stumble while excellerating - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tom · 05-23-2005, 03:42 AM

My truck started to stumble while speeding up about a week ago. Its gotten worse over time. When I was changing the timing I got shocked, so I got a new cap and rotor. Also found my fuel pressure dropping to 2psi at idle when it was fully hot. Fixed that with some header wrap around the exhaust where the electric fuel pump is mounted. Also tried dropping the timing down 4 degrees to 10 initial, no help. Does anyone have any ideas? The carb is a 6 month old 1405, brand new 14x5" K&N, R42LTS plugs, MSD 6a box and blaster 2, muncie M20 and 3.73 gears. Wires are also new and not touching the headers anywhere.

72 CustomCamper · 05-23-2005, 04:07 PM

My truck had a bad stumble too. I fixed it with a new fuel filter. Something to check at least...

Chuck

Hoods69BadBowTie · 05-23-2005, 04:27 PM

My truck had a bad stumble to and it was the damn choke on the carburatot. Might try new fuel filter too. Or there could be some crap in the fuel line effectin the flow.
-Later

Tom · 05-23-2005, 04:38 PM

Fuel filter is new and clear so I can see if it gets clogged. Choke is wired full open. Thanks for the ideas guys, keep em coming.

Hoods69BadBowTie · 05-23-2005, 05:29 PM

New spark plugs, did you get them gapped up right??
Nevermind, just re-read your first post and saw that you had put in new spark plugs.
"When you say speeding up" Do you mean when your flooring it or when your just start to pick up some speed gradually? Is it all the time or just once and awhile?
-Later

Tom · 05-23-2005, 05:48 PM

Speeding up as in not flooring it. It stumbles and kicks too much to try flooring it. It is a random thing but happens every time Im excellerating.

jermasaurus · 05-23-2005, 06:45 PM

Is it a vibration like one or two cylinders, or like a stumbling bogging type thing?

1405 is an edelbrock carb I think? If it may be fuel related, have you looked into the power enrichment system for the carb?

Tom · 05-23-2005, 07:50 PM

Quote:

Originally Posted by jermasaurus

Is it a vibration like one or two cylinders, or like a stumbling bogging type thing?

Stumbling bogging sort of thing. Idle is perfect, cruising is perfect once Im at a steady speed. Starts up great too.

superchevy · 05-23-2005, 07:55 PM

The Edelbrock 750 on my 454 was waaay rich from the factory, and stumbled/popped whenever I would floor-it...idled/cruised fine...leaned her out...runs great now.
SC

Tom · 05-23-2005, 09:48 PM

Ok so I tried leaning the carb out, I did have it richer then factory. Driving got worse. When I got back from my short trip I had only 4psi at idle of fuel pressure. Im pretty sure at this point its the fuel pump not working when Im actually driving down the road. I took the carb apart, took off and checked all the plugs and wires, nothing else is wrong.

ureckme · 05-23-2005, 10:02 PM

Its think its fuel pump or its sucking air. If you want you can put the carb from my truck on it. If it still runs the same you know its not the carb. Matt

K Dubb · 05-23-2005, 10:41 PM

I had that problem kinda.... Trying turning the rotor a tooth.....

f.monroe · 05-23-2005, 11:37 PM

Did the problem start before or after the new plug wires . I have had a couple of our work trucks do the exact same thing and it was the wires . They all bucked under light acceleration . It didnt show up under heavy acceleration or at idle . You have a nice ignition system and I think it may have killed the wires . I would definitely give them a close look . Even new wires can be bad sometimes. Frank

jermasaurus · 05-24-2005, 01:03 AM

Fuel pump sounds kinda responsible for your problems like you thought. You have an electric fuel pump? Then you have the benefit of doing a flow test. Just because you have fuel pressure doesn't mean it can maintain that pressure and supply a constant flow of it. And since it got really hot from the headers and dropped to 2 psi, I am sure that took some life out of it

ureckme · 05-24-2005, 02:52 AM

What about vaper lock/tank vent/elec to pump. what kind of pump do you Tom. When I took my truck thru emissions every thing was fine even the line of cars wasnt to bad but when I left I got 300 feet down the street and bog/lost power just like some one turned off the key. No poping no jumping just OH NO! Then just as quik every thing was back to the way it was. If your vent is blocked it will only pull gas slowly but running out of gas in the carb it should buck/pop etc. it may only get enough gas to cruse and idol. Do you have a filter in the carb?. Your trucks ben sit'n for a long time? could have junk in the fuel line. Once I had a Holley red fuel pump mounted to the frame. The moter on the pump mounted down, fuel leaked in to the elec. part of the pump it started slowing down a little at a time I found out when it locked up.
Hope you find the problem. Matt

