one cylinder not pulling its weight? (video)

airkooledchris · Samba Member Joined: January 25, 2005 Posts: 2709

short history. a recent compression test showed Cyl 1&2 were very low in compression, while 3&4 seemed to be almost brand new....

what im a little fuzzy on, and perhaps I need to just ignore this whole fact, but why is it that if Cyl #1 and #2 have the lowest compression and #3 and 4 the highest, why does pulling the spark from 1 or 2 nearly kill the engine and when you pull it from #3 the motor can barely tell the difference?
I took a little video of it just now:

Link

you can see it's getting spark, it just seems like the engine isn't seeing much benifit from the #3 side even being there....

1975 Kombi · Posted: Thu Jul 16, 2009 4:12 pm Post subject:

What were the numbers and were the valves adjusted before the test.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

airkooledchris · Samba Member Joined: January 25, 2005 Posts: 2709

the first time we checked compression, after a valve adjustment, was:

#1 - 66
#2 - 85
#3 - 110
#4 - 120

with a bit of oil we got

#1 - 90
#2 - 110
#3 - 150
#4 - 160

after we ran it to burn up the oil inside

#1 - 90
#2 - 85
#3 - 90
#4 - 120

1975 Kombi · Posted: Thu Jul 16, 2009 4:21 pm Post subject:

There is a procedure somewhere. I think on Ratwell's site. The engine warm the throttle body wide open, I do normally five or six rotations with all the plugs out, watch the pumps on the gauge to see if it jumps well to the max or if it slowly builds, battery full, Just to make sure you have the most accurate test.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

1975 Kombi · Posted: Thu Jul 16, 2009 4:24 pm Post subject:

I say 3 is not firing. Pull the plug and check spark grounded on the case.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

EZ Gruv · Posted: Thu Jul 16, 2009 4:27 pm Post subject:

I wonder if there is a short along the plug wire somewhere, and it's not reaching the plug.

[/quote]
_________________
Eric
1977 Deluxe Westfalia - 2.0L FI Type IV, Completely Original
Photographer for HotVWs, VolksWorld, AirMighty, VW Camper & Commercial, Hayburner, and more.
My Photography Page.

airkooledchris · Samba Member Joined: January 25, 2005 Posts: 2709

I had Colin the aircooled itinerant help me with the compression test, using his gauge so I know those numbers are good.

I actually swapped out that plug wire with a used bosch and had the same result. if you look really close in the video, you can see that when I hold the wire close to the dist cap there are sparks, and when you see them you an hear a very faint change in the sound of the motor, but almost none.

are you saying to pull the plug itself and start it and run it without any plug in the #3 side, then hold the end of the plug near the case to verify there is spark there as well?

1975 Kombi · Posted: Thu Jul 16, 2009 4:37 pm Post subject:

Well just have someone turn it over and you watch the plug for spark. The plug could be bad. And later run it in the dark and look closely for spark jumping somewhere in the system.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

airkooledchris · Samba Member Joined: January 25, 2005 Posts: 2709

1975 Kombi · Posted: Thu Jul 16, 2009 4:46 pm Post subject:

I am not sure but a spark from the cap to the wire may not translate into a spark at the gap. If it was firing there would be a difference in the motor.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50336

If you have a shorted plug you will see a spark at the cap, but get no power from that cylinder. You could also have a problem with the injector for that cylinder, or an air leak that is affecting #3 worse than the others.

1975 Kombi · Posted: Thu Jul 16, 2009 6:32 pm Post subject:

The lack of #3 probably balances out the opposite side cylinders.
_________________
Brett

“He’s decieving you boy! Reach into his pocket and take what he’s got.” Mr. Crabbs.

75 Westy auto
03 Jetta TDI
71 SB
74 Westy
Licensed pilot (single engine land VFR)
--
Rust In Pieces: 72 Bug, 73 Bug, 81 Rabbit LS D 2D, 83 Rabbit D 2D, 84 Jetta TD GL, 85 Jetta D, 68 Z28 RS 302, 91 Passat 16v

airkooledchris · Samba Member Joined: January 25, 2005 Posts: 2709

SGKent · Posted: Thu Jul 16, 2009 7:48 pm Post subject:

I would check the rubber boots on the plenum to see if #3 has a leak. If it doesn't then I would have the injectors cleaned.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin


Hello! Log in or Register \| Help \| Donate \| Buy Shirts	See all banner ads \| Advertise on TheSamba.com

	Forum Index -> Bay Window Bus	All times are Mountain Standard Time/Pacific Daylight Savings Time
Page 1 of 1