Real Fiero Tech

My 3.4 DOHC gradually lost power at my last track day and then I ran out of gas and/or the fuel pump died. As it was gradually losing the power the intake started sounding weird -- it was making a lot more noise. I'm not sure how much gas was left in the tank, but I added 5 gallons and it still wouldn't start. The paddock was pretty noisy so it was hard to tell for sure, but I don't think the pump was running. I assumed the fuel pump died and I burned some intake valves or something.

After I towed the car home, I pulled the fuel tank, replaced the fuel pump and filter, and put 3 gallons of gas in the tank. It started and ran, but was only running on a few cylinders and had no power. I swapped in my freshly cleaned and tested injectors (from Fuel Injector Clinic) and then it wouldn't start at all. As it turns out, all the injectors that were cleaned by Fuel Injector Clinic are completely stuck shut. After swapping fuel injectors back to a not-so-great spare set and replacing the spark plugs, it sounded like it was running on 6 cylinders again but at any reasonable throttle level it just crapped out. It was operating at maybe 30% power. The intake noise sounded weird also. Back to the burnt valve idea... we ran a compression check and all cylinders measure 150 to 160 psi. No problem there.

Next idea: catalytic converter melted?

I drove it around the block to get a baseline and then was going to pull off the exhaust to see if it made a difference. While pulling back up the street the engine died and acted like it was out of gas. Since I only had put 3 gallons in the tank, I thought maybe it was out of gas. Put 3 gallons in it and still won't start. I can hear the fuel pump running. With the pump running and a fuel pressure gauge attached to the rail it only gets up to about 5 psi. I pulled the fuel pressure regulator vacuum line and no fuel is coming out of it with the pump running, so the regulator diaphragm is not punctured.

Any ideas?

I can't remember if I replaced the pulsator with the short piece of fuel line that came with the pump, or just put the pulsator back in.

in tank leak, another bad pump, or a blockage somewhere. You could try disconnecting all the lines and blowing air through it. Listen and see if it sounds like there is a blockage. fuel filter installed in the correct orientation?

Five PSI at the rail tells the story. Did the Fuel Injector Clinic also clean your new fuel pump?

Forgot to mention I tested pressure at the rail while diagnosing the fuel injector issue and it was steady at ~40psi. I didn't ever get to test it under load though. After the car stopped running I haven't measured any significant pressure.

The pump is a brand new AC Delco EP381. The pump I replaced was also an EP381; it lasted about 8 years. The new pump still sounds fine. I can hear fuel flow.

Could the pressure regulator fail into full bypass?

Shaun41178(2) wrote:in tank leak, another bad pump, or a blockage somewhere. You could try disconnecting all the lines and blowing air through it. Listen and see if it sounds like there is a blockage. fuel filter installed in the correct orientation?

Filter is in the correct orientation.

Could be an in-tank leak. I hear fuel flowing back to the tank when I run the pump. Just can't tell if it's the return or the pressure side...

I'll try blocking the return line and running the pump.

Running the pump for longer than a few seconds with the return blocked may rupture the bypass diaphragm.

Disconnect the fuel return line and prime the fuel system. You should be able to hear the pitch of the pump noise change as the pump loads up loads up against the regulator and you should get fuel out of the return side of the fuel rail. Check the return line to make sure you can get air through it and into the tank (and out the filler neck... leave the gas cap off)

If you don't hear a change in the pump noise and/or don't get fuel out the return, pull the pressure line on the outlet side of the fuel filter and A) check the pressure line for a blockage between the filter and rail B) prime the system again to see if you get fuel out the filter.

Your pulsator or its replacement may be leaking inside the tank.

It's an in-tank (or filter) problem... still no pressure when I blocked the return, so I pulled the pressure line and it barely dribbles out while priming. Probably a broken / split fuel hose or pulsator.

Series8217 wrote:Probably a broken / split fuel hose or pulsator.

It was this.

Shitty, it's not a small amount of work to drop the tank on a fiero.

Say what? Its a 20 min job to remove.. 5 hose clamps a connector, 6 bolts, done. What car is easier?

Tanks can be a bit of a pain on the Fiero, those hoses always stick, and previous owners are good at orienting hose clamps in impossible positions. But comparable to other cars, they're easy.

Yeah, I don't think dropping a Fiero fuel tank is bad at all. Especially when compared to some other things.

Series post a pic of where it broke!

Series8217 wrote:Say what? Its a 20 min job to remove.. 5 hose clamps a connector, 6 bolts, done. What car is easier?

The FIRST time you drop it since the car came off the assembly line, it really sucks. After that it's not too bad.

It's certainly hella easier than a 3rd gen F-body tank, which requires dropping the rear axle. The same goes for the tank in my Girlfriend's C5 A6, with the caveat that that car has an access hatch to fuel pump replacement, we only had to drop the tank because something way worse was wrong. Most BMW's have fuel pump access hatches as well, apparently.

My E34 has that access hatch in the trunk also.

post a pic of where it broke!

Sorry, all I have is a crappy cell phone pic of the ruptured coupling hose:

Woops.

Yeah I just remember doing mine to install the LT1 fuel pump. The hoses were near impossible to remove from the tank.

Pretty much all my JDM cars have the access panels as well, way easier.

The C4 Vette is probably the easiest fuel pump to replace. Just remove the rectangular flip up fuel fill panel between the rear hatch glass and the rear bumper (4 bolts - I think). Then you have direct access to pull the pump... all while standing behind the car.