Glow Plugs Module & Cold Start stuff

Brody · **Posted:** Tue Nov 15, 2022 12:49 pm

Hi guys,

I have this 06 CRD and it's had a hard time starting in cold weather (previous owner says it just wouldn't start during winter last year). We took the glow plugs out and tested them and 3 out of the 4 glow plugs worked fine so I'm guessing this might not have been the source of the issue. Nevertheless we changed them all.
I'm wondering if there's a way to test if the glow plugs module / relay is working correctly?

When hooked up the computer we see activity of the glow plugs but hard to know what data we should be seeing on there.

Any input? Or anything else I'm missing that could cause a CRD to refuse to start in cold weather besides glow plugs & module, and the obvious battery issues, etc?

Thanks a bunch !

WWDiesel · **Posted:** Tue Nov 15, 2022 6:05 pm

A voltmeter or 12v test light connected to a single one of the output leds for one of the glow plugs.
Observe indication of voltage or test light during a cold startup.
This would give you an indication of the Glow Plug Relay output and function.

Brody · **Posted:** Thu Nov 17, 2022 3:08 pm

Thanks for your answer ! When we hooked up the computer to the Jeep there was definitely power readings being registered to the glow plugs. What I was wondering is if despite this the relay could still potentially malfunction, sending inappropriate power to the plugs in relation to the weather data being read by the atmospheric sensor I believe, or any other malfunction that would prevent the relay to send current to the plugs at all the appropriate times.

WWDiesel · **Posted:** Thu Nov 17, 2022 11:56 pm

There is NOT a simple or easy answer to explain the logic and how the glow plugs operate.
The Glow Plug Module is controlled and operated by the ECM that uses pulse width modulation to pulse the glow plugs current levels as needed based several input signals to the ECM.
Lots of variables that affect their operation and duty cycles. (heating time)
It has been determined that the GP heating times chart in the FSM may be incorrect on actual times.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

Brody wrote:

Hi guys,

I have this 06 CRD and it's had a hard time starting in cold weather (previous owner says it just wouldn't start during winter last year). We took the glow plugs out and tested them and 3 out of the 4 glow plugs worked fine so I'm guessing this might not have been the source of the issue. Nevertheless we changed them all.
I'm wondering if there's a way to test if the glow plugs module / relay is working correctly?

When hooked up the computer we see activity of the glow plugs but hard to know what data we should be seeing on there.

Any input? Or anything else I'm missing that could cause a CRD to refuse to start in cold weather besides glow plugs & module, and the obvious battery issues, etc?

Thanks a bunch !

Check your block heater to see if it is functioning properly and use it!

Better yet, purchase a Webasto heater and install it; this will do and end run around any potential glow plug problems. Webasto diesel fueled engine coolant heaters will do a better job of warming up your engine than running it will; they are about 12.5 times the power of your block heater. Preheating your diesel engine will go a long way to increasing the life of your engine, especially up here in the Great White North.

Brody · **Posted:** Fri Nov 18, 2022 11:25 am

Thanks a lot for your input and graphics you shared WWDiesel. Plug operation & logic is quite useful.
So bottom line, would you say that if the glow plugs have been replaced, and the Jeep still struggles or can't start in cold weather, the next step would be to look at the module / relay? And because it's so complex, I would need to swap it out to see if it addresses the issues ?

Other thing I'm thinking about that could be faulty is the coolant temp sensor that then tells the ECM what to do. There isn't another temp sensor linked to the GP module and ECM is there?

Brody · **Posted:** Fri Nov 18, 2022 11:32 am

TURBO-DIESEL-FREAK wrote:

Check your block heater to see if it is functioning properly and use it!
Better yet, purchase a Webasto heater and install it;

Thanks for chipping in ! Yes I do use the block heater at all times when possible. When going out spontaneously or parking somewhere for an extended time it's not possible to do so though.

As for a Webasto coolant heater, I really considered installing it. But high cost and complex install made me not go this route. I find the block heater works pretty well and I usually can use it. I just need the glow plugs to work properly (or whatever else is the issue) when block heater hasn't been plugged in.

