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  #1  
Old 04-08-2014, 07:06 PM
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Need help reading GP oHm test results...

Hey guys,

The truck has been struggling to start all winter without it plugged in. First start in the morning has been a struggle. It will always fire after about 7 seconds of cranking. So i got around to running some tests..

Test 1 - Glow Plug Relay - tested good (12.5V from the battery, 11.5V to the GP's)

Test 2 - oHm test the relay (key off) GP are showing 0.5 (RED FLAG)

Test 3 - Pulled the connectors on each valve cover and tested each prong. Below are each prongs results in ohms.

PS DS
(0.0) (1.0)
(1.0) (1.0)
(0.0) (1.0)
(1.0) (0.0)
Front of Truck

My question is does each prong correspond with each GP/Cylinder accordingly??? I might just replace all the plugs since I'm in there. I plan to do a 50 Cent mod while in there this time. Do you recommend changing out the Harness as well?

Your guy's advice is appreciated! Thanks.
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Old 04-09-2014, 07:53 AM
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You definitely want to change them ALL now (no reason to back-in each time another one fails, they're all the same age, experienced the same conditions)

The 50cent mod is a good idea, just be sure to look closely at the pins on both sides for signs of arcing and deterioration. If they look OK then there's no need to replace them.
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Old 04-09-2014, 08:36 AM
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your glow plugs are perfect values, they've probably been replaced within the past few years.

they should be somewhere between 0.3 and 3 ohms. your meter isn't accurate enough to read the lower values of resistance. if the ones testing 0 ohms were actually zero, your wiring and connectors would have burned up instantly.

next step is to replace the glow plug relay if it's stock and more than a year or two old.

if you go to an HVAC supplier you can see if they have or can order a white rodgers 586-902


or order one online or spend a little more for a stock one that will burn up.

the stock glow plug relay is a roulette wheel every time you turn it on. it has contacts that are underrated that turn every time it turns on. some spots inside will have burnt up contacts, some spots won't.

if you still have cold start problems after this, your problem is most likely worn injectors. 5w40 synthetic oil will help greatly with cold starts.

here is some good reading on injectors
http://www.swampsdiesel.com/files/7....Diagnostic.pdf
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Old 04-09-2014, 09:57 AM
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Did I misread 0.0 on 3-of-8 ??

Doesn't sound perfect to me....
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Old 04-09-2014, 10:20 AM
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0 ohms is good. Infinite ohms bad.

It's hard to get many meters to read within 0.5 ohms unless it's a calibrated high end fluke meter
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Old 04-09-2014, 11:43 AM
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Quote:
Originally Posted by steve604 View Post
your glow plugs are perfect values, they've probably been replaced within the past few years.

they should be somewhere between 0.3 and 3 ohms. your meter isn't accurate enough to read the lower values of resistance. if the ones testing 0 ohms were actually zero, your wiring and connectors would have burned up instantly.

next step is to replace the glow plug relay if it's stock and more than a year or two old.

if you go to an HVAC supplier you can see if they have or can order a white rodgers 586-902


or order one online or spend a little more for a stock one that will burn up.

the stock glow plug relay is a roulette wheel every time you turn it on. it has contacts that are underrated that turn every time it turns on. some spots inside will have burnt up contacts, some spots won't.

if you still have cold start problems after this, your problem is most likely worn injectors. 5w40 synthetic oil will help greatly with cold starts.

here is some good reading on injectors
http://www.swampsdiesel.com/files/7....Diagnostic.pdf
Hey Steve,

Good to know before I drop an order for glow plugs... I think I'm going to pull the valve covers and test continuity at the GP heads just to be safe, do the 50 Cent mod while in in there. I recently did Injector Cups (2,000 Miles ago) and replaced all the injector O-rings.

I read through the link you posted. The truck has 171,000 miles right now. It was beat to sh*t by the previous owner as it was used by a landscaping business to haul a huge trailer and plow snow. I'm really hoping I don't need to do Injectors. Once it fires, it blows a big puff of white smoke (guessing a lot of unburnt fuel) then clears up pretty quick. No smoking or running issues after the truck is running.

It is due for an oil change and fuel filter, so 5w40 Full Synth it is.

I will report back my findings when I find the time to get under the valve covers.
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Old 04-09-2014, 01:41 PM
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If youre getting those resistance values at the valve cover harness, don't waste your time with pulling the covers.

Rotella t6 oil made a world of difference in my truck for cold starts with worn injectors. I would start with that.
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Old 04-09-2014, 02:20 PM
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Quote:
Originally Posted by steve604 View Post
It's hard to get many meters to read within 0.5 ohms unless it's a calibrated high end fluke meter
Is that possible? I guess I only have "high end" meters then...

You would certainly Have to be able to make a scale change and read <1 Ohm - wouldn't you?

To the OP, you're GPR tested good though I though.

I think you have Other problems than the GP system. How many miles on the engine? After all these years we're seeing a lot of 250K trucks that are getting hard to start because of warn injectors
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Old 04-09-2014, 04:23 PM
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Originally Posted by NoRalPh View Post
Is that possible? I guess I only have "high end" meters then...

You would certainly Have to be able to make a scale change and read <1 Ohm - wouldn't you?

To the OP, you're GPR tested good though I though.

I think you have Other problems than the GP system. How many miles on the engine? After all these years we're seeing a lot of 250K trucks that are getting hard to start because of warn injectors
Truck has 171,000 miles. Not sure if they are the original injectors and Glow plugs or not. I'm guessing that they are. I think I'm gonna poke around under the covers anyway just to confirm the GP's are ok and nothing came loose in there.

Then see how an oil change and fuel filter affect it.
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Old 04-09-2014, 05:48 PM
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So I did a continuity test on the plugs. Same verdict... Plugs #3 and #7 show broken connection, See the below video...

GPContinuityTest - YouTube

This should confirm that the GP show burnt out elements correct?

I also checked the voltage at the harness, Glow Plug relay is kicking out 11.5 to the plugs and the harness is showing 11.5 to all pins. So the relay is good.
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