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98 K2500HD runs rough, possible IP?

Probe ECM voltage. Why would it pop ECM fuses aka what else is on that fuse? Maybe it was fixed and high amp fuse left in. An amp meter in place of the fuse could indicate excessive current still going on causing a voltage drop to the ECM. It could be an intermittent short not getting the fuse hot enough to melt.

The alternator plug goes direct into the regulator. Magic Smoke from the regulator failing could leave a ring around the plug. Did any bulbs fail at the same time indicating a high voltage surge? Generally they would be silver colored on the envelope from high voltage flash off failure. If so the ECM could be damaged. Note: high voltage and static may not immediately kill electronics as they can act goofy till they fail completely. The charge in memory saying "1" can leak off through HV or static damage and become so low a voltage it is read as a "0" now and then. Heat and other factors increase the random occurrences of the misread bits.

Alternator failure can be from shorts or opens on the big battery/charging wire itself. Any wire upgrades for the high amp unit? An inspection and wiggle test of the fusible links on the alternator battery wire is in order. A loose connection that arcs at the lug can blow an alternator on either end of the cable. Melted or burned off insulation can be a random partial short that doesn't burn the fuses out, but, makes enough "noise" to confuse an ECM. Battery cables arcing to ground when a heat shield got hot near a knock sensor is an example I recall from a 454 motor home.

Choose now to check wiring with a fine tooth comb or get a scanner as your other throw parts at it choices are ECM or IP. Swapping an optical sensor is a blind guess if it doesn't cure the problem. (Did I screw the job up and cause another problem on top of an existing problem? A scanner will give you better clues. )

How does the clear return line look? Even with 2 PSI at WOT and Full RPM air will mess with things. Kinked hoses worse with engine movement come to mind.
 
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alternator was shot when I got it, but all the bulbs are working, and nothing was melted around alt.

Charge wire got mangled when the belt let go after vac pump let go, so it got replaced.


As far as air, no air when running, but after sitting a few days there is a bubble at the top of the line.
 
well, moved a trailer down to the edge of a field in the ditch to pluck a cornheader off it with the combine, and it took me about 10-15 starts to make it back the 1/2 mile to the farmstead.

on 2 or 3 of those starts, hitting the key yielded absolutely nothing, wouldnt even turn over. swapped relay with a/c relay and no change.

Also was running the unknown PMD that it came with, and after the 10th restart, I swapped PMDs to the used one that was still running the 95 GMC fine (it was an old intake mount though) on the leroy heatsink and harness, with zero change.

I need to inspect deeper, but under the hood I cannot detect any comprimised wiring, and overall it looks un-cobbled. The ignition switch does feel a little sloppy. DO you think being an ex-Co-op pickup that the ignition switch stands a good chance of being wore out and not making contact all the time?
 
That sounds like more of an ignition problem. The trucks at the elevator I worked at for awhile always had ignition problems from getting started 20 times a day.
 
I guess I forgot to mention, it did get a complete new AC Delco OE grade reman starter a couple weeks ago. it quit me in town and had to tow it home. New starter and it starts great now.

When it wouldnt start just a few days back, post starter replacement, no clicking or anything, just all of a sudden zero attempt.
 
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OK, figure I better return to this thread, same basket case pickup.

After sitting all spring summer and fall I finally tore into it again. I pulled the ignition switch and swapped it with a used one I got from a guy who pulled it off a pickup that was known runner with a blown engine, so the switch was known to be good.

On both mine and his we broke the key in ignition alarm button, IDK how that thing can come out without destruction. I dont think its related, but I tried both shorted across and unhooked to be sure.

I am waiting on a deep E4 socket to get here to remove the old switch, but I plugged in the new one, turned the key (assuming with the little connector on the key tumbler the key needed turned as well) and then ran the switch with a pair of pliers, and it will crank fine, but I have no glow plugs, and no lift pump, and no smoke at the tailpipe.

I had dad under the hood shorting across the glow plug relay and he said he could here it "cough" into the intake, claimed sounded like a bad valve. It has made this sound before when the engine was stumbling.

Going off the previous codes on this and other symptoms, do you think the ECM finally gave up the ghost, or do you guys think this is a Passlock issue from swapping ignition switches?

If I was to swap ECMs with the other 98 K2500HD with identical powertrain, (dads ECSB push button 4wd) what will I need to do to keep Passlock happy?
 
What do the lights tell you? SES/STS light on after bulb check? May not have power to the ECM.
 
Fired right up today, let it idle, shut it off, wont start back up. let it sit for a few hours, fired right up. I only had glow plugs and lift pump prime on the second start (3rd attempt)

I agree, possible ECM voltage issues. any common points in the harness to fail? remember, earlier on she did drop a 606? code for ECM failure/ voltage, so its definitely leaning that way.

I think next step is to pull the ECM and see if there is a loose terminal in the connector and any obvious chafed areas.
 
OK, tried it out again this evening. first key cycle, dead dash, no lights. turn off, immediately turn back on, dash light up, glows came on, LP primed, etc. fired right up.

We are chasing something electrical for sure.
 
just changed it though with a known good one. I'll bust out the new one if I have to, but changing the switch changed nothing, and it did give the ECM death/starvation code earlier (P0606 IIRC)
 
Is there a relay to the ECM or is it direct wire? Known good switch means there could be a load (short) browning out everything or a bad connection doing the same. I would think things would be hot and fail the 2nd try. Jiggle switch in the run position - does it get the lights to come on? Switch adjustable like is the linkage to the key bent (thinking 1993 design)? Look close at the connectors at the column a this gets all the vibration from the switch.

Are you testing the batteries off the posts or terminals you are using? ECM ground: Cut the ground rings off the end of the wire and solder and crimp new ones on. (Don't matter what they look like, eliminate it.) Look for fusible links (on ECM circuit) and wiggle them.

Pull fuses and clean the corrosion off them...
 
Unplug switch at bottom of column and do ohm check maybe? Possibly do the whole harness shake test? When you had key on and nothing, then turned key off do you shake truck from body movement, slap steering wheel, anything else?

@ak diesel driver and @WarWagon : quit reading my mind and stealing my answers- Haha.
 
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