CIS Issue
 

I have read a lot of posts here but none seem to describe my exact problem. Most posts are either cold start issues or warm start issues. Mine is neither, well more of a warm issue but not with starting.

Some back ground. I have an 83 SC (US) that I have owned for a couple of years now. The engine is stock 3.0 with the exception of the usual upgrade mods (i.e., chain tensioners, heat backdate, pop off valve, etc.). Engine always starts right up, whether it’s cold or warm.

The problem, rough warm idle for a short time, appears in 2 scenarios :

1) if the engine is warm, parked for a bit, then restarted, the car starts right up, but the idle will be low (500) and run rough for 5 minutes or so, then normal out.

2) if the ambient temperature is warm to hot, after normal engine cold startup, approximately 5 to 10 seconds later the idle drops to 500 rpm and will stall if no gas is applied. Again, after 5 minutes or so, the idle comes back up to normal (around 1000).

I do not have a fuel pressure gauge to take reading at this point. I am just looking for some thoughts to what parts I should be focusing on to test. I have done some reading on CIS and it seems there is a lot of component overlap so I am confused on where to start testing.

BTW, this problem has been with the car since I purchased it. I did check for vacuum leaks and I don't think I have any. At least not any that would be a problem. Removing the oil cap definitely drops the RPM's.

Any ideas? I appreciate your feedback.
Thanks.

the place to start testing is fuel pressure, google jim CIS primer for some good info.

More reading here:

http://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies.html?highlight=CIS+Dummies

The five minute time you mention is around the same time as it takes for the bimetallic strip in the WUR to warm up. A quick test there would be to make sure you are getting 12v at the electrical connection on the WUR with the key in the ON position (but not started). Also, the AAR uses a similar electrical connection/bimetallic strip to close it's valve. Without that happening, it would have to rely on engine heat to close off.

The thread I linked to above has a test for the AAR. I would do that and check the power to the WUR first since those are relatively easy to do. If that turns up nothing I would move on to the fuel pressures test.

Edit. Duplicate post.

tirwin,

Thanks for the tips. I will check out the voltages and do some more reading.

Put a fat nail in the timing retard hose for fun.

Plugging the retard hose at the dist will give you a wee bit more advance at idle and that sometimes overcomes some of the "age" issues if the CIS components.

This assumes no false air leaks and all the other stuff mentioned is correct.

If it helps, still buy pressure gauges and perform some assurance work as there may be issues that are correctable that you are masking by a slight nudge in timing.

I finally got a round to taking a couple of measurements.

With the WUR power connector unplugged, I turned the ignition to the on position (without starting the car) and measured power. I got a reading of 29 milli volts. I guess that is as close to zero as it gets.

I also measured the WUR resistance and got 9.4 ohms.

Both these measurements were taken with a warm engine. Not sure that matters or not.

Any suggestions?

Thanks.

Cold engine........
 

Lou,

Allow the car/engine to sit over-night and measure the WUR resistance. Or do at night when it is cooler. Do you have WUR-090 (0-438-140-090)? Without a fuel pressure gauge, there are so many things we assume to be good which complicates the troubleshooting process. Keep us posted.

Tony

Tony,

Yes, I do have WUR-090. I will take the measurements again later tonight and report back.

Thanks!

Lou,

I had to look back over the thread. I forgot to tell you that you'll have to jump the fuel pump relay. My bad. If you read the post in the Dummies thread I posted earlier, the instructions on how to test the fuel pressures are there and it covers how to jump the relay.

As Tony said the fuel pressures are the key test. I was just thinking that your symptoms seem like one of the components in the start up process isn't working correctly. Checking for power on the wiring harness for the WUR and the AAR is easy -- they are on the same circuit as the fuel pump -- but you'll have to jump the circuit to test it because it normally isn't energized until the car is started.

Ah, that makes sense. I did read your CIS For Dummies. I should have picked up on that.
I did read somewhere that 9 ohms is out of adjustment for a WUR. Is that for a cold WUR?
Thanks for the help.

Believe 9 ohms is a little lean. Tony can confirm. In the high 20's for my 81 US WUR.

