Wiring help wanted…

Jeffncs

Jeffncs

Well-Known Member
Joined
Apr 4, 2017
Location
Wake Forest
I may need some help from the trust…

I swapped a 98 4.0 engine, ecu and slimmed down harness into my CJ7. My buddy did all of the wire work… and he’s excellent at it.

Here’s the issue. All wiring is connected with 2 relays (fuel pump and auto-shutoff) and the other connections into the Jeep harness.

We can’t get the relays to trigger the fuel pump and I can’t get the engine to fire. The engine spins as expected when cranking it over.

I have an auto ecu and manual ecu. Neither makes a difference here. I’ve checked relays, swapped fuses, etc. Anything you’d recommend I check?
 
Jeffncs said:
I may need some help from the trust…

I swapped a 98 4.0 engine, ecu and slimmed down harness into my CJ7. My buddy did all of the wire work… and he’s excellent at it.

Here’s the issue. All wiring is connected with 2 relays (fuel pump and auto-shutoff) and the other connections into the Jeep harness.

We can’t get the relays to trigger the fuel pump and I can’t get the engine to fire. The engine spins as expected when cranking it over.

I have an auto ecu and manual ecu. Neither makes a difference here. I’ve checked relays, swapped fuses, etc. Anything you’d recommend I check?
Click to expand...

Only thing that comes to mind for me is to make sure you slimmed the harness down based on the correct schematics. The 97, 98, and 99 harnesses are all different. 98 and 99 are more alike than different, but still not the same.
 
dumb question, but are you sure that's the only issue ? IE if you hard wire the fuel pump, is the engine starting ?
If not, the fuel pump relay isn't your issue.
 
Here’s what I’ve done so far….

Swapped relays around to rule them out - no change
I can direct wire the fuel pump - runs fine and pumps fuel; ignition/computer won’t activate the pump
Once fuel rail pressurized and with the fuel pump bypassed, engine will NOT fire up (doesn’t even sound like it wants to start)
I’ve swapped ECUs back-forth - no change to anything.

Planning to trace all wiring and revisit the Hesco CPS, VSS and all o2 sensor wiring connections. Will also trace all engine harness from computer pin outs to the engine/Jeep harness/etc.

I’m thinking there’s a missing ground or incorrect computer pin preventing the computer from working.

If I still had the old carb and air cleaner, I’d be contemplating dropping the 4.2 back into this thing.

I’m very frustrated at this point….
 
Harness is from a XJ.

@Charles is talking me through some things off the thread too. I need to check several grounds and also need to confirm the OBD port is working too.
 
My son's 98 xj died once and it was all bad grounds. As in dirty, I know this is all new but make sure they are all hooked up and you didn't miss one. I hope you guys used the 98 xj wiring diagrams because they are different then the TJ from my understanding.
 
Updated info…

The OBD port is dead, so the ECU doesn’t have power.

I have 3 grounds, all are connected.

Heres a map of my current wiring and KNOW that I messed something up. Can anyone help diagnose my electrical dilemma?
51C85ADA-66C5-4488-8A71-DE2E1554F3F9.jpeg
 
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You got a constant loop, except it's open at the relay and can't close because you're trying to make it close with no command.

wiring.png


Hypothesis (not sure) : You need to bring a different batt+ to pin 85 of that relay
But really, you got a bunch of feedback loops in this deal and I'm not sure that's needed/wanted
 
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Sure enough!! It’s Alice (again)!!!

Huge thanks to @Charles and my buddy Ron for getting me through this chapter in the Jeep’s life!!

 
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