Running Rich - CO adjustment has no effect
 

I have an '85 Carrera I am struggling to get to run correctly and would really appreciate some input on. My problem is the engine is running rich at idle no matter how far I back out the CO adjusting screw. I determined this by disconnecting the oxygen sensor and reading the voltage with a multimeter. It won't go below 0.8v and turning the screw out seems to have no effect. I believe this rich condition is also causing the car to stall out on me when cold when I disengage the clutch while coming to a stop. I found that by loosening the oil cap to allow a vacuum leak I was able to make the mixture go lean (0.1v). I was even able to dial it in to close to 0.5v by holding the cap carefully to control the amount of air coming in, but as soon as I tightened it up the voltage shot back up to 0.8 or higher.

There is one other issue that is concerning me, but I am not sure if it is related or not. At idle I hear a distinct tapping sound that is somewhat intermittent. I thought it might be lose valves, but I carefully set the valve lash and it made no difference. I also think loose valves would make a more consistent sound. Sometimes the tapping sound fades away as the engine idles, and this seems to correlate with a change in the way the engine runs. The sound also seems to fade away at higher RPM.

Here is a summary of the work I have done up to this point:

Replaced O2 sensor.
Set valve lash.
Replaced idle control valve.
Replaced crankshaft position sensors.
Replaced cylinder head temperature sensor.
Verified the idle switch on the throttle body is working correctly.

Replaced fuel pressure regulator and dampener. Also confirmed there is vacuum applied to them by disconnecting the rubber elbow and feeling the suction.

Had fuel injectors cleaned. - the report indicated 2 were dripping and flowing a little slow before the cleaning. I was able to lean out the mixture with the CO adjustment screw before having the cleaning done, but can no longer do so.

Opened the air flow meter and moved the wiper arm to a fresh track. - I did not adjust the spring, but it appeared someone may have in the past.

I have a couple of theories about what may be causing the rich condition. First, could the CO adjustment mechanism in the air flow meter simply be clogged? Second, if someone loosened the air flow meter spring a few notches, could that cause the rich condition?

I also have a theory about the tapping noise. Setting the valve lash tightens up the rotation of the rocker arms and eliminates tappet noise, but the rockers also have some end play on the rocker shafts. Could the noise simply be a rocker arm slapping back and forth on its shaft? I can post a youtube video with the sound if that would help. I know 911 engines are famous for clattering, but this sound seems a little out of the ordinary.

I would really appreciate any suggestions or input on these problems. I have searched all over this forum and tried a lot of different things, but still can't get it dialed in. I think I am really close to solving this, but I can't quite figure it out.

Thanks

You really need or borrow a LM1 or LM2 to properly adjust AFR at the AFM at operating temps with O2S disconnected and after reconnect and adjust the Base Idle dependent on the chip you have in her.

PM and I will explain.

But don't those meters require that you drill into the exhaust and install (weld) a sensor first?

These cars have an O2 sensor. The adjustment is done with the stock O2 sensor disconnected so you just put in the wideband sensor while you are adjusting.

When people permanently put in a wide band sensor they replace the stock one and there are some electronics that piggyback the sensor to feed the correct signal back to the DME.

I think I see... So the O2 sensor is removed, then replaced with the one from the metering unit to obtain the readings? I was thinking there were units that read the O2 levels at the tailpipe. Is that a different kind of unit?

Oh no, you just disconnect the o2 sensor and put the LM sensor via the sniffer into the tail pipe.

It is best to remove the o2s and place then LM sensor before the cat for the most optimal AFR adjustment but most will not due to the inconvenience.

Car must be hot when testing and adjusting then set base idle.

I suggest a fuel pressure test. With engine at idle should read 30PSI then remove the vacuum line from the regulator and the pressure should go up to 36PSI. Have you tested this yet?

You asked if someone loosened the spring in the AFM a few notches could it cause rich condition? absolute YES! If you suspect this is the case then tighten the spring 2 notches and test again, do you have any idea where it may have been originally? Did someone leave a mark or something on the wheel?

Other possibility is that the injectors are now somehow leaking after they have been cleaned? Or that injectors from the RHS are now in the LHS? The O2 sensor only sees exhaust from the LHS so try swapping injectors from LHS to the RHS and see what happens. Also do you have the flow details for the injectors?

And you are correct that it is possible to set the base mixture by just using the stock O2 sensor as you are doing. Disconnect the sensor and monitor the signal line, <0.3vdc lean : >0.7vdc rich so you simply adjust the AFM mixture screw by turning it out till it leans then turn it in while counting turns till it richens. Then set the screw half way between those 2 points and your in the ballpark, not perfect but close.

Thanks for all the replies, I really appreciate it.

