1973.5 CIS - no throttle response - Help!

[Dave Kost]

I just purchased a 1972 w/ a 1973 CIS non running engine. The PO said it had a leaking fuel pump that needed replaced. The car sat for ~2 years without running and the PO assured me that all that was needed was to fix the fuel pump leak.

I worked on it yesterday and found out that the leak was the fuel line between the banjo fitting at the rear gas tank and tunnel that had chaffed. I re routed the line underneath the steering rack and re-clamped to the banjo fitting. After working thru a starter issue- the battery cable wasn't connected to the starter I tried firing her up. Within a few minutes it fired up and ran but there is no response from the the throttle. (The pedal throttle works back to the bell crank in the engine compartment.) I let it run for about 5 minutes until it started smoking in the engine compartment. Here mice had nested in the engine fan cooling duct and packed in all sorts of paper trash! The fan nut wouldn't come off, so I took off the the side engine heater covers to clean out the paper trash.

What should the next step be assuming doing the work myself? (The engine sounded strong.)

The big picture is to have it safely running this summer to enjoy then dropping the engine this winter to clean/sort it out.

Any and all advise welcomed.

Thank you.

[ossiblue]

Welcome to the board Dave, and congratulations on your Black Beauty--very nice!

Since you have CIS, it will pay you greatly to read up on the system both here and other sites (like this, for example: http://members.rennlist.com/jimwms/CIS/CIShome.html ).

Your symptoms could still be from a fuel pump that is below specs in pressure for the system but the only way to know is to do some basic fuel pressure tests. You may have an obstruction in the feed line or the pump may be malfunctioning. Typically, the first step in diagnosing CIS problems such as yours is to run the pressure tests--they are not difficult to do with the gauges or you could have a knowledgable Porsche mechanic perform the tests. There are many threads on the Technical fourm that explains the test procedure so I'll let you read some rather than explain the details here. (Simply use the "search" button at the top right of the page, click "advanced search" and when the page appears type in what you are looking for.)

Your problem doesn't sound too serious but you don't want to throw money away by replacing unnecessary parts. If you are sure your timing is correct, that your spark is advancing, and your valves are properly adjusted, check the fuel system pressures as a starting point.

BTW, for anyone who is new to these cars, especially the CIS, I always recommend that they spend a few bucks and take it to a known and experienced CIS Porsche mechanic to get an initial set up of the engine so they will have a baseline of a well running engine from which to measure any future problems. It is money well spent, IMO.

Let us know what you find and any and all questions are welcomed!

[Walter_Middie]

Dave,

It sounds to me like your fuel distributor plunger is stuck. This is common with cars that have been sitting - especially if they are supposed to run fine (we're assuming that the previous owner was being honest with you). The air flow sensor plate moves the plunger up and down to regulate fuel flow. If you move the air flow sensor plate up and down by hand (with the engine off of course), you should be able to tell if the plunger in the fuel distributor is following it. Gravity is the only thing that drops it down after the sensor plate pushes it up. It should fall freely.

The other thing to check is the ignition distributor advance as ossiblue mentioned.

[Dave Kost]

L.T./Rex-

Thanks for the quick responses. One of the reasons I took a shot with this 911 was because of the good support this forum offers. ( I've been lurking since I have a 1969 912.) I just didn't know where to start exactly and didn't just want to start replacing parts. Learning how the system works is fun any ways. I'm pretty happy that the engine kicked over and ran well.

Looks like I need to do more research and buy a pressure kit.

Can I get into any trouble pulling the CIS system off at the intake runner manifolds to do some cleaning? I'm thinking of dried up fuel clogging the system. The car came with new fuel injectors and plastic fuel lines- from the injectors to fuel distributor- not installed yet.

Dave

[Walter_Middie]

Can you get into trouble? Oh yes - just ask me how. I've plenty of experience with that.

