Anyone know YJ's?

[Alan_Scott]

94' YJ 4.0 5-speed, all original, new O2 sensor last July

It's been running fine, then I shut it off uptown and now it won't start but still turns over just fine. The only thing I've tried so far was to check the schrader valve on the fuel rail (it dribbled a bit) and then tried to start it on ether.

All of the gauges, tach and speedometer no longer function (while being towed with the key on, I tried letting the clutch out in 4th) but the dash lights are still working. The check engine light and buzzer are also dead right now.

I'm thinking that I've either lost power to the ECM or had a ECM failure. Anyone else had this type of glitch before?

 

[86 century]

Re: Anyone know YJ's?

The only time I have seen anything like what you describe the computer had come unplugged for unknown reasons.

 

[Wind dog]

Re: Anyone know YJ's?

Could it be the nut behind the steering wheel?

 

[oldjeep]

Re: Anyone know YJ's?

Yup - ECM failure. Luckily you should be able to swap one in from a cherokee of the same vintage/manual trans.

 

[Fireman431]

Re: Anyone know YJ's?

Yup - ECM failure. Luckily you should be able to swap one in from a cherokee of the same vintage/manual trans.

Get the number off of the old ECM and get a replacement. Too many engine differences in vehicles, You may or may not get it running with an old one from a different model.

 

[oldjeep]

Re: Anyone know YJ's?

Get the number off of the old ECM and get a replacement. Too many engine differences in vehicles, You may or may not get it running with an old one from a different model.

Sounds like you don't know jeeps very well

 

[888]

Re: Anyone know YJ's?

94' YJ 4.0 5-speed, all original, new O2 sensor last July

It's been running fine, then I shut it off uptown and now it won't start but still turns over just fine. The only thing I've tried so far was to check the schrader valve on the fuel rail (it dribbled a bit) and then tried to start it on ether.

All of the gauges, tach and speedometer no longer function (while being towed with the key on, I tried letting the clutch out in 4th) but the dash lights are still working. The check engine light and buzzer are also dead right now.

I'm thinking that I've either lost power to the ECM or had a ECM failure. Anyone else had this type of glitch before?

I had the same issues and turned out to be crank sensor. Located on drivers side, on top of tranny. Its miserable but doable. 2Ft of extensions and a swivel helped. One test you can try is unplug the sensor, turn the key on, and see if your fuel gauge and voltmeter come up to normal or if they stay down.

 

[888]

Re: Anyone know YJ's?

And if that doesn't work,Clean and inspect all 3 plugs on ecm under the hood on passenger side firewall. If that doesnt help then try all all plugs you see one at a time and turn key. If dash comes alive you know you found your short. Its not your ecm ,don't waste the money.

 

[888]

Re: Anyone know YJ's?

Just thought of another issue I had with my jeep and it did the same thing with dash going screwy and no start. That turned out to be a wire in the rubber boot on drivers side door rubbed the insulation off and was creating a short on the body.

 

[Alan_Scott]

Re: Anyone know YJ's?

Could it be the nut behind the steering wheel?

That, from a guy that lives in Prunedale, a place that can't grow plums lol

 

[Alan_Scott]

Re: Anyone know YJ's?

I haven't had much time to mess with it today but I'll hit it harder tomorrow.

This morning I hit the key and the fuel pump pressured up and it started, but no check engine light and the dash was still dead. After shutting it off, it wouldn't start again and the fuel pump did not come on. This evening I tried it again and it started but the dash was still dead. I checked the volts at the battery while it was still running, 14.21. After shutting it off, it would not start again.

So far I've pulled and cleaned all of the fuses, all of the ones under the dash had a bit of green corrosion while the ones in the power box by the battery were all clean.

I've checked the wiring running down to the O2 sensor to make sure it didn't short out somehow.

I pulled the plug off of the ECU and tested some of the cavities on the socket
3 - 12.2v
11- no continuity
12- no continuity
19- 1.7v
57- 1.7v
I wish I could find something showing expected values because #19 and #57 seem strange. I'll attach the pin readout I'm using.

I've found several threads on different web sites saying there are 3 capacitors on the ECU that can cause this problem, after I finish checking out the wiring, maybe I'll swap out those capacitors and see what happens.

888, is yours a hardtop? I'm not finding any wiring on the drivers side past the interior light by the parking brake and it's a soft top.

 

[oldjeep]

Re: Anyone know YJ's?

May be different where you live, but around here a cherokee/YJ ECM costs $20 at the u-pull. As a YJ owner you should have a spare anyways. As you already found out, they are famous for blowing caps in the ECU. The FSM for a 94 YJ doesn't list any test values for those pins, it calls out use of the DRB2 scanner.

Just for grins, this is my 94 YJ

 

[12vMan]

Re: Anyone know YJ's?

Just for grins, this is my 94 YJ

Sorry for the detour, but ha, that's not old. 67 is old

 

[oldjeep]

Re: Anyone know YJ's?

Sorry for the detour, but ha, that's not old. 67 is old

This was the old one - my 46

 

[Wind dog]

Re: Anyone know YJ's?

About the only thing that grows here is Oaks, Eucalyptus & poison oak.


Did ya get her fixed?

 

[Alan_Scott]

Re: Anyone know YJ's?

I sure remember what poison oak can do to you...

Not yet, I'm thinking the ECU went bad and I haven't been able to locate another one yet.

 

[12vMan]

Re: Anyone know YJ's?

This was the old one - my 46

Nice! Old flat top. I used to have a '53 Willys. Never should have sold it.

 

[Augoose]

Re: Anyone know YJ's?

I think I have an old ECM from a '94 I6 YJ in the garage - its yours if you want it - no clue if it works or not but I had it left over from upgrading my CJ7 tub with the YJ.
PM me if you want it and I'll dig it out.