Fuel tank vapor lock issue? (Page 1/1)
fierobear AUG 29, 01:47 PM
I was driving my GT last weekend. The weather was hot, and we did a club drive up a mountain road. As I got back home, which was about 50 miles away from our destination, I noticed a sound when I pulled into a stoplight that was like wrrrr-wrrrr-wrrrr. At first I thought it might be the AC compressor. But then listening more closely, it sounded like it was coming from the fuel tank, like the fuel pump is having trouble sucking fuel. I am wondering if I’m having a paper for back pressure issue in the fuel tank?

I was looking at the factory service manual thinking that it might be a problem with the vapor canister. There is a vacuum operated valve on top, and I trace the lines but according to the manual it says that the ECM can command vacuum on this. I don’t see any type of solenoid or any other device where the ECM can control the vacuum going to evaporative canister valve. Does anyone have any idea how the ECM commands vacuum here? Is there something else I should be checking for back pressure in the fuel tank?
theogre AUG 29, 03:12 PM
The EVAP can is very dump, not connected to ECM, and won't cause your "problem."
Is run by engine vacuum and again won't cause your "problem" even if vac valve is open or close all the time. (But crap valve can cause a vac leak and maybe raise the idle etc.)
Tank vent line isn't block at any time even in the EVAP can unless maybe the EVAP can bottom is plugged w/ crap or some fool crushed the line.

Pump in Tank can make noise or not as fuel move mostly front to back in Fiero and at different fill level from full to empty and back.

Connect fuel pressure gauge to engine and what pressure and different RPM are stable at that RPM.

EVAP plumbing in on label on inside of rear deck lid.

------------------
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fierobear AUG 29, 03:37 PM
I’m sorry, I forgot to note that the fuel pump is very new (couple thousand miles), and this is the first time I’ve had this issue at least since I replaced the pump.
Gall757 AUG 29, 06:01 PM

quote
Originally posted by fierobear:

I’m sorry, I forgot to note that the fuel pump is very new (couple thousand miles), and this is the first time I’ve had this issue at least since I replaced the pump.



The fuel pump got some air. It may be a one-time thing or maybe the pickup tube is higher than it should be, or you were nearly out of fuel. I would wait until it happens again before I decided I had a problem, (the lazy solution)..

Raydar AUG 29, 06:42 PM
One of our late club members had an issue where his car was starving and stalling. It was due to a buildup of vacuum in the tank, that the fuel pump could not overcome.
I forget what the fix was, but it seems like he replaced the vacuum canister.

So yeah... it's "a thing".
Patrick AUG 29, 06:55 PM

quote
Originally posted by fierobear:

I noticed a sound when I pulled into a stoplight that was like wrrrr-wrrrr-wrrrr... I am wondering if I’m having a paper for back pressure issue in the fuel tank?




quote
Originally posted by Raydar:

One of our late club members had an issue where his car was starving and stalling. It was due to a buildup of vacuum in the tank, that the fuel pump could not overcome.



I suppose the easiest way to check for a potential vacuum problem in the gas tank would be to open the gas cap the next time the "wrrrr-wrrrr-wrrrr" is heard, and see if it stops.

[This message has been edited by Patrick (edited 08-29-2019).]

fierobear AUG 30, 01:44 PM

quote
Originally posted by Patrick:

I suppose the easiest way to check for a potential vacuum problem in the gas tank would be to open the gas cap the next time the "wrrrr-wrrrr-wrrrr" is heard, and see if it stops.




Good idea, will do. I did that, but it was the next day. I’m assuming any pressure would have been equilized.

Is there a source for new vapor canisters and vacuum valves?
fierofool AUG 30, 08:05 PM

quote
Originally posted by Patrick:

I suppose the easiest way to check for a potential vacuum problem in the gas tank would be to open the gas cap the next time the "wrrrr-wrrrr-wrrrr" is heard, and see if it stops.




That was what the former club member that Raydar referred to would do. And it did turn out to be the vacuum canister was full of something. He said he blew it with compressed air and some kind of muck came out of it so he replaed it.

phonedawgz SEP 01, 09:20 PM
On the 2.8 there are two lines to the EVAP purge control valve. One is manifold vacuum. The other is ported vacuum from the throttle body. The port receives vacuum when the throttle he held past an off-idle position. When the throttle is held open past idle, that control line will have vacuum on it. And that will trip the EVAP purge control valve to allow full manifold vacuum to purge the EVAP cansiter.