MFI and Gunson gas tester

brokke · 03-31-2003, 05:52 AM

Hi,
This weekend I have been busy with adjusting my 2.4S MFI engine. I am using a Gunson gastester. I have read on this board that 7% CO stationary at 2500 rpm and 4% at idle are proper values. I am having problems getting 7% CO at 2500 rpm. When I rev the engine at 2500 - 3000 rpm the CO is slowly rising from 3 to 8 - 9 %. When I adjust the mixture leaner the performance of the car is getting worse (stumbling etc..) and the CO stays at 8 - 9 %. Looks as if I reached a bottom limit. Slightly above this limit (2 clicks richer) the car drives great, but the spark plugs (Bosch wr4dpo) look at the lean site. I don't get it. The gunson tester says a little rich, the plugs lean. ?????? Idle is 3 - 4 %, the idle rpm a little on the low site (750 rpm).

Any suggestions............

Peter
911 2.4S

jstobo · 03-31-2003, 06:38 AM

Peter,
The part load CO is adjusted at part load not stationary. According to the manual you must (I am using my memory so if my numbers are off the technigue isn't) open the thorttle plates 7 degrees put the car in second gear and drive then brake the RPM down to 2500 RPM and read CO.(of course at the Porshe dealer they probably have a dyno) Once that is set then the idle can be set. I drove my E for 15 years and never had a problem. Also 7% idle is too rich in my opinion. I think people need to put it there because they do the part load adjustment incorrectly. Look at the copy of check, measure and adjust here at Pelican. It shows the CO% for your engine. You are lucky. The 2.4 didn't need temperature correction. Prior to the 2.4 you had to measure the intake air temp to get the right percentage of CO. Remember you have a +- 0.5% range. Hope this helps. Good Luck.

Jim

jstobo · 03-31-2003, 07:50 AM

Peter,
Just checked the manual. For the 2.4 the throttle opening should be 9 degrees for part load and 2400 rpm, 2nd gear. It should read 2-2.5% CO. Idle at 900 RPM should read 1.5-2.5% CO. Now everyone will say that is too lean but it is factory settings.

Jim

brokke · 03-31-2003, 08:00 AM

Jim,

I know. I have read all the manuals. 7 degrees, 2500 rpm with the brake on. I wonder if there are Porsche dealers around who ever used this procedure. I have stand next to a experienced wrench who learned to work with MFI back in the 60/70's. He was just changing the rpm between idle and 2500 - 3000 rpm while he was looking at the CO tester. Also on this board I have read that it is posible to adjust mfi stationary, 3 - 5% CO at idle and 7 % CO at 2500 rpm.
The problem is that I can get the CO at 2500 rpm not any lower than 8 -9 % (with the Gunson gas tester). It started at 12% CO, after 2 clicks leaner it was 8 %, and it stayed there, also after two clicks leaner. The spark plugs also tells me that the mixture was too lean. The idle mixture was 3 - 4 %. The calibration of the tester is ok ( 2 %).

Peter
911 2.4S