RS Compression Results!

[Jandrews]

Alright, a little update.

You may remember that I have been wrestling with a non-firing plug in cylinder #3. After changing plugs and verifying 3,300 ohms of resistance in the Beru connector, I had to move on to the compression test. This was done with warm engine, wide open throttle, all spark plugs removed, and triple checked.

Well, some staggering (for me) results today.

Here they are:

#1 - 167 psi
#2 - 125 psi
#3 - 162 psi
#4 - 166 psi
#5 - 167 psi
#6 - 167 psi

You read this correctly. It is number 2 that has the suspect reading!!! Number 3 looks great, as do all the other cylinders.

I have mixed feelings about this. Obviously this is probably good news for number 3, as it leaves only another Beru or possibly an injector as the culprits.

For number 2 however, that number look BAAAAD!! Interestingly enough, as some of you might recall, number 2 is the one my "ex-mechanic" supposedly repaired a bent valve in last year after a mechanical over-rev incident!!!

Sheesh... I don't know what to think now. I just took a break to come inside and post this, and I will go back out and put her back together and try to address the non-firing plug in number 3. I think it would also be prudent to verify the reading in number 2 by running the engine again and making sure the valve seats are not obstructed from spark plug removal.

Anyway... that's the story.

Any comments?

Thanks,

JA

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John
70/73 RS Spec Coupe

[pwd72s]

I just hope you don't need some more head work. Hopefully by somebody who knows what he's doing this time around. Good luck..Paul

[Early_S_Man]

John,

Do you have a leakdown test gauge? How about the flex-hose and adapter for your compression gauge ... can it be removed to couple it to a source of compressed air? If so, turn your engine over by hand until it is on the firing position for #2 at TDC. Put your trans in 5th gear and put on the E-brake.

Apply 100 psi air pressure to the cylinder, and listen at oil tank filler, intake stack, and exhaust pipe for hissing or leaking sounds. Let us know what you find!
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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 10-28-2001).]

[Jandrews]

Okay,

I have not been able to do the leakdown test on number 2 yet (dependent on an air compressor and leakdown tester of which I have neither).

But, the reason for this post, is that I am still having trouble with number three. That cylinder just does not seem to have combustion occuring. To-date, I have done the following on that cylinder:

1) Compression test of 162 psi
2) Switched out 3 different spark plugs
3) Ohm tested three different plug wires
4) Swapped and verified different injectors
5) Swapped two distributor caps
6) Verified firing plug outside of engine

The plug in number three just keeps coming out shiny clean and just slightly wet.

I cannot figure this out. I have not checked the cam on the distributor shaft to make sure it is not excluding number 3 for some odd reason, but that is about the only thing I have not done. Completely puzzled.

Any other ideas?

Thanks,

JA

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John
70/73 RS Spec Coupe

[Early_S_Man]

Well, a long shot, maybe! The 'Blue Book' mentions the possibility of a carbon build-up in 'front' of the injector in the intake port, and suggests a drill bit be run down the injector path to clear out the carbon.

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

[Superman]

If you want to learn more about what's going on with #2, use compressed air as Warren suggests. wiht the cylinder pressurized, hissing through the intake would mean a bent or intake valve. Hissing in the exhaust would mean a bent or burned exhaust valve. Hissing heard through the oil take filler neck should be expected, this is air moving past the rings.

On #3, also a long shot (really long shot), but I wonder if there could be enough corrosion to make a poor electrical ground between the cylinder head and the case. No, that's too long a shot. Still, I'd pull that wire, put a good spark plug in it, and use a test lead to connect it electrically to the head. Then start the engine and see if the #3 plug is firing.

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'83 SC

[Wayne 962]

Right - sounds like it might be more of a fuel problem now than an ignition problem. You must get good atomization of the fuel (under pressure) in order to get the cylinder to fire correctly. Clogs can certainly prevent that. Remove the injector and take a look at the spray pattern (compare it to another cylinder). This may give you a clue.

Also make sure that the valve adjustments are 100% correct...

-Wayne

[Jdub]

Yes, what Wayne has said: how is your valve clearance? Also, have you dropped 20oz of Techron in an empty gas tank and then taken the car out for a good, hard run?

My car had spotty comp/leakdown and the results after driving the bejabbers out of it after two Techron runs was night and day. I believe I unstuck a stuck ring and generally removed *some* but not all of the carbon and other detris in the engine/fuel system. EDIT: Perform the Techron run AFTER the valve job! Nobody wants burned edges on the valves!

Anyway, that might help the low number cylinder. I wonder if he got the valve angles correct and got the valve lined up nice and right on the seat-stem alignment.

Jw

[This message has been edited by Jdub (edited 10-31-2001).]

[Jandrews]

Still no progress on finding out why no combustion appears to be occuring in cylinder #3. I tried the drill bit down through the injector path, but there seemed to be no obstruction (as far as I could reach with a 4" drill bit.

I also verifed that the points were indeed opening at the proper time for firing, and the rocker arm seems to be working the valves fine. The valve clearance was good as well.

I feel like I have checked everything imagineable on this, but the plug still comes out looking untouched by combustion gases. Is there anything else at all that I should check?

I am thinking that with the questionable compression result in cylinder #2, along with this puzzling situation in #3, a tear-down may be in order. I have not done the leakdown on #2 yet, but I did pick up a nice Milton leakdown tester. As soon as I can get my hands on a compressor I will close that task out.

Any other ideas on what might be going on in #3 would be appreciated, as well as any advice on whether it seems time to pull the engine and start taking things apart.

As always,

Thanks.

JA

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John
70/73 RS Spec Coupe

[Reg]

Similar situaltion here too John. I thought I only had a problem with cyl 6, and it turned out that 2 was giving me lower compression.

I'll post my results once I get my car back with its newly rebuilt carbs! Hope the snow is'nt flying by that time.