Draco, the LM1/LM2 look like a good way to measure the CO. I will have to think about ordering one. I think there is something wrong beyond the adjustment since I can't get the O2 sensor voltage to come down below 0.8 with the adjustment screw. I would really like to figure out why I can't lean out the mixture and get it in the ballpark. My multimeter has a record function and will display the average voltage it reads from the O2 sensor and I think I can get the mixture set reasonably close that way. Will take it to a shop with a smog machine or order one of those LM1/LM2 devices to dial it in from there.

My car has no cats, so it's easy to put in a smog sniffer to set the mixture.

Scarceller,

I have not yet checked the fuel pressure. I will have to track down a pressure gauge and test it. Can anyone recommend a good pressure gauge that will fit on the fuel rail fitting?

When I opened the AFM, it was clear I was not the first person to do so. Someone did leave a mark in there, but I couldn't figure out how to interpret it. I am tempted to try tightening up the spring a couple of clicks to try to get the mixture to lean out, but am very nervous about messing with that setting. I'll open up the meter again and look closely for any evidence of where the spring might have been set in the past. Can also check for any obstruction of the CO adjustment mechanism while I have it out.

I didn't keep track of where the injectors came from when I removed them. The report from the injector shop indicates two of them had a dripping spray pattern and the flow rates varied from 217 to 235 cc/min before the cleaning. After the cleaning, the report says they all have an excellent spray pattern and vary from 239-241 cc/min. I had not thought about the O2 sensor only reading the left bank. The cleaning report suggests the injectors should all perform the same, but if I switch them and it changes the O2 sensor reading that would surely indicate something is amiss with the injectors.

Does anyone have any thoughts about the tapping sound? I have been looking through a lot of old threads on the subject and have found a few possibilities. So far I have come up with axial play of the rocker arms, a broken valve spring, or a collapsing chain tensioner. I didn't notice any broken valve springs when I did the valve adjustment, but I wasn't really looking for one. In addition, replaced all the valve springs when I rebuilt the engine (I know that doesn't rule out a broken spring). I don't think the tapping sound is consistent with a loose chain dragging in the case, and I remember the tensioners were very hard to compress when I took them out for the rebuild. Not sure I can rule that issue out 100% though. The axial play of the rockers sounds like a strong possibility. When adjusting the valves, I have noticed significant axial play of the rockers, and wiggling them back and forth makes a tapping sound against the cam tower. I found this video from an old thread that demonstrates the tapping sound generated by axial rocker play:

To test Fuel Pressure just get any gauge then attach it to a hose that fits over the port on the LHS rail and use a hose clamp to clamp the hose to the port. You don't need a exact gauge that thread to the port, you just need a gauge that can use a hose to clamp to the port.

I hear that the Harbor Freight gauge will work well.

Also note what the Fuel Inj numbers tell you. You went from 217-235 cc/min up to 239-241 cc/min they came back flowing more fuel then they did before cleaning.

As for the AFM spring tension don't worry about tightening it just go ahead and try it. But before you do mark the current location with a good marker or nail polish.

If you PM me I'd be happy to share my doc on the theory of how that AFM works. I spent significant time understanding these AFMs a few years back and I wrote a nice doc.

Thanks for all the replies, I really appreciate it.

Draco, the LM1/LM2 look like a good way to measure the CO. I will have to think about ordering one. I think there is something wrong beyond the adjustment since I can't get the O2 sensor voltage to come down below 0.8 with the adjustment screw. I would really like to figure out why I can't lean out the mixture and get it in the ballpark. My multimeter has a record function and will display the average voltage it reads from the O2 sensor and I think I can get the mixture set reasonably close that way. Will take it to a shop with a smog machine or order one of those LM1/LM2 devices to dial it in from there.

My car has no cats, so it's easy to put in a smog sniffer to set the mixture.

Scarceller,

I have not yet checked the fuel pressure. I will have to track down a pressure gauge and test it. Can anyone recommend a good pressure gauge that will fit on the fuel rail fitting?

When I opened the AFM, it was clear I was not the first person to do so. Someone did leave a mark in there, but I couldn't figure out how to interpret it. I am tempted to try tightening up the spring a couple of clicks to try to get the mixture to lean out, but am very nervous about messing with that setting. I'll open up the meter again and look closely for any evidence of where the spring might have been set in the past. Can also check for any obstruction of the CO adjustment mechanism while I have it out.

I didn't keep track of where the injectors came from when I removed them. The report from the injector shop indicates two of them had a dripping spray pattern and the flow rates varied from 217 to 235 cc/min before the cleaning. After the cleaning, the report says they all have an excellent spray pattern and vary from 239-241 cc/min. I had not thought about the O2 sensor only reading the left bank. The cleaning report suggests the injectors should all perform the same, but if I switch them and it changes the O2 sensor reading that would surely indicate something is amiss with the injectors.

