I6 surging/struggling under acceleration - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Anorak · 02-26-2017, 09:50 AM

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

**MikeB** · 02-26-2017, 10:26 AM

Vacuum leaks? EGR valve?

How much manifold vacuum do you have at idle?

Anorak · 02-26-2017, 10:27 AM

No idea, how do you check that?

78chevstepside · 02-26-2017, 10:50 AM

check the fuel filter

Anorak · 02-26-2017, 11:02 AM

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.

**MikeB** · 02-26-2017, 11:13 AM

Quote:

Originally Posted by 78chevstepside

check the fuel filter

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

**MikeB** · 02-26-2017, 11:21 AM

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.

D13 · 02-27-2017, 07:05 AM

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.

**MikeB** · 03-06-2017, 10:56 PM

Quote:

Originally Posted by D13

83 would be an integral head if a 250. Notorious for vacuum leaks and a finicky carb.

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

02-26-2017, 09:50 AM	#1
Anorak Registered User Join Date: Feb 2015 Location: Chicago, IL Posts: 9	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

02-26-2017, 10:26 AM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,425	Re: I6 surging/struggling under acceleration Vacuum leaks? EGR valve? How much manifold vacuum do you have at idle? __________________ Mike 1969 C10 LWB -- owned for 34 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 23 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

02-26-2017, 10:27 AM	#3
Anorak Registered User Join Date: Feb 2015 Location: Chicago, IL Posts: 9	Re: I6 surging/struggling under acceleration No idea, how do you check that?

02-26-2017, 10:50 AM	#4
78chevstepside Registered User Join Date: Nov 2002 Location: lacenter, washington Posts: 718	Re: I6 surging/struggling under acceleration check the fuel filter __________________ 1978 c10 stepside 4/6 drop 350 vortec crate 2011 camaro ss2 6.2 automatic 2017 tahoe lt 2002 silverado lt 1500 5.3 automatic. 1981 el camino

02-26-2017, 11:02 AM	#5
Anorak Registered User Join Date: Feb 2015 Location: Chicago, IL Posts: 9	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.

02-26-2017, 11:21 AM	#7
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,425	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. __________________ Mike 1969 C10 LWB -- owned for 34 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 23 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

02-27-2017, 07:05 AM	#8
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	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. __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors



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