Troubleshooting help desperately needed...

[budbeater]

This is going to take some background so it will end up long. Please bear with me because I need the help.

My truck (1971 Chev, 355ci, Edelbrock 650 Carb, HEI ignition) was idling high so about a month ago I messed with the choke (electric) because it seemed like it wasn't set right to disengage. I cranked the setting down and it seemed fixed until the next morning. The next morning I went out hunting (about 1 1/2 hour drive) I stopped in a small town to top off on gas. About 3/4 mile outside of town the problem started. The truck would be driving fine and then with no warning would violently shudder as the engine would cut out and restart several times in less that a couple of seconds. Then the engine would shut off completely. Sometimes it would just shut down with no warning. Sometimes it would just buck and jump as the engine would cut out and restart rapidly. The lights and the rest of the electrical system would never even flicker and the truck would start back up easily even while we were still at speed. Getting home on the freeway was horrible. In what seemed to be completely at random the truck would rapidly stumble and shut off like described before.

At first I thought I had over adjusted the choke, so I adjusted it back incrementally several times. This has not helped. In fact yesterday I disconnect the electrical input to the choke and the problem stayed exactly the same. Then I thought that I got bad gas at the station in Snowville, so I added some water remover and I have checked my filter, but nothing seems clogged and I have put in 4-5 tanks of gas since. The stalling seems to be too rapid to be fuel loss.

I have noticed that the problem is somewhat temperature related. It doesn't seem to start until the coolant temp guage goes over 180. It also seems to be worse when the air temp is warmer.

Also the problem seems to be slightly worse under some type of load (going up a hill, starting from a stop, accelerating)

I am wondering if the problem is a short in the HEI ignition. I don't know what else it could be, but I don't want to spend money on a new coil, module etc if that isn't the problem.

I have only had this truck about 18months and I am slowly going through it to upgrage and replace anything worn or broken, so I know that I have inherited someone else's issues.

Any Ideas? Any trouble shooting that I have missed?

Bud

[Ron 586]

Just grabbing straws so here goes. I had a V twin 18 1/2 horse lawnmower that did the same thing. It would run fine then start cutting out like it was running out of gas. I rebuilt the carb replaced the line and filter and even the air cleaner. Some days it ran fine all day others would hardly get out of the shed. I was ready to scrap it out in fact had pulled the deck and started to pull engine. Unplugged wires and pulled harness out from under front of engine and felt a rough spot. It was the kill wire and had rubbed a hole in the insulation. Taped wire and rerouted it not a miss since. So check wire to dist. and anything else that has to do with firing . Don't cost nothing to look and check simple things first. Good luck.

[wibilly]

i would check the wires from the pick up coil to the modual they are constantly flexing as the vacume advance alters ignition timing and are prone to breakage inside the insulation

[pjmoreland]

Where is your HEI getting its power from? Just make sure you aren't using the original ignition wire because it has high resistance and drops the voltage down too low for HEI.

[VetteVet]

I am inclined to think that you got some water in the gas at that station. Water is heavier than gas so it would stay in the bottom of the tank and it might take several tanks of fuel to get it all out. An ignition module will sometimes fail after it gets warmed up but they usually have to cool down for a while before they work again. It should have just quit firing and died if the module was bad. Check the feed wire to the distributor for breaks or poor connections. I think I would disconnect the fuel line at the carb and run some gas into a pail and see if it has any water in it.
these thing s are tough to diagnose unless it's obvious. What you need to do is determine if it's fuel or ignition. A bad fuel pump or a key switch will cause the same symptoms. It sure sounds like water in the gas to me though. Good luck.

[special-K]

This sounds like a coinsidence unrelated to your carb/fuel.Do you have an HEI?First,take a real good look at the two wires from the base to the coil.Look real hard for any breaks in the insulation.It sounds like you are losing all fire at once,breifly.It could be your coil,but I think it sound more like the module.When they go,they can act like that.

[russellmarling]

I vote module. I had an '83 Camaro that did the bucking thing you describe and the problem was completely solved after I replaced the HEI module. just my two cents.

[dougs69c10]

usually though a module either works or it doesnt

[junkyardjohn]

Originally Posted by dougs69c10

usually though a module either works or it doesnt

THATS BEEN MY EXPERIANCE ALSO. IF YOU PAY THE POSTAGE I'LL SEND YOU A USED COIL & I'M PRETTY SURE I HAVE AN EXTRA MODUAL ALSO. P.M. ME IF YOU WANT THEM. JOHN

[cdowns]

with the hei was a new wire run to it for power ?//using original wiring will cause mod to fry from lovoltage

[Huck]

List of possibilities in order of my best guess based on 45 years of wrenching--module, wires to module, wire from ignition to HEI Dist--needs to be at least 2 gauges heavier then stock, ignition switch-wiring, coil-coil wires, fuel filter, fuel. Finally, check the plug wires (are they in good condition?) and check for oxidation inside the dist cap plug wire housings. If you see any white powerdy crap, you need to get it out, clean and dry. Check to see how your plugs are running---center insulator should be light brown. Finally stick a vacuum gauge on the motor--and or check for vacuum leaks, the vacuum advance from the carb to the distirbutor. I've seen cracked hoses give you fits with no advance that only showed on occasion!
A good check of the above will not cost much and will eliminate the most common ignition/running problems---.

