OK, I have an 80 300d non turbo that I just checked the GP plug harness plug readings. The car engine was stone cold and has not been started in a month or so. Outside air temp around 60. I had the digital multimeter black lead grounded to my negative battery terminal and I used the red lead to insert into the harness plug holes. My mm stayed at 1, never fluctuated or flinched for all of the holes. Just stayed at 1. Sound fishy? Battery tested around 12.2. Had similar readings at the three points on the relay. Btw, I was following the procedure outlined on Diesel Giants site...great write up I then cleaned the battery terminals and the negative ground contact point by the hood hinge, all for good measure and still had NO START! Could the negative cable be bad?

Fyi, I just went through and tested and changed out a GP on another 80 300d non turbo a 1/2 hour before test on the above car. The car had been demonstrating hard starts for the last week or so. Its my daily driver and the morning starts were getting longer and longer Had good readings under 1 for 4 plugs at the harness plug head holes but one had something like 56

Your battery tested at 12.2 volts. Was your multi-meter set on RESISTANCE or VOLTS when you checked the plugs? You are looking for about .9ohms.

-Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

If you're testing resistance and using the neg terminal as the ground and getting good readings, the negative cable at least has continuity. Was cranking speed good or did it seem slow?

I would suggest getting a helper to turn the key to run for you and then verify voltage at the glow plugs.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I believe I was set on resistance 200ohm setting as shown in the dieselgiant.com write up.

Cranking speed seemed kind of slow. Why would I need a helper? Is there a time issue to check the gp's within a certain time from when the key is turned?

Resistance is the only check on a multimeter that requires the MM's internal battery to do much work. Maybe your MM's battery is near dead.

-Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

nueman,

Some multimeters read a "1" on an open circuit. I suspect that is what U were getting.

Test the meter circuit by connecting both leads to a good ground on the engine to see if meter reads almost 0. If it does then test the GP resistance.

P E H

Yes. The glow plugs are timed and from the time the key is turned you get 60 seconds at most. If you have a helper turn the key for you, you can probably get the voltage at all five plugs before the relay kicks off.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

I hadn't thought of that. Mine just says O.L. (open leads) in an open circuit situation.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

O.L. can aslo indicate that the reading is below the scale set for the meter.
My Fluke does that.

Disconnect all the connecting wires to the plugs and test the plugs individually.
Black lead to ground. Red lead to the tip of the glow plug while still in the engine block.

I thought the setting was supposed to be 20 ????

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

unkl300d,

1. It doesn't matter which end of the meter goes to ground or tip of GP for a resistance reading.

2. Removing the GP connector from the GP relay disconnects all the wires to the GP in a much easier way. Then plug one lead of meter into the Hole in the GP cable connector to take GP resistance readings.

P E H

I always thought O.L. was Over Load, as in - when the leads aren't forming a circuit, there is such infinitely high resistance (because there is in fact no circuit at all) that it couldn't be measured.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

PEH, more than one way to skin a cat !! Thanks . Yes I have seen the diesel giant site but that example referred to the glow plug relay that is found in the engine bay. Federal.
Since mine is a California model, the glow plug relay is a different one mounted under the steering wheel dash area.
Both methods work !

Busted benz, O.L. may represent both scenarios. Look online for an operating manual for your meter. If it is a Fluke, they are available free as pdf files.
Fluke.com

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

It's an Extech.

Either way we're only arguing over what the initials mean. What they're indicating (an open or nearly open circuit) is the same regardless of what we say the words stand for.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Ok, so if I have a reading of "1" as is the case on my mm or "OL" on others, what could be the problem in this no start situation?

I read this on a mm tutorial website...... However, this time we get a strange response, a 1. which means out of range. Some meters will display an OL which you may remember from the continuity secion as meaning "open loop" here it means "the measurement is higher than the range"


I had my ohm setting at 200. Could it mean that all my gp's were at least 200 resistance point out of whack? I could test each plug by remving the wire and pulling each plug...correct?