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84 M1009 not starting

Z

zcamarokid

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I have a 84 M1009 with the stock 6.2. Last week it started to get harder and harder to start and now it will not start at all. The engine cranks good. This week I replaced all the glow plugs with Wellman 70's, and the glow plug relay with a NAPA ST85. I do run a 50/50 mix of waste oil and diesel.

I started troubleshooting my glow plug system per the tech manual and here are the results:

Purple/white - 10V and the manual says it should be 12V Problem?
Light Blue - tests good and has the new relay
Dark blue - good
Pink/black - good
Orange - 24V the manual says it should have 12V. Not sure why it has 24V instead. Was not sure if this is my problem
Yellow - good and the temp switch is new
Black - 2600 ohms the manual states greater than 800 so this appears to be good
Pink/black - 13 ohms the manual says it should be 6-10 ohms. The relay is new so not sure if this is a problem

The batteries are good. They have 25.5V and 21.7V while cranking.

Any input would be greatly appreciated
 
mistaken1

mistaken1

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Is this orange wire the small wire on the top (large) post along with a red wire?

In a stock system you have 24V passing through the resistor on the firewall then to the glow plug relay (larger red wire). You will read 24v there until you energize the glow plugs and have current flow through the resistor. When current flows through the resistor it develops a voltage drop (ideally 12V) leaving the rest of the voltage (ideally12V) to be dropped across the glow plugs.

There are two other larger wires on the other large post that feed the glow plugs. If I recall correctly that small orange wire is supposed to be on the same post as the larger orange wires. The manual shows it on the post with the larger red wire but that is indeed incorrect.

http://www.steelsoldiers.com/cucv/67079-wiring-st85-relay.html

You need to be able to measure the voltage at the post where the three orange wires are terminated while the glow plugs are energized. That will tell you what voltage the glow plugs see when the glow plug relay is activated. When it is not activated there should not be any voltage on those orange wires.
 
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Z

zcamarokid

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Ok did some more testing and looking. On the relay the top large post has a large red wire coming from the resistor as you mentioned. This post has 25V. The top small side post has a blue wire that has 0V when sitting and 12V with the key in the run position. The bottom small side post has a red with a black striped wire. It has 0V when sitting and 12V with the key in the run position. The large bottom post has two big and one small orange wires. Sitting these three orange wires have 0V and 0V with the key in the run position.

I cranked the truck with the meter hooked to the orange wires and ground and they cycled between 0V and 21V. I am assuming that it was cycling from 0V to 21V when the glow plugs were kicking on and off. So now my question is why do I have 21V instead of only 12V?
 
dstang97

dstang97

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I don't have the manual in front of me. If it was me working on the truck this is what I would do.

1 Remove glow plugs and physically test each one to verify they work.
2 by pass the resistor and feed the top of the relay to 12v positive front battery.

if your voltage is not dropping down you have either
A) bad resistor
B bad glow plugs

and remember a bad resistor also means bad glow plugs.
Hope this helps
 
mistaken1

mistaken1

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You should have 0V on the orange wires with the key off.

With the glow plug controller in place (and working) and when the key is on (you do not have to crank the motor) the glow plug controller will energize the glow plug relay when the engine is cold. At that time you will get voltage on the orange wires.

With everything working correctly you should drop approximately half of your voltage at the resistor and half at the glow plugs. In a nominal 24V system that would be 12V, meaning you should read 12V (or something close) at the orange wire when the glow plugs are heating.

Your glow plugs are seeing 21V which will cause the controller to short cycle the glow plug relay which is what I understand you to report is happening.

If you are reading 21V that tells me that your glow plugs are probably bad or perhaps the wiring to them is bad. Like dstang97 said remove each glow plug and check it with an ohm meter. If they are all good (I doubt it) then check for voltage at each one to verify that the wires (fuse links) are good between the glow plug and the glow plug relay.

If the glow plugs are bad and you replace them that may not solve the problem, as dstang97 said the resistor could be shorted sending all 24V to the glow plugs any time they are energized (resistor not dropping half the voltage because in essence a shorted resistor becomes a wire).

I believe the TM has the information to troubleshoot the resistor.

Or as dstang97 pointed out you can refeed the glow plug relay with 12V either by connecting a fuselink from the glow plug relay to the diamond shaped 12V bus above it or by running a new wire with a fuse or fuselink to the front battery positive post.
 
Z

zcamarokid

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Thanks for all of the information. It sounds like there is a good chance I ruined my brand new glow plugs. I will have to wait until tomorrow to check it out again.
 
Z

zcamarokid

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Thought I fixed my glow plug issue, but I was mistaken. I have ran a 2 gauge wire from the front battery positive directly to the glow plug relay. I put in 8 new AC60G glow plugs and the truck fired instantly. However, everyday that goes by the truck gets harder and harder to start. Bought yet another set of AC60G glow plugs, but I am worried I will fry this set too overtime. Ran all of the tests in the tech manual again. Everything seems to check out except for the ohm reading between the two posts on the relay. The manual says between 6-10 ohms but I am getting 18 ohms. I checked a new relay and it had the same 18 ohm reading. What else could be causing my glow plugs to burn out prematurely? I checked the voltage at the glow plugs and it is in deed 12.XXX volts until the relay drops out. The relay appears to be functioning correctly. Any ideas?

Scott
 
mistaken1

mistaken1

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The glow plug control card switches the light blue wire to ground to allow current flow through the relay coil so yes you should see voltage on both small posts.

When the truck is running do you measure voltage on both large posts?
 
Z

zcamarokid

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I only have voltage on the top post once the truck is running. I checked for about five minutes continuously after the truck was running to make sure the relay was not passing power.
 
mistaken1

mistaken1

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So it looks like the relay is not burning up the glow plugs.

I believe others have mentioned bad injectors as a possible source of glow plug damage.
 
Wolf.Dose

Wolf.Dose

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The engine will not start, if your starter will not provide at least some 200 rpm.
So may be your starter is bad. Change to the new replacement starter, for the original starter is known to be not reliable. The number for the replacement starter is 6598N.
Wolf
 
Z

zcamarokid

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Oh the starter and motor cranks forever. It is definitely turning over quite well. If I put in new glow plugs it will fire instantly. However, every time I start the truck it gets harder and harder to start until the glow plugs are fried. In one of my previous posts I posted an update on what I have done to figure out the problem. I have tested the entire glow plug circuit and everything tests good, but I am still eating glow plugs.
 
M1008driver

M1008driver

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Z

zcamarokid

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I have already done the resistor bypass. I ran a cable from the front battery positive directly to the glow plug relay. I am also using AC Delco AC60G glow plugs with a new ST85 glow plug relay.
 
M1008driver

M1008driver

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Oops! Maybe mistaken1 and others are on the right track. Sorry for my useless information. I hope you find the problem soon as gp's can add up quick.

I do run a 50/50 mix of waste oil and diesel.
Click to expand...
I would not do this for awhile until I figured out what the problem is. Several posters have had problems in this area.
 
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