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16Volt 16Volt is offline
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Join Date: Oct 2013
Location: Seattle, WA
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Originally Posted by Ronnie's.930 View Post
Regarding your mechanic's comment that all 930s surge somewhat at steady cruise - he's mistaken about that. Is that John Walker you are referring to? If so, I'm surprised to read that.
Its entirely possible I miss-heard him. Not a big deal, at the end of the day the surge is an issue and our first attempt to resolve it was purely focused on mixture.

Originally Posted by Ronnie's.930 View Post
The first thing you need to do is replace all of the small vacuum hoses as they are, no doubt, all in the same shape as the ones in your picture. Along with that, you need to try and check for any other vacuum leaks as those will upset the the K-Jet system in a big way (such as - vacuum leak causing a false rich condition which can then result in missing/bucking/hesitation).
Yeah, I am decently versed in CIS on other vehicles. I have the car torn down to the intake manifold at this point. You can see in this pic where the black line from the distributor vacuum canister goes into the throttle body.

IMG_5719 by thecrashingdoor, on Flickr

The red line from the other side continues back to the crankcase breather. Is there anything special about the red hose material wise? All my replacement hose is black. All the other lines do in fact look ok, I am hesitant to go in and cut the one time use clamps off since I know what a pain that is. Keep in mind the motor is in the car.

Originally Posted by Ronnie's.930 View Post
Do you have an air-to-fuel ratio meter on your car? It would be interesting to see what your AFR is at steady cruise - too rich and too lean can both cause the running situation that you describe.
I do not have the WB 02 installed in the car unfortunately. It will probably be mid march before I can get the time/help to get all that stuff wired in (I have a PLX unit).

Originally Posted by Ronnie's.930 View Post
Also, insufficient charging voltage can be a cause (but probably wouldn't show at just steady cruise, though) - can you take voltage readings at different RPMs?

Also bad electrical grounds - I had a bad ground (ground for the engine wiring harness - bolts to the coil bracket) that made the Lambda system erratic, and I chased my tail with that for a couple of months until I found it!
I read your thread on that, what a nightmare. The grounds look great but I will go over them again just to be sure.

Originally Posted by Ronnie's.930 View Post
Another thing worth mentioning - with the Lambda assist, K-Jet (like you have), you can't just unplug the O2 sensor, set idle CO2/AFR, and expect it to run right at steady cruise as it will now likely be too rich at that engine speed without the Lambda computer raising control pressure. You would need an onboard AFR meter to check this. If it is then too rich, then you would need an adjustable WUR so that you could tune for a good cruise AFR of 14.5 - 14.7. Also, running the RPM up, at a stand still, with a tailpipe sniffer in place doesn't do any good because there is no load on the engine. I'm not saying that any of this has been done to your car, but thought it might be something to consider since you made mention of the disconnected O2 sensor.
You're correct and I have read as much in various threads. I have also read the counter threads like Mark relates that its possible to run open loop as with good results as well. I guess the real test here would be to pony up for a new stock 02 sensor and test.

The ignition leads were likely removed as a part of the tune up but given how great it ran before I fixed the vacuum line I am pretty confident they are fine.

OilOnly - I got your PM and will give you a ring tonight when I am in front of the motor.

Does anyone have any guesses on why hooking up the vacuum line would have brought back all the issues?
- 86 Porsche 930 - Mr.Hyde
- 86 BMW 635CSi - Dr.Jeykell
- 2006 Infiniti M45 Sport
Old 02-18-2014, 09:28 AM
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