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Topic: stalls during accelleration

in Forum: C3 Engines


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stalls during accelleration (1/23)
 9/4/09 9:28am
DStoffel
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    1978 L-82 emissions removed. Engine runs fine when cold,as it warms up it will shut down during accelleration. It will restart after a couple of pumps on the gas pedal but will continue to stall during accelleration. I have been completely through the fuel system from tank to carb.,replaced fuel pump and all rubber hoses on fuel lines on my mechanics recomendation, after he went through the carb. I also replaced the screen in the tank and checked the vent line. Mechanic says problem isn't elecrical. I have also noticed one of the header pipes starting to glow just before engine shuts down.Frustrated and out of ideas. Any thoughts?             Dave

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stalls during accelleration (2/23)
 9/4/09 9:51am
sundevil74
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I'll bet your timing is off.  I've seen that make the headers get real hot and glow. Don't know why it would run smooth at idle.  I'm sure one of the experts will chime in . . .

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stalls during accelleration (3/23)
 9/4/09 11:30am
VetteSpecialties
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It sure sounds like it is running very lean.  It would run better when the choke was not yet wide open, and gradually get worse.  It could be an internal carb problem, or maybe it was not re-jetted when the smog equipment was removed.  Or it could be vacuum leak.  Do you have other intake or exhaust modifications?  That would make it run lean.

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Larry
stalls during accelleration (4/23)
 9/4/09 12:48pm
DStoffel
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No intake mods. Original Rochester Quadrajet. Had it rebuilt 2 years ago right after I removed what was left of the emission components (charcoal cannister and items related to the exhaust system). Car Was running great until last month.  At operating temp. I tried to maintain 2500 rpm while manually closing choke about 3/4 and it still stalled out after a minute or2. 

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stalls during accelleration (5/23)
 9/4/09 1:01pm
lukesvetteLifetime Member
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Definitely  a lean condition if you have header pipes glowing. If you have access to another carb, I'd try it to see it there's a difference. How much advance are you running?
stalls during accelleration (6/23)
 9/4/09 1:47pm
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You say "One of the header pipes"...do you mean the car has headers, and only one of the tubes is glowing? Or...does it have the stock type exhaust, and the front pipe that is bolted to the exhaust manifold is getting red?

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stalls during accelleration (7/23)
 9/4/09 3:21pm
DStoffel
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Couldn't get my timing light to work so i can't answer that question right now. The car has headers and a true dual exhaust, no convertor. The left rear (#7) is the only tube glowing and that only happens just before the engine shuts down.

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stalls during accelleration (8/23)
 9/4/09 9:04pm
anips
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werird, double check the HEI

stalls during accelleration (9/23)
 9/18/09 10:19am
DStoffel
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after having ignition module tested  and checking the timing  I was almost certain that the carb. was my problem. I replaced carb this morning- no change.  Then I put the vacuum gauge on. Vacuum was low but constant (12 psi). The manual indicated possible intake manifold leak. With engine running I tried spraying carb cleaner around edges of manifold. I immediately got my answer. Engine idle fluxuated and I was seeing bubbles especially around left rear. I guess its time to pull the intake manifold and replace the gasket.

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stalls during accelleration (10/23)
 9/18/09 12:52pm
KeBo
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This sounds exactly what I was experiencing. I had the qjet rebuilt and it was just not right..  Long story stort - I swapped a Edlebrock 650 w/a non-egr manifold and the car runs DOPE!  My car is also de-smogged. Best thing I did was ditch the quardabog 
stalls during accelleration (11/23)
 9/18/09 12:58pm
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That was the purpose of finding out if it had headers...if only ONE cylinder/tube was getting red hot, then that would have led me to think a vacuum leak in the area of that intake port. Sometimes, since the main vac. take-off point is in that area, a vac. leak will effect only the rear-most cylinders.
Looks like you found the problem...sux that the intake has to come off, tho...


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stalls during accelleration (12/23)
 11/12/09 7:52pm
DStoffel
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 New intake manifold gaskets took care of vacuum leak. Car still wouldn't run. Tested new (reman.) fuel pump - it failed miserably. Replaced that fuel pump. Seemed like problem was solved after a couple of 10 min. test drives. I decided to go for a Sun. afternoon drive last weekend. Just after entering the interstate (about 15 min. from home) it started acting like it was running out of fuel.(The tank is full) Engine would barely idle as we limped home. Tested this fuel pump - flow and pressure was correct. I have 2 questions.
1) What is the purpose of the return line from pump to tank and should it have fuel in it? The 2nd fuel pump was sending most of the fuel straight back to the tank. 
2)ANY IDEAS ?


