fuel pressure 98z28

**dklowrider** · 03-10-2009, 05:04 PM

i saw a problem w/a car taking 2-3tries to fire when cold but ok when warm. i have opposite :starts 1st try when cold but takes usually 2 tries rarely3 to fire when warm. less than2k on fuel filter, plugs and wires yesterday. i expect it to fire 1st time every time. maybe asking too much. 112k miles 62# fuel pressure at idle, but is it it normal for these cars not to hold pressure when pump shuts off? turn key on pumps up to 62, when pump stops pressure drops to 0, then jumps back up to 62 when cranking and engine fires. only checked pressure cold so far, dont know what it does warm. any opinions?

**0rion** · 03-10-2009, 05:40 PM

sounds like your pressur regulator is bad. Next time it's warm cycle the key twice before starting it. In other words turn the key but don't start it...then turn it off and try to start it then.

**dklowrider** · 03-10-2009, 05:51 PM

thats not good. i think the regulator is in the tank w/pump module on 98? could be cutting the trap door in the back as one of my first mods.

**dklowrider** · 03-10-2009, 06:15 PM

sorry- forgot to ask what the fuel pressure is supposed to be!

**bills98ta** · 03-10-2009, 06:56 PM

58lb is average. I heard the 98's have a check valve in the fuel filter... It should hold / or slowly loose pressure when shut off. I'd lean towards the holding check valve, or you have a faulty injector dumping into a cylinder. You should see that on the spark plugs.

**dklowrider** · 03-10-2009, 07:20 PM

the plugs i pulled out while they were old they were all even color which looked good so im not leaning toward the injectors. filters are cheap so i might try another new one. seems to me you can dump fuel out of one end but not the other when you pull the old one off so that would make sense. thanks to both for the input. my wallet is hoping its a faulty filter, but the motor pulls strong all the way without any stumbling or missing so i might live with hitting the starter twice if its not.

**dklowrider** · 03-11-2009, 11:13 AM

found some info today that may be helpful to someone: 97-98 ls1 cars have an external FPR with pressure and return lines to tank, 99 and up have the regulator in the tank w/ pump, single feed line to fuel rails!

**JoshieDoom** · 03-11-2009, 11:19 AM

Originally Posted by dklowrider

found some info today that may be helpful to someone: 97-98 ls1 cars have an external FPR with pressure and return lines to tank, 99 and up have the regulator in the tank w/ pump, single feed line to fuel rails!

Where the heck is it?!?!?

**dklowrider** · 03-11-2009, 12:01 PM

this may be the blind leading the blind for a little, but i just came in from the garage and right there it is on the crossover tube between the fuel rails! it looks like it is held in by a snap ring. easy to replace ,but mine doesnt have the hose barb out the side like the one in your picture. not that its a problem but now im looking for the return line, dont see anything off the fuel rails, and the feed line goes to the back of the FPR which the enters the crossover tube to the fuel rails. only other thing is the EVAP line? coming off the intake behind the TB. evidently the 98 f-body and 97-98 corvette are the oddballs. any body got anything on this? dont be bashful if im totaly wrong on any of this cuz i just left another forum and they were talking about return lines on an 02. if they do have theFPR in the tank why would you need a return line? maybe a select few know what theyre talking about and the rest just think they do? ill go either way[so to speak] just tell me.

**0rion** · 03-11-2009, 02:22 PM

the 98 f-bodies fpr is in the tank....that's a balancer between the fuel rails.

**dklowrider** · 03-11-2009, 02:48 PM

thats a big help! it does look like it could be a regulator tho when you look at it. so im back to maybe replacing the in tank unit. if the regulator was working properly would it hold the pressure to 58# and not allow the 62# to get to the rails like im getting? thanks for coming back here for me! oh, and does this mean i do not have a return line then?

**bills98ta** · 03-11-2009, 05:18 PM

You don't need the return or regulator with the 97 & 98's !!! I just installed the LS7 intake and went with this fuel rail kit. Had to get the adaptor O-rings for the injectors, for the intake holes...

http://www.msperformanceonline.com/10612-gto.html

**bills98ta** · 03-11-2009, 05:19 PM

BTW, My fuel pressure averages 60 - 62lb... That's OK !!!

**JoshieDoom** · 03-11-2009, 05:20 PM

Originally Posted by 0rion

the 98 f-bodies fpr is in the tank....that's a balancer between the fuel rails.

