88 XJ Problems

[PBF]

I have access to a ODBII computer error if you are showing a fault. Have Factory Manual and digital meter if needed for sensor trouble shooting.

Would be glad to help if you still have the problem. It can be a lunch time thing if you are in the SLC area. Got a couple of Jeep Geeks here at work and a couple of XJ's to compare with.

 

[Brett]

Originally posted by PBF
I have access to a ODBII computer error if you are showing a fault. Have Factory Manual and digital meter if needed for sensor trouble shooting.

Would be glad to help if you still have the problem. It can be a lunch time thing if you are in the SLC area. Got a couple of Jeep Geeks here at work and a couple of XJ's to compare with.

Yeah, i am in the SLC area, right out in Murray actually. If you know where Mepco is, you'll find me behind the counter pretending to work.

If you're willing to help out, just let me know a day......


Thanks!

 

[PBF]

Your XJ is an 88 right?. It will need an OBD1 reader (I've got an OBD II, but it might work). I have the factory service manual and will read up checking on the sensors tonight / tommorrow.

 

[Brett]

Thanks, I really appreciate it!

 

[PBF]

4.0 L Engine Multi Point Fuel Injection System

My Trouble Shooting Guide: (Part 1 of 6)

1). Turn ignition ON.
2). Listen for Fuel Pump On and OFF (aprox. 1 second).
3). Check for Up Shift light illuminated (manual trans only).
4). Turn ignition OFF.
5). Check Oxygen sensor heater resistance.
Located at bottom of exhaust manifold.
Disconnect 3-wire sensor plug.
Check resistance between A and B on Oxygen sensor plug.
5 ohms (Good)
Open (Fail)
Reconnect sensor plug if good.

6). Check ERG solenoid valve operation.
Located on fender well by air cleaner.
Disconnect two-position vacuum plug (Output A & B).
Disconnect single position vacuum plug (Input C)
Start engine.
Check for vacuum at Vacuum Input C.
If vacuum present (Good)
No vacuum (Bad).

Reconnect single position plug (Input C) if good.
Check for vacuum at output B.
B is closest to valve body.
No vacuum (Good).
If vacuum present (Bad).

Disconnect ERG solenoid wire plug.
Check for vacuum at output B.
If vacuum present (Good).
No vacuum (Bad).
Reconnect two-position plug (Output A & B) if good.

7). Check Coolant Temperature Sensor.
Located on block under #2 cylinder.
Disconnect the wire harness plug to the CTS.
Check CTS resistance (Ambient or Hot)
Hot (200 F) 500 ohms.
Ambient (70 F) 3,400 ohms.
Cold (32 F) 10,000 ohms.
If resistance good reconnect CTS wire harness plug.

8). Check Manifold Air Temperature Sensor:
Located on intake manifold by throttle body.
Disconnect the wire harness plug to the MAP.
Check MAP resistance (Ambient or Hot).
Hot (200 F) 185 ohms.
Ambient (70 F) 3,400 ohms.
Cold (32 F) 10,000 ohms.
If resistance good reconnect MAP wire harness plug.

9). Check Manifold Pressure Sensor:
Located on firewall under the hood.
Turn ignition ON.
Measure MAP voltage at connector terminal B.
Voltage 4 to 5 VDC (Good).
Turn ignition ON.
Voltage 1.5 to 2.1 VDC (Good).
Measure MAP voltage supply at connector terminal C.
Voltage 5 VDC (Good)
Measure MAP ground at connector terminal A.
Ground 0 ohms (Good).

 

[Brett]

Is that measurement correct for the CTS when cold? 3,400 ohms?? I have nothing that can read that

 

[PBF]

Yes.... Factory Service Manual (Chapter 14 page 84) has a table for 9 different temperature readings with matching resistance readings. I have a DMM to make the reading.

 

[Brett]

Thanks for the help Patrick.....it seems to be working a bit better. I used some vacuum line over the few that I had cracked until the harness arrives for it. It's not hesitating quite as much as it was before, so I think that I will try to replace the CTS on it and see if that helps out with the rest. I really appreciate your assist on this!

Brett

 

[PBF]

I did not check the coolant sensor as we needed to get it on a lift to get access.

I also unplugged the sensor on the Throtle Body and it had no effect what so ever (which is not right and needs to be looked at further).

I know you need to do a little work on the wiring and vacuum lines first. The EGR sessor itself was bad and we installed the new one you had. The MAT and MAP sensors were good.

We may try again next week some time. Your XJ was a little low on gas so we did not take it for a test drive.

 

[Brett]

Originally posted by PBF
I did not check the coolant sensor as we needed to get it on a lift to get access.

I also unplugged the sensor on the Throtle Body and it had no effect what so ever (which is not right and needs to be looked at further).

I know you need to do a little work on the wiring and vacuum lines first. The EGR sessor itself was bad and we installed the new one you had. The MAT and MAP sensors were good.

We may try again next week some time. Your XJ was a little low on gas so we did not take it for a test drive.

Which sensor did you unplug and it didn't affect it? the IAC or the TPS?

 

[PBF]

TPS for sure (4 wire square connector). The other had no effect either (8 wire connector). I did not look at them carefully as we had to get back to work (talk about a long lunch).

If the TPS is bad the ECU will think it is at WOT and will add gas and timing to the engine. Resullt is usually backfire and surging (either happen to you?).

 

[Brett]

Originally posted by PBF
TPS for sure (4 wire square connector). The other had no effect either (8 wire connector). I did not look at them carefully as we had to get back to work (talk about a long lunch).

If the TPS is bad the ECU will think it is at WOT and will add gas and timing to the engine. Resullt is usually backfire and surging (either happen to you?).

Hmmm....when I disconnected the IAC on it before if revved itself up to about 2500. We are talking about the two sensors right on the throttle body itself, right?

I've had some backfires a few times and it smells like it's running a bit rich now and then. As for surging, now and then at higher RPMs it feels like it drops off and then regains power.

I'll check it out further...

Thanks again....

 

[PBF]

Any update???

 

[Brett]

Any update???

Well, not really...I haven't had much time to check out stuff on it. I've just been running around with it the way it was after you played with it. So far it's okay, other than a slightly rough idle. I am gonna throw some new vacuum lines on it today and see how that helps out.

Update later on in the day!

 

[Brett]

Okay, so i was lazy and sick and didn't do it...maybe tommorow

 

[Brett]

Well, I changed out all the vacuum lines....seems to run a bit smoother now too. I still am waiting on the vacuum tank under the bumper and the lines that run off of that. That'll be monday I think.

However, new thing going on......whenever I am driving and I let off the gas a bit, it feels like the computer (or something) drops the throttle further than it should and then catches back up. That makes sense? It's weird and I don't know what could be causing that problem.

Ideas?





















Damn Jeeps

 

[Brett]

bump...bump

 

[Hickey]

Maybe you should sell it, and get a newer one.

 

[Brett]

Maybe you should sell it, and get a newer one.

It's an option!

 

[Brett]

All fixed now. All new vacuum harness for the engine bay. New TPS and IAC sensors and it's running like a champ now. Gonna throw some new plugs, wires, cap and rotor on it when I get home this evening.