CIS Problem - Tested, Have Results. Opinions?

[j_mancini]

Hi All,

I'm looking for opinions on possible problems for poor running conditions. Here are the details:

78SC, 153K (yup, its orange)




Was running fine about 3 weeks ago, mechanic had to "lean considerably" to pass emissions - 2.8% CO (failed twice, finally passed). After test, mechanic richens it up "a bit" to improve driveability.

Ran well and drove fine for a week or so, then developed warm-up idle problem: started fine, idled high for about a minute, then idled poorly (hunting, 400-800 RPM) until warm. Once warm, idled fine at about 900 RPM. OK, no problem, I can feather the throttle at idle until warm. Seems like aux air regulator decided to not work (has opening when cold, but I haven't checked warm or removed it yet).

Then, one day at lunch it decided to run poorly - no power, "bogging", wont rev over 4 - 4.5K RPM, smells bad (rich?).

OK, I get the CIS pressure tester and measure the following:

Cold system pressure - 4.6 bar
Cold control pressure - 2.0 bar

Warm system pressure - same 4.6 bar
Warm control pressure - 2.8 bar (after 3-5 minutes of "on"). Getting 10.8V at plug.

Shut it off (valve open), pressure drops to 2.0 bar immediately. After about 20 min., pressure is steady at 1.5 bar. Did the same with valve closed, same pressures.

So...pressures seem in spec. I suspect AAR is not working properly. Why no power when warm?
- Would AAR affect warm running?
- I've done a cursory vacuum leak check (starter fluid) with no response.
- Ignition wires appear original (metal braided), but no stray sparking or arcing visible (at dark).
- Timing is good 5 deg. BTDC at idle, advances when rev'd. Cap is relatively new
- fuel filter new 5k miles ago, pulled and emptied, seems to be ok, no obvious blockage
- I have not yet checked cold start valve for leakage (holding pressure, so...?).
- Air flow meter seems to function fine (smooth, no binding).

??? Looking for opinons and possible next steps. THANKS!!

[OldTee]

What happens when you remove the oil filler cap. Does the RPM change? Sounds like you may have a vac leak. Check hose to distributor. You might consider a smoke test. Also some injectors seals may be leaking.

[Paulporsche]

Try leaning the mixture a litle in 1/16 turn increments until the warmup hunting goes away. Then drive the warm car and see if the engine revs higher.

Has it been hotter/more humid where you live lately?

[j_mancini]

Thanks for the replys!

OldTee - when I pull the oil tank cap (like to check oil level), it idles really rough - tries to die. The big vent hose on attached to the filler neck look pretty old and worn. Distrib vac line is old too - I'll replace that. Can you enlighten me on the "smoke test"? What does that involve (equipment wise). Being nearly 30 yrs old and looking quite original, probably there's a leak somewhere I'm guessing.

Paulporsche - I will try the mixture adjustment. It's been hot, but not humid (UT - maybe 20% humidity at most). One thing I've noted: on the idle mixture screw, isn't it supposed to "click" in discrete steps when you turn it? Mine seems to be smooth, and somewhat loose too.

[Paulporsche]

John,

I've never encountered a mixture screw that has distinct clicks.

The looseness...I don't know. It should turn freely w/ the wrench but not feel as though it will spin on its own, say through vibrations. Is it possible there is some excessive lubricant down into the threads?

BTW you're lucky to have only 20% humidity. These cars, and this driver, don't respond as well to hot and humid conditions!

[OldTee]

Couple of ways to check for leaks. One is to use a water spray bottle and spray water at the base of each injector. You will note a change in operation if one is leaking. Oil cap operation is normal. Good. I disagree about trying to set the mixture with ear alone. You need to check and set via CO2.

Another way to check for leaks is to use a propane torch, moving it around the areas that may leak. Use carefully. If rpm increases you have found a potential leak.

Note the big knob on the drivers side of the is for idle adjustment. It does not click. Warning, do not operate the throttle with the mixture allen in the screw. Expensive problems start here.

I would bet when the mechanic changed the mixture he also dislodged a hose. Did he have the Popes hat off. A leak there will cause problems.

Start with the water, then use propane (unlighted).

Oh, yes. Smoke test. Basically you put smoke from a smoke machine (snapon makes an expensive one and most well equipped shops have one). It pumps smoke into the intake and you look for leaks. Good for use on the exhaust side also. Do you have any exhaust leaks? They too will screw up the CIS.

Compression test results?

Good Luck.

[Moke81]

How about the sensor plate, it may be sticking or dirty. When running lift up on the arm inside airbox does it smooth out at all?
I cleaned mine and made a big difference in ideling and starting.
_____________
1981 SC Coupe

[cmonref]

"Did he have the Popes hat off?"

What is a "Popes hat?"

[lespaul]

Originally Posted by Moke81

How about the sensor plate, it may be sticking or dirty. When running lift up on the arm inside airbox does it smooth out at all?
I cleaned mine and made a big difference in ideling and starting.
_____________
1981 SC Coupe

Moke,

I am thinking my starting problems may be related to dirty sensor plate. Any special advice on how to clean it?

[Paulporsche]

Brian and les,

I think he is calling the large rubber cap over the mixture control unit the Pope's hat.

If you remove that you can access the top of the sensor plate. If you remove the airbox cover and filter you access the sensor plate underside.

