Hesitation under load - Team Camaro Tech
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post #1 of 20 (permalink) Old Apr 12th, 01, 03:40 PM Thread Starter
 
Join Date: Apr 2001
Location: Bedford,Nova Scotia, Canada
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Hi people. This is my first time posting. However I have been a reader for some time. Awesome resource for tech info.

Well here is my problem. When I accelerate up to say 3000RPM on average I get a hesitation from the engine. While the pedal is depressed half or beyond the RPM's dont't drop off from 3000 but they sure don't climb very fast either. If you let off the gas and drop back below 3000 it runs fine. In fact it runs perfect at idle and in any gear as long as you dont go over 3000 RPM.

Changed the cap, rotor, plugs, wires and fuel filter, module and capacitor and it made no difference to the problem.

It is the original fuel pump on a 305, not the high output 305.
The carb is the original Rochester Q jet 4 barrel and the distributor is original to.

Here is one of the weird things that happens through it all. Some times as you shift from 3 to 4 or 4 to 5 The rpm's drop off to zero and she dies. Pop the clutch and bang catches right away. Now if you keep your foot on the gas a little in the same situation it will keep the RPM's up without a problem, however let off the gas all together and bye bye it dies out. I think it might be the fuel pump myself but I would like some other opinions before I go and spend some money. The car has never seen a winter and it is killing me to drive it this way.

Any ideas would be greatly appreciated.

Thanks from 1983Z28
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post #2 of 20 (permalink) Old Apr 13th, 01, 05:48 AM
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I would look for a little trash in the carb
I had the same problem on a old truck I had.
Took the carb apart and cleaned out the nastys and it ran fine.
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post #3 of 20 (permalink) Old Apr 13th, 01, 01:01 PM
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I agree with blowncamaro.
Clean out that carb and reset the mixture with a vacume gauge.
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post #4 of 20 (permalink) Old Apr 13th, 01, 07:14 PM
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Check your vaccuum advance. Also, I had similar problems with blown head gasket. It would only open up and cause problems after the motor had run for a while. Also, check for a vaccuum leak. Could be a fuel blockage (fuel pump, filter, line, or carb). Really narrows it down, huh? Steve Laabs
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post #5 of 20 (permalink) Old Apr 16th, 01, 10:00 AM Thread Starter
 
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Location: Bedford,Nova Scotia, Canada
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Thanks guys for the tips. I'll give the carb and vacumn lines a shot and let you know.

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post #6 of 20 (permalink) Old May 2nd, 01, 12:37 PM Thread Starter
 
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Well I had the Carb rebuilt at a local Speed Shop and indeed there was some problem with the needles being ceased. I also changed the fuel pump, Distributor module and capacitor, cap coil and rotor, wires and checked all the vacumn lines. However I still have the same problem. Press the pedal lightly and she will accelerate slowly. Press it hard and she shudders like crazy. Also if you press the clutch in and hold it she will stall but only if you try to accellerate. Still stumped anybody got any other ideas?
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post #7 of 20 (permalink) Old May 2nd, 01, 01:06 PM
 
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Knowing some details regarding the driveline would help. Is this system computer controlled? I have seen the distributor at times give the same problems. It is possible for certain emission controls to give similar problems. Knowing details like model year, with or without emission controls will help me isolate certain possibilities. I am an engine performance expert on most domestic and many foreign models; my specialty is driveability. Questions can be e-mailed or will be responded to here. Ray
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post #8 of 20 (permalink) Old May 2nd, 01, 01:10 PM
 
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One thought here is the carb. Q-jets are notorious for the secondary metering rod cam dying, causing a severe lean out when the air valves open. You can test this without the engine running. Remove the air cleaner top, and while watching the metering rod hanger, manually open the air valves by hand. The secondary metering rod hanger should lift the rods, following the air valves. This is easy to overlook even during an overhaul. Ray
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post #9 of 20 (permalink) Old May 3rd, 01, 11:49 AM Thread Starter
 
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Hi Ray. Appreciate the reply any help is needed. The car is a 1983 305 regular not HO 4 barrel carburated - no computer control, no Air Conditioning, No electrical power options. I will try the test on the carb tonight to see if there is movement there.

Thanks again.
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post #10 of 20 (permalink) Old May 4th, 01, 03:11 PM
 
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Did you check your fuel lines for kinks?

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[This message has been edited by 86z28 (edited 05-04-2001).]
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post #11 of 20 (permalink) Old May 4th, 01, 03:50 PM
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I think RABarrett has the right idea. Take off the air cleaner and push down on the air valve the metering rod hanger should rise in the front as you open the valve.

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post #12 of 20 (permalink) Old May 5th, 01, 06:22 PM
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If you drove it for a while with the metering rods stuck you may have melted the catalytic converter, assuming you have one.
This would restrict the exhaust to the point where the engine would not rev up.
Stop by a muffler shop and get it tested.
Does the engine seem too quiet?
David

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[This message has been edited by davidpozzi (edited 05-05-2001).]
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post #13 of 20 (permalink) Old May 5th, 01, 08:10 PM Thread Starter
 
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Hi Guys.. Well we are certainly narrowing the area down. I tried the metering rods and they seem to move ok. The car has no catalytic converter so that is out and there seems to be a good flow of exhaust out the pipes. I am really stumped by this. At idle and even under really light acceleration she drives fine, accelerates slowly but it will accelerate. It is only when yout push the pedal down hard in any gear after you hit 3000 rpm that it hesitates and vibrates. There are no pops, snaps or backfires either just the hesitation and vibration. Crazy little problem. Keep the ideas coming. Thanks everyone.
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post #14 of 20 (permalink) Old May 6th, 01, 03:00 AM
 
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I would also check carefully the advance systems. Make sure both operate smoothly. Also check plug wires. This sounds similar to primary metering rods sticking. Try using a thin screw driver carefully placed into the bowl vent. The power piston should move freely up and dowm, following the screw driver. It is this piston that enriches the mixtures under loads. Ray
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post #15 of 20 (permalink) Old Aug 23rd, 01, 08:13 AM
 
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Had the same hesitation problem with my car.
Disconnected the vacuum advance and capped off the hose. the problem went away and I am still driving like that. Should probably change my diaphram on the distributer.
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