4.0HO No Start, No Spark

[ihscoutlover]

I know this is kind of off IH, but I have run into a situation with EFI, that I am not sure what I should be checking, so Bill chime in here if you get a chance.

Vehicle: 1994 J**p Cherokee, 4.0 AW4, 242, D30, 8.25

Problem: No start, no spark, no fuel pressure at fuel rail.

Tested: Relays are testing according to specs. Still checking grounds to verify all sensors and computer are grounded correctly. All fuses are good and have continuity.

Replaced: Crank Position sensor(which is a common issue on these vehicles), swapped out various relays as well, all which give me nothing.

I have no spark at the coil. I am manually starting the solenoid via a remote starter switch. This is due to either a bad NSS, or the one in place is needing adjustment. The cranking is being done with the ignition in the on position. I am wanting to know whether I should be chasing down sensors, and verifying they are operating within their specs, or am I missing something else. I can and am willing to get the other parts off JY units in an attempt to fix this. I know I know, its a J**p and not an IH, but this is the wintertime beater, to take some duty off Melissa's Traveler, and heck I only paid $375 for it, so I don't have but $450 into it now. Thoughts and or suggestions??

Jeff

[Mt Hood Carl]

I have a copy of the factory diagnostic procedures for '94 Jeeps. Are you able to pull OBD trouble codes stored in the PCM?

Check that ASD relay is providing voltage to the coil. Cavity one (DG/OR wire) of the two pin connector at he coil should be above 10VDC.

[Bill usn-1]

As Carl said, I would start with the ignition side.
Most systems will not run the fuel if there is no spark.

IIRC Jeep also has the ignition in the PCM. I have heard of work arounds to run an external ignition bypassing the one in the PCM.

I have also found some good troubleshooting and diagrams on autozone.com under the repair section. And it's all free. Just log in and select your vehicle.

1991-98 Jeep vehicles are not equipped with an ignition control module. However, the functions of the ignition control module are performed by the Electronic Control Unit (ECU), also known as the Powertrain Control Module (PCM).

The Crankshaft Position Sensor, or CKP sensor provides the PCM with information about engine speed and crankshaft position. It is located near the bellhousing.

The CKP sensor contains a Hall effect device which sends either a 0.0 volt or a 5.0 volt signal to the PCM depending on the position of the distributor shaft.

The PCM uses the CKP sensor signal to determine fuel injection event time among other things. The engine will not run without the CKP sensor signal.

http://www.autozone.com/autozone/rep...00c152800a9b52

[Isa Ismail]

The Jeep came with a factory security system,(It triggers the auto shut down) If you pulled all the electrical from the Jeep to transplant, You will need to include the security system module and bypass it.
It will not work otherwise with out doing so.

[Bill usn-1]

Isa,
It's still in the original cherokee.

[IH64Scout]

ray cass EFI'd his 258 with the stuff off my '95 GC 4.0. he wired it all in, had some security issues, he may be able to help!

[ihscoutlover]

Update:

Upon checking the ASD relay, contacts 86 and 85 show continuity upon turning the ignition switch on, which from my checks would mean that the ASD has or is getting the signal from the PCM, which effectively grounds it to then pass on the signal to the FP relay to operate that.

To answer a couple of previous questions, The Cherokee doesn't have a factory or aftermarket security system. I have already ruled this issue out.

I checked all the underdash fuses, and they are all good. There are a few cavities missing fuses, one which is for power windows/locks, which this J**p doesn't have. If anyone has a J**p Cherokee owners manual and can get me either a copy of what fuses go where, or even have an extra owner's manual they want to part with, PM me and I will get it from you.

There are no diagnostic codes in the computer as of right now.

I checked the coil wire briefly and I wasn't getting more than about 4.5 volts at it, however, I am currently testing it to see if it meets the factory specs for now, but I was planning on upgrading it to a hotter coil to get more MPG's out of this thing. Im trying for low to mid 20's.

I have a FSM. I have other sensors to check but as of now I want to start with spark, and then see if that affects or not the fuel settings. The fuel pump is also not coming on, which would lead me to believe that its something connecting both. I found some insulation that was stripped some from one of the two coil wires. I will be taping that up, and checking out grounds, but everything appears to be grounded correctly. Keep the ideas coming and we'll see what develops.

Jeff

[ihscoutlover]

Coil wasn't within specs, but the ASD relay is getting continuity, so its something else further down the line. Im gonna try and start it with the TBS and cam sensors disconnected in the morning and see if I can get anything out of it then. I also need to check the O2 sensor and see if its shorted out or there are other wires that I haven't found messed up beisdes the coil wiring.

Jeff

[ihscoutlover]

Ok, both the ASD, and the Fuel Pump relays were getting their power correctly. The NSS is slightly still out of adjustment, but I can now start it in Neutral, just not Park. I am working on testing the fuel pump to verify its operation. One item to note, I was getting the CEL when I have started all this testing, but as of now, no CEL, so I am wondering if the PCM is actually bad? These PCM's control a lot of everything. I don't really know if there is a true way of testing it, but I had half a notion to go to the local pick n pull and grab a couple and see if that does or doesn't fix it. When I used a wire to ground the fuel pump relay(which was like a 22-24g wire), it started melting the insulation, and the rest of the insulation on that test wire got real warm. I was told there is a short in the fuel pump wiring, or even the relay itself, as when I did the test, I had the relay in place, and had the wire running alongside the tab of the relay that when it grounds, allows the fuel pump to work. Thoughts or suggestions here? I am also on the hunt for a 4.0 computer from a 93-96 Cherokee with an automatic transmission. Thanks for the help and hopefully I can get it running soon.

Jeff

[Bill usn-1]

What pin did you short on the relay?

If you look at the diagram try to follow along the paths:
(the full diagram is attached as a zip below)

You have 12v going to the FP relay from fuse F8 on the blu/red wire.
Pin 51 of the ECC sends the ground on the pink wire to the ASD and the FP relay to energize them.
Now, there is also 12 volts from fuse F15 that is battery 12v that goes to the FP relay on the red wire.
When the relay is energized by the pink wire, it causes the 12v on the red wire to pass thru to the org/dk blu wire that turns the pump on.
If you want to test the pump then just jumper 12v to the org/dk blu wire of the relay.

Now for the ASD- Fuse F2 sends 12v also on a red wire. When the ECC sends the ground through the pink wire (when the key is turned on) the relay should energize and pass the 12v out to pin 57 of the ECC.

So if you have shorted any wires the lead to the ECC then the ECC is probably bad now if it wasn't before.