What could be the problem? Help

[Ruben911]

I ordered a set of SSI heat exchangers from Pelican and they arrived yesterday. This morning I removed the old heat exchangers and upon looking at the exhaust ports I noticed that 5 of them have typical exhaust deposit (black soot - perhaps a little rich on the fuel). However, one of the ports is beige color, like no exhaust is exiting this piston. I did a compression test a couple of months back and all pistons checked ok. What can this be? Clogged injector, fuel distributor, etc. I'm looking for ideas on how to diagnoze the problem. Can I start the engine without the exhaust manifolds to see if exhaust is in fact not being discharged. By the way, I have often felt that the car lacks power and there has been this small miss that I have been trying to find but no luck so far. Maybe I found the problem. Thanks

Ruben
1976 911s 2.7L

[Ruben911]

I pulled out the injector and verified that it was delivering fuel (spray pattern). So there is in fact fuel getting to that cylinder. It may just be that this particular cylinder is running lean and the others may be on the rich side. Anyone else seen something similar on their cars when you have taken out the exhaust manifolds. Thanks

Ruben

[Ruben911]

Still looking for suggestions\ideas. Anybody out there? Thanks

[sammyg2]

About a hundred years ago when I first started working on cars, my dad told me that I should always check the ignition system first. After I get it all checked it out and I am sure there is nothing wrong with the ignition system, i should go back and check it again because I must have missed something.

Point is, we always seem to blame the fuel system too much, when the ignition system is usually the culprit. I would start your car with that spark plug wire off and see if it changes the way it idles. My money is on a bad spark plug wire/connection/plug (just a hunch).

[Ruben911]

Sam, thanks for the feedback. I just pulled the suspect spark plug wire at idle and confirmed that it changes the way it idles (slight drop in rpm). The efect is similar to that of the other wires when pulled. Therefore, I'm beginning to feel as though even though fuel is being delivered to this cylinder, the following may be happening:

1) less fuel being delivered to this cylinder than to the others (lean mixture)
2) vacumn leak somewhere in the intake runner to that cylinder (again lean the mixture)

I will test 1) by pulling the injector to this cyclinder and another injector and measuring to se if there is a difference in the amount of fuel being delivered by each.

I know this is contrary to your fuel system hypothesis, but I have nothing else to go on at this point.

Thanks

[Jim Smolka]

Most likely Fuel, have you tried the techtron thing?

Another option is to double check the spark.
Temp. replace the old spark wire with a plain cheap new one from Autozone (VW bug type wire). See if the car runs a little better.

[pjv911]

vaccum leak most likely at the center air box were the manifold connects to the airbox. Spray some carb cleaner or open your propane torch(not lit !) all around the entire intake system and see if the rpm goes higher. If so you should pinpoint the area and fix it. A lean running cylinder will cause damage to youe expensive engine. A light brown exhaust port sounds lean to me.
Had any intake backfires lately ????????? Could be a cracked air box too.

Kurt Williams

[Ruben911]

Thanks for the feedback

Jim,

I tried Techron several months ago and I checked the injector on the suspect cylinder and it seems to be working fine (good spray). Tomorrow I'm going to do a side by side comparison of this injector against an adjacent (known to be rich) injector to note any differences in spray pattern and gas volumes delivered.

I will also check the spark strength tomorrow by comparing the spark with the current wire to the spark with a spare wire I have, and to other cylinder wires. While on this subject, has anyone noticed improved performance with an MSD.

Kurt,

I have used carb cleaner to detect previous leaks. However, on the number 5 cylinder (lean mixture), since the connection from the intake runner is underneath the air box, I have a rough time getting carb cleaner in all joints. How would I know and where should I look for an airbox crack. I have had many backfires but I also have a pop-off valve which is supposed to protect the airbox against backfires.

Ruben

[Ruben911]

Today I compared the spray pattern and volume of gas delivered between the suspect #5 and the #1 P/C, which is known to be rich. I replaced the injector on #5 yesterday with an injector which was removed from the engine a couple of years ago. The results with the replacement injector shows that the spray pattern and volume of fuel delivered are the same between #5 and #1. This confirms that the fuel distributor is working properly. I will remove the heat exchangers next weekend to install new SSIs (could not install the SSI's this weekend because I did not order the relacement oil lines) and check to see what the exhaust signature looks like. If it still shows lean then the spark is not strong enough in #5 or I have a air leak somewhere in the intake.

Thanks

[pjv911]

Ruben , forget about the spark being your problem. Keep in mind that a leaner mixture takes more spark energy to fire than a comfortably rich mixture. In other words secondary voltage to the plug is fine if that cyl is running. Did you see if the injector O`rings are good ? Thats another good place to check for a vacumm leak . If you get no change in RPM when spraying carb cleaner all around the intake then it is most likely not cracked or leaking from a runner connection. Keep in mind that a light brown color in the exhaust port is not nessesarily a problem .
Although it may be a different color the mixture may be equal under a load, and that color was formed by idling when last run.
How about this for a possible answer. You have 5 bad exhaust valve seals(guides). Did that come to mind ? Does it smoke alot when first started in the morning ?

Kurt Williams

[Ruben911]

Kurt, It just smokes on start-up and then it clears right away. I thought this was typical of flat-six engines and residual oil on the cylinders. Checked for leakage on the injector o-rings and did not find any. I want to see what the exhaust port on #5 looks like this weekend when I replace the heat exchangers and see if the replacement injector makes a difference. On a side note, the car appears to be more responsive since I replaced that injector and swapped the old beat up OEM muffler with a Dansk muffler this weekend. Can't wait to replace my inefficient OEM heat echanger with the SSI's this weekend. Thanks