Hunting at idle when in gear

[Patch]

Hello Guys 

I have a 5.9 24 valve cummins in my F250.

Im experiencing hunting at idle when in gear, worse when warm.Ive done the hot wire test and taking the ECM out of the equation and runs fine with no hunting, that said as expected no.

I made up jumper wires from the VP44 disconnecting data link from the ECM and runs smooth but only 1000rpm....since doing the test Ive emphasized the problem, now I have skipping and bucking but no hunting up through the throttle range.Can only get fault codes from PCM not ECM ?...Im on the fence on whitch way to go APPS, VP44 or dirty signal from ECM....any help would be much appreciated..Im on the west of Australia 

Here are the fault codes I'm getting from PCM 

 

 

 

 

Edited July 14 by 01_Cummins_4x4

[Tractorman]

Since you are getting several DTC's that are all over the map and your engine is not an OEM application, I would double check the integrity of all related wiring connections (both positive connections and ground connections) that you performed to make this conversion work. 

 

Also, make sure that the APPS home position at idle activates the idle validation switch.  An engine idle stop that is mis-adjusted could provide some of the symptoms you mentioned.  You could disconnect the APPS and check for smooth operation using an ohmmeter and also check the operation of the idle validation switch at the same time.

 

- John

[Patch]

Hello @Tractorman where is the idle validation switch 

Also where is this 

Miss or buck

This usually only happens on really old versions of our FMS boxes and can be diagnosed by shaking the box in your hand and if you hear a rattle, then it PROBABLY has melted the power resistors off of the circuit board. This can be repaired and upgraded to the newer style for about $65.00, plus return UPS shipping. Please call for unique address for where to send it for repair.

[Tractorman]

I am assuming that you used a Mopar APPS to communicate with the a Cummins ECM for the era of engine you put into your F250.

 

The idle validation switch is part of the APPS.  When the throttle is released, the mechanical throttle stop should allow for the idle validation switch inside the APPS to be activated.  This action removes all inputs to the ECM and allows only the ECM to maintain idle rpm.

 

When you installed this engine and controls into your F250, did you use the ECM, PCM, APPS, etc. from a sacrificial Dodge Cummins truck?

 

It is hard to offer help in your situation, mainly because I don't know how your conversion was done or what parts were involved.

 

- John

[Patch]

Hello @Tractorman

I wasn’t the one that carried out the conversion.

This is my current APPS sensor

[Tractorman]

It appears that you have an OEM style APPS.  It appears that there is a hand throttle connected to the throttle (in your photo).  Make sure that the hand throttle is not interfering with the idle stop adjustment.  

 

The link below should help with checking the operation of the APPS.

 

- John

 

 

[Patch]

Hello @Tractormanthank you very much OEM  APPS for the ford 7.3 or 5.9 Cummins ?

Timbo's APPS could solve all my problems.

 

Patch 

[Patch]

Hello @Tractorman

The links here did not work can you send them please 

 

[Great work!]

Worn out or really big injectors can cause hunting issues usually in neutral though. The ECU can only compensate the fuel governor so far. It has some expectations for a commanded fuel rate to cause a reasonable idle then adapts a limited amount. If the engine has changed a lot from stock or is damaged/worn out the needed fuel rate can go out of the ECU expected fuel limits for idle than hunting or lope can happen.

 

Check your fuel pressure and incorrect timing ex P0216 can cause lots of problems. 

 

Technical stuff if you want to verify APPS and ECU wiring and communication. 

 

PIN 34 is an idle valid signal from the ECM to VP. It is 12V at idle and 0V when pressed. it is  pulled up to 12V in the VP on pin 4.

 

The APPS has 2 idle outputs that are open collector that are always in opposite states.  APPS pin 2 is 12v =idle,  0V = pressed. APPS pin 6 is inverted.

 

The ECM monitors the idle signals and pot. when APPS is pressed the signals flip and is sensed by the  ECM. The ECM then outputs pin 34 to change state it is sensed at VP pin 4 LGS (German)

the VP then changes a byte in the CAN message going to the ECM as a cross check  then The ECM increases the fuel command byte.  If the pump is Hot wired, grounding pin 4 makes the engine run at a higher RPM.

