Running lean now??

[jonbot]

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?

[Paulporsche]

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

[snbush67]

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

[boyt911sc]

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

[jonbot]

Originally Posted by Paulporsche

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

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.

[jonbot]

Originally Posted by snbush67

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

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

[jonbot]

Originally Posted by boyt911sc

Jon,
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

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

[Paulporsche]

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.

[stlrj]

"...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

[jonbot]

Originally Posted by Paulporsche

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.

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.

[jonbot]

Originally Posted by stlrj

"...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

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...

[waynesco1]

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

[jonbot]

Originally Posted by waynesco1

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.

[fred cook]

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.

[JFairman]

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.

[safe]

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.

[JFairman]

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.

[jonbot]

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

[safe]

Originally Posted by JFairman

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.

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.

Originally Posted by JFairman

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.

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

[jonbot]

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?