glow plugs (yes, again)

[cosmobius]

before i begin, i will say that i have read MANY threads and the glow plug testing information in the TMs.

I tested one of the plugs with an ohm meter (i am an electrician and know exactly how to use one) and got a reading that was well outside of the acceptable limits. just to double check, i turned the key on and cycled the gp system then removed the same gp and it was extremely hot. after installing it again warm, the ohm reading was much more acceptable but still not within range. i know that heat affects resistance but the manuals are not clear whether the plugs should be tested cold, warm, or hot. If the plugs need to be within a specific resistance range, i dont see how the test light can be of any use since a light will come on from no resistance to a fairly high resistance. Any help would be appreciated.

Thanks in advance!

 

[doghead]

What test light? I don't recall anything about test lights in the TMs.

test cold

I have posted a link in the past, that shows time/temp/resistance/ampdraw for several brands of GP for the cucv

 

[ida34]

The test light is a quick and dirty method to find a plug that is bad not weak. Weak plugs will pass the test light test. When they go completely bad they short and there will not be continuity between the terminal and the outside casing. It is not in the TM.

 

[cosmobius]

What test light? I don't recall anything about test lights in the TMs.

test cold

I have posted a link in the past, that shows time/temp/resistance/ampdraw for several brands of GP for the cucv

there is obviously nothing in the TMs about test lights but you can't miss the innumerable posts which indicate that the way to test a GP is with a test light. I am simply making the point that it may not be the most accurate way to troubleshoot your GP system.

"cold". Thanks!

Thanks.

 

[allrevup]

Not sure if this will clear things up.
As stated, the test light test to the tip (connector) of a glow plug(with the green electric wire disconnected) from a 12-14v. power source "is too quickly confirm or find out if your glow plug is bad, Not to determine if is going bad" . That you most do with an ohm meter.
The ohm's reading of new A/C 13g Glow Plugs I tested out of the box was 1.1-1.2ohm's, in the past A/C 13g was 1.3ohm's, The WAP,Inc. Wellman's G070 was 1.5-3.0ohm's. (?) The post and/or the manuals say .5-3.0 ohm's, I am not sure why the pronounce difference.

Turn out "MY" problem was the 24v. resistor in the fire wall. I had previously check it and it was 24-26v. and sometimes at the GPR it testes at around 12-13v. but something most likely the GPR was sticking and making the system malfunction. I took the resistor out, clean the terminals and I only measure 1.2ohm. I think the TM said it should be 3 ohm's. Now I am bypassing it, I am not suggesting to do that but it a compromised I can live with until I find a good resistor and/or I am ready to start changing plugs regularly.
For now , I am getting my power from the 12v. diamond shape connector in the firewall, to my GP relay, So far so good, with out the block heater (purposely) and with temperatures ranging from 20* to mid. 30*'s, she starts on the first cycle, goes to fast idles and after she has run and is up to temp the "WAIT LIGHT" does not come ON in subsequent starts. I changed the Glow plug temp switch, the fast idle temp switch and to rule out a sticking contacts, the GP relay.

GOOD LUCK!

 

[cosmobius]

Not sure if this will clear things up.
As stated, the test light test to the tip (connector) of a glow plug(with the green electric wire disconnected) from a 12-14v. power source "is too quickly confirm or find out if your glow plug is bad, Not to determine if is going bad" . That you most do with an ohm meter.
The ohm's reading of new A/C 13g Glow Plugs I tested out of the box was 1.1-1.2ohm's, in the past A/C 13g was 1.3ohm's, The WAP,Inc. Wellman's G070 was 1.5-3.0ohm's. (?) The post and/or the manuals say .5-3.0 ohm's, I am not sure why the pronounce difference.

Turn out "MY" problem was the 24v. resistor in the fire wall. I had previously check it and it was 24-26v. and sometimes at the GPR it testes at around 12-13v. but something most likely the GPR was sticking and making the system malfunction. I took the resistor out, clean the terminals and I only measure 1.2ohm. I think the TM said it should be 3 ohm's. Now I am bypassing it, I am not suggesting to do that but it a compromised I can live with until I find a good resistor and/or I am ready to start changing plugs regularly.
For now , I am getting my power from the 12v. diamond shape connector in the firewall, to my GP relay, So far so good, with out the block heater (purposely) and with temperatures ranging from 20* to mid. 30*'s, she starts on the first cycle, goes to fast idles and after she has run and is up to temp the "WAIT LIGHT" does not come ON in subsequent starts. I changed the Glow plug temp switch, the fast idle temp switch and to rule out a sticking contacts, the GP relay.

GOOD LUCK!

Thanks for the info. I got wildly different ohm readings on the plugs i tested so i suppose they are all in a different stage of failure. 3 of them were shot completely. I just installed AC 60G plugs and I thought i read somewhere that you should bypass the resistor when installing them in a stock truck due to the different rate of heating. Do you know if this is correct?

 

[allrevup]

The only thing written in stone is that you will have CUCV electrical issues!
you should follow the TM trouble shooting sequence and determine the source of your problem first, it could be one or a combination of starting issues that are leading to your present problem with burn plugs.

