3.0L CIS CO% measuring! Is it Lean?

[stlrj]

The contours of the walls on the air flow meter dictate what the mixture will be on throttle and since the CIS system was designed and based on smog restrictions, on throttle CO readings are difficult to measure since they typically run in the zero range. That's why a little fat at idle is a good thing.


Joe

[diy83sc]

I finally got my Gunson and timing light. Set the CO to 3.5% and advance to 12 deg BTDC at 950RPM with the hoses disconnected and plugged. I checked total advance with the hoses connected and it is somewhere between 33 and 35 deg. The problem I have is that the left bank (123) plugs have light carbon and the right are just about clean. Number 2 has a bit more carbon than the other two. The engine idles smooth until I raise the RPM above 1200. It then begins to "shake" as if some of the plugs are not firing. I just replaced the 20 year old wire with new beru wires (OEM) and replaced the cap, rotor, and plugs. About 4K miles ago, I replaced the injectors.

For 83 CIS cars, is there a way to balance the mixture across the two banks of cylinders? Where should I be focusing my attention?

Tony

[tsuter]

Too much advance. Try 5 deg BTDC at 950 with the vacuum hose disconnected. With a total mechanical advance of 20 more degrees to 25 BTDC at 6000. The reconnect the vacuum line.

[diy83sc]

That's where I started (factory spec.) I basically had the same problem with an rough running engine past 1200 rpm. I then read some of the other posts of replacing the cat with OEM pre-muffler, disconnecting the 02 sensor, and then advancing the timing to 35 deg total. Several posts showed that by setting the timing to 9-12 degrees, I would effectively be setting total advance to 31-35 deg. How would timing affect the fuel distribution? I am assuming that the fuel distrib may be the problem as most of the ignition related components have been replaced.

Tony

[tsuter]

Too rich can also make it run really rough under any load. Will sound OK when you push the throttle linkage down but as soon as you get in 2-3 gear - very rough. Means too rich. If you are at 3.5% or less - OK. How old are the plug wires - arcing etc. will also make it run very bad under load as well. But first get the timing to factory spec. Then check your CO, then check your wires and boots. There is no way to compensate left bank right bank in CIS. Bad injectors can account for some things as can a bad fuel distributor but check the easy and cheap things first.

[diy83sc]

I replaced all of the things you mentioned, including plug wires and injectors. For the fun of it I retimed the car to 5 BTDC. The idle plug is all the way out, barely making the 900 rpms. Could this have anything to do with my problem? Sorry to take over the thread, but were still talking CIS and mixture...

Tony

[tsuter]

If that idle adjusting screw is that far out, then you likely got an air leak somewhere (air getting in past the throttle body butterfly). So best to start a new thread or search on CIS and maybe leaks.

[Gunter]

Tony: If the large, slotted idle adjustment screw is all the way out and you barely get 900 RPM, maybe you need to check the basic setting of the throttle plate. There is a small adjusting screw, with a counter nut, on the outside of the housing. It's a dead-stop for the throttle plate and not meant to adjust idle. The basic settings are explained in the Bentley (240-4)

[stlrj]

If you can see any carbon on the tips of the plugs, that might be a sign that they are misfiring even if only 4,000 miles old. Start with a fresh set and then see how it revs.

Joe

[MotoSook]

just to steer this more off topic...

Tony, has the motor been behaving like that prior to your changes?

If you varified that the ignition is good, and you are still not getting proper combustion on the left side, have you checked for proper fuel on that side? Pull the injectors and see if they spray properly. Search the BBS for procedure or start a new thread (better to get your solution).

If you are running only on one side (mostly), it would explain your over compensation with fuel and air to maintain idle.

Don't rule out your new plugs as having been fouled....it can happen.

I would not change anything else on the motor until you check your work and some of the more simple tasks. Read the manual (Bentley is good to some point) and understand the system. Although the CIS is not too complicated to those that have spent time with it, it might be enough to have you going in circles (ask me how I know). Make sure you know what to expect when you make a change.

[diy83sc]

All,

I don't have a bently manual yet but will soon. I have the Haynes, which looks like an abbreviated guide to a 911 ...

Thanks for your help. I'll most likely start another thread after I do some more tests.

Tony