move and "NO BUS" shows up on the odometer, chances are the PCM is dead. Ask me how I know.
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cruiser54 (02-06-2022)
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#8
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That is correct, I have an 88'. I do have issues with the fuel gauge, replaced the fuel pump over a year ago. Maybe a loose instrument panel ground, but i don't think that would cause a no start. So, there are 5vdc at the TPS "A" wire, could it be the signal side that got shorted? Going to replace the injectors today and clean up those connectors, I got some 746's last week.
#9
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This is what i've done, so far:
replaced ignition coil
cleaned up engine grounds and sensor grounds
replaced IAC
replaced TPS
replaced fuel filter
replaced a couple vacuum lines
and to reiterate, it was running(rough) til i screwed with the TPS.
replaced ignition coil
cleaned up engine grounds and sensor grounds
replaced IAC
replaced TPS
replaced fuel filter
replaced a couple vacuum lines
and to reiterate, it was running(rough) til i screwed with the TPS.
#10
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
Might be worth trying another computer at this point. I can't see how shorting the TPS signal wire to either +5 or ground could damage it though, since the since swings between those two voltages. The Renix TPS voltages run backward from the HO TPS, in that 5-volts means closed throttle and 0-volts means wide open (also the reason for the dual output TPS if you have an automatic). I thought maybe the single wire could be shorted to ground and the computer was trying to do flood clearing, but you said you measured 5v on the signal wire with it disconnected.
#11
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Is it possible for a bad coolant temp sensor to keep my XJ from starting? When I crank the engine, only the engine temp light comes on, no battery light, no oil pressure light, etc..only the engine temp light.
#13
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
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#14
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Year: 1990
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Makes me wonder if you have a bad ignition switch. Check the 5 volt reference on the TPS for starters.
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