Mudd
NAXJA Forum User
- Location
- Bethel Acres, Oklahoma
Trying to do a little troublshooting, here is the history:
1988 XJ 4.0 4x4 auto 91,000 miles (possibly mostly towed behind RV)
Recently purchased and it runs good. After throttle body cleaning it runs better. After plugs, wires, cap, rotor it runs even better.
It looked like the o2 sensor was original so I installed a new Bosch. The heating element in the old sensor tested bad (open). But now that I have the new o2 sensor installed I have a problem during warmup:
After cold startup it runs great for about 15-20 seconds then starts to slowly die like it's running out of gas. It might die or it might "catch" and rev back up to normal. After 15-20 seconds it starts to die again. This cycle continues until the engine is fully warm. Then it runs just great. So the problem is during the warmup loop.
I thought it could be EGR but there is no vacuum to the EGR valve during warmup and the EGR valve seems to operate normally after warmup.
The MAT and CTS sensors test o.k. per resistance/temp chart.
Then I tried testing the MAP sensor. This is where I get confused. My 1988 Cherokee service manual says to disconnect the harness from the MAP sensor and, with ignition on/engine off OUTPUT voltage at pin B (middle) should be 4-5 volts as well as terminal C-6 of the ECU. I get no output voltage from the ECU with the ignition on/engine off.
I do get 5 volts INPUT voltage at pin C.
If the RENIX ECU should be giving MAP sensor input and output of 5 volts with the ignition on/engine off and MAP harness disconnected then it looks like I have a bad ECU. But I can't find any other reference to testing the circuit in this fashion. Searching the archives I only find reference to testing the output values with the engine running. My manual doesn't mention it.
So I'm looking for clarification of the proper way to tell if my MAP sensor and ECU are working properly and also the root problem which is why I have a warmup issue after changing the o2 sensor when it ran fine with the old one which didn't have a functioning heater element.
Thanks,
John
1988 XJ 4.0 4x4 auto 91,000 miles (possibly mostly towed behind RV)
Recently purchased and it runs good. After throttle body cleaning it runs better. After plugs, wires, cap, rotor it runs even better.
It looked like the o2 sensor was original so I installed a new Bosch. The heating element in the old sensor tested bad (open). But now that I have the new o2 sensor installed I have a problem during warmup:
After cold startup it runs great for about 15-20 seconds then starts to slowly die like it's running out of gas. It might die or it might "catch" and rev back up to normal. After 15-20 seconds it starts to die again. This cycle continues until the engine is fully warm. Then it runs just great. So the problem is during the warmup loop.
I thought it could be EGR but there is no vacuum to the EGR valve during warmup and the EGR valve seems to operate normally after warmup.
The MAT and CTS sensors test o.k. per resistance/temp chart.
Then I tried testing the MAP sensor. This is where I get confused. My 1988 Cherokee service manual says to disconnect the harness from the MAP sensor and, with ignition on/engine off OUTPUT voltage at pin B (middle) should be 4-5 volts as well as terminal C-6 of the ECU. I get no output voltage from the ECU with the ignition on/engine off.
I do get 5 volts INPUT voltage at pin C.
If the RENIX ECU should be giving MAP sensor input and output of 5 volts with the ignition on/engine off and MAP harness disconnected then it looks like I have a bad ECU. But I can't find any other reference to testing the circuit in this fashion. Searching the archives I only find reference to testing the output values with the engine running. My manual doesn't mention it.
So I'm looking for clarification of the proper way to tell if my MAP sensor and ECU are working properly and also the root problem which is why I have a warmup issue after changing the o2 sensor when it ran fine with the old one which didn't have a functioning heater element.
Thanks,
John
