My truck will not run when charging

HELEN BAILEY

MEMBER
1988 CHEVROLET S-10
2.5L
4 CYL
2WD
100,200 MILES

Hi, I have been on here before. I have an on going problem, forty five days long now. When I first broke down I was traveling home and my truck started sputtering and misfired a little and acted like it was going to stall. I pulled over shut it off and waited several minutes then started it again. It was hard to start but did get it going and started home again. Less than mile it started to run bad again. This time it back fired pretty bad and just shut down, had to leave it because it would not start this time. A side note, my truck had always run well, no problems and gave no warning, just started to run bad.

I have had it looked at by three licensed mechanics. Misdiagnosis, and almost $500.00 later, I am left with several new parts that were mostly unnecessary and a non running truck.

IGN. Module /cap/rotor/air filter /plugs /wires /fuel pump /fuel injector /fuel filter/fuel relay/TPS/starter /two batteries /two alternator and the large positive cable running from the battery to the starter. Previous owner had spliced it together.

Compression has been checked, perfect. New map sensor was the last sensor replaced, it was not bad BTW.

I have got good spark and fuel pump is pumping. I borrowed an ECM to test to see if mine could be bad, but no change. Checked most of the rest of the sensors all good. Replaced the ground strap, it was black and very dirty. Also checked and cleaned the rest of the grounds. No change.

After all that we got to the main problem finally. When the alternator is unplugged the truck will start and run, when plugged in it dies. I have a three wire alt w/brown wire that runs to the light in the dash and to the ignition switch and a pink and black one to the fuse box. Both wires have been tested getting proper volts so they are working.

By testing all of this stuff and BTW I have an obd1 and showing no codes, we have come to realize the alternator plug is not even the problem. We have now put a charger on it while running, plug the alt in, it dose not die until the volts rise to above 13.

So the truck will start and run between 10 and 13 plugged in but only connected to the charger. As the volts rise to 13 it starts to chug, sputter, misfire and will eventually die. Have no idea what to do.

I did take the new ignition module and the original one and the new alternator and had them all tested again. All good about a week ago, until today my alt was tested again only to find it had a bad diode. Got another one. Any ideas? Please help. Frustrated and lost.

1 Reply

HMAC300

MECHANIC
48,601 POSTS

If voltage goes off the chart like over 14.5 then the battery could be sulfated and make it charge too high. Unless something is tagged into one of the alternator wires it should run and this should make no difference. There is a pink/black wire from ECM/ignition fuse that goes to ECM, EGR, and switches to red to fuel injector. It also goes to a/c compressor relay. There is a pink wire that goes directly to coil from ignition switch. It may be that the problem lies with one o f these mentioned that is causing the problem and toasting the alternator at same time. These 2.5L had trouble with distributor reluctors cracking and would quit running due to not getting spark or running erratic. Best thing to do here is or at least I would try is to eliminate items not critical to running like relay, EGR etc. One at a time to see if its a difference or not. I would recommend printing this so you and mechanic can test these items. But unless vehicle is in really good shape and you can afford it dump it and get something else. It could also be an ECM problem or ignition switch.