WUR loaner program......
 

Lou,

I could give you a loaner (WUR-090) and try it on your car. PM me if your are interested. Please do it quick because I'll be leaving for Carmel, CA this weekend and would be away for another 4 weeks.

There are couple of WUR-090's that I recently refurbished, tested and calibrated. All you have to do is mount it and connect the fuel line and electrical plug. PM sent.

Tony

From my 74 owners manual... one must still pull up the hand throttle when engine is at operating temp. I'm assuming because a hot 4 stroke engine demands more air on restarting.

Not familiar with your year CIS, but perhaps you could try and start with gas pedal depressed some to see if starts are easier and to take into account a malfunctioning AAR valve etc.

Tony,

Sent you a PM.

Bob and Manbridge, thanks for the replies.

I did measure the resistance again on the WUR this morning when it was cold. The resistance was the same, 9.4 ohms.

Lou, My 83 is doing exactly the same thing as yours was. I'm in the middle of tracking it down. Can I ask what ended up being the culprit?

Thanks,

Chris

Chris,

Sorry to say, I am not sure yet. I put off the repair until Tony (boyt911sc) gets back from vacation.

Tony thinks it's my WUR. When he returns in September, he is going to loan me one to see if it fixes the problem.

I will certainly keep you in the loop with my results.

WUR loaner........
 

Lou,

I'll be back home on the 27th of August to continue my unfinished work regarding this WUR loaner arrangements. I had two (2) overseas commitments that need to be tested multiple times before shipment. And one for South Carolina.

And a couple more awaiting for the arrival of the cores. PM sent regarding shipping address and other information. I've been very cautious lately because I have a successful unbroken streak with this exchange and wants to keep it going.

Tony

Lou, well I just timed my WUR warm up time. It went from a cold press of about 2 bar to warm press of 3.4 bar in about minute 10 seconds. I believe that is way too fast.

That does seem fast. According to my Bentley manual chart, that's a temperature range of 57 to 93 degrees F in 10 seconds.

Hopefully one of the experts will chime in.

An update. I sent Tony my WUR for testing and it came up bad (the usual 9.4 ohms all the time, also bad warm and cold fuel pressures. So, Tony sent me a rebuilt one over the weekend and I installed it yesterday. Thanks Tony!

I can definitely tell a difference after a cold startup. The car starts immediately and acts like it should, no problems. The car cruises well too.

After my 100 mile ride today, I shut the car off and let it sit for 5-10 minutes. Upon restart, the car idles low and stumbles.
If I keep it rev'd up for a couple of minutes and then remove my foot from the gas, it will be okay and settle in at 1000 rpms.
If I don't give it any gas when it is stumbling (at warm restart) it will stall. The car will start right up again but still stumble until rev'd or driven.

It appears the WUR was not causing my initial problem I described in the beginning of this post but was definitely not working correctly.

Next step is to purchase some fuel pressure gauges and take some measurements...

Test your accumulator for leaking if you are having warm engine start troubles.
Check your bleed down times with your pressure gauge. Should take a long time to drop off.

Sounds like your mixture is too rich when the car is started when warm. As the CIS "thinks" the engine is warming up further, the mixture leans out gradually. This is often caused by a too low warm control pressure, a too rich mixture setting or a combination of both.

If Tony has set the control pressures correctly (and I don't see why he wouldn't) I would then check your mixture setting. It's possible a PO set the mixture too rich to make up for the WUR not working correctly.

Of course if you want to verify Tony's settings w/ your own testing, then why not?...

BTW always verify that all your ignition components are working correctly and check your timing and look for vac leaks, as others have said. Similar to what I said above, often someone will change a mixture setting to make up for vac leaks.

I have the same feeling........
 

Paul,

I had the same feeling about the fuel mixture setting but requested the owner to wait till he gets the pressure gauge. While I had set the control fuel pressures accordingly to spec. before shipping the WUR, checking the actual control fuel pressure in operation is another thing. I like to eliminate the residual pressure too before going to the critical and sensitive adjustment for the mixture. Will keep you guys posted.

