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88 4L Renix cranking issue

DaveVmax

NAXJA Forum User
Location
Georgetown, ON
Ok this has been an ongoing issue

the jeep cranks and it sounds like it wants to run but it just doesnt run

Ive replaced this:

-all the main grounds plus a new ground from battery to body
-plugs
-wires
-cap/rotor
-coil
-TPS
-IAC
-starter
-ICM
-CPS
-injector seals
-cleaned the injectors
-check valve went bad so i replaced with in line check valve

I had replaced the ICM tonight and the truck actually started up and ran great the idle was dancing a little though seemed kinda odd..

all of the above has been changed this week

i turned the truck off and went inside came back out and went to crank it just kept cranking like it did before... seemed like i was back to square one... my friend opened the throttle half way and it managed to start no problem after that...

im out of ideas..

but one thing i did notice since i bought this truck in the fall that the fuel pump is always running (example: i will turn the key forward and the pump will come on but it just stays on).... is that normal? I own a 92 HO and it doesnt do that same with my 2000.
 
ok i decided to put the truck in my garage over night so i could warm up a little.... i went out to start it and its cranking fine now.... can the cold really have a lot to do with this?

it was -20C last night when we were having issues in the driveway.
 
The motor must spin ~300 RPMs before it generates enough current at the CPS for the Renix ECU to decide to start the motor. If the cold was keeping it from spinning that fast, yes, it would not start.

FWIW normal key on in the renix is the fuel pump runs 3-5 seconds, then turns off until you move the key to the "start" position. If the ECU does not see CPS signal that says the motor is running it will kill the pump when the key leaves start.
 
ok just wanted to update this...

i disconnected the battery and touched the - and + together for over a minute

connected and the truck runs PERFECT now starts perfectly drives great for the last 2 days...

does the computer need to re learn after you install a new ICM?
 
i have no idea but it runs perfect now.... i wonder if there is a bad wire somewhere

Or connection.

My suggestion is to buy a can of electronics cleaner. Napa has it. Take 15 to 20 minutes some day and unplug every engine management connector in the engine bay one by one. Flush each side out with the cleaner and plug it back in. What the heck. Do every one you can see including the ones near the rear of the valve cover that go to the trans.

I do this on every Renix Jeep I work on.

Sinci it's an 88, do a thorough cleaning and pin tightening on the infamous C101 connector on the firewall behind the brake booster.
 
Or connection.

My suggestion is to buy a can of electronics cleaner. Napa has it. Take 15 to 20 minutes some day and unplug every engine management connector in the engine bay one by one. Flush each side out with the cleaner and plug it back in. What the heck. Do every one you can see including the ones near the rear of the valve cover that go to the trans.

I do this on every Renix Jeep I work on.

Sinci it's an 88, do a thorough cleaning and pin tightening on the infamous C101 connector on the firewall behind the brake booster.

Good advice here on cleaning engine mgmt. connectors and also that C101 connector. It is known to cause problems..........

I always keep a spray can of electrical contact cleaner in my toolbox. Available anywhere including Wally World for about $5.00
 
yup ive done this already on every connection under the hood and some electrical grease


im thinking maybe a wire is rubbing somewhere... ill take a good look around today.
 
bump truck runs but has an intermittent cranking issue still..

it will crank then die as if the starter is giving out kicks it down and has barely enough power to get it going.

i dont think the power is getting cut from it because instantly its cranking again....but it will repeat this 2 or 3 times before it will run.. when it runs it runs perfect.

it will never do this on cold starts only after its been driven then parked and cranked again 5-10-15 minutes later.

im out of ideas?

can the manifold air temp sensor be involed? or 02 sensor?


dont say starter because its brand new.
 
Last edited:
I'm betting on a bad mains cable, or the braided ground strap that runs from the head to the firewall.
 
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