I am in CIS hell - advice or ideas appreciated

[AFJuvat]

Have one of those problems that make you pound you head in the wall. I'm throwing this one out to see if anyone else has had something similar to this.

1983 911 SC, US version (930.16)
Mileage undetermined (broken odo)
No Oxygen sensor
Lambda controls (Jetronic box and assorted wiring) disconnected.

Problem: Car idles poorly. runs excessively lean (CO .2 - .3%)
This problem is erratic The car will start fine 2 or 3 times in a row, then will run poorly. Adjust fuel\air mixture (with no cat, I like them 1.5 - 2.0%), and the car runs fine, turn it off and start it again 5 minutes later, problem is back.

This problem is NOT confined to a hot or cold start.
This problem exhibits itself regardless if the Jetronic controls are connected or not.

Corrective action done so far:

Warm-up regulator replaced with New OE unit
Fuel distributor is not binding, plunger is not damaged, o-ring replaced
Sensor plate is properly centered, not binding, and is at correct height.
Fuel pressure is within specifications
No detectable vacuum leaks.
Car does NOT have a pop-off valve. However, there is no indications that the airbox is cracked.
Timing is correct when the engine runs properly.
Cold start valve IS functioning properly
All jetronic components seem to be working properly when they are connected. (frequency valve, etc)
Fuel throughput from fuel distributor to WUR is a little on the high side, but still within specifications as set by Bosch (240CC in 60 seconds)
Fuelpump output is within specifications

This is one of my customers cars. I have spent an hour or two every day for the last 2 weeks trying to nail this problem down. I feel bad enough about it that I am not charging him any labor to fix it, and I'm about ready to refund the money he paid for the WUR that we installed about a month and a half ago.

I am beginning to think it is a problem in the fuel distributor or the air flow sensor - both rather expensive to diagnose by swapping parts.

In 10 years of doing this, I have not had a car kick my as$ like this before.

If anyone has ideas, or you are seeing something that I am missing I am all ears (err... eyes)

AFJuvat

[Mike Kast]

Have you removed the fuel distributor? I'm just throwing this out because it caused me all sorts of grief. I'm not experienced enough to know but my whole system was clogged up with 25 years of gunk.
The fuel dist was clogged with rust and the mechanic who diagnosed the problem changed it and added some Hi test fuel system cleaner. My theory is that it had never been added before and it let loose a whole $hitload of built up crap into the system. I added it and more a few more times.
I fought it for about 6 months changing injectors, WUR, cleaning all the lines and fittings and gas tank. It turned out the injectors and WUR had been changed less than 20,000 miles before but were clogged.
I could have cleaned the WUR, but... well, now I have 2. grrr... live and learn. The gas tank was nasty but I don't know how it got past the filter.
I battled it for a long time and the problem seems to be gone now. My fingers are crossed. There was no one thing I did that solved the problem and it just sort of faded away.
Certainly would have been a mechanics nightmare. Thank you Zeke
and Souk
Probably not your problem though?

[IROC]

Originally posted by AFJuvat

Problem: Car idles poorly. runs excessively lean (CO .2 - .3%)
This problem is erratic The car will start fine 2 or 3 times in a row, then will run poorly. Adjust fuel\air mixture (with no cat, I like them 1.5 - 2.0%), and the car runs fine, turn it off and start it again 5 minutes later, problem is back.

Are you saying that after setting the mixture it reverts back to the lean running condition? If this is the case, I would focus on the fuel distributor as something seems to be wrong there. Either that or a vacuum leak that you just haven't found yet.

Mike

[bigchillcar]

is it possible you have a dirty fuel filter that doesn't affect driveability until after the car has warmed up and the debris gets stirred up and begins affecting fuelflow? this would cause it to run lean. it is typical for cars to start fine, begin to worsen as driven.
sticking control plunger in the fd could certainly cause a lean condition. and does the owner use injector cleaner like techron at all? how about the injector spray patterns...good spray?
ryan

[Mike Kast]

By the way... Souk is the guy with the lucky CIS gift. IM him but keep it public if you could. This stuff is going to become a bigger more common problem as these cars age if it is rust and sediment.

And the gift tip from Zeke was to clean everything with lacquer thinner. I soaked and blew laquer thiner through ever part of the system. I can't imagine how you could charge for it. I'm sure my methods were primitive and cost me time it wouldn't have cost a seasoned mechanic but still.
There is a place here in Raleigh that has a CIS cleaning machine. It is a loop that runs a cleaning chemical through the system. The guy told me they run it for a few hours then change the oil. The only problem I could think of was that the large sediment that gets caught in the screens would never flush out. Unless the chemical dissolves it.

