GLOW PLUG ANALYSIS - Diesel Forum

welder79 · 03-15-2005, 12:21 PM

BECAUSE OF THE FASTER CYCLING NOT INITIAL WTS LAMP TIME MOST PEOPLE HERE HAVE TOLD ME TO CHECK THE GLOW PLUGS.

YESTERDAY I CHECKED THEM WITH A TEST LIGHT - LIGHT LIT UP ON ALL PLUGS

TODAY I CHECKED THEM WITH A METER - NOT SURE IF I USED THE METER CORRECTLY SINCE I AM NOT FAMILIAR WITH THE METER BUT HERE'S WHAT I DID - I SET THE METER TO THE RESISTANCE SCALE OF 200...NOT 200K NOT 200M BUT PLAIN OLD 200. THE METER READ CONSISTANT ON ALL PLUGS GIVING ME A VALUE OF .004 - .005 IS THIS GOOD?

I HAD READ ON ANOTHER POST TO CONNECT THE BLACK LEAD TO THE NEGATIVE BATTERY POST AND THE RED LEAD TO THE GLOWPLUG AND I SHOULD GET 1~2 OHMS.

THIS IS HOW I SET UP MY TEST BUT I GOT .004 - .005

SOMEONE PLEASE TELL ME IF MY TEST WAS GOOD OR BAD AND IF MY VALUES MEAN GOOD OR BAD PLUGS?!!!

OkieGringo · 03-15-2005, 01:11 PM

Please turn off THE CAPS LOCK. As I remember, and how I checked mine, I REMOVED all the GPs and then tested them. But the most IMPORTANT thing you need to do is check the side of EACH GP to see if it says BERU made in Germany. If they are not Beru, PULL THEM ALL OUT OF THERE IF YOU STILL CAN!!!!!! Autolite GPs will ONLY last a few starts if you're lucky. And if you're real lucky they won't curl up inside the head and make you remove the head to get them out!!! Are you getting the picture yet? My best advice, when it comes to GPs is to go to Autozone and buy new Motorcraft GPs(about $9.00 each x8). Motorcraft GPs are MADE IN GERMANY by a company named ?????, yep, you got it, BERU. This is when you CAN use the CAPS LOCK .... NEVER, NEVER, NEVER, NEVER, NEVER, NEVER USE AUTOLITE GLOW PLUGS IN THESE ENGINES. [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/smokin.gif[/img]Baja

pnose · 03-15-2005, 02:16 PM

YESTERDAY I CHECKED THEM WITH A TEST LIGHT - LIGHT LIT UP ON ALL PLUGS

Just to be clear on how you used the test light.When putting the probe to the gp only touch the part that the wire connects to,if you go below that(from the hex down,including the hex) the light will come on.

d9d · 03-15-2005, 02:59 PM

yah, turn off that caps-lock...makes my eyes cross and my head hurt... [img]/ubbthreads/images/graemlins/grin.gif[/img]

Something's wrong with that meter-reading. Unless you have a 6.5 digit portable DMM... [img]/ubbthreads/images/graemlins/grin.gif[/img]

I'm assuming your meter is a typical $10-$50 3.5 digit digital-multimeter, yes?

If so, you shouldn't be seeing anything like ".005". Are you sure there was a decimal point at the left end?

On my meter, the only range that will produce a reading with 2 leading zeroes is the 2000mv range, i.e. the 2-volt range. And even then, there's no decimal on the left. With the leads 'open', I get "002", i.e. 2mv of noise picked up from the air. Leads shorted, I get "000".
But no decimal point in either case.

On the 200 ohm range, with leads shorted, I get "00.4", which means 4-tenths of a single ohm. A low resistance. You don't get a zero reading because the test-leads themselves have a little bit of resistance.

What you SHOULD be seeing on a typical 3.5 digit meter is a reading like: "01.2", meaning 1.2 ohms.

Check the meter by putting it on the 200 ohms range, leaving the leads open (not touching each other), and you should see "OL" or "1__" (1 at the left and empty space to the right).

Now touch the leads together. You should see "00.4" or "00.7" or something like that. A reading in tenths of an ohm.

Now, to test the GP's, you need the black lead on a CLEAN ground. Jamming the point into the top of the NEGATIVE (-) battery-terminal is fine, but kinda hard to hold it there while you're other arm is waving around the engine... [img]/ubbthreads/images/graemlins/grin.gif[/img]

I usually just scratch the point into the hex of the GP I'm testing at that moment.

Since I worry that defects in the wiring on other GP's or in the GP-controller might short out the harness, I always REMOVE the connector from the tops of the GP's before I test them.

If you do that, then it's easy to get the meter lead on the right place. While keeping the black lead firmly on a CLEAN ground, touch the the red meter lead to the very TOP of the GP...the part that the wire-connector pushes down on to. You should now get that "01.2" reading that the other guys mentioned.

If you get "OL" or "1__), then the glow plug is "open". In other words, burnt out.

If you get much less than an ohm, i.e. "00.7" or similar, then I'd have to wonder if it was shorted to ground; although that's a rare failure-mode.

Mostly, you're just looking for "open" GP's. You'll almost always get either "OL" (bad), or a reading somehwere around 1 ohm (good).

