Sorry about the title - but I have been through soo much with my truck lately that I didn't know what to post.

My 79 F-150 Custom with a 302 and C6 auto tranny just is not right yet. Had some popping in the carb and some power issues - some of which are continuing - i.e. -
When in park, I can rev it right up - sounds like a champ - but some stuttering when it comes back to idle (though this is not consistent).
When in drive, especially going up hill, you have to accelerate really slowly to get any power out of it - put it to the floor and get basically nothing power wise - note that it does this some days, but not everyday.
When it gets up over 40 KM's, there is some shimmy/shake/stuttering like it is working to all heck to make power.
What I have done so far:
1) New Carb and Gasket (this seemed to solve some of the problem).
2) New Ignition Module (this seemed to have helped some as well).
3) Checked Vaccuum advance via manual 'air suck' test - works fine.
4) Replaced Vaccuum hose on advance for good measure.
5) New Fuel pump last year
6) New tranny Vaccuum Modulator last year

What am I over looking? I have noted some slack in timming chain - but it had new gears and chain put in 4 or 5 years ago. Should I advance/check timing?
Any help at this point is greatly appreciated.
Cheers,
Alex

 

Yes,I would ck timing,you didnt mention if it had an automatic or manual choke,if it is automatic,I would check this also,sometimes they hangup alittle.
there are a bunch of other things that come to mind,sticky valves,weak lifters,fuel starvation,so try not to get too frustrated,some times it just takes alot of testing to get things right.Do you have a vacuum guage?

 

It is an Automatic choke - will check it out -
Unfortunately no, I don't have a vaccuum gauge - but it sounds like I should get one.
Fuel starvation - how so - do you mean something like problems with pickup in fuel tank??
Some times I think it is getting too much fuel, other times I think it is not getting enough.
What gets me is it sounds good when in park. Arrrrrgh!
Something just dawned on me - it occaisionally has troubles starting when hot....does this help?
Patience and more checking, tinkering and replacing....
Back at it I go.....

 

Well,the first thing is to check the timing,and if after that,you still dont see an improvement,then the vacuum guage will help us figure whats happening,the fuel starvation I mentioned related to going uphill and noticing it loosing power,

Sorry it took so long to reply,some dummy hit a fiber optic line last night and took out 2/3 of the phonelines in upper michigan

 

From the symptoms you describe I would take a good look at the mechanical advance mechanism to see if it is rusty/sticking. Also the initial timing setting. I'd also check the fuel filter and try a flow test by running the delivery hose into a can (with caution!).

Also a vacuum gauge can be your friend for trouble shooting and they aren't too expensive. I have one next to the tach.

 

Well, I'm glad the new e-box helped.

It stutters under load and only intermittantly stutters when not under load. That's could (still) be an intermittant timing fault but it's not clear that it's not a vacuum leak (or something bad internally).

You really need to put a guage on it and at least eliminate that as the problem before you start hacking on the distributor or the timing chain.

ash
['Fuel pumps are cheap tho.']

 

I have the same type of problem, Quadiquizm. Low power when under load, shuddering under load at low rpms, and I get the best throttle response with the gas pedal pushed about 1/4 of the way. Pushing the pedal down more than that yields no more power with a little louder engine noise ( a low note, like a bogged down engine). My differences from your truck are that I have a 74 f100 360 and NP 435. I have done the same things as you, except I rebuilt the carb instead of replacing, and I dont have tranny vacuum. The K&N air filter is clean and oiled. I also ran the truck down the road with no air cleaner to see if the air filter was restricting. No change.
I have tried adjusting the timing from 6 degrees BTDC all the way to about 30 degrees, and the truck is still a toad. But still idles nicely and seems to rev fine with no load.
I hooked up a vacuum guage to the manifold, and at 700 rpm idle I am getting 13 inches of vacuum which drops slowly and steadily to about 10 inches after a minute or two. I havent done a compression test yet.
I'm thinking my valves or intake manifold is leaking.
I get alot of blue smoke on startup after sitting overnight, especially when it is cold outside. I dont get any blue smoke once the motor has warmed up. My spark plugs are a little white, except for the rear most plugs on each side, those two have oil fouling.
I think I have a couple bad, burnt, or leaking valves on the 2 rearmost cylinders (near the firewall), and a vacuum leak where the intake manifold meets the heads and/or block.
Please post everything else you try to fix the problem, and what the results are. Any info on my situation is greatly appreciated.

"Keep the hood latched lubed"

 

That is way way too low vacuum. You got a bad leak. And you never want to adjust you static timing to 30 degrees. The timing isn't causing your problem anyways, and advancing it can only compensate somewhat for vacuum leaks. And it's burning up your plugs.

Oh, yeah. Going from cold with 13" to warm with 10" suggests you've got an exhaust clog. How old is the muffler and/or cat?

The smoke and the fouled plugs are probably because the oil drain holes in the cylinder head are clogged. Get a can of B-12 and put half a can in and idle it for 20 minutes and then change the oil.

You got a bad vacuum leak somewhere. You maybe want to disconnect all the auxilary vacuum crap and cap the tree and what it's like with nothing but the minimum attached.

A compression test wouldn't hurt.

ash
['Wow.']

 

Just food for thought,depending on your carb-you may have burnt up your power valve in the carb especially if you've had alot of backfiring,but I would do a compression check and further vaccum checks,one other check may be the accelerator pump if equipped.

 

Just wanted to thank everyone for the input they have provided.
Nothing new to report yet - I have yet to do the compression test and vaccuum test - but hopefully over the week-end I will get this done.
I did advance the distributor as far as I could (A/C pump is in the way of going too far) - no change.
Though based on behaviour, I am really starting to suspect a valve issue (just a gut feeling).
Today's excitement - blew a brakeline connection on the front left!
Cheers!