98 ls1 fuel pressure question

**sjd73ss** · 07-27-2010, 05:42 PM

Ive been going nuts my car has been running like a 4 cylinder and I think Ive finally figured it out but want to know what you guys think.

Ive been told that low fuel pressure will bring up oxygen sensor and catalytic failure codes which I have on all 4 sensors and both cats. I thought it was grounds and they have been all cleaned. I thought it was crack sensor because I have no RPM's showing on my scanner when the car is hooked up and running? Changed it and it still does the same thing? Thougt maybe the TPS was bad and changed that still no fix. Now I checked the fuel pressure. My haynes manual says 55-60 with key on and car not running. I tried that and get 44 pounds. I started the car and it runs 55-56 pounds but when I rev the car up the pressure drops to 40 lbs. What do you guys think about my pump? Should the pressure be a definate 55-60 key on car not running and whats with the pressure drop? Is it just because the car is using more fuel when reving so the pressure drops at gauge? Would a faulty pump cause the codes because of a lean fuel condition? Thanks for youe help in advance.

98 formula m6

**pajeff02** · 07-27-2010, 05:48 PM

I would start with the fuel filter before jumping into a pump change. Then, if you still have a pressure drop, it has to be the pump or the regulator. Not sure how the '98 is setup though.

**Knight** · 07-27-2010, 05:55 PM

Originally Posted by pajeff02

I would start with the fuel filter before jumping into a pump change. Then, if you still have a pressure drop, it has to be the pump or the regulator. Not sure how the '98 is setup though.

+1. Filter is the easiest check. Plus the usual cause, if it hasn't been changed in a while. As Jeff said, after that you would move on to checking the regulator and the pump.

**sjd73ss** · 07-27-2010, 06:02 PM

Changed the filter about a month ago. I went to autozone to get a regulator and after looking it uo and pulling it out of the box the regulator they have is a smaller diameter and has a vacuum port. Mine is bigger with no port. I had them check 97 98 99 vette and f-body and they did not have one that would work? Whats up with that? I get parts all the time there and never had a problem getting the right parts. What the hell do I have ?

**sjd73ss** · 07-27-2010, 06:03 PM

The regulator is on the fuel rail in my 98 and it was a one year only deal. Anybody out there have an aftermarket part number for my regulator?

**0rion** · 07-27-2010, 06:37 PM

Originally Posted by sjd73ss

The regulator is on the fuel rail in my 98 and it was a one year only deal. Anybody out there have an aftermarket part number for my regulator?

your regulator is in the tank on the pump module.....98 vettes had it in between the rails. What you're looking at is a pulse dampner.

**sjd73ss** · 07-28-2010, 08:15 AM

I just got off phone with gm parts and that is the fuel pressure regulator in the middle of fuel rail. I just dont know why I cant get one that will fit from the parts stores?

**sjd73ss** · 07-28-2010, 08:16 AM

Can I just buy a pump by itself and switch it out into my sending unit? Will it come apart without breaking something like a glue joint?

**0rion** · 07-28-2010, 08:55 AM

I've read in the past where people have found that regulator ( which is in the tank by the way

) separate of the whole module but I have no idea where they find it at. I'll chime in this last time and then you're gonna have to learn things your way......that piece in the middle of the fuel rails is not a fpr......it's a pulse dampner. It maintains pressure to the passenger rail so there's no huge drop when the passenger side injectors fire. I have a 98 and have had my pump out and stared in the eyes of the fpr.....it's in the tank on the module.

**sjd73ss** · 07-28-2010, 03:26 PM

Originally Posted by 0rion

I've read in the past where people have found that regulator ( which is in the tank by the way

) separate of the whole module but I have no idea where they find it at. I'll chime in this last time and then you're gonna have to learn things your way......that piece in the middle of the fuel rails is not a fpr......it's a pulse dampner. It maintains pressure to the passenger rail so there's no huge drop when the passenger side injectors fire. I have a 98 and have had my pump out and stared in the eyes of the fpr.....it's in the tank on the module.

Ok Ok I believe you but the parts deparment at GM describes the part as a fuel pressure regulator. If you look up 99-02 at autozones website it says its on the fuel pump. If you look up 98 it says on fuel rail??

**sjd73ss** · 07-28-2010, 03:29 PM

QUOTE=0rion;2400631]I've read in the past where people have found that regulator ( which is in the tank by the way

) separate of the whole module but I have no idea where they find it at. I'll chime in this last time and then you're gonna have to learn things your way......that piece in the middle of the fuel rails is not a fpr......it's a pulse dampner. It maintains pressure to the passenger rail so there's no huge drop when the passenger side injectors fire. I have a 98 and have had my pump out and stared in the eyes of the fpr.....it's in the tank on the module.[/QUOTE]

Could it be that you have a late 98 that has 99-02 fuel pump and mine is early with 98 only pump? Who knows this car is driving me crazy

**Cutlass** · 07-28-2010, 06:19 PM

^^^Dude....NO...its in the tank. There is no return line up to the fuel rail, therefore no possible way there can be a FPR there.

**sjd73ss** · 07-28-2010, 09:05 PM

GM part number 89060420

GM Performance 89060420 - GM Performance Fuel Pressure Regulators

This is what summit racing calls it.

**sjd73ss** · 07-28-2010, 09:11 PM

Here is a picture and notice that there is two fuel lines in the picture. [IMG]

[/IMG]

**sjd73ss** · 07-28-2010, 09:16 PM

Closer picture

[IMG]

[/IMG]

**0rion** · 07-28-2010, 09:24 PM

I don't know what else to tell you really....go ahead and order that one from Summit I guess.

**sjd73ss** · 07-28-2010, 09:46 PM

Originally Posted by 0rion

I don't know what else to tell you really....go ahead and order that one from Summit I guess.

Does your 98 have that same setup on it?

**0rion** · 07-28-2010, 10:23 PM

once again, they all do. 98-02 f-bodies all have a returnless fuel system with the regulator in the tank.

**shady milkman** · 07-29-2010, 09:55 AM

Originally Posted by 0rion

once again, they all do. 98-02 f-bodies all have a returnless fuel system with the regulator in the tank.

x2 ...what you are looking at is a pulse dampener

**Too Fast** · 07-29-2010, 01:56 PM

OP, you have a 95% chance that your fuel pump is dieing. The pressure should stay over 55, especially when the engine is under load. A free rev isn't really a load on the engine, so if the psi drops like that, imagine how far it falls when you are driving.