Taking the CIS off for a cleaning and replacing old dried out rubber parts is an excellent idea. There are "O" rings where the injectors are pushed into that are a typical air leak. That and the large rubber boot over the throttle body are places to check.

Although cleaning and replacing are good ideas, I might suggest starting with the simple things first and see if you can get it working. After you are more familiar with it, may be a better time to tear it all apart.

Check the fuel dist plunger, ignition advance, and put the injectors in glass jars and run the fuel injection system to see if all are spraying nicely and the fuel pump is working.

[Dave Kost]

Rex,

I pulled down on the disc arm and it seemed to move back freely. Now when I start the engine it goes directly to red line? The throttle valve is open slightly at idle? Is that correct? I'm doing this on the blind and I don't feel comfortable.

Dave

[Walter_Middie]

Dave,

I'm not sure what you did, but something seems to be hanging up in this area. When the throttle is opened, more air is allowed into the engine. This deflects the air flow sensor plate upward. The other end of the sensor plate arm moves downward, allowing the plunger to fall, which increases the amount of fuel in proportion to the incoming air.

I am confused because you should have pushed up (not pulled down) on the sensor arm and released to see if the plunger was freely following it. If the plunger was stuck, this would change the amount of fuel going in, and shouldn't make it rev up. It almost sounds like your throttle is stuck open. Can you operate the throttle by hand in the engine compartment?

[T77911S]

very good advice from walter. it sounds like he may have pulled down on the weighted end and pushed the plunger further in. too much and it will be too rich to run.

[Grady Clay]

Welcome to the Forum
You will find a lot of help here.
Good advice above.

The high revving must be from the throttle held open, not some mixture issue. Check the throttle is on the stop at the butterfly. If not, see why.

You want fresh premium gasoline and clean oil.

When you raise the sensor plate with the fuel pump on, you should be able to hear the fuel injection nozzles operating. Don’t do this long or you will ‘flood’ the engine.

While idling, you can slightly raise the sensor plate and the engine should stumble and die from too rich.

With the distributor cap off, rotate the rotor and see if it returns easily. Use a timing light to see if the advance curve is approximately correct.

The CIS gauges are necessary. This will tell you where you are at. Another issue may be the fuel flow. That can be restricted by the fuel filter or fuel tank screen.

Before you get chasing your tail with the fine points, measure the cranking compression and cylinder leakegs. Check (not adjust) the valve clearance and confirm the cam timing is in spec.

At some point before your ‘final’ adjustments, you will want to put several hundreds of miles on the engine with sustained and some ‘sporting’ driving.


There are a few other critical issues with a 911 that has been sitting. It is all too common for the brake master cylinder to fail. You should check the fluid level EVERY time you drive. If there is a change in the ‘feel’, STOP.

The ’73.5 engine originally had the hard rubber chain guides. Hopefully they have been updated. It would be wise to confirm that update and possibly rebuild the tensioners with kits. Cheap insurance from a possible catastrophic failure.

What are the manufacture dates on the tires?

Enjoy.

Best,
Grady

[Sunroof]

I am inclined to think the fuel tank may be an issue as well since the car sat for two years and you have a non-CIS tank for a CIS system. The 73.5T tank was unique strictly for that model. If the fuel in the tank now is low, it would not be a bad idea to drain it. You probably have water in it and it could be rusted inside. Check to see and if a large "screw in" recessed screen fitting is located on the underside of the tank. If so, after you drain and inert, remove the fitting and inspect the internal filter (replacement part - $30.00). Porsche CIS cars do not like dirty fuel! Consider as well replacement of the fuel filter (was it updated with the smaller filter?).

By the way pulling injectors on these cars is as difficult as pulling a tooth from an elephant! They are set into the cylinder in sleeves and once the rubber gasket hardens its a tough job. I had to literally set up block and tackle to yank these out and I still have the scars on my knuckles to prove it.

Good luck

Bob
1973.5T

[Dave Kost]

WOW....Thanks for everyones comments. I travel during the week, so I apologize for not responding earlier.

