Cascade Crew

blue89 · Posted: Mon Oct 12, 2009 9:53 am Post subject: Cherokee, no fuel, no run

I'm trying to track this problem down for my brother-in-law. Need help. It's a 1990 jeep cherokee, 4.0L Auto. It has a Bendix (?) ECM, power to the sensors, starts with starting fluid, lots of spark, but the fuel injectors are not firing. I've checked the MAP output, it's good. I've checked the tps, it's good. There's another connector coming out of the tps which i assume is the WOT sensor. Other than a bad ECM, I have no clue where to go. The only weird thing I've picked up on so far is that the ground for the injectors changes resistance. It's a controlled power setup so the ground should be ground. When it's cranking though, the resistance on the ground side of the injector plug goes to 34+ ohms. Since it's a 16 ohm injector, I assume this is bad. I'm tracking it down right now but someone give me some idea's.

Twilightoptics · Posted: Mon Oct 12, 2009 10:27 am Post subject:

If it runs on alternate fuel, I'd go straight for fuel pressure.

If you're certain the injectors aren't firing, go to the Crank Sensor.
1. Unplug the Crankshaft Position (CKP) sensor connector.

2. Check the AC voltage from the Crankshaft Position (CKP) sensor. It should be at least 300 mVAC.

Also check to make sure you're getting proper power to the PCM.

Engine cranks but is a no start. Have spark but no fuel injector pulse. Tests/Procedures: 1. Verify that the engine will run on an alternate fuel source. If it does, gain access to the Powertrain Control Module (PCM). It is located near the accelerator pedal. Find terminals D10 and C11. Both should be Orange wires. Start and run the engine with another fuel source. With the engine running, check for charging system voltage at these terminals. If it is less than charging system voltage, go to the fuel pump relay located near the ignition coil on the passenger's side fender. The relay sends power to the PCM for the fuel injectors. With the key on, locate the Orange/Black wire and ground it with the relay still plugged in. Turn the ignition key on and the fuel pump should be running. There should be battery voltage coming out of the relay on the Orange wire. This is the circuit to PCM cavities D10 and C11. If battery voltage is present at the relay but not at the PCM, check the harness splice. Follow the Orange wire into the harness and the splice will be found within 12".

Sounds like PCM could be bad.

blue89 · Posted: Mon Oct 12, 2009 10:46 am Post subject:

Verified the CPS is good. 218 ohms and generates ~.400mVac when cranking. Found a service bulletin from Chrysler saying the harness from the CPS to the ECM can be faulty. I'm in process of printing/incorporating the bulletin.

Fuel pressure is 42psi prime and 42psi cranking. I'm thinking what your thinking but I'm hoping that it's a bad CPS harness. Thanks for the brainstorm. I'll post results.

blue89 · Posted: Mon Oct 12, 2009 11:17 am Post subject:

Bypassed harness for the CPS. No change. I'm going to do what you described and post.

blue89 · Posted: Mon Oct 12, 2009 12:14 pm Post subject:

No power on pins D10 or C11. Relay's seem to be working fine. There is a splice for the orange wires about 12" from the relay and it looks good as well.

The large orange wire that seems to feed other things is missing a lot of insulation. Either corrosion or overheating of the wire. Do you have a schematic? I'd like to bypass the relay and supply power directly to those two orange pins at the ECM. Thanks a million.

Addition:

Multimeter had a bad ground. Power is going to those pins. Must be a bad ECM. Dag.

GREG DAVIDSON · Posted: Mon Oct 12, 2009 4:16 pm Post subject:

fuel pump ?

Twilightoptics · Posted: Mon Oct 12, 2009 7:53 pm Post subject:

blue89 · Posted: Tue Oct 13, 2009 7:13 am Post subject:

Twilightoptics · Posted: Tue Oct 13, 2009 9:07 am Post subject:

blue89 · Posted: Tue Oct 13, 2009 9:29 am Post subject:

This setup uses a switched power. Ground of the injectors are supposed to be grounded to chassis. I'm going to look into the sync sensor under the distributor cap and then hunt down that system ground for the injectors.

And for anyone else with a Renix 87-90 jeep cherokee, here's the manual for the ECU

http://www.pirate4x4.com/tech/billavista/PDFs/Jeep_Renix_Fuel_Injection_manual.pdf

chevymad · Posted: Tue Oct 13, 2009 12:57 pm Post subject:

Renault/bendix. Aint it fuN?

blue89 · Posted: Wed Oct 14, 2009 6:51 am Post subject:

Ya, it's swell. If you can verify that all the inputs are there for the ECU though, not much else you can do.

chevymad · Posted: Wed Oct 14, 2009 6:56 am Post subject:

Pretty much what you do for any car really. But with no onboard diagnostics it just kinda sucks. That and the fact they seem to go at everything backwards.

Twilightoptics · Posted: Wed Oct 14, 2009 6:56 am Post subject:

chevymad · Posted: Wed Oct 14, 2009 6:57 am Post subject:

The distributor is probably motorcraft.

blue89 · Posted: Fri Oct 16, 2009 6:31 am Post subject:

I think the distributor must be a renault....... Nothing I've ever seen before.

New computer on the way. Might be here today so we'll see. Sure hope that's the problem. Not bad for $85 though. I like the guys at Oly 4x4.

blue89 · Posted: Sun Oct 18, 2009 10:48 am Post subject:

Plugged in the new computer and it fired right up. Running a little rough though it still has 2 year old gas in it. All it needs now is a tune up to take care of the little stuff. Maybe clean the injectors and a new o2 sensor. Thanks for the help!