What the puck, over?!!

fastRob · **Posted:** Mon Apr 07, 2008 9:30 pm

warp2diesel wrote:

........................................................................................

If you have no fuel leakage at the heater plug and your unit is stock, you better buy a lottery ticket before your luck runs out.

So far my lift pump has fixed my problem.

Thanks for the design flaw analysis. The price of repair/replacement is relatively low, inconvenience high.
This of course could be the straw that broke the owners back and causes a vehicle to be sold.
When I go to the dealer the reward should be worth the time, if the rig is still under warranty. Makes me think of the T/C.

CATCRD · **Posted:** Mon Apr 07, 2008 9:47 pm

Here's what I don't understand about the blame the heater has gotten so far: The material is designed so the resistance increases with temperature, and to safely self limit at a certain temp. Sooooo, how does the material know if it's in fuel or air? Even if it were turned on in open air, the temp of the element would increase to about 85F and then throttle back current to stay there. It shouldn't fry. This is called the heatsink environment of the element. If it suddenly stalled, the wattage should fall off. I think gmctd is onto the real problem with the quality of the connections.

Turbo Tim · **Posted:** Mon Apr 07, 2008 11:35 pm

I believe that it is the “Pinch” connections to the electrical connector. If that gets any resistance at all to it, it will glow and burn the plastic where it goes through to the connector.
Big question is: Can that connection be soldered? If so, there goes one problem.
If those two connecting contacts are different metals, there is another problem.

If you don’t mind taking the old one there, try soldering that slip-fit connection for us. I would like to know.

gmctd · **Posted:** Mon Apr 07, 2008 11:56 pm

Always been kinda difficult to solder aluminum to anything, in my experience............

But that connection(s) is the problem - goes resistive, current meant for the varistors is dissipated in the connection - the varistors don't warm up and continue to draw max current - the pins, having insufficient area to dissipate any therms into the fuel, heat up, burning the plastic and the epoxy seal, prolly boiling the surrounding fuel in the process (still not nearly hot enuff to ignite the raw fuel even with oxygen source, so no immediate hazard, there)

Howzzat fer predilection fer failure, eh?

CATCRD · **Posted:** Tue Apr 08, 2008 12:16 am

gmctd wrote:

But that connection(s) is the problem - goes resistive, current meant for the varistors is dissipated in the connection - the varistors don't warm up and continue to draw max current - the pins, having insufficient area to dissipate any therms into the fuel, heat up, burning the plastic and the epoxy seal, prolly boiling the surrounding fuel in the process

I believe you have it there.

danoid · **Posted:** Wed Apr 09, 2008 10:10 am

Find the relay named 'fuel heater', pull it from the junction box (near the battery under the hood). Pry cover off of relay with small screwdriver. Remove armature of relay. Reinstall relay cover onto relay and relay into juction box.

You should be good to -20°. If it's going to get that cold, buy a new mini ISO relay and put that into the juction box. When it gets warm, put the special relay back in.

The heater really isn't needed unless there's risk of fuel gelling. Otherwise it's just a (large) current draw.

gmctd · **Posted:** Wed Apr 09, 2008 10:58 am

Soon's I read the symptom here, right after we got the KJ, I called #2son, had him pull the connector, fold it around the IFT sensor leads - that brown color on the heater connector on the evicted head is 10kmi road film, not overheat discoloration - actual non-retouched color can be seen on the dissected puck, so ours showed no indication of failure in progress at ~50kmi - musta been a Tuesday or Thursday production-line session...............

Goglio704 · **Posted:** Thu Apr 10, 2008 8:03 pm

I also think the failure is in the transition from pin to plate.

Click picture for larger view.

http://www.lostjeeps.com/forum/phpBB3/vie ... hp?t=16472

gmctd · **Posted:** Thu Apr 10, 2008 9:59 pm

Proof positive............

onthehunt · **Posted:** Fri Apr 11, 2008 6:18 am

This the one that was left with the key on/engine not running all night? What a great picture. Wish they were all like that,very easy to see. If my fuel heater were to fail I hope it does exactly what yours did.

gmctd · **Posted:** Fri Apr 11, 2008 11:06 am

Did you keep that failed module for posteriority's sake? If so, and you can use a DVM, do a resistance reading of that top plate to the undamaged connector pin, which is the lower plate - that destruction looks more like a direct short between the plates, which would indicate a shorted Varistor(s) - submerged or open-air, they will go hi-resistive at 85*F, running at reduced current until the temp drops - they are inherently self-regulating - failure mode is open or short - I don't see any darkened area(s) on the plate which would indicate over-current\over-heating - a shorted coin would do damage to that reduced-mass area of the plate B4 having time to scorch the plate

Goglio704 · **Posted:** Fri Apr 11, 2008 6:18 pm

GMCTD,

I did much the same thing you did to yours in trying to cut the temperature probe out of the puck. It is in pieces, but I think I still have all of them. There were no other signs of heat on the plates or the resistors. I could take some comparative resistance readings this weekend if I can find the pieces. I seem to remember there being three of the resistors. Does that match yours ? You're right, the point that failed could have simply been the weakest link, but if the fuse is sized correctly, it should have blown in a short circuit condition rather than fry this joint.

Onthehunt,

The key was left on all night around the time this occurred, but I don't remember for sure which came first. At the time I didn't associate the two things, so I can"t say for sure. I think the same logic that was applied to the fuel pump relay should have been applied to the fuel heater. There is no reason for it to run if the engine isn't.

gmctd · **Posted:** Fri Apr 11, 2008 10:35 pm

Yes, three coins, one under each spring - just measure to the conductive surface on each side - it's flashed copper, silver-plated - a short on any coin would be obvious

Were you successful with the surgery - are you using the IFT sensor with a different head?

Goglio704 · **Posted:** Sat Apr 12, 2008 8:05 am

No, surgery wasn't really a success, but I got carried away and tried to get all the way down to the thermistor. Should have stopped when I got to the epoxy or at least slowed down.

Turbo Tim · **Posted:** Sat Apr 12, 2008 11:52 am

You have to understand the type of failure you (and I) could or did have here.
The varisitors in the circuit will open up or get more resistive as the temperature goes up. Since they are attached to a large heat sink (to heat the fuel), the total power drawn from the electrical system will be a decent amount until the whole thing gets to temperature.

Now if the electrical connection to the heating unit has a problem, most of the heat will occur in that teeny-weeny area. Understand that since the varisitors are not up to temp, they are still calling for maximum power. The connection is resistive, and when it starts getting hotter, it gets to the point where arcing starts. Now we have a little arc welder really heating up that connection point.

Another way to look at it is: Instead of heating up an aluminum plate that has say 5 or 6 square inches, you are now taking all of that power to heat up an area the size of a tip on a ball point pen. Much more focused and of course, more catastrophic…

gmctd · **Posted:** Sat Apr 12, 2008 12:22 pm

Guess they thought the 5amp fuse would protect it - musta been a Friday-late decision...............

Turbo Tim · **Posted:** Sat Apr 12, 2008 7:29 pm

5 Amps is more than enough to protect it.
Lets say that you were to draw 4 amps, X 12 Volts, that’s 48 watts of heat dissipated over 5 square inches. Plenty to heat fuel and only about 10 watts of heat per square inch.
Now put 50 watts of heat into the area of a ball point pen tip. I’ll bet it even glows.
Go grab a Halogen 55 watt driving light after it’s been on for a minute or so. I’ll bet it leaves a mark.

The 5 amp fuse is there to protect against a short circuit. Basically to protect the wiring harness of the Jeep. As long as it is drawing below 5 amps that is acceptable for a fuse type of circuit protection. Now if one were to add an “Arc Fault Suppression” type of circuit protection, that would be a different story. Then the problem would be solved with the fuel heater. Problem now is that the circuit protection would cost way more than just designing the fuel heater correctly in the first place..

Goglio704 · **Posted:** Sat Apr 12, 2008 11:14 pm

It is a 20 amp fuse according to the owner's manual...
...and whatever the amperage is, it has to flow through the transition where mine failed.

I'd trust it for 5, but not 20. Maybe a smaller fuse is in order.

cxturboboost · **Posted:** Wed Apr 16, 2008 6:38 pm

GMCTD

Do you know the connector number for installing the Cummins fuel filter. I have the filter assembly, but would like to hook things up so they work? Will it trip a light if something isn't hooked up to the fuel filter like the heater? Thanks for any input.

Pete

gmctd · **Posted:** Wed Apr 16, 2008 7:01 pm

I still need to do this myself: take the fuel manager to a local Dodge parts guy, get the connector wiring repair kit for the heater and WIF connectors - they won't DTC if not hooked up, but the Inlet Fuel Temperature will DTC if not connected - just cut the IFT sensor outta the puck, like I did, connect it, tyrap it to the Cummins head - that'll do till I figger out something else

What the puck, over?!!

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