1979 truck - untraceable stalling

newfarmer

Anyone have any ideas?

I bought a 1979 pickup with a 350 v6,79K original miles (yes i have the original bill of sale and all registrations.
The truck runs fine but will stall occasionally even after riding for hours on the hwy at 60+ mph.
 A mechanic looked at the carburator,fuel pump, fuel lines, alternator, battery and says he cant figure it out. any ideas?

Mr_Shiftright

Most '79 cars run pretty lousy as they age, so could be a lot of things. Most common problems would suggest a vacuum leak in hoses, intake manifold or carb base plate. Also the EGR valve is suspect, and the carburator itself. With so few miles, lots of things can get gummed up, and gaskets can shrink and leak as well. Also hoses crack and belts dry up.

It's just a matter of snooping I think.

swschrad

with a windex-type bottle and see if the idle changes. places like the base of the carburetor, ends of hose connections, etc. to find vacuum leaks. look at the top of the carb... those autolite carbs with a big old flat plate over the float were prone to cracking, and you could have air leakage there. if so, sand it and epoxy the top (don't seal the bloody thing up, just cover the flat area against cracks.)

make sure the vacuum advance motors at the distributor and the carburetor move when you pull their hoses off, or push in the diaphragm with the hose off, cover the nipple with your thumb to seal in the "vacuum," and release the pushing on the diaphragm. if it stays in, good motor. if it doesn't, diaphragm probably leaks, replace it.

little tricks like this will find a LOT of performance problems in a 60s or 70s engine.

mullins87

You don't say, but I'm assuming you have a GM product. Have you done any "testing" when the truck dies? Only three ingredients are needed for the engine to run. Those being fuel, air and ignition. I have a '78 Grand Prix. Several years ago it would just quit, as if I turn the key off. I checked for fuel delivery and verified everything was OK. I checked the intake. While vacuum leaks and a faulty EGR valve will cause an engine to idle roughly or die, they won't keep an engine from running when revved up. Everything was OK there. When I checked for ignition, there was no spark. However, the car would restart shortly thereafter. I checked for a bad coil, wires, and anything else I could think of, but nothing. One day a person told me that car had a little ignition module, similar to a computer chip, hidden beneath a plate under the advance mechanism. This little chip would overheat at somepoint while driving and would shut down. I never would have looked for a "computer" chip on this car had someone not suggested it.

I'm sure your mechanic has already checked this possibility. Just a suggestion.

Mr_Shiftright

If the vacuum leak is bad enough, it can stall the engine as soon as you let off the gas--but know, it won't stop running while you are applying the gas.

mullins87

when it stalls. If it stalls everytime he lets off the gas after the engine is hot, a vacuum leak IS most likely the culprit.

I'm glad I read this thread. I had never thought to use a spray bottle to check for vacuum leaks.

oldharry

Chevy v-8 that stalled occasionaly because the float pivot would stick, shutting off the fuel if I slowed to a stop suddenly after driving at speed. Re-aligning the ears on the float that the pivot shaft passed through fixed it. A worn needle and seat in the float valve can stick too.

Did your mechanic remove the top of the carbuerator, or just check mixtures while the engine was running?

Harry

swschrad

I didn't notice in the original post that it runs for hours and then goes out. I say replace the ignition module under the HEI distributor cap. two screws and two wires and it's done.

BE SURE to get some dielectric grease at the parts counter when you get this dingus. you need to spread a pea-sized bit of that HV grease on the metal plate under the ignition module to get the heat out.

it's a pity that it's heatsinked to a distributor boss that is going to get warm. weren't those 350 distributors behind the engine? the ignition module from an aftermarket like Wells was cheap enough you should maybe get two and put one in the glovebox.

I had a 231 V6 buick with one of these, and took a long time before it got intermittent, a long time. mine showed up as intermittent rough running.. but the distributor on that mill was way up front, and stayed cooler.

0patience

Read his profile. He has a Ford.
A 70 ford has the electronic ignition module on the fenderwell. When they get hot, they have a tendancy to disconnect. Check wiring and make sure that the fuel lines are routed away from the exhaust. If they are close, then get some heat wrap and wrap the fuel lines.
It may be that the fuel system is vapro locking.

