PJSXJ

okay so back in August me and my buddy were mudding, my friend went with his gauges not working, after a couple hours of wheeling and one large mud pit, his engine overheated pretty badly, while we were waiting for it to cool down we took his dash apart to look for a bad ground or wiring fault to fix the gauges, we found nothing. after putting everything back together and waiting for the engine to cool, the engine cranks but wont start and wont scan when we put the scan tool on it. It has fuel delivery and compression but so spark. So far we have replaced:

spark plug wires
distributor/cam sensor
ASD relay
ignition coil
CPS
ECU
Battery

After all this it still cranks and turns over but wont spark or scan. What are we missing here. Any advice is greatly appreciated

cmartin2112

Sounds like there is short... How in depth did you go when checking the wire harness for splits? Did you test your electrical connections?

PJSXJ

We pulled and checked all fuses, checked relevant relays, inspected for damage to the wiring harnesses under the hood, on the underside of the engine and inside under the dash by the scan port and didn't see any damaged/grounded wires, we've taken off the grounds and cleaned them, we tested the cps and ignition coil with a multimeter. What else should we check?

belvedere

First thoughts are a wiring issue or maybe ignition switch. Have you verified voltage at the coil while cranking?

PJSXJ

How do we check the ignition switch and what's a good procedure for checking the coil while cranking?

Radi

The primary coil connector has two electrical connections, one is the "positive", which has constant +12V, the other is the "negative", which is disconnected from ground every time the coil should fire.

So with the key ON, you should have battery voltage at both coil terminals.
With the engine cranking, you should have full battery voltage at the positive coil terminal, and a lesser voltage- approx 6-7V at the negative coil terminal.

PJSXJ

Okay update: we tested the coil, no power at all. So we took the dash back apart and found two severed wires by the ignition switch, they were paired together with a ton of tape and went into a plug which converted them into two white wires, the two white wires went somewhere to the fuse box inside but I'm not exactly sure where. Any ideas?

PJSXJ

I traced the wires back to the passenger side airbag, which has been out for a year so it doesn't really matter. Any help to why the coil isn't getting power would be appreceated. If there's a particular circuit we should look for a short in or anything

Radi

What year XJ? 4.0? Might be able to cough up a wiring diagram to follow from the coil on back.

CCKen

This is a WAG, but I'm thinking this is a '97+ but not a 2K or 2K1.

Couple of questions:

1. Does this Jeep have Sentry Key Immobilizer?

A defective SKIM will prevent the engine from starting and may corrupt the CCD Data Bus and prevent a scan tool from communicating with the PCM.


2. When you plug your scan tool in to the DLC does it power up? Or does it power up but does not connect to the PCM?

3. Do the headlights work?

The DLC is powered from fuse F17 in the PDC, which also powers the headlight switch. If F17 is blown you won't have 12 VDC to pin 16 of the DLC to power the scanner and you may not have headlights.