Poor Fuel Mileage and Low Power

[BMC330]

Ok.  Im not sure if it has all the options as my truck as mine is loaded and the other is a work truck.  I will order a new one and go from there.

 

Thank you.

[Mopar1973Man]

It might work for the test to verify but not a replacement. So it worth it for the testing aspect but create its own issues. Like I've found mismatched PCM vs ECM will cause communication problems as well. For what we want it for and testing the APPS sensor just plugging in the donor PCM and turn the key on and cycling the throttle up and own with your scan tool will tell us if its the problem.

[BMC330]

I have learned a lesson on this adventure.  Mechanical problems are much more enjoyable to work on.   Wiring issues are really a pain.  I have used a Fluke Meter more in the past two days than in my entire life.

[RipnRam99]

I have been having some similar issues with power/boost/milage... Lots of good information here! 

One thing that I was not aware of is that the ECM and PCM must be matched to the options in the truck... As I am just about a day or two from beginning to tear down the truck I wrecked, to pull out modified motor/trans, and replace stock drive train in the newer (to me, both 1999s) truck... I am wondering if I should swap ECM & PCM as well? Would I need to use my old instrument cluster as well? I think they are linked.

Sorry if I'm side tracking this thread a little. I am just trying to get a big picture game plan together, and organize this potential fiasco as best I can.

[Mopar1973Man]

I would keep your pair of ECM and PCM. If the other donor truck is a matching truck with same options then I would take the ECM and PCM for spares.

[BMC330]

I called auto computer spectlist.  They said the PCM had no bearing on the APPS voltage being erratic.  It was the ECU that controlled the APPS. 

 

Im confused as to is the issue in the PCM or the ECM.

 

I know PCM has something to do with the APPS due to unpluging the PCM corrects my erratic APPS.

 

Which should i be looking to replace PCM or ECU?

[Mopar1973Man]

2 minutes ago, BMC330 said:

I called auto computer spectlist.  They said the PCM had no bearing on the APPS voltage being erratic.  It was the ECU that controlled the APPS. 

 

Im confused as to is the issue in the PCM or the ECM.

 

I know PCM has something to do with the APPS due to unpluging the PCM corrects my erratic APPS.

 

Which should i be looking to replace PCM or ECU?

 

Automatic or manual?

 

If you are manual like me then the PCM does control the APPS sensor line because there is no vacuum cruise motor like the automatics use. So my PCM is directly connected to the ECM sharing the APPS sensor wires. Where automatics still share it but only for sense of how much TPS signal for shift signal. If you unplugged the PCM and the signal is now stable it still lean back on the fact the PCM is screwing up the signal. 

 

Look at C1 pin 22 that is APPS sensor signal.

 

Now look here at Pin 28... Yes, they are connected and share the signal.

 

[BMC330]

It is a 6 speed truck not auto.  Im at the point i will replace both if needed.

 

I will call them back and specify i have a 6 speed truck.

 

Thanks for the reply.

[dripley]

Year makes a difference also. I was thinking 01 and 02 manuals have the fly by wire cruise. Not for sure on the years fhough.

[RipnRam99]

2 hours ago, Mopar1973Man said:

I would keep your pair of ECM and PCM. If the other donor truck is a matching truck with same options then I would take the ECM and PCM for spares.

What options should I pay attention to? So far, the only difference I see is the donor truck has posi rear axle, and the new truck doesn't... Also little things like my doors don't auto lock at 10mph, and the O/D on-off button on the end of the shifter doesn't do anything. No light on the dash either. Even when I first turn the key to the on position... Other than that, everything is the same, as far as I can tell... Someone deleted badges on new truck. Old truck was an SLT.

[Mopar1973Man]

Electrical options. Anything different between the PCM options and ECM options. 

[RipnRam99]

1 minute ago, Mopar1973Man said:

Electrical options. Anything different between the PCM options and ECM options. 

I have no idea what options those would be... 

Like I said... The only thing I see that is different is the O/D on-off button... It's not marked on the shifter, and it does nothing when I push the button... The donor trucks is marked, and it down shifts to 3rd when you push it, and the dash has a O/D off light ... Ever heard of an auto truck not having the O/D off option?

[Mopar1973Man]

Like for example.

• Manual or Automatic transmission
• HO or SO engine
• Highline central timer with security feature

This are just some of the things that can make trading PCM and ECM hard at times. 

[BMC330]

Got new PCM in today.  Cleaned ground and installed the new PCM.  I still have no change in the truck.  No power above about 1/8 peddle.  

 

I do not have the scanner to plug into the truck at this time,  it belongs to my nephew and he has to use at his shop during the week.  It will be this weekend before I can get it back.

 

I have new codes with the new PCM by key display.

 

P0122

P1698

P0522

P0123

P1295

 

Still chasing the problem.

[Mopar1973Man]

 

 

 

 

[BMC330]

On 4/19/2018 at 8:38 PM, Mopar1973Man said:

 

 

 

 

Got new PCM in today.  Cleaned ground and installed the new PCM.  I still have no change in the truck.  No power above about 1/8 peddle.  

 

I do not have the scanner to plug into the truck at this time,  it belongs to my nephew and he has to use at his shop during the week.  It will be this weekend before I can get it back.

 

I have new codes with the new PCM by key display.

 

P0122

P1698

P0522

P0123

P1295

 

Still chasing the problem.

 

 

Completed APPS voltage to high test.  At the end I got to replace ECM.  I was allowed to borrow an ECM from a truck very close to mine.  Only thing I could find was 2WD where mine is 4WD.  The other ECM did not change anything on my performance.

 

I purchased a Load Pro.  I am about to start load testing ground wires.  Maybe I will find the problem today.

 

[Dieselfuture]

Check your 5v loop, possibly oil sender shorted out.

[Mopar1973Man]

22 minutes ago, Dieselfuture said:

Check your 5v loop, possibly oil sender shorted out.

You could just unplug it for a test drive. The gauge will not work but it'll prove the short idea.

[LorenS]

This is a really good thread for those of us with similar vehicular ailments, listing possible causes and diagnostic approaches.

Was there ever a resolution to this particular problem?