VolVette

My '75 with a ZZ4 crate engine (less than 20K miles) and original automobile tranny is dying on me. When I am in drive maintaining about 2000 RPM's it does not stall but feels like it is surging. When I stopped a stoplight, while still in park, the engine will die. But when in park or neutral, it will not die but does runs roughly. When starting from stop or accelerating, it bogs or will not accelerate and then hits me with a quick powerful surge. This is a brand new problem and I drive my Vette almost daily. After getting home from the drive when this began I smelled something that kind of made me think something was getting to the exhaust pipes and was burning. I checked that thoroughly and found nothing. I also checked all my fluides, water good, oil good, tranny fluid low. I put new transmission fluid in, let it run for a few minutes, then put it back into drive with no improvement- it died. I have also considered that the quick change in weather may be adding to the problem but I don't know.

Please help me troubleshoot this problem. My guess would be poor timing or detonation, poorly calibrated carburetor, but I really don't know?

I appreciate any and all advice. Thank you.

Cheers,
Stephen :cry

daniel77350

perhaps its a carb problem. Sounds almost like the car isn't getting enough fuel. But im defanitly no expert. Also check the vacuum lines, maybe a vacuum leak...??

Daniel

Rocket Ron

Wild guess....Check for a burned through vaccume line.

VolVette

I went back outside and tried to troubleshoot more. Here is what happened:

Started fine.

Idled roughly (900 RPM) when given gas, bogged and sluggishly increased RPM's

Put in Drive, and RPM's dropped to 400-500, and was ready to die. I couldn't bear to listen to it, so I put it back in Park.

It recovered to 900 RPM's and ran a bit rough.

Please any help is greatly appreciated.

Thank you.

jeffnles1

Check your fuel filter. Same thing happened to me. Just all of a sudden she started acting like you describe. It seemed like fuel. Surging, quitting in idle, rough running, etc. I put a new fuel filter in and it solved the problem.

It's an inexpensive thing to try before digging through all the other stuff.

Jeff

VolVette

JeffnLes1,

Interesing suggestion because I just replaced my fuel filter about 2 weeks ago. I read in my Chilton's and Hayne's manual about checking this as well. I just looked at it about 5 mins ago and it looked to be ok. I will check it again.

Thanks for your help and please everyone keep them coming!

jeffnles1

Do you have fuel pressure at idle? could be fuel pump or an obstruction in the line. Given the way it's acting could be vacuum or fuel and my guess is it's not getting enough gas. You could check the vacuum lines to be sure none of them came off or has a hole in it. One way to check is to take a piece of hose and use it as a "stethescope" to listen to the vacuum lines to see if you hear a "hissing" sound which would indicate vacuum leak in the line.

Do you have pcv, egr and the other fun emissions stuff? could be a leak there.

If you have a fuel filter in the carb (i.e. Rochester Qjet) is it in right and is the spring in the right place?

Good luck with it.

Jeff

VolVette

Jeff,

Thank you for your continued help.

The fuel pump is something that I had not considered. I am uncertain how to diagnose that problem but I would suspect that it may not be that because it idles sufficiently.

I keep going back to the possibility of a bad vacuum line somewhere... Hmm...

I have an external fuel filter on a Holley 650CFM carb.

Thanks again for your help, and as always keep it coming!

Cheers,

Stephen

VolVette

It's just a bit past 1:00AM EST and it's time for me to call it quits and give up for the night... :cry

But just before coming back inside, I was listening for any noises and heard a peculiar hissing coming from what sounded to be inside the barrels of my carburetor? There could be a leak, you think?

Thanks for all of your help and diagnosis.

Stephen

vettfixr

I had the same type of problem in my 74 and it was caused by a bad load of gas that was clogging the filter sock in the tank. Get a flashlight and take a look in the tank to see if there is crud floating around in there. If there is there's a good chance that the fuel pump can't draw enough gas into the line. Also look for any damage to the fuel lines. It's possible that a rock or something else kinked a line. If that checks out get a fuel pump guage and see how much pressure the pump is putting out. It should be about 5 to 8 pounds (I think). One other place to check is the vacuum advance. If you have a ruptured diaphram you will have a vacuum leak which would give you a bad idle and no advance which would give you dead spots in acceleration. Just disconnect the line at the vacuum unit and plug it. If the problem goes away test the vacuum unit with a pump to see if it holds vacuum. If none of this is the cause you may have an internal problem with the carb. Good luck. :seeya

VolVette

I woke this morning after about 5 hours of rest from tinkering/troubleshooting. I started my Vette up, let it run for 2-3 minutes, and then shifted to Drive... It died. So, no luck with the problem being circumstantial and fixing itself.

