glow plugs

[Baron]

hello again... ..... maybe if I refrase a question again I will get an answer... ..... how does the engine start preheat system work on the cummins? Is there some kind of electrical relay? Where is it located? Does it have a part #? thanks baron

 

[B.G. Smith]

Please don't say glowplugs

Can't help you much but, yes there is a relay and I believe it is located under or near the battery on the drivers side fender well. The heating element is located in the top of the intake manifold where the air enters. bg

 

[rkubicki]

The grid heater is powered by two coils that convert the LT voltage to HT voltage... . The grid heater is mounted between the intake manifold and the square intake plumbing flange... . The heater's element has very high resistance and builds up heat quickly when a lot of electrical current is pushed through it. (up to 2. 6 Kilowatts!)



You can spot the coils mounted on the driver's side behind the battery... . An easy way to locate them is to look for the two "spark-plug wire" looking cables mounted to studs on the back of the heater and tracing them back to the coils.



DANGER: Never touch these cables, the coils, or the grid heater while the engine is running or the key is in the "run" position... The system controller power cycles these coils at random when the engine temp. is within range... . When the coils are "live" there is enough current to throw you across the garage, if not kill - use extreme caution!!



I could not find a Cummins part number for the coils... Perhaps they are Dodge parts.



This is probably more than you care to know about the heater - I hope this helps.



Rob

 

[Baron]

Thanks for the info... ... . I have a feeling that my coil heater is not working in the mornings or at all in fact... . it is becoming more of an issue as the mornings get colder... ... one of the spark plug type wires has MELTED the post it sits on and I need to replace the whole assembly of posts.

If anyone has had to do this or has some more info on part # or such please advise... ..... thanks baron

 

[B.G. Smith]

Grid heater

Baron, if you can't find the relays from the dealer, go to NAPA auto parts and ask them to find you a 12 volt relay that will handle at least 95 amps at 12 volts. Just about any starter relay will carry that much current but you will probably need a relay that has both ends of the trigger coil coming to the outside of the relay. These things look very much like the starter relay on the big Mercury outboards. bg

 

[Joe G.]

rkubicki,



Where can I measure more than 12 volts in the heater grid system? I don't think there is any high voltage anywhere. High current thru the grids for sure, but it's still 12 volts.

 

[LarryB]

The "coils" are actually heavy duty relays. Still only 12V but high amperage. Only time 12V is really dangerous is if you are wearing metal jewelry. Shorting can cause bad burns. I doubt it will toss you across the garage like a gasser ign coil though. Maybe if you stick your tongue on it.

 

[formula]

Ok, not to be a PIA, but the only way for a coil (transformer) to increase or decrease the input voltage is if it's being fed alternating current or pulsed direct current. The induction of a voltage on the secondary of any transformer is accomplished by the expanding and collapsing of the magnetic field around the windings.



I'll take some voltage readings from the heater grid and make a post with the readings, if anyone is interested.



SP

 

[Joe G.]

formula is exactly right. The heater grids are very LOW resistance not "very high resistance and builds up heat". You can't beat Ohm's law. If you have 12 volts and want to pass a lot of current (amps) you have to have low resistance. Notice how your headlights dim a little every time the hearter grid cycles. That's because so much current is going thru the heater grids. No dangerous high voltage any where around or there would be warning labels.

 

[formula]

Or worse... ... . there could be SPARK PLUGS :--)









sp

 

[LarryB]

Here is a wiring diagram showing the relays.

#ad

 

[dan brooks]

I just took a look at mine and the tags are still legible. Here are the numbers - hopefully this will help or at least give you a place to start:



120-105111-1

12 V DC CONT

9128



I couldn't see any other markings without removing them.

 

[Baron]

actually this has turned into an interesting thread . I just wanted a part # for something I know little about..... now I know some more. I will try those numbers at the dealer. But they did say something about the part being discontinued... . hard to believe though.

I wonder if anyone has ever had to replace theirs??? baron

 

[rkubicki]

Baron,



The studded part that bolts to the heater you are looking for is Cummins part#3914417 (unless you were talking about the other end of the heavy cable - then I can't help you)... It may be junkyard time!



Rob

 

[Baron]

yea i'm refering to the four post unit that the "spark plug type" wires plug onto... ..... ( I think) baron

 

[rkubicki]

My mistake:

All,



Please ignore my first posting - it was very late at night when I typed that and I had another engine's pre-heat system in mind...



