Been through everything, What am I missing?

[AASmedic]

OK Peeps. I need some input. I began having an issue back in February while driving at 65 mph on the interstate. The motor began to sputter and jerk and I thought it was vapor locking (as it was rather warm that week) or the fuel pump was going bad. I got off the freeway and drove surface street speeds (45 or less) and the issue seemed to resolve itself.

I finally got some time over the next few months so I replaced the fuel pump and all of the filters. Nothing changed. I then moved on to the carb and rebuilt it. I wrapped the fuel line with heat resistant tape and put a sleeve on it. Nothing changed.

I read another forum that addressed the same symptoms I am experiencing and it suggested that the pick up in the distributor was bad. I replaced the distributor, cap, rotor and coil, re-timed everything and nothing changed.
Another recommendation was to change out the thermostat. I put in a 160 degree thermostat and still, you guessed it, nothing changed.

What am I missing? Any help or suggestion would be appreciated.

Thanks,
Kevin

[kwmech]

Did you check the rubber fuel lines themselves?

[AASmedic]

Originally Posted by kwmech

Did you check the rubber fuel lines themselves?

Yep, checked all the fuel lines, no leaks

[garyd1961]

Originally Posted by AASmedic

Yep, checked all the fuel lines, no leaks

If the lines are old they may not leak but still suck air at higher speeds. I had this happen years ago on my 69 442, the rubber line coming from the tank had a crack. It would run perfect at slow speeds but if I got into it it would just die.

[AASmedic]

Originally Posted by davepl

I must say it does indeed sound like a fuel starvation (delivery) issue from the symptioms.

I'd say fill the float bowls with fuel so it'll run a few seconds, then disconnect the fuel line at the carb and put it into a clear bottle so you can see what's happening. Fire the motor so it'll run for a few seconds using the residual fuel in the carb.

You -should- get a strong and steady flow of gasoline into the glass jug. If it's anything but an impressive flow of fuel, I'd imagine you've confirmed it.

Goes without saying, but gasoline is evil and dangerous. Be paranoid and safe around it.

(BTW, if its q-jet, don't forget the filter and screen in the inlet of the carb itself)

Originally Posted by KJSR

Those RPM's are not that high. Does it start at 2500 and continues to max rpm (over 3k)?

You may want to run the truck in the driveway at night and see if you have spark jumping from anywhere at higher RPM's. That is after its warm and is missing.

Originally Posted by KJSR

Oh yeah, I didn't see.....HEI or points? You mentioned a "pick up" in the distributor so I'm guessing electronic. I would also consider the ignition module if its an HEI. The coil can cause this as well especially since its doing it after its warm.

Originally Posted by Already Gone

I just cured a similar problem with my truck. I too changed the fuel pump and everything else is new. My truck kinda died at fast idle then sputtered while driving and even backfired sometime. A friend told me to try running Premium Gas in the truck. I have been gassing my truck at the same place for 10 years always running regular unleaded but was at my wits end so filled it up on Saturday with premium and it seems to have cured the problem the last 2 days driving around city and highway.

Originally Posted by 68 P.O.S.

Clogged fuel sock on sending unit in the tank? What carb do you have? What is your timing set at?

Originally Posted by custom10nut

Did you check the filter on the pickup line in the tank?

Originally Posted by rsgt

Check the crimps and connections that power the HEI. Where do you power it from?

Originally Posted by whtgmc68

I had nearly the same problem with my truck when it still had the 350 that was in it when I bought it. I replaced the carb, fuel pump and filters. Turned out there was so much gunk in the fuel tank that I just replaced it since it was about the same price to have the orignal boiled out and properly cleaned.

Never had another problem and when the engine finally got a proper flow of fuel, it ran so well that I almost hated to replace it with the 383.

Originally Posted by garyd1961

If the lines are old they may not leak but still suck air at higher speeds. I had this happen years ago on my 69 442, the rubber line coming from the tank had a crack. It would run perfect at slow speeds but if I got into it it would just die.

OK Guys, I have read all of the comments and have some feedback.
I have an HEI which is powered directly from the fuse block (replaced the harness in the rebuild) with all new components installed. Timing is set to 12 degrees BTDC and starts instantly and runs well. Tanks were cleaned during rebuild as well. I do need to re-inspect the rubber lines that connect the tank to the frame rail line and then to the pump.

Here's something that may be of significance though. I do not have a vented fuel cap nor do I have the vapor canister system. It was removed at some point before I owned the truck. Logic would tell me that if all of the air/vapor has been sucked out of the tank by the fuel pump and no air to replace it then the rubber lines collapsing would make sense as well as the fuel starvation issue. Thoughts on this theory?