f.monroe · 05-28-2005, 10:33 PM

Any updates ??? Frank

Tom · 05-29-2005, 03:47 AM

Sure thing

I narrowed it down to the fuel system for sure. Droped the fuel tank, no problems there. I put a 3/8" return line and a holley dead head regulator modify'd for return style on. Put a fuel filter before the pump and replaced the one before the regulator. Also replaced the 14g wire that ran from the starter to the switch inside the cab with 10g wire. Re-did the carb back to a richer setting. Now it seems like my fuel pressure is holding steady, at least anytime I check it [pull over and open the hood] its at 5.5psi like I set it. Truck will run smooth now if I speed up very slowly, but the hesitation/poping is still there. I think Im getting it worked out, Im going to re-do the entire electrical supply once again to include a relay and better wire. I'll post updates as I can. Right now Im driving my dads 99 miata lol

f.monroe · 05-29-2005, 10:44 AM

I re-read the post and noticed you retarded the timing . I think I would try advancing it . My truck I had in high school would do the same thing on occasion . I found that the timing was backing down on its own over time . Advancing it fixed it when this started to pop under acceleration . It sounds like you fixed your fuel problem and the problem you set out to fix is still there . I would look at advancing the timing and take a good look at the wires . Keep us posted on this . Frank

jermasaurus · 05-29-2005, 11:14 AM

I noticed that you mentioned how it just started a week before your first post. If it happend for no reason like that heres an idea, and it won't take long to check this out. If you are thinking that you may not be getting enough fuel, check out the flow of your electric pump.
First, check that you are getting at least 12.6 volts at the pump. I'm not sure which one you have, try and find the gallons per minute it can provide (GPM).
Hook it directly to the battery and make sure it can flow that much. Like if it is supposed to flow 2 GPM, make sure it could fill a gallon container in 30 seconds.

If the voltage and flow of the pump is fine, then try adjusting the accelerator pump or any other power enrichment devices that edelbrocks have. I am not familiar with edelbrocks, so I couldn't say what else to adjust. Definately check your float level if nothing else.
-Jeremy

05-23-2005, 03:42 AM	#1
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	stumble while excellerating My truck started to stumble while speeding up about a week ago. Its gotten worse over time. When I was changing the timing I got shocked, so I got a new cap and rotor. Also found my fuel pressure dropping to 2psi at idle when it was fully hot. Fixed that with some header wrap around the exhaust where the electric fuel pump is mounted. Also tried dropping the timing down 4 degrees to 10 initial, no help. Does anyone have any ideas? The carb is a 6 month old 1405, brand new 14x5" K&N, R42LTS plugs, MSD 6a box and blaster 2, muncie M20 and 3.73 gears. Wires are also new and not touching the headers anywhere. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me. Last edited by Tom; 05-23-2005 at 03:43 AM.

05-23-2005, 04:07 PM	#2
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,369	My truck had a bad stumble too. I fixed it with a new fuel filter. Something to check at least... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

05-23-2005, 04:27 PM	#3
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	My truck had a bad stumble to and it was the damn choke on the carburatot. Might try new fuel filter too. Or there could be some crap in the fuel line effectin the flow. -Later __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!! Last edited by Hoods69BadBowTie; 05-23-2005 at 04:29 PM.

05-23-2005, 04:38 PM	#4
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Fuel filter is new and clear so I can see if it gets clogged. Choke is wired full open. Thanks for the ideas guys, keep em coming. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

05-23-2005, 05:29 PM	#5
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	New spark plugs, did you get them gapped up right?? Nevermind, just re-read your first post and saw that you had put in new spark plugs. "When you say speeding up" Do you mean when your flooring it or when your just start to pick up some speed gradually? Is it all the time or just once and awhile? -Later __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!! Last edited by Hoods69BadBowTie; 05-23-2005 at 05:34 PM.

05-23-2005, 05:48 PM	#6
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Speeding up as in not flooring it. It stumbles and kicks too much to try flooring it. It is a random thing but happens every time Im excellerating. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

05-23-2005, 06:45 PM	#7
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	Is it a vibration like one or two cylinders, or like a stumbling bogging type thing? 1405 is an edelbrock carb I think? If it may be fuel related, have you looked into the power enrichment system for the carb?

