S60 DDEC mystery

[RichardEntrekin]

First, this is a problem I can live with.

The problem is the replacement DDEC IV produces 3 psig less boost at max than the original DDEC III.

The background is important. DDEC III ECM was replaced because of Non Volatile Check Sum Error. It still runs the engine just fine, only the mileage accumulated goes wonky from time to time. No amount of voltage checking, ground cleaning, or reflashing this ECM would correct this problem.

I decided to replace the ECM rather than have a failure while on the road. At the time of replacement, the only DD Reman ECM I could source was a DDEC IV. It was programmed to the serial number of the engine by a Stuart and Stevenson shop. I immediately noticed the loss of max boost on long grades. The DDEC III will produce 29.5 psig and the DDEC IV will only produce 26.5. I have swapped the two ECMs back and forth twice with the same result. The boost numbers are confirmed with both a mechanical gauge and a VMSPc reading the ECM bus.

I have taken both ECMs to an authorized DD shop. They have read them both and swear it’s the exact same program.

Strangest thing is that I feel the coach climbs at least as well as before, maybe even a bit stronger although the boost is lower. Fuel mileage is the same.

As I said earlier, I can live with this. It’s just the curious cat in me that has me asking what could be the difference.

Thanks in advance.

[freds]

Well boost pressure climbs when it is working harder. Maybe the new DDEC is just getting the work done with less effort because it's more efficient in another area?

Probably the only way to tell would be back to back dyno runs.

[robertglines1]

I have a 2000yr 60 series with DDEC IV pre emissions Could not be a altitude setting? There was a period from 1998 till 2001 there were allot of emissions changes made to ecms   Like you just curious.  I am running a 10 spd autoshift W/307 rear end. on flats close to 9mpg.   Bob

[thomasinnv]

Wonder if they set the injector codes properly?

[luvrbus]

The DDEC IV reads faster and more efficiently than the lll ,every one I have changed over to  the IV has a few pounds drop on the boost even on the 8v92 and 6v92 engines and seem to run better with more power and less smoke. You can change  the pulse width ban on the injectors and get a small increase but you don't accomplish anything except more fuel usage 

[Van]

The DDEC IV reads faster and more efficiently than the lll ,every one I have changed over to  the IV has a few pounds drop on the boost even on the 8v92 and 6v92 engines and seem to run better with more power and less smoke. You can change  the pulse width ban on the injectors and get a small increase but you don't accomplish anything except more fuel usage

  There you have it😉now you know the rest of the story.

[RichardEntrekin]

Thank you Mr. Clifford. Nothing like the voice of experience.

[RJ]

The DDEC IV reads faster and more efficiently than the lll ,every one I have changed over to  the IV has a few pounds drop on the boost even on the 8v92 and 6v92 engines and seem to run better with more power and less smoke. You can change  the pulse width ban on the injectors and get a small increase but you don't accomplish anything except more fuel usage

Say, Clifford -

Will a DDEC iV swap right into a DDEC II harness?  My 8V92T runs fine with a rebuilt DDEC II ECM, so just curious for future reference. . .

RJ

[Van]

Rj maybe this will help ya
https://www.busconversionmagazine.com/forum/index.php?topic=10750.0