The grid heater is in fact supplied by two heavy-duty relays... When switched on by the engine controller, they pass current from the battery through heavy-gage wiring and then through the grid heater... The grid heater element is very thin gage in comparison to the rest of the circuit and there is no resistence... The current shoots way up and gets the element very hot because it cannot carry as much current as the heavy wiring.



It is essentially the same principal as if you took a 9v Duracell battery and connected the + and - terminals together with a thin wire.



Baron, it may be worth your time to check the the grid heater element - if your switch's post is melted then I'd bet the thin element wires are in pretty bad shape too... . Sounds almost like the heater could not switch off and things got really hot... . If you do find the parts to get the system back to normal, it would be a good idea to check your temp sensor and/or the circuit that is grounded through the engine controller to make sure that it opens before it destroys itself again.



Rob



PS - Thanks to everyone who posted for keeping me honest... Now if I could only get you all to reply to my threads with that much vigor...

 

[FFL8N]

I might have another reason for the wire being melted. When I was checking the nuts on the relays (the Dodge people call them solenoids. SP?), I may have grounded my wrench. :--) oooppppsssss. There was a small explosion and about 3" of wire disappeared. Yes, it evaporated!!!! The wrench got very hot also. Because it comes right off the battery, they are always hot. It is very easy to ground them out. I know. I was trying to be careful. Dodge does still carry the wires. I was quoted about 35. 00 for them (one wire splits into two). I have not purchased it yet. I can't remember the part number for sure, but the one posted didn't seem right. Also, they had to go back to a 97 year truck to find the part. It hasn't changed. The part was not listed for my truck. Let us know how it all turns out and what the fix is. Mine is still not fixed yet!



David

 

[Baron]

well I think you are right to ck the system and see WHY the air heater relay has melted. It seems the wires are pretty well protected so I don't think an accidental wrench caused the problem. No sense finding a new relay and melting it as well. So where would one START in trouble-shooting this condition???? Where is the grid heater and should I take it apart to inspect the wires? And the controller?? where is it?? etc ect??? much thanks baron

 

[rkubicki]

Baron,



The first thing I would do is remove the right-angle intake "runner" with the square flange and look down at the heater element... . If you look between your intake on the engine and this intake "runner" you will see what looks like a thick spacer - this is actually the heater... . You are looking for something like one of the metal element wires separated and grounding itself on the intake somewhere... . If your system overheated to the point where the stud on the solenoid melted then I imagine the heater element would be in bad shape... If you need to replace the heater the Cummins P/N is 3913348... The gasket is P/N 3913352... .



Restore the system to its full integrity by replacing the damaged parts... . Then disconnect the 12ga fusible link wires from the input side of the solenoid to avoid damage while you troubleshoot the circuit.



With a cold engine have a helper switch on the key (no engine start) while you have your voltmeter connected to the solenoid's primary connector (small) wires... After about 20 seconds you should hear the solenoids click off and voltage on the meter should drop at or near zero... If not then you should check the ground through the engine controller.



Locate the engine controller inside the fender to the right of the battery... Pin #15 on the controller is the ground for this circuit... Check for continuity between pin 15 of the computer's disconnected harness connector and the negative side wires of each solenoid... . its better if you disconnect the wires from the solenoids while you do this... The purpose of this check is to determine if the wires were damaged and are grouding to something else on the body - this would keep the heater on full time.



If the wiring checks out then check the controller's grouding function... . Reconnect the controller's harness connector, set your meter to ohms and connect one probe to the negative solenoid wire and the other to a good body ground... . Have a helper turn on the key again (no start)... You should observe low resistence for about 20 seconds and then very high resistence or open circuit... If you do not then the controller is faulty and needs to be replaced.



If all seems to be ok the final check is the thermister on the top of the head closest to the intake "runner"... The best check for this is to warm the engine up to normal operating temp and connect your ohm meter to the switch terminals... If there is fairly low resistence (lower than 1K perhaps) replace the switch... The Cummins part number for the switch is 3918461...



These steps should isolate your problem.



Good luck, Rob

 

[Philip]

The Dodge part number for the relay is 4428102.



Now the bad news. These might not be available anymore. I had one welded itself up inside, three years ago. (There are two on our trucks). My dealer said three were showing up in a WI dealer. None in any warehouses. The price on them were under $30 each.







The relay is showing



White_Rogers/RBM

120-105111-1

Coil 12V DC cont. 9730