air sensor plate issue?

waynegrease · 11-12-2008, 09:49 PM

I working on one of '72 911 2.7 cis system, the problem was fuel flood. From what I diagnosed, fuel pump was permanent running when ignition key turn in "ON" position without engine running. And I checked up the air plate sensor and there is no resistance at all when I lifted air plate up. And even fuel did flow through to injector squirted all the time without lift the air plate sensor or not running engine.

What's the problem do you guys think?

afterburn 549 · 11-13-2008, 02:07 AM

as far as I know with eng off, fuel pump running , there will be no fuel going in till the plate is moved

T77911S · 11-13-2008, 03:15 AM

the plunger in the fuel distributor (FD) is stuck in the "up" position.
pull the FD off. you may be able to pull it back down. pull it out and maybe all you will have to do is clean it. if you cant, you will have to take the FD apart. they get corroted inside

ruf-porsche · ruf-porsche's Garage

Quote:

Originally Posted by T77911S

the plunger in the fuel distributor (FD) is stuck in the "up" position.
pull the FD off. you may be able to pull it back down. pull it out and maybe all you will have to do is clean it. if you cant, you will have to take the FD apart. they get corroded inside

Don't take the FD apart or you'll end up buying a new one (do a search for how many people tore their fd apart and end up buying a new one. Plunger is probably sticking. If you can't unstick it better to send it out to have it rebuilt.

RoninLB · 11-13-2008, 04:12 AM

a Bosch tech told me on a phone call to never open up a Bosch fuel pump or fuel distributor. That leaks were always a present and future possibility because of the tight tolerances. He stressed that it's a pro job with pro tools.

FDs are pretty complicated inside anyway to just mess with.

T77911S · 05:11 AM

if it is stuck and he cant get it out, it may not rebuildable anyway due to corrosion. so what does he have to loose as in my case back in the early 90's. we bought an old volvo 242. it would idle but you could not drive it without it stalling. i new NOTHING about CIS, maybe i still dont, but when i tried to move the senor plate, it would not move past the idle postion. so i pulled the FD off, took the top off, puilled the plunger out and cleaned it up. put it back together and the car ran perfect! that car got past around to all the family members as an "emergency" car for many years. i even drove it daily for a while. it was the most reliable car we had. 4 on the floor, heavy as a tank, ugly cloth interior, but fun.

i would not do this if it runs, ONLY as a last resort to get the plunger out. it sounds like it is running, if so, he may try some injection cleaner first. he can still pull the FD off, the plunger should come out easy and inspect it for corrosion

CIS fuel distributer cleanout w/pics

Paulporsche · 11-13-2008, 05:02 AM

If you do pull the FD hold your hand under it to make sure the plunger does not fall out of the bottom. If it hits the floor apparently that's it, you've thrown it out of its tolerances. Manuals suggest using crocus cloth, which is like emory cloth, to clean it.

T77911S · 11-13-2008, 05:12 AM

i think i used somthing like 0000 steel wool. something that will not leave scratches

waynegrease · 11-13-2008, 07:06 PM

today I pulled FD out and diagnosed it, yep plunger is stuck in "up" position. I tried to pulling the plunger out but its hardcore stuck obviously there is tons of built up corrosion in FD... Is another way to get it fix or clean up without send them off for rebuild or core exchange with new one? I just give a try, I sprayed alot of PB-blaster on the plunger area and leave them alone for a overnight to see if its could get slippage in next day....Attached picture here.

oneblueyedog · oneblueyedog's Garage

I'd try some techron to let it soak . I'd soak it in solvent to get the gum off before anything abrasive after you get it out. I'm just not gutsy enough to use anything abrasive on that pintle. Maybe oven cleaner? Paint remover?

oneblueyedog · oneblueyedog's Garage

sometimes a fried fuel pump relay will make the pump run on with the key.

afterburn 549 · 11-14-2008, 07:31 AM

lacquer thinner

1982911SCTarga · 11-14-2008, 07:40 AM

You can safely grab the exposed bottom portion of the plunger with needle-nose pliers and gently try to tug it straight out. Handle it with care once you've got it out and gently clean it. You could could then soak the fuel distributor in something like Berryman's for a day or so -- maybe even cycle it a few times with clean solvent each time -- and blow dry, compressed air through all the passages to hopefully clear the crud out.

