Surging At Idle

[jkojiro]

I have a Pro-Flo that has sat in a car that wasn't running for a couple of years and the fuel gummed up inside the fuel injection system.

Anyhow, I decide to put the system in another car that actualy drives and have run into a few problems. The car the pro-flo is currently in has a milder cam (single pattern 228@.05/480 versus a dual pattern 234/244@.05 488/510 which it was originaly chipped for).

I was told it could be tuned by the module since the cam wasn't different enough, but it sis urging pretty badly at idle right now. Is surging induced more by fuel or timing?

Keep in mind the system sat for a couple years and I replaced the injectors with a 29lb/hr, which is what I think it came with). Also, I replaced the fuel pump with an MSD unit.

I was planning on putting my wideband on it and seeing what it was getting for A/F reading. Oddly enough the pressure has changed a couple of time from 40psi to 58psi at idle so I am going to replace the regulator as well.

[jkojiro]

Looks like it was just running way lean. The wideband said it was running at about 17 for an A/R, so that cam makes a big difference on how the engine runs. It's also the cause of the surging at idle. Oh yeah and I forgot to mention it a .06 overbore with a 400 crank so the larger displacement probably doesn't help any.

Now on to further tuning, but the fuel pressure regulator seems to be stable now as well at 58psi. BTW is that pressure normal? It seems a big high.

[S. Armish]

58 psi is high. Normal is 42-45 key on engine off and 32 - 38 psi at idle (depends on idle vacuum).

[jkojiro]

hmmm, maybe I need to change that regulator out afterall. How do you hook up a different regulator with an input, output and return line (it's the edelbrock EFI regulator). Can you tie the output of the regulator to the driver side fuel log? Is it possible to tie the two rails together with a straight hose and regulate the output? If so where does the output of the regulator go?

[S. Armish]

hmmm, maybe I need to change that regulator out afterall. How do you hook up a different regulator with an input, output and return line (it's the edelbrock EFI regulator). Can you tie the output of the regulator to the driver side fuel log? Is it possible to tie the two rails together with a straight hose and regulate the output? If so where does the output of the regulator go?

It can be done various ways. In most cases, we like to bring the feed line up to a "Y fitting" and split the supply to both fuel rails (normally in the front of the engine). Then you run the outlet of both fuel rails (at the back of the engine) into each side port on the regulator. The bottom port then is used as the return to the tank. This method does a good job dampening the pressure fluctuations caused by the injectors opening and closing.

FYI: Most of the time when we are doing fuel injection tuning here, we use our P/N 1728 fuel pressure regulator. It has -6AN ports, a vacuum reference port and is fully adjustable. It's the same regulator supplied with our Edelbrock/Musi 555 cubic inch EFI crate engine that makes over 675 hp.