[junkyardjohn]

Thats All Good Advice. If It Only Happens After The Motor Heats Up, It Points To Ignition Problems. Most Likely A Short In The Hei Dist. Somewhere. Probably The Coil Or Cap Or The Wires Under The Cap Leading To The Modual. As It Heats Up The Short Seperates & The Electrical Flow Is Interupted. As It Cools Off The Short Goes Back Together. Intermitten Electrical Failures Are The Hardest Things For Me To Diagnose. I Ussually Start With The Cheapest Parts That Can Be The Problem, As Electrical Items Are Not Ussually Returnable After They've Been Installed. I Always Have An Extra Complete Hei Dist That I Can Throw In To Determine If The Culprit Is In There. John

[luisduran]

check the ign switch pig tail, some times you can tell by touching the back of the switch,if is very hot is making a false contact. (be carefull may be very hot)

[budbeater]

Update: I replaced the coil, cap and rotor. I found a corroded terminal on the cap and a bad plug wire. I pulled the bad wire, but I still have the problem.

The module to coil wires appeared fine. The module will usually have black goo/shoot on it when it goes bad. Plus once they go bad the are usually bad all the time. I am going to look past it for the time being. I am going to look over the whole length of the power wire. It should be adequate in size since I have been driving the truck 18months with no problem, but it could have been burned on a header tube so it is still suspect.

This is only a recent problem that started about a month ago. So I am looking for burned wires, new shorts, or wornout parts. It was time for the cap/rotor to be replaced. They were not terrible, but below acceptable standards for me. I am going to replace the fuel filter next, but I think it won't matter much as it is a clear filter and the element looks clean. I am worried that there might be an issue with the plug wires. They were on when I bought the truck, so they will probably get changed next week to eliminate them.

Bud

[Fmspeed]

gonna go a different way, the edlebrock will overflow internally, if u have too much fuel pressure it will overflow and drip into the manifold, therefore creating the " choke problem" also it will run fine under choke when cold till it warms up, if the plugs are fouled, may tell u, if u have an electric pump, turn it on with nothing running, and listen, chased a similar problem for weeks, till i hooked up the pump alone, and heard it dripping fuel into manifold.

[tcoop68]

To me if it was water in the gas it would do it cold or hot.If you did'nt change out the whole distibitor that is what I would do first.Alot of the time you can't see the bad wire running your pick up coil advance timing like wilbilly advised.I have ran hei on stock ingnition wire for years and have'nt as of yet had a voltage problem.It sounds like you did'nt replace a very important piece and that is the module no matter what it looks like you should and if that is'nt the problem you should always carry a extra with you anyway.Change pick up coil,module,then you will have a good chance of solving your problem.

[68C15]

you DO have the ground strap under the coil, right?

[budbeater]

Originally Posted by 68C15

you DO have the ground strap under the coil, right?

Yes, its there, no corrosion and looks healthy.

Further update. I changed the fuel filter today. It was much dirtier than expected. I havn't driven it enough to determine if it was the source of evil. I blew through it and it wasn't totally clogged, but could have been enough to slow fuel passage under load. We will see.

I am starting to think it is something mechanically wrong with the electric choke (like a bad spring etc).

Bud

[budbeater]

Finally fixed the problem.

1. Replaced the cap and rotor and burned/corroded plug wire. Replaced coil. Did not fix problem.

2. Replaced fuel filter. Slight, brief relief but then problem persists.

3. Readjustment of carb. No change in problem, but gas mileage getting better.

4. Seems that electric choke spring is broken. Can't fix choke setting. Solution? Replace carb (with 750 instead of 600).
Problem persists, infact got much worse for about 5.5miles and then the truck died completely.

5. Replace fuel pump. NO MORE PROBLEM. Ran a little rich, but new jet and rod change has solved that issue. Truck is currently running better than ever and it doesn't nose over on the top end like it used to.

It seems that the problem was twofold. Bad choke (also must have been shorting out because when it was reattached I got my dash lights back, and a dying fuel pump. The total cost of the correct parts would have been about $70. I spent much more than that! And a whole lot less than taking it to a mechanic.

Budbeater

[Brainchild]

Didn't read far enough