Fuel Pressure jumping around!

[Ironlung]

I've had a dancing fuel pressure problem for quite a while now. I've done everything I can think of the fix it with no results. I can set the pressure at 38lb with vacuum off. Everytime I start the car it jumps to a different pressure. Sometimes up to 60-90psi. You can shut the car off again and re-start and you'll get something different. Of course when the pressure is up, the car runs extremely rich and floods out. I'm at a loss for what to try next. What I've done so far:

New fuel pump
New fuel pressure regulator (tried 3)
New fuel filter
Dropped tank, blew out return line, no blockage
Checked return line through sending unit, no blockage
Different chip

Help!!!!

 

[Jack Evers]

Any chance it's electrical. What's happening with your system voltage when the fuel pressure jumps?

 

[Ironlung]

I don't think it is electrical. When you start the car, the fuel pressure will basline somewhere, say 60psi. It will run at 60psi and higher, according to rpm and boost until you turn the car off and re-start. Nothing else usual is happening with the electronics, good volts according to the scan master and no codes. Sometimes I'll get lucky and re-start a couple of times and the fuel pressure will baseline at a normal psi. The rest of the time I have to shift into neutral at red lights to keep it from flooding out and dying.

 

[John Larkin]

I think there is a rubber hose on the return line behind the driver fenderwell. It might be collapsing or be pinched which would cause a blockage and thus higher fuel pressure. I've never had to mess with mine but I recall seeing a rubber line in that area. Might trace your return line to see if this is in fact the hose then replace it since it's fairly cheap to do. It does sound mechanical by your description.

 

[Lee_Burough]

Have you tried another fuel pressure gauge? Just a thought

 

[Jack Evers]

Just for kicks...do you have a "volt booster" on the car?

 

[Ironlung]

Jack, no volt booster

lburou, the fuel pressure guage has crossed my mind, but it is definately running rich when the pressure is up. When I happen to catch it at the correct fuel pressure base, it runs great!

John, I checked the rubber lines at the tank, but didn't realize their was another rubber line in the engine compartment. I'll check it too.

Thanks!

 

[Mustang 1]

I had the same problem and it was the gauge.The fuel pressure would drop and I would adjust the fuel pressure regulator.After driving the car the fuel pressure would seemingly go down.When you restarted the car the fuel pressure would be to high.After replacing the entire fuel system I replaced the gauge and even with the old gauge only reading 30 psi upon starting the car the actual fuel pressure at idle was more like 68psi.Gauge re cheap-I would change that first!

 

[Ironlung]

Mustang 1, good idea! I didn't think about the baseline setting being off. I've got a good guage on the beater GN, the car with the problem is the one my dad now ownes. I'll try swapping them.

 

[Lee_Burough]

I just put the stock TTA 237 fuel pressure regulator back on with a Translator and extender chip. YOu'll prolly never have to worry about fuel pressure again if you go that way. The extender chip is set up for 45 psi Experts report that they have never seen a bosch 237 regulator vary more than one half psi from 45....

 

[Mustang 1]

If your luck is like mine the problem will be your gauge.I replaced the fuel tank,fuel hoses and clamps,fuel filter,fuel pressure regulator,and the fuel pump and sock.At least now I have extra parts !On mine I kept adjusting the fuel pressure up and was over fueling at static and didn,t even know it!At times I probably had as much as 90 psi! Hopefully it will be your gauge,it is by far the cheapest....at least now I have a 340 instead of a 307...Ya always gotta lok at the good side.

 

[Ironlung]

Well guys, I finally had a chance to work on it. We put another fuel pressure guage on and the readings stayed exactly the same. Also I noticed that on my beater GN, the fuel pressure is rock stead, with smooth rise and fall while driving. On this car the fuel pressure jumps around and the needle is always fluciating on the guage. I also checked the rubber parts of the the return line and all looked fine. Previously I had blown out the return line with air and didn't find any blockages. I think the only thing in the fuel system that I haven't changed or tested are the injectors. I don't see how they would cause this problem though..

Help

 

[Ironlung]

Just had another thought... I'm running one of the original Modern Muscle Car LT1 MAF with a Translator on it. If it went screwy, would it cause this problem?

 

[325DR]

Its got to be sometihng AFTER the FPR. The FPR is what controlls the pressure between the pump and the FPR. Even if the fuel pump would spit out 3x's as much fuel for a second, the gauge shouldn't even move because the FPR will keep the pressure steady. Ill bet it is the return line somewhere. Its got to be.....

If an injector was stuck closed, your spark plugs would reflect that. Pull the plugs and see if one or more is saturated in fuel or burnt white.

Have you checked the vacuum line from the vacuum block to the FPR? Shouldnt make that much of a difference though.


And no, the translator would have NO effect on fuel pressure.

 

[Ironlung]

I finally got it fixed!!!!!!!!!!!! I've fought this problem for over 3 years! It was the return line to the tank. I had previously blew the line out with air, and the air made it through, but I guess it has a partial blockage that slowed the gas down. I started with a 90deg fitting on the bottom of the regulator and ran a rubber line down to a gas tank on the ground. Started it up and the fuel pressure was normal for the very first time. So I put that back together and went to the back of the car, over the axle and disconnected the rubber hose there. Fuel pressure was screwed up again. So this cleared the tank lines and pick up. Went back to the front of the car and unhooked the rubber line from the motor to the frame, fuel pressure back to normal. So now my blockage is in the steel line running from the front to the back of the car. This line runs between the frame and the body at the back and I didn't want to tackle changing it, even if I could find a replacement line. Instead, I took the vapor return line from the charcoal canister, teed my return line to it and now have gas returning to the tank via both lines. The charcoal canister is just venting to the atmosphere now. It drives like a new car now . Does anyone see any problems with using the vent line as a return line?

 

[Black Car]

The only things that I see is that the tank won't be vented and that the fuel from the vent line will splash on top of the other fuel which will airate (sp) it somewhat.
You might pressureize the tank.
I guess that you could always leave the gas cap loose.