Does anyone have any thoughts about the tapping sound? I have been looking through a lot of old threads on the subject and have found a few possibilities. So far I have come up with axial play of the rocker arms, a broken valve spring, or a collapsing chain tensioner. I didn't notice any broken valve springs when I did the valve adjustment, but I wasn't really looking for one. In addition, I replaced all the valve springs when I rebuilt the engine (I know that doesn't rule out a broken spring). I don't think the tapping sound is consistent with a loose chain dragging in the case, and I remember the tensioners were very hard to compress when I took them out for the rebuild. Not sure I can rule that issue out 100% though. The axial play of the rockers sounds like a strong possibility. When adjusting the valves, I have noticed significant axial play of the rockers, and wiggling them back and forth makes a tapping sound against the cam tower. I found this video from an old thread that demonstrates the tapping sound generated by axial rocker play:

rocker_motion.m4v - YouTube

Thanks again for all the input. I feel like I am finally seeing some light at the end of the tunnel and hope to get my engine running properly soon.

Update!
 

Last night I made some progress. First, I pulled the intake valve covers. I rotated the crankshaft until each intake rocker was clear of the cam and did the "thumb test" for broken valve springs. I found all the valves were extremely hard to press open, requiring pushing a plastic screwdriver handle against the adjustment screw with both hands. Unfortunately, I don't think this is sufficient to rule out the possibility of a broken valve spring. Is there any clever way to rule out a broken spring short of removing the rockers? Is it possible to see the springs well enough with an inspection mirror?

I also checked the axial play of the rockers. Looking up a few old threads gave a spec of .5mm or 0.020 inches as the limit. I was unable to insert a 0.020 feeler gauge next to any of the intake rockers. I think I can safely rule out an axial play issue on the intakes.

After I finished looking over the intake valves, I pulled the AFM and removed the cover. I found a mark had been scored in one of the teeth on the plastic spring wheel. This mark was about 7 notches away from the retaining spring. I tightened the wheel ~7 notches to align the mark with the retaining spring. After warming the car up, I was able to dial in the O2 sensor to ~0.5V with the adjustment screw backed out about 2 turns. The throttle response has improved significantly and the car seems to run much smoother now. The engine speed drop issue when I pop the clutch while coasting to a stop has been reduced significantly. When the car is warn, the speed drop is barely noticeable, but when the engine was cold this morning it still stalled out on me once when I put the clutch in. I'll check the O2 sensor voltage tonight to confirm it is still dialed in.

Anyone have any thoughts on the tapping sound?

Thanks

Set the base mixture slightly rich, find the mid point and then turn in an extra 1/4 turn see if that helps the idle dip issue.

The very best solution is a custom chip to fix the idle dip, most decent chip tuners already address this area, I know I do. Especially for light fly wheels. The problem is that the injectors don't come back on from decel fuel cut till 1200RPMs in the stock chips. Raising this to 1400 or 1600 RPMs really helps fix the idle dip. The other thing that helps is to set the base idle at 900RPMs when setting base idle.

Update
 

It has not stalled again, but will dip to a near stall when the engine is cold. I will keep checking the CO adjustment, then see about setting it with a shop sniffer once I get it consistent. I am finding the O2 sensor voltage trends to the rich side the longer the car idles. Is it best to set it immediately after stopping the car with a warm engine before it has a chance to idle for too long?

I think adjusting the AFM based on the mark I found was one of the best things I have done for the car so far. It runs noticibly smoother all around.

Scarceller,

My car has the lightweight aluminum pressure plate. That must encourage it to stall faster than the computer can react. I currently am running a Steve Wong chip. In a previous thread about my stalling problem it was suggested that going back to the factory chip would eliminate the issue. I tried that and found the factory chip mitigated the drop in rpms when coming to a stop and eliminated engine stalls. Despite this, I felt the car ran much better in all other respects with the Steve Wong chip and believed that my engine had other problems. Interestingly, the Wong chip starts the injectors at 1200-1300 rpm compared to the factory chip which picks up somewhere around 900. What I have found strange about the engine stalls is they only occured below the 1200-1300 rpm threshold and above ~500 rpm or so.


Anyone have any thoughts on what could be causing the tapping sound. I have noticed it with the engine hot and cold, but it seems to happen more often hot. It is also intermittent and will often tap for a little bit, then fade out and sound perfect, then come back again. It is most pronounced at idle, is noticable under 2000 rpm and becomes inaudible by 3000.

Thanks

The stock chips all turn injectors back on at 1200RPMs you can actually feel this if you decel in 2nd gear and let it coast down. Right at 1200RPMs you should feel the injectors kick back in and the car lurches forward.

You can then do the same for any performance aftermarket chip to find that injector on RPM.

If you are running a reduced weight flywheel or any reduced weight crank setup then you certainly can benefit from a much higher fuel cut point. In my setup I have my chip set at 1600-1800RPMs, I can set it at whatever is appropriate for the motor.

still no video hard to tell from your description. :-/