Shuts off while driving - Stalling

[Chad Mac]

I feel like a professional on this subject because I have fixed stalling problems on my truck on 4 seperate occasions.

The first time was the ignition harness that was mentioned earlier. When mine went out it would stall while driving and no dash lights would come on. I could work the key switch back and forth til the dash lights came on and it would start right up. New ignition harness and problem solved.

The second time was the infamous PMD/FSD. When mine went out it would stall while driving and sometimes start right back up, sometimes I would have to crank on it for a while. New PMD/FSD and problem solved.

The third time was the also infamous OPS. It would only stall shortly after restart when the truck had been driven and shut down for a short time period and would require some cranking to get it going again. New OPS and problem solved.

The fourth time was the in-line fuel lift pump that assists the injection pump. Symptoms were serious hiccups under acceleration and stalling after startup with lots of cranking to get it going again. My lift pump sounded like it was working fine (humming when the key was turned forward and when the truck was running) but all it was doing was making noise and not pumping any fuel. New fuel lift pump and problem solved.

I don't know how to explain it but I love the truck. My next truck will be a 6.5 also. I guess because I know the engine so well that I feel like I can diagnose and fix almost anything on it now. Good luck with your problem!

[nealpellecchia]

I feel like a professional on this subject because I have fixed stalling problems on my truck on 4 seperate occasions.

The first time was the ignition harness that was mentioned earlier. When mine went out it would stall while driving and no dash lights would come on. I could work the key switch back and forth til the dash lights came on and it would start right up. New ignition harness and problem solved.

The second time was the infamous PMD/FSD. When mine went out it would stall while driving and sometimes start right back up, sometimes I would have to crank on it for a while. New PMD/FSD and problem solved.

The third time was the also infamous OPS. It would only stall shortly after restart when the truck had been driven and shut down for a short time period and would require some cranking to get it going again. New OPS and problem solved.

The fourth time was the in-line fuel lift pump that assists the injection pump. Symptoms were serious hiccups under acceleration and stalling after startup with lots of cranking to get it going again. My lift pump sounded like it was working fine (humming when the key was turned forward and when the truck was running) but all it was doing was making noise and not pumping any fuel. New fuel lift pump and problem solved.

I don't know how to explain it but I love the truck. My next truck will be a 6.5 also. I guess because I know the engine so well that I feel like I can diagnose and fix almost anything on it now. Good luck with your problem!

Ok, my 1993 6.5 has a severe suction when you take off the "new" vented gas cap. The others too. It didn't have this before the last few mos. or I would have noticed it I think. Well when empty it's always like normal right? Anyway I've fixed suction leaks at the fuel mgr., top return hose, new hoses and clamps in between. It's run like a champ! with the higher fuel pressure. And then dogged 2.5 hrs. into a trip, with even a backfire. I pulled over and loosened the cap...left it loose, Then it takes fuel normally again. The best answer I've gotten is that it's a symtom of a clogged sock; that high suction. Is this true?? Before I spill for a injector pump I want to cover everything. Air is coming in again. Stalled cold starting and hot starting. Both require bleeding the air out of the system. Tank is suspect. Clogged bi-pass valve? holes in lines back there?? Anybody know some stuff about this area?

[More Power]

Ok, my 1993 6.5 has a severe suction when you take off the "new" vented gas cap.

I suspect you meant diesel cap, but it's helpful that everyone knows that there is a big difference between a fuel tank cap made for a gas powered truck versus a 6.5 diesel truck. You must specify a "diesel" fuel cap when buying a replacement.

According to GM, a diesel fuel cap should vent when internal fuel tank pressure exceeds 2-psi or 1" vaccum. Gas caps are generally not vented, which would create huge vacuum as fuel in drawn down in the tank.

Jim

[Firstoneman]

Greetings:
I have a 94 Suburban, auto trans. Drove this from Cali to Michigan Jan 2015. During the trip I developed a stall problem leaving Denver. But it restarted and I went on my way. Later it also gave me a check engine signal at higher speeds (70-73mph), slow down 5mph and the light went out. Sometimes it would show up at 65mph - but go away just by letting off accelerator. I did have some bucking, like not enough fuel, when climbing a few grades leaving Cali towards Utah and in Colorado. I made it to Michigan. Once I got here, I had a situation where it would start in the parking lot and stall after about 12 secs of running. It kept doing this for about 10 tries. I went home for the evening, headed back the next day and started it up and it kept running - headed back home only ¼ mile away. Made it. After that it stranded me in another lot. I had to travel out of US for 7 months so it sat there. I haven't tried to start it since I returned because it is 2.5 hours away. I've read a number of posts and I think it is either a lift pump, PMD/FSD, or maybe even the fuel solenoid. In this thread, and the sticky on the PMD, I do not see much in recent years on the matter.

I'm going to buy some parts - that way, when I do go to that part of the State, I can fix it. I am tempted to just try the PMD/FSD but I don't want to short it if it's fuel solenoid. What brand PMD is recommended these days? Also, how about the fuel solenoid…what brand is best? Is the fuel solenoid the same as the "fuel cut-off solenoid"? If they are separate products what is good brand for the "fuel cut-off solenoid"? And what brand for a lift pump? Thanks for help. This has been a learning curve and a good experience so far.

Cheers!
David

[Lug]

I would bet on the PMD. Unfortunately the only way to really eliminate the PMD is to put one in and see if the problem goes away. Also check your grounds and power connections. The 6.5 tends to be voltage sensitive. The first time My 94 was doing this I bought a Heath relocation PMD and that worked for several years. The next time it started to do this it turned out to be the power connections on the firewall terminal strip were not tight enough and had corrosion buildup. A quick and cheap shotgun shell is to take those connections off (one post at a time) and clean them up and reinstall them. Use some sort of grease on them to seal the terminals from further corrosion. I used Dow Corning DC-4.
Justin

[strykerAKAmack]

When my pmd failed I replaced it with a DTech pmd , been running fine ever since .

[Firstoneman]

Greetings.
Well, got the notice today that a new msg came into the thread, thought I'd look at it for fun. Realized I never reported outcomes (though a very observant person might've noticed that I have an Accurate Diesel PMD listed in my mod list).
Anyhow…that's what I did. I changed out the PMD. And voila…nothing. Wouldn't start, and there it was the sweet fragrance of diesel…arghh. Opened hood smell diesel, can't see any. Nada. Well, I tried to start again. Then had wife try to start and I see a leak in hose at IP pump fitting. Whew. Must be that when I removed the original PMD plug to attach the relocation harness I jostled the fuel line and it being brittle decided to crack. Got new hoses, rid myself of previous owner mod in that line and it started right up. Then decided to change fuel filter. That was a research project all of it's own due to previous owner mod and which I finally resolved. Getting it primed was hassle and when I found the info on how to jumper pins on OBD-1 to activate the lift pump I was happy. Now I have a nice setup for fuel filtration. Only thing I want to do is remove a 1st owner filter just after tank on the lower frame - seems unnecessary.
Per previous suggestions…I looked at as many electrical fittings as I could and no corrosion could be found and all seemed solidly seated.
Will have to do something about the position of the new PMD for winter driving - it's on the inside of bumper near air scoop at moment - ripe for salt exposure and subsequent corrosion.
Thanks for all the suggestions. Everything worked out happily. Hoping it will continue so. Enjoying the diesel experience.
Cheers!