m998 hard starting with cold engine

My '86 m998 doesn't want to start when the engine is cooled down, it restarts just fine when out running around as long as I restart within a couple hours. The truck was starting right up after letting the glow plugs cycle until sometime over the winter & when the issue started I just assumed that it was because it was below freezing & I hadn't put any additives in the diesel, but now its in the 70s & the truck is getting even harder to start. The truck had a new glow plug controller put in about 2 years ago & a rebuilt injector pump installed March a year ago.
At this point it seams like the only way I can get it to start is after the glow plug cycle, I have to crank & crank & crank the starter while rapidly pumping the accelerator & the truck eventually starts.

Any smoke? White? smell like unburned diesel?

Without knowing more specifics, I’m guessing it’s glowpugs. Highly unlikely they’d all die all at once. Circuit’s blown, not heating. Pull a cap off one, attach a VOM to it and ground and turn switch to position 1. You should read 24 volts. No power, no glow, hard to start.

Low voltage, no voltage? control box.

Which PCB did you install? Latest model, Nartron S3 straightened starting problems right up for me (the one with the three plugs, one port aft not used).

The compression on these things is something like 23 to 1. Pumping enough diesel into the chamber should change the PV=nRT equation enough to hit diesel’s flashpoint eventually. Only takes one cylinder to fire, backpressure/warm exhaust bringing up the temp of a few other cylinders.

Does your engine kind of start, rattle, ping, smooth out in a minute or so?

Protective Control Box sounds like the culprit. Not the first time one of those has gone t!ts up not long after installation, grounding problems, not disconnecting batteries when working on wiring, the older boxes weren’t that robust. Simpler, but less protection to ground faults.

Oh, and do you have the grounding harness (Kascar type) installed?



That’s all I got.

Good luck.

White smoke while cranking, goes away very quickly once is starts.
Once it starts it smooth out to regular idle sound within seconds.
Its the newer "good" glow plug controller box.
I don't remember if the previous owner installed the grounding harness (I think he said he did, but that is a 2 year old memory), how would I check?

crazzyrman said:

White smoke while cranking, goes away very quickly once is starts.
Once it starts it smooth out to regular idle sound within seconds.
Its the newer "good" glow plug controller box.
I don't remember if the previous owner installed the grounding harness (I think he said he did, but that is a 2 year old memory), how would I check?

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The gound wire connects battery, engine, PCB (up top at head bolts), starter, frame IIRC, all wires come together to one larger lug bolted to the most convient place on the engine to do it, which is under the dog house.

Was the gpc or pcb replaced 2 years ago? What does the wait light do when cold?

Action said:

Was the gpc or pcb replaced 2 years ago? What does the wait light do when cold?

Click to expand...

Yes the glow plug controller was new 2 years ago, its the new "good" version, the wait light comes on with the ignition at position 1 for about 10-15 seconds (I haven't actually timed it) like it always did.

10-15 seconds seems long. I think the upper end of wait should be about 9 seconds. May want to time it.

Cap

The GPC is round and on top/front of the motor.

There is a temp switch in the pass head at the back of the block (coolant) and its function is to retard the timing at the injector pump until the temp is up a bit. Mine was bad and had the same problem and when replaced the problem was gone. Just a thought.

Mark