Help! Trouble with CIS fuel injection

Hi everyone,
I have a '76 911S with CIS fuel injection. I've only had this car(my first Porsche) for about 3 months so I don't have a great deal of experience with Porsches. I need some help regarding the CIS fuel injection. When the engine is cold, it is impossible to start(it starts when warm, though). The motor cranks but it seems like fuel just isn't getting into the cylinders. I have checked my cold start valve and found that it wasn't connected to it's power supply. I connected it and tried to start the engine. Now it sounds like it's almost going to start, but once it does, it immediately dies. That said, I noticed that when the cold start valve wasn't receiving electricity, the fuel pump starts working as soon as the key is switched to the "on" position, but once the cold start valve is connected, the fuel pump doesn't start operating unless key is switched to the "start" position. Is that normal?
What I have done so far to try to start it is bleed the fuel system everytime before starting. Then engine cranks for a little while, then starts, sounding like it's struggling for fuel. If I don't press the accelerator a bit and give it a little gas, it will die. I have just changed the fuel pump, the fuel acummulator, the fuel filter, and the cold start valve(although I don't know whether or not it actually helps in starting the car) within the last 100 miles.
Once the car does get started, usually the idle is quite rough, usually it's at about 1100rpm; every few seconds it rises to about 2200rpm and back down to 1100rpm. The engine also backfires into both the intake(yes the pop-up valve was already installed) and the exhaust. What's going on? Should I have the cold start valve plugged in? I haven't replaced the injectors...would that be part of the solution?
One more thing that I have noticed. While I'm driving and reach a red light, when I press the clutch, shift into neutral(maybe I should start putting it in 1st like it says on one of the messages on this board) the rpms still stay at where they were when it was still in gear. After a few seconds, it goes back down to idle. Any help with this problem of mine will be greatly appreciated.

Jeff

Jeff, do you have the Haynes 911 manual and the BOSCH Technical Instruction manual for K-jetronic injection? It doesn't sound like a 'shotgunning' approach to changing components is going to fix your problem! You may have already spent enough to buy a set of factory service manuals. There are relays, and a thermo-time switch that could be causing your problems, and it sounds like you have multiple problems in your electrical controls for the CIS system! Logical troubleshooting per BOSCH or factory publications (Haynes might help) are my best suggestion for a successful remedy. A voltmeter and test lamp will be useful in troubleshooting, and hopefully you are comfortable following an electrical schematic! Otherwise, help from a friend experienced in this area, or a competent mechanic is your best direction to proceed.

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Warren Hall
1973 911S Targa

Hi Warren,
Thanks for your reply. The answers to your questions are yes, I do have the Haynes 911 Manual, but no, I don't have the Bosch Technical Instruction manual. I actually do have a set of factory manuals coming any day now. Yes, I realize that "shotgunning" as you call it is not the way to go, but the parts that I have changed so far, are what I considered necessary. I have tried reading my Haynes manual but it doesn't give a real good explanation of what's going on. I really haven't had too much time to read and work on my car since I'm a full time student in college, but I do try whenever I have spare time. Yes, it definitely sounds like I have a lot of problems with the electrical controls for my CIS fuel injection. As I have mentioned before, I don't have too much experience working with Porsches as this is my first one. I am pretty familiar with following schematics, but I have yet to study the one for my year. Hopefully I can get something out of the books so that I won't go broke. Thanks.

Jeff

Jeff, I applaud your efforts to solve your Porsche's problems by getting the documentation and doing your own work! There is no better way to get to know your car. I was not being critical of your 'shotgunning' technique ... many professional mechanics do the same thing (though seldom admit it) to save time ... sometimes a 'hunch' works, but it can get expensive! I do hope you have saved all of your 'replaced' parts so far, as they may be perfectly good spares! You can test that used pump on a bench, out of the car. I think you will love the factory service manual with the color-coded schematics! It may take some 'getting used to' to interpret the 'current-flow diagrams' ... I prefer the 'old-style' location-oriented diagrams, myself, but they can get a little complicated!

There are two more publications you may want to get. Pelican has 'Solving BOSCH Continuous Injection Systems (CIS) Problems' PEL-BK-BFI-3 @ $38.50 and Performance Products ... www.************************ has 'BOSCH Technical Instruction: K-Jetronic' 903278 @ $19.95.

