24 Valve ECM overheating?

[KATOOM]

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...

[dripley]

Next time it happens see if your getting power from  ecm to trigger the relay. See if the WTS comes on during these episodes. It should come on very briefly at key on when everything is warmed up. We have seen many people with this issue thru the years but usually it happens on every start up and not just when it's up to temp. It is a bit of a guess but easy to eliminate.

[Scottfunk]

Well I explained the whole issue at the beginning of the thread but basically it cranks and won't startstart. But I'm pretty sure the ecm isn't the problem because one of the symptoms is also that the auxiliary trans cooler doesn't run at key on like it's supposed to (or like it's wired to more accurately). It's something in the truck's ignition wiring that feeds ignition on to the pdc. And no wait to start, check the sig

[dripley]

I have read your signature and pointed that out very early on in the thread. Is your ECM different from mine? For some reason I was thinking you had a Dodge instrument panel in the Suburban. Not sure how much if any of a Dodge you had to put in the Chevy.to make the Cummins work. Just throwing ideas out there.

Edited July 14, 2018 by dripley

[KATOOM]

Sounds like you're experiencing the hard hot start problem which is common for most people who have a reman VP and an aggressive aftermarket fuel pump like the FASS.

The FASS is tied into the wiring using its own loom and relay correct?  Thats how FASS sells their fuel pumps so I'm assuming yes, thats how its wired up.

If so, then you have a single fuse somewhere on that wire loom which runs to the FASS.  Most likely a single blade fuse holder.  If yes then the next time the engine cranks and cranks but wont start, open the hood and pull that fuse and try starting again.  If it starts more normal then we've found your problem.  Just be sure you dont let the engine run for more than a few seconds with the fuse out.  Either shut it down or immediately replace the fuse.  Let us know if that works...

[Scottfunk]

Will do!

[dripley]

36 minutes ago, KATOOM said:

Sounds like you're experiencing the hard hot start problem which is common for most people who have a reman VP and an aggressive aftermarket fuel pump like the FASS.

The FASS is tied into the wiring using its own loom and relay correct?  Thats how FASS sells their fuel pumps so I'm assuming yes, thats how its wired up.

If so, then you have a single fuse somewhere on that wire loom which runs to the FASS.  Most likely a single blade fuse holder.  If yes then the next time the engine cranks and cranks but wont start, open the hood and pull that fuse and try starting again.  If it starts more normal then we've found your problem.  Just be sure you dont let the engine run for more than a few seconds with the fuse out.  Either shut it down or immediately replace the fuse.  Let us know if that works...

another good idea. overpressure to the VP. I did think thru all of this the ECM had control of the lift pump. Did I miss something?

[KATOOM]

Sounds like the way he has the FASS wired is using the ECM as the ON/OFF source and all amperage going through a relay, which is normal for those applications.  But its not uncommon for the FASS to over pressurize the VP during engine cranking and hydro-lock the fuel solenoid and timing ring solenoid.  Most of the time the additional cranking will allow the higher fuel pressure to bleed off and the engine will eventually start, but not always.

 

Remember, the OEM lift pump was regulated at 15 psi and was barely capable of achieving that.  During cranking if everything was in picture perfect theoretical condition then the Carter lift pump would produce 7 psi during engine cranking.  As rare as it was, there's even a TSB for the Carter creating the same hard hot start problem.

So you can only imagine how much more able the FASS is at delivering fuel during engine cranking...which ends up with situations like this. 

[dripley]

1 hour ago, KATOOM said:

Sounds like the way he has the FASS wired is using the ECM as the ON/OFF source and all amperage going through a relay, which is normal for those applications.  But its not uncommon for the FASS to over pressurize the VP during engine cranking and hydro-lock the fuel solenoid and timing ring solenoid.  Most of the time the additional cranking will allow the higher fuel pressure to bleed off and the engine will eventually start, but not always.