[SC-targa]

[QUOTE]Originally posted by AFJuvat
"Lambda controls (Jetronic box and assorted wiring) disconnected.

Problem: Car idles poorly. runs excessively lean (CO .2 - .3%)
This problem is erratic The car will start fine 2 or 3 times in a row, then will run poorly. Adjust fuel\air mixture (with no cat, I like them 1.5 - 2.0%), and the car runs fine, turn it off and start it again 5 minutes later, problem is back.

This problem is NOT confined to a hot or cold start.
This problem exhibits itself regardless if the Jetronic controls are connected or not."

As a baseline, doesn't the lambda box need to be hooked up to even hope to run correctly on an 81-83 US Spec 911? If I unplug the box on my 82, it won't run.

You said the frequency valve is working. Have you checked the duty cycle of the frequency valve when the box is hooked up?

Good Luck,

Jerry Kroeger

[oneblueyedog]

How is the perimeter gasket/cushion between the airflow meter and the airbox? Are the springed bolts tightened correctly?They shouldn't be tight.

I made the mistake of silicone sealing the meter to the airbox once and it idled like crap. The cushion gasket lets it float to some extent. I couldn't believe how essential it was.

My plunger only works oriented one way from 26 years of use. There were shiny wear areas on one side. After I turned it in its bore to the worn in orientation, it ran fine.

Since the car has an O2 sensor circuit, I don't have any ideas about that but from what I've read if it malfunctions it goes rich. Maybe it goes lean in some cases?

The new oem WUR doesn't have the same warm up pressure graph as what was on my car in '78. It's a superceded part, but it works well. I doubt that's a factor in your case. Unless the voltage to the unit zero.

Lee78sc

[MotoSook]

The best thing one can do for a CIS car...any car really..is to clean the fuel delivery system.

That's where you start. It should be recommended to the customer that it is needed. It is a necessary job for old cars. Check the tank strainer. It don't have to be replaced if the screen is not ripped. You can clean it. But one could just buy a new one and sleep better at nights.

I found it easy to put a hose on the fuel line at the engine compartment, before the filter, and run that hose to a gas can(s). Then run the pump until the tank is dry. Mine the pump and don't let it run dry too long. A clear hose is nice to watch the crude that comes out of the tank. I use an old filter fitting from an old filter and screw it into the clear hose, then connect that to the fuel line. You can clamp it if you like, but there is very little prsssure there. Once the tank is dry, pour a gallon or two into the tank and flush with clean gas.

Clean the fuel accumulator too! No need to get a new one if the old one is not leaking and maintains good pressure.

Obviously a new filter is due....

The key to troubleshooting in my experience is to eliminate the easy stuff, and in the case of CIS, the tank to filter is the easiest! Do it! Start eliminating the easy suspects...

You mentioned that you replaced the o-ring. I assume that is the o-ring between the fuel distributor and the airbox. I would hope that that someone has not screwed with the plunger and machined an o-ring groove and installed an o-ring. Sounds like you are a wrench who's done this before, so I don't mean to offend, but I had to ask.

You replaced the WUR, but did you check the pressures? That is the next easy suspect. Even with a new WUR, there is a chance that the pressure is not correct.

I should mentioned that you need to flush the CIS after the tank flush...Clean everything again (fuel dist and WUR). If a new WUR was put into an dirty system, it will clog soon enough. Flush the fuel lines to the injectors and check the spray pattern one you flush the lines.

This is a lot of work, but you don't want to be guessing. That is the easy work. It sounds like you have spent more time guessing than you might have spent doing the above (again no offense...just going through the routine here).

Clean the sensor plate pivot. There is not much differential across the plate during operation...sometimes less than your finger pressure when you check plate movement. Without fuel pressure the sensor plate should bounce off the spring stop.

With the air boot removed, you can clean the air sensore plate and housing top and bottom. You can also clean the throttle body...open the throttle plate and clean around it too.

Once you do all that, does that car still behave funny?


Now...

From the description:

"Problem: Car idles poorly. runs excessively lean (CO .2 - .3%)
This problem is erratic The car will start fine 2 or 3 times in a row, then will run poorly. Adjust fuel\air mixture (with no cat, I like them 1.5 - 2.0%), and the car runs fine, turn it off and start it again 5 minutes later, problem is back.

