losing overdrive after truck warms up

[ORS243]

I am looking for some help with my 1993 D250, 5.9 L Cummins. It is stock, no mods other than the rims. After 325,000 mi of trouble free operation I am having issues. After driving for 10 - 20 min the voltmeter drops to around 10 v. The A/C stops working and it will not shift into overdrive. At first it seemed to be heating related as the temp gauge would read high prior to the voltage drop. However, lately it has been locking overdrive out at just above normal operating temp (gauge reads in the middle). If I let the truck sit for 30 min it is good to go, but will act up again once driven. Any thoughts?

One of the problems with owning one of these is the are so trouble free I have not had to develop a close relationship with a good mechanic. I live in Vista Ca. does anyone know of a good 1st gen mechanic in my area.

Thanks

Bill Gallagher
1993 D250 SE 5.9L
325705
Stock

 

[Fastback67]

I have a similar issue with my 1990 W250, only it keeps eating the external Voltage Regulators. I don't believe engine temps have anything to do with it however, electrical connection temperatures on the other hand are a prime suspect. 30 year old terminals in bulkhead and harness connections, could be tarnished and/or dirty, generating high resistance conditions, leading to voltage drops and/or intermittent operation. In my case, the issues always start showing up at night when the headlights and dash lights etc. are putting an extra load on the system. Once the VR gives up and goes off line, the battery voltage starts dropping. When that happens, my Gear Vendors Overdrive will not engage. The control circuitry for the GV unit needs full voltage at startup or it will not engage. I have cleaned a few minor connections between the VR and the Alternator at this point and the situation has improved dramatically. I do still need to clean all of the contacts and connections between the Battery and the Ignition now however since my dash lights are still pulsing somewhat (nothing like before), and my latest VR just went south last evening after several weeks of flawless operation. More to follow of course, but it is something you might want to think about. Just a thought...

 

[ORS243]

Thanks for the input! The mechanic I have used to service the truck is of the same mind; thinks it is an electrical issue, not engine / transmission heat related. I will have time to work on the truck this weekend. I'll let you know if I have any luck

Thanks again

 

[DavidC]

Thought I read there was a temp sensor that would keep overdrive from engaging. Maybe bad connections/conductivity with that circuit. Just my .02 cents. I think the sensor is in the trans. ?

Dave

 

[ORS243]

Thanks, I am aware of the sensor in the transmission. Had the transmission checked by two shops and both said it was working as intended. But, I am still suspect of the sensor, since it is the only thing I can find in my shop manual that would cause the problem. I might just replace it to rule out a mis-reading for the unit.

Thanks,

Bill

 

[dodgenstein]

The common thread between A/C, overdrive and charging is the CPS or crankshaft position sensor. It is located by the harmonic balancer. May be a bad sensor, bad connection, bad wiring or a shutdown relay problem. You need to get a shop manual and a mutimeter and start testing.

 

[ORS243]

Thanks, a testing we will go. I'll let you know what happens.

 

[ORS243]

I hope everyone had a nice fourth of July. Here s an update on my truck problems. I tested the CPS and all is good. It was old so I changed it and the harness out anyway. I swapped the AC relay for the auto shutdown relay, again with no change. I am being told to send my PCM in for testing, which I can do. Before I ship it off want to clarify what is happening.

The truck starts and runs fine for 15 to 20 min. sometimes more. Once it warms up the problems start. The first thing I notice is a slight drop in voltage shown on my gauge. When I slow down and the transmission shifts out of OD it will not shift back into OD. I also lose my air conditioner. Now here is what I find confusing. Once it goes into this state (low voltage / no OD or AC) it will not come out until the truck sits for 30 min, or so. I can drive it in third or let it sit, it does not matter much. After about 30 min the voltage returns to normal and things works for awhile then repeat. To me it seems like I has a heat related sensor that needs to cool down before it will allow the truck to operate normally. Is the consistency of the rest interval a clue to what is going on?

Thanks again for your help.

Bill Gallagher
1993 D250
bone stock & beautiful

 

[Gumby79]

Almost sounds like a circuit breaker, but our trucks dont have any. Check your fuseabke links(on passenger finder skirt near the battery) maby a braker was instaled and has gotten weak.

 

[Simplysmn]

Also what control's overdrive is the TPS .I used the TPS delete kit when I had my 518 as I could never get my tps to work right so after bypassing it I didn't have any more troubles .

 

[ORS243]

Thanks for the input. I thought I had it figured out this weekend. My money was on the thermal sensor (trans fluid temp) on my transmission. Tried to find a replacement only to learn they were discontinued some time ago. I bypassed the thermal sensor on the transmission with a resistor (paper clip) and the truck ran fine for a short test. Drove it 40 miles into San Diego today and acted up again; got to drive side streets back to Vista. I will test my TPS tomorrow and replace it if needed. If that does not work I will send the PCM for testing.

 

[cerberusiam]

PCM is going open on several circuits internally when it warms up, that is a typical failure with these units.

 

[ORS243]

Thank you! I am sending the PCM in for testing / repair on Monday. Keeping my fingers crossed and rubbing the rabbits foot wishing for good luck. If they cannot rebuild the PCM, what are my options? Is there an after market replacement part?

Thanks again for your advice.

Bill

 

[Simplysmn]

The good thing is you have a 93 truck and you can find them used but tested on e bay or even craigslist. Be Happy you Don't have a 91.5 they are like a good running ford Impossible to find

 

[ORS243]

well that is good to hear!

 

[Gumby79]

... Be Happy you Don't have a 91.5 they are like a good running ford Impossible to find

what build dates are the bad 91.5's? I have 6/91,eek. Get the wrong parts sent offten.
518 IC 350k ish(odo striped out@298k volt meter has a severe case of happy butt( Wags like a happy dog)

 

[Simplysmn]

you have 1 of them .91.5 I call the ******* yr of truck's Because Nothing wiring wise from a 92-93 will interchange with it and to boot the PCM you can't rebuild or find unless you find 1 from a part's yard .Maybe .

 

[ORS243]

Here is an update on my truck. It is back on the road running better than is has in a long time. The problem was the PCM. I had it rebuilt at Module Experts in Fl. Very good service, good information, fast turnaround and it fixed my issues. Thanks to all that added comments to my post, your help was appreciated.

On to my next task. How do you keep the vent window's seal from leaking. When I drive at freeway speeds the wind noise is significant. I can't find replacement weather seals for the 1993 D250. Any suggestions?

 

[Simplysmn]

Remove the pin that hold's the wind wing lock down and there is a screw that you can tighten up once you do that it should stop the wind noise .

 

[ORS243]

Thanks. I'll give it a try.