I'm battling a frustrating issue where (either at idle, slow or highway speed driving) I lose power, can't bump start it, can't start it by cranking UNTIL I turn the key from On to Off before back On again and trying to crank, then it starts up easily. This happens something like every five minutes or so, sometimes twice in quicker succession. I thought the ignition wiring was undersized as I'd wired it through a relay socket which was pre-wired with ~14-16 gauge. I ran a new larger wire (~10 gauge) straight from the alternator positive to the relay and relay to distributor but the cutout persists unchanged.

What else could it be? The way it requires the ignition to turn off feels like an electrical problem to me, but could it be fuel related? Could my electric fuel pump be poorly regulated (turns on with ignition) or the fuel vapor-locking? The fuel lines do feel pretty warm in the radiator blast. I'm also using a fuel pump better suited to EFI with lots of bypass as I already had the pump and just bought the regulator when swapping from EFI back to carb. Thoughts?

Setup:
stroked 383, iron block
Mighty Demon 750
Mallory HEI distributor
AFR plastic intake manifold
Comp Cams XR286R solid roller
"Pro Topline" 200cc aluminum heads
Hooker super comp headers, 3" exhaust

Aeromotive in-line high pressure pump (A750? Don't recall)
Aeromotive 13301 fuel pressure regulator
Also a big Aeromotive filter as big as the pump, don't remember the spec.


Regardless it's good to have her back out again for a little play in the rain now that I've upgraded from 330lb to 360lb/in spring and QA-1 adjustable shocks replacing blown stock type in the rear!

 

When it stalls couldnt you pull a plug wire insert a metal rod/screwdriver and place near a ground to check if you have spark?

 

A general rule, electronics don't like voltage surges.
Run your 10ga wire from your relay to a direct battery source- like the starter solenoid or direct to the battery +.
I'd also take a close look at the ignition switch. I had one on a Monte Carlo that was just plain worn out. No start, replaced the switch and ran fine. Curious me, I took the old switch apart to see what was going on- the contacts INSIDE the switch were worn clean thru.

 

U can eliminate the fuel system by connecting a fuel pressure gauge. Many will tape it to the windshield while test driving - but i have an electric gauge permanently installed (Holley $75).

Next step would be to look at the ignition. Ever use a auto diagnostic probe/light? Looks like an ice pick with screwdriver handle with a ground wire & clip. Just use the wired clip to connect to a ground. Now u can check terminals for voltage as 12v will light up that handle. U can "back pin" connectors also - this means slip the ice pick probe into the wire side of connectors to check for voltage. Do not pierce the wires insulation with this probe as it will create shorts - but its ok to "back pin" connectors to check for voltage/power.

Hope this helps,
cardo0

 

You didn't say whether or not you had changed over to an electronic tach.

If you did- here's a real easy way to determine whether it's fuel or ignition-

When you loose power- if the tach drops to zero- it's ignition. If the tach drops slowly -it's a fuel issue.

Richard

 

Thanks for the diagnostic ideas. The carb has a fuel gauge so maybe I can buy an electric gauge and put the sensor where the gauge currently is. I'm using the factory tach drive but the distributor does have a tach output so I could connect it to a light and see if it goes dark! I will try these ASAP but I'll be away this weekend.

 

Sometimes HEI modules have a thermal cutoff. Had a bad one once and replaced it with a GM unit and problem went away. Not sure how to check though.

 

Your list in the first post indicates Mallory HEI. The HEI modules can break down when hot and stall when they go bad. Usually there is a longer cool down period before it'll restart. Used to be able to take them out & bring to the parts store to test.

If your getting fuel & have voltage to the distributor, this is where I would start

Jim

 

I had the same problem.
It was the ignition switch.
When it cuts out try turning the key slightly towards the start position.
If it starts that is the problem.
This must be done quickly as it can remove large portions of the mufflers.

 

Two votes for ignition switch, I will have to try jiggling it, quick test. I have had a few backfires when this happened through either intake or exhaust. Fortunately my exhaust is all steel and pretty stout (Flowmaster 40's), though I have been worried I'm going to shatter the plastic intake or bend a carb part.


