71' C-10 cutting out intermittently

[Hennyhog]

Hello all,
I've been trying to rectify this issue for about a month now and it is still kicking my AZZ. When driving, the motor is cutting out like loss of fuel, not running on all cylinders, and loss of power. I pull over shut it down for a minute or so then take off with no issues. It may happen 5 minutes into a cruise or 45 minutes. Here is what I've done so far.

New fuel tank (filters kept getting clogged thought I solved problem...nah)
Clear fuel filter
Changed over to HEI last week (REALLY thought I solved it this time...nope)
New plugs

I guess what I'm going to throw against the wall next is could it be a problem with the fuel pump? Can a mechanical pump fail intermittently?

Or could it be plug wire that fails/misfires intermittently? It's a 350 with a Holley 650 dbl pump if that helps.

As always love the feedback and what you guys suggest!

Henny

[rripp]

I had a similar problem and it turned out to be the plug wires. They are easy to check, just get it in a dark place and look under the hood for the lazer show

[MagmaJct]

Originally Posted by Hennyhog

Hello all,
I've been trying to rectify this issue for about a month now and it is still kicking my AZZ. When driving, the motor is cutting out like loss of fuel, not running on all cylinders, and loss of power. I pull over shut it down for a minute or so then take off with no issues. It may happen 5 minutes into a cruise or 45 minutes. Here is what I've done so far.

New fuel tank (filters kept getting clogged thought I solved problem...nah)
Clear fuel filter
Changed over to HEI last week (REALLY thought I solved it this time...nope)
New plugs

I guess what I'm going to throw against the wall next is could it be a problem with the fuel pump? Can a mechanical pump fail intermittently?

Or could it be plug wire that fails/misfires intermittently? It's a 350 with a Holley 650 dbl pump if that helps.

As always love the feedback and what you guys suggest!

Henny

YES!! I have had this happen first hand. It would only happen in city driving or at the landfill in the middle of summer. Once it died, I could kill the battery trying to start it. Once it cooled off a bit, it would fire right up. After a jump, of course.

I suspected vapor lock. With it being a nearly stock truck, I suspected something was broken. Internet research suggested a bad fan clutch. A way to test it would've been to get a reflective tachometer and a piece of reflective tape. Stick the tape to the fan, measure the fan's speed.

Block the radiator with a piece of cardboard or something, and monitor the RPM change relative to change in temps. Once I realized the cost of the reflective tachometer was more than a fan clutch, I replaced the clutch.

No improvement whatsoever. Eventually the truck died for good. It would not start under any conditions. Had to have it towed home. :-( I checked for fuel to the carburetor, it was bone dry. Replaced the pump. Have not had a single problem in quite a few years now!

But before you throw anymore part at this problem, you should consider testing your pump first. It was too late for me. If I'd considered a failing pump, I would have tested it before it failed. Check it for pressure at the outlet, vacuum at the inlet, and flow.

You may find you're getting vacuum buildup in your tank! Good Luck, and keep us posted!

Regards,
Mike

[Grumpy old man]

Hi , You already said you've had fuel filter issues pull the tank and clean it and clean/replace the lines ,Fuel is being pumped until the filter clogs ...and you pull to the side of the road once shut down fuel returns back towards the tank and flushes the clog until it happens again . Ahhh! you have to love 1960's technology

[swamp rat]

Did the new fuel tank come with a new sending unit/pickup tube? so it has a new filter sock on it? I would also test the fuel pump, hook a length of hose to it and route it to a containor, have someone turn the enging and see that fuel is squirting out. Also, if there is no filter between the tank and carb its possible you have crap in the carb restructing fuel.

Per electrical, excess heat creates resistance, if the plug wires are next to the manafold they could be getting hot..

[jessemthompson]

I had this issue once. It ended up being a kink in the hose that fed the fuel pump.

[7tee]

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[7tee]

Is it possible you could have the wrong gas cap installed, vented vs non vented, just had to ask...
Posted via Mobile Device

[Boog]

Henny the next time it shuts down pull over and remove the air cleaner and peer down into the carb while you work the throttle lever. See if there is fuel spraying down. Have someone try to start the engine while you remove a plug wire to check for spark to the plugs.
Many of us have been through this over the years. One of mine was a broken wire going into the distributor that occasionally lost connection. That took a while to figure out.
Be sure you have a 12v power source to the HEI distributor too.
Look at all rubber hoses on the fuel lines. Some can collapse with age.
Maybe something here will help.

