Fuel Head

[JFairman]

Before putting the top and bottom half's of the fuel head back together I did oil the control plunger barrel and fuel slit o-rings so they would slide and not be damaged while pressing the upper and lower half's together. You don't just press them straight together in a hydraulic press or whatever, you do it by hand and press down on the opposite sides with opposing force so it rocks side to side a little on the control plunger o-rings. They have a little give. It's hard to describe what I'm trying to say in words alone.

This video helped.
It's Mercedes V8 fuel head he's working on so it's different but similar to a 930 fuel head.
https://www.youtube.com/watch?v=HQFhmVHp65o

Around 5:30 he starts pressing the fuel head back together by hand. He's sort of rocking the upper half side to side at first so the o-rings don't get rolled over or torn as the control plunger cylinder gets pushed into place.

Like him I did it by eye with no guide pins and used the bolts to align and pull the upper and lower halfs together once they would start threading in place. If you turn the fuel head sideways before the gap closes up the white plastic metering discs can fall out and you have to take it back apart and start over so I kept it level while pressing them together.

This PDF link for a 928 fuel head is helpful too.
http://www.porsche928forums.com/download/manuals/CISRebuild.pdf

[T77911S]

as soon as you turned the allen adjusters you changed how much the head will flow unless it was set to flow max.
for my euro head the stock setting is 20% below its max flow. I had larry increase mine to 10% of max. that was done with the 3mm allen screws. so the screws set the flow rate and the balance,

the screws ADD pressure to the springs that push open the valve seat. the system pressure on the lower chamber is trying to close the seat. I look at it as a balancing act between the top pressure+spring and the lower pressure.

in the euro head and the SC heads, that fiber "gasket" is a metal shim or gasket which I would think would be better but according to larry the metal ones "dimple" and cause issues.

I would be curious if larry checks the springs to see if they are all the same PSI or if he checks the thickness of those plastic disks.

sorry, I love CIS. its so reliable,
I told larry I would love to come work for him but I know he could not pay me what I make now.

[Rawknees'Turbo]

Originally Posted by T77911S

sorry, I love CIS. its so reliable,

???

You've been posting for several years that your 930 has yet to run right despite vast amounts of work and component swapping (persistent, random changes in AFR is one problem I recall) - I would have thought you hated CIS by now.

[JFairman]

"as soon as you turned the allen adjusters you changed how much the head will flow unless it was set to flow max."
It is an aluminum fuel head that was set and balanced to flow max or approximately 20% more than stock by Larry in 2006 a few months after I bought the car. One of the 3mm allen adjusters was turned clockwise or tightened all the way and that proves it. The other 5 adjusters were not turned clockwise all the way. They were close but not all the way because they were adjusted to flow the same as the one that was tightened all the way.

"for my euro head the stock setting is 20% below its max flow. I had larry increase mine to 10% of max. that was done with the 3mm allen screws. so the screws set the flow rate and the balance,"
I've read that the cast iron fuel heads can not be adjusted to flow more than 10% over stock because the stainless steel diaphragm inside them is a lot stiffer than the aluminum fuel head's rubber diaphragm so it can't flex enough to allow it.

"the screws ADD pressure to the springs that push open the valve seat. the system pressure on the lower chamber is trying to close the seat. I look at it as a balancing act between the top pressure+spring and the lower pressure."

If you turn the 3mm allen head spring tension adjusters clockwise compressing the spring, the white plastic discs and rubber diaphram are pushed downwards away from the metering orifices in the top half of the fuel head or upper chamber increasing flow to the injectors and balancing them when adjusted correctly.

The position of the metering piston inside the metering slit cylinder controls the overall fuel injector flow. The 3mm allen adjusters can increase flow up to around 20% more than stock settings in the aluminum fuel heads and balances the fuel flow from the individual injector lines to the one that can flow the most when it is turned clockwise all the way maxing it out.

[T77911S]

Originally Posted by Rawknees'Turbo

???

You've been posting for several years that your 930 has yet to run right despite vast amounts of work and component swapping (persistent, random changes in AFR is one problem I recall) - I would have thought you hated CIS by now.

I love it. I think it is a very neat system and I like the engineering that had to go into it, much like a Porsche. I do realize its short comings.
wish it was easier for me to do flow tests.
my 77s had flexible lines so it was very easy to pop the injectors out and do tests.
I did many many hrs of testing on my fuel head on the 930 and changing the flow but it was a royal pain because of the metal lines.
I also did lots of testing on my 77 with timing vs mixture and heat.

the car has been running really well. its still not "perfect" but only I notice and my brother and others think I am nit picking about it.
my problems were air leaks. some I created by venting my DV to atmosphere, some were the synopse leaking air.
I also had problems with the manifold flanges not being flat and causing air leaks at the intake gaskets.

[JFairman]

I'd like to know why they invented it.
CIS reminds me a little of old SU and Bing constant velocity carburators.

[Rawknees'Turbo]

^^^

And along with that, I'd like to know why Porsche continued to use such a silly, over-engineered, dinosaur tech system on their flagship car for more than a decade after Motronic was being used on non-turbo 911s. That really seems asinine to me.

[JFairman]

I put my rebuilt fuel head back on today. Hooked up the lines, did a flow test with and without the injectors into the plastic bottles, and it seems to be working perfectly!
All the injectors squeal and spray equally like they should and they all shut off completely when the air flow sensor plate is at rest.
I had to fiddle with the spring tension adjusters under the button head screws and go through the process 5 times and finally got them pretty close to equal.
I was worried the fuel head would still spray fuel from #4 at rest like it was doing before but the rebuild kit fixed it!

[RarlyL8]

Nice goin' Jim!

[JFairman]

Thanks Brian
It's a good feeling and I saved a lot of $ and time doing it myself. Good learning experience too. The you tube videos really helped.

[Rawknees'Turbo]

Man, really good to hear!

[JFairman]

yeah man!

[OSI930]

Nice work, Jim.

[356911930]

You must be walking on air! Congratulations Jim.

Rahl

[smurfbus]

Good job Jim and good read for archives too when needed.

[boosted79]

Alright!

[Tippy]

Originally Posted by Rawknees'Turbo

^^^

And along with that, I'd like to know why Porsche continued to use such a silly, over-engineered, dinosaur tech system on their flagship car for more than a decade after Motronic was being used on non-turbo 911s. That really seems asinine to me.

Agreed, when they simply could have used a MAP sensor with the 930's and the O2 sensor for fine tuning as normal.

[heliolps2]

Great job sir......Did you get a chance to do a test drive yet

[RarlyL8]

And along with that, I'd like to know why Porsche continued to use such a silly, over-engineered, dinosaur tech system on their flagship car for more than a decade after Motronic was being used on non-turbo 911s. That really seems asinine to me.

The way I understand it Porsche had a bunch of 3.3T CIS 930 engines when the 965 was stillborn in the late 80's (partially due to price overrun). They used the engines they had through 1994 in the 964T saving a ton of money. The Carrera went on in '84 with Motronic/EFI and then the 964 in '89.

[JFairman]

Today it's cloudy and not mind bending hot out so I put the intercooler back on and fired it up. It started right up and runs perfectly smooth on all 6 cylinders!
It's a wonderful thing
I think I like the car again...