Thats the "fuel pressure regulator" when you look it up for 1998 f-bodies.

Doesnt look like much of a regulator to me

**dklowrider** · 03-11-2009, 05:52 PM

thats a good lookin set of rails. o-rings are for stock ls1 injectors to fit ls7 intake? not ready for intake swap and stuff yet tho. looking to get what i got working as good as i can while doing sfc,lca phr,wheels etc. so i need to get back to the fpr. you say you dont need it with your setup, but where was it before you had this setup? i thought i knew what i was talking about when i found the 99 and up in the tank article, then orion says its in the tank on 98, and joshie doom says its on the crossover tube, and i find another site that agrees with orion, and im ready to just cut the hole,replace the pump module, the filter and whatever the hell that is on the fuel rail crossover,and that ought to cover it! god this is fun and ive barely touched the car yet! thanks for the headsup on the pressure by the way.

**bills98ta** · 03-11-2009, 06:58 PM

It's in the back on the 98. I have, what looks like a regulator on my stock rail too, but it's not it. It's gone now, and I still hold 60 - 62lb of fuel presure with out it !
I think it's there just to look cool !!! LOL !!!

**dklowrider** · 03-12-2009, 02:57 PM

well im convinced who to listen to when you need somebody who knows their shit! fpr, pump and all is in the module in the tank.[but you knew that]. fuel filter is a regular old everyday filter, no check valve or anything. still dont see where you have a return line tho, 98 has 4 ports on the pump, supply, 2 for evap i think, which leaves 1 for the return. but i guess my life will go on without this knowledge.

**JoshieDoom** · 03-12-2009, 05:15 PM

Originally Posted by bills98ta

It's in the back on the 98. I have, what looks like a regulator on my stock rail too, but it's not it. It's gone now, and I still hold 60 - 62lb of fuel presure with out it !
I think it's there just to look cool !!! LOL !!!

How do you delete it?

**dklowrider** · 03-12-2009, 05:36 PM

im going to take a stab at this before the guys who know stuff get here! you probably have to replace your fuel rails with aftermarkets. i think the factory routing and delivery point for fuel, and or rail design is what requires the balancer betweenthe 2 sides to ensure even fuel delivery. [how did i do?]

**0rion** · 03-12-2009, 05:56 PM

this is copy paste but might help you.....

The fuel sender assembly is inside the fuel tank attached to the top of the fuel tank. The fuel sender assembly consists of the following major components:

The fuel level sensor (3).
The fuel tank pressure sensor (1).
The fuel pump (7).
The fuel pressure regulator (8).
The fuel pump strainer (6).
The fuel pump (7) attaches to the fuel sender assembly inside the fuel tank. The fuel pump is an electric high pressure gear rotor pump. The fuel pump pumps fuel to the fuel rail assembly at a specified flow and pressure. Excess fuel returns to the fuel tank by the return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The PCM controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe has a quick-connect fitting. The fuel return hose attaches to the fuel pressure regulator (8). The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

The fuel pressure regulator is a part of the fuel sender assembly fuel return pipe. The fuel pressure regulator is a diaphragm operated relief valve. A software bias compensates the injector on-time because the fuel pressure regulator is not referenced to manifold vacuum. The fuel injector pulse width varies with the signal from the MAP sensor. With the ignition ON and the engine OFF, system fuel pressure at the pressure test connection should be 380-410 kPa (55-60 psi). If the pressure is too low, poor performance could result. If the pressure is too high, excessive odor and a Diagnostic Trouble Code (DTC) P0132, P0152, P0172 or P0175 may result. Refer to Fuel System Diagnosis for information on diagnosing fuel pressure conditions.

The fuel feed pipe carries fuel from the fuel tank to the fuel rail assembly. The fuel return pipe carries fuel from the T-connector located on the outlet side of the fuel filter back to the fuel tank. The fuel pipes consist of three sections:

The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of nylon.
The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the engine compartment connecting fuel pipe. These pipes are constructed of steel.
The engine compartment connecting fuel pipe connects the chassis fuel pipe to the engine fuel rail. This fuel pipe is constructed of nylon.

Document ID# 232124
1998 Chevrolet/Geo Camaro

the "thing" between the rails is called a pulse dampner and I've also heard it called a balancer. It maintains equal pressure between the rails so there's no pulse when the injectors fire.