Hot start issues, poor fuel mileage and no comm with BCM

altdiesel · **Posted:** Fri Jun 15, 2012 1:24 pm

Happy Friday everyone!

It has not been about 3 months since I have had my CRD. Since I have had it I have done the following:

-EHM
-Oil Change full syn with larger oil filter
-In tank lift pump
-New Fuel heater head, and fuel filter
-Samco hoses
-Air filter

I have averaged about 18 city, and 23.6 best highway, all hand calculated. My wife primarily drives it. And both of us have experienced an unusual hot start problem. Oh, and since I live in CO, we took the Jeep to the top of Pikes Peak, elevation 14,110 feet! On the 19 mile trip to the top, the transmission hot light turned on, and I pulled over at the 12 mile mark, and let it cool down in N, with the Jeep running, like the manual says to. In the 19 miles, I realized the Jeep consumed 1/4 tank, and after, I was only able to get 250 mile range, and 13.8 MPG

I figured it would eat a little more diesel than normal, but it sure took a lot to get to the top of the world!

In short, what happens is after the Jeep is driven and up to temp, and after sitting for about 2 hours or so, when you start and drive away, it starts lugging, and sometimes just shuts off. This typically does not ever happen from a cold start, just hot start. It does not have an issue starting, starts right up.

The Jeep is not throwing any relevant codes, which I almost wish it would. It is at my mechanic at the moment, and all he can see when he plugs it in his scanner, is he has no communication with the Body Control Module (BCM). Yet, the radio works, the windows all work, and the alarm works. He has tried to replicate the hot start problem, and no luck :banghead:

Based on all the other specs, fuel pressure, and watching the system run while pluged into his reader, he says it all looks good :shock:

I am planning a cross country road trip in a couple weeks, and really hope to get this worked out before I leave.

Please let me know your thoughts, and if I need to supply any other information to help trouble shoot.

Thanks for all your help in advance!!!!

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

A few CRD owners have had hot start issues and some of these were due to a bad crank position sensor. It does not seem to set a fault when it goes bad. The high temps cause the sensor to drift and change internal resistance or impedence. Might be worth a shot on yours.

The trans overheat was most likely due to running in 1,2 or 3 gears at low enough speeds as to not lock up the torque converter. Driving 19 miles up a grade without lockup can heat the fluid up something fierce. If you do this type of driving regularly, I would recommend an auxilliary trans cooler. Some folks on this forum have these and could assist you.

Your fuel economy is about average for a stock CRD. The drop in altitude to about ~14mpg is not normal and the overheating may have had an impact. If the FE does not come back up in the coming days, you might consider checking the brakes and possibly a tranny fluid change.

altdiesel · **Posted:** Fri Jun 15, 2012 6:50 pm

Just got word back from my mechanic. He does not think it is the crank position sensor, and thinks for sure it is the tranny :BANANA:

Only celebrating because now I know what the problem is and I have a warranty that will cover the repair :BANANA:

The transmission shop that I have gone to, and is the best in the Springs where I live, used Precision (http://www.gopnh.com/) Torque converters. I know many people recommend Suncoast, however, Don at the Transmission Clinic, swears by Precision.

I talked to Keith at Green Diesel, and he said as long as they can guarantee 400ft/lbs capcity on lockup, strengthened the springs, and have a larger friction area, it should be fine.

Any advice on tranny issues? I am going to read as much as I can!!!

papaindigo · **Posted:** Sat Jun 16, 2012 8:34 am

Several thoughts for what it's worth:
1. box stock mpg tends to run 18-20 in town and 24-28 on hwy depending on speed driven and nature of the terrain. I'd also note that hand calculated is only good if you have checked your odometer against a GPS and added in that correction factor which can be significant.
2. while I agree a tranny cooler is a decent idea for an overheat the very first things I'd check is proper function of both the electric AC fan just behind the grill and the viscous fan in front of the engine. The electric fan motor can burn out or the sensor running it not function correctly and the viscous clutch on the mechanical fan is prone to failure and known for engaging the fan way to late in a heat up cycle. I'd also check coolant circulation (you may want to drain the coolant and gently flush the radiator and heater core) and replace existing coolant with HOAT antifreeze (Zerex G-05, Mopar, or Ford HOAT) as other coolants have been known to clog the system.
3. similar with the tranny I'd make darn sure it was filled with ATF+4 and nothing else; as with coolant the wrong ATF fluid does strange things.
4. dragging brakes due to calipars hanging on the slider pins (lack of grease and a swollen rubber boot) are not uncommon can cut mpg. Get wheel off ground a manually spin to check; checking while driving only works if you drive a bit with minimal to no braking.
5. a failed crank position sensor is not that hard to diagnose; pull sensor off (most folks seem to do this from underneath - remove 2 bolts holding heat shield then remove sensor); check resistance cold then check while warming with a heat gun (hand held hair dryer may do); if resistence goes nut s when hot sensor is bad.

As to BCM communication. The KJ electronic system is something of a klug of various electronics such that the only scanners that can "talk" to all the systems are those at a dealer or equivalent systems at a very well equiped private shop. Translation if your mechanic doesn't have one of those systems I'm not too surprised he cannot talk to the BCM.

Given your location in the Springs you might want to PM/email Sir Sam, in Ft. Collins IIRC, for his thoughts as he rebuilds CRD for fun and profit.

ATXKJ · **Posted:** Sat Jun 16, 2012 9:24 am

Just as an FYI - when my CRD was new - it's first trip was Colorado Springs and Pike Peak - no overheat, no problems - average 24mpg for the trip.

Hot start issues, poor fuel mileage and no comm with BCM

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