WWDiesel · **Posted:** Fri Nov 18, 2022 11:37 am

TURBO-DIESEL-FREAK wrote:

Better yet, purchase a Webasto heater and install it;

Listing Options, correct or best Model Number to use, Best Pricing, and Vendor availability information could be most helpful for any forum members thinking of installing an auxiliary diesel fired engine heater.

Neither IDParts or Sasquatch list any auxiliary heaters for purchase for the Jeep Liberty Diesel! (I checked :shock:

)
Sasquatch does list a custom battery tray/mount for a Webasto Heater. https://shop.sasquatchparts.com/product ... -2-8l-crd/

WWDiesel · **Posted:** Fri Nov 18, 2022 11:45 am

Brody wrote:

TURBO-DIESEL-FREAK wrote:

Check your block heater to see if it is functioning properly and use it!
Better yet, purchase a Webasto heater and install it;

Thanks for chipping in ! Yes I do use the block heater at all times when possible. When going out spontaneously or parking somewhere for an extended time it's not possible to do so though.
As for a Webasto coolant heater, I really considered installing it. But high cost and complex install made me not go this route. I find the block heater works pretty well and I usually can use it. I just need the glow plugs to work properly (or whatever else is the issue) when block heater hasn't been plugged in.

What Glow Plugs do you have installed?? 5v or 7v?
For improved GP performance, many owners are now installing the Bosch 5v GPs and running them on the OEM 7v programing which they say is working very well with no adverse problems.
And they report much better and improved cold temperature starting performance! :wink:

IDParts list them along with new GP wiring harnesses if needed:
https://www.idparts.com/glow-plug-bosch ... -2858.html

Brody · **Posted:** Fri Nov 18, 2022 12:38 pm

Yes we swapped the GPs with those Bosch 5V and didn't reprogram anything so running at 7V. 3 of them were still working well when we replaced them, and they were also the Bosch 5V. That's why I'm thinking it's something else than the GPs.

Any input on my previous reply, included here below again:

Quote:

So bottom line, would you say that if the glow plugs have been replaced, and the Jeep still struggles or can't start in cold weather, the next step would be to look at the module / relay? And because it's so complex, I would need to swap it out to see if it addresses the issues ?

Other thing I'm thinking about that could be faulty is the coolant temp sensor that then tells the ECM what to do. There isn't another temp sensor linked to the GP module and ECM is there?

WWDiesel · **Posted:** Fri Nov 18, 2022 1:39 pm

Brody wrote:

Yes we swapped the GPs with those Bosch 5V and didn't reprogram anything so running at 7V. 3 of them were still working well when we replaced them, and they were also the Bosch 5V. That's why I'm thinking it's something else than the GPs.
Any input on my previous reply, included here below again:

Quote:

So bottom line, would you say that if the glow plugs have been replaced, and the Jeep still struggles or can't start in cold weather, the next step would be to look at the module / relay? And because it's so complex, I would need to swap it out to see if it addresses the issues ?
Other thing I'm thinking about that could be faulty is the coolant temp sensor that then tells the ECM what to do. There isn't another temp sensor linked to the GP module and ECM is there?

See my original post earlier in this threat that lists all the sensors that the ECM uses to control the GP module.
The ECM is looking at several inputs to determine how long and how much current flow is required.
So if any of the sensors that the ECM uses for GP module operation are not providing an accurate reading/signal, it could greatly impact GP heating cycles and thus cranking performance. :cry:

If you could find someone with a scope, they could see how well the GP module is performing by graphing the time and voltage duty cycles being outputted to the GPs.
or
Replace the GP module with a known good module or a new one. But this still would not tell you if the problem is an issue with the control coming from the ECM and all the ancillary inputs it uses for determining GP operation. :banghead:

IDParts sales new GP modules.
https://www.idparts.com/liberty-crd-glo ... -2749.html

Glow Plugs Module & Cold Start stuff

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