Can't figure out my issue at cruising speed

[OkieFishMan]

So when I'm driving down the road at 60mph the engine is turning about 2700-2800rpm, but it either is missing or surging. The sound of the engine changes, and it will have noticiable more power for a sec, then the sound changes and it feels more sluggish. I have changed the plugs twice, the distributor twice, it has new plug wires, new coil, new cap, new rotor, and the carb has been rebuilt. I think it is cylinder 1 based on the plugs. Where the hell do I go next with this???????? Help!!!!

 

[smoothandlow84]

When was the last time you changed the in line fuel filter (along the passenger side frame rIl) or better yet the in tank filters/pumps?

 

[MrMarty51]

What does the no. 1 plug look like after You pull it out ? Oil soaked, fuel soaked, carboned up, etc. ?

 

[OkieFishMan]

Plug in cylinder 1 is darker than the others. Not black, but definitely darker than the nice tan tinge the others have.

I have not changed a frame rail filter. I've looked for one and never saw one. I have not pulled the tanks, so nothing changed in there, but with it being carbureted, I didn't know the tanks would have a filter.

I have changed the filter in the carburetor, its only got 200 miles on it.

 

[1987 GMC Jimmy]

The tanks have strainer socks at the ends of the pick ups, which can be inundated with debris over time. So I guess you're saying the No. 1 plug is seeing a richer mixture than the rest. I had a fairly new Delco wire burn the contact on the plug side to where it looked completely charred on the No. 1 cylinder. I would check for this just to make sure your spark has the best route possible to get between the cap and the plug. Would a pre-TBI truck have a frame rail filter?

 

[smoothandlow84]

If its not tbi...then probably not. I saw the year and assumed it was tbi.

 

[theBIGnaud]

Do you still have your EGR connected? Is it functioning correctly?

 

[crazy4offroad]

What carb? I've heard (and seen) the pickup tube falling off the top plate of the q-jet and causing it to run badly. If your rebuild guy didn't epoxy them it's possible one came loose.

 

[87ChevyR10]

Does your speedo needle bounce? If so, could be why your engine surges when cruise is on.

 

[OkieFishMan]

Hell, I forgot to update this thread. It ended up being I had a damaged boot that got a little too close to the headers. Once it got heated up a couple of cylinders would start arcing to the header, causing a weak fire or miss. I replaced the wires, and put fiberglass foil backed boot sleeves on. Problem is fixed now. Thanks though!