One other common problem I have seen on the older vehicles is that the pin for the lever on the fuel pump becomes worn. At idle, the pump will pump enough to fill the carb bowl, but at higher rpms, there is too much slop in the pin to allow the pump to pump enoug fuel to keep up with the demand.
While the pump may look good, if you can move the pump lever more than 1/8" before you feel resistance, then it may be the problem.

andre1969

...would stall out from time to time. Turned out it was the distributor. It would never stall at high speed, but sometimes idling at a traffic light it would. Every once in a great while it would just refuse to start, until it was good and ready. One hot summer day back in '99 it refused to start. Wouldn't start for 3 days. I finally got fed up, tied it to my Dart, and pulled it down to the K-mart up the street, which had an auto shop back then. Naturally, it fired right up for them!

Two years later, it died on me again. I had to go on a business trip to Florida, so I just left it where it was, in my grandmother's yard, and decided to mess with it when I got back. 5 days later, it started right up.

Third time was a charm though. About 15 months ago, it tried the same stunt. This time though, it never did re-start. It was just a spare car by this time, so it was no big deal. Every once in awhile I'd just go out and try it, but it never di start. Finally I got tired of looking at it sit at the curb, and had it towed to the mechanic.

mullins87

When he said he had a 350, I just assumed it was a GM. I had to go back and look at the subject. Well, my thought of the little HEI module is out the window. But, I still think the problem is most likely electrical in nature. The fender/firewall mounted module could still be the problem.

0patience

My eyes aren't that great, because I didn't notice the 350, I assumed it was F-350 when I read his profile, but it says 350 V-6.
Huh? I didn't see that!
A 79 Ford with a V-6?? No that is a new one on me, unless it is a very big Ford.

Beginning to look like one of those test threads to me.

swschrad

how do you get that, JB-weld two blocks together for more stroke?

at any rate, if you have a magic transistorized ignition box that bolts to hot metal, suspect it.

andre1969

...the guy just said a '79 350 V-6. I just figured the V-6 part was a typo. GM was the only one to have a 350 in '79 (well technically, they had 4!). Ford had a 351 and Chrysler had a 360.

Now Ford *did* have a really big inline-6 (often incorrectly referred to nowadays as a V-6, kinda like how people say "V-4") back then, which was a 300 CID unit.

I have heard of some Ford commercial trucks from back then, that had engines I'd never heard of. Awhile back, when I had to supervise an office move, one of the vans had, the guy said, a 352. Maybe Ford did have some big V-6 back then, too? At one time, GMC had a pretty big V-6, but I forget its displacement. I think it was a 60-degree engine too. They mated two of 'em together to make a V-12!

mullins87

He hasn't replied, has he?

swschrad

if it doesn't work out, not only do you have a couple V5s hanging around that are cranky and make bad noises all the time, but you can have a couple of one-bangers whining constantly and keep getting in the way when you try to fix something

andre1969

At 702 CID, one of these suckers would come out to a 351, which I'm sure has been rounded down to 350.

I wonder how long they made this engine for? (the V-12 and the V-6 version?) It wasn't still around in the '70's, was it?

swschrad

standard generator, very old design a/c compressor sticking way up there, dual carbs for all your carb synchronizing headache needs... a grand old engine from way back. that compressor tells me the engine was almost certainly not made past the mid or late 60s for a start. notice all the oil filler caps on the left bank(s)... probably had things positioned so you could do valve lash adjustments without taking the valve covers off, just pull those caps.

and yes, it would take a LOT of oil for that thing. I bet they had twin oil pumps and maybe twin mechanical fuel pumps on that beast. idle or power issues would be fun to troubleshoot on that monster.

tboner

I was thinking an air compressor for air brakes. (Me thinking about this being used in a truck.)

Of course that was just speculation, I have no experience with such engines.

TB

swschrad

for accessories. there were old a/c compressors that were patterned on the 1 or 2 cylinder air compressor we are all familiar with.

and indeed, you make sense here, tboner. I yield, air brakes would go with this engine's applications.

brain fade compliments of 1040 fever... catch it, my ( )!

andre1969

...that thing is some kind of compressor for air brakes, too. Air conditioning, even in cars was pretty rare back then...I'd imagine it was almost non-existent on a medium-to-heavy duty truck!

I don't know what GM a/c compressors looked like back in the early '60's, but the one on my '67 Catalina is just the typical long cylinder. Chrysler used a V-2 a/c compressor. I don't know when they started, but my '67 Newport and '68/69 Darts had it. I think they used it up through '78, on the RWD cars, at least...I couldn't see a '78 Omni or Horizon with a compressor that big!

swschrad

that look like little oil-sump shop air compressors of the 2 to 5 gallon tank variety. they were on mopars, come to think of it.