CIS Fuel Pressure Adjust???

patkeefe · 09-06-2007, 05:29 PM

I have a 78 SC, CIS. I need to turn the fuel pressure up a bit at the fuel head (turbo enrichment experiment). I believe the FP regulator is the allen screw with the locknut on the right side of the fuel distributor. Is adjusting the fuel pressure as simple as turning the screw, or is there some other mechanism or procedure involved?

Thanks!
Pat

ianc · 09-06-2007, 07:26 PM

I believe that if you remove that plug, you'll find some shims underneath, and to actually alter the fuel pressue, you need to add\remove shims to get you where you need to be.

That is, if I recall correctly...

ianc

Paulporsche · 09-07-2007, 04:51 AM

Ianc is correct. You can get the shims @ the dealer. I don't know if PP can get them (probably can). Some people merely slightly stretch the spring found inside that cavity but that's a lot less precise than the shim method, and if this is an experiment, then you probably want to be as precise as possible.

patkeefe · 09-07-2007, 06:50 AM

Thank you Paul,
So, to increase pressure, more shims are required? Is it analagous to the alternator belt pulley, where the amount of shims needs to be consistent?
Pat

fredmeister · fredmeister's Garage

I agree that there are shims under the plug that can be used to adjust the pressure. There is also an o-ring seal I think that should be checked for function as well (though not sure).

However, What pressure is being adjusted here? System or Control pressure?
If so then wouldn't you want to decrease the pressure to richen the mixture?
Also, why do it here when the WUR (warm-up regulator) is doing the same job?
When you make the WUR adjustable are't yuo achieving the same results?

I have always had these questions, but have never seen someone address them on the forum......good questions Pat!

sand_man · 09-07-2007, 07:36 AM

Quote:

Originally Posted by fredmeister

I agree that there are shims under the plug that can be used to adjust the pressure. There is also an o-ring seal I think that should be checked for function as well (though not sure).

However, What pressure is being adjusted here? System or Control pressure?
If so then wouldn't you want to decrease the pressure to richen the mixture?
Also, why do it here when the WUR (warm-up regulator) is doing the same job?
When you make the WUR adjustable are't yuo achieving the same results?

I have always had these questions, but have never seen someone address them on the forum......good questions Pat!

At the fuel head, the shims adjust the system pressure.
At the WUR, control pressure is managed.

If I'm not mistaken (and I often am) with system pressure, higher pressure equals more fuel; the opposite of the WUR in which lower pressure (on a CIS pressure tester gauge) equals more rich.

sand_man · 09-07-2007, 07:42 AM

I have an Imagine Auto modified fuel head on my car. The internals have been machined (enlarged) to flow more fuel. I removed the pressure regulator on it to run some checks and noticed that it only had one shim installed. The workshop manual indicates that there should always be three shims - of course the manual deals with non-modified factory parts. I'm guessing that because the head was modified to flow more fuel, that the system pressure needed to be lowered or I'd have gas pouring out of my ass! Hey that rhymes!

patkeefe · 07:54 AM

Fred:
I have a special Brian Leask 930 WUR, which is adjustable for warm, cold and boost enrichment pressures. My SC has a turbo, an old BAE kit. I have percieved fuel delivery issues if I run boost over 6 PSI...what happens is my mixture goes a bit lean. I do not have these issues at 5 PSI boost pressure. Also, I do not use an extra fuel injector for supplemental enrichment. As such, I would like to try and see if I can tweak a few extra PSI of SYSTEM pressure to the fuel head.

My warm and cold CONTROL pressures are set exactly where I want them. If I lower my control pressure, I will get an across the board enrichment. I may get an across the board enrichment if I raise the system pressure, but I figure I'll give it a try, as that becomes only an expenditure of time. Another thing is addition of a second fuel pump, like a 930 has, but that costs money.

I only need to get a few more PSI SYSTEM pressure for the purposes of this test. I currentl have 72 PSI system pressure, which is right in spec for a NA SC.
Pat

edit:
sand_man: I have an IA modded head also. It does flow more fuel (it runs richer now than before I sent it to IA, which was the purpose of sending it to them). I just need to raise the pressure a bit.

sand_man · 09-07-2007, 08:02 AM

I've got the Leask WUR also, and his RPM solenoid trigger. All of this was needed to control the IA fuel head and obtain a flat AFR curve.

sand_man · 08:37 AM

I just noticed that you have a 930 WUR. Have you adjusted the boost enrichment? My WUR has a large disc on the underside...part of Brian Leask's modifications. Knocking this disc in increases boost control pressure - more lean. Backing this disc out, reduces control pressure - more rich. Mine also has adjustments for the "threshold"...the three screws on the bottom around the large disc. Consult the Leask manual for an understanding of this.

Mike_Lettrich · 09-07-2007, 12:01 PM

Pat,

Sorry to go OT on your thread, but why are you not interested in adding a 7th injector? I'm in the process of installing a BAE kit, too, and plan to go down the supplemental injector route. Certainly, if you could get addtional fuel from each injector, you could be sure that each cylinder is being fed equally. But it seems like the supplemental injector has worked well for a number of people on this board. Plus, I would think that having the 7th injector further upstream would help to cool the charge through the latent heat of vaporization of the extra fuel. I'm new to the turbocharging world, and am trying to learn as much as possible. Your thoughts would be greatly appreciated.

Paulporsche · 09-07-2007, 01:02 PM

Patkeefe,
No it's not like the fan belt. The number of shims is just whatever is required. I think there are even shims of different thicknesses.

patkeefe · 09-07-2007, 02:03 PM

Paul
Thanks!
Mike:
A couple of reasons for not wanting to add additional injection..
I don't have a blow off valve, it is actually a vacuum operated dump, which sends the compressed air back into the inlet side of the turbo, so when I chop the throttle, I'd be dumping fuel air mix back into the compressor. Also, I have water injection, so now I would have two liquid streams to evaporate. I just feel that I can support the necessary fuel requirements with the infrastructure I have; just needs to be tweaked. If you search my username and BAE, you will find out how not to reinvent the wheel.