Big Mac

Truck won't start when the temperature drops down to around 10 d F. If I plug it in for 15 min, it fires right up. As the temp drops below 32 d F, it gets harder to start, but doesn't blow any smoke. Dealership said bad injectors ($300 to check which one, $800 each to replace any bad ones and $150 to replace). Didn't do that one! Went to my local Diesel guy. He says no problems with injectors; no leak down or return fuel, grid heaters work fine. Mechanic checked temperature sensor in head/block - working OK. It's as if there's a temperature related fuel delivery problem, which doesn't make sense to the mechanic. Truck is out of warranty with 108,500 miles on it. Original lift pump and injectors. Mechanic measured pump output (psi and volume/10 sec) and specs are good. Mechanic and I are perplexed. I don't want to start replacing parts until I know what the bad part is and can prove it through testing. What on earth is the matter?

darkvader

i would double check grid heaters. not just voltage but current draw
Clark

justme-

fuel heater?
Plugging it in for that short of time is not enough to raise the block temp- owner manual says minimal 4 hours so it must be something related to the plug in OR something that is warming up right next to the block heater element- is there a temp sensor near it?

Big Mac

Thanks for those suggestions. Mechanic supposedly tested the resistance on the grid heaters, and measured the temp with a heat gun and they seem to be working properly and within specs. Also, after starting it when temps are around freezing, you can see and hear the grid heater duty cycle kicking on and off (interior lights dimming etc). The fuel heater problem is an interesting question. We run winter fuel here from October to May and I buy from a reputable Diesel station (lots of big rigs, etc.) so for sure I have winter fuel in it (@ $1.18/liter too!). I thought the fuel heater was to prevent gel/wax from forming if it was cold out and non-winter fuel was present. I'll check with the mechanic that the fuel heater is working properly anyways because it's at the shop again. We had one last blast of winter yesterday and last night it dropped down to about 15 d F. Truck was parked outside the shop all night. Hopefully the mechanic will be able to see what is not working on the fuel supply/heating/delivery system today! If not, I probably won't be able to fix it until the next cold season this fall/winter.

justme-

Also make sure to empty the fuel/water separator- could be freezing.
Diesel thickens and even treated fuel will gel when cold enough. The heater it to thaw it and allow it to flow properly. Untreated fuel will gel at $35* F

FWIW, My 96 had a very similar issue apparently from new. (I bought the truck at 2 years old and evidence suggests the problem existed) It would not start cold, plugging in helped when it was not so cold, running a space heater under the engine compartment would usually do the trick. I thought water, gelled fuel, broken fuel heater, etc. After driving and getting the engine to op temp it would restart fine.
Traced it to the fuel shutoff solenoid not "pulling". It would hold when cold, but not pull- so I resorted to manually setting it under the hood when starting cold. After 4-5 days at a local 5 star Dodge dealer of 3 techs working on it freezing and heating everything under the hood they found the relay for the fuel solenoid was the culprit. (I only go to 5 star dealers- they actually know what they're doing and will be more respective and up front (honest) with the customers and I believed the solenoid was bad which was warranty).
This problem had cost the previous owner at minimal 2 new batteries, lots of jump starts, and several tows.

Your system works different from mine, but that may give you some insight.

TIMMY22

Fuel heater prevents gelling. Really will not effect cold starts. Stop and think, the fuel from the fuel heater will not make it to the injectors till about 30 seconds after the truck fires off.

Redleg

The early trucks advanced the timing mechanicly on cold starts. I'd look into how this gets done on a 3rd gen and make sure it's functioning there.

justme-

As in 2nd gens or 1st gens? wouldn't the ECM handle it through the electronic IP on 24V and 3rd gens?

It doesn't take that long for the fuel to go through the fuel heater- plus the fuel travels from the heater to the filter to the IP- the heater is designed to warm the fuel enough that it isn't and doesn't gel all the way into the IP- so yes, in theory it could cause this if you also throw in gelling fuel which is possible in the temp ranges the OP mentioned with improperly treated fuel (not every batch that makes it to the local truck stop gets properly treated)

BigIron70

There is a Flash for long crank time in ambient temp below freezing. TSB 18-017-05. Might want to check if that applies to your truck.

Big Mac

The mechanic checked out the lift pump fuel flow 2 mornings ago. when it was cold (15 d F), very low flow, well below spec. Plugged it in for a couple of hours and checked it again: lots of flow, well within spec. Verdict: failing lift pump. FASS 95/95 ordered yesterday and will be installed early next week. Thanks to all for your advice. Big Iron, I checked out the TSB: This bulletin applies to vehicles equipped with a Diesel engine (sales code
ETC/ETH) which has been converted to the in tank mounted fuel transfer pump, which mine doesn't have (if it had been under warrenty, that is the dealer fix - replace with a new in-tank lift pump as in 04 and up). Hopefully this will be the end of my cold start problems.