In Bentley's and maybe here through a search you will find a drawing of the plate alignment. Check to see if it moves up and down freely w/ no binding. Clean the plate and cone w/ a cleat cloth and solvent to remove any built up oil etc. Wipe it clean and dry. Make sure the "hat" is placed on correctly and strap snugged down.

I would also check that the airbox is clean, and the popoff valve is working correctly and there are no visible airbox cracks or loose screws.

[lespaul]

Why should removal of oil filler cap change RPM and cause engine to idle rough? When I check oil and engine is running, I notice no difference in idle. Should I get a new filler cap/filler cap gasket to keep air from entering system through it?

[cmonref]

LesPaul,

The engine puts the oil tank in a vacuum condition, so when you remove the oil tank filler cap, the engine draws extra air, creating a lean running condition which is rough. If you remove the filler cap and it does NOT change the character of the idle, you have other vacuum leaks that you have already compensated for.

[lespaul]

I must then have other vaccum leaks that I have already compensated for. Now, to find them.

Thanks Brian.

[Scott R]

I kind of watched a cool vacuum leak test this weekend, I watched a guy place a chunk of dry ice inside a shop vac, he added some water and placed the output hose into the intake of the car. You could easily see the leaks from the places. In this case the intake was above everything else and of course the dry ice fog falls. Don't know if this would work on a p-car, however I'm inclined to try.

[patkeefe]

Fuel filter?
Check the injector spray patterns and quantities. Maybe the fuel head is gummed up a bit. From the description you give, everything else seems normal.

[j_mancini]

Finally as of this week my problems have been fixed! Here's the process and outcome:

- pulled entire CIS system off car and replaced all the rubber fittings, hoses, and gaskets. The runner boots were bulging, and had lots of old oil in them, but the biggest leaker was the EGR tube. It was flopping all over the place, as the rubber seal was hard. This was the primary vacuum leak, I believe. I ditched the EGR system (wasn't working anyway), and JB Welded the port closed.

- tested the CIS intake box, and found it leaking along the glue joint. I fixed that by grinding out the seam and filling it with JB Weld. Re-tested and it was tight!

- tested aux air regulator - it passed (put in freezer, it opened, applied 12v. and it closed in about 5 minutes).

- sent cold start valve to Witchhunter Performance for cleaning and testing. Turns out it was a little dirty.

- thoroughly cleaned runners (bead blasted), throttle body, air flow meter, and boot. Did NOT mess with the fuel distributor.

- re-assembled with all new hoses and gaskets, new injector o-rings, injector sleeves and o-rings.

I put it all back together, and it started right up. Then, fuel pump promptly died! OK, new fuel pump and new filter. Started up again, but ran poorly - no power, backfiring, rough idle. Timing checked correct. Tested fuel pressures, and both 1) control and 2) system pressures checked out in-spec. Next I pulled the injectors (easy, with the new seals), and measured flow of all 6. Problem found! Two of the injectors flowed about 25% less than the other four. Cleaned the injectors as best as I could, with some improvement but still a weak spray pattern at low flow (high flow pattern looked better). I knew mixture and idle were not correct, but since I have no gas analyzer - off to the shop we go!

Friendly local Porsche mechanic did a thorough check and found:
- mixture way off, re-set to spec.
- 2 poor injectors replaced with new
- all new plugs
He says it then ran much better, but still was not firing on all cylinders. So he pulled off the fuel distributor and found two screens jammed together in one chamber (someone in the past must have monkeyed with it). He pulled out all of the small screens, gave it a thorough cleaning, re-installed.

Now it runs like a scalded dog - pulls HARD to redline!

So, in summary, the problems were:

- substantial vacuum leak at EGR tube
- minor vacuum leaks at airbox glue joint
- 30-yr old hoses and intake runner boots
- two partially clogged injectors
- dirty fuel distributor with clogged screen
- 2 partially plugged injectors
- dirty fuel distributor

When I purchased it, the car ran OK, with moderate power up to about 5,000 RPM, but not much after that. Then it suddenly ran like crap - that's what started this whole process. The PO did say that the owner before him stored the car "for 10 years". I do have a receipt that shows shop work for new filter, new fuel lines, injector cleaner, and inspection of the fuel tank. Obviously somebody attempted to check out the fuel system, probably after years of storage.

Hope that helps some of you out there. My lesson - keep the fuel system clean! I see lots of bottles of Techron in the future. And fuel filters. And Stabil.

[j_mancini]

Oh, one more thing - there is no idle problem now when I pull off the oil tank lid to check oil level. The crankcase breather hose crumbled into pieces when I pulled it off! But after 30 yrs of heat and oil, that's no surprise.

[Targa4now]

Nice detective work. This sounds like a path I'll be following next spring!

[Paulporsche]

That's great. Thanks for the update.

[Cipotifoso]

John,

I really appreciate your update as I am going through some of the same problems that you experienced. Many threads end on this subject end with no conclusion or outcome posted, so someone searching the threads finds nothing to help them. Your thread will help me immensely.
Can you answer a couple of questions?
- How did you test the airbox to determine that the seam was leaking?
- Your mechanic was able to basically rebuild your fuel distributor. There have been theads on this board on how to do that, but the common element was always the lack of a kit or spare parts to facilitate this. Was your mechanic able to source a kit and what did he use to seal the body on reassembly?

Thanks,
Dave