Here is a good poor-man's compression test, based on cranking the engine without glowing the plugs.

Make sure:
* the engine is COLD = not run in 24 hours.
* The valves are adjusted correctly.
* Ambient temperature 50° Fahrenheit or higher.

#1. Disconnect the glow plug relay.
#2. If it fires up immediately (within 60 seconds) with zero glow then it's got decent compression.

Injection timing plays a large role in the engines ability to start with no GP's. So this is not always a true indication of engine health if the injection timing is unknown.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

And temperature....at 20* the car should get an award for starting with no glow :-)

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1985 300D 172,110mi and goin' strong

Or has a little pick me up in the fuel?

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Not to mention the condition of the starter, and or battery.

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1981 300TD 4 speed manual
Euro bumpers, zender valance and skirts, H&R springs, billy HD's, leveled sls, real AMG Pentas 16x8 et11, vdo boost/egt gauges intergrated into ash tray, eurolights, led 3rd brake light

Sounds like a good way to kill the battery!

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

x2

or

cook the starter motor.

Interesting thought: If you measured the amperage draw vs. time for the starter, it might be possible to distinguish a cylinder with lower compression than the rest due to the lower current drawn on its compression stroke. There'd be no way to convert this accurately into real numbers, but it ought to work as a relative indication of cylinder balance.

I know when I've had a spark plug removed on one cylinder of a gas engine (so 0 compression on that hole) and turned it over, the variation in cranking speed was pretty obvious.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

Not if it starts instantly.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

This is actually a good way to measure relative compression. My friends 6.0 PowerStroke can actually do this over a scan tool! 1970s VWs had a diagnostic port you could hook up to his honkin shop computer and do the same test.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Mercedes Sprinters can measure compression with a scan tool from what I've read. But 70's VW??? Can you name the model and years where such is possible? What about VW TDI's I have not heard they have this capability.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Here's a commercial: http://www.youtube.com/watch?v=mU-zI2fKdY0

The cars just had a bunch of extra wires going back to a test plug under the hood. It was only available for a couple of years.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Dang, I'd totally forgotten about that! Yup, my '75 Bus had that. It was offered on the early fuel-injected models -- the ones with Bosch D-Jetronic and L-Jetronic. Keep in mind these were fuel injection systems based on analog electronics; they had no self-diagnosis capability, so this was VW's attempt to make it easier for dealers to troubleshoot them quickly. The only other way was to test each component in logical order until you found the one that case causing the engine not to run.

There was a crank position sensor and a *lot* of extra wiring in the wiring harness, all terminating in a big plug. It must have cost them a lot to implement, and from what I hear it never worked all that well. A lot of current owners cut that stuff out to clean up the engine compartment wiring.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png