Horseradish

Hey guys. I’ve tried searching the forums for this issue, and while I’ve found some similar ones, I haven’t found anyone seeing the same symptoms as me. Here’s a breakdown of what’s happening.

I’ve been using this car as my daily since I bought it about 10 months ago. It had a bad fuel pump when I bought it and I fixed it that day. It’s driven fine ever since. But once temps crept up to triple digits a month or two ago, it began dying on my way home from work (around 4pm and 100+ degree weather). It makes it to work perfectly fine in the morning (around 4am and 70-80 degree weather). It drives great until the second it dies. No power loss, no surging, no delay in throttle response. The pump just shuts off. And won’t start until the car cools down. I’ve since installed a toggle switch to bypass all the electrical system to try to isolate the issue and it is still happening. The pump was replaced middle of last October, so I’m not confident that the fuel pump is bad, and believe a new fuel pump would just die in the heat as well. Do I need to find a way to insulate the tank from heat?

ShiftyCapone

iTrader: (7)

It sounds like vapor lock which I suppose can happen in extreme heat (not typical with fuel injection, but TBI is very low pressure). It is rare though since there should be enough flow going through the regulator and back through the return line. How did you verify that the pump stopped working? Does it not prime when hot? Can you not hear it run when cranking?

91banditt2

iTrader: (1)

Just throwing these out there, because of the pressures involved these are geared more towards a carb system.
Any fuel lines close to the exhaust manifolds/headers?
Condition fuel tank vent?
Severely dirty fuel filter?
Hot weather in stop-and-go traffic at higher altitudes?
​​​​​​​Is the cooling fan working to reduce ambient temps?

Horseradish

Shifty, I listened for my fuel pump when I turn the key to run, and when it cranks, and there is no sound from the pump.

Bandit, there aren't any fuel lines too close to the exhaust manifold, not sure on the vent, I'll have to check in the morning, I just replaced the fuel filter a week ago, It happens at random times during the hottest part of the day (it even occured within a minute of starting it yesterday, didn't even make it out of the parking lot). Cooling fan is working, my engine stays cool at about 200F even in the heat.

Schurkey

"Vapor lock" is, I suppose, possible. Of the top hundred potential causes, that would be about #87. Vapor lock is extremely unlikely when the pump is submerged in fuel, and essentially the entire system is pressurized. In the old days, most of the fuel plumbing was under partial vacuum (suction) because the pump was up front, bolted to the hot engine near the even-hotter exhaust manifold.

Connect a fuel pressure gauge, so that you're not guessing about having or not having fuel pressure.

If the pump doesn't prime at key-on, everything is suspect, from the ECM to the battery, the fuel pump relay, all the fuel-pump power supply wiring back to the gas tank, and the ground wires from pump to chassis to battery negative.

Do you have power at the fuel pump fuse when the ignition is on, but the pump fails to run?

Does the engine have spark after the fuel pump quits? No spark, no fuel pump is often a failure within the distributor--pickup coil or (less likely) the ignition module. But if that were the only problem, the pump should still prime.

If the wire harness were good, and the fuel pump fuse has power, the fuel pump should turn on as soon as the engine cranks long enough to build a few PSI of oil pressure.

Wild Guess with little evidence: Your car has multiple failures. The oil-pressure switch/fuel pump bypass circuit isn't working reliably, AND the ECM--Fuel Pump Relay circuit has a failure (which could be the ECM, the fuel pump relay, and/or the wire harness that connects them.) The engine runs off of the fuel pump relay when cool, when that fails, (from heat?) the oil-pressure bypass system does not keep the fuel pump running.

A plain ol' wire harness problem--loose connections, corrosion, etc. would probably not be affected by temperature change as this seems to be. Possible, not likely.

Horseradish

I have already replaced the ECM for this issue, the relay was the first thing I replaced, I will check if I have power at the rear connector tomorrow if the issue persists. I do have spark when cranking. The bypass that I set up just straight applies power to the connector behind the rear seats, in an attempt to narrow down the issue as much as possible. Even with that, the fuel pump doesn't turn on anymore after it dies in the hot weather.

DIGGLER

iTrader: (1)

back in the day i worked on a 4th gen that had fueling issues in the heat. i had driven the car for a bit, and when i got out i heard what sounded like bubbling in the fuel tank. i started screwing the gas cap off and that sucker started whistling like a tea kettle! At the time it scared me to death. Allegedly a new fuel pump fixed it, but i cant say for sure.
What kind/type of fuel pump did you install?

91banditt2

iTrader: (1)

With the gas cap hissing couldn't that be an indicator of a bad gas tank vent valve not allowing pressure out? Do 4th gens use a vented gas cap?

91banditt2

iTrader: (1)

Horseradish, have you looked into your vent valve?

Fuel Tank Venting (tanksinc.com)

DIGGLER

iTrader: (1)

i believe at that point the car was stock on the fuel system aside from a 255 pump, but it could have had a vent malfunction or something. the fuel was definitely boiling in the tank. with the car off it was very easy to hear.

Horseradish

Diggler, I don’t remember what brand I bought for the fuel pump last year. It wasn’t a high end one though so it could’ve just gone out on me already.
Bandit, I have not looked into the tank venting yet. I’ll drop the tank and look into the venting on my day off tomorrow.
Since I’ll have the tank down, might as well cover my bases and replace the pump so I don’t have to drop it twice.

RBob

iTrader: (1)

Odds are the fuel pump is bad.

Tank pressure venting is via the CCP system, not the tank mushroom valve. And it is supposed to hold some pressure.

RBob.

Horseradish

The delivery for the new pump got delayed so I’ll be waiting until Wednesday to change it out. I am becoming more and more convinced that it is just a shotty fuel pump I installed and the heat is making it overheat easier and fail.

91banditt2

iTrader: (1)

Is there anything on the market that would provide thermal insulation?
There are these, but they're for sound dampening, may cause it heat up faster?
Walbro 122-332 Walbro Fuel Pump Insulator Sleeves | Summit Racing
Have you notice if this happens when the tank is at a certain fuel level? Full vs. 1/4 tank?

dlinger

iTrader: (4)

Did you try replacing the fuel filter? I know it's my go to question, but its inexpensive start to troubleshooting. I was told most mechanics will always start with that, even if they are told it was just replaced. In my case, it cured my problem twice. But then my tank was rusting out. It would run good in morning also, then die on way home.

Horseradish

It happens no matter the level. It happened when it was under half, down to a quarter, as well as 15 minutes after filling the tank.

Horseradish

I did replace the fuel filter. It was the first thing I did. And the next day, the car died on my way home.