Interesting Discover

[Jandrews]

Hello,

During my last track event, while sweeping intensely through a nice third gear carousel, my RS Spec couple sort of lost power fell on its face. I slowed a bit and noticed that the car felt really anemic all of a sudden, so I eased my way into the pits.

I changed distributor cap, rotor, ignition wires and spark plugs at the track with no improvement. I then filled up with fresh gas and limped home.

A week later or so after I had some time, I did a complete revamping of the fuel system. This included removing, and steaming and sealing of the fuel tank, all new hoses, new inline filter and canister filter (for MFI), new vacuum lines, and finished off with a fuel volume test that yieled approximately 1,000 cc's in 30 seconds. Fuel system good.

Today I figured with the ignition and fuel out of the way (there are still a few ignition goodies that have not been checked like the CD box and coil), it was time for a compression check. (See thread from me from a few minutes ago).

Warmed the car up, disabled the fuel pump, wired the throttle bodies wide open, and proceeded to remove the spark plugs. Started with number four and worked my way around to number three. All looked typical for a typical rich running MFI engine, black carbon around the base and a light brown, clean burning electrode. That is until I got to number three. It looked like it just came out of the spark plug box! No exaggeration!! It was perfectly clean metal, without a trace of anything. It literally looked like it had never fired!!

Now remember, I installed these plugs at the track after "the incident", so they only have about 150 miles on them.

What could be going on here? If I had a problem in the combustion chamber like a bent valve or a piston or ring problem, what would the plug look like? It would still be firing and show some signs of combustion wouldn't it? Even though compression may be low in that cylinder? I have not been able to do the compression test yet, due to the challenges in my other post, but I wanted to get some preliminary opinions on what could cause a plug to look brand new after 150 or so miles of driving in a rich running MFI engine. As I said, the difference between the visual appearance of this number 3 plug and the other five is night and day!!

Interested in hearing your feedback.


Thanks,

JA


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John
70/73 RS Spec Coupe

[Early_S_Man]

Bad 'BERU' connector on your #3 wire. Unscrew the end from the wire and test it with a digital multimeter, and I suspect tou will find it is open -- infinite resistance! It is supposed to measure at 3000 Ohms, +/- 10%, but I have seen them vary a little more with aging, up to 3500 Ohms. And, if there is a resistor end at the distributor cap, it is supposed to be 1000 Ohms, +/- 10%.
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 10-20-2001).]

[oldE]

Spark plug is indicating there has been no combustion in that cylinder. Either no spark (check gap, check wire and dist. cap) or no fuel (possible plugged injector) good luck
Les

[CamB]

I concur with Warren. I had a couple of bad Berus (one was intermittent - when hot I think) and the feeling was that the car was running "ok" but a little rough and no power.

Of course, this only applies if you changed the wires using the original Berus. If you have aftermarket or replaced the Berus too, then there is likely to be another problem.

Cam

[Jandrews]

Ok, a little update.

While the wires that I had replaced at the track were brand new OEM wires with new Beru's, I figured it made sense to go ahead and ohm out each of them to rule out any possibilities with the wires. They all came back between 3,000 and 3,300 ohms. Good.

I also figured I would go ahead and swap in another distributor cap, just in case I got a bad one from the parts supply. No change.

Next, all new plugs, just in case the high schooler behind the counter accidentally dropped a case of Bosch plugs on the concrete floor directly before selling me a handful. No help in performance.

I pulled the plug wire on number three and held the end against the steel throttle cross-rod to see if there was spark. Indeed there was. Next I went ahead and pulled the "new" number three plug, and it also looked as though it had never fired. It was clean and wet, I presume with gas.

I had forgotten to mention in my original post that I had previously had all the fuel injectors pattern tested, and they came back beautiful. I began to think... what could be going on here?

Per Warren's suggestion, I will be making a trip to the industrial hose supply on Monday to get a good hose made for my compression tester so I can finish that effort. That may be totally revealing and make the rest of this searching unnecessary. But, I still think that cylinder ought to be showing some signs of combustion, even if there is low compression. Am I off base here? Even if there wasn't even a piston in that cylinder, wouldn't the plug ignite the gas and create some signs of carbon trace on the plug? How low would the compression have to be for the plug to show NO signs of combusion whatsoever?

