Hesitation in acceleration and high rpm "cough" - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Longhorn Al · 10-13-2002, 02:50 PM

My truck has had a hesitation when I press the gas pedal off idle. It sort of almost stalls, then catches and goes. We advanced the timing awhile back and it went away. But now it's back. I've talked to some guys and they can't think of what it could be. It did it before and now after I had the heads replaced. And I have an electronic ignition.

Also, I've always had a problem with what seems to be a high rpm cough. Off the line, it'll squeal the tires for quite a ways, then you can hear it really get into it. When I reach about 55 or 60, the engine coughs pretty hard. The whole truck will sort of rock. It's like it's not getting fuel, but we're not exactly sure. I've got the original 4 barrel carb on it. Is it most likely something wrong with that?

Thanks for any help. These are extremely annoying problems.

*Zkast* · 10-13-2002, 03:36 PM

Take a reading on the spark plugs, see how the fuel system is doing. Right off the bat it sounds like you have a accelerator pump problem (low or no output). You also could be leaning out on the top end or having an ignition problem.

Finding the exact cause is going to take some inspection work on your part. First I would check the accelerator pump operation. Then check the plugs, all plugs, for cracks and condition (rich,lean,oil fouled). Verify your wires are not touching a header/manifold. Inspect the cap and rotor, Look for carbon tracking or a burned rotor (pull the rotor and check underneath for marks/burns). The rotor will do what your describing, any time its under high load/high voltage it tries to find the path of least resistance.

Good luck with it.

NOTE: This is assuming you have an HEI? If so, do you have a "good" 12v 12guage wire going directly to the HEI from the fuse block or ignition switch?

If you have points, I'll need to add more to this list.. bad condensors will act this way also.

cableguy0 · 10-13-2002, 03:45 PM

in addition to what zcast is saying what kind of dizzy do u have. stock gm heis are known to cut out and almost die in the 4500 rpm neighborhood. if u have a stock dizzy do urself a favor and go out and get a msd or a proform. the proform will only set u back like 160 bucks compared to the msd's 300 dollars. i run a proform and love it havent had a bit of problem out of it and its seen the better side of 6500 rpm quite frequently. got better gas mileage over the stock unit as well

HvyChevy454 · 10-13-2002, 04:29 PM

i kinda had the same problem with the high end cough, problem was my purolator fuel pump couldnt refill the bowls fast enough, got a holley blue pump and fixed the problem

71k5 · 10-13-2002, 07:44 PM

Make sure your centrifugal weights are free to move in your distrubutor; I had one once that rusted up and caused the same problems. Good luck....

bigjimzlll · 10-13-2002, 07:48 PM

I just had a proform go south..it wore out the shaft..the mechanical advance would come in and not go out..it had a good 1/8" of play in all directions

Chevy409 · 10-14-2002, 06:51 PM

Try advancing your timing. I had the exact same hesitation and it wasn't the acceleraor pump or bad fuel pump or anything. i just played with the timing and fixed it about five minutes ago, can't stop spinning the tires now, it's perky

Hope that helps

Hooter · 10-14-2002, 08:59 PM

also check to see if you are sucking air into the fuel line anywhere

Paul Clark · 10-14-2002, 09:21 PM

Just ideas. Don't really know what I'm talking about, but -
Leak or corrosion in the fuel line?
Bad fuel pump?
Clogged fuel filter?
I'd check the filter first 'cause it would be the easiest to fix.
How's your air filter and carb gaskets?
Maybe check the bolts that hold the carb to the intake.
Like I said - just guessing.
Good luck.

Longhorn Al · 10-15-2002, 03:22 PM

Thanks everyone for your suggestions. I now have a project for this weekend.

bigjimzlll · 10-15-2002, 09:14 PM

I put a new distributor in....now it works great..no more poping

Paul Clark · 10-15-2002, 09:28 PM

Just curious.
What was your MPH when you turned the 14.88?
How about 60' times?

10-13-2002, 02:50 PM	#1
Longhorn Al Texas Longhorn For Life Join Date: Jun 2000 Location: Austin, Texas Posts: 698	Hesitation in acceleration and high rpm "cough" My truck has had a hesitation when I press the gas pedal off idle. It sort of almost stalls, then catches and goes. We advanced the timing awhile back and it went away. But now it's back. I've talked to some guys and they can't think of what it could be. It did it before and now after I had the heads replaced. And I have an electronic ignition. Also, I've always had a problem with what seems to be a high rpm cough. Off the line, it'll squeal the tires for quite a ways, then you can hear it really get into it. When I reach about 55 or 60, the engine coughs pretty hard. The whole truck will sort of rock. It's like it's not getting fuel, but we're not exactly sure. I've got the original 4 barrel carb on it. Is it most likely something wrong with that? Thanks for any help. These are extremely annoying problems. __________________ 1970 C-10 named HOSS 400SB/TH350, PS, PB, 3.07 gears \m/ Hook 'Em from Austin, TEXAS

