Check engine light-No Code-FIXED

[Brokex]

I think I solved a long running intermittent problem and wanted to share what I found. My 91 explorer would occasionally have the CIL come on and run poorly or stall. Turn off motor, restart, and everything would be OK until next time. No codes. Most of my sporadic efforts first focused on relays and wiring around the power box because it seemed like the computer was losing power.

Back at this thread: http://www.explorerforum.com/forums/showthread.php?t=267027 I decided I needed new plugs and wires, I changed them and it cut down on the frequency but didn't fixed it. I started looking at the coil pack, ignition module, and associated wiring.

I ended up finding that at the ignition module there are two wires (PIP and SPOUT) that the module and the computer use to communicate with each other on spark timing and both have a grounded braid on them, which Y's together to a common ground.

The SPOUT wire's braid right near where it passes by/under the battery tray was corroded nearly all the way through, although the wire harness itself looked ok until I open it up and looked more closely.

A splice and some heat shrink---problem solved!!

I'm glad its fixed although the geek in me wouldn't mind knowing the mad scientist reason why there wasn't a code for what was going on.

 

[shaggymane]

Because mechanical problems don't throw codes and a short is a mechanical problem. Codes come off sensors being tested.

That'd be my answer. We'll see what other say.

 

[Tbars4]

...Nice job on tracking this down...

...Although your vehicle has a computer, they are not smart...They only read what few sensor's and their values the vehicle has, and one of the reasons electrical problems are such a pain to locate and resolve...

...This is also why it is common to have a code for one thing such as o2 sensor's and why people suggest looking upstream of those to find the problem...

 

[Brokex]

Yah, at least once or twice I've had cars with a code for an oxygen sensor or what have you, and the source of the issue was at the other end of the car. I'd just be interested in knowing the nuts and bolt of what actually illuminated the light. Goofy check engine light isn't even on any of the electrical diagrams I've seen.