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My 78 (california emissions) will idle great and it will rev up high great but just crack the throttle off of idle and it will kick, sputter, and miss like crazy. If I pull the vac hose off of the EGR valve it will run fine except ping alot (normal with a non working EGR). I've checked the EGR and it functions properly it even passed smog like this (I couldn't believe it myself). Iv'e changed plugs and wires and the previous owner says he had the carb rebuilt (it looks fresh and clean). All the vac lines are good and I think are run correctly. I don't know where to look next. Any sugestions? Ron.

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OK, I'm over it. Where's the beer?

Sounds like a vac leak in the EGR somewhere given the troubleshooting you've done. Could be in the back pressure transducer, the thermal valve, or the EGR valve itself. It could also be in any of the hoses to those parts. If it does anything different when it is cold vs when it is warmed up I would suspect the thermal valve, but other than that I can't think of any specific ways of narrowing it down.

Take a look at the vac diagrams in in this thread as they may help:
http://forums.luvtruck.com/viewtopic.php?t=4747

I put vaccuum to the valve and it held no problem. The thermal switch worked fine when I tested hot open cold closed. What and where is the transducer?

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OK, I'm over it. Where's the beer?

The transducer is a small black can that should be the next hop up hose from the thermal valve. It is sorta shaped like a UFO and is held in a clip on the front side of the intake manifold pretty much out in the open. (at least it is on the 79 I have that is still smog complete)

Sounds like you've tracked this quite a bit already. It does sound like a vac leak sort of, but maybe disconnecting the EGR just masks the symptom. You might as well do a complete sweep for vac leaks. Check manifold/head joints and carb base spraying with carb cleaner and listening for RPM change, plug off the brake booster line, cap the stuff leading up to the air cleaner. Eliminate every thing else, and what remains, however improbable must be the truth.

It might have something to do with the idle mixture adjustment. If the carb got rebuilt but never tuned back in, maybe that is causing the trouble. It gets a bit more air just as the throttle opens, maybe the idle mix isn't enough for it to run and the main fuel circuit hasn't kicked in yet. The EGR behavior could just be a coincidence.

Ok. Thanks for the help. I plugged off alot of stuff just playing around but forgot about the brake booster .
Also on the air pump, mine has hardly any air coming out of it even when reved up. Should it be blowing reallly hard or what? I'm checking right out of the pump before any valves or or anything.

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OK, I'm over it. Where's the beer?

the backpressure transducer went out on my truck too... i looked at chevrolet and the laughed at me. i checked isusu and they said its about $75. so i went to the jeep dealer and got one for a mid 90's jeep cherokee. it fits in the little clip and everything. (not perfect but it works!) it was only $30. might want to go that way if you cant locate one cheaper

MMMMM. I don't have a transducer. On mine the hose goes from the egr to the thermal switch and then from there to the port under the carb on the right side. I wonder if my 78 should have one or if that was something added in 79???

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OK, I'm over it. Where's the beer?

How did you tell if it was the back pressure transducer that went out? What specifically did it do? I think I'm fighting the same problem.

Mine idels fine and revs up just fine. I just had the carb rebuilt. It runs better than ever. But when trying to run on the street it sputters and throughs fits. On the highway its a pain. 55 Max. It keeps running, but it misses here and there.