If your problem turns out to be just a old or a bad set of plugs or a bad controller card, Many 6.2-6.5 owners in this and and other forums have switch to the self regulating A/C 60g or their Wellman G050 equivalent, with a manual temp button bypass (even with good controller card )
I still think that with a properly working system all you need is the TM recommended and ORIGINAL equipped A/C 13g. But around were I live you have to order then and have become more expensive then any other, go figure!
My last set of A/C 13g were replaced under warranty so that is what I re-used then, but as I mention earlier "because of the resistor failure". Next time I have to replace then, I am going to try the "Busch Duraterm Premium" # BS80034 also self regulating but with a 3 years warranty and around $12.00 a piece.

 

[allrevup]

Thanks for the info. I got wildly different ohm readings on the plugs i tested so i suppose they are all in a different stage of failure. 3 of them were shot completely. I just installed AC 60G plugs and I thought i read somewhere that you should bypass the resistor when installing them in a stock truck due to the different rate of heating. Do you know if this is correct?

There are a couple of treads about bypassing the resistor (disadvantages). If you are sure it has failed (according to some very rarely) mine did.
If the resistor fails, it will almost certainly burn the GP's or worse. That is one clear disadvantage of the original system design and 25 years Old parts.

PS. I have family in Mersing, ID. your avatar looks like their oudoor winter photos

 

[Keith_J]

All glow plugs have positive temperature coefficients meaning the resistance increases with temperature.

This means the plugs will self regulate, up to a point. The problem with the stock GP system is the series resistors (ok, there are 2 resistors in parallel but that doesn't matter) and the parallel glow plugs. The problem is cascade glow plug failure since loss to open of one plug increases the current to the remaining plugs by 12%. Then the next failure increases the current by another 12% until the whole lot fail.

Resistors in series decrease current by increasing resistance in simple addition. 8 ohms plus 6 ohms in series means a total of 14 ohms and proportionally less current. Resistors in parallel reduce resistance by the reciprocal rule. 8 ohms plus 6 ohms in parallel would be 1/(1/8 + 1/6) or 3.43 ohms.

Finally, the glow plugs in IDI diesels are ravaged by the injection flame. At idle, this isn't a problem. But if you use heavy throttle when the GP controller is in the after glow period, the combination of the high flame temperatures with the electrical heating will cause swelling.

 

[ida34]

Ohm's law is fun.

 

[allrevup]

Keith_J
Paragraph 1, 2 & 3 over my head (I do get the cascade effect of one failure on to the next) paragraph 4, is that to say wait until the after glow cycle has ended or to wait until the fast idle cuts-off?

from your post on this and other issues, You have a grip on this electrical stuff, I just look for the + and - symbols

 

[cosmobius]

There are a couple of treads about bypassing the resistor (disadvantages). If you are sure it has failed (according to some very rarely) mine did.
If the resistor fails, it will almost certainly burn the GP's or worse. That is one clear disadvantage of the original system design and 25 years Old parts.

PS. I have family in Mersing, ID. your avatar looks like their oudoor winter photos

After searching for the resistor, i realized tonight that my M1028 has already had the resistor bypass. it is non existent.... gone. I will now have to go through the wiring diagrams to determine whether this was done correctly. i have just replaced the 070 plugs with the 60g plugs, now i realize that the resistor is gone. I was not opposed to bypassing the resistor but was not ready to proceed without more information. I guess i no longer have a choice.

We should have three times this much snow here right now. Hopefully Marsing is doing better.

 

[Keith_J]

Keith_J
Paragraph 1, 2 & 3 over my head (I do get the cascade effect of one failure on to the next) paragraph 4, is that to say wait until the after glow cycle has ended or to wait until the fast idle cuts-off?

from your post on this and other issues, You have a grip on this electrical stuff, I just look for the + and - symbols

Yes, wait for the fast idle to cut off. The injected quantity between normal and fast idle is tiny, don't worry about it. But DO avoid heavy accelerator while still cold, unless you have some form of indicator on glow plug status.

I saw a few swollen glow plugs when I was in the Army (1980s). And always it was some young soldier as the driver who had a lead foot.

Resistance is far easier to understand with the water hose analogy. A resistor is nothing more than an orifice in a hose flowing water. Voltage is the pressure, current is the flow rate (gallons per minute, drops per second etc).

Now with regards to the positive temperature coefficient, all resistance heaters from the Calrod in your electric oven to the incandescent light bulb exhibit this effect.

 

[cosmobius]

After replacing a bad lot of glowplugs and realizing that i was missing the resistors, i went back to the wiring schematics and started tracing wires. i found that there was a circuit breaker (not a fuse) installed on the firewall and that it was in failure. it would run the glow plugs for several seconds before tripping and then resetting itself. i verified acceptable ampacity of the circuit and bypassed it until i can install a new fuse. The truck started immediately at 30 degrees which has not happened since i purchased it.

Be cautious about who you listen to and read the TMs as others recommend. Arm yourself with an understanding of the basics so that you can distinguish between those who know what they are talking about and those who think they know what they are talking about.

Thanks to ALL in this thread for your assistance with this problem!