I am open to any other ideas, but I think I have covered just about everything but the compression check. The other thought that occurred to me, although I would think very unlikely, is what if the injector in that cylinder was not atomizing and just dumping raw gas? Would that just saturate the spark and drown it out? Supposedly they all checked out great, but you know how that goes. I guess I could swap injectors across cylinders and see if the problem follows.

Any ideas would be greatly appreciated.

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John
70/73 RS Spec Coupe

[mike911]

Sounds like blocked injector. Swap it round like you suggested. If it is go back to shop that spray tested and give em hell.

[Early_S_Man]

John,

You didn't say whether you tested the non-firing plug out of the engine on wire #3 ... don't hold it, use a jumper cable or some test lead clip large enough to grab the body of the spark plug to connect to ground. The reason I say test it is that there have been cases of internally-shorted spark plugs, or a medium/low-resisitance fault! If no spark appears, check the resistance of the center electrode to the grounded body.

Wet plug/gas smell ... seems to eliminate the stuck injector theory! Also, the Beru could be intermittent, and handling/removal might have 'shaken' the connection back into place!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[Early_S_Man]

John,

Did you, by any chance, save your old spark plug wires? I still think it is a bad Beru connector, and I recommend that you try chnaging the cable back to one of the old ones ... #3, #4, #5, or #6 will be fine since we're only talking about troubleshooting!

At this point, about the only thing that will prove or disprove ignition problems is to put the engine on an ignition scope of the Sun Analyzer type!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[Jandrews]

Thanks for the suggestions.

Couple of comments:

I have not yet tried the following:
1) Testing the operation of the sparkplug outside of the engine.

2) Switching the injectors to see if the problem follows.

3) Switching the wire to another cylinder or putting one of my old wires on the "dead" cylinder.

I am encouraged by Warren's thoughts that it is still the Beru connector. Easy fix. I guess I should have tested another wire first thing, but these are new OEM wires, so I felt really strongly that they would be good, especially after the resistance test.

I am at work now, but will try another wire next. This is really puzzling. Again, I am encouraged by the fact that there has been no mention here of any likely internal engine problems.

I have also considered the ignition scope, but I have gotten to the point where I just do not trust any mechanics. I wish I were in Seattle, because I would run, not walk, to see John Walker. Unfortunately, I do not trust either of the Porsche guys in my area. One seems ok, but he is pretty far away, super busy, and seems rather disinterested about everything I approach him on.

Can any old mechanic test these cars with an ignition scope? There is a pretty good shop near my house that I have had good luck with other vehicles, but I highly doubt that they understand CD ignition.

Thanks again.


JA

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John
70/73 RS Spec Coupe

[Early_S_Man]

John,

Yes, any shop, including a GM dealer, can put it on an analyzer, and you need to be there with the car when it is done. What you will see is a series of six pulses on the scope, one for each cylinder. If all six look the same, shape and height on the display ... then all is well with the entire ignition system.

Last year I was discussing testing Beru connectors with a board member on ICQ, and the subject of an intermittent Beru came up because of a miss. The Beru copnnector tested good with an Ohmmeter, but there was this miss ... ultimately, I told him to grab the test leads securely and hold them pressed into contact with the Beru ... and shake them without hitting anything while
observing the meter. Voila ... intermittent shook itself open! Miss disappeared with new Beru.

The reason I hadn't mentioned mechanical damage is the missing compression test data!
But, since you mentioned it ... you need to pull the left intake valve cover and look for evidence of a #3 broken intake rocker arm ... ASAP! IF YOUR INTAKE VALVE ISN'T OPERATING, OR IS OPEN ALL THE TIME ... NO FIRE IN THE HOLE!!! A similar incident a year or so ago was a board member who ended up with a broken rocker and bent intake valve. Others have had multiple bent intake valves.

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler