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Sluggish smokey cold start - APPS gives minimal response on 1996 6.5L

A

ambulanceCamper

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It's a 1996 6.5L K3500 with 4x4. 4" exhaust
Description: Only the first start of the day, when temps have been 50-60 or less overnight, I have a sluggish cold start condition. The RPMS fluctuate between 400-100 it sounds like, and the engine is barely running and shaking for 5 seconds to over a minute or 2 depending how cold. Also during this time I get minimal response from accelerator pedal position sensor (gas pedal). I have a momentary disconnect for the ect sensor in crossover so unplugs the sensor doesn't help but on the scan tool I can see the PCM thinks it's -40°F when the sensor is unplugged. Have a glow plug button that doesn't help to extend glow time either.
After it's done being grumpy it finally responds to APPS or on it's own gets to a stable idle and the smoke is gone, and full pedal response is back.
After this first start of cold day it doesn't happen again till next day.
I've tested my glow plugs and they are all working, they're Bosch, new in early 2021.
I tried a new PMD and no difference. Changed fuel and air filters a few times, new injectors no difference.
I've uploaded a couple videos showing this condition here and here. It does seem electronic!!
I have a fast idle switch which doesn't work during this condition either.
A scan tool shows LOAD_PCT 100% during this condition which is the APPS input normally. When it "wakes up" this reading goes back to where the pedal is actually at.
Been trying to solve for a couple years.
First time posting here - I'd really like to fix this.
 
Had the exact same issue as OP.

`Smokey Starts getting worse with the colder weather

Notice while up in MT last summer trying to be of help to Big-T that my first starts were starting to have a little smoke. Hmmm Acrid diesel smoke that cleared up quickly as engine came to life. It was kinda hit and miss up there but, when it ‘hit’, the smokewas getting a little worse. Longer...
www.thetruckstop.us
Pull and check Glow plugs w/ 12v. Replace any not coming up to heat/red glow quickly. Then glow plug harness and connectors. Connectors at glow plugs need to be tight/very snug.
Next, if the glows check out. Sorry to say, injectors…
 
Paveltolz said:
Had the exact same issue as OP.

`Smokey Starts getting worse with the colder weather

Notice while up in MT last summer trying to be of help to Big-T that my first starts were starting to have a little smoke. Hmmm Acrid diesel smoke that cleared up quickly as engine came to life. It was kinda hit and miss up there but, when it ‘hit’, the smokewas getting a little worse. Longer...
www.thetruckstop.us
Pull and check Glow plugs w/ 12v. Replace any not coming up to heat/red glow quickly. Then glow plug harness and connectors. Connectors at glow plugs need to be tight/very snug.
Next, if the glows check out. Sorry to say, injectors…
Click to expand...
Is it necessary to pull the glow plugs? I tested 7 out of 8 successfully by testing that they draw 13-15 amps when given power in the block.
 
100% pull them.
Ohm test, amp draw test can be flawed- I proved it.

Gp can become crystallized, which raises ohm.
Swolled and or burn off small amount of the tip- either of these can lower ohm.
Ohm changes causes different draw (amp change).

I have tested GPs and had good readings which didn’t get half as hot as they should. I have tested them as bad- then replaced them only to bench test and see them work awesome.

The comment of eliminating the bosch for the AC Delco 60G is 100%. I can dig up picks of my ruined piston from a failed Bosch with under 10,000 miles on them.
Only by them from a proven authorized distributor like Napa. There is a ton of knockoffs around online. Spend the extra couple bucks to protect the engine.

As to verification if the GP are the cause of it being too cold- block heater.
If only the cold is impacting it- eliminate the cold.
Test it - what coolant temperature does the problem go away… with engine cold- get coolant up to that temperature before starting. External heater hose inline block heater if needed. Keeping the ip cold and heating everything else to see if the cold ip is the issue like AK DD is thinking.
 
Will L. said:
As to verification if the GP are the cause of it being too cold- block heater.
If only the cold is impacting it- eliminate the cold.
Test it - what coolant temperature does the problem go away… with engine cold- get coolant up to that temperature before starting. External heater hose inline block heater if needed. Keeping the ip cold and heating everything else to see if the cold ip is the issue like AK DD is thinking.
Click to expand...

Good information. Yes if I plug in a block heater the problem is non-existent. Something is too cold. I just think that it's something electronic because I get no response from pedal sensor. Unplugging the ect sensor in crossover doesn't help much. Between that and pushing the pedal in and out it seems to eventually fool it into "waking up". Also tried jumping the fuel heater(has a thermostatic switch) and it doesn't help.

As for buying the gp from an authorized dealer. What's your opinion on RockAuto? And if using NAPA should I buy it at a store or online or is the same?

Also on another forum someone mentioned maybe the injectors are leaking fuel into the cylinders overnight but again it's an electronic issue. I've replaced 6 injectors anyways. The last 2 were knocking so I reverted back to the old ones and never . The truck starts and runs perfect when warm

The Bosch I have are Duraterm from RockAuto. Other opinions said they are fine but I will reconsider. You guys at truckstop have helped me A LOT over the years from existing answers. Maybe I will pull and test if there isn't anything else I can try first.
 
Plugging in the truck solved/reduced the issue with my cold start grey acrid smoke, chugging, one cylinder ‘Fopping’ for a couple of seconds etc.
As for the APP, my guess is the computer isn’t going to give the APP full command authority until the engine is happy but, that’s PURE CONJECTURE on my part. More like the engine can’t do anything with what the APP is commanding until its happy.

