Howdy all.

I've been driving the '87 (4.9L 4 speed) regularly for a month now without a hint of trouble until this morning. I got in it to run some errands this morning ran into problems right off the bat. At first it would crank, but not start. When I did get it started, it was running rich, cutting out, and struggling to get past 35 MPH. Limped it on home figuring the TFI module was on its way out. I replaced the module this afternoon and it fired right up and ran great. A couple hours later I go out to run another errand the tach goes bananas jumping all over the place and then dies in the driveway. When it finally restarted, it was back to cutting out and running rich.

I scanned for codes and got a code 67 (clutch safety switch I believe), code 10 (not sure - it's been popping up lately), code 15 (Loss of power - disconnected battery while changing module), and then stopped without giving me a code 11. I attempted to re-run the test and it took 2 or 3 attempts to get it started, but when it did, it showed just the 67 and then 11.

I suspect the ECM is going bad, but I've heard that the PIP module can wreak havoc as well. There's also the possibility of a flaky coil I guess. What do y'all think?

Just for the sake of disclosure - over the winter, I replaced the intake gaskets, lower intake manifold, fuel pressure regulator, fuel injectors, IAC valve, EGR valve, and Air charge temp sensor.

 

What I experienced with mine was somewhat like yours. It is like 7 minutes to pull the PCM and check the caps.

 

Pulled the PCM, but the caps all look normal - no bulging or apparent leaking - but looking good and working good are two different things. Some of the pins in the connector look like there's some corrosion or something on them...

 

You can clean them pins with a brass barrel brush from a gun cleaning kit.

IIRC code 10 is a separator code, not a fault code.

 

Dixie is 100% correct.

 

Well - I'm still struggling to figure this out...

Do I have to have an identical part number for the replacement PCM or can I get away with one that's set up for the same engine/transmission combination but not the same part number?

I really don't want to drop $100 on something that isn't the problem...

 

I decided to channel my inner geek and broke out my Nikon and macro lens in an attempt to get a better look at the capacitors. I was hoping to find bulging, but found something I would have never seen other wise. Check it out...



If I'm not mistaken, I believe I might have found the problem...

 

Just got the replacement PCM installed and taken it for the first of 2 test hops. So far it is almost like a different vehicle. The engine is running silky smooth and much quieter than before. The idle has been steady and the tach is behaving itself. I'm letting it sit a bit and then I'll go on test hop #2 and see how it goes.

Compared to the last time out with it, all looks good. If the 2nd goes just as well, I'll take it to the office in the morning for a longer stretch.

 

2nd test went just as smooth (literally) as the first! It's amazing what a difference the PCM has made.

 

Ran into another issue that I think is tied to a dying PIP sensor. Distributor swapped out for a new one - so far so good.

One would think that they would have used parts that would have lasted more than 27 years.. LOL

 

Hey, how is the truck doing?

I'd say 27 years is pretty damn good for electronic components given the conditions they operate in.

 

Yep, nobody makes capacitors that are rated to last that long. Visual inspection is useless, insofar as they don't leak or bulge till they've already been dead a long time, usually not even then.

 

It's still giving me pains, but I think I finally located the problem. I started it up this evening and started wiggling harnesses around until it objected. I quickly narrowed it down to the ECM harness where it plugs into the ECM. It was getting dark and I couldn't tell just what's going on with it, but I suspect that the plug is going to have to be replaced.

I'm probably going to have to go pull that part of the harness from a similarly equipped donor truck and hope for the best.

 

Replaced the harness with a clean harness from a parts yard and still had problems. I pulled the ECU and took a good look at its pins and noticed that a few of them were loose in the connector. Returned it for a replacement (thank you warranty) and, so far, the replacement is working properly and I haven't experienced any issues yet.

Lets hope it lasts.