Hope this helps...

ThePunisher · 03-15-2005, 05:05 PM

When using a multi-meter/ohm-meter to test the glow plugs you must remember to subtract the resistance of the wires/test leads from the final reading .. The test light test is really the best way of testing the glow plugs because they are "positive coefficient (PTC) glow plugs" meaning that the resistance changes as the temperature rises ..

welder79 · 03-15-2005, 05:22 PM

so what do my readings mean???

agnem · 03-15-2005, 08:24 PM

Well, [img]/ubbthreads/images/graemlins/shrug.gif[/img] if I had to guess, I'd say your plugs are good. Next thing to look at would be a bad ground on the glow plug controller, or a wiring harness problem.

jdkline · 03-15-2005, 08:31 PM

First thing is to make sure all your connectors are securely plugged in and clean, and second check to see if you have a good ground. If that doesn't help you you might want to retest those glow plugs. I would agree with Baja about the AUTOLITES. They don't work well in these engines and can drop in and damage them, same with Chumpions which are also made by Johnson Controls, which makes good other electrical stuff to my knowledge but can't make a glow plug which is worth a crap. If you have berus or anything other than autolites and chumps, you're proabbly safe just leaving them in and replacing any bad ones as needed.

welder79 · 03-15-2005, 11:19 PM

I do have berus. I checked the gpc ground and it looked and felt fine. What problems would a bad gpc ground cause anyways because all I notice different is the faster clicking of the relay after the normal operation of the wts lamp.

Also, what is the plug in relay that plugs into the gp harness right at the front passenger side gp. It is right at the same location as the two prong cold advance plug(something like that) right behind the radiator hose. The relay is a sqaure shaped relay that plugs into a pigtail off of the gp harness...

cdnsarguy · 03-15-2005, 11:31 PM

That is related to the fuel heater it is the module I believe.

d9d · 03-16-2005, 03:41 AM

[ QUOTE ]
When using a multi-meter/ohm-meter to test the glow plugs you must remember to subtract the resistance of the wires/test leads from the final reading .. The test light test is really the best way of testing the glow plugs because they are "positive coefficient (PTC) glow plugs" meaning that the resistance changes as the temperature rises ..

[/ QUOTE ]

I'd have to disagree. The test-light is subjective...'reading' it is dependent on sunlight levels, etc.. I like to know the resistance. I've had GP's that would light a test-light, but didnt' heat properly.

For that matter, the BEST way to test is to remove the GP, hook power to it briefly and make sure it gets HOT. When I first got my '86, two of the GP's were low-resistance, but did NOT heat the tip. They were shorted internally.

But the ohmmeter/test-light is probably fine for normal/quick work.

agnem · 03-16-2005, 11:01 AM

Seems her problems started with someone crawling around under the hood, so I'm figuring the problem is damage done external to the glow plugs, although if it were a bad glow plug or two, it would be very bad timing.

aaklingler · 03-16-2005, 12:24 PM

I just had a brain fart, did you hit a heat wave when it started clicking faster?

d9d · 03-16-2005, 03:32 PM

[ QUOTE ]
Seems her problems started with someone crawling around under the hood, so I'm figuring the problem is damage done external to the glow plugs, although if it were a bad glow plug or two, it would be very bad timing.

[/ QUOTE ]

ahhh...roger that, Mel.

I kinda lost track of the beginning of the thread... [img]/ubbthreads/images/graemlins/grin.gif[/img]

ThePunisher · 03-16-2005, 05:05 PM

[ QUOTE ]
[ QUOTE ]
When using a multi-meter/ohm-meter to test the glow plugs you must remember to subtract the resistance of the wires/test leads from the final reading .. The test light test is really the best way of testing the glow plugs because they are "positive coefficient (PTC) glow plugs" meaning that the resistance changes as the temperature rises ..

[/ QUOTE ]

I'd have to disagree. The test-light is subjective...'reading' it is dependent on sunlight levels, etc.. I like to know the resistance. I've had GP's that would light a test-light, but didnt' heat properly.

For that matter, the BEST way to test is to remove the GP, hook power to it briefly and make sure it gets HOT. When I first got my '86, two of the GP's were low-resistance, but did NOT heat the tip. They were shorted internally.

But the ohmmeter/test-light is probably fine for normal/quick work.

[/ QUOTE ]

Im just going by my Ford shop manual it has 13 pages of GP/relay/controller tests... They recommend testing the glow plugs with a test light because the resistance changes with temperature ..Any ohm tests are tested at 20c (68f) .. I have 3 Fluke meters that I have for work 2 are high end Flukes (model 88 automotive & model 863 graphical) I don't have a spare new glow plug right now (at $30.84CDN each I don't keep spares on hand) but next time I have a new glow plug I'm going to warm it up to about +80 (like I was testing it in Mexico) then put it in the freezer to -30 (like I was testing it in Canada just to see how much the resistances vary ..

I see welder79 said:I HAD READ ON ANOTHER POST TO CONNECT THE BLACK LEAD TO THE NEGATIVE BATTERY POST AND THE RED LEAD TO THE GLOWPLUG AND I SHOULD GET 1~2 OHMS...what manual is this test in..?..was it Haynes or Clymer..?