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Warren Hall
1973 911S Targa

definitely try changing the thermal temp sensor. I had the smae problem with my '74 911 and did all usualls (accumulator, cold start, fuel pump valve check). My cold start valve wasn't getting current either til I found a bad wire then it worked like it was suppose to but didn't totally solve my problem. A new thermal time switch did.

Jeff,

Here are a couple of web sites that may help you out about your CSI. They both have a lot of info about the bosh CSI
http://www.students.tut.fi/~hezekiel/bosch.htm
http://www.volvoclub.org.uk/volvo/k_jetronic.htm

Both of thest sites explain the fuel injection system in detail and how each component interacts with the other.

Good luck

Steve

found one other site
http://www.cs.brandeis.edu/~darwen/boschfi.html#presreg

Regards

Steve

Hi everyone,
Thanks to all of those who has helped me on this subject. Warren, yes, I have saved all of the parts I've taken off so far. Thanks for the suggestions for the books, if I can't figure these problems out I might just have to go and buy them. I spent the weekend doing mostly bodywork, but when I pulled out my injectors, I would say 5 of them had rust on them; two of which are stuck on the connector of the fuel line..it seems like it has corroded. Could this be the cause of any of the problems I'm having? Since most of the injectors are rusting, do I need to replace them? Although my '76 911S has a relatively low 112K miles, it seems like most of the CIS parts are quite old. Matt, when I do get home(I'm at school right now) I will look up the whereabouts of the thermal temp sensor and see if I can do any trouble shooting with that in my Haynes manual. I will also check my cold start wire. Steve, thank you for the web sites. Just a minor note. The 3rd web site you mentioned (the cs.brandeis.edu) is a dead link. I will look at the websites as soon as possible, and I will keep everyone updated. Thanks!

Jeff, Automotion has the CIS Tech. Instruction book clearance priced right now for $7-8 ... I doubt the rust on the injectors is inside, try brushing them off with one of those stainless steel toothbrushes, then soak in WD-40 or Marvel Mystery Oil. The rust MAY not be a significant problem ... I suspect the moisture was just in the air and came in through the exhaust ports and rusted any unprotected iron alloys. That thermo-time switch can be tested off the engine by putting in a freezer or refrigerator overnight, then testing the appropriate contacts with an Ohmmeter or Digital Multimeter ... if Haynes doesn't have a good diagram, email me. You don't want to buy a $75 thermo-time switch unless it is really defective!!!

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Warren Hall
1973 911S Targa

Hi everyone,
I haven't done much these past few days, but here's what I have found out. I took out my fuel injectors, and soaked 4 of them in the Gumout fuel injection cleaner. The 2 remaining that were stuck onto the fuel line connector, I took off the entire fuel line up to the fuel distributor and soaked the fuel injectors in WD-40. When I put everything back today, I bled the fuel system by turning the ignition on (right now the pump was operating) and pushing up on the air flow sensor, as said in the Haynes manual. I then attempted to start the car. It started up after a good 5-6 seconds, and since I had needed to before, I tapped the accelerator till it revved to about 3k rpm for a few seconds, and let it idle. It seems to be running better...at least it no longers backfires into the intake or the exhaust. The only thing is that it still has quite a rough idle, going from 950rpm all the way up to 2k, then back down, then up again.

I hooked up a multimeter to the cold start valve plug and found out that while cranking, I'd get about 3-4 volts...is this normal? The only thing is, when the cold start valve is plugged in, the car will start but will immediately die.

I've just received my factory manuals and I will be looking up the whereabouts of the thermal-time switch. Please let me know if anyone has other suggestions! Thanks!

Jeff

The rough idle and 'hunting' are addressed in the Bosch 'Solving CIS Problems'. One big cause of this is the Air Flow Sensor and how it relate to the small wheel under it that controls the plunger into the fuel distributor. I can't tell you how may 'technicians' investigated this hunting problem on my 80' 911, but when I read the manual within 5 minutes my problem was solved. You should probably try going slightly lean with the mixture at idle (that is what solved my problem). You will need the long 3mm allen and turn about 1/4 turn ccw. The 'hunting' can also be caused by flat spots on the small wheel that rides on the Air flow Sensor arm. At idle, the wheel rolls back and forth looking to stabilize itself but because of the flat spot (due to wear) the idle will hunt. This type of hunting is independent of whether the engine is warm or cold, where my problem existed only during warm-up. As far as the starting goes, you need to think of what is involved in simply getting the engine started, and THEN what is involved with keeping it running. The Cold Start Valve is certainly for the first case, but then other curcuitry (vacuum and fuel) come in to play. Good luck and keep us posted.

