6.5 timing issues, poor fuel economy please advise

[grader6.5td]

Hey folks, got my 6.5 optimizer in a couple months ago, got it installed and it runs decent. I had swapped my old injectors and IP to this new engine(mostly because they didn't have many miles on them since I replaced them last) while the engine was out I did new motor mounts, new flex plate, new torque converter seal, wicked wheel 2 etc...
But my main issue is this: I can't seem to be able to get the engine to relearn its timing for the TDC offset. When I swapped pumps to this new engine I took an educated guess in where to clock it. I have a tech 1 scan tool, and it currently shows -1.50 for TDC offset, which is what it had been set to at the shop I paid to time it when I replaced that pump on the old engine. I waited till engine was at operating temp, then attempted to do the procedure several times.
The truck runs okay, but it doesn't start as perky as it used to and my mpgs have tanked! From 17.5 average with the old wore out engine to 13.5 as of yesterday with this new engine. Mostly highway miles!!
The only thing I can figure is either the wicked wheel, or the timing really has affected the fuel economy. Not much white smoke with start up, and not even much black smoke under acceleration, having been around these engines for a while now I'd say it really does run well overall...but the fuel economy is awful for a half ton diesel. Please advise

 

[ak diesel driver]

You need to do the time set procedure first before trying to do the TDCO.

 

[grader6.5td]

Is there a thread for that procedure?

 

[grader6.5td]

I finally found a good step by step procedure. My initial base timing was 1.5 instead of the desired 3.5 degrees. Then once that was set with the tool I went ahead and set the TDC relearn and got it to -.70.
It already starts much better. Just gotta check out real life MPGs and throttle response.
Thank you for the initial help AK Diesel Driver!!

 

[Wreckinball67]

One other Thing to consider is; did you swap the same configuration of engine? There are different models through the series of trucks, vans,etc. I'm mostly referring to the "pre-cup" sizes. Your 1/2 ton would have smaller pre-cups (light duty) than say heavy duty version with larger pre-cups. The smaller the pre-cup the better the mileage, etc.
I did the exact same swap (1/2 ton) to a GEP 6.5 with larger pre-cups and my mileage is down a bit but, I have slightly more power (still stock everything). Just for you to keep in mind.

 

[MrMarty51]