I am a little upset with myself for not knowing how the system works before jumping into it. I have a Bosch book coming along with a set of pressure gages for this weekend.

I did pull down on the arm.

On first blush, I think the throttle valve plate is open too much at idle or not closing to the stop. I have to force the throttle linkage down to close the plate to the body. Also, if this is done it clicks a spring lever at the back of the throttle body. There is a thumb nail adjustment screw in back of the throttle body. Does this adjust the by pass air idle like in a carb?

My plan is to replace the gas tank, fuel filter and check the vacuum lines for leaks.

Oil- another foul up. I tried reading the dipstick and added 4 quarts because I couldn't read the mark- of course....wrong! I understand you need to have the engine hot before it will read on the dipstick -right?

I can trace the ownership back about 27 years and can't figure out why this car has a 1973 CIS engine? Maybe this was a common replacement warranter engine in the mid 70's? There is another member that has a 73CIS engine in a 72 too- gogar.

Need to find out how to adjust the throttle at the valve.

Looks like a have a busy weekend ahead. Brakes, tires-2 years old, compression

Fun Fun Fun!

Dave K

[Jim Sims]

"I understand you need to have the engine hot before it will read on the dipstick -right?"

Well, at least have it warmed up (oil temperature around 155F), the engine running at idle speed (~1000 rpm ) and the car sitting level when reading the dipstick. Only fill the oil level to halfway between the marks on the dipstick. The range between the two marks is about two quarts.

I've rebuilt/restored a 911 73.5T CIS engine from the crankshaft outward so I may be able help with your future questions.

Cheers, Jim

[Jim Sims]

Proper starting procedure from the owner's manual for the 911T 1973.5 CIS engine follows:

The owners manual for a 1973.5 CIS states that the hand lever should be pulled fully up (so the micro-switch on the throttle body closes and sends power to the cold start valve) for all starts when the engine temperature is less than "very high". Very high is defined as an engine temperature of 212 to 250 F. Unless the engine is running hot and the stop is very brief (so the engine doesn't cool off) this in a practical sense means the lever is pulled up for every start. The manual further states that when the ambient air temperature is below -5F the lever should be fully pulled up and the gas pedal partially depressed; then when the engine starts, the lever is positioned for a 1200 RPM warm up speed. For "nominal cold starts" (air temp above -5F and engine oil temperature below 155F) the lever should be pulled fully up without gas pedal application and then once the engine starts the lever is lowered to set the engine RPM at 1200 for warm up. When the engine is warmed up (~155-160F oil temp) the lever is fully lowered. When starting a warm (as opposed to a "very high" temperature) engine the lever is pulled up for starting and immediately pushed back down after the engine starts. For the very high temperature case (212 to 250 F oil temperature) the hand lever is left down and the gas pedal is fully depressed during starting. It is important to note that the '73.5T CIS cold start valve (CSV) circuit does not incorporate a thermal time switch so the driver has to control this function. Note though that as usual the CSV only operates while the starter is turning, it does nothing for cold running after that time.

[Jim Sims]

One possible cause of your throttle issue could missing, broken or disconnected springs on the throttle linkage on the top of the engine (forward, driver's side); these springs pull the throttle closed and if they are missing the linakge can "hang".
Also, the plastic bushings the throttle bell cranks turns within could be "gummed up" or broken thereby making the linkage sticky.

Pictures of the relevant part of a cleaned up 911 1973.5 T engine follow to assist you in locating these throttle return springs.

[Dave Kost]

Jim,

That's one sweet engine! Thanks for the pictures.

I see that I'm missing the vacuum tube coming from the top of the valve behind the throttle valve. I think all the springs are in place though. So I must check to see if the linkage is binding from the foot pedal. (I think it is.)

Is the butterfly plate in the throttle closed against the body during start up or idle? The boot has to come off to see this relationship. Am I making any sense? Just trying to get a starting reference point.

