Issues with my 86 ~*~*~ HELP ~*~*~*~

[dwatts1984]

I have an 86 GMC 1500 LWB
5.7L 350 , 4 bolt main
trans is a 4 speed auto

Basically bought the truck as my "good ol boy " truck and love it. Got a great deal on it at $400, running, however didn't stop so well. After replacing the brakes all the way around, and installing a 600 Edelbrock carb... truck came to life...
Until after a fishing trip... truck just started back firing in all gear all the way through the rev... Literally out of no where... Now once you hit 4th gear (which is a task) the whole truck shakes...
I'm thinking the drive shaft... maybe trans ... but really not sure. Anyone had issues like this before. Mind you my trans doesn't shift right anyhow. Doesn't shift at any of the right point... and when in 4th when you stomp on the pedal it doesn't downshift to rev up... just bogs... Help!!! I miss my truck. Any info would be of some use!

Dwatts

[terryj]

How does it idle? Is it "misfiring" or "backfiring" there two different things. From what your describing it sounds like a misfire, which in most cases is ignition related, worst case, valve train and camshaft.
Have you done any work on the ignition system, distributor. spark plugs, spark plug wires, ect.
Check your timing, this could be the ignition module in the HEI system or a timing chain problem, but do the easy stuff first.

[john_p]

back firing all of a sudden,, timing slipped.. tranny sounds dead,, for my money get a 4 speed and a clutch

[dwatts1984]

Originally Posted by john_p

back firing all of a sudden,, timing slipped.. tranny sounds dead,, for my money get a 4 speed and a clutch

Yup... all of a sudden... Whats most funny is it stopped also... Just got done driving it... and doesnt backfire or misfire at all... No idea... Im frickin lost.

Tranny I have no idea. Shifts super late... kills what bit of gas mileage is possible... So just thought maybe someone had the same issue and could steer me in the right direction. I have lost all faith in mechanics and shops in my area. They're nothing but crooks, and thieves.

[dwatts1984]

Originally Posted by terryj

How does it idle? Is it "misfiring" or "backfiring" there two different things. From what your describing it sounds like a misfire, which in most cases is ignition related, worst case, valve train and camshaft.
Have you done any work on the ignition system, distributor. spark plugs, spark plug wires, ect.
Check your timing, this could be the ignition module in the HEI system or a timing chain problem, but do the easy stuff first.

I think your right... it may have been more of misfire... At one point when the truck was in 4th gear... when it dropped to about 44... the truck would "hiccup" as in blow out the carb instead of sucking... which lead me to believe a timing issue... but that has since stopped as has the backfiring/ misfiring... Or that I can hear at least.

[terryj]

Originally Posted by dwatts1984

I think your right... it may have been more of misfire... At one point when the truck was in 4th gear... when it dropped to about 44... the truck would "hiccup" as in blow out the carb instead of sucking... which lead me to believe a timing issue... but that has since stopped as has the backfiring/ misfiring... Or that I can hear at least.

I'm at a loss here, normally a timing issue will not cure itself. a backfire issue is normally noticed during deceleration, which tends to be a vacuum leak issue.
As far as the tranny goes, hows the fluid, I'm sure you have already checked that.

[terryj]

When was the last time the tranny fluid was changed and the filter? That would be a quick cheap fix it that were the problem. That what I'd do if mine were acting that way, before investing in a tranny rebuild.

[dwatts1984]

Originally Posted by terryj

I'm at a loss here, normally a timing issue will not cure itself. a backfire issue is normally noticed during deceleration, which tends to be a vacuum leak issue.
As far as the tranny goes, hows the fluid, I'm sure you have already checked that.

You're telling me. Im sitting here wondering whats going on... I have no idea.
Fluid is a little high... in the trans that is. Was going to flush it and replace the fluids... see if it helps... if not... just have it rebuild or something.

[donut]

A timing won't "cure" itself. Is there a knock sensor on the truck? I've read that if it's detecting a "knock" (or bad) it can retard the timing up to 20deg. ( I was trying to figure stuff out on my '86) My first reaction was timing chain stretched, some circumstances timing will be fine, however you start getting into all the slack in the chain, it can throw the cam timing way off. Trans issues, dunno. haven't had a 700r4 in years, and even then didn't have to do much with them.

Might not help much, but may get you looking in another direction.

[rwhit57]

Only a few things I can think of that might cure themselves. One is vacuum advance in the distributor, another is maybe plug wires if they are really bad they could be arcing out and then they got away from each other, one more is if anything got wet. Was it raining? Or did you run it through any water?

[Steve-W]

Did you fill the tank with low octane gas? had a Grand Marquis that developed terrible misfire and knock after putting in octane 87 instead of 95..