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MJ still won’t start! 🥺

RavenMocker

NAXJA Forum User
Location
PNW
1988 MJ 2.5 with manual. One day it just stopped running. So I troubleshoot it down to the fuel pump. Bought a new fuel pump and it ran. Everything was going well and then it wouldn’t start. I can hear the fuel pump turn on when ever I turn on the ignition. I have spark and fuel but it won’t start.

I decided to do a tune up. It needed one anyway. Replaced spark plugs, rotor and cap, spark plug wires, the CPS. Even after all the cranking the battery still reads 13.7 vdc. I put new grounding straps in battery to body, body to engine, battery to engine. Still won’t start.

I’m at a dead end. Any other suggestions? This is driving me crazy.
 
As you try to start it 98% of the time it won't fire up at all. It won't even act like its going to start. It just turns over and over again doing nothing. But the few times it tried to start the engine started and then rambled and popped and backfired through the throttle body.

I checked the CPS again and it ohms out correctly and the voltage it proper.

I eliminated C-101, one wire at a time and second checked all wires prior to solder and heat shrink. Still not starting up. I rechecked all the spark plug gaps, the new spark plug wires to be certain they are clicking down on the spark plug and the distributor cap. We still have spark. I checked all vacuum lines and other wiring and their connectors. The battery still reads 13.5 VDC. I have not ran number one cylinder up to TDC and checked the rotor bug. I wanted to try all this first.

We are getting fuel but I don't know what the new fuel pump is putting out in pressure.

This came from the factory as a 2.5L with an Automatic 2x4. The PO swapped it to a manual. I'm dreading pulling the dash and checking all wires and those running down the steering column.
 
I replaced the ECU with a known good unit and it won’t start. Cylinder one to TDC and rotor bug points to plug one on the distributor cap. I retested the new CPS and the ohms/voltage is dead on. Now moving onto the TPS and MAP.
 
I mean...fuel, spark, air. That's all there is to it. You said you're confident in the fuel going into the cylinder? Spark tested at the spark plugs right? Beyond that, just verify valves are letting air in.

Sent from my Pixel 4 using Tapatalk
 
Cleaned all grounds and added a few others. Cleaned all terminals and sensors, like pretty much anything I haven’t done and did a few over. I did notice the CPS male pins were bent to one side. The boy must have bent them... after I straightened them out and made certain they were in the female sides it started up and he has been driving it for the past two days. I hope to gawd that’s it.
 
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