3.0L CIS CO% measuring! Is it Lean?
 

Hi guys,

I am setting the mixture on my 3.0L Euro motor that I just put in my 70 targa.

It's a 3L with no cat, no air pump, and the older CIS with no O2 sensor.

The Gunson CO meter that I am using shows the idle mixture to be 5.0%. It know that this should be around 3-3.5%.

But went I hit the throttle. The CO drops to less that 1.0%. Is this too lean? I have idle mixture set at 5.0 CO because I don't want to run lean in mid range. What should the mid-range and high rpm CO measurement be?

Should I remove shimms from the check-valve in the fuel distributor to richen up midrange?

Also my Distributor advance is set at max of 40 btd. It doesn't run very well if I drop it to the recommended 35. It 40 too much? I don't think its detonating.

This is my first Cis car so please any help is appreciated.


Thanks

Get yourself a CIS fuel pressure testor. Very handy for diagnosing CIS issues. I spent forever trying to get my mixture correct until I found out it was the WUR malfunctioning.

Rob
1980SC

5% is still too rich. idle mix doesn't have much, if any effect on mid range on CIS cars. yes, 40° total advance is too much. yes, decreasing the main system pressure by removing a shim or two. provided they're the real thin ones, will help to richen mid range.

I received my Gunston Gastester last week. Keep in mind that it is only accurate to + .50, so a 3.0 reading could actually be a 2.5 or 3.5. I found this in the fine print somewhere in the documentation provided with the unit. Still not bad for a $125 unit.

I adjusted my 78SC (no O2, no air pump) down to 2.5 and it had NO power under acceleration. Finally raised it to 3.5 on the meter and it runs very well.

Follow-on question:

My recent smog check result for CO% was ".02" . Does this mean 2 percent or 2 hundredths of a percent? I realize that either way it sounds like I'm too lean and I hope that richening the mixture will help the hunting idle.

Thanks,

When they do a smog check they measure the CO% from the tail pipe after the catalytic converter. To set the mixture you have to measure it before the cat. ".02" CO% after the catalytic converter has cleaned it up.



Any one know what the CO% should be for a 79 3L with CIS. When I set idle to 3.5, I get midrang CO% less than 1.0. Is this too lean?

I set my 930 to 3%. I think that in the manual it says that your reading will go down if you rev the motor. I also noticed when I take the allen wrench out while adj. the mixture went from 3% to 1%. That little bit of air really makes a diff.

John Walker, anyone one who may know..

quick question..
To get the max performance or of my car.
what would you set the co setting to if you had this set up.

82SC motor
SSI's
GHL 2 in 2 out exhaust.
what would be a good co setting to get the th to run well and not to rich but not to lean?

Thanks I am asking as I am trying to find that happy / sweet spot
IS it also true to always make adjustments while the car is off.. then start her up to see the setting? so only adjust the mixture while car is off.

Thanks Guys
EricSmileWavy

Hit the 3-3.5% range. If you have your O2 sensor connected, disconnect it. Then set your timing to 35* max advance. It will run like a top!

You'll need to make adjustment w/ the car at idle then give her a few to stabilize and check your CO reading. After I finish adjusting I take it out for a run around the block and check it again. More than not I need to make an adjustment after this.

That seems very rich... as the factory setting says only to have it at like .06% so you think 3-3,5 % is the way to go with having all the listed items.. I do not have a 02 sensor car...

Thanks!

JW swears by it and many of us have done the same and loved it. Really smoothes out the idle and low end surging that many CIS car experience. Work for me!

Thanks..
you say that the setting are once again clockwise to lean and counter to fatten?

LOL

We really need to stay on one thread here! LOL!

HAHHA.. I have what I need.. Thanks brother! HAHAHAH1 I know I was jumping back and forth.. HAHAH
Thanks again.
:)

Eric

eric, clockwise to richen.

Eric, Simple Memory....Right to Rich, Left to Lean....

As far as i understand it , idle CO-adjustment screw only affects idle CO and is hardly noticeable as soon as you step on a accellerator.

When me and Jocke did sniff-tests on our 930's we both got 0.1% CO @ idle...(i also got 4.5% with non-warmed up engine, WUR fully on).

So i doubt that adjusting that will make engine run smoother troughout rev range, as that screw is only adjusting end-position for CIS-flapper and is out-of-the-loop as soon as you step on it and flapper goes down in the rush of the air.

From what I have read in the Bosch Technical manual on CIS, the adjustment is linear throughout the RPM range of the engine. 5% at idle will result in 5% at 3500RPM. Unlike carburetor systems, where the idle adjustment screw is adjusting the metering in the idle circuit, the CIS idle adjustment adjusts fuel pressure. The adjustment is fairly sensitive to even minute turns with the tool.

It seemed to me that the adjustment affected the whole rpm range. If it is fat at idle it is fat high rpm. Unless you have a high boost motor.

You can adj. the mixture while the motor is idleing. Just don't rev it with the tool in the hole. My CO meter settles very quickly (1-2 secs) after an adjustment.

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

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

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.

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

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.

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

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.

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) :)

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

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.

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 ... :D

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

Tony