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Today's head scratcher


Restorer32

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'68 Eldorado. Replaced the fuel pump, and tested its output, no problem. Rebuilt carb, checked float level several times, no problem. Replaced all lines between pump and tank. Checked vacume and centrifugal advance of dist, works as it should. Now for the problem...car runs very well indeed but at speed above 45 mph or so if you step on the gas the engine just dies like you turned off the ignition. Let it return to idle and you can tramp on it again and it accelerates smoothly until the engine just cuts out, no sputtering like it is running out of gas. If, when the engine cuts out, you keep your foot on the gas pedal the engine will shut off completely. Ideas?

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Sounds like maybe a flake of rust in the line from the pump to the carburetor. I had that very same problem once in a 1957 Chevy truck. Took a couple of hours to figure it out.

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Ideas?

Yeah. Before randomly replacing parts, temporarily connect a fuel pressure gauge at the carb inlet and tape it to the windshield so you can read it while you drive. Watch what's going on when the car noses over. This could be fuel pressure related, or carb related, or ignition related. Free troubleshooting beats randomly throwing dollars at it.

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Thank you Captain Obvious (typed while smiling). We aren't total rubes. We tested the original pump before replacing it and the new one after replacing it. The carb obviously needed rebuilt. New lines from tank to pump were desperately needed. We don't randomly throw money at these things, far from it.

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had the same problem on an internation truck the pig tail on the condenson was to short

when the dist. went to full advance it would pull the wire out of the cond. and the engine

would quit running, as soon as the engine quit the dist would retard and the wire went back into

the cond. and start right back up. just my 2 cents.

Bob

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Yea, this seems to be one of those "can't happen in a million years" flukes. Tomorrow we are going to bypass the coil, ign switch and condensor with another unit we have here and see if that tells us anything. Your experience did make me smile. What are the chances?

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A couple of possibilities:

(1) When ignition coil rotates to certain RPM, primary wire is pulled and there is an "open circuit".

(2) There are a couple of fuel valve designs for the carburetor that are still floating around that might give this symptom. As I got in trouble ;) with the moderator for mentioning a specific company once before, you will have to call if you want more information. 573-392-7378 (9-4 Mon-Tues central time).

Jon.

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I had a '72 442 that would do exactly as you describe, run fine until you put your foot in it....turned out to be the filter sock on the tank end of the gas line....that big engine would suck the sock closed, shutting off gas to the fuel pump.....and seconds later engine would die.....

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Similar problem with a slant six. It had a ball of solder from the tank's construction rolling around in the tank. When it sucked against the intake, instant off. As soon as the engine died it rolled back in the tank until the fuel movement pulled it back into the line.

Ended up removing the tank and shaking the little *#^&@* out.

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We bypassed the fuel line and ran the car off an auxiliary tank we use for just such purposes. No change. We've had the carb apart twice since the rebuild and have gone thru it carefully and everything looks to be as specified. We also bypassed the ignition switch with no change. Last night we found another carb that we will swap out and see what effect that has.

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For what it is worth I had a similar issue when I bought my '38 Buick. It would run fine for about two miles or heavy acceleration and then just die. On the day of delivery the previous owner told me do not try to drive it home. It was running fine so of course I did, with my buddy following with the trailer. Three stalls in five miles and we trailered it up then spent the rest of that summer trying to figure it out. Carb, pump, electric pump, etc.- nothing helped.

Finally I had my head under the hood with a friend helping and he noticed a slight movement in the semi-clear in line fuel filter. Replaced it and things were fine. Turns out there was a small 'pile' of powdery sediment in the filter that hid in the element and under the inlet tube from the tank completely invisible to the eye. When fuel demand reached a certain level this mass would get sucked up enough to block the outlet and starve the engine.

I am sure you probably checked this but it was one of the most frustrating, fixes I ever had to diagnose. Nice shiny new toy and lost a whole summer to a dollar filter!

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Problem isolated! The owner of the car had supplied a very hard to find NOS fuel filter. At normal driving speeds the car ran fine. Upon serious acceleration the filter was limiting fuel flow. Not quite as simple as simply removing the filter since it incorporates a return line to the tank. Seems obvious now but while in the shop the car ran fine and fuel pressure was good but upon acceleration the filter proved faulty. Can't be that the new filter became clogged. We put a hidden generic filter in line to prevent the expensive "show" filter from becoming clogged. Thanks all for your suggestions.

