1993 Jeep Grand Wagoneer will not start.

[James LeValley]

Long story short, ZJ was getting harder to start, had to leave key in on position longer and longer as it got colder. Had to wait to hear the auto shut off rely kick in and then the fuel pump rely would kick in and then I would hear the fuel pump, then it would start. Took it to two mechanics and no go. I replaced the ECM with a rebuilt from Flagship one with a lifetime guarantee. Replaced these parts, crank senor, coil packs, relays, checked for corrosion on all ground points including at the relay box and ohm and voltage checked all the wires in the wire harness, which all checked good. Had placed the ignition switch before this problem occurred,

The issue is now when the key is turned on the check engine light does not come on and no communication, ECM not reading data. My current mechanic who is an old mopar mechanic is at a loss.

Anybody have any Ideas? I may change the ignition switch again, or take out the electronics, replace intake manifold and put a carburetor on it ?
Thanks

 

[superj]

try pushing on the harness where it goes into the ecu while someone turns the key. maybe the ecu is bad again?

I semi remember reading bout someone having some problem similar to yours on jeepforums, years ago

 

[James LeValley]

would a bad ignition switch create a no engine light? These things started to happen about 4 months after replacing the ignition switch.

 

[superj]

I don't know but if it started around that time I would sure start there

 

[greg92jeepxj]

Sorry I don't have proper reference for your ZJ , I tried to follow along with my 1992 factory service manual to see if it would be if any help . I could not find the battery + input for the PCM which is supposed to be through the ignition switch to my knowledge but unable to confirm that . So as it stands , no communication with PCM . As SuperJ posted to verify PCM harness connectors secure but never apply heavy pressure to connectors to avoid breaking solder joints on PC boards internally . If all fuses , especially alternator and ignition MAXI fuses are good and power is found across them , do verify power at ignition switch terminals by back probing wires left plugged into switch . No communication normally means no,power to PCM . Try looking for 5 volt reference at TPS and map sensors and 8 volt reference at cam and crank sensors . If not found , that would confirm no communication . Noid lights and in line spark checkers could be helpful but most likely aren't going to yield results . I'm hoping someone with a proper wiring diagram could be sought . A dealer would be good if one were near by . Sometimes the autozone on line diagrams are helpful . But a proper diagram will be needed . The key is to find the battery + input to PCM . It must be verified that power is there . The auto shut down relay should be looked up as well since it interrupts injector and ignition grounds to terminate the engine of oil pressure drops or coolant temp too high . Years ago , I had a bad PCM in my XJ which would not allow starting in deep cold but communication wasn't lost , only low voltage to ignition coil due to bad PCM voltage regulator . Has either mechanic tried to scan the PCM ? Wondering if any hard code was set confirming no reference or communication . I think that was a code 12 on Chrysler but not sure . I know this dosen't serve much direction but I hope that something here will . Often the harness connectors are cause for no communication but it sounds like this was an on going problem with some history .

 

[greg92jeepxj]

Although I cannot provide correct firewall bulkhead connector or PCM cavity pin out to probe with a computer safe test light it low impediance digital voltmeter , it is still good practice to carry on a visual inspection to find if any part of the under hood or under dash harness has any damage inn the way of short to ground . If any is found , that could provide some direction to proceed .