HELP!! '72 Chevy C-10 engine ‘cuts out’

[Miles]

Greetings!

I have a ’72 C-10 (3 speed on the column) with a problem that has been tough to diagnose.

Problem: while driving on the highway at a steady 60 MPH, the engine ‘cuts out.’ This lasts for anywhere from 2 to10 seconds after which it starts to run again (it jump starts since I usually have not taken it out of gear). It seems to occur after I come over a rise in the road and am backing off the throttle to lower the RPMs / remain at the same speed (it does not seem to happen when going up hill/ accelerating).

I suspect either an electrical or a fuel-delivery problem.

In trying to solve the problem I initially replaced the gas filter (the old one looked OK) and tuned it up; no help. I then had the Edelbrock carburetor rebuilt (it is 5 years old), and switched the ignition from the original points to electronic ignition, put on a new vacuum advance, plugs, wires, and again tuned it up – no help. The carburetor gas mixture seems to be correct. I have started to use a bottle of Lucas Oil gas treatment with each fill up just for luck!

The engine was replaced with a ‘crate engine’ 2 years/10,00 miles ago and ran well until about 6 months ago when the intermittent cutting out started. The cutting out can occur once or multiple times over a 20 – 50 mile stretch and then not occur for sometimes hundreds of miles.

I learned the hard way to immediately take my foot off the gas when it cuts out: if I don’t, once it kicks back in (jump starts) in it will backfire: I have blown out 2 mufflers, so far!

The reason I now suspect an electrical short is this: Saturday when I had come over a rise, it cut out. I put it in neutral rather than leaving it in 3rd. I noticed the radio had lost power and after about 5 to 7 seconds the oil pressure ‘idiot’ light on the dash illuminated at the same time the radio went back on. I then turned the ignition key to start it in neutral before putting it back in gear to avoid ‘jumping’ it. The battery is a 3 years old but is still good (lights work well when engine off/ the engine turns over briskly). How about something to do with the alternator since it seems to be RPM related (or is that coincidental)?

With respect to fuel delivery theories, could debris in the gas tank temporarily getting sucked up, blocking flow, and then falling back into the tank after the suction ceases? (The gas tank has never neen cleaned/messed with). More doubtful is the idea that the hose portions of the gas line are contracting (like some sort of vapor lock) since the problem seems to occur when the load is the lightest. Any thoughts about the about the fuel pump?

Thanks for any constructive thought/suggestions!

Miles

[boundstaffpress]

Check the wire that comes off of your positive battery cable and goes to your fusable link. I had a 69 Impala give me some trouble like this. The battery shifted enough to pull the wire out of contact, then would shift back and regain contact. Finally after an abrupt stop, the wire pulled loose, and I was dead in traffic.

Not sure if this is it, but it is a good place to check out anyway.

[RicksTrucks]

If you have HEI, it could be something in it. Mine would die and not restart right away.

[farside847]

I would take the alternator to napa and get it tested to make sure (do they still do that?)

[Rusty Old Chevy]

on my 70 that i had back in HS it was the fuel filter on the carb itself....i know some ppl get cheap and throw a universal one in but forget or decide not to take out the carb filter.....it would just build up fuel pressure and just die, let it sit bout 15 mins it would run for like 5 mins and die again.... changed the carb filter, removed my tank, cleaned it out and put in new lines and it ran just fine...now i know you said you changed your carb but nevermind what iam saying im still learning

[jimfulco]

The backfiring thing makes me think the power to the ignition is being interrupted. Check the wires to the distributor & coil, including the wire from the starter solenoid to the coil, if you still have it. See if one's not rubbing somewhere, or hanging real close to something it could rub on. I've had a couple of intermittent cut-out incidents that involved a wire or cable that would lean into something due to inertia and short out. The battery cable leaning on the headers was really spectacular, but only on right turns.

[motocrosschump]

Seconding the fuel filter

[birdie]

It sounds to me like the fuel filter or possibly the fuel pump.

[70STOVEBOLT]

I am having a somewhat similar problem. Mine started out as a miss under acceleration, but it would only do it in 3rd gear (it's a 3 on the tree), so I changed the fuel filters (it has one in the carb and one inline between the pump and carb). The problem went away for a day or so, but now it's back.
But it's also doing something else. Intermittently, it will idle down to about 300 or 400 rpm. Usually it won't die, but sometimes it does. Anyway, if I goose it and let it come back down, it will idle ok. Could it be that the float is filling up with gas and closing the needle and seat partially? The other thing I thought about is the fuel pump. I noticed yesterday that the inline filter didn't have any fuel in it, normally it is about half to three quarters full (it is a see-through Purolator filter). Anybody have any ideas/advice?

[Miles]

Thank you one and all for the advice -- I think "Jimfulco" got me headed down the path to salvation. I found that the positive battery cable was too close to the exhaust maniford and the plastic covering was charred. I will try to make a heat shield since I have heard of a similar problem where the wires to the solenoid arc when the manifold/exhaust pipe get hot and prevent starting until it cools down.

Replacing the $5 part was like an episode out of 'I Love Lucy:' when tightening the end of the new cable onto the solenoid, the porcelin cover broke...end up replacing the solenoid/starter. Had a very hard time getting the bolts to thread (was worried about stripping the threads). Anyway, I have a 200 mile drive this afternoon for a road test.

Thanks again,

Miles