So I did the 4.6 to 5.4 swap and kept the 4.6 pcm. My 4.6 at times seemed like it was really down on power, but I attributed it to old gas, manifold to collector leak and rotted off egr tube. Oddly at times it would still seem great, but I thought it was from ideal humidity, temp, etc.

Once I got the 5.4 in with long tubes, the truck idled and ran ok, but seemed low on power, but at times seemed to really pull well. I attributed this to needing a tune. The pcm threw no codes over 200+ miles of random driving.

I took it in for tuning to a reputable ford tuner and this is what he could tell me:
- He tried everything to do on road data logging, but the signal would constantly drop and the device would "lock up" after only 15-20 seconds.
- He tried another device and several different cables and got the same result.
- He checked the port pins and even checked at the computer and got no improvement.
- The little bit of info he got showed him that the truck would operate in closed loop at idle, but would not go into open loop under any circumstance. Could this explain the lack of power?
- He told me that in the 10 years he has been tuning, he has NEVER seen this and had little advice on how to proceed.
- He suspects the pcm could be bad, but has no way to determine positively. Pcm is FOU1.

Guru's, I have come so far, please help!

 

What was he logging with?

If it was not going into OL, yes, that will explain the lack of power.

My first guess would be O2 related, especially with longtubes installed...

 

I think he was using a laptop with SCT software.

Have you ever heard of a bad O2 not throwing a code?

I'm wondering if a dealer's equipment might help pinpoint the problem?

 

its rare to not have it throw a code, but did he actually check for codes, or are you basing the lack of codes on a lack of a CEL?

A bad PCM will generally throw a code as well

Could there be a chip on the PCM?
If you dont have something to check codes with, run it by an auto parts store and see if they can pull any codes.

 

I don't know for certain if he checked for codes. There is no Cel.
I've had the truck for 13 years. The PCM has never been touched by me or the 1st owner.
Any idea why he is having the intermittant connection issue?

 

make sure the cigarette lighter fuse contacts are clean and it seats properly....try changing it for a new one....

this circuit provides power to the obdii port also

just a thought....

 

Thanks 88. He did check that and other fuses.

 

Check codes

 

I'll check for codes.

I hate guessing, but I'll through this one out too:
- Because the 5.4 is about an inch taller, I had a hard time plugging the fuel line into the fuel rail. I really had to pull and stretch the line. Could I have restricted the fuel line enough to cause a fuel pressure/volume drop make the PCM reluctant to go open loop?
I don't have a fuel pressure guage. What's the quickest/cheapest way to determine if this is contributing to the problem? ..if at all.

 

No, the PCM would at least command OL, even if it couldn't get the required fuel volume...

Another thought, is the TPS working properly for sure?

 

I was told by the tuner that when he had good connectivity, everything seemed to be functioning normally.

 

Update for the guru's.
-Using an Actron reader from autozone we came up with no codes engine off or on.
-We also saw no change to open loop, but did not road test. Revd and held rpms high. No change.
-Had a consistent signal with no loss for over 5 minutes. Tuner could not get more than 20 seconds. Does this mean the tuner had an equipment issue?

Thanks for all the comments and help so far. Hopefully we can flush this gremlin out!

 

Yes, IMO, there was a hardware issue if you were able to talk with another tool.

Transitioning from CL to OL will generally require some load, revving it in neutral will not do it most likely....

 

Update:
- Fuel pressure checked out. No one here suspected it but I had a local Ford tech question it.
- I found another lesser-known tuner (although experienced) that claims he has seen this before and will be able to take care of it. I have am appointment for the 29th.

On one hand I have concerns bc this Guy will give me no detail on what he plans to do, but on the other, if I had a fix I wouldn't give away my secrets either. The best part is he promises he won't charge me a dime if he can't make it work.

 

good luck....hope he can help....