[Mr Chevorlet]

That is the same issue i was having, i could drive for a while and after about 20 minutes it would cut out and after it set it would run and idle fine and did this over and over. Still could not find the issue. So one day in the shop i noticed i had a intake oil leak in the back that was bothering me so i decided to pull the intake, put in new gaskets and front and back seal and reassembled everything, oil leak stopped and low and behold i drove it around and have been for a couple of months and the no cutting out or missing no nothing. I know this is not going to help you because i do not know what it was for the life of me. I think it was either the carb gasket or something with the distributer.















.

[Hennyhog]

First off...thanks for all the feedback! Ok...so I put on a new set of plug wires Thursday evening. Truck ran great to and from work Friday and even work and errands Saturday morning. Then as my wife and I were out for a spin in the afternoon it happened again. Yeah....it's a bummer but have to keep at it so what am I going to try?

1. Some have mentioned that fuel lines near exhaust and even leaning against radiator hose may be vaporizing due to heat. The truck has had this happen to it 3 miles from home after having only been running for 5-8 minutes or 40 minutes after running it. So I kinda want to rule that out.

2. I'm pretty sure my fuel cap has a pressure relief doohicky in the center (little blue plastic piece) and when I fill it up I've never had that "whoosh" of air escaping while undoing the cap.

3. Still haven't read too many posts about intermittent mechanical fuel pump issues that act the way my truck is suffering from.

So with the crappy weather up here in MA I'm going to wait till later in the week to pull line off fuel tank sending unit, inlet side of pump, blow it out, and put a new pump in. They are cheap and it'll be another thing to rule out.

I still can't wrap my head around how it can be the pump (my brain tells me it works like a light switch. it's either off/on or pumps fuel or doesn't. I surely will keep you posted!

Thanks,
Henny

[88Ironduke]

From outside the normal thought process.
I had an issue similar to this while I was stationed overseas in the UK. 86' VW Passat with a Audi 5 cylinder... That bugger would move. Would lose power and eventually shut off. Let it sit for 10 or 15 minutes it would fire off no problem. Finally caught it one day. The wonderful cool moist air of the UK was causing my venturies in the carb to freeze up solid. I ran full time vacuum to my hot air unit on the air cleaner housing and problem solved. You wouldn't see it unless you pulled the air cleaner when it happened. It would happen quickly sometimes or you may drive for an hour before it freeze.

Paul

[smoked68]

Had same issue yrs ago. Bad fuel pump. The little diapham was appearently going bad. New pump for the happy tune of 18.00 and it fixed. Have since went to a summit 100gph and runs like a champ. that is all. Good luck

[MagmaJct]

Originally Posted by Hennyhog

First off...thanks for all the feedback! Ok...so I put on a new set of plug wires Thursday evening. Truck ran great to and from work Friday and even work and errands Saturday morning. Then as my wife and I were out for a spin in the afternoon it happened again. Yeah....it's a bummer but have to keep at it so what am I going to try?

1. Some have mentioned that fuel lines near exhaust and even leaning against radiator hose may be vaporizing due to heat. The truck has had this happen to it 3 miles from home after having only been running for 5-8 minutes or 40 minutes after running it. So I kinda want to rule that out.

2. I'm pretty sure my fuel cap has a pressure relief doohicky in the center (little blue plastic piece) and when I fill it up I've never had that "whoosh" of air escaping while undoing the cap.

3. Still haven't read too many posts about intermittent mechanical fuel pump issues that act the way my truck is suffering from.

So with the crappy weather up here in MA I'm going to wait till later in the week to pull line off fuel tank sending unit, inlet side of pump, blow it out, and put a new pump in. They are cheap and it'll be another thing to rule out.

I still can't wrap my head around how it can be the pump (my brain tells me it works like a light switch. it's either off/on or pumps fuel or doesn't. I surely will keep you posted!

Thanks,
Henny

I told you my story. Perhaps my story doesn't sound like yours to you, but your story sounds like mine to me.