Brian

john walker's workshop · 11-14-2008, 10:01 AM

they usually do come out with small pliers on the tit. spray into the top center hole too. do not drop or abuse the plunger in any way. don't sand it with emory, steel wool or anything like that. use a soft cloth only. gingerly wiggle it back in so it doesn't bind in the process.

Superman · 11-14-2008, 10:11 AM

Quote:

Originally Posted by john walker's workshop

they usually do come out with small pliers on the tit. spray into the top center hole too. do not drop or abuse the plunger in any way. don't sand it with emory, steel wool or anything like that. use a soft cloth only. gingerly wiggle it back in so it doesn't bind in the process.

Interesting factoid: The tolerances between the plunger and its bore are so tight that the plunger can move freely in and out, while staying so close to the bore that gasoline, under 60 psi, will not leak out. No kidding. There is no o-ring in there.

1982911SCTarga · 11-14-2008, 11:21 AM

There's no question that the tolerance of the fuel distributor plunger to its bore is very, very close.

Still, the thing about the tolerances being so close that gasoline doesn't leak around the plunger gets repeated so often that it makes me wonder if we're not missing some other essential fact or facts. Another aspect that makes me wonder is why Porsche said crocus cloth (still an abrasive, however mild) is OK to polish the plunger with.

Anyway, are we missing something in terms of the interaction of the lower and upper chambers and fluid dynamics that explains why fuel does not leak into our airboxes under pressure? Even consider the installed height of the fuel distributor/airplate sensor assembly. It's above the level of the fuel tank. (Yeah, yeah, I know the accumulator keeps pressure in the system.)

I'm just suggesting there was a heck of a lot of fluid dynamics theory applied in our CIS setups. Even with that, the system, to me at least, is devastatingly simple and reliable.

I apologize in advance if this has hijacked our thread-starters' original problems and answers.

Brian

afterburn 549 · 11-14-2008, 11:26 AM

The reason I suggest lacquer thinner is in the day when one had to pull a lifter out of a American style car ...they were STUCK ohh you could move them with in their tolerance but not beyond that...a good dose of L.T. and and the puller YES !

ruf-porsche · ruf-porsche's Garage

Quote:

Originally Posted by 1982911SCTarga

You can safely grab the exposed bottom portion of the plunger with needle-nose pliers and gently try to tug it straight out. Handle it with care once you've got it out and gently clean it. You could could then soak the fuel distributor in something like Berryman's for a day or so -- maybe even cycle it a few times with clean solvent each time -- and blow dry, compressed air through all the passages to hopefully clear the crud out.

Brian

If you are going to garb it with something use a set of forcept that you can lock. Needle nose plier will just slip.

waynegrease · 11-14-2008, 08:04 PM

Today it wasn't successful that plunger was still stuck after sprayed load of pb blaster on it for overnight. So I went with lacquer thinner and soaked them for a hour then I pulled the plunger out with the mini needle nose pliers so easy. I never thought of lacquer thinner since I worked on cars for long time. I think that Im gonna put LT in my high priority for work cars in some ways for reason to use it.

I cleaned up the air plate box in solvent then dried it up with air blows then sprayed it with brake cleaner and I used a blue shop towel with alcohol isopropyl cleaned on the plunger and its bore. Then applied some lube assembly engine on both. Plunger move up and down so freely, no trouble with stuck in any ways. I assembled FD and put it back on the engine. I started up the engine was running right way. But of course, its kinda of bit little rough idle and i gave some gas on it and its running smooth. Note, car has been sitting for long time-drained the old gas, cleaned up gas tank, and changed oil...then had troubled with fuel floods. Now I solved the problem with plunger and see whats happening when I take a drive test in next days and in long term.

After ran the engine and I observed around the FD to make sure there is no leaks and let it ran for like 10 mins then shut down as Im done for day. In somehow, I noticed that there has alot of fuel spreading on the floor directly from the muffler. Make me puzzled for a while then realized that its been sitting in the cylinder and header due of fuel floods. I hope that its will going away in next day when I take a drive test.

1982911SCTarga: no problem, as long as I nailed the problem. Very interesting about CIS set up and thats why Porsche engineering guy stayed in the lab 24/7 and probably turned in a millionaire guy?

Paulporsche · 11-15-2008, 06:58 AM

Good job, waynegrease!

Nice tip, afterburn.