2005 Ram 5.9 Cummins G56 Manual Trans Surging When Dropping to idle unless ABS module unplugged

[dieselpower]

This is the second 2005 Cummins Manual Trans to have this issue that we have seen.

We are familiar with the (normal) if you will surge/hesitation on a decel that you see while doing a wide open throttle snap. (Usually amplified by high return issues). This is different.

This customer has complained of even a stall at times as this surge creates an under run dropping below a normal idle at times twice or more. The customer also is stating a delayed or intermittent hard start cold.

Just several months ago we replaced the Injection pump because of a starting problem. At that time we had return volume, tested the injectors and verified the relief valve was okay before replacing the injection pump. The injectors and relief valve were fine at that time. The customer does have a Fass fuel system and does filters maintenance regularly. I can revisit the return issue to verify. We did just change the FCA regulator in the event that there was a problem with the problem remaining. Also disconnected the fan clutch which we had replaced at the time of the injection pump replacement just to make sure it wasn't interfering as we have seen that cause surging, stalling issues (old Fan clutch's).

Checked batteries, cleaned terminals that were dirty but now tight and clean. Disconnect the charging wire to the alternator just in case a bad diode and AC voltage leakage are still there. Thought about disconnecting the Fass system or at least checking fuel supply pressure to verify it, but have not yet.

This truck along with another 2005 manual trans both when unhooking the ABS module the surging issue went away. On the one nearly two years ago I had even tried unhooking front sensors vs rear, (temporarily adding a ground etc. )

That customer reported more of a surge/misfire on decel when we diagnosed that truck nearly two years ago. That customer sent off his ABS unit for repair, saying it improved the problem but didn't solve it.
Because of that I am a little reluctant to believe it will completely solve the problem, but why does unhooking the ABS system cause the surging issues to go away?
I think it's likely ECM monitoring the road speed may be trying to prepare the Engine to match upcoming load. Without road speed the ECM doesn't have that input to go off of therefore there isn't the effect. But again maybe there is a problem with the ABS.
As far as any codes it did have a P0532,P2607,P0191. While I could spend a lot of time on those, it is still puzzling the ABS removal stopping both issues while unhooked.
Any thoughts,

Matthew
Diesel Systems Sales and Service L.L.C
9669 Mountain Brook Road
Saint Thomas PA 17252
717-369-4343

 

[Topzide]

When you say; "checked batteries", what does this mean? They need to be load tested, charging system confirmed to be working. Voltage issues can cause all types of gremlins in our trucks! By unhooking the ABS units, you are removing a voltage load from the system and allowing the grounds to work better. Check grounds for clean and tightness. Is the FASS system pulling to much current and is it wired with a relay vs. pulling the high current through the ECM? Lot of issues going on that needed clarification. Hope this helps in find an answer. Good luck.

 

[Darkbloodmon]

As far as any codes it did have a P0532,P2607,P0191. While I could spend a lot of time on those, it is still puzzling the ABS removal stopping both issues while unhooked.
Any thoughts,

Like @Topzide mentioned the ABS system has an electrical load on the system.

I would clean the terminals and high draw contact points, The air intake heater being one of them and then charge the batteries. Try to replicate the symptoms again.

You mentioned a surge that can stall and hard start conditions, off the top of my head that sounds like an injector related issue.

 

[Tuesdak]

As far as any codes it did have a P0532,P2607,P0191. While I could spend a lot of time on those, it is still puzzling the ABS removal stopping both issues while unhooked.
Any thoughts,

These are ALL low voltage codes. Generally a bad connection, bad ignition switch, relay, corroded ground, bad battery, short, etc. With a high resistance connection, say from loose and/or corroded, the more load current through it the more voltage is lost at the bad spot. Eventually the voltage is so low elsewhere that things quit working. At some low voltage "0's" are not made into "1's" and the ECM even fails to operate.

So as above when you remove the ABS it's removing load/Amps going through a bad connection.

Verify voltage to the ECM at the ECM when it's surging. Probe both + and it's ground pins. Either could be dropping voltage.

Separate and load test batteries. Look for battery cables that are stiff from wicking up battery acid and corroded internally. Take apart grounds and clean them as corrosion loves to hide under the bolt/nut.

Offhand a known trouble area is the HVAC blower current may have damaged the ignition switch connector.