Hi Towen,
Thanks for your message. The only thing is, I believe the small wheel under the air-flow sensor was put on by Porsche with the introduction of the 911SCs. Mine has a little clip thing. I read in the Haynes manual that it can be adjusted using a pair of pliers. I will go home and read up on that. Hopefully that might solve a few problems. Come to think of it, I've never observed the air-flow sensor when the engine was "hunting." I think I will do that real soon. Yes, my problem happens both when the engine is cold and warm. Whether or not the engine is running rich, I don't know. How can you tell whether the engine is running rich or lean? I've never adjusted the idle before, so I'd have to read my manual first.

For the hard starting part, I think you're right in saying that could be either the vacuum or fuel. When I first bought the car about 3 months ago, it took a little while to start when cold, but it would eventually start. Now I have to bleed the fuel system first before it will start. The fuel pump is a new rebuilt unit, and the fuel accumulator and filter is brand new. The cold start valve is also new...where and how would I check for vacuum leaks? Any help and suggestions will be greatly appreciated.

Jeff

Hi everyone,
Here's an update. Yesterday I tried to start my car without bleeding the fuel system. I had the car cranking for about 30 seconds (not continuously) but eventually it did start. Then the rough idle ("hunting") started. I went to the engine compartment to investigate. I took off the air box cover and went for the air flow sensor. I felt around it, tried to move it a little, and the hunting stopped. There was my problem. It had something to do with the sensor plate. After I turned the engine off I took of the clip that determined the height of the sensor plate. I squeezed the clip to make it smaller and I put it back on. Then I went ahead and cleaned out the intake boot, wiping all the grease that had accumulated there and on the sensor plate. I decided that since it felt like my engine had a loss of power, I adjusted the fuel/air mixture and made it one click richer. Then I put everything together and started the car. The "hunting" had went away. I took it out for a drive, but I noticed as soon as I stepped on the clutch, the rpms would stay at where they were, or drop down to usually about 1800rpm. I went home, and adjusted the speed screw by the throttle body while the engine was idling at 1800rpm. The idle dropped down, and now it's idling where it should be, around 950rpm.

I still have a problem with it starting, but only when it's cold, when the car's been sitting overnight. I think it's probably the cold start valve...how many volts am I supposed to be getting at the connection?

The obvious problem to my rough idle would be the sensor plate. What can I do to adjust it, or do I need to get a new one? All suggestions and help is greatly appreciated.

Jeff

Hi everyone,
It's been a while since I worked on my '76 911S. Midterms really screws with my schedule. I've called the mechanic who sold me the Porsche and asked him about my problem. He said that the connector I was using doesn't go on the cold start valve; there's another one that goes on there. I was told to tie the other connector up and never touch it.
Yesterday a friend of my sister who recently graduated from UTI(Universal Technical Institute) came and tried to help. Eventually we found that there were two wires at the rear of the engine, one yellow and one red/black. According to the schematic on the factory manuals, wires of those two colors connect to the cold start valve. Meanwhile, we found another receptacle on the back of the mass air flow sensor after we took the intake boot off. Does anyone know what this is for and whether or not it should be plugged in? I have a feeling the reason why my car hasn't been starting cold is because of a cut connector for the cold start valve. Any suggestions? Thanks,

Jeff

Where is the "thermo time switch" on a '74

Thanks!

Mike

Mike,
I believe the thermo time switch on your '74 911 (it's the 2.7L, right?) is on the left(driver) side tensioner cover, towards the top of the cover you should see something sticking out with wires plugging into it.

Jeff
'76 911S

Found it...now how do you test it.

m

Jeff, I answered your last question on the other thread.


Placerville, The Thermo-time switch is a thermostat switch designed to operate at 45 degrees C, or 113 degrees F, and has a buil-in heater element. It can be tested in-place on the engine ... the yellow wire is to the heater element, and should measure some fixed amount of resistance to ground with the Yellow wire removed from the 'G' terminal. The Red/Black wire is the switched terminal and should measure less than one Ohm with a digital multimeter connected between the 'W' terminal and the sensor body (ground), when the sensor is 'cool' to the touch (less than body temperature), and an infinite resistance (open) when the sensor body is hot or warmer than 113 degrees F.


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Warren Hall
1973 911S Targa