CIS modifications
Thread Starter
Drifting
Joined: Jun 2001
Posts: 2,446
Likes: 1
From: Florida
CIS modifications
Hey guys,
I'm a regular on the 928 list but I needed help on another car of mine. I have a Mercedes 560 SEC with CIS-E fuel injection and an ATI Procharger pumping in 12 psi of boost. I'm running very lean after 3500 rpm and my power is suffering dearly. My power is peaking at 315 RWHP and 365 RWTQ at 3500 rpm due to the fuel starvation. Not to mention, I had to retard my timing by almost 15 degrees to avoid detonation.
My big question: Can I use an inline rising rate boost sensitive fuel pressure regulator to get the needed fuel? I've seen other cars with the RRFPR on the fuel return line that is used in series with the stock fuel pressure regulator, but I'm not sure if this would be compatible with the Bosch CIS.
Any help is greatly appreciated,
Jim Nowak
I'm a regular on the 928 list but I needed help on another car of mine. I have a Mercedes 560 SEC with CIS-E fuel injection and an ATI Procharger pumping in 12 psi of boost. I'm running very lean after 3500 rpm and my power is suffering dearly. My power is peaking at 315 RWHP and 365 RWTQ at 3500 rpm due to the fuel starvation. Not to mention, I had to retard my timing by almost 15 degrees to avoid detonation.
My big question: Can I use an inline rising rate boost sensitive fuel pressure regulator to get the needed fuel? I've seen other cars with the RRFPR on the fuel return line that is used in series with the stock fuel pressure regulator, but I'm not sure if this would be compatible with the Bosch CIS.
Any help is greatly appreciated,
Jim Nowak
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Joined: Oct 2002
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From: Cheshire, England
Jim,
On our 930's we use 7th (and sometimes 8th) injectors supplied with fuel pressure from the cold start injector feed pipe. There are many systems on the market, but we think that ours is unique.
We basically interrupt the trigger signal from the distributor to the CDI ignition box, add in a MAP sensor and by using a PC interface we have load sensitive ignition and supplementary fuel mapping. For a blown engine running no boost/no fuel and boost retard is a piece of cake.
BUT do not ask me if it will fit a Merc, I have not got a clue!!!
On our 930's we use 7th (and sometimes 8th) injectors supplied with fuel pressure from the cold start injector feed pipe. There are many systems on the market, but we think that ours is unique.
We basically interrupt the trigger signal from the distributor to the CDI ignition box, add in a MAP sensor and by using a PC interface we have load sensitive ignition and supplementary fuel mapping. For a blown engine running no boost/no fuel and boost retard is a piece of cake.
BUT do not ask me if it will fit a Merc, I have not got a clue!!!
Thread Starter
Drifting
Joined: Jun 2001
Posts: 2,446
Likes: 1
From: Florida
Colin,
Wow, with all that work why don't you just remove the POS CIS and do an engine management system. I had to do an Electromotive engine management system and rip-out the CIS in my 928 because it couldn't handle the power after extensive modifications.
I would like to modify the CIS in my Mercedes in an effort to save money. I'm not going to spend the money and the effort to try and salvage such an antiquated system. Like I said, I'll rip the CIS out before I spend $2,000 on a band aid.
Hasn't any of the 911 turbo owners tried the rising rate boost sensitve fuel pressure regulator? I ordered one to go inline with my stock FPR so maybe I'll be able to help y'all with my project and R&D. The people who sold the FPR said 911 turbo owners have used it with great success.
Basically, the unit gives between one and seven extra psi of fuel pressure per pound of boost. The FPR is made to work in conjuction with the stock FPR.
I guess I'll let y'all know how it goes.
Here are a couple of pics of my set-up for those that are interested:
<a href="http://boards.rennlist.com/upload/560SEC6.jpg" target="_blank">http://boards.rennlist.com/upload/560SEC6.jpg</a>
<a href="http://boards.rennlist.com/upload/560SEC7.jpg" target="_blank">http://boards.rennlist.com/upload/560SEC7.jpg</a>
Jim
Wow, with all that work why don't you just remove the POS CIS and do an engine management system. I had to do an Electromotive engine management system and rip-out the CIS in my 928 because it couldn't handle the power after extensive modifications.
I would like to modify the CIS in my Mercedes in an effort to save money. I'm not going to spend the money and the effort to try and salvage such an antiquated system. Like I said, I'll rip the CIS out before I spend $2,000 on a band aid.
Hasn't any of the 911 turbo owners tried the rising rate boost sensitve fuel pressure regulator? I ordered one to go inline with my stock FPR so maybe I'll be able to help y'all with my project and R&D. The people who sold the FPR said 911 turbo owners have used it with great success.
Basically, the unit gives between one and seven extra psi of fuel pressure per pound of boost. The FPR is made to work in conjuction with the stock FPR.
I guess I'll let y'all know how it goes.
Here are a couple of pics of my set-up for those that are interested:
<a href="http://boards.rennlist.com/upload/560SEC6.jpg" target="_blank">http://boards.rennlist.com/upload/560SEC6.jpg</a>
<a href="http://boards.rennlist.com/upload/560SEC7.jpg" target="_blank">http://boards.rennlist.com/upload/560SEC7.jpg</a>
Jim
Rennlist Lifetime Member
Joined: Jun 2001
Posts: 4,577
Likes: 9
From: Kansas City
Colin,
The 7th and 8th injector systems are a great quick fix but in time WILL cause something to hole. The flow of the CIS intake is terrible and we have seen as much as 33% difference between runner to runner. The other problem is the CIS manifold is poor in flowing it is meant to flow air, not fuel which is more dense and therefore also causes a bigger difference in flow. You get severe hot spots and one good punch and WHAM. We no longer will use 7th injectors for this reason. As weekend drivers you may not see it that much, but driving it everyday as Monster and BB was you see these things quickly. If you really wanted to use a 7th system then the HKS AIC is the way to go, but new blocks are needed to evenly distribute the fuel. An injector per runner at the base is the best. Of course pushing above 500HP consistently is a challenge as the intake CFM rate is still very poor in comparison to the 3.2. By the time the project is done you could have picked up 50+ HP, if not more with a Carrera intake and aftermarket injection/ignition.
The 7th and 8th injector systems are a great quick fix but in time WILL cause something to hole. The flow of the CIS intake is terrible and we have seen as much as 33% difference between runner to runner. The other problem is the CIS manifold is poor in flowing it is meant to flow air, not fuel which is more dense and therefore also causes a bigger difference in flow. You get severe hot spots and one good punch and WHAM. We no longer will use 7th injectors for this reason. As weekend drivers you may not see it that much, but driving it everyday as Monster and BB was you see these things quickly. If you really wanted to use a 7th system then the HKS AIC is the way to go, but new blocks are needed to evenly distribute the fuel. An injector per runner at the base is the best. Of course pushing above 500HP consistently is a challenge as the intake CFM rate is still very poor in comparison to the 3.2. By the time the project is done you could have picked up 50+ HP, if not more with a Carrera intake and aftermarket injection/ignition.
