Daryl

DR,
Is you bypass connected to the manifold at a different location that ours? I am thinking about the idle issues.

CMW

This has to be the longest most well thought out, sharing of ideas and problem solving S/C post amongest a varity of cars and S/C kits to date. I'm learning alot.

DR

Hi Daryl,

>Is you bypass connected to the manifold at a different location that ours?
>I am thinking about the idle issues.

I have had 2 different styles of Bypass Valves mounted in 3-4 different locations and none of them affected or caused idle issues. Heck I have even done testing and dyno runs without a bypass (temporarily) and that didn't affect idle either.

I am not completely sure of where your bypass is located and routed as I have seen Andy do them a few different ways. Give me a refresher (or pic) on where/how yours is done and I can tell you if I have tested that configuration.

BrianG

I am amazed at the rate of discovery and learning that is going on recently, regarding understanding the LH EFI system. A year ago we were hearing that the LH firmware was proprietary and unassailable.

Jim_H

Dave,

Mine is located at the back, drivers side corner of the SC, below the BEGI

https://rennlist.com/forums/attachme...chmentid=52437

Daryl

DR
Best picture I can come up with right now. Someone elses install. I hope they don't mind.
I am trying to understand why one cylinder is running differently than the other seven cylinders. On my car it's number six and Bills car is number seven. When we disconnect the injector wire from that cylinder it makes very little difference to the idle speed. All other cylinders show a clear drop. We have checked every thing we can think of including swapping injectors. I would like to understand why this is happening before moving on to computer tuning. Others are complaining about idle issues but no one else has tried this cylinder drop test that I am aware of.

DR

Hi Jim,

It looks from the photo that yours has the bolted flange on the rear plenum (pre-SC) and then plumbed into the intake "after" the intercooler. I have used this layout with no problems. Are you plumbing he vacuum line from the port on the bypass body to the vacuum actuator? If so it seems to be OK. It is my understanding that the vacuum source should come from after the SC which it picks up on the boosted side of the throttle plate on that bypass. I have tried it both ways, i.e., vacuum from after SC and pre-SC, can't tell any difference either way but I know Andy is adimate about it coming from the boosted side so it sees vacuum and boost. Honestly, I am totally sure why it needs to see boost, but I have questioned some of Andy's procedures before.. and have proven myself wrong on a few :-)

DR

Daryl,

That photo has just solved the "cylinder 7" issue in my mind. To me it is now obvious why you guys are having issues with #7 at Idle and when not on Boost. What I think is happening is when the Bypass valve is open it is circulating air from that hole right beside of #7 and putting it back into the rear of the SC and therefore robbing air when the bypass is open (idle and off-bosst).

My locations have all been on the rear top middle of the upper Intake or on the rear backside of the lower intake, no where near a cylinder where it can suck air away from it.!!

DR

In addition I think a pretty easy fix would be to plug that hole/port and create a new hole/port on the backside of the lower intake. Plenty of room there and should be an easy update.

DR

Also, here is a quick easy test you can try. When you are having the warm idle problem and you see #7 is no doing anything, try unpluging the vacuum source for the bypass valve (and plug the vac supply port so to prevent a vac leak) which will close the valve. If you idle improves and/or #7 starts working better you will know this is the problem.

BTW, do not leave the bypass valve "unhooked" for any lenght of time as this could cause other problems and void your warranty.

John Speake

Hi
There are several "sub threads" inside this general one, but on the subject of injector duty cycle...

Porsche/Bosch were quite clever with the post 87 engine setup. They use 19# injectors (maybe they were more available at that time), then run them at a higher fuel pressure to get the flow rating up, and then play the trick that Louie mentions where they switch from switching the injetors on/off every engine rpm to once every 2 x rpm. That way they can keep the injector on for approx 1mS longer (this is the opening time of the injector)

Even with all these tricks the injectors are actually on 100% of the time at max power, for these cars. This has been observed on Louie's car when he was testing with the SharkTuner. As he observed, a road car running at 100% will be for relatively short periods, so overall longevity probably doesn't suffer.

80% is usually taken as being a good rule to work to.

I would think a good design rule for a s/c car would be to use a large injector, so you can keep the duty cycle and max fuel pressure as low as possible. Until the Sharktuner, it wasn't possible to run 42# injectors and get a good idle unless the fuel pressure was dropped to such a low level that spray pattern and pick up response were unaccepatable. That problem is now solved.

I am not a fan of very high fuel pressures ! Some books state that the injectors cannot handle very high pressures - can't shut off properly - although evidence of such problems is hard to come by.

Regards

Daryl

DR,
That would make perfect sense on cylinder number seven. In my case number seven and eight show a definite drop in RPM but number six shows very little change.
I think I am going back through the total diagnostic stages again just to be sure I haven't over looked something.

I wish others with this problem would check the rpm drop and let us know what they find.

BC

Does higher fuel pressures not atomize the fuel better then lower pressures?

mspiegle

I think higher pressures DO help, but the issue is (correct me if i'm wrong) that the injector can't close the pintle quick enough (or at all) because the pressure is so high.

Tony

ford makes a 104mm throttle body and I have the 4" tubing in the garage.


How do you recalibrated it?

I wonder what gains if any would be had?