Use it or Lose it

[bonedaddy]

I'm trying to get my '75 911S running again after a five year sit. I know that was a stupid thing to do, and I won't go into the reasons and mea culpas since I'm now busy doing the penance.

With much effort, I can eventually get it started, accompanied by a lot of white exhaust (smells RICH). If I keep the throttle open enough to keep it running at 1000-1500 rpm the exhaust will eventually clear up, but it will periodically stumble, lose revs, and backfire. It sounds like there's a steady miss which I've isolated to one cylinder (although that cylinder's ignition lead is getting juice). I won't run well enough to even begin to drive it.

I've replaced plugs, ignition wires, rotor, cap, points, etc.. I've freed up the sticking centrifugal advance in the distributor. I drained out the old fuel and added fresh, replaced the fuel filter and accumulator; warm and cold control pressures are within specification, cold start valve works okay. I replaced the fuel distributor. I'm beginning to think there's some sort of mechanical damage to the valves, so I pulled the covers to look at the valve train. I will check clearances. Next thing is to check compression--probably something I should have done a long time ago. Any other ideas?

[wckrause]

Check the spray pattern on your injectors, replace any that look bad. Techron, Techron, Techron...

[Superman]

Ignition ignition, ignition. I found out recently that you can put a timing light on each ignition wire to see whether that cylinder is firing each time or if there is a 'miss'. You can also place each injector in its own glass jar (be careful) and watch them spray (run the fuel pump and displace the sensor plate by hand). Then measure their individual volume outputs.

[bonedaddy]

I've done so many things to this car over the past few months that I forgot to mention that I replaced all of the injectors and added techron to the fresh fuel. The old injectors were shot. The new ones seem to have an okay pattern.

I'll check ALL of the cylinders with the timing light, although I can't imagine what's left that could be wrong with the ignition system--about the only thing I didn't replace is the distributor. At one point I wasn't getting anything out of the coil, so I put in a coiless Permatune.

Thanks for the advice--all thoughts are welcome. I used to think I was a pretty good mechanic, but this has me baffled.

[wckrause]

Maybe you've got a bad vacuum leak, like a cracked intake runner sleave or leaking intake gasket, something that would only effect one cylinder.

When it backfires, is it an intake backfire or an exhaust backfire?

[Jim Smolka]

Check the injector patterns again. There still could be some Gunk in the fuel distributor. From what I have been told, some CIS cars had a screen type filter that has to be cleaned also...

Do you have the compression #'s???

[Early_S_Man]

Techron in the fuel tank will NOT provide a quick restoration of power and performance, so I suggest a much more aggresive solvent treatment to remedy carbon build-up after sitting for years -- the problem is, most likely, that moisture has been absorbed by carbon in the ports and combustion chamber, and cracked and broken/fallen loose, and may be trapped under one or more valves!

Be sure to pull the 3-pin connector off the CDI-unit before starting the compression test!

You probably have some carbon chunks stuck under the valves for the cylinder that is misfiring, since that is a classic symptom of a burnt valve, and carbon trapped can mimic a burnt valve ... a compression test will tell which are the problem cylinder(s). If there is low compression (below 100 psi) in a particular cylinder during the test, pull that cylinder's injector after turning the engine over to TDC firing point for that cylinder, and squirt a large amount of B-12 Chemtool into that intake port and allow it to sit for one hour ... then crank the engine over for one-to-two minutes, 20 seconds at a time, allowing the starter to rest for two minutes between cranking sessions ... and continue to spray the B-12 Chemtool (or Techron -- you will have to use a syringe) while the engine is cranking.

After you have flushed all low cyliders with Chemtool, repeat the compression test. If the compression is improved, but not up to the average for all of the 'good' cylinders, then turn the engine to the bad cylinder's TDC firing point, and put 1-2 oz. of B-12 Chemtool in the intake port, and allow the engine to sit overnight. Repeat the compression test after all bad cylinders have had the overnight treatment.

Before you dismiss the above time-consuming procedure -- consider that it has restored the compression of a few Pelicanhead's engines -- at least THREE that I know of -- that had bad compression and leakdown numbers, and that professional shops had recommended teardowns on! All were cars that had been recently purchased after sitting for years! The carbon buildup problem is mentioned in Bruce Anderson's Porsche 911 Performance Handbook, and B-12 Chemtool has been recommended in Porsche factory fuel injection publications for several years for removing carbon.

[bonedaddy]

Thanks. Will give it a try. I jumped to checking the valve train before doing the compression test because I had a awful vision of a broken rocker arm or something worse.

Now that I've seen that the valve train doesn't appear damaged, the possibility of something under a valve seat seems a good bet. Should also show up as excessive gap when I check the valve clearances. As soon as I can, I will check the compression and post the numbers.

Thanks again to all replies--this forum is very helpful. I will keep the thread updated asap--since everybody likes a good mystery story.

[bonedaddy]

Well, here's some more info. When I checked the valves, most were a little tight. When I removed the plugs to do the compression test, I noticed that both 3 and 5 looked like they've never fired. The compression test showed the following: 1-147, 2-150, 3-138, 4-138, 5-135, 6-140. Not great, but no indication of major trouble (I don't think).

Putting the inductive pick-up for the timing light on each wire indicated that each cylinder is getting spark.

Sooo...I'm going back to check the injectors. Even though they're relatively new, I suspect that the ones in the suspect cylinders may have a problem. Question is: would a couple of problem injectors cause the fuel rich white smoke that is evident when trying to start?

[Siena911]

Hi

Mine had a split inlet manifold gasket, which produced a lumpy idle. When spraying some silicone spray around each of the intake gaskets she settled briefly on the culprit.

Hope this helps
Jakes

[Jim Sims]

WARNING! Don't use silicone spray for this test if you have a 911 with the oxygen sensor and/or catalytic converter; the silicone in the spray will poison (ruin permanently) the O2 sensor and possibly the catalyst in the convertor. Jim

[bonedaddy]

Just in the interest of providing closure, I found out that the new injectors were re-contaminated. I decided I'd better find the source of the problem, which led back to the fuel tank. I took out the tank and used Methyl Ethyl Ketone to dissolve the sludge that I found there (nothing else would touch this stuff). You would not believe what gasoline does after sitting for five + years! After thoroughly cleaning the tank ( alborious process) and using the prep chemicals and coating from Eastwood, I installed new injectors and voila!

Thanks to all who helped!

[stuttgart]

Well maybe i'll see on the road sometime on 75 ... enjoy her Bonedaddy! try not to let her sit so long next time!! hahaha

[bigchillcar]

hey,

what did you do with all that sludge you removed? howsabout sending it down here to arkansas and we'll donate it to the new 'clinton library' being built in little rock...

hey...who said that...?!

[bonedaddy]

Hey, watch what you say about Boy Clinton...you may get a visit from the thugs at the IRS!