05-23-2005, 07:55 PM	#9
superchevy Got big-block? Join Date: Jul 2000 Location: Austin, Texas Posts: 2,453	The Edelbrock 750 on my 454 was waaay rich from the factory, and stumbled/popped whenever I would floor-it...idled/cruised fine...leaned her out...runs great now. SC __________________ '68 CST SWB factory 396/T400 buddy buckets, a/c, ps, pb '72 Corvette convertible 454/4spd/ac, ps, pb '73 GMC Sierra Grande short wide 454/T400 ps, pb, ac '77 K5 Blazer black on red, 350/T350/NP205 ps, pb, ac all original '78 GMC Sierra Classic short wide 454/T400 ps, pb, ac '72 GMC Sprint SP454. 1 of 38 built. '73 GMC Sprint SP454. 1 of 71 built. '75 GMC Sprint SP454. 1 of 25 built. SOLD! '72 GMC K25 4x4 468/4L80e/NP205 build thread http://67-72chevytrucks.com/vboard/s...23#post4324423 SOLD!'55 Chevy gasser 496/4spd build thread http://67-72chevytrucks.com/vboard/s...96#post4324396

05-23-2005, 09:48 PM	#10
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Ok so I tried leaning the carb out, I did have it richer then factory. Driving got worse. When I got back from my short trip I had only 4psi at idle of fuel pressure. Im pretty sure at this point its the fuel pump not working when Im actually driving down the road. I took the carb apart, took off and checked all the plugs and wires, nothing else is wrong. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

05-23-2005, 10:02 PM	#11
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	Its think its fuel pump or its sucking air. If you want you can put the carb from my truck on it. If it still runs the same you know its not the carb. Matt

05-23-2005, 10:41 PM	#12
K Dubb www.Dubbmotorsports.com Join Date: Jul 2004 Location: Michigan Posts: 110	I had that problem kinda.... Trying turning the rotor a tooth..... __________________ DubbMotorSports Edition

05-23-2005, 11:37 PM	#13
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	Did the problem start before or after the new plug wires . I have had a couple of our work trucks do the exact same thing and it was the wires . They all bucked under light acceleration . It didnt show up under heavy acceleration or at idle . You have a nice ignition system and I think it may have killed the wires . I would definitely give them a close look . Even new wires can be bad sometimes. Frank

05-24-2005, 01:03 AM	#14
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	Fuel pump sounds kinda responsible for your problems like you thought. You have an electric fuel pump? Then you have the benefit of doing a flow test. Just because you have fuel pressure doesn't mean it can maintain that pressure and supply a constant flow of it. And since it got really hot from the headers and dropped to 2 psi, I am sure that took some life out of it

05-24-2005, 02:52 AM	#15
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	What about vaper lock/tank vent/elec to pump. what kind of pump do you Tom. When I took my truck thru emissions every thing was fine even the line of cars wasnt to bad but when I left I got 300 feet down the street and bog/lost power just like some one turned off the key. No poping no jumping just OH NO! Then just as quik every thing was back to the way it was. If your vent is blocked it will only pull gas slowly but running out of gas in the carb it should buck/pop etc. it may only get enough gas to cruse and idol. Do you have a filter in the carb?. Your trucks ben sit'n for a long time? could have junk in the fuel line. Once I had a Holley red fuel pump mounted to the frame. The moter on the pump mounted down, fuel leaked in to the elec. part of the pump it started slowing down a little at a time I found out when it locked up. Hope you find the problem. Matt

05-28-2005, 10:33 PM	#16
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	Any updates ??? Frank



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05-29-2005, 03:47 AM	#17
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Sure thing I narrowed it down to the fuel system for sure. Droped the fuel tank, no problems there. I put a 3/8" return line and a holley dead head regulator modify'd for return style on. Put a fuel filter before the pump and replaced the one before the regulator. Also replaced the 14g wire that ran from the starter to the switch inside the cab with 10g wire. Re-did the carb back to a richer setting. Now it seems like my fuel pressure is holding steady, at least anytime I check it [pull over and open the hood] its at 5.5psi like I set it. Truck will run smooth now if I speed up very slowly, but the hesitation/poping is still there. I think Im getting it worked out, Im going to re-do the entire electrical supply once again to include a relay and better wire. I'll post updates as I can. Right now Im driving my dads 99 miata lol __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

05-29-2005, 10:44 AM	#18
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	I re-read the post and noticed you retarded the timing . I think I would try advancing it . My truck I had in high school would do the same thing on occasion . I found that the timing was backing down on its own over time . Advancing it fixed it when this started to pop under acceleration . It sounds like you fixed your fuel problem and the problem you set out to fix is still there . I would look at advancing the timing and take a good look at the wires . Keep us posted on this . Frank

05-29-2005, 11:14 AM	#19
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	I noticed that you mentioned how it just started a week before your first post. If it happend for no reason like that heres an idea, and it won't take long to check this out. If you are thinking that you may not be getting enough fuel, check out the flow of your electric pump. First, check that you are getting at least 12.6 volts at the pump. I'm not sure which one you have, try and find the gallons per minute it can provide (GPM). Hook it directly to the battery and make sure it can flow that much. Like if it is supposed to flow 2 GPM, make sure it could fill a gallon container in 30 seconds. If the voltage and flow of the pump is fine, then try adjusting the accelerator pump or any other power enrichment devices that edelbrocks have. I am not familiar with edelbrocks, so I couldn't say what else to adjust. Definately check your float level if nothing else. -Jeremy

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