Renix Jeep suddenly won't start...
05-14-2016, 07:06 AM
#1
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Year: 1988
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Engine: 4.6L I6 Stroker with port matched +99 intake and 62mm TB
Renix Jeep suddenly won't start...
Like the title says, my MJ won't start...
I JUST got plates back on it this morning and on the way home, radiator busted and overheated right as I was getting on my road. It shut off before I got to my driveway and I coasted to the parking pad. I let it cool, swapped in a new radiator, washed the engine and entire bay (since it had antifreeze all over it), started it up and let it run till operating temp. Idle RPMs kept going up, and I figured out the manifold bolts were loose, so I tightened them. TRIED to start it again after that, and nothing. Just turns over and over, but no fire.
Checked CPS, TPS, MAP, coil, plugs, the harnesses, etc. The only thing I noticed is that the injector plugs weren't showing any voltage on my multimeter when I tried cranking it. Seems logical that it would pulse the injectors to give fuel when starting, but nothing showed on the MM in either DC or AC voltage mode... Could that be my issue? Did I somehow fry my ECU?
I JUST got plates back on it this morning and on the way home, radiator busted and overheated right as I was getting on my road. It shut off before I got to my driveway and I coasted to the parking pad. I let it cool, swapped in a new radiator, washed the engine and entire bay (since it had antifreeze all over it), started it up and let it run till operating temp. Idle RPMs kept going up, and I figured out the manifold bolts were loose, so I tightened them. TRIED to start it again after that, and nothing. Just turns over and over, but no fire.
Checked CPS, TPS, MAP, coil, plugs, the harnesses, etc. The only thing I noticed is that the injector plugs weren't showing any voltage on my multimeter when I tried cranking it. Seems logical that it would pulse the injectors to give fuel when starting, but nothing showed on the MM in either DC or AC voltage mode... Could that be my issue? Did I somehow fry my ECU?
05-14-2016, 10:02 AM
#2
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
You won't see an injector pulse if the ECU sees no CPS input.
05-14-2016, 09:34 PM
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Year: 1988
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Even though the CPS tested fine using your method, could it still be malfunctioning?
05-14-2016, 10:54 PM
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But, is the signal getting to the ECU?
Still got the C101 connector? If so, that could very well keep the CPS signal from getting to the ECU.
What is the AC output voltage of the CPS when cranking?
Last edited by cruiser54; 05-15-2016 at 09:20 AM.
05-16-2016, 07:15 AM
#6
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Figured it out... TPS died. Strange since it tested alright, but unplugging it allowed it to start... Can't quite wrap my mind around that. 
05-16-2016, 07:25 AM
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05-16-2016, 07:53 AM
#8
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Any wiring compromised up the line from it?
I would test for ground and 5 volt reference voltage at the harness plug.
A should be about 5 volts with key On.
B should be an ohm or less with key Off.
05-16-2016, 08:04 AM
#9
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My guess is the harness is fine. I put another TPS on it and it starts and runs fine.
05-16-2016, 08:05 AM
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