 

CAN message from VP :  22 40 8 [04 ]00 85 23 xx  yy 79 13.

The Byte in braces is:

0C HEX = not running

04 HEX = idle valid state (as detected via ECM pin 34 to VP pin 4)

00 HEX = above idle operation      "" 

yy HEX is the pump RPM MSB

xx HEX is the pump RPM LSB

79 13 is the fuel temp in Kelvin encoded ?

 

BTW the harness lay out causes electrical noise on the TPS signals that shows up with automatic transmission trucks causing converter rapid locks and unlocking.

 

When hot wired the VP uses a ball park fuel rate for idling.

[Patch]

Thank you very much @Great work! will test these voltages and come back to you...must say I'm a bit over all theses electricidal issues, so tempted to rip it all out and go Ppump ? 

[Tractorman]

On 7/14/2024 at 5:49 PM, Patch said:

Hello @Tractormanthank you very much OEM  APPS for the ford 7.3 or 5.9 Cummins ?

 

I have been camping for the past few days, consequently I am giving a late response.

 

The APPS is for the '98.5-'02 Cummins VP44 fueling system. 

[Patch]

Hello @Tractorman hope you had an awesome time camping.

Thank you, Im going to buy Timbo's APPS and see how I go, can't help think I'm clutching at straws tbh...since piggy backing the VP44  to try to determine the problem..what ever I've done it defiantly emphasized the problem now less or no hunting when in gear but now skipping and bucking through throttle range?

Thank you Patch 

[Patch]

Hello @Tractorman  I fiited timbos new apps sensor tonight, same issue truck runs great when cold, but as soon as the engine is warm, my hunting at idle when placed in gear still happens...where to go from here ?  replace VPP44 ?  

[Tractorman]

Before replacing the APPS, you wrote:

 

On 7/18/2024 at 4:39 AM, Patch said:

Im going to buy Timbo's APPS and see how I go, can't help think I'm clutching at straws tbh...since piggy backing the VP44  to try to determine the problem..what ever I've done it defiantly emphasized the problem now less or no hunting when in gear but now skipping and bucking through throttle range?

 

After replacing the APPS with a Timbo unit, you wrote:

 

2 hours ago, Patch said:

I fiited timbos new apps sensor tonight, same issue truck runs great when cold, but as soon as the engine is warm, my hunting at idle when placed in gear still happens.

 

Has the "skipping and bucking" disappeared? 

 

What horse power injectors are you using?  As @Great work! mentioned, high horse power injectors can cause hunting.  Different torque converters can apply different engine loads when the transmission is placed into gear.

 

- John

[Mopar1973Man]

32 minutes ago, Tractorman said:

Different torque converters can apply different engine loads when the transmission is placed into gear.

Yeah good point low stall converter can drag the engine down. But in Neutral it should go away same with park.

[Great work!]

How does it idle in the vp44 hot wire mode after warmed up and in gear and out of gear? By those pictures I would say someone really wanted to cram that engine in a F250. Definitely custom.

 

You may have electrical noise. Find the WT ground mod on this site and see if you can apply it. Especially the elimination of the large ground wire going across the front of the engine and the joining together of the ECM,Vp44 and sensor grounds and then terminating them to the timing cover box.

[Patch]

Hello Guys, skipping and buck is fixed, it was a loose connection on the back of the VP44.

I'm running stock injectors now.

With hot wire test no hunting at idle when warm, runs nice...obviously no throttle with hot wire test though  

I have simple shift trans controller running the stage 3 4r100 its not connected to APPS.

Stall converter used was for 7.3 ? 

Why only when engine is warm hunting occurs ? I've done the   WT ground test makes no difference for me.

 

Thank you very much 

[Patch]

[Great work!]

Try moving the ground wire(s) from the transmission control box to the engine block temporarily, see if that changes anything. 

 

Are those fault codes current? Some of them need addressed. 

[Patch]

Yes codes are current, and now no start, pump is done ?

 

 

Make any difference if EVm  is set up for manual and your running auto trans ?

Either way its going to mean a pump, im on the fence going Ppump tbh, I know the majority on here are not fans but why ?...cost aside if you get a good ppump...shields for example will drivability be any different from VP..not chasing huge numbers just daily 400 hp max