When I bought the truck, it ran rough. I did a full tune up, down to the coil, battery, and battery cables. Ran like a champ. Then it had non-start issue. Did the starter, starter/ignition solenoid, and the ignition relay module (the one under the steering column). Started up, but ever since that job, it has been surging and stalling, even at speed (loss of power while on the throttle, then a surge).

One thing I did notice was that while it does this surge/stall, the battery indicator jumps down a half inch and then back up, and the 'check engine light' fades or goes out, and then comes back on (it has been on since I gutted the cat). This jumping of the battery needle and flickering of the light is the only reason I think it is electrical and not fuel related (new fuel filter as well).

Any insight as to where I should look next would be much appreciated.

 

Check all your grounds and have the alternator tested. Just a thought but if your voltage is dropping the alternator may be failing.

 

I think the alternator is a good call. I was out in the truck thinking about it, trying to get it to pop a code (which I do not know how to do, btw... I will search after I post this) when I noticed the fuel pump relay making noise, and the fuel pump trying to send fuel repeatedly. The relay was HOT... so I'll try that first. Totally unrelated, but what can you do?

 

Agreed on the relay. I've bought bad ones brand new. A bad relay will cause all kinds of headaches. I usually grab hand fulls of relays for .50@piece at the salvage yard. Never found a bad one there. I've bought several at $10@piece that did not work from the parts store. If you tackle the alternator, you may as well go with a 130a G3. Again, if you've got a salvage yard close by, I'd find one there. Just open it up before you walk out of the yard with it and check the brushes. Looks like the '92 4.9 has an external cooling fan on the alternator, so it might need the G3 conversion done and alternator bracket replaced. Everything you need can be found in the salvage yard for cheap plus you can buy everything and have the alternator rebuilt for less than the cost of a new alternator in most cases. There are quite a few write ups on here for the G3 swap and I think it's worth every second of the labor to do it.

 

OK... relay didn't help. Went ahead and did the fuel pump. Did the ignition switch (BWD, that one under the steering column). Did the alternator. Started up, drove through the back neighborhoods and was fine. Got it up to speed (4th gear) on the road and it came right back: bucking like crazy, RPMs jumping (just installed a tach while I was at it), CEL coming on synchronized with the stalling, and eventually a stall. Once it has stalled, it doesn't want to start back up, but will with some coaxing only to behave the same way until it eventually conks out.

Any help would be appreciated. Maybe another electronic module? ECM?

 

Did the ignition control module today. Ran for about two miles to where it usually acts up, so I pushed it a little further... was feeling good, and then all of a sudden, a spike in RPM, a CEL, a stutter, and a stall... had to keep a foot on the gas and ride the clutch in 2nd gear to get home.

This has been tough. Again, any advice is appreciated.

 

Pull codes. That's almost always step one

 

I did end up pulling codes. The first two were 33 and 13 (from what I can tell: TPS and "DC Motor did not move"). There were some others after that, the next being 25, but the five flashes were very fast, which made me think it meant something else (I was reading off the dash).

I noticed during all of this that the check engine light started stuttering the same way the light and tach do when the truck is stalling during the Key-on-engine-off test. The same flashing, the ECU was essentially stalling, restarting, hesitating, etc. When I reached down to check the unit, the top bolt was MISSING. CLearly some water had got in. I removed the unit and there was some corrosion, but no sign of burning.

I replaced the ECU, TPS, and ICV today. Truck started, but I didn't have time to get it up to operating temperature (it was dark by then and Halloween... too many kids on the road for that!). I will try again tomorrow. At this point, I feel as though the only thing left after this is some kind of loose or bad ground... any hidden ones that could be the culprit? Any advice is appreciated as I won't have much of a clue where to look and what to check... I think this primarily because the truck was acting the same way whether on or off, as long as it was warm.

 

Let her warm up in the driveway with the new TPS, ECU, and ICV all installed... I was nervous when I took her out at first, because every time I'd depress the clutch and take her out of gear, the RPMs would surge. With the surge/stall issue, I was only able to get about 3 miles, but I took her out for 8+ miles and had no issues. In fact, I stopped for gas (tank was still low from the fuel pump job), and when I started her back up, the RPM spikes seemed to be gone. I'm guessing the ECU just needed to learn a few things (as it was its first time running, and is working with aftermarket BWD parts).

For future readers, the ECU had corrosion along some of the outside of it, but did not show any signs of being burned out (no smell or visible marks). I probably should have caught the ECU issue earlier, considering it was missing the top bolt and had been compromised (it was a replacement ECU to boot... from a 93... looks like the dude had lost a bolt and tried to tack it with some black goop... not smart... just like his jury rigged PVC pipe fuel line with no vent), but I'm glad the truck has new parts for a lot of the problem spots... hopefully I won't have to worry about any of these for the rest of its life!

Thanks for the suggestions as well...

 

Omg !