CIS Metering Plate Sticking Closed - No Start

[spoke]

Car is '86 930 with CIS. I've had a no-start issue on and off for a while. With a shot of starting fluid, the engine fires up enough to pull the plate down then the engine runs fine. It will start right back up if started within a hour or so. After that I need to give it a shot of starting fluid.

About a year ago when looking into this, I noticed when pushing down on the plate with engine not running, there would be extra resistance and an audible squeak when first pushed. I blew some WD40 into the cavity with the metering plate arm and the squeak went away and the no-start condition abated.

Now it's back but the squeak doesn't happen and applying WD40 doesn't help the no-start situation.

What could be causing the metering plate and any mechanical parts to stick closed?

A couple of other characteristics now is that when started back up after about 15 minutes or so, sometimes the idle may be high like 1200-1500 RPM for a bit then go down. Also noticed sometimes when driving the idle may go up as high as 1500 RPM.

Every once in a while, I'll get dieseling when turning the engine off. All these characteristics seem to point to a sticking or gummed-up metering plate when the plate is closed or near closed.

TIA

[john walker's workshop]

Take the air cleaner off and see if the sensor plate is hanging up on the edge of the housing. May need to be centered.

[theiceman]

yeah you should have a static gap all the way around you can check with feeler guage. I think it is about 1.0 mm but am not 100% on the number. Pete sent it to me years ago when i was setting up my CIS after a rebuild.

[T77911S]

when you turn it off the ignition stays on for a few seconds and the pumps shut off. that is normal

my first thought was your cold start valve is not working.
could also be what JW said,

when you push on the sensor plate and the key is on you should feel resistance. as you push the injectors should start to squeal as they spray fuel.

the hi idle could be the decal valve.
if you have been removing things you could have also introduced an air leak.

[HaroldMHedge]

On my 82 SC, the sensor plate was not moving freely and sticking. This turned out to be from dried out grease at the sensor plate pivot pin. Using the Porsche 911 (1965-1989) for Coupe, Targa & Cabriolet Haynes Repair Manual, I was able to clean and relube my sensor plate.

[jpnovak]

Yes, to all of the above. Also check for a gummed up fuel piston inside the fuel head.

Time for some CIS maintenance.

[theiceman]

Originally Posted by HaroldMHedge

On my 82 SC, the sensor plate was not moving freely and sticking. This turned out to be from dried out grease at the sensor plate pivot pin. Using the Porsche 911 (1965-1989) for Coupe, Targa & Cabriolet Haynes Repair Manual, I was able to clean and relube my sensor plate.

wow thats amazing, all i use that thing for is to hold the door open to the garage so i dont get grease on the door knob.

[HaroldMHedge]

Originally Posted by theiceman

wow thats amazing, all i use that thing for is to hold the door open to the garage so i dont get grease on the door knob.

It's the only reference that I've found on teardown and reassembly of the sensor plate.

[spoke]

Originally Posted by jpnovak

Yes, to all of the above. Also check for a gummed up fuel piston inside the fuel head.

Time for some CIS maintenance.

Thanks all for the suggestions. I'll check the centering of the plate.

About the gummed up fuel piston inside the fuel head, it would seem that the only way to get to this is to disassemble the fuel distributor, correct?

[john walker's workshop]

If it runs ok, the piston isn't sticking.

[spoke]

Couple of days driving it to work. When sitting for a while (hours), have to use starting fluid to get it started. Then immediately after it starts up, it idles smoothly at 900RPM and runs great.

Today I had a new wrinkle or a hint of what's really wrong. Yesterday and today I noticed a couple of times when I turned the key to ON but didn't start it, the fuel pumps did not run for the 1/2-1 second to prime. Turn key OFF then back ON and got the 1/2 second prime.

Tonight, there is no 1/2 second prime every time I turn the ignition ON. Maybe the time delay relay is screwing with me. Have to try bypassing it in the morning.

Also, even if I get the 1/2 second prime and try to start and it doesn't catch, when I stop cranking it I noticed the fuel pumps were not running. Hmmm.

Any thoughts on this occurrence?

Question about the fuel distributor: There is a small electrical connector on the backside of the FD. I thought this was for sensing if there's airflow to keep the fuel pumps running. What does this sensor or switch do?

[timmy2]

Air flow switch kills the fuel pump relay when in the run position and no air lifting the plate.
Safety switch for when you wreck with key in run and engine stalls.
Stops fuel pumping all over.

[spoke]

Originally Posted by timmy2

Air flow switch kills the fuel pump relay when in the run position and no air lifting the plate.
Safety switch for when you wreck with key in run and engine stalls.
Stops fuel pumping all over.

That's what I thought it did. Not sure now why I'm not getting the 1/2 prime. Gotta look into that. Until I fix the prime and check out the air flow switch and fuel distributor, I've temporarily rewired the fuel pump relays so they come on with the ignition. Engine starts right up now.

[boosted79]

Contact surfaces for the safety "switch" in the meter housing need to be cleaned which requires the housing to be split to get at them. Maybe try spraying some brake cleaner up in there when engine is off and holding the plate down.

[spoke]

Originally Posted by boosted79

Contact surfaces for the safety "switch" in the meter housing need to be cleaned which requires the housing to be split to get at them. Maybe try spraying some brake cleaner up in there when engine is off and holding the plate down.

Thanks. I need to remove the connector and measure the resistance of the switch as the plate is pressed down.

BTW, today reminded me of how nice the engine used to start when I turned the key. No starting fluid; no blipping the throttle when trying to start.

[47silver]

if you need to center the plate, I used cigarette rolling papers in the yellow packet (note to the authorities i do not smoke anything). Wet the edge and place them on the inside of the bore what is nice is that they stick when wet. They centered the plate perfectly and that was over 5 years or so ago and have had no concerns as the 75 2.7L runs great.

[T77911S]

its probably the yellow relay in the back.

I would not mess with the metering plate yet.

when you turn the key to ON the pumps run for maybe .5 seconds. the contact in the AFM is closed when you do this. the delay may be built into the yellow relay,.
if the contacts in the AFM are bad the pump would run ALL the time.

[T77911S]

the delay relay is for the CD unit. it keeps power to the CD AFTER you turn the key off.

[boosted79]

"if the contacts in the AFM are bad the pump would run ALL the time."
That is true. I would check the relay. Or better yet sh*&can the relay and install an inertia switch and manual sw to control the pump relays. Manual sw lets you shut the pumps off with ign on and inertia sw kills the pumps if you get in a wreck and can't kill the ign.

[spoke]

Thanks for the replies.

Now I don't think the throttle plate is sticking. With the pumps running with key ON, the engine starts w/o starting fluid or blipping the throttle. I think the switch in the fuel distributor needs some attention. I've temporarily shorted pin 30 of the yellow relay to keep the pumps running.

Up until yesterday I had the 1/2 second FP prime when turning the key to ON. I noticed a couple of times over the weekend when turning the key to ON I didn't get the 1/2 second prime. Now no 1/2 second FP prime every time I turn the key to ON. Need to investigate that now.