Running lean now??
 

Okay, so I recently dropped my engine/tranny to replace my transmission, and I figured while I was in there I'd replace all the rubber parts on the outside of the engine, and clean things up. So I replaced all the vacuum lines, oil seals, CIS air-flow plate gasket, and rubber o-rings like the ones on the throttle body, fuel metering block, and the injectors and injector sleeves, etc...etc... The list goes on and on, I just don't want to bore you with details. I also cleaned the injectors in an ultrasonic cleaner and then had them tested afterwards, they performed perfectly. To finish it off, I installed a "pop-valve" just for precaution. To summarize, all the possible points for vacuum leaks were replaced/fixed. After I got the engine and tranny put back in, I expected that if the mixture were to change at all, from fixing all the vacuum leaks and everything, it would be running too rich now, but instead it appears to be running leaner than when I started! How can this be, any ideas?

Tell us why you feel it is running leaner. What symptoms?

Is it backfiring? You can really only tell if it is lean , or rich if it is hooked up to a sensor.

Start Fresh With a Baseline Data........
 

Jon,

What you had before were based on your perceptions? Did you have an engine analyzer measure your gas exhaust? Have your CIS set properly using a gas analyzer and start from there. Being able to perform the "Souk technique' is a plus and has been done by many, but itself is not as good baseline data as having done by a gas analyzer.

Did you ever get the chance to measure your cold control pressure? For all you know, the WUR could be the culprit. My two-cents.

Tony

Here's my experience starting and running it after the engine was put back in.

When starting it from cold, it almost immediately fires (like the CSV valve is working properly) but then after that initial rev, the engine drops down and dies. After starting it like this about 6-8 times, it will eventually start to idle roughly, then after about 10 seconds even out to a slightly high idle. After you let it run for a little bit, maybe about 5-10 minutes, the idle starts to drop down lower, but if you try to rev the engine a bit, and then let off the gas, the engine drops down and dies. If I start it again, then rev it a bit, then very very gradually let off the accelerator, decreasing the engine speed back to idle, it will run on it's own, but then the idle will start "hunting" (where the idle speed starts to oscillate up and down and up and down). Another thing I notice is that I don't smell that slightly rich smell you normally smell from the exhaust when you run a cold engine, and the mixture is richened up.

Those are the symptoms in a nutshell, I have yet to put it on my emissions analyzer, it's at my shop in millbrae, but I can't drive it up there until the CV joint gets here this evening, then I'll be able to see what the mixture actually is.

No backfiring whatsoever, I'll put it on the emissions analyzer this evening or tomorrow.

Once I get the mixture adjusted, I'll check the control pressure and make sure the WUR is working as it should. I found that gauge you were telling me about that's sold by JC whitney. Thanks for the tip ;)

Jon

Sure sounds like the cold control pressure is too high, resulting in a too lean condition @ start. A secondary cause might be the AAR.

Do you have a Bentley manual? Are you aware of the control pressure graph based on ambient temp?

If you buy the Whitney gauge, make sure it is the one for CIS.

"...but then after that initial rev, the engine drops down and dies. After starting it like this about 6-8 times, it will eventually start to idle roughly, then after about 10 seconds even out to a slightly high idle. After you let it run for a little bit, maybe about 5-10 minutes, the idle starts to drop down lower, but if you try to rev the engine a bit, and then let off the gas, the engine drops down and dies."

This tells me that you corrected some vacuum leaks so you need to raise the idle speed to compensate and now it's too rich, not lean at all.

Joe

Yeah I've got it, I wasn't aware of the graph in there, I'll have a look at it. Thanks for double checking on the gauge, the one I saw is for $59 and is advertised as a CIS gauge, it has the diverter valve in it.

I did have to raise the idle speed a bit to keep it running, perhaps it is richer now, well, I'll put it on the emissions analyzer first and check it out. Maybe now that the vacuum leaks are fixed, it has revealed another problem in the system...

pop off valve ? did you drill into metal plennum / pilot bit on hole saw.

No, I was real careful about that, I had the air box on the workbench and took extreme care not to hit the CSV metal plenum inside there.

Runnin' Lean............
 

I have just done the same job on my SC! I hope to get the engine/tranny back into the chassis this weekend. I'm subscribing to this thread "just in case" I run into the same issues! Good luck with your project.

Oscillating idle and dropping below idle after blipping the throttle are classic symptoms of a fuel injection system set too rich.

If it's lean it won't do any of that at all... it will idle rough and weak and stumble when being revved.

You can't go by smell except when under load and it's too rich.

As a quick mixture setting try the push-pull method of adjusting the mixture.
With the car running at idle remove the air filter.
Carefully push the metering plate up or pull it down (by the arm).

If the revs increase when pushing up your mixture is lean, if it increases when pulling down you rich. This will probably get you a mixture that is richer than the US specifications.

It sounds crude, but you will easy get your engine running at its best, if the rest of your components are operating correctly.

I don't have a 911 SC, mine is a 930 and airflow pulls the plate down which raises fuel pressure at the injectors on a turbocharged 930.
If I recall correctly airflow over the sensorplate on the normally aspirated cars with CIS or K-jetronic is the opposite direction... anotherwords airflow pushes the plate up to increase fuel pressure going to the injectors. It does that by lowering the amount of fuel that returns to the gas tank.

If that is correct you have it backwards... pushing up on the arm would enrichen the mixture or increase pressure and flow at the injectors and pushing down on it would lean it out.
Pushing on it much while the motors running is also a good way to create a backfire and possibly bend the arm that the plate is fastened to as it backfires through the sensor plate housing.

It's easier to do it right, and you don't have to remove anything...

