After a recently blown head gasket, I replaced the head and cam with uprated parts from Ted @ Engnbldr on my 86 carbed PU.

The engine runs great – mostly – it will cruise at 80 all day long and pull strongly, especially in the right rev band. If I try and accelerate in a gear slightly too high (4th @ 40), it will hesitate and miss.

Its worst on the over-run. Cruising downhill, off the gas, try and pick it up again and it really stutters

If I tap the throttle form idle, it hesitates and then picks up.

Before the re-build, everything ran great.

It’s got new plugs, wires, timing chain, filters. Cleaned all EGR parts and checked the routing (repeatedly) of the VAC lines. All ground wires are in good shape.




Other than this, any ideas on the hesitation????

Thanks

 

 

Sorry, screwed up the post. See above. Thanks for checking

 

Are you sure that all of the vacuum lines are hooked up correctly ?. Its possible that the carb needs to be rebuilt.

 

Check your timing? Mine ran after I did my hg, but wouldnt rev up. Sounds like vacuum lines though. cracked or hooked up wrong.

 

Am planning to replace all vac lines this w/end. Have checked the routing multiple times but will do it again.
The timing is already 6 degrees BTDC, my hood panel says 0 degrees. Ted at Engbldr suggested advancing until pinging became a problem.
The worst is on long downhill over runs. On my drive in this morning, it was stalling at the lights after a long downhill cruise.!!!
Thanks for the help.

 

whoa try 0 degress on the timing, that's what the carb'd trucks should be. He told me the same thing with the timing, but mine runs like doo doo with the timing at 6 degrees. Especially at idle/closed throttle for an extended amount of time. Which I would assume is close to a down hill run as your describing.

Alot of guys experienced this on my truck our last off-road trip to Rausch Creek. Was running really weird at idle. I had advanced the timing to give me a little more bottom end, but that combined with the fact I was running the weber at 1.5psi was too much. After I reset it back to 0 degrees ran fine the rest of the day and the next.

 

Thanks, I'll try this morning. Gotta check the vac lines too. I'll let you know.

 

My truck used to have LOUD misfires, And sometimes when I turn off the engine, it keeps running for a little more time (hesitating)...
I don't know if this may help you, but, the EGR was cancelled and the misfires, and the turn off problem stoped.
Good luck.

 

I replaced all the vac lines and found a nipple on the BVSV was cracked. I'd fixed this before but it cracked again so I sealed the whole body with chemetal. Also retarded the timing back to 0......still hesitating badly.

Any chance its the EGR. I stripped and cleaned it a year ago and made sure it wasn't sticky. Do these fail or act up?

All this was as a result of a blown Head gasket. The engine got super-hot and did boil but not for long. Could I have damaged any of the VSV's BVSV etc. etc.?

thanks

 

Reset the timing to 6 degrees advanced - runs much better but still hesitates down hill, either carb closed or even accelerating.

Performed the EGR test by applying vacuum to the valve and there was no change in revs. Could feel the valve clicking open and closed as I did the test. I used human vacuum so not sustained. Mine's a CA version so no modulator above the EGR to clean.

EGR Failed? They're pretty expensive so I want to be sure before spending more money.

Help appreciated. Thanks

 

Desmog the truck and you can eliminate 75% of the vacumm lines, when i did that to my truck it idled better ran better etc. the best part is all of the loud backfiers quit too. then reset the timing and try it.

 

the backfires are pretty awesome though if i do say so myself ..freaking HILARIOUS to down shift slowing down and scare the living CRAP out of the cars around you when your exhaust shoots a 4ft flame out the exhaust (dumped under the cab) and sounds like a shotgun..

for the record, mine no longer does this, lol

 

Do that in the middle of Philly and you'll get shot at by a bunch of hoods with UZI's. Not cool. lol

 

I'm on the left coast - gotta pass smog - EGR needs to stay. The backfires would be fun.

No clues on the EGR?

 

if I had a block off plate you could have mine. I don't need, it. Gots a weber carb and it deletes the piping, but the valve is still on the head. Freshly painted with high temp paint and verified working. Have you looked into the modulator? Wait nevermind you said cali emmission and no modulator?

 

x2...!!

 

Thanks xtreme22R, I appreciate the offer. I think I'll buying a new one soon!

 

while the truck is running, pull each plug wire and see if you can notice a change in the sound/running of the motor. I had a injector wire that had broke and was grounding itself out causing my truck to miss. when i pulled plug #1, no change. pulled two, three or four and the truck would die. Noticed the broke wires when I went to replace injectors. fixed all my problems.

just something to look into...

 

If you aply vacuum to the EGR and the idle doesn`t change (stumble) then the EGR is bad and needs to to be replaced. Check to see if its not plugged with carbon first.