 

Remember, the OEM lift pump was regulated at 15 psi and was barely capable of achieving that.  During cranking if everything was in picture perfect theoretical condition then the Carter lift pump would produce 7 psi during engine cranking.  As rare as it was, there's even a TSB for the Carter creating the same hard hot start problem.

So you can only imagine how much more able the FASS is at delivering fuel during engine cranking...which ends up with situations like this. 

My AD uses the ECM for a trigger and when you turn the key it cuts the power on and off rapidly and reduces the pressure by near 50%. You can hear the relay clicking on and off. Is it different for a Fass than an AD? I always believed the Carter was able to reduce pressure in the same manner. Now wired to a key on hot that is not possible. By that i mean it gets full pressure.

Edited July 15, 2018 by dripley

[KATOOM]

Yes, FASS and AD work the same and wire up the same using that relay.  And yes, the ECM rapidly cycles voltage to reduce fuel pressure but for some reason this can still result in too much initial fuel pressure for some VP's.  Tighter tolerances, heat, voltages, resistance, combination of all?.....not sure, but its more a problem for anyone using a fuel pump like the FASS or AD or Raptor.

 

Either way, its been found that by adding another relay to cut all power to the fuel pump during engine cranking removes all head pressure to the VP.  The result is immediate starting of the engine.  As long as the fuel line prime is retained then this seems to be the best method too.

[dripley]

Well, I cant say I have ever heard of that before. That's not necessarily surprising though.

[SilverMoose]

2 hours ago, KATOOM said:

Yes, FASS and AD work the same and wire up the same using that relay.  And yes, the ECM rapidly cycles voltage to reduce fuel pressure but for some reason this can still result in too much initial fuel pressure for some VP's.  Tighter tolerances, heat, voltages, resistance, combination of all?.....not sure, but its more a problem for anyone using a fuel pump like the FASS or AD or Raptor.

 

Either way, its been found that by adding another relay to cut all power to the fuel pump during engine cranking removes all head pressure to the VP.  The result is immediate starting of the engine.  As long as the fuel line prime is retained then this seems to be the best method too.

Very good info there

 

L8tr

D

[KATOOM]

The things we learn over the years.  Some of it useful.....most of it worthless.  Either way, its makes for good small talk.

[Scottfunk]

Well the Chummy left me stranded at the gym last night so I had no choice but to try and figure out what was wrong. Bad connector in the power distribution block that powers everything hooked up too the engine. I run my ignition hot signal to a relay that in turn signals all the other relays (ecm, tcm, pcm) that the ignition is on. What a relief to know for sure it's not the ecm.

Edited July 17, 2018 by Scottfunk

[KATOOM]

Thanks for the update...

[Mopar1973Man]

1 hour ago, Scottfunk said:

Well the Chummy left me stranded at the gym last night so I had no choice but to try and figure out what was wrong. Bad connector in the power distribution block that powers everything hooked up too the engine. I run my ignition hot signal to a relay that in turn signals all the other relays (ecm, tcm, pcm) that the ignition is on.

 

Bad connectors have been always an electrical trick to learn. No signs of failure (melted, blown fuses, etc.) just the connector is weak and randomly opens the circuit. I've found in the past to sometimes to light bend the contacts slightly to make a better connection if this works then you know the connector is at fault.

[dripley]

Good news, glad your making progress.

[Scottfunk]

Electrical issues are always the worst. When I was in the Navy my mos was Aviation electronics. You'd be amazed by how many boxes would come back over and over to be repaired. It could be so simple as a unit fails when placed in the sun because a weak connection expands. In my case, with the pdc I used, I had to do some internal modifications to make it work for my purposes. All of the #86 pins on the relays were hooked to a common ground making them useless for cooling unit fans. I have a spare now that I'm working on and a complete new under hood wire harness I built, just waiting for the right timing.

[SilverMoose]

Glad to hear the good news.

 

L8tr

D

 

 

 

[mossyoak71]

Glad you were forced to find the fault. Sometimes that's the only way I can figure out things. Put me in a bind and I'll get it!