Ducman82

nope, no issues.

pokegama

Ducman, what did you hook up the vacuum line from the FPR to? Other than that my fuel lines are run just like yours.

Once again...Thank you guys. I really do appreciate the help!

Ducman82

i hooked the vac line to one of the vacuum "nipples" on the front of the throttle body, near the idle screw... AND OR depending on the throttle body, they are on the opposite side under the plenum.

now i failed to hook that vacuum line up and the car ran for YEARS, with minimal issues. but i could never get the tune to do what i want.... until i had that bone head moment....

what did you set the regulator at?

pokegama

Well I hooked up a vacuum line to a nipple on the front of the throttle body. To took the fuel pressure down from 44 to 35 PSI. It did not stop the pulsing. I can feel it in the fuel lines but the sound seems to be coming from the passenger footwell. Is there anything under the fender that could be making that thumping sound?

I had the regulator set to 44 at idle with the vacuum open.

Ducman82

Hmmmmm. How violent is the pulsating? You do hear the injectors making racket , being a batch fire system. Does the pressure pulsate on the gauge? If you jump the fuel pump relay does it pulse still ? (Car not running)

pokegama

The pulsing in the fuel lines isn't real strong but you can feel it. It's the thumping sound, like a distant helicopter, coming from the footwell that is really noticeable. The FPR gauge stays steady. I have to say I don't hear the injectors clicking any more than usual. I will have to try jumping the pump relay.

Ducman82

id start the car and walk around and try to hunt down the sound even more..... thats just odd

pokegama

That's my plan now. Put the car back up and check around the area behind the right front tire. I'm going to start looking at fuel dampers too.

pokegama

Carl, I tried the vacuum line off the brake booster. It made the same change in pressure as hooking it up to the nipple on the throttle body that Ducman had mentioned.

Earlier in this thread you have mentioned that the FPR should be set to 43 as a start point. Is that with the vacuum line hooked up or not? With the vacuum line hooked up the pressure is around 35. Without the vacuum line hooked up its at 44 now.

Could it be surging because it's not getting enough pressure?

Ducman82

without the vac hook up when at WOT or higher loads the rails get "drained" faster that the regulator lets the fuel in. when the vac is hooked up a diaphragm allows more fuel in, up to the set amount"..

i think you have some other kind of issue. i had pressures at different settings, looks to be the same regulator and lines (basically), and never had any issues. you can "feel" the pulsing, but never any physical banging around... can you post a video ?

GregBBRD

As close to the rails as possible.

Carl Fausett

I have just had two 1984 L-Jets in here, and both of them had the stock factory fuel pump pulsing so loud you could hear it in the car. On-off-on-off like a throb. Neither of these were supercharged (yet) and both had all-stock fuel rails, dampers and FPR's.

The pulsing was only audible at idle, because off idle the engine is actually using some of the fuel and the fuel pump can run more consistently. One theory is that the pulsing of the fuel pump at idle is cause by a restriction in the return to the tank. Again, off-idle, the pulsing goes away, and the system is not returning as much fuel to the tank as some is being consumed.

I also noticed that the fuel pump pulsing/noise was only on cold days, and got worse on colder days, went away on warmer days. That observation is contrary to the theory above - so it is clear to me we still do not know for sure what the cause is.

We went on to supercharge these cars, and again, the pulsing that we noticed stock was now gone. If i dialed up the FMU too far, I could bring it back. So it did seem to correlate to too much fuel pressure at idle.

As to your question whether to set the FPR with vac line on or off, set he pressure with the vac line ON.
I like to adjust it on a warm engine at idle, and I turn down the pressure until it is idling really really smoothly, then I turn up the pressure until the idle just begins to stumble for being too rich. Back it up to the spot just before that, and lock it in.

Carl Fausett

The only difference I can see between his install and yours, Ducman, is that he has added extensions from the fuel rails to the injectors to clear his coil-near-plug install. Do not know what ID those extensions are, etc.

GregBBRD

Interesting. I've worked on literally hundreds of these cars and have never heard this problem on a stock application.

Maybe the difference in latitude...

Also very interesting that you use the fuel pressure regulator to set the idle mixture. Instinctively, I would have thought that you would use the fuel pressure to set the WOT mixture....

There's not a whole bunch of ways to control the mixture at WOT on an L-jet engine, without using fuel pressure, since the "mixture door" is certainly wide open with any increased air volume (Supercharger increases air volume.)

How do you set the WOT mixture if you use the fuel pressure to set idle?

Carl Fausett

NO NO NO, You would not normally use the FPR to set the fuel mixture. Of course. Assuming it was idling good before and he has not turned the idle mixture screw, he could adjust his new FPR to return to that good idle he previously had.

Remember: we suggested he START at X psi. Something between 38 and 42 psi is a good place to start, the car should fire and run. Then adjust the psi to see what the car LIKES at idle with these injectors, that's all I am saying.

Of course, all tuning should be confirmed on a chassis dyno to ensure you do not run lean at WOT under load. I would not expect a problem as Pokegama's car is NA, I believe.