Edit: Didn't think this was worth a new post but my lock cylinder fell out of my motorcycle today! Explains why I couldn't get the fork lock to engage the last few days... If that turns out to be the Vette's problem too I've had quite the spate of switch issues. I only have the fuel cap key and a small but moderately heavy keyring thing. I hate carrying around a bunch of junk so mine tend to be minimal with just enough "flair" to tell vehicles apart.

 

Do you have a lot of baggage on your keychain? Try running the car with JUST the ignition key in. The baggage wears hard on a switch - maybe the PO had a lot of keys on their keychain. Its a known problem causing premature wear on the switch. Also, as the baggage swings around with the car moving, it can turn a worn switch off.

 

I managed to determine it's not the switch as jiggling it around when it happens has no effect. Also ran with just the key in and no baggage hanging. I also discovered that contrary to my prior assertion, you don't necessarily have to turn the key off to get it to start up again. On the highway I was able to just let it coast in gear for a few seconds and then touch the gas again to get it going.

That is: keeping the gas down always made the shut-off condition continue, letting off the gas or otherwise giving it a chance to recover allowed it to get going again. I don't know quite what to make of that but there it is.

One more thing, my vac advance is currently not connected (plugged on the carb side of course) on the advice of a shop which did an initial dyno run for me. I can try reconnecting this and seeing if it changes the behavior, hopefully without excessive advance...

 

Check the fuel line from the frame to the fuel tank. It could be going bad and the Aeromotive pump is sucking it shut. If you're still running the factory pump too, check the hose there too.

 

I believe your problem is with the plastic intake manifold.

The electrical ground for the Chevy ignition system is the pathway via the distributor housing-distributor hold down clamp-hold down bolt-intake manifold-engine block. Your intake is plastic and can't pass electricity; so the ground is trying to be made through the distributor body-distributor gear-camshaft-cam bearings-engine block path. Not a "solid" ground path, by any means.

Connect a wire to the distributor housing and run it to terminal placed under a bolt to the engine block somewhere. It should solve your problem...unless you don't have a standard GM ignition system.

 

If it backfires when it starts back up it has lost ignition not fuel.
Clip a test wire straight to the coil from non switched power.

 

Oh very interesting, I will try adding a ground path to the distributor tonight. Consarned new-fangled technology. I would have been surprised if it had been fuel boiling with the plastic insulating the carb, but didn't think of the electrical insulation! It is a GM-style HEI in the cap, no separate ignition module. It has indeed backfired sometimes when it cuts out so there's been a combustible mixture present.

As for the fuel, the Aeromotive pump only has about a foot of -10 from the tank to the pump (mounted inside the spare tire carrier) so that's possible but it'd have to have really come apart. No mechanical pump, though the regulator I added when going from EFI back to carb is up from and sending the return fuel all the way back. (-8 I think.) Of course everything past the pump should be pressurized.

 

I missed that the first time I read the list. He states a Mallory HEI distributor which I believe is also grounded through the body to the intake. Add a ground wire as 7T1Vette suggests and go for a test drive. Probably losing ground momentarily when the drive gear loses contact with the cam (or the body of the distributor with the block). That's why you can restart in gear with out touching the key.

Jim

 

I am not familiar with this unit but a random ignition cut-out on GM HEI can be caused by a break in the small wire inside the distributor. They allow for rotation as the advance moves (broken wire, not insulation so you can't see it). When the advance moves back, wire reconnects.
Try swapping out the Mallory with a good HEI or check continuity of your wires by moving them around inside the Mallory unit. IIRC there are 2 wires to the module and 2 other wires from the module - the latter ones are the ones to check (changing the module will not fix that).

 

Disappointing result this morning, added a ground strap from the distributor to the head last night, problem was still present this morning. Thought that was it for sure but it must be conducting through the cam decently! On to the next suspect... I noticed it does seem to be running, just very poorly and unable to carry load when it "cuts out."

 

An idea occurred to me, I'm going to check the fuel filter next. Maybe giving it a rest is enough to allow a blockage to float back away from the filter? I have a big prefilter before the Aeromotive pump.