I got a 6.5TD 1994.

It started stalling on me. It restarts ok.
I took it to the mechanic. They say that for some reason
the ECM turns the lift pump off while you driving.

Any idea why it would do that?
Do i need a new pump or ECM or ...?

It has the PMD relocated with FSD cooler.

thankshttp://www.dieselplace.com/forum/smileys/Disapprove.gif

That's right, the ECM turns off the power to the fuel pump relay.
but... The OPS is sapposed to power the lift from the moment it senses oil pressure.
So, your mechanic is correct in what he see's, but if he knew about the OPS, he would have said something.
It's best to wire a relay to power the lift pump switched by the OPS.
That way the 1amp rated OPS doesn't have to carry the 4amp load of the lift pump.

the "G" pin of the ALDL shows if the lift pump is powered.

You problem is most likely a failed FSD. Even with a cooler I have had 2 fail while the cooler was mounted in the engine compartment. Before you spend a ton of money with a mechanic, who realy didn't know how your truck works, replace the FSD as a test because a failed FSD will not set a code and there is no other way to test it. If this does correct your problem conside relocating the cooler outside the engine area as heat is the problem.


You can see details on FSD relocation and OPS rewiring on my site.

I talked to the mechanic. He said that their is a fault code indicating the ECM. They removed the ECM and sent it out to be tested.

The truck has a new PMD and a new Lift pump.

If your new FSD is on the engine it's worse than on the pump, except that you can easily replace it.

remote wiring harnesses will take it off the block and extra wire helps fuel delivery in my opinion.

Looking at the pump circuit I can not see a way the ECM could turn the pump off unless it shorted circuit #120 to ground and that would blow the fuse and most likely kill the OPS because of excess current. Neither do I think would be considered good design.


The only time the ECM is involved witht the pump is during the glow plug cycle when it pulls in the pump relay to prime the system and make sure there is fuel at the Injection pump.


What code did the mechanic mention?

put a new oil sending switch in it or a manual switch and be done with itEdited by: Texas Diesel Guy

put a new oil sending switch in it or a manual switch and be done with it


I'm with Tex. If the truck will start, open the petcock by the thermostat housing with engine running. If it stumbles and dies within half a minute your OPS is dead (since you're sure the lift pump is fine).


$25 and a half-hour of your time and you'll be back on the road. You'll have to find an OPS socket to r&r.

Thanks guys.


I talked to the mechanic today. Nothing wrong with the ECM. He ordered a new PMD. After he installed it I will drive it around, see if it makes any difference.


I'm also gonna try to change the OPS and put a relay on it.


Where is the OPS?

Proview!


Check the OPS first, before replacing it. All you have to do is open the little valve by the thermostat housing while the engine is running. It's located front and center, right in front of you when you open the hood! Takes 1 minute tops to see if your OPS is bad or not. When you open the valve, if engine dies then OPS bad. If not, then OPS good.


PMD is awfully expensive part to replace not knowing that it is the problem. But I suppose it never hurts to have a spare.


The OPS is under the fuel filter, in the back of the engine valley. Easiest to get at if you loosen the fuel filter housing. One takes a couple minutes to replace if you have the OPS socket.Edited by: w_huisman

It's all the way back between the block and the firewall.