Every once in a while, if I floor the accelerator, I'll lose all power and my car feels like it is going to stall. As soon as I let up on the gas, it's fine again. Any ideas? Thanks.

 

Does this happen only occasionally, or can you make it happen every time you are, for instance, going fast on the highway?

If only occasional, I would consider a deteriorated fuel pickup sock and debris in the gas tank, though an electrical problem, like a bare spot on the points wire, is not out of the question.

If you can reliably reproduce it under high power, then I'd look more toward the fuel pump, fuel filter, or porous fuel lines.

- Eric

 

It only happens once in a while, usually when I'm pulling out into traffic and the throttle is all the way to the floor.

 

Does it have a q-jet on it? Possible vacuum leak at the base plate, maybe a weak accelerator pump plunger.

 

It does have the Qjet carb. Are there any simple tests to conduct to find the source? This is not my area of expertise. Thanks.

 

The first thing you have to do is to figure out whether you can reproduce this problem reliably.

If so, then a base gasket leak or bad accelerator pump is at least a possibility.
If not, then you have to look to things that are intermittent conditions.

If it seem like this has happened frequently in one particular place, or under specific circumstances, you need to go back there and see whether you can make it do this every time.

- Eric

 

Yes, x2 on above. I was using my standard flow chart diagnostic system.
1. Open hood.
2. Do you see a Q-jet?
3. If "yes", problem solved. If "no", look at everything else., lol!
Try taking it to a safe area and tromping on it a few times. If it falls on its face more than a few times, try "pumping" the accelerator up to RPM's.


Things that would lead me to go towards the carb route would be excessive gas staining around the accelerator pump pin/linkage, and loose/worn throttle plate bushings. If you grab the linkage and can "woller" it a lot, it could be a contributing issue.


In reality it could be a million different things, it just seems the Q-jet has been the weak link in my past experience. They always told me that you couldn't beat a well tuned Q-jet, but finding the right person can be tricky.

 

Easy check for accelerator pump. After driving, shut the car off, remove the air cleaner. Look down the primaries. Pump the accelerator once to full throttle. You should see 2 steady streams of fuel spaying down the throats.

 

Seems like its running out of fuel, restricted fuel delivery or perhaps crb float level too low.

 

My money is on the accelerator pump.

 

It sounds like your saying it accelerates from a stop ok; and as you lay into the throttle it starts losing power to the point it almost stalls. If so that rules out the accel pump.This is indicative of poor fuel delivery. A way to check for this is to take the fuel line off the carb, get a clear glass bottle, put a piece of hose over the fuel line and point it into the bottle. Have someone start the engine and watch the fuel flow into the bottle, 1 pint in about 20 seconds is acceptable fuel flow. You can also check the bottle of fuel for contaminates. If you have a vacuum gauge handy they will usually work as a low press. Psi gauge, fuel pressure should be 3 to 6 psi. If you find that there is fuel contamination (debris in the fuel sample). You probably have a fuel pickup sock in the tank plugging up. When you shut the engine off a lot of the debris will fall off of the sock until it slowly sucks it back up again and you start losing fuel flow again, that is why it is intermittent.

 

As always, much appreciation for everyone's input. Now I have some avenues to venture down. Cheers!

 

I cured a similar problem by tightening the secondary air valve tension spring on my Q-jet. It was opening up too fast under WOT, causing a lean condition and stall. This is extremely easy to test.

 

I would go with Seffs suggestion, if the air valve flops open the engine will bog down bigtime and feel like it's going to stall out. The lower the engine RPM is when the gas pedal gets floored, the worse the problem will be...... If the RPM is high enough when you floor it, the problem lessens.....

 

Please provide the year, model, engine and ignition system being used.

If it is an original HEI distributor it could be caused by a failing pickup coil in the distributor; although, the fuel related advice given by others is more likely the problem. Temporarily disconnecting the vacuum advance to see if the problem goes away will tell if the pick up coil wires are starting to break. If the problem stops the pick up coil is failing.

Good luck!

 

Just finished a 350 mile round trip road trip....I let off gas for a second and then re applied....it felt like the car ran out of gas. I let off pedal and slowly depress pedal and I am fine. Scares the $%^& when it happens especially on empty county roads.
The same happens sometimes during a hard take off from a complete stop. During the trip it ran w/o an issue but for the 'cough'. Sooooo frustrating. I feel your pain!!!!!

 

I did not read everything posted so maybe this was said, Likely running out of gas. Float wrong, Pickup in tank, Restriction in line... I myself have had the very same thing on two differant cars and both times it was the fuel pump getting weak. New pump fixed it both times.

 

In the case of NavVet above, THAT sounds like an accelerator pump.

- Eric

 

After reading everyone's posts and some self research, this seems the best starting point. Thanks again to all.

 

Check youtube for how to adjust the QJet secondaries spring. Easier to see than explain sometimes. There is a little hex set screw underneath the adjusting screw holding it in place. Does not take much adjustment to make a difference. Mark the exact screw position on the carb body with a pencil before changing anything so you can go back to where you started if needed.

 

MDchanic......oh you were right on!!!! Big differance. Thanks a ton.

 

You're welcome.

- Eric

 

I was going to suggest perhaps the link from the vacuum break diaphragm to the secondary air valve was left off, or the VBD perhaps has failed, and is allowing the secondary air valve to open too quickly. Easy to check also.

 

I had a similar problem. Turned out to be the fuel line from the tank to the pump. The old line had a leak and was replaced with a long rubber line. Once the new long rubber line was replaced with metal, the problem was gone.