I6 surging/struggling under acceleration
 

So I have a 1983 Chevy square body pickup, 3 speed with a granny gear, with a I6 in it, recently I started to notice that when I was accelerating in 2nd gear it would start to surge/struggle, but when I let off of the gas for a second it would be fine, and i could still accelerate passed that. That led me to think it was the fuel pump on the engine going out, because it seemed like it was starving for fuel, but I just put a new one in and it didn't change anything.

So I'm out of ideas of what it might be, so I was curious to see what you guys thought.

Thanks

Re: I6 surging/struggling under acceleration
 

Vacuum leaks? EGR valve?

How much manifold vacuum do you have at idle?

Re: I6 surging/struggling under acceleration
 

No idea, how do you check that?

Re: I6 surging/struggling under acceleration
 

check the fuel filter

Re: I6 surging/struggling under acceleration
 

I also changed the fuel filter recently, the only thing is it said that it was a crankcase air filter or something like that, but the people at o'rileys said it was the same, and it looked exactly the same as a normal fuel filter.

Re: I6 surging/struggling under acceleration
 

That may be the first thing to check. I mentioned the vacuum leak because the 250 six in my truck had more than one leak when I bought it. The symptoms were similar to yours. Found a hose with a slit in it and a bad EGR gasket.

Even if changing the fuel filter solves the problem, it's always a good idea to visibly check vacuum hoses, and it never hurts to check manifold vacuum using a gauge like the one below. A stock six should probably make around 18"-20" at idle depending a condition of rings and valves.

https://www.summitracing.com/parts/a...sGQaAm9M8P8HAQ
https://static.summitracing.com/glob...-CP7803_ml.jpg

Re: I6 surging/struggling under acceleration
 

OK, just read that you changed the fuel filter. If the problem is not a vacuum leak, it may be somewhere else in the fuel system, including the carburetor.

Usually when the problem clears up after you get up to speed, it's fuel related.

Re: I6 surging/struggling under acceleration
 

83 would be an integral head if a 250. Notorious for vacuum leaks and a finicky carb. Check / replace every vacuum hose ( probably due anyways) but more likely the carb needs to be addressed. The 2bbl's on these are touchy on being clean and also a little tricky to adjust. My guess is dirt in the carb. It doesn't take much to plug those itty bitty holes.

The other thing that will give you this is a distributor with worn out bushings.

One of the quirks of the six is they will run under fuel and timing conditions that would cause every other motor to die, which can make it hard to diagnose. But my bet is in the carb.

Re: I6 surging/struggling under acceleration
 

Worst design ever, including the carb! Had I kept my 250, I would have used an older model head and manifolds.