Fuel Pump Runs But Sometimes Makes No Pressure

Hello-

I'm having a problem with my 1-month old Autozone fuel pump in my 2000 Bravada. The pump runs when the key is turned to on/off (noisy too), but sometimes makes no pressure, resulting in no start. After cycling it a few times, it eventually makes good pressure and the truck starts and runs fine. There has been no stalling and no related codes.

Fuel pressure (or lack thereof) confirmed by a gauge routed out under the hood and up against the windshield, so I can watch it.

Fuel filter was replaced with the pump.

Is this just a bad pump, or could there be something preventing pressure from building? The pump is definitely running - the noise is unmistakable.

Thanks.

Good diagnosis, sounds like a bad pump to me too. Did you put a Delco in it?
Present your info to the parts store manager to secure some warranty and you might goose him for some labor consideration...Grooms Engines in Tennessee gives very good labor consideration for defective engine assemblies(a rare event).

yes on fuel pump i believe that's why there life time waranty any way as long as you own the car.

Unfortunately this is an autozone pump (not a delco) that I installed myself. Unlikely I'll get anything more from the parts store than a replacement pump.

Sure am getting tired of dropping this tank.

Taking the spare tire out gets you more room and bunji cords holds the tank so you can use both hands disconnecting the lines & electrics (thanks VMag's Jim in Phoenix).
Don't forget proper placed jack stands to hold up your Bravada safely.

OK, here's a big update.

First off, this is a 2000 Bravada, if that isn't clear from my username.

I just put her up on the lift and started poking around. Had trouble starting, so moved to relieve the fuel pressure at the tank, and got a BIG GUSH of gas under pressure - way more than I expected (from prior experience) when disconnecting the fuel send line at the pump.

Started thinking that the problem could be at the filter, so I replaced the filter. No change. No start. Same gushing fuel. Finally got her started, let it run for a bit, then shutdown and pulled the fuel line... much less fuel at much lower pressure.

During all of this the fuel pressure gauge on the rail never went above about 60. Putting heads together at the garage came up with only one possible diagnosis:

The fuel pressure test port must be on the RETURN side of the regulator. The regulator is sticking closed, causing the send side of the pump to create very high pressure in the line but nothing at the injectors, and no change at the gauge. The return line keeps its pressure because of the check valve in the pump.

Once stopped, the regulator closes (it's vacume operated). Sometimes, when it operates properly, the regulator opens up and the truck runs fine. Other times it stays closed, the pump runs anyway, and very high pressure builds. During these times the pump whines loudly (note my first post where I talk about the noise). But when the truck starts and is idling, the pump is quiet.

So, I need a new regulator.

Right?

I'm in the manual and see the pressure test port is on the supply line.
The pressure spec is 60 to 66 psi.
So we're looking at a no pump run event. The fuel pump relay is in the glove box on a '97 and can be swapped with the daytime running light relay and the other one...maybe a horn relay.
If you have fuel pressure in spec when you try to start the motor, your fueling should be ok.

So we're looking at a no pump run event.

The pump is running, there is no doubt about it. I can hear the pump running. It also overpressurizes the line, as explained above.

I tried a new pump relay, no change. I tried no relay, no pump run (obviously).

The line will have pressure, and the pump will run, but a pressure test gauge won't move. I will cycle the key on an off, cycling the pump on and off, until the needle on the gauge jumps - then the truck will start.

Once I get the truck started, it runs fine. Never a stall, never a hiccup.

Today I will pop the plenum and check out the regulator.

Well, the regulator was definately leaking - lots of washing below it. So, that was a useful replacement.

However, with the pipe kit removed (the fuel rail), I activated the fuel pump. While I heard it running, no fuel flowed from the lines. I cycled the pump a few times with no luck (as usually happens when it wont start).

I had an assistant take my place and cycle the pump while I got under the vehicle and wiggled the lines exiting the pump. The pump noise changed and fuel began flowing. It then flowed normally.

I reassembled the engine and tried it again - it started without issue. We'll see how long that lasts.

The lines from the pump are not kinked or damaged. I suspect instead some type of blockage between the pump and the rail - perhaps a piece of debris that got caught at a connection, sometimes turning and blocking the fuel flow. Hopefully I flushed it out when the rail was removed.

If that fails, my next option is to put a gauge on the fuel line on the pump side of the filter (since I still believe that the pump is generating pressure but that it is somehow blocked).

I don't believe in changing the fuel filter until running at least a half tank of fuel after a pump change. The 2000 has a “well” around the fuel pump to hold fuel around the pump to act as coolant. This “well” also collects a lot of heavier than gas contaminants. Dropping the tank stirs up a lot of sediment and other contaminants that can cause the problems that your Bravada has exhibited.

I replaced the filter with the pump, and then again a couple of days ago. No effect.

Sometimes the impellar on the lift pump of a Dodge w/Cummins diesel will slip on the pump shaft. You hear the pump run but get no squirt.
Have you put a new Delco pump on yet?

No, it's a non-delco aftermarket pump.

Problem recurred this morning. I removed the fuel send line from the pump and cycled it - noise but no fuel. Cycled a few more times and got fuel.

So the problem is definately in the pump.

Really getting sick of dropping this tank...

Well, still haven't dropped the tank (garage has been closed and the weather too bad to work in the drive), but I have some new ideas about the issue.

First, the pump is running but not moving any fuel. However, spoke to a GM tech today who says it should only run when the key is turned forward, not when the key is turned back (to off). Strange, I thought, since to my memory it's always run a second time when turning to off. Anyway, his thought: crossed wires in the harness causing the pump to run wrong.

Also, it's having more trouble starting. This afternoon I nearly killed the battery trying to get pressure (cycle pump on and off, occasionally try to start the vehicle). However, when it did start pumping fuel the pump went from whining (and putting out no pressure) to groaning (and putting out good pressure).

I'd think that the intake is somehow clogged, but this doesn't explain why the pump has never failed while the vehicle is running. In fact, once started it runs great...

Hopefully I'll get the tank dropped tomorrow (I'll check the harness too).

New pump, no problem.

In its last moments, the old pump started pumping consistently at slightly reduced presure (remember, it always ran), but wouldn't hold any pressure once it stopped. This says to me that the problem was with the impeller - perhaps it was siezed, allowing the motor to run without turning the impeller until it broke itself free, and ultimately something broke allowing the impeller to turn freely but permitting leak-down.

BTW, I tested the leak down by blocking the return line at the pump, confirming that the problem was not the recently-replaced fuel pressure regulator.

Anyway, hopefully this morning was the last time I'll drop the tank. Thanks to those who put in their $0.02!

You have experienced a VERY common problem that the Airtex pumps have. There is a check valve built into the pump output that doesn't operate correctly, poor design I suppose. The valve retains pressure in the line after the engine is shut off, to reduce prime up time on the next start. (You are correct, the pump is supposed to run briefly after the key is shut off for the same reason.) I have seen this happen on countless Airtex pumps. Don't be surprised if it happens again, like I said, VERY common problem. I recall one vehicle in the shop, we went through 3 Airtex pumps in a row...all bad, same problem. Vehicle never left the shop until we installed a Delco pump. Needless to say, we don't use Airtex pumps any more. The first sentence in your first post was a dead give away to me.

FYI, in the future... Blocking the return line can do permanent damage to the fuel pressure regulator if pressure is allowed to rise above 75psi.

Glad you figured it out and got her going.