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stalls during accelleration (13/23)
 11/12/09 8:35pm
anips
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the gas tank vents through the charcoal canister with a non vented gas cap, if you plugged the canister lines and still have a non vented cap the the fuel rubber hoses might be closing shut on ya.  
stalls during accelleration (14/23)
 11/12/09 8:37pm
lukesvetteLifetime Member
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Kinda sorts sounds like a plugged fuel filter that settles after sitting and takes a while to get plugged up again. Ever have the tank down?
stalls during accelleration (15/23)
 11/12/09 8:44pm
DStoffel
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The charcoal canister was removed but I left the line open. I even blew compressed air through the line.

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stalls during accelleration (16/23)
 11/12/09 8:58pm
KDADDY79
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How about the small fuel filter inside the (Q-Jet) carb?
Might be worth a look.
Let us know how you make out.
Kevin
stalls during accelleration (17/23)
 11/12/09 9:18pm
DStoffel
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I dropped the fuel tank back in August when this problem first developed. The tank was clean and in good shape. I did replace the screen on the pick-up tube at that time. The filter at carb. was replaced recently too but I will check it again.
                                                Thanks for the sugestions, Dave


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stalls during accelleration (18/23)
 11/13/09 9:12am
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The return line is to keep from having too much dead-head pressure at the carb, AND it helps cool the fuel so vapor lock isn't an issue.
If you're just looking at the fuel going back thru the return line, it may seem like a lot, but consider that the carb doesn't really need an abundant flow of fuel while idling.
You may need to install a fuel pressure gauge at the carb and drive it, and see what the pressure is when the problem appears. You may also want to block the return line for a test and see if it has any effect,and maybe even leave the gas cap loose.
Have you blown thru the actual fuel supply line from the tank to the pump, or otherwise checked it for restrictions? How about the rubber line from the frame to the pump? Is there a kink in it?

Seems like we're all looking for a fuel problem, when it may not be one. The pressure reading will confirm that. If the fuel pressure is not dropping when the problem occurs, the the fuel system is fine, and we need to concentrate on another area...


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stalls during accelleration (19/23)
 11/13/09 10:20pm
Autom8r
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I have a Q-Jet and found the problem was the choke getting sucked shut on high RPM. Let it warm up to choke full open then jam your choke wide open with a piece of cardboard matchbook or something similar. Then hammer the thing and see if it goes away. I had my Q-Jet professsionally rebuilt and it acted up on me again this spring at Beech Bend Dragstrip.... Jammed the choke open and no more problems. The guy who rebuilt mine pop riveted the spring tension adjustment on and I have to drill out the pop rivets to tighten the spring tension, which I haven't gottn around to.

Dave
stalls during accelleration (20/23)
 11/13/09 10:25pm
Autom8r
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BTW... Don't buy these guys poo-pooing your Q-Jet... It's the best street carb ever....

Dave
stalls during accelleration (21/23)
 11/15/09 6:57pm
DStoffel
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I installed the fuel pressure gauge in a way that would allow me to read it while driving. I found that pressure would drop to 0 psi. during accelleration. Then I started looking at fuel lines (again). I noticed that the rubber line going from the steel line to the pump looked a little flat. Once I replaced that hose the problem went away. I still can't believe a .50 cent hose could cause me so much grief. On a more positive note, my baby is running again, the odometer has at 1000 mi. less than it would had I solved the problem sooner, and I found the original build sheet when I dropped the tank, and it was still legible. Smile Thanks for all of of your input.
                                                                                    Dave


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stalls during accelleration (22/23)
 11/15/09 8:07pm
RedwingvetteLifetime Member
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[QUOTE=DStoffel]No intake mods. Original Rochester Quadrajet. Had it rebuilt 2 years ago right after I removed what was left of the emission components (charcoal cannister and items related to the exhaust system). Car Was running great until last month.  At operating temp. I tried to maintain 2500 rpm while manually closing choke about 3/4 and it still stalled out after a minute or2. [/QUOTE]
 
Just a thought, did you change to a vented gas cap or leave the line from the charcoal canister open. If not you could be creating a vacuum in the tank causing the loss of fuel flow to the carb.


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stalls during accelleration (23/23)
 11/15/09 11:13pm
dskopp
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My 1981 with the ECM and Q carb had almost the same symptoms.  Had the ECM replaced, did not fix problem.  Had the carb rebuilt.  She has been running great ever since.  I still have all original componants of the emmissions system.  She is stock, inside and out.

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