Newbie seeks CIS guru with GSOH

[2.8jonny]

Newby Modified engine k jetronic woes
Hi all,

I have often observed this site as an outsider with great interest and hope that you wont mind me leaning for help the second i joined!!

I have a k jet without lambda fuel injection system factory fitted to a European Ford Capri 2.8 V6. I know this is not a manufacturer you guys deal with but i'm hoping that the fueling system we share may sway you towards reading on.


My engine has had extensive top end work done,
Full big valve race heads skimmed by 1.5mm with a comp ratio of 9.5:1 (std 9.2:1)
Plenum and inlet are flowed and port matched origionals
Exhausts are matched, tubular, high flow after market units
The cam is a very mild fast road item
The capacity of the engine remains as factory ie std bore and stroke.

When i fitted all of this in order to achieve a smooth idle i had to lean out the idle mixture with the CO screw a fair bit.

Some weeks went by and with a substantially faster but more highly strung engine i went to the local rolling road.

The engine made substantially more torque and power than standard BUT the fueling was very lean. With CO, control pressures and system pressure at factory she ran lean at all but full throttle. Even at full throttle she was lean until 4500rpm.

I have made the WUR adjustable as many web sites suggest but tapping the cold control pressure plunger and uncovering the hot control adjusting allen screw in the base. Still the full throttle mix was lean at low revs. So I made the brass seat that the vacuum enrichement diaphragm falls on to adjustable by pressing in a machined alternative that can be adjusted simply with a screw driver.

So then i had an adjustable WOT (wide open throttle) adjustment that meant i could set the afrs where i wanted at full throttle.

Still no amount of fiddling with the hot control pressure would give me a a rich enough afr at anything but WOT. Any gains made by dropping the control pressure were lost as the idle ended up so rich that when brought back to a usable level with the CO screw any gains from the control pressure drop were lost!!

Next i experimented with Audi 5 cylinder air metering units, to see if there cone profile would be better suited to my engine but it ran rich. I then turned new proiles in to the audi units with some success but not to a satisfactory conclusion.

Sadly i am on rather a junk yard budget and i only have a narrow band lamda set up to measure the fueling but i should at least be able to get i to run near to stoich 14.7:1, shouldn't i? I should also mention that i have made a test rig with pressure guage to monitor the controll and system pressure.

I have tried swapping many different parts on the fuel injection system including the distributor with no improvement.

So my questions after that introduction are, has anyone experienced similar leaning problems on a modified engine using k jet and what was your sollution? Or does anyone have any idea what went wrong and how i can resolve it?


Many thanks to anyone who takes the time to read my post.


Jon....

[Danglerb]

CIS isn't really made for tuning, as you have found the adjustments interact and are very limited. That said, with a mild cam you should be able to beat it into shape, but may have to decide which is more important, idle or WOT.

Volvo sites may have some good tuning info, also take a look at, 928 Motorsports - Performance Parts - Adjustable CIS Control Regulator for the Porsche® 928