Tony

Just got back from a two week trip and finally ordered my Fuel Pressure Gauge. I should have it by the end of the week.

Today, since Paul and Tony both think it may be a rich mixture problem I am having, I tried a couple of things that I read on Jim's 911 CIS Primer Site. Since I do not have a CO meter, I looked into the "Testing" -> "Mixture" section. I have not touched the mixture screw. Matter of fact, I can't even see where it is. But that's another problem.

Okay, the CIS Primer states the following:
"An approximation of the correct idle mixture can be made by the folllowing:
With the engine warm and running, slightly lift the air flow sensor plate.
If the RPM immediately falls off, the mixture is probably too rich.
If you pull down, and the idle falls off, you could either be too lean, or about right. Do the step immediately below to find out.
If the RPM slightly rises, then falls off as you continue to raise the sensor plate, it may be close to right.
You are trying for about 14.7:1.
The required movement of the sensor plate is slight, on the order of maybe a 1/16" or less."

With my engine warm and running, I lifted the airflow sensor plate very slightly, the RPM slightly increased then dropped way down quickly after and started to sputter for a bit until it eventually went back to normal.
When I pulled down on the airflow sensor plate the idle drops down.

I am not sure if these tests mean anything but I thought I would give it a shot. Any thoughts?

As I mentioned above, I will have the fuel pressure gauge by next weekend and will post some pressure measurements soon there after.

Pressure test.........
 

Lou,

The fuel mixture could be rich and could be verified with a gas analyzer. Before you even think of adjusting the fuel mixture screw, check for unmetered air. Not being able to find air leak does not mean you don't have any. A quick test for your vacuum is to check the idle speed of a fully warmed up CIS engine by removing the oil filler cap (assuming the oil cap is good and sealing). If the engine speed (idle) does not change (decrease) at all, this is a sign of trouble. Could you do this test for us. Thanks.

Tony

Tony,

Engine warm and idling. When I remove the oil cap, the engine idle drops quite a bit. Almost wants to stall but doesn't.

The rpm drop is a good sign.
Wait for your gauges and order or borrow a CO tester. The small investment in both will pay for itself after a couple of uses. The Gunson tester on E-bay works well.
Then you can adjust as needed and properly...:)

Thanks Dennis.

It seems it will be a while now before I get the K-jetronic gauge. They are out of stock at several places I tried to purchase from. I will get one eventually.

I will check out ebay as well for the Gunsen tester.

eBay may have the Bosch K-Jetronic Fuel injection pressure tester as well if you can't find one anywhere else!
Here's one:
http://bit.ly/19wOtLB
Or:
http://m.ebay.com/itm/331031345235

It could also be a residual pressure issue. Testing value with warm engine after 10 min. at least 1.3 bar. After 20 min. 1.1 bar.

It's tough to test without pressure gauges, but you could feel the residual pressure by reaching under the sensor plate and pushing up on it. If you feel any resistance, you're in luck...you have residual pressure. If you feel no resistance after 10 min. then you found your problem.


Cheers,

Joe

Dennis, thanks for the link. I will order one.

Joe, Thanks for the tip. I know I need the gauge but I will try your suggestion.

I experienced a low idle issue tonight that has not happened before. It felt just like the warm start issue I am having.

I was stuck in bumper to bumper traffic tonight on my way home from work. After sitting idle for a while and moving slowing forward for 20 minutes or so, my idle began to drop to 700 rpm and was acting like it was going to stall. If I rev'd it for a while as I sat there, it would improve. After a while, it would drop again. After I got out of the heavy traffic and started moving it was fine, ran great.

Is my problem getting worse or is this the same thing showing it's ugly head in another situation?

So, this keeps getting better and better.

Dennis, I ordered the K-Jetronic Pressure Tester on Ebay from your link. I pay for 2nd day shipping to get it for the weekend. It comes a day early but with no gauge. Just the hoses and fittings....oh brother...

Going up North this weekend.......
 

