How To Adjust Open Loop Fuel Mixture for Porsche 911 Bosch CIS K-Jetronic Fuel Injection
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- เผยแพร่เมื่อ 28 ส.ค. 2024
- Porsche 911 DIY Repair Blog: joe-engineer.com/
Tips on how to adjust the fuel mixture on air-cooled Porsche 911s running Bosch CIS K-Jetronic Fuel Injection. This is the complete adjustment for 1979 and earlier cars.
Additional Notes:
1. Applicable for Bosch CIS K-Jetronic cars 1973-1983.
2. Note: I am focusing on NA cars but 930 Turbo and early 965 Turbo cars running CIS also apply.
3. Bentley Manual 1978-1983: amzn.to/3LgjrCG
4. Please take all necessary safety precautions. Not responsible for any personal injury or vehicle damage.
5. Links to prerequisites before performing fuel mixture adjustment:
A. CIS Subcomponents Testing: joe-engineer.c...
B. Smoke Test for Vacuum Leaks: • How To Perform Smoke T...
C. CIS Fuel Pressures Test: • How To Test Fuel Press...
D. Valve Adjustment: joe-engineer.c...
E. Initial Fuel Mixture Setup: • How To Setup Initial F...
F: Ignition Timing: (link TBD)
G: Set your idle. This may need iterative adjustment as you dial in the mixture.
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IG: / joe_engineer
Great video explanation. That's exactly how I adjusted my K-Jetronic '83 BMW 320i. Your ear is the best instrument on these finicky systems.
FYI: Here in NC we have non-ethanol fuel readily available. I run pure Sunoco 95 octane. It's pricey fuel. Keep up the good work. I subscribed.
perfect video. my car has been set up like this for a long time and this finally gets me a better understanding on how the previous owners set it up. Its almost like adjusting a carburetor! LOL! one note I know from my old carburation cars that if you don't have a o2 meter then you can check how your plugs are burning. Clean one, run it 50 miles or so and check again to see how it is burning. Mine was white and running lean on all 6 plugs. Adjusting it now and hope to dial it in soon. Cheers....
Thanks Jose, like all your videos, this was another very informative one. Keep up the good work. I’ve got a ‘78 that I hope to one day have running as well as yours.
Thanks Joe. First video I have seen from you and that's a nice explanation. My car is a 1977 2,7 CIS and I seem to be having the same problems with a surging idol but only during the warm up cycle. During the first start up I get surging and the revs are really bouncing up and down until the car is up to temp. After that, the revs sit at a solid 950. This problem is really annoying and something that i have lived with for a few years, since I did the rebuild. Now, it needs to get sorted out. I think it is far too rich during the warm up cycle and it's like it's not getting enough air, but I am struggling to locate the issue. The Engine loom is new, the WUR & Fuel Distributer was rebuilt. The Thermo valve is new, the AAR is working correctly. All components in the system have power when the engine is running and seem to be functioning correctly. My fuel pressures are in spec etc etc. It's a real head scratcher but i will be using your videos as a guide to cross the t's and dot the i's! Thanks for positing.
Another great one. Thanks a lot for that
Great video , thank you got making it.
Thank you for the great videos. Please make a closed loop video. My AFR swings quite a bit in closed loop...
I suspect mine does too based on the sound it makes when fully warm. You can hear the corrections the lambda is making.
When you say "without a Lamda system"
Are you referring to those unfortunate owners who have a completely deleted lamda system (like myself)?
ie. Nothing there
Correct. No factory lambda, deleted or otherwise.
Thanks Joe.
So I can't find ANY lamda rel wiring or the FV. And my WUR has tubing to the vacuum adv circuit. Guessing I must have the "pre lamda" ktronic.
It seems like all there is to control the mixture is that screw and the WUR & cold start valve. 🙃
So the mixtrue screw only adjusts the flapper height up or down? Thanks for the video.
It adjusts the position of the piston inside the fuel distributor at idle, and therefore the idle fuel mixture.
@JoeEngineer thanks Joe. I followed all the steps you outlined on my 1982 911 SC. The 3mm allen appeared to be stuck as I cannot turn it. Probably hasn't been moved in years. I can smooth out the idle and eliminate the backfire by slightly lifting the plunger so by smell and the idle, it seems lean. I'll hit it with a bit of penitrating oil and let it sit overnight.
So my car has a pretty significant amount of idle surge. I'm going to smoke test it this weekend, but looking ahead here, how do you set the idle at 900 for this test when it's surging from like 1400 down to 500 back to 1400? If it's rocketing back and forth pretty quickly, I'm not sure how you're supposed to dial that in.
Generally if it's surging it's on the richer side and if it's popping and backfiring it's on the lean side. But I would fix all vacuum leaks before messing with the mixture.
To follow up on this, there was a vacuum leak at the manifold. The shop I sent it to didn’t bother to smoke test it when they set it up, so when I got it, they had set it to run REALLY rich. I found the leak and had them fix it and I’ve been working on correcting the mixture the past hour. I verified it was running rich (not that the copious amount of black smoke and surge didn’t tell me that) with the test by pulling and pushing on the plate flap. Idle cleaned up when pulling it down. So I let it warm up and tried to back the idle down. Got it down to where it was surging between like 800-1200 and started leaning it out. As I leaned it (which took a few clicks), the idle came up to like 1200. Dialed the idle back down a bit and the surging came back. Tested it, idle improved leaning it again. Gave it two more clicks and it cleaned up again, but idle went back up to like 1300. Repeated the process again.
At this point, the idle is pretty good, but is sitting at around 1100. No more surging, no backfires, etc. I think that if I did it again, I might be able to get it to idle down to where it should be, but I’m not doing anymore tonight.
Point is, that’s how badly the shop has the thing set up. It ran and drove, but it was so unbelievably rich that they had the idle screw really turned way past where it should be and the mixture screw at least one full turn to rich. At least.
It’s no wonder the gas mileage was atrocious.
Hi Jose, all the tuning applies while the engine is warm?
Correct! Open and closed loop. The only one you can do while cold is setting the initial mixture to just get the injectors to spray enough to start the engine (earlier video).
Hi Jose, quick question, in Ireland we have now been mandated to use E10 grade fuel, no E5 or full leaded fuel available at all. It is causing a lot of consternation in the classic car community. Obviously the higher ethanol content can be very problematic for older vehicles, particularly those with carburettors. I know E10 fuel has been available for about 30 years in the US, but I think you have a range of fuels available. What fuel grade do people typically use in classics, 30 years +?
I believe most of the fuel around here (southern California) is E10. While I was rebuilding my fuel system I replaced all my lines with E85 compatible rubber, for future proofing.
There is nothing that click's. It is just a screw.
You might want to watch the video again. Start at 11:00. He comments on the click @ 11:44 and then again and again and...
'promo sm' 🙃