This problem is NOT confined to a hot or cold start.
This problem exhibits itself regardless if the Jetronic controls are connected or not."

I'm guessing you have an internal air leak. Check the aux. air valve, and the aux. air regulator. It they stick intermittently, that may cause sympthoms as you describe. The Bentley manual has some good diagrams of the flow (internal to CIS) and how the components work.

I would clean the AAR just because..it needs to be cleaned. You can check the AAV with a vacuum source to determine if it is sealing when it should.

And you can't forget the decel valve on the later CIS 3.0.


One last thing...when you adjust the idle and CO, do you do it hot and when the idle is stable?

Without being there, it will be much harder to fix this, but keep posting your findings.....

[echrisconnor]

How do you recommend cleaning these things? Carb cleaner on anything that takes vacuum and lacquer thinner on anything that takes fuel? Or just blast everything with carb?

[MotoSook]

I've never use lacquer thinner to clean auto parts.

I just use carb cleaner...be very careful with the fuel distributor and plunger. Make sure you have a clean area to work in.

I posted some tips on fuel distributor cleaning some time ago...search for it...

[vash]

i am the king of rust, when i comes to CIS hell. my gas tank looked like the water in the bottom of a wet tile cutter, after a day of cutting red tile. i almost puked when i dumped it. i had to change everything from the tank back except the CSV. the FD is original but i had to clean and unlock the plunger. your problem is so severe, i cant help to feel it is the FD. do you think the steel diaphram in the FD can be clogged? if the plunger is doing its job, it is for nothing if the diaphram is not allowing the fuel to move between the chambers easily. you have got to keep us posted!

[emcon5]

Originally posted by SC-targa As a baseline, doesn't the lambda box need to be hooked up to even hope to run correctly on an 81-83 US Spec 911? If I unplug the box on my 82, it won't run.

Yes. If you have the stock fuel distributor for a CIS Lamda there is a second lower chamber for the input from the freq valve. The control pressure is varied by the freq valve, to adjust the mixture. As I understand it, if the lamda box and it's power relay under the seat need to be connected and functioning for it to run right, even if the O2 sensor is unhooked. On Lamda cars, if you unplug the relay it really runs like crap.

You said the frequency valve is working. Have you checked the duty cycle of the frequency valve when the box is hooked up?

How is the frequency valve working without the Lamda brain?

Tom

[911nut]

I think that you have to confirm that the airbox os either cracked or ok and go from there.

[AFJuvat]

Thanks for the replies all. Here are a few updates\clarifications:

Fuel system is clear. No rust or crud in the tank or fuel lines. Fuel filter was replaced one month ago

The fuel distributor was flushed out when I removed it. No O-ring on the plunger, just the small o-ring between the distributor and the airbox.

Sensor plate, venturi, and airbox were cleaned out when I removed the fuel distributor. This includes cleaning out the air bypass with a pipe cleaner.

Did not clean out the AAV - will look into this tomorrow.

Gasket between AFS and airbox seems fine, this will be replaced tomorrow.

Reconfirmed that there are no detectable vacuum leaks, no noticable cracks in the airbox. (debating on pulling the airbox tomorrow)

All mixture and idle adjustments were done after the car completed its warmup cycle.

AFJuvat

[emcon5]

Does your dome light work?

Tom

[bigchillcar]

Does your dome light work?

ahh...'a little humor now and then is relished by the wisest men...'

ryan

[AFJuvat]

Originally posted by emcon5
Does your dome light work?

Tom

As a matter of fact.... No

AFJuvat

[emcon5]

Originally posted by AFJuvat
As a matter of fact.... No

AFJuvat

Not humor, lamda brain and O2 sensor system are powered of the dome light fuse.

Tom

[Oracle]

My car had similiar problems some days it was fine others was stuttering like hell...The problem was: -drums here-
The stupid Air Flow sensor boot had the tiniest crack on the neck
http://www.pelicanparts.com/catalog/images/fuel_injection/new_images/fi_fielsystem_1-7-2a18.jpg

So that was enough to be erratic and difficult to find..


Good luck
-J

[Mike Kast]

Hey Oracle,
Did you notice any reason for the difference of when it ran well or poorly? Like outside Temperature?
My problem has completely resolved itself since it has become warm outside. The last time it acted up was the last time I drove it during freezing temps. It was too consistent to be coincidence.
I have this gnawing feeling the problem will return in the winter.