Lou,

I am planning to go up north this weekend on my way to Bangor and Newfoundland. I'll bring my tools and gauges just in case I would need them. PM me your address so I could make travel plan and schedule my trip. Or do it on my way back home. Keep me posted.

Tony

That really sucks about the tester showing up without the gauge. I hope the seller takes care of you.
I just put in the search terms and posted the cheapest one that claimed to have any in stock...

Tony,

That would be great if you are willing to do that. I will PM my address to you.

Dennis,

The missing gauge is not your fault. That was the third one I have ordered in a week. The other 2 places canceled my order because they were no longer in stock. These K-Jetronic testers seem to be very popular. Hopefully the seller will send me the gauge eventually.

Thanks guys.

Today I had the pleasure of meeting Tony and Amore. They were nice enough to stop by my house on their way up north today to take a look at my CIS problem. Very nice people, I enjoyed meeting them.

The CIS pressure measurements we took are as follows:
Ambient Temp 75 degrees F

Start 20.0 psi
1 min 28.0
2 min 38.0
3 min 44.0
4 min 47.0
5 min 50.0
6 min 52.0

After some testing, Tony felt it was a fuel mixture setting (too rich). Unfortunately I do not have a CO analyzer so we couldn't adjust it to work properly.

Next step, bring it somewhere to check the mixture. I will post the information when I get it.

Many Thanks Tony!

Mis-diagnose your problem.......
 

Lou,

I was driving towards Portsmouth, NH and all of a sudden I realized I might have mis-diagnosed the problem about the rich mixture!!!!!! Without verifying the integrity of the vacuum system or knowing the exhaust CO level, there are many variables to consider. Sent you a PM for you to try some tests. And I'll give you a call once I finalized it.

My wife made a remark on our way to NH that she just met two very nice individuals in 2 days!!!! After meeting Matt G. (Newport, RI) and Lou F. (Chelmsford, MA) made my 300 miles drive feels like a 30 mile drive!!!!!! Then I replied to her; "birds of the same feather flocks together". And she looked at me and shook her head.......

I'll get back to you.

Tony

Okay, Tony thought about the results we got when testing my car and he asked me to take more measurements.

Here they are:



Original Readings with car off and fuel pump running

The CIS pressure measurements we took are as follows:
Ambient Temp 75 degrees F

Start 20.0 psi
1 min 28.0
2 min 38.0
3 min 44.0
4 min 47.0
5 min 50.0
6 min 52.0

CIS Pressure Measurements taken on 10/5/2013, temperature 61 degrees F

Car started with CIS Pressure Gauge Connected (valve open, WUR connected)
COLD START

Time Pressure (psi) RPM’s

Start 20 1800
1 min 35 1800
1.5 42 1200
2 min 50 950
2.5 50 stumbling then stalled

Note: Pressure dropped from 50 to 40 immediately upon stalling

RESTARTED immediately after stall

Start 50 1000
.5 min 50 950
1 min 50 stumbling then stalled

I couldn’t keep the car running at this point. I increased the idle just a bit (I lowered it the other day) then upon startup, rev’d it a bit until it stabled out. This took about 2 minutes. Then I recorded the pressure and RPM

2 min 52 1200
3 min 52 1200
4 min 52 1100
5 min 52 1100

I let it run for 10 minutes, it never stumbled or dropped in idle.

I now recorded the Residual Pressure.

Shut off the car and watched the pressure drop.

Time Pressure (psi)

Shutoff Drops from 50 to 40 immediately
.5 min 40
1 min 40
5 min 33
10 min 29
15 min 24
30 min 20

RESTARTED AFTER 30 minutes of residual testing

Time Pressure (psi) RPM

Start 50 1100
.5 min 52 950

note: car started to stumble at this point

1 min 52 950
1.5 min 52 650
2 min 52 Stalled

Interested...
 

My '82 just started doing the same thing after several years of fine running.

Runs fine cold or hot, but if I shut it off while warm (short trip) or hot (long trip) it will stall and I have to feather the clutch/throttle and use the handbrake (I e-brake is really good) to stop when idling (at a stop light, etc..).

Please keep us up to date on the solution!