The connectors on the harness, if not making good contact with the GP blades will toss AMP draw to the wind as well. Mine were not tight like new when I checked. I’ve had my set up apart many times chasing what turned out to be bad valves/heads. After that got sorted out, It was almost two years before the smoky starts developed.

GPs were my main suspect but, after removing and testing them I knew they were good (Duraterms, 12 years old so, not the nightmare others have had the last few years). For me, a new harness took care of the issue.

Yes, Injectors leaking down can be the problem too and others have replaced theirs with new and that took care of the issue…for them. Remember, ‘new doesn’t mean good anymore.’ So, get recommendations on where to send the ‘new’ injectors to get them pop tested and balanced.
 
Your glowplugs are EXACTLY what I had and where I bought them. And I used to recommend them- until mine destroyed my engine. And saw multiple others having the same problem with them from Rock auto, and other sources.

Rockauto is supposed to be an authorized dealer for AC Delco now- but I don’t trust them for it. Everytime there is a problem with RA it becomes a complete mess. So no- I wouldn’t buy from them.

Go into a Napa personally is my recommendation.

I believe you should replace them ASAP

Imo- if a block heater solves it- then glow plugs, relay, etc are the issue 99.99% of the time.
 
Paveltolz said:
The connectors on the harness, if not making good contact with the GP blades will toss AMP draw to the wind as well. Mine were not tight like new when I checked. I’ve had my set up apart many times chasing what turned out to be bad valves/heads. After that got sorted out, It was almost two years before the smoky starts developed.

GPs were my main suspect but, after removing and testing them I knew they were good (Duraterms, 12 years old so, not the nightmare others have had the last few years). For me, a new harness took care of the issue.

Yes, Injectors leaking down can be the problem too and others have replaced theirs with new and that took care of the issue…for them. Remember, ‘new doesn’t mean good anymore.’ So, get recommendations on where to send the ‘new’ injectors to get them pop tested and balanced.
Click to expand...
Are you talking about a new glow plug harness?
I made my own part of harness for the passenger side and used cheap Chinese connectors on like 5 GP connections. I'm gonna replace those with some beefier usa connectors first, then I guess it would be try AC Delco plugs from napa. If that doesn't work then I guess try a new harness.

I wish I would have ordered a complete new harness from that guy that was making them until a couple years ago but the ones online now don't have any fusible links on them so almost have to make my own now?
 
GenBiltstein said:
It would be nice if a PCM could do an auto-test on glow plugs. That is not the case because of era involved for GM 6.5. The computer could take a resistance or current reading on all eight GPs give you results.
Click to expand...
Nope. There is specifications for ohms, amps, etc. that you can do. But I proved those tests are invalid.
As ohms (resistance) go up so does the amps.

In the fleet we would do the quick amp test then ohm test rather than down the trucks. It would measure fine but still not work well.
Then in frustration just throw in new plugs and found it worked.

So I took readings out of the truck and they would test ok, but hook up power on the bench and some would glow properly and others wouldn’t.
It turned out the glow plug can actually wear away the element in length which shortened the part that got hot, lowering resistance and lowering amperage draw. But as it continued the element starts to get deteriorated and increased the resistance & amps. Each step of the way having less surface area to heat so not working like they should.

Also would not glow anywhere near as hot- like a new one would glow red hot cloe to the threads and the tips white hot. While the older one would barely get the tip red and the majority a dull orange.

Then we started just swapping all 8 when in doubt and would test them all, discarding the bad and reusing the good - always being sure to never mix used with new. If one was new they all got new in interest of down time.
And we started seeing some that would have out of spec readings on ohm- but would work perfectly.

A couple of us owned 6.2/6.5 personally and one guy who commuted from Pahrump where it snows in winter would use starting fluid. SMH. We pulled his plugs after work one day and could see crystals formed on them. So a bit of playing around and we found out it comes from the starting fluid. Found out that it takes very little starting fluid to ruin even a new set of glow plugs.

So we learned to not bother with a meter. When you suspect glow plugs- install a new set. Then remove and bench test the old ones with a battery and a bit of wire.
We just ran a wire from battery negative to vice and vice held the part your socket goes on. Then positive to the tab and make the connection at the battery last or wear a welding glove to plug onto the glow plug. A switch inline isn’t a bad idea…
 
There was a way to make some money on the side when I was in the military. It required you taking a couple of glow plugs and solder them in series on a four foot lead. Call an infantryman over and say "hey watch this!" and demonstrate to him how you could heat up a cup of coffee with it and then sell it to him for five bucks. He in turn had something to heat his coffee up with and you got $5. Just sayin...
 
ambulanceCamper said:
Are you talking about a new glow plug harness?
I made my own part of harness for the passenger side and used cheap Chinese connectors on like 5 GP connections. I'm gonna replace those with some beefier usa connectors first, then I guess it would be try AC Delco plugs from napa. If that doesn't work then I guess try a new harness.

I wish I would have ordered a complete new harness from that guy that was making them until a couple years ago but the ones online now don't have any fusible links on them so almost have to make my own now?
Click to expand...
I’m just saying if the wires pass visual and tech. and are otherwise good but, the connectors are loose, repair or replace the connectors.
 
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