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Renix Issue!!!!

J

JustinTurney

NAXJA Forum User
Location
Reno,NV
my 1990 4.0 just will not run. it'll crank and it will attempt to start, but once the key is in the run position, immediately the engine just dies. everytime, i try to start it, the same issue crank tries to catch, let go of key, nothing. i've replaced the ignition switch due to a burnt connection and the lock cylinder followed suit, checked power to the ballast, tps, cps, did relay swap with another jeep, checked the power to the ignition switch, and still having the same issue, could this be related to a ecm or the neutral safety switch? if not any suggestions, also does anyone have a good wiring schematic for the ignition switch and engine control system for the 1990 year? haynes is brainless!!!!!!
 
Same response as in the other forum. Please update here too when you check the FP.
 
You say you checked power to the ballast but did you bypass the ballast as I suggested before?

A faulty NSS will prevent cranking in the first place.
 
First thing I would check is for steady spark. If no spark, check the CPS, you want to see >.50 AC cranking voltage out of an isolated CPS. Use a low AC volt setting on a volt meter.

Check the fuel pressure regulator for a leak into the vacuum line connected to the FPR. Check the fuel pressure in the on and start positions. Needs to be at least 29-30 psi. That fuel pressure should hold with the engine off!!!!

Try pressing the gas peddle to the floor and hold while cranking. If it starts and runs, it was flooded!!!!!
 
Update: I have replaced and bypassed ballast, replaced cps, replaced ECM and ICM, and I have cleaned and relocated dipstick grounds to engine battery ground location. The jeep is acting better with wanting to start, but it still will not. It's making a solid effort at running, but still will not run. Oh, I did check spark plugs and distributor cap. The distributor looked slightly but still good, and the plugs had slight carbon foul, but stilll looked fine. I cleaned the plugs and put them back and still nothing. Any new sugestions or am I in serious trouble? Please help.
 
Did you verify that you have spark? Pull a plug, keep the plug wire on and touch the plug to ground and observe what colour spark you have. Spark + fuel usually equals run so both of those need to be checked. Do you have good pressure at the fuel rail?
 
JustinTurney said:
Update: I have replaced and bypassed ballast, replaced cps, replaced ECM and ICM, and I have cleaned and relocated dipstick grounds to engine battery ground location. The jeep is acting better with wanting to start, but it still will not. It's making a solid effort at running, but still will not run. Oh, I did check spark plugs and distributor cap. The distributor looked slightly but still good, and the plugs had slight carbon foul, but stilll looked fine. I cleaned the plugs and put them back and still nothing. Any new sugestions or am I in serious trouble? Please help.
Click to expand...


But, allas, you have doing nothing I suggested yet? Not sure moving the grounds at the dip stick was a wise choice either.
 
I had this same exact thing happen on my 89 a few days ago where the engine would fire up but once I release the key from the start position it would die off, ended up being a bad Relay, fuel pump relay I think.

You mentioned in the first post that you did a relay swap (not sure if it was just the starter relay you checked, or all of them), but may be worth double checking those relays and the sockets/wiring associated with them (if you burned up the ignition switch wiring, you could have burned up some wiring at the relays too).
 
Last edited:
I have seen a defective ignition switch cause similar issues. The things that have been listed are far more common, but if you have ruled them out, I would think switch.

I would measure the voltage on the fuel pump relay drive and see if it goes away when you quit cranking.
 
old_man said:
I have seen a defective ignition switch cause similar issues. The things that have been listed are far more common, but if you have ruled them out, I would think switch.

I would measure the voltage on the fuel pump relay drive and see if it goes away when you quit cranking.
Click to expand...

"i've replaced the ignition switch due to a burnt connection and the lock cylinder followed suit,
Click to expand...
Post #1, OP.

He already replaced the ignition switch (post #1), so I was thinking the new one may not be bolted down in the sweet spot, linkage wise, or the wiring may need repairs (He did say it was burned) but I wanted to see the other test results, tests I suggested before suggesting the switch path. Not sure how good the OP is with a multi meter??? Seems to be a throw parts at it, swap parts person?
 
1. Check for spark
2. Check for fuel
3. Check for air

You must have all 3 to run. Once you've verified you have all 3, then you perform advanced troubleshooting.
 
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