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I spent a very frustrating Summer with a '60 Corvair, my first car. Same symptoms, it would shut off at random times. If it sat for an hour it would start up and run fine until it stopped again. Turned out that one of the valves in the fuel pump was loose in its bore and would "float", stopping the fuel flow to the carbs. After it sat a while the valve would settle back into position and all would be fine.

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Had a Jeep Wagon back in the day that would do that. Randomly die. Run sometimes for weeks, sometimes for minutes.

I was changing some tires one day and saw against the chassis where two metal fuel lines came together. Just for grins I opened up the connection to find a tiny stone in the coupler. It was acting like a valve. Only messed with that one for a couple of years.

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Problem isolated! The owner of the car had supplied a very hard to find NOS fuel filter. At normal driving speeds the car ran fine. Upon serious acceleration the filter was limiting fuel flow. Not quite as simple as simply removing the filter since it incorporates a return line to the tank. Seems obvious now but while in the shop the car ran fine and fuel pressure was good but upon acceleration the filter proved faulty. Can't be that the new filter became clogged. We put a hidden generic filter in line to prevent the expensive "show" filter from becoming clogged. Thanks all for your suggestions.

Did you provide a "map" of the hidden filter to the owner, so when he/she sells the car the new owner will not have the same headache? ;)

Jon.

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Well, we're kinda laying low 'til the shock of paying over $100 for a NOS but junk fuel filter passes. Happily, for us at least, the owner found and purchased the filter himself so we don't have to eat the cost. Hopefully he can get a refund. So it goes working on old stuff.

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Yeah. Before randomly replacing parts, temporarily connect a fuel pressure guage at the carb inlet and tape it to the windshield so you can read it while you drive. Watch what's going on when the car noses over. This could be fuel pressure related, or carb related, or ignition related. Free troubleshooting beats randomly throwing dollars at it.

Captain Obvious, Thank you from someone myself who has felt like a total rube sometimes. I think this has happened to all of us when we assume things without testing. (All of this typed while smiling.)

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Problem isolated! The owner of the car had supplied a very hard to find NOS fuel filter. At normal driving speeds the car ran fine. Upon serious acceleration the filter was limiting fuel flow. Not quite as simple as simply removing the filter since it incorporates a return line to the tank. Seems obvious now but while in the shop the car ran fine and fuel pressure was good but upon acceleration the filter proved faulty. Can't be that the new filter became clogged. We put a hidden generic filter in line to prevent the expensive "show" filter from becoming clogged. Thanks all for your suggestions, AND ESPECIALLY TO JOE.

;)

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Problem isolated! The owner of the car had supplied a very hard to find NOS fuel filter. At normal driving speeds the car ran fine. Upon serious acceleration the filter was limiting fuel flow. Not quite as simple as simply removing the filter since it incorporates a return line to the tank. Seems obvious now but while in the shop the car ran fine and fuel pressure was good but upon acceleration the filter proved faulty. Can't be that the new filter became clogged. We put a hidden generic filter in line to prevent the expensive "show" filter from becoming clogged. Thanks all for your suggestions.

I have heard of old NOS sealed canister oil filters spreading deteriorated paper throughout the lube system, but this is the first horror story I have heard concerning an old NOS fuel filter. If it turns out to be non returnable, I hope you will cut it open. I would be interested to hear what you find the condition of its insides to be.

Edited by Guest (see edit history)
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Yeah. Before randomly replacing parts, temporarily connect a fuel pressure gauge at the carb inlet and tape it to the windshield so you can read it while you drive. Watch what's going on when the car noses over. This could be fuel pressure related, or carb related, or ignition related. Free troubleshooting beats randomly throwing dollars at it.

yep Joe (captain obivious) stated the obvious and hit it right on the head... drive it with the test equipment on till it acts up. a proper procedural diagnosis is overlooked many times.

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Guest exbcmc

Have the EXACT problem w/my '73 GMC truck. Dual tanks and I "think" it occurs only with the right tank being used. Runs fine, get on it and bam, cough, spitter, die. Just had the fuel lines changed, a every 5 yr project, but it just did it to me the other day. Someone mentioned a sock in the tank? Anyone know if these dual tank systems have socks in them? I also put electronic ignition on this truck and someone mentioned that.....irritating to say the least.

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