I converted my car to a Retrotek fuel injection system. I have a new tank with a internal fuel pump and the regulater at the tank with a return. My problem is the fuel pressure gauge at idle the needle bounces all over the place cant even begin to tell what the pressure is. As i rev up the engine the needle settles in at 45 psi. but as soon as i let off the throttle the gauge goes crazy. Everything in the fuel system is brand new. The engine is a 502 big block. Also the car idles a little rough the tack jumps about 500 rpm up and down. Any help would be apreciated. Thanks.

If you remover the vacuum line at the pressure regulator, does fuel pressure indication smooth out?

With a rough idle and vacuum line hooked up, regulator is going to be varying fuel pressure.

I did not run a vacum line to the regulator. I thought you only needed to do that on blown engines.

I did not run a vacum line to the regulator. I thought you only needed to do that on blown engines.

Not real sure of the fuel pressure regulator, but if it's similar to a few factory style EFI style systems (like the TPI or LT1), you need to hook a vacuum line up to the regulator. Then the regulator sees vacuum, it lowers the pressure, when the vacuum goes away (under acceleration), it increases fuel pressure.

The system you are thinking about is a bypass regulator, like for a supercharged or turbocharged application)......when the regulator sees pressure (boost), it squeezes off the return line to the tank giving more fuel pressure. Almost the same thing as a standard regulator, but it works off of boost.

I would highly doubt the EFI kit would come with a bypass regulator unless you specifically ordered it with it.....so yeah, hook a vacuum line up to it and see what happens.....hell, it couldn't hurt anything.

Just for reference, it should have full manifold vacuum at all times.

Joe

yes as everett said it needs vacumn at idle. the vacumn is the thing that regulates the pressure in the system. so you probally flooding engine at idle. if you have a vacumn pump you can put that on there and pump it up to 14 or so to see if that fixes it.almost all cars have the pressure regulater near throttle body and not near tank.

What does the a/f ratio look like while the fuel pressure is fluctuating? As suggested above, get the vac line connected to the FPR.

Thanks for the replies. I will run a vacum line to the by pass regulater and see what happens. I will try to do it today and report back. Thanks everbody.

Thanks for the replies. I will run a vacum line to the by pass regulater and see what happens. I will try to do it today and report back. Thanks everbody.

So it is a by-pass regulator.....just so you know, there is a difference between a "fuel pressure regulator" and a "by-pass fuel pressure regulator".

Which one did your kit come with?

you don't have to run a vacuum line to the regulator. On factory cars they do that as it probably reduces wear on the pump a bit and since they've got to look long time, warranties, etc. it's the way they do it. You can remove it on a stock car also, but you'd have to re-tune as it'll richen it up in the vacuum areas. It's not a bad idea to run one, but certainly not a requirement.

Either way, with or without a vacuum line shouldn't make the fuel pressure jump around so it can't be read. A good test just to see, but it shouldn't be the issue. A bad regulator, restricted/kinked return line, or cheap fp gauge could be another reason. I had this happen to me in the past where the needle of the gauge "vibrates" back and forth 5-10 psi, so fast it was a blur. Replaced the gauge and it stopped.

If that system comes with a tune and wants a vacuum reference line on the setup, then you'll be rich as far as a/f, but it still shouldn't have fuel pressure issues as far as steadiness. If the a/f seems steady then I doubt the fp is really jumping, leading me to lean towards the gauge or location of the sender. If this is one of their cheaper Autometer gauges that's only $100 or so I've had issues with those before. I always end up with the ones that have a nice electrical standalone sender, setup costs $250 or so, and that's a non liquid-filled gauge.

I feel that the reason the gauge is jumping is because.....since the regulator is not hooked up, there is no regulation, therefore, you have a solid line of fuel pressure....the pump is not causing the jumping, the opening and closing of the injectors is what is causing the jumping. As the RPM increases, the gauge smooths out due to a higher injector open/close frequency.

Just my $0.02

~Joe

I feel that the reason the gauge is jumping is because.....since the regulator is not hooked up, there is no regulation, therefore, you have a solid line of fuel pressure....the pump is not causing the jumping, the opening and closing of the injectors is what is causing the jumping. As the RPM increases, the gauge smooths out due to a higher injector open/close frequency.

Just my $0.02

~Joe

I've run many cars without a vacuum line hooked to the regulator and the fuel pressure is dead steady (other than that one bad gauge/sender). My current car was this way initially and was fine; I added a boost reference to help out since the injectors aren't really big enough for the power range.

Jody

Robert, your Retrotek sounds a little like mine. Mine's a Boss 1200cfm on my L88. I had to move the Aeromotive regulator to the top of the engine to more rapidly purge air from the fuel. But it idles too fast after warm up and Cody said to install a return spring on the secondaries. I did. Still fast, over 1300rpm. Sounds like the IAC. But I don't run a vacuum line to the regulator either. Hmmm. Easy to check. And the laptop shows fuel idle pressure bouncing a little. And the digital reading bounces too. But not much.
Retrotek says to set fuel pressure to 45psi. It holds that pressure no mater what the engine is doing. Are you guys saying it should be lower at idle????? That might help stop the gasoline shower with the air cleaner off. (remember, the injectors are above the throttle plates.) Here's a current view. I removed the vacuum nipple from the regulator.
http://epitomesrebuild.com/images/311.jpg

Fred, My idle speed is fine around 800rpm. The problem is it lopes up and down around 75rpm. Also my fuel pressure gauge bounces so wildly at idle you can barely see the needle. I also get gas coming out of the top of the throttle body also. And yes it is the same system as yours. The other problem is me, I am really having a hard time understanding how to tune this thing. Thats why I bought this unit hoping that it will self learn and do its own thing. I have to say the throttle response is instant and it runs great off of idle. Just need to figure out this fuel pressure issue. I am going to order the fuel pressure sensor from Retrotek tommorow and see what the computer says verses the gauge. Any help you have to offer would be very appreciated.

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