There's something under the hood of my truck that doesn't like the heat. During spring I never had any problems, as it started to warm up symptoms got more frequent, and now that the temps are nearing 100° I can only drive for about an hour and the ecm shuts off. If I wait for about a half hour it will come back on again. The ignition system is working because my volt gauge works, and the truck turns over, but the fuel pump and my trans cooler fan that is also controlled by ecm power doesn't run. Any ideas where to start?

Edited July 9, 20186 yr by Scottfunk

I would start by eliminating all the AC noise possible and doing the ground mods, damage could be already done but you'll prevent next one from frying, if that's the case.

A.Cummins has no spark plugs so I'm not sure what ac noise means. The ecm is bolted to the block and grounded to the frame and body.

He is talking about stray ac voltage from the alternator. And the mod he is speaking of is one a lot of us have done to our dodge Cummins. @Dieselfuture is not thinking you have suburban with with Cummins in it.

 

 Is the fuel pump and transcooler fans powered off of the ECM? Or just controlling a relay for power?

 

Edited July 9, 20186 yr by dripley

12 minutes ago, Scottfunk said:

A.Cummins has no spark plugs so I'm not sure what ac noise means.

 

First of the AC noise is created by a bad diode in the alternator. Remember all vehicles have this issue. Watch this video...

 

 

13 minutes ago, Scottfunk said:

The ecm is bolted to the block and grounded to the frame and body.

 

Doesn't matter. AC noise can be generated on both planes. There is a ground wire mod for fixing this somewhat. 

 

 

The alternator diode failure stems from the grid heater. It places a huge electrical load on the alternator while the truck is idling eventually the diodes overheat and fail. It best to disconnect the grid heater in the summer time and reduce the loading on the diodes. Hence why I sell the diode packs for the Denso alternators. 

 

 

7 hours ago, Scottfunk said:

There's something under the hood of my truck that doesn't like the heat. During spring I never had any problems, as it started to warm up symptoms got more frequent, and now that the temps are nearing 100° I can only drive for about an hour and the ecm shuts off. If I wait for about a half hour it will come back on again. The ignition system is working because my volt gauge works, and the truck turns over, but the fuel pump and my trans cooler fan that is also controlled by ecm power doesn't run. Any ideas where to start?

 

Is the FASS wired in using the FASS wire loom and relay?  I would guess yes since I didnt think FASS sold them without that loom.  And if the relay is in place then you're loosing the fuel pump "ON" signal.  You can wire to a keyed source but you'll loose the prime feature.

But I am questioning the trans cooler fan.  What is it and how you have that wired?  The ECM should have nothing to do with controlling an aftermarket cooling fan but rather it should be wired to a keyed source and controlled by a thermostat of its own.  If it is tied into the ECM somehow then it could be placing way too much amperage load.

21 hours ago, KATOOM said:

 

Is the FASS wired in using the FASS wire loom and relay?  I would guess yes since I didnt think FASS sold them without that loom.  And if the relay is in place then you're loosing the fuel pump "ON" signal.  You can wire to a keyed source but you'll loose the prime feature.

But I am questioning the trans cooler fan.  What is it and how you have that wired?  The ECM should have nothing to do with controlling an aftermarket cooling fan but rather it should be wired to a keyed source and controlled by a thermostat of its own.  If it is tied into the ECM somehow then it could be placing way too much amperage load.

 

L8tr

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You know, I think my original plan was to tap into the vp signal to run a relay to power all the new under hood systems, ie the fan, trans cooler fan, intercooler fan and pump, etc but now that you mention it I think I decided against that and used an abandoned ignition hot instead. No there is definitely not anything being powered directly by the ecm that was not originally designed that way. So that's good news I guess, it's not the ecm. Still no closed to a solution.

Remember that pose a safety issue. If the ignition is on and the electric pump is running and you have an accident that pump can potentially fuel a fire because there is no shutdown signal like the ECM does. The ECM watches the tach signal soon as it drops (accident) then the lift pump is turned off for safety. 

54 minutes ago, Scottfunk said:

You know, I think my original plan was to tap into the vp signal to run a relay to power all the new under hood systems, ie the fan, trans cooler fan, intercooler fan and pump, etc but now that you mention it I think I decided against that and used an abandoned ignition hot instead. No there is definitely not anything being powered directly by the ecm that was not originally designed that way. So that's good news I guess, it's not the ecm. Still no closed to a solution.

 

So the FASS is controlled by the ECM through a secondary wire loom?  At this point I'm kinda confused and not really sure what the problem is...  Can you explain again what exactly is going on?

9 minutes ago, KATOOM said:

 

So the FASS is controlled by the ECM through a secondary wire loom?  At this point I'm kinda confused and not really sure what the problem is...  Can you explain again what exactly is going on?

Me too.  Is the lift pump controlled directly by the ECM or a relay using ECM signal?

Everything under the hood is controlled through a secondary loom. Check the signature, hehe. She's not stock. But no, the fass is controlled by the ecm just like it should be, that was what got me thinking the problem was in the ecm. But after saying trans cooler enough times I remembered the control for that comes from the vehicle ignition hot. So it would appear the problem comes from something before the ecm.

Edited July 11, 20186 yr by Scottfunk

Stock the lift pump ran off of the ECM. The electric lift pumps most of us run today use a relay and the only thing the ecm does is trigger the relay and the pump power comes from another source. I think everyone is trying to figure out whether you are powering the lift off of the ECM as originally designed or the ECM is just providing a trigger for a relay to run the pump. Running the pump off of the ECM puts a lot load on it.

No, the ecm provides only trigger for the fass, sorry I'm extremely add and sometimes I think I said something when I didn't. Anyways I think I've determined the problem is upstream from the ecm. Thank you guys for making think through this all the way.

Have you figured it out? 

Nope but it left me stranded at the pizza parlor last night so I plan to take my electrical tester today and drive it till she acts top.

Have you tried just to power the relays with another key on source, and see if it happens. Just do your fuel pump and see if it still does it. I use a key on power wire, not the ECM wire for it. No issues as of yet.

I hope you find it.

 

In the old days when I first bought my 02 I worried about heat damage and ran an old vac hose from the front on up to the ECM to help cool it. Did the same for the VP with a second hose and put an inline bilge blower to blow cool air.

2 hours ago, Scottfunk said:

Nope but it left me stranded at the pizza parlor last night so I plan to take my electrical tester today and drive it till she acts top.

 

How did it leave you stranded?  What happened?  Whats it doing, or not doing?

Something stops working when it gets hot. I thought it was the ecm overheating but I think I've concluded it's upstream from there. Something in the ignition wire that runs from the truck's ignition system to the main power distribution center that runs the engine and trans and all associated equipment.

So...something stops working means that nothing happens like a dead battery.  Or nothing happens like it cranks and cranks but no start?  I get that somethings getting hot but without understanding what is exactly happening...