The major auto parts stores usually have an automated test gizmo that can test alternators while on the vehicle, I have had it done on other vehicles. Of course, getting it hooked up on the Trooper might be a bit of a chore given the alts position...

What about testing off the vehicle? The problem doesnt show up until after about 20 min of operation when something probably gets hot.

I thought the alt has a computer thingy in it that controls when it puts out and when it doesnt too. Will it work not hooked up on the vehicle?

There is a regulator internal to the case. It simply, um, regulates the voltage. It is by far not a computer.

On or off the vehicle, I don't think it will matter. I am guessing it is not putting out the correct voltage or wave-form at all times, if it is bad.

Good Luck,
Michael

Well, the alternator tested good. But I swapped it anyway. Since the problems only occur when the vehicle is hot and been running for at least 20 min, I didnt know what to think about it passing.

Drove it , took 30-40 min but eventually it started bucking under acceleration again.

Oil pressure gauge still drops out at idle.

So, wtf could this be? ECM? Time will tell if it dies etc again, that could have been a totally separate problem from the other stuff, unfortunately. Ignition module might cause the acceleration problem IF the tranny light never comes back on, it wouldnt have caused that. The ECM could cause it all though.

If I had a dealer close, I would take it to them. Im thinking of just scrapping that darn thing, I dont have time to fool with it anymore.

Went to drive it tonight, it was pretty much undriveable. Stumbling, hesitating at all speeds and from the start.Not just after prolonged time driving like before. It was colder tonight, but no colder than some other times. The oil pressure gauge never did fall out, I guess since it ran so poor I never got it heated up enough to do that, thats obviously an unrelated problem now.

It hasnt died again yet since replacing the alternator.

I connected a pressure gauge to look at while driving and ducttaped it to my windshield. When I hit the accelerator and try to accelerate at low speed, the pressure stays on ~42psig while it stumbles, sags, doesnt go, etc.

When it does catch and speed up if you ease it up slowly, the fuel pressure decreases and may go as low as 25psig at high speed and high engine load under certain conditions, but its running pretty smooth then.

Seems to be idling pretty rough too, but all cyls are firing, get rpm drop when pull each plug wire off.

I may replace the ignition module for the hell of it before I give up on this thing.

The mitchell manual at the library has good diagrams of the ECM connectors, which pins are what, and the voltage they should run. My factory manuals may too, but I dont recall seeing that in them. I may try testing that. You can sort of check the ground voltages on the ECM that way, as well as inputs and outputs, etc without a scan tool and compare them to what they should be, maybe find out if there is a bad wire/connector somewhere, but thats a lot of work.

well, i got the idea that a bad knock sensor connection or such could cause the ignition to be retarded, when the voltage drops ignition timing gets retarded.

So I go to look for the knock sensor, havent found it yet. So I look for the module, manual says should be next to the evap purge cannister under the big electrical connectors. I dont have a knock sensor module. I have a plug there, but no module, doesnt appear to have had one in a long time if ever either since there is dirt in the plug.

Is it located somewhere else, ??? Anyone know??? I would think that I would get a code if it was missing, but I know I didnt get an EGR code when I unplugged the VSV for that so who knows.

apparently only the dohc has a knock sensor.

When I removed the fuel pressure gauge it ran better. dont know for sure if having that tubing full of air attached to the fuel line caused any problems , but seems that way. 18" or 1/4" hose with the schrader fitting, and then 3' of 1/8" od (1/16" id ) tubing to a pressure gauge, and it just would not run. I suppose that the airspace in the hose was causing some issues. I left the bleeder out when I installed it cause I was afraid it might leak at hwy speeds.

Well, Im hopeful the problem is solved. My remaining problem after changing the alt SEEMED to be like the tcm was cutting the engine out for a shift that never came, repeatedly, rythmically, it wasnt really like a misfire or such. But it was the same as behavior as occurred with the bad battery/alt/clamps, only with those problems it occured at relatively easy acceleration, without them it occurred only under hard accel (kickdown) and after driving for 30 min or so.

Before when I tested it with the TCM unplugged, I had not yet changed battery and alternator. So they were still jacking with it.

So on a whim, I check tranny fluid level, thinking it might not be shifting quite right due to low fluid when it got very hot, and that would jack with the engine thru the ECM.

It was a qt low. In goes a qt of transmission fluid and it seems to shift better at the high rpm/high speed shifts under accel. In any case, that problem hasnt resurfaced yet and I drove it ~70 miles today.

My problems look like a combination of low tranny fluid, bad battery, and bad alternator. Man I hope this is it.

Now I got to fix the #$%^ing A/C. I cant complain, 14 yrs on an AC system with no failures at all until now is pretty good. The condenser is parallel path , the evap is called a single tank so I dont think it is. I think I may just flush everything well extensively and put a filter in the compressor suction line to catch any minor debris I might miss. I really dont want to pay the $ on this old vehicle for new evap and cond.

Yeah fixing AC is expensive...and the main reason mine is still inoperative...