Lean out the fuel mixture which is too rich from your description of how it runs with a 3mm allen wrench inserted into the idle CO adjusting screw by turning it counter clockwise slowly or left for lean in small increments till it idles rough, then turn it back clockwise slowly again, and in small steps till the idle smooths out and is not oscillating and doesn't drop below idle speed after reving or blipping the throttle.

Do Not rev it while the allen wrench is inserted and make the final turn to the right for rich.. thats clockwise.

You guys are awesome, thank you so much! I'll let you know how it goes :)

You are right, but I don't have it backwards ;) The point is to temporarily enrichen it to see if it is running on the lean side.

Never happened me, besides, he has a pop off valve.
You should only move it slightly, if the rpm falls let it go.

Okay, so I used the technique you guys mentioned about pulling the arm down a little bit, and pushing it up a little bit, and I've got it adjusted to where if I push up a little on the arm the idle drops a little, or pull down a little on the arm the idle drops, so it should be set correct now right? The oscillating idle has gone away, and when I blip the throttle now it doesn't drop down afterwords, that problem seems to be fixed, but now a new one...

Under hard acceleration the car pulls strong and evenly, but when puttering along at a constant speed, I can feel it surging a little. I assume my next step is to check my control pressures, correct?

The surging is probably a lean condition. Try richening up the CO adjustment a little bit. You can always turn it back.
If you have an O2 sensor disconnect it before setting the CO.
Some cars run better with it left disconnected.

Okay, tried richening it up just a little bit, but then I get the problem again where the idle drops after revving. Seems like there's no way (just through mixture adjustments) i can get both problems to disappear at the same time. Any ideas?

set your idle up at about 1000 and see if it goes away.

There is an adjustable fuel pressure regulator built in to the CIS head. You could try raising the pressure there and then readjust the idle CO to compensate.
You can always put it back to where it was before if you don't like the results.

You should get or borrow the fuel and control pressure gauge set up with diverter valve for CIS or you'll never know what you're actually doing.

A wide band AFR kit like the Innovate LC-1 and gauge is a big help too.

Okay, I ordered the JC Whitney CIS gauge today, when it gets here I'll hook it up and see where I'm at. In the mean time, I'll try raising the idle speed like snbush suggested, I'll take a look at the timing, and try a couple of other things, I'll report back any findings. In the mean time, if anyone else has any more recommendations, please post them.

Progress...
 

Today I put a timing light on the car and found the ignition was advanced too far. I brought it back down to 5 degrees BTDC. Instantly the car idled smoother and more consistently. I then adjusted the CO% to 3.5, and the results... great! The car idles smooth, accelerates linearly, doesn't surge, and all in all runs great. I did notice while timing it that the timing mark would occasionally bounce around. There maybe something wrong with one of the advance springs, maybe bouncing around in there. Right now, it is running smooth which is a huge relief. I also noticed while on the test run that the RPMS wouldn't come straight back down to idle all the time. After I let off the gas, there were times it would hang at around 1500 RPMs, for a second or two, then come back down to idle. Could it be related to the distributor? As soon as I get some time I'll have a look at the distributor, but right now it's 10 times better than before. :D Thank you everyone for your help so far, I'll post my findings in this thread as they pop up.

I think your next project would be to clean up the internals on that dist. Gunter has a good DIY on this. My car had the same "hang up" when warm and I found the advance weights sticking as the clearances tightened up with longer running time and higher ambient temps. Your bouncy timing points to this also.

good luck

Every car I've ever put a timing light on with a mechanical distributor has bounced around a degree or 2 at idle. They usually become more stable as the revs increase.
Unless you can feel the center shaft of the distributor is loose like worn bearings or anything else inside seems to be too loose or worn out I wouldn't worry about it.

Great results!
Did you check maximum advance at 6000?

The engine speed hanging @ 1500 for a second or so before dropping to idle speed is a normal part of the function of the decel valve. If you have the one on the driver's side of the engine w/ a hose off the top, you can adjust it via the screw that surrounds the port for that hose. Some guys plug the line altogether so there is no hang.

Reopening this thread again as I'm still having issues with the car surging during off-idle operation, and the rpms dipping down after letting off the accelerator. I have the warm idle set to 1000 rpms because if it's set any lower, then when the car is cold, the dipping after acceleration will cause it to die.

I finally got around to checking the CSV to make sure it wasn't leaking, which it's not, and checking the control pressures. The pressure were a little high, but I thought I'd run the numbers by you guys to see what you thought:

System Pressure: ~70psi

Control Pressures:
Cold (engine off): 25psi
Cold (idling): 29psi
Warm (engine off): 47psi
Warm (idling, vacuum line connected): 54psi
Warm (idling, vacuum line disconnected): 48psi

I also performed the residual pressure test and it passed with flying colors.

Do you guys have any ideas?

Did you check your control pressures against the chart? @ what temp did you get your cold readings? Do you have the 945 0r 069 WUR?

Maybe someone can help here, but aren't you supposed to have 30 -35 deg advance @ 6000rpm? Did you try that? Was the vac line disconnected or not?

If all the above is OK then maybe your dizzy as you suggest. Are you sure it is tight and not rotating?

Check your timing specs some cars are 5 degrees ATDC...

surging and dipping = TOO RICH
the slow return to idle could be the decel valve.
you should see about a 1 bar drop in presure when the vacuum line is removed from the WUR.
is 3.5% spec for your car?
if you want to lean it some more, try turning the mixture screw CCW in small increments until it stops surging or dipping when you blip the throttle. then, look at where the allen is pointing, turn it about a half turn CCW and then CW back to where it was. i have mine set so it is just on the edge of wanting to dip down in rpm when i let off the gas.

Also maybe pull your injectors out again and re-check the pressures. I had one that started opening at a real low pressure and fouling out the plug after it I cleaned it... easy to check.