rambo benson

Help:

My Fuel Pressure Gauge is buried at over 120 psi! (94 355 Z28 with Vortech) and the engine runs rough.

Wonder if the FPR or FMU is bad....FMU has the bleeder valve and car sat for a year.

I know how to check the FPR and will do so tonight, but How to tell if FMU is good or not?

Anyone else had this problem?

Sean94Z

One way to check is to take the FMU off and see what your fuel pressure is. You can also take off the vacuum line that runs to it and see what happens. Try hooking up an air compressor and blow air through it and see what happens.

--Sean

rambo benson

Thanks Sean, we are trying it now....

rambo benson

Thanks Sean but no dice...

Somebody must have had a similar problem out there???:

Crazy high fuel pressure (over 120) and rough running engine.

A little history...Illionis shop called Turbo Connection had the engine rebuilt with a blower cam, set the FMU bleeder valve unscrewed all the way out, put in 42 # injectors and programmed the computer based on some "black vette canned tune", bypassing the Retard box. I had them put in KB boost-a-pump in the trunk.

It started running rough and on the phone they suspected they miswired KB boostapump and sure enought it fixed it. It ran well for couple thousand miles.

It sat for over a year with a blown up tranny. Ran well again just last week with a new tranny installation....Now, only 25 miles later it started running rough with high FP.

OK, Friday night we took the FMU out of the loop. Bypassed the MSD ignition box (since those go a lot).... Still runs rough / high FP.

FPR seemed OK since we took vac line off and found no wet fuel in the tube. FP did not drop when I took the line off... We did fail to put a vacuum on it with engine running to see if rpm changed ...oops

Now we took the fuel rails and injectors out to see better...we didn't like the way the fuel connections seemed so loose on the back of the rails, they swivel very easily, even wobbly. (normal?) no leaks though.

Cannot find pinched return fuel lines around engine or under the car or vac lines off intake. Tightened a ground wire to the T-Rex pump a little bit.

No blown head gasket, no oil in coolant and no coolant in oil. Rings are OK, no puffing out the valve cover.

What the hell is going on??? Should I just get a new FPR and put it back together? Should I get a Stock FPR or like a Holley adjustable....?

Should we suspect the KB unit? T-Rex gone mad? But Most likely it should be something holding up the fuel return line - right?

Would 120 psi lock up the 42 lb. injectors?

I have not checked impedance on injectors yet (what impedance should 42 lb# injectors be? (manual suggests 14-18 ohms but that may be just for stock injectors) .

Still have not checked each electrical connector with noid light yet...

Sorry so wordy!

Appriciate any wisdom / experience !
Ram

Sean94Z

I would bet it's the regulator.. That it's job .. To control fuel, so, if it's shot, it could just dump fuel in and that's what is making it run rough .. Know anyone who could lend you a regulator?

rambo benson

Sean,

Maybe I'll check around, or I'll just get one then.... For my application - just stock or go for Adjustable?

Thanks for your help!
Rambo

Sean94Z

Well, there's some debate about whether or not an adjustable fuel pressure regulator is worth it. Some people claim the PCM will adjust for the added fuel pressure. So, unless you are planning on programming the added fuel into your PCM, I would get a non adjustable.

markinkc69z

I doubt its your regulator unless something passed through the system and is lodged inside it. It would appear to me that the pump is being deadheaded. My guess is even though you've tried to look, that during the transmission install/jack stand period that your return line has been completely pinched closed. If taking the fmu out of the system did not lower fuel pressure its a pretty safe bet. You can check for yourself by taking the fuel line that went into the fmu and running it to a bucket and turning the key on. If you get pleanty of fuel then your regulator is not to blame for the high pressure. The return is being restricted in the line back to the tank.

Luna

As a test, program the computer for 42 at 120psi and see if it is more stable.

Wouldn't the FPR limit the pressure even with a crushed return? I guess it has limits that when breached goes ballz to the wallz

Sean94Z

That's a real good point.. I had that happen once where the return line was crimped and I got high fuel pressure. Never even though of that.

rambo benson

Sorry, I haven't checked back in a while. Thanks for the advice guys.

After installing new FPR and filter we find The FPG is bad and actually the FP is fine, (47) ! What a run around.

In the meantime painted valve covers sparkly silver, intake stripes and Fuel Rails Metalcast blue...Purty!

We then thought electrical - so all new wires, plugs AND OPTI .....still runs rough!

Couple plugs on DR side were a little damp. Maybe an injector sticking open.... They are all ticking, next we will run impedence test. (should be 14 ohms according to manual, but these are 42# so don't know???)

Then see if one is stuck open. Mechanic thought we would take the rail off and turn the key and see if one squirts all the time....Hate to ruin my paint job...any other ideas?

Sure appriciate it!