But I did notice that there was an unusual exhaust stain on the concrete floor. I doubt this has anything to do with the problem but it may. Immediately behind the muffler (Flowmaster) where the weld was made, there must have been an exhaust leak causing black soot to collect on pavement. it is just another thing to make this problem interesting, isn't it?

As always, I appreciate your help.

VolVette

Vettfixr,

Thank you for your suggestions. May I ask a couple questions?

If something was preventing my fuel system from fuctioning correctly (be it debris in the line, fuel pump, etc.) wouldn't that also prevent me from idling? My idle is rough but it will not die as it does when I put it in gear.

Would a ruptured diaphram also cause it to completely die as well as poor accelaration and idling?

Tom454

My first guess(s) would be a vacuum leak or water in the gas.
The best way to test for a hard to find vacuum leak is to cap off ALL vacuum ports on the intake & carb, and then run the engine if it runs smoother and stops acting up, then you know it's vacuum and can go from there. For water in the gas, that is hard to see unless the tank is nearly empty. There is an area near the tube/sock in the tank where about 1 quart of water can sit, just barely out of reach of the pickup tube. Slight movement of the car agitates the pool of water and some of it gets drawn into the tube, and the car surges and stalls. When enough gets into the carb, a pool of water then sits in the fuel bowls just below the jets..... same result.... when it moves, it gets drawn into the passages. There are several other malfunctions that can cause your symptoms. For example, defective internal carb gaskets. I would start by eliminating the vacuum & water, and then go on to the more difficult possibilities.

VolVette

Tom,

I will look into your suggestions. I am not sure if this helps, but my Vette shuts off even when it is not moving. What I mean is when I am sitting in my garage, ready to back out, I put it in drive or reverse and it shuts off before moving. So, I am uncertain how much the fuel/water could slosh around? But there is always the chance that the fuel is poor and has so much water in it that motion does little to agitate the problem.

Thanks again. I will certainly check your advise.

Any other ideas?

Mayo_007

Check the vacuum line from the rear of the intake to the transmission. Before I disassembled my car, my line kept disconnecting itself between trans and intake and ran horrible also. Just a thought.

73Ken73

Have you set the float levels on the carburator. Have someone look into the carb as the car stalls. See if the carb is flooding.

vettfixr

Hi Volvette
Sorry to take so long to answer but I had to wait until I got home to log on again. the synmptoms I had were that the car would idle fine but as soon as I took it up to 2000 rpm it would start to choke. If I got off the gas fast enough it would go back to an idle. I had to drive home for about 2 miles in second gear just above idle. That was a fun trip. What happens is that the sock allows some gas to pass through but not enough to support any kind of rpm. My problem was a load of crud from a bad gas pump. I had to vacuum it out of the tank with a bottle and a vacuum pump hooked up to a length of tubing that I could fish into the gas tank. It worked but took a while. I ended up replacing the sock in the tank because it was fouled with whatever sludge was in the tank and never really worked well again. I also went through the fuel system and flushed the lines and replaced the filter in the carb. As far as having a ruptured diaphram I'm pretty sure that you wouldn't be getting any gas at all to the carb under those conditions. I may be wrong but I don't think the pump would draw. Hope this helps.

VolVette

Thank all of you for your help! I actually like having little challenges like this so that I can learn so much from you resident Corvette gurus.

The problem is now fixed. And just as many, if not all, suspected, it was a vacuum problem. I tried and checked seemingly everything last night but I overlooked or carelessly tested the vacuum hose going from the Carb to the Vacuum advance. The diaphram in the vacuum advance held a vacuum well but the 12" hose was faulty (not by eyesight) and did would not hold a vacuum. So... My problem was luckily a $0.20 piece of hose.

Thank you again for all of your help.

Cheers,

Stephen