[Stocker]

The only thing I can think of is did you change the little filter at the fuel inlet (if it's a q-jet)?

[AASmedic]

Originally Posted by Stocker

The only thing I can think of is did you change the little filter at the fuel inlet (if it's a q-jet)?

Replaced the tiny rascal at the inlet too.

[SIXTY9]

Have you checked the screen on the fuel send unit in the tank?

[AASmedic]

Originally Posted by SIXTY9

Have you checked the screen on the fuel send unit in the tank?

No hadn't thought about that one but if that was clogged, wouldn't it act like it was starving for fuel throughout the RPM range and not just at the top end?

[SIXTY9]

Guess on how bad it is. Just a thought.

[Nh4clo4]

Sixty9 probably is right. I had a similar issue with one many years ago. Only did it at highway speeds.

[CUSTOM/10]

Same here, was fine at low speed but would sputter and even die on the hi-way. Check it out !

[67 chevelle]

1 vent line or cap , when it does it again , pull over and take the gas cap off and resume ride , if that fixes it you will know , 2 your fuel line may be bent or the rubber swollen also

[special-K]

Is there a hard line all the way to the pump? If there is rubber between tank and pump it could be collapsing at higher RPMs.

[Mike C]

I mention this a lot, but there is an old hot rodders adage that says "90% of carb problems are ignition".

Make sure everything is in tip top shape. Plug wires are routed away from anything they may arc to and are in good shape. You don't have a broken plug, cracked cap or damaged rotor. That all connections are clean and tight.

Once that is 100% squared away and it still has issues start looking at the fuel again.

[KJSR]

Will it do it at the same RPM in a different gear? Does it take a bit to start happening or is it as soon as you get to 65ish? Try driving in a lower gear at the same RPM range and see what happens

[AASmedic]

Thanks for all the pointers guys. The problem seems to be in the 2500-3k rpm range or about 65mph. It is generally after it has been driven a few miles. I hadn't thought about the vent issue either. I will check pick up screen and re check incoming fuel line. Cap, rotor, plugs and wires all new.

[michael bustamante]

also don't forget to check the rubber fuel lines for softness, my line would actually pinch itself almost shut last year with how hot it was

[davepl]

I must say it does indeed sound like a fuel starvation (delivery) issue from the symptioms.

I'd say fill the float bowls with fuel so it'll run a few seconds, then disconnect the fuel line at the carb and put it into a clear bottle so you can see what's happening. Fire the motor so it'll run for a few seconds using the residual fuel in the carb.

You -should- get a strong and steady flow of gasoline into the glass jug. If it's anything but an impressive flow of fuel, I'd imagine you've confirmed it.

Goes without saying, but gasoline is evil and dangerous. Be paranoid and safe around it.

(BTW, if its q-jet, don't forget the filter and screen in the inlet of the carb itself)

[KJSR]

Those RPM's are not that high. Does it start at 2500 and continues to max rpm (over 3k)?

You may want to run the truck in the driveway at night and see if you have spark jumping from anywhere at higher RPM's. That is after its warm and is missing.

[KJSR]

Oh yeah, I didn't see.....HEI or points? You mentioned a "pick up" in the distributor so I'm guessing electronic. I would also consider the ignition module if its an HEI. The coil can cause this as well especially since its doing it after its warm.

[Already Gone]

I just cured a similar problem with my truck. I too changed the fuel pump and everything else is new. My truck kinda died at fast idle then sputtered while driving and even backfired sometime. A friend told me to try running Premium Gas in the truck. I have been gassing my truck at the same place for 10 years always running regular unleaded but was at my wits end so filled it up on Saturday with premium and it seems to have cured the problem the last 2 days driving around city and highway.

[68 P.O.S.]

Clogged fuel sock on sending unit in the tank? What carb do you have? What is your timing set at?

[custom10nut]

Did you check the filter on the pickup line in the tank?

[ManNamedJed]

Sounds like you've already addressed these, but I'll add them here in case someone with similar problems reads these threads.

I had similar issues in a jeep. Finally tracked it down to the foil 'High Energy' sticker on the ignition module in the distributor had come loose and would occasionally flutter around and cause the engine to sputter and die.

Had another similar issue with another jeep. Turned out the rotor in the distributor was cracked and was rotating 15 degrees or so on the shaft. There was enough tension still there that it would return to normal at idle, but move around at anything above that.