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Guest 9812VCTD

Pump Stumble.....

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Guest 9812VCTD

Heah my truck has developed a pump stumble. It is really noticeable when I free Rev it, it cuts in and out and blows alot of white smoke. It also effects my top end it does the same thing in the higher RPM's. But for casual everyday driving no problems. I just put in a new overflow valve which didn't help. I am thinking of changing out my Lift pump next and if that don't work check out my timing to see if it has slipped. Any other idea's or suggestions. This is really annoying and need to get it fixed.

Thanks,

Justin

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posted this in the moon light thread as well justin you might be sucking air when you replaced one of the filters that pre filter is very pickie about sealing i know terry does a great job maybe its your stock lift pump giveing up the ghost just a thought or two

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I suppose there's a dozen reasons for a stumble, but it seems to me there are only a couple of reasons, maybe, for white smoke. Isn't the white smoke due to unburned fuel?

When a diesel is started up cold, especially big rigs and other large-engine machines (earth movers, etc.) you'll often see white smoke. Isn't this due to excessive fuel going through an engine that's not up to temp and isn't getting burned?

Also, when your timing slips, white smoke is seen because fuel is injected into the cylinders late the cycle and some of it is not getting burned, its just getting vaporized by the heat of what actually was burned.

My truck has developed a bit of stumble when I blip the throttle from idle. I get some black smoke as well as a bit of white. This summer I went from 370's to DDP4's, modified the AFC, and now I have a ported head. I'm beginning to think when I blip the throttle a bit more fuel is going in then can be burned and shows up as a white puff.

So I'm wondering if something is going on that is causing a bit of excessive fuel and that may either be causing the stumble, or the stumble is causing uburned fuel resulting in white smoke.

You might consider sliding the AFC back a bit or even moving the plate back a little to cut fuel and see what happens. It's fast and easy and just as easy to set back the way it was.

Another cause for the white smoke, and possibly the stumble, is a weak injector or two. When they get weak and won't "pop", the fuel just squirts out the holes and doesn't have a sharp, definite start and stop point. That could cause fuel to be squirted into the cylinder past the point of ignition and thus not really getting burned. 2 of my old 370's were shot and I noticed some white smoke sometimes when I rolled into it with those.

Just some "idle" thoughts,

-Jay

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Guest 9812VCTD

Jay thanks for the great thought out reply appreciate it. The thought of a weak injector or two has crossed my mind also. I am going to get my fuel pressure checked first and see if it is weak, then if that isn't the problem check the timing. I could also try your advice on moving the plate and AFC housing and starwheel back to see if any difference is made. Then if none of that works pull the injectors and get them checked out I am really wanting to step up to a bigger injector. Once again thanks for all the info!:thumbup:

Justin

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Guest Smokin Monster

One of these days we need to get together and do some fine tuning and timing and get that thing going! Now if it would just warm up a little outside....8-)

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Guest 9812VCTD
One of these days we need to get together and do some fine tuning and timing and get that thing going! Now if it would just warm up a little outside....8-)

That would be cool Kev...If I can get this thing running right we'll have to put a tack in it and hopefully try hooking to a sled this summer.:D

Justin

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Guest Smokin Monster
That would be cool Kev...WHEN I can get this thing running right we'll have to put a tack in it and hopefully try hooking to a sled this summer.:D

Justin

Heck ya!:thumbup: :thumbup:

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Guest 9812VCTD

I'm going to see if I can get the fuel pressure checked this week and see if that is what is causing my problems, I'll let you know what I find out.

Justin

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Guest 9812VCTD

I got my fuel pressure checked on Tuesday I got 20psi at Idle and while driving down the road averaged 30psi. Under full acceleration the lowest it got was 18. SO it definetely sounds like getting the timing set will be the next step.

Justin

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