I too wouldn't have thought a mechanical fuel pump would be intermittent until it died completely forcing me to see that it was indeed bad. Once replaced, years later the truck has never died from lack of fuel.

That "whoosh" from the gas cap does have me a bit concerned. It is my understanding the cap is supposed to let air in to prevent a vacuum, but block vapors from escaping, instead allowing them to vent into the charcoal canister. If the tank developed a vacuum this can cause fuel vaporization ahead of the pump.

Regards,
Mike

[Hennyhog]

Ok.....so 99.9% sure I rectified this issue having driven it for a few weeks without skipping a beat (watch it happen to me this afternoon!!!)

So I took all your suggestions as well with people I seek out daily to tell them what was going on. I went back and forth...one day I was sure it was a fuel issue...just to jump a few days later to the other side of the coin thinking it was no doubt it was an electrical/ignition issue. Here is what I did since adding the new plug wires.

1. I hooked up my VOM to power going into HEI. At idle I'd get 11.9 volts and when driving it it'd go as low as 10.1 volts. So...having read up online forums I came up with a few GREAT leads on solving my problem. One was do not use power/wire going to old distributor to power up HEI and two you can't give HEI's enough voltage. So....I came off my "unfused power" terminal on my fuse block, installed a 20 amp inline fuse, and ran it right to power in to HEI (next to lead coming off Tach). Started it up and had 12.9-13.2 volts constant at idle and under load. I thought FOR SURE this was it and drove it confidently for almost 3 days before it happened again and then after much disapointment I was back to go over to the "fuel" side of the coin.

2. I purchased a carb rebuild kit for my Holley 650 dbl pump & a new mechanical fuel pump. Because of limited time over the 4th of July weekend (kids and wife) I rebuilt the carb on Saturday afternoon which was LOADED with crap...and then installed fuel pump Sunday morning.

I like to do one thing at a time so as to know what the culprit was but not having the time to rip around with it after just doing the carb rebuild....I have been driving it since without the issue occuring.

So...that's it fellas. We can debate whether it was all the junk in the carb or possibly a fuel pump that was slowly getting ready to croak....I just know she's been running strong since having done everything on the ignition side of the coin....and now on the fuel side.

Hope this helps any and all.

Thanks,
Henny

[Mike_The_Grad]

@hennyhog,
I've read your thread and I hope you have finally resolved this frustrating issue. I myself had a similar problem. Two things ended up compounding together to keep my mind boggled for a while. #1, I also had a clear inline fuel filter. Mine was located after fuel pump before carb,level with valve covers. After a TON of research I realized the design of the fuel system for this era of trucks. When these vehicles rolled off the assembly line, they did not have inline fuel filters. They only came with two main ways of filtering what went into the engine as far as fuel is concerned, first was bronze sending unit pickup "sock" for any type of debris large enough to clog fuel lines, second was on most Rochester equipped models was a small filter located in carbuerator body.For particulates,impurity's and the like. Based upon the mechanical fuel pumps design,which is more pumping than sucking, having an additional filter element installed anywhere on this system effects the delivery of fuel to the engine. Either before the pump,or after,it wasn't designed to have this extra element installed.my truck ran like crap both when I had the filter after and before the pump. My conclusion for my configuration was that, if the tank ain't dirty and I don't introduce crap to the system the original design is sufficient. I actually did need an inline filter when I originally purchased the vehicle because I had an auxiliary aftermarket tank,which had a lot of crap accumulated in it from the installation and maintenance of it. Once I eliminated all the outside factors,and got it back to the stock system.there really wasn't a need for the extra filter.#2 thing that caused similar behavior was wiring to the starter,which I note that you did mention as a possibility for the occurrence. Yes run unfused from ignition to starter.I recently rewired my truck with an American Autowire Classic Update kit. It provides this by means of a fuseable link in series with connection. How I found this to be an issues was I modified the recommended installation by making this connection with a easy connect/disconnect terminal connection rather than the spade metal to metal connection. (This decision left me on the side of the road at midnight for almost two hours before a good Samaritan with automotive knowledge happend upon me.) What I'm basically trying to say is try it without the inline filter as long as there's no visible crap in your clear filter,replace in-carb filter and fire It up. seems like you may have resolved the electrical side of it hopefully. Good luck.