Hey everyone,

My car is an 84 T/A with 350, factory CC Qjet and a retro-fitted in-tank electric pump (Wahlboro 255lph). I was driving my car back to Salt Lake City from Los Angeles when out of nowhere it the cruise seemed to stick, the engine tone changed, leveled out, sputtered, then slowly dropped RPM until it died. Giving it gas while it was dying would cause the rpm's to stutter and try to go up but ultimately die. I coasted to the side of the road and sat there baffled. I could crank the car over, it would sputtter, start, run rough for a few moments then die even with the throttle pushed down.

I checked to make sure the fuel pump was still running and it was. However, my fuel pressure gauge on my fuel regulator wouldn't read (I've had this problem with it for some time).

I let the engine fan run (it was hot enough that it came on with the key to "on" position) and after about 5 min it started and stayed running through it didn't want to stay running at idle very well. 400-500rpm.

About 300 miles later it did it again. I would try and start it immediately and it would fire up, I could rev it up to about 3000 rpm and hold it, but it would die. Rinse/repeat.

Again, after leaving it for a while, it would start.

My temp gauge hovered around 220* on the gauge, little more, ambient temp was 95-100*.

The only conclusion that I could come up with was vapor lock but with a pusher in-tank pump I find this unlikely. Could the regulator be getting head-soaked and causing vapor lock or fuel issues? Could it be something else?

Any thoughts or ideas are welcome because I was almost stranded twice and that's a terrible feeling.

 

Almost got stranded 60 miles from home about two weeks ago. My '91 Firebird V6 3.1 did the same thing. Got it started and limped home at 55mph with the AC off. Did the FPR test and after about 20 seconds fuel began coming out of the vacuum port indicating a damaged diaphragm. Changed that and tried it again. Same result. Ohmd the injectors and found two bad. That was my experience but the vehicle symptoms were very similar. Good luck.

 

I have a 92 305tbi was doing the same thing. people kept saying the same thing "sounds like vapor lock, but it cant be bc it has an electric pump"... well im here to tell everyone that's wrong. reason being yes its an electric pump but at what fuel pressure? its not no 60psi like fi cars, its 13psi. just like what a mechanical pump would put out.

so a co-worker, old school car guy, asked me can I fill my car up holding the gas pump handle up all the way? I said no. he said its vapor lock, leave your gas cap off. so I did car hasn't shut off once since then, even in hot weather. hundreds of dollars spent replacing censors and tune-up and the problem was vapor locking.

on my tank (not sure of yours) theres a purge valve in front of the tank (discontenued part ofc) but mine was super dirty so I cleaned it (apparently these things don't die, only get dirty. found the cleaning tip from someone else on the board) and so far ive been able to drive fine, with the gas cap on.

 

Im not so sure I buy that logic. Carb cars dont have consistent pressure through the whole fuel system which leads to vapor lock, even if pressures were the same (they're not). There's a purge valve the computer controls and a tank vent which you cleaned. That may well be problematic but Im not sure I'd call that vapor lock. That would just give the pump a hard time trying to get fuel out of the tank. Similar symptoms but the mechanism is different. You may want to try leaving the gas cap off to see if that helps, though, it's a good idea and a good thing to rule out, regardless of whether you call it vapor lock.

You need to devise a way to rule out fuel or spark issues. I would take some carb cleaner and experiment to see if that cures it. Otherwise I would imagine you may still be having vapor lock issues, but between your regulator and your carb. I have a similar problem between my regulator and carb during the summer after I turn the car off and the line depressurizes. It's hot enough that the fuel will boil off in the line. You may have fuel pressure that's very low after the regulator, perhaps low enough to allow vapor lock type symptoms. I dont think you're having vapor lock between the pump and the regulator unless your pump isnt able to draw in fuel due to there not being any way to vent in new air to the fuel tank like darkmj16 mentioned.

 

Vapor lock is highly unlikely with your system and the symptoms you posted don't support it. Your regulator is circulating fuel through the return system and will provide constant pressure up to the carb inlet. A few ideas:

Check your feed line from regulator to carb for possible heat soak conditions. Fuel could get hot enough in this line to boil once it enters the lower pressure of the carb float bowl.

An issue related to the tank not venting could starve the pump and carb. If this happens the carb will be dry or near empty. You probably won't see a good fuel squirt from the booster pump into the primary throat.

Don't discount an ignition issue. Failing components will act up when hot and spark could be erratic. How new is the distributor?

 

I have my factory Dizzy. the cap, rotor, plugs and plug wires are a little more than a year old, all MSD. I also have a newish module (three years old). I've been thinking of getting a D.U.I. rebuilt unit, maybe this is the time to do it?

The feed line from regulator to carb is long, I'm using steel braded tubing but it's 3-ft long from regulator to carb so I've got it coiled around the shock tower before going to the carb. Also, the regulator is bolted to the shock tower mount so it's "above" the headers on the passenger side, almost directly above where the stock fuel lines end. I don't really know of a better place to put it or better way way to route it because even if I come strait out of the regulator and to the carb I'm going over top of the header area. I've also heard the Mallory Regulators can get funny when they get hot, something I read here on the boards if I recall correctly.

 

How do I fix the fuel pressure between the regulator and carb? My in-tank pump is cranking around 40 psi, but with the regulator and return line, I've got it set to 5psi, though the mallory unit I'm using is wierd. I get one PSI reading with the car off but in "run" (pump wired to ignition power), then it changes when the car is s tarted,usually dropping several PSI.

 

Your pressure reading after the regulator will change with the engine running as the needle opens allowing fuel to flow into the bowl. Higher/steady pressure with it closed.

 

Ok, so when I set the pressure for the carb, I'll want to use the "running" pressure?

Any thoughts on a regulator? I'm running the Mallory right now, but I've also been looking at a Holley return regulator. Do you have any preference?

 

You're likely fine with the psi set to 5 with the needle closed. Didn't have any starvation issues did you?

Mallory should be fine. I've used one before. Don't have any experience with the Holley.

Carry a small container of gas with you. When it does it again, add some gas. If it starts up with gas added, it's a no-fuel issue.

 

It's only done it on the freeway after several hours of driving, but I have experienced a fall off whenI hammer on the gas from a stop. When the car hits 4000 RPM or so it acts like it wants to stall out, but if I take my foot off the gas for a moment it'll catch up and run the rest of the way to 6000rpm.

Other than that, I can't think of any "starvation" issues or anything that seemed like starvation.