Hooked up battery incorrectly on 1997 Explorer 4.0, not getting a spark. PCM fried?

[wellthatwasdumb]

Hey guys, I have a problem that I need some help with. I am troubleshooting a friend's 97 Ford Explorer 4.0 that sat for four years and was supposedly running when it was parked, but is now not getting a spark at the plugs. I made the gloriously stupid mistake of attempting to hook the battery up backwards, and current was flowing for a solid two seconds before I realized what I was doing. Now my problem is that I am not getting a spark at the plugs, and I suspect I may have fried the PCM. I do not know whether it was sparking before I hooked the battery up backwards, but the owner says that he got it to sputter using ether six months ago, so I'm assuming that spark existed. I have checked all of the fuses for the PCM, and they are all good, and the PCM relay is clicking. I switched the AC and PCM diodes in the fuse box under the hood thinking that the diode was possibly bad, but still nothing. Both diodes read ~56k ohms in the direction of the current flow, which seems way too high to me, but my meter is a POS, so the readings might be wrong, and at any rate, the relays are clicking. I plugged a basic computer diagnostic scanner up to the diagnostic port, and it seems to read the computer fine, but the computer isn't throwing any codes, which I find odd. The ignition was off when the battery was being connected, but it seems that on some cars, the PCM can fry with reverse current flow even with the ignition off.

From what I've gathered from searching on the internet, this ignition system has three main parts: the crankshaft sensor, which sends a signal to the PCM, which the PCM uses to determine ignition timing, and then sends a ground signal to the coil pack to initiate ignition, so it seems I have three possible culprits. My first question is: does anyone have any knowledge of an instance where someone hooked the battery up backwards on an Explorer with a similar ignition system, and if so, what was the result? Second question: is there a way to test the PCM and crankshaft sensor that does not require specialized equipment? Third question: does anyone have a link to the procedure to test the coil pack? Fourth question: what is the procedure for replacing the PCM? A guy at O'Reilly's told me that there are three different PCM models for this specific year and engine. I assume that I will need to find a computer with the same 'AJB' code that this computer has. Is that all? Are they plug and play, no reprogramming required? Fifth question: what the hell was I thinking?

Thanks in advance.

 

[budwich]

does the cel light come on during cranking AND eventually go out? There are lots of posts on the test sequences to go thru for a no start problems.

As to what you were thinking???? maybe you thought you could reverse flushing the electricals to clean them out ...

 

[wellthatwasdumb]

does the cel light come on during cranking AND eventually go out? There are lots of posts on the test sequences to go thru for a no start problems.

I was about to ask what the ceiling light had to do with anything, but then I googled a bit...

I don't have a check engine light lighting up at all. Not with the ignition on, not while it's cranking, nada.

 

[budwich]

as suggested, do some searching in this forum (there is a search tool), for checking the no start sequences of testing. Odds are high that the cel light is burnt but also odds are high that you have a burnt fuse. Since you can connect via a code reader, that would indicate some "sanity" in the PCM.

 

[wellthatwasdumb]

Okay, I see that the CEL light and the cigarette lighter are on the same fuse. What the...?

Anyways, I'll check that fuse and report back.

 

[wellthatwasdumb]

Thanks for your help guys. After researching threads on this forum for an hour or so, I decided to check the crankshaft position sensor connector. I unplugged it and plugged it back in a few times, and voila! She crunk. Turns out that Ford was thoughtful enough to wire up some one-way diodes that act as electrical check valves just in case someone hooks the battery up backwards.