idles fine; stalls under load at 2K

[aintmisbehavinn]

Murphy is giving me hell. Just started 72 GMC truck with rebuilt original motor 35K miles that was in storage for 8 years. Plenty compression, no knocks or ticks. Tank drained before storage, pick up cleaned, no clogs in line, new fuel pump, holley 4150 dual pump rebuilt with no leaks, bowls adjusted idle perfect with small torquer camshaft. New ACDELCO cap and rotor on MSD OEM replacement distributor with MSD 6A box. New MSD wires and ACDELCO plugs. New fuel filter, pump and lines. Fresh 93 octane gas. Truck ran perfect daily for 2 weeks then began to stutter at 2 k when warmed up. Occasionally stalled but restarted immediately. Truck now will not rev under load over 2K however will rev to 5K at idle. Beginning hard start on 180 temp. I have changed everything but cannot figure out why it only stalls under load. Does anyone have any suggestions where to look next. Timing is dead on and advancing properly, the only thing I haven't changed is the coil; alternator seems to be working properly according to the gauge. What would cause it to sputter and stall over 2K under load? Truck ran perfect before storage and shortly after. Just getting worse. Don't understand why it would idle perfect, rev perfect, soon as I hit passing gear motor just drops like a rock. No change after fuel pump and carb rebuild. No leaks except for trans pan overnight.

I'm wide open and running out of solutions.

[JimKshortstep4x4]

From your description I would be inclined to believe that it is in the ignition.

Do you have another distributor and coil that you can try?

Jim

[truckdude239]

i believe the coil is going out

[aintmisbehavinn]

No other distributor, this one has 35K on it and is tight. If the coil was bad, isn't it one of those it either works or no? I checked the mech adv and worked tried freeing them up more with WD seemed to help, at least it didn't stall but it is hesitating like a MF. Still at it....

[cdowns]

coils can go intermittent when heated and with a load applied
electrical connections including grouding can do that same thing too

[68gmsee]

Yes, coils can have a weak output and not totally fail.

Another thing to check is spark plug gap. Not sure what your specs recommend but on my 69 I gapped them to .045. (Personally, I've never cared for AC Delco plugs since I've had some bad experiences with them, but that's for another post.)

Even though you say that all the fuel components are good, I'd still check the fuel pump output by placing the cab fuel line in a container and measure that it pumps out at least a pint or more in 30 seconds or less.

And last, I'd take the carb apart and see if there's any debris that may have gotten in there.

[vasquezmrysvll]

whats "dead on timing?" when does full advance occur? and whats the total advance?

[aintmisbehavinn]

Originally Posted by 68gmsee

Yes, coils can have a weak output and not totally fail.

Another thing to check is spark plug gap. Not sure what your specs recommend but on my 69 I gapped them to .045. (Personally, I've never cared for AC Delco plugs since I've had some bad experiences with them, but that's for another post.)

Even though you say that all the fuel components are good, I'd still check the fuel pump output by placing the cab fuel line in a container and measure that it pumps out at least a pint or more in 30 seconds or less.

And last, I'd take the carb apart and see if there's any debris that may have gotten in there.

MSD recommends 60 with the 6AL, they are close. I pulled a few plugs, black with raw gas, surely it's dumping to much fuel. Holley was rebuilt last week by a pro.

Originally Posted by vasquezmrysvll

whats "dead on timing?" when does full advance occur? and whats the total advance?

I started with 8; factory spec, with manifold vac, at idle, idles choppy with cam. Switched to 10 with ported vac, black plug sindrome. I think I'll go back to 8 with manifold adv, seems to start easier when hot. At least 33 total checking on driveway without real road conditions.

I'm beginning to think it is the coil but I hate to dump another 50 clams on something if it's not going to work. Black plugs must mean something with float bowl height...ignition, back to the drawing board...

Keep um coming, thanks guys....