Stalling issue after revving?

[88 K30]

One of my 6.2's developed an odd thing recently. I think it actually started prior to my replacing the tank, but I can't swear to it. After the tank replacement, it starts just as quick as before and runs the same. I changed the fllter after I noticed this problem, just in case and it didn't help.

Basically, after it warms up enough that the fast idle comes off, if you rev the engine a bit (in gear or Park), when it idles back down, it will usually stall. If it doesn't stall, the idle drops really low and then catches and comes back to normal. At highway speed, the trans keeps the engine from stalling when you let off the throttle, but moving the truck around the yard, where you back up a bit or pull forward with just a goose of the throttle is really where it gets you. It's a real pain. Hooking up to a trailer by yourself where you need to back up a foot and get out to check distance can result in several stalls if you're not really gingerly with the application/release of the pedal. Even just backing into the garage it will stall when I let off the throttle.

I'm not sure if it does it when the engine is really hot (haven't had the chance to test that), but it does it after the cold idle goes off pretty readily on a cool engine.

What would cause this symptom? Could something in the IP be gummed up and sticking? I put fresh fuel in and some PS additive after the tank swap, but have not been able to drive the truck very much lately. The truck is a CUCV with 18,xxx original miles, so I doubt the IP is worn out, but I'm open to suggestions?

Thanks!

[88 K30]

So, I've been thinking about this problem and having no luck solving it and I thought I would check back with another possible cause.

Will low fuel pressure cause this type of symptom? That's why I changed the filter, because I thought it might be clogged. However, I am now thinking that another cause of low pressure could be a bad fuel lift pump. If it is not putting out enough pressure, would that cause the symptom?

Unfortunately, there's no easy way to determine if the pressure is low, aside from putting a tee and a guage in the feed line, but that's my next guess, unless someone has a better suggestion.

Any help or suggesstions are appreciated. Thanks!

[DmaxMaverick]

Sounds like it could be a sticky governor, in the injection pump. I'd suggest a couple tanks of heavy dose fuel additive ("injector cleaner"), and perhaps some 2 cycle oil mixed in.

You can test your fuel lift pump w/o a gage. The pressure can't be "low". It only needs to be present. With the engine running, open the filter bleed valve. If fuel comes out and the engine doesn't die, you have sufficient fuel pressure/flow. If no fuel comes out, and/or the engine dies, you have a fuel delivery issue. If your IP is healthy, the engine will run, essentially, normal with a defunct LP at lower RPM's and power demands.

[jogl]

I'll second the IP governor motion. I'm not so familiar (yet) with these IP's but on a tractor rotory pump (ours are mostly CAV's) idling problems and surges are a pretty good indicator that the IP wants rebuilding. The parts that the injection shop replaces are often governor parts.

But, as you know, you need to rule out everything else first (like, as mentioned, the lift pump) because IP rebuilding is a fair amount of work and expense.

You could also rig up an independent fuel supply to the IP to rule out problems with the fuel delivery systems. We call it the IV tank. It is a 5 gallon tank of fuel sitting on the roof of the vehicle. It gets plumbed in directly to the IP (with a cheapy inline filter). I also temporarily plumb the return line into the IV tank because one time, when I didn't, all of the fuel from the IV ran right through the IP into the regular return line and overflowed the vehicles regular tank all over the floor.

Good Day,
JP.

[88 K30]

I'll give the filter bleeder test a try this weekend. I didn't have any 2-cycle oil handy, but I added a bottle of ATF, since I have read it does a nice job of cleaning up the fuel system.

Now, I just need the weather and work schedules to cooperate so I can put some miles on it to see if it improves.

Thanks for the tips!

[Subzilla]

Not intending to add to any confusion but I put on a rebuilt IP some 3 years ago or so, and straight from the supplier, mine did and still does the exact same thing. Called up the supplier and he really didn't have any suggestions. The symptoms really show when the pump hasn't warmed up, yet but have shown up at random. I fiddled with the timing and replaced filters with no change.

Still runs fairly well so I don't know......

[lower]

im a noob to these myself but mine was doing the same thing and it turned out to be the plunger on the passenger side of the pump was sticking......

[john8662]

im a noob to these myself but mine was doing the same thing and it turned out to be the plunger on the passenger side of the pump was sticking......

That is the advance piston on the bottom/side of the pump.

Usually means rebuilding time...

I have a 91 R10 suburban that did something very similar to the dying thing. I would rev it up and it would almost just die, regardless of injection pump. It ended up being a fuel supply line that had a bend in it and that bend had pinched, just as if you'd turned the hose too sharply.

It was on the driver's side underneath, in the frame rail, just a connection between two metal lines.

Replaced that hose, away the symptom went.

Check supply lines for kinks.

J