Dave K

[T77911S]

that hose you are talking about goes to the decel valve.

the throttle plate should be closed.

nice engine jim. wow, the 73 is so clean in the back, none of the plumbing the later engines have. nice paint job on the runners too. anything special to do that?

what is that hose from the bottom of the TB to the FD for?

[berettafan]

Dave.....if you've got tired fuel lines and evidence of mice then, IMO, you NEED to go over the exterior of the motor (pull the shroud to look for nests, etc) very carefully as well as replace all fuel lines from the tank back.

Be aware that CIS gas tanks have the damned plastic 'swirl pot' in them. You wanna be careful before dunking, dipping, whatever with that tank.

[Sunroof]

Always great photos to look at Jim................

Dave......you mentioned replacing the injectors, so as you can see in the photo the injectors are not installed in the intake manifold as in the 1974 CIS model onward. The injectors sit in a small metal well that can easily be damaged. This is another unique charactersitic about the 2.4 CIS. The rubber sleeves retaining the injectors are fairly big and have a lip that holds the injectors in. The rubber will get hot over the years and stiffen, thereby making it difficult to remove without special tools. With the injector lines off you can match the thread and buy a screw cap to fit over the injector. Take the new injector to the hardware store. Placing a washer under the cap will add the anchor point for retraction. I bought a small "v" notch nail puller and used a wood block to set the puller on to yank, but the resistance was unreal! I then used another large flat bar placed under the nail puller to gain more leverage and that got four of them out. One shot out like a bullet!! Wear safety glasses. It was the block and tackle set up above on the garage door motor anchor brace that was the kicker. With my son yanking on the bar and nail puller on the block I used picture handing wire over the anchor washer and yanked from above with my 3 to 1 purchase set up. Unbelieveable!!!!!!!!!!!!!!!! Like I said before, for me it was comparable to pulling teeth from an elephant! Maybe your experience will be much easier.

Some other tidbits....Try and avoid spraying too much lubricant around the injector as it might weep into the cylinder. I hit the base of the injector with some light oil to help lube up the rubber sleeve, but I have to wonder how affective that was.

Good luck.

Keep us posted on your progress.

Bob
73.5T

[ossiblue]

Dave,

Lots of good advice so far, and lots of answers to your questions. The picture posted by Jim is an excellent helper.

You also asked, "On first blush, I think the throttle valve plate is open too much at idle or not closing to the stop. I have to force the throttle linkage down to close the plate to the body. Also, if this is done it clicks a spring lever at the back of the throttle body. There is a thumb nail adjustment screw in back of the throttle body. Does this adjust the by pass air idle like in a carb?" It does sound like you have a hang up somewhere in the linkage. Have you checked to see if your hand throttle is all the way down? Have you checked to see if the hand throttle moves the throttle lever/butterfly? This is where there may be a problem.

That little "Click" you hear when you seat the throttle valve is the micro switch that activates the CSV and is adjusted by the small screw you mention in your post--it does not affect the idle. When the spring on the switch is released (by the throttle lever moving away), the CSV is activated during cranking of the starter (that's one purpose of the hand throttle, to open the switch during cold start.) You can see the switch in Jim's second picture very clearly, the black rectangle with the two wires coming out.

The idle adjustment screw for the CIS is the large slot-head screw, just to the right of the decel valve shown in the second picture.

[Jim Sims]

"nice paint job on the runners too. anything special to do that?"

Old paint stripped to bare metal, then Wurth RustGuard Black (thinned with lacquer thinner so it can be sprayed) applied with a spray gun to the parts hanging in the open air from a rack.

"what is that hose from the bottom of the TB to the FD for?"

That is a pressurized fuel line from the throttle enrichment valve. This valve is attached to the throttle valve shaft and varies the fuel enrichment of the FD depending on the throttle position - leaner for economy cruising, richer for full thottle. I believe this throttle enrichment valve was only used on the 911 '73.5T and '74 CIS engines.


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