how do I test a relay? so I jump two of its leads?

 

I think the AC relay is the same unit - just swap them...or find out which one is the same and swap them. Otherwise yes, you can pull it a jump the 2 primary leads and listen for a click. Even if it clicks though, the internal contact might be broke.

 

The truck shouldn't run without the PCM having power as it is a distributorless fuel injected motor.

 

Yeah I just thought about that...little distracted earlier with kids all floating about here. The distributor is not the problem as the PCM on conditions the spark curve through SPOUT. The ICM controls the coils.

The fuel injectors though are controlled by the PCM...but...is the "limp home" mode of the OBD-I powered off the KAM power input or the main PCM power relay power input? I don't know but interesting question.

This is a really wierd one with all those codes. I'm never one to point to a PCM as the culprit but this one sounds really wacked and the PCM might just be it....

 

I know you're sick of maybe hearing me :-) - I still think you should have the codes read to double check your findings... I would, before I'd spend the money on a new PCM - They are not cheap, and you will hate yourself if that is not the problem.

or, I think you can actually pull the PCM, and have a tech bench test it for you - this way, if you are really getting all those codes at once like that, you will know for sure if it's bad, or if it's a wiring harness situation, or?? This I would do, if you are really leaning that way, and with all those codes, could be.

Codes are usually stored until cleared, so the other big question is, did all these codes happen at once, or a couple at a time, over time? I would think the PCM either works or it doesn't - I don't think I've ever heard of one "starting to fail" but anything is possible I guess...

 

Certain functions of the PCM can fail without the whole unit failing. For instance, the idle control function on my PCM failed, but everything else worked fine. Replaced the PCM and the idle returned to normal.

P.S. I'm betting Mr. Ski was just waiting for me to chime in on this one.

 

It seems that most PCM failures I hear of usually involve one circuit or SRC or driver or whatever is inside there (I'm not an good with computer boards and their terminology). For example, mine acts like the "driver" or "switch" inside the computer for the CANP solenoid doesn't close, but the engine runs fine otherwise (probably because the CANP solenoid isn't real critical to engine operation).

Another comment: According to my code list, many of those codes can be either KOEO codes or CM codes. However, a few of those codes (such as the 513 and the 565) are listed as only KOEO codes. KOEO codes aren't stored in any memory or otherwise have any "permanence." They represent hard faults that exist at the time the test was performed. They aren't stored in any memory. This is why one resolves KOEO codes first. The OP hasn't specified which codes are KOEO and which are CM and which are both, so we have to make some assumptions. CM codes are the stored codes that are kept with KAM.

The way I usually test a relay in the vehicle is to measure the voltage drop across the relay when open and closed. EEC relay should be closed whenever the key is in the on position. When open, the relay should show about B+ voltage drop. If there is any kind of appreciable voltage drop across the relay (more than a few mV) when closed, then the relay isn't closing completely (or there's a bad connection in the plug since I'm usually backprobing the connector).

Also note that the EEC relay powers the injectors, the ICM, and a whole host of other things. If the engine starts and runs (however poorly), that suggests that the EEC relay is closing.

 

Would be nice to have the design spec for these PCM's wouldn't it. It's tough guessing where the electrons are supposed to be at different times.

 

Just an additional tidbit of info you may want given what I read above. I had disconnected the battery for a while (over an hour) because I wanted to see the spark plugs (yes, black soot-big surprise given what I saw earlier coming out the tailpipe. The codes were pulled after the battery was reconnected for a couple of hours, then I started the engine which idled horribly and died unless the gas was pressed or I drove around the block.
Would it be stupid to buy a junkyard PCM ?

 

I don't understand the relay test above, but I did swap AC and EEG relays and the car won't start. I'm not sure they're the same but it fits in the slots (sl different part number). I replaced the relays in their original slots.
I disconnected the battery and tested the voltage: almost 13 V.
I tried to start the engine several times - it won't start but turns
Rechecked the codes - identical to before

 

only if the junkyard PCM is certified that it is in perfect shape(been tested) - but you could do that for sure, as opposed to testing the one that is in there - if the price was right... I think $100 or less would be my gamble limit, since that is about 2x the cost to have the PCM tested, so, you'd be out $50ish worst case - or less, if they don't know how much they cost new... of course, it seems that pricing on stuff like the PCM changes so much year to year - it would be interesting for you to call the stealership to see how much a new one would be, just for kicks... maybe they aren't too bad? But I think they are if memory serves... you might try eBay also.

It's good you did the unhook the batt thing... and let it off for a while...

I don't remember if this was asked, but did it ever overheat? that year was prone to cracked blocks, even if the engine ran hot for 10 mins... a cracked head will make the engine run like crap, but with all those codes?

Black soot would not usually mean that though... more of a mixture problem - how many are black like that? all of them?

I would check your compression for each black plug for that cylinder... but you may not want to do all that right now - PCM is a good place to start I think.

Good Luck

 

One problem many people have when trying to understand the PCM trouble codes, is getting confused with where to start testing when multiple codes are given.
1. Run the Key on engine off self test and get any codes given.
2. Work ONLY on the first code given as the remainder may be related/caused by the first code.
3. Repeat steps 1 and 2 till all KOEO codes are gone.
4. Clear the PCM codes and try to start/run the engine.
5. If it runs OK, go for a drive and see if it sets any codes after a 5-10 mile trip.
6. If it doesn't run well, try the Key on Engine running test to check sensors in an actively running engine mode.
7. Again, ONLY work on the first code given, repeat as necessary.

 

I got a "very rare" PCM as a back-up off eBay for about $40 shipped. You need the F37F-12A650-xxx (whatever the last 2 -3 digits are) code plus the calibration code...usually 3 letters and a number like "COW-1"...both numbers need to match to fit your vehicle. The numbers are on the PCM.

 

the engine never overheated in its history as far as I know. When I got it it ran cold all the time, and wasted fuel. So I changed the thermostat and the problem went away and since then it has run well until that stupid light went on...

I only checked two spark plugs, and they are both sooty.

 

So you mean I should change the coolant temp sensor? Code 117 was the first to appear in my code sequence.