10-13-2002, 03:45 PM	#3
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	in addition to what zcast is saying what kind of dizzy do u have. stock gm heis are known to cut out and almost die in the 4500 rpm neighborhood. if u have a stock dizzy do urself a favor and go out and get a msd or a proform. the proform will only set u back like 160 bucks compared to the msd's 300 dollars. i run a proform and love it havent had a bit of problem out of it and its seen the better side of 6500 rpm quite frequently. got better gas mileage over the stock unit as well __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-13-2002, 04:29 PM	#4
HvyChevy454 Slowly getting CRSS... Join Date: Jul 2001 Location: Lutz, Florida Posts: 656	i kinda had the same problem with the high end cough, problem was my purolator fuel pump couldnt refill the bowls fast enough, got a holley blue pump and fixed the problem __________________ -Nic Lutz, Fl My Team Website The Heavy Chevy Website ------------------ 72 Cheyenne 10 LWB GM 12-bolt 3.08 w/ Auburn Posi 91 454 Edel Performer RPM Intake 750 cfm carb Comp Cam 268/.495 Hedman Headers Dual 3'' Exhaust 71 Cheyenne 20 4x4 Fact. A/C PS PB Tilt Currently in the works... Speak Softly and Carry A Big Block... There is No replacement for Displacement... "If everything seems under control, you're just not going fast enough." - Mario Andretti

10-13-2002, 07:48 PM	#6
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	I just had a proform go south..it wore out the shaft..the mechanical advance would come in and not go out..it had a good 1/8" of play in all directions __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

10-14-2002, 06:51 PM	#7
Chevy409 Giddy up giddy up... Join Date: Feb 2001 Location: US Posts: 483	Try advancing your timing. I had the exact same hesitation and it wasn't the acceleraor pump or bad fuel pump or anything. i just played with the timing and fixed it about five minutes ago, can't stop spinning the tires now, it's perky Hope that helps __________________ 72 with 69 grille and custom 73-87 stepside. BIG BLOCK 409, SM465, NP205, 3/4 axles slung under a 5" lift, 3"bodylift, 112" frame, and 35inch Pro Comp X-terrains... "BUILT NOT BOUGHT" Here's the site...

10-13-2002, 03:36 PM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	Take a reading on the spark plugs, see how the fuel system is doing. Right off the bat it sounds like you have a accelerator pump problem (low or no output). You also could be leaning out on the top end or having an ignition problem. Finding the exact cause is going to take some inspection work on your part. First I would check the accelerator pump operation. Then check the plugs, all plugs, for cracks and condition (rich,lean,oil fouled). Verify your wires are not touching a header/manifold. Inspect the cap and rotor, Look for carbon tracking or a burned rotor (pull the rotor and check underneath for marks/burns). The rotor will do what your describing, any time its under high load/high voltage it tries to find the path of least resistance. Good luck with it. NOTE: This is assuming you have an HEI? If so, do you have a "good" 12v 12guage wire going directly to the HEI from the fuse block or ignition switch? If you have points, I'll need to add more to this list.. bad condensors will act this way also.

10-13-2002, 07:44 PM	#5
71k5 Registered User Join Date: Feb 2002 Location: Manchester, PA Posts: 138	Make sure your centrifugal weights are free to move in your distrubutor; I had one once that rusted up and caused the same problems. Good luck....

10-14-2002, 08:59 PM	#8
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	also check to see if you are sucking air into the fuel line anywhere __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

10-14-2002, 09:21 PM	#9
Paul Clark Registered User Join Date: Apr 2002 Location: Center Point, IA Posts: 502	Just ideas. Don't really know what I'm talking about, but - Leak or corrosion in the fuel line? Bad fuel pump? Clogged fuel filter? I'd check the filter first 'cause it would be the easiest to fix. How's your air filter and carb gaskets? Maybe check the bolts that hold the carb to the intake. Like I said - just guessing. Good luck.

10-15-2002, 03:22 PM	#10
Longhorn Al Texas Longhorn For Life Join Date: Jun 2000 Location: Austin, Texas Posts: 698	Thanks everyone for your suggestions. I now have a project for this weekend. __________________ 1970 C-10 named HOSS 400SB/TH350, PS, PB, 3.07 gears \m/ Hook 'Em from Austin, TEXAS

10-15-2002, 09:14 PM	#11
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	I put a new distributor in....now it works great..no more poping __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

10-15-2002, 09:28 PM	#12
Paul Clark Registered User Join Date: Apr 2002 Location: Center Point, IA Posts: 502	Just curious. What was your MPH when you turned the 14.88? How about 60' times?



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.