After months of troubleshooting my hot start problem I took my car to the Mazda dealership. They called me today and said that they suspect the fuel pump, or the check valve in the pump.

It seems that the car starts fine when the pressure is 34psi. Every time it didn't want to start, the fuel pressure was reading between 8-14psi. They did the leakdown test on the injectors and rails and it held perfect - but on the pump side it dropped off almost instantly (something that I had noticed but attributed to my home made fuel pressure gauge that leaked).

I'm just wondering if this means the whole pump is bad, or if there is a way just to replace the check valve? They said that the pump is $500, so any alternatives you guys could suggest would be great.

Thanks,
-Charlie

 

did they do a compression test? or is that already taken care of..

related:
my walbro fuel pump went out and the pressure dropped to like 8psi while it was idling and would barely start, so im guessing you're going to have to get a new pump. just my 2 cents

 

It might also be a leak inside the tank. It is pretty easy to remove the fuel pump, so it might be worth a look to see if there is anything wrong with the plumbing in there. It is kind of surprising how the pump is just pushed up inside a little metal hood with an o-ring and some plastic bits. That said, I don't really think leaks in this area are common with the stock pump setup (so it is probably better than it appears), but by appearances it doesn't seem like that great of a connection.

If you decide to replace the pump, you can get a Supra pump or another Denso pump that will be a perfect replacement for the stock pump for much less than $500. And again, it is quite easy to replace the pump, particularly if you use a Denso replacement (the stock pump is a Denso unit).

-Max

 

I agree with max...A supra pump is inexpensive and a nice addition if you plan on future mods.

I had a similar problem as you do when I installed the supra pump...the o-ring on the top of the pump broke and fuel leaked out of it. I would still get some pressure but no where near where it should be. I would take the pump out and check the o-ring to make sure it's not broken or damaged.

-Dan

 

Am I correct in assuming that the check valve that prevents pressure bleed off is built into the fuel pump? The factory service manual says to replace the fuel pump if pressure doesn't hold between the line to the rail and the pump.

-Charlie

 

Yes, the check valve is in the pump.

Or at least, there is no separate component that could server the purpose of a check valve between the pump and the fuel rails. I am not sure if there is an actual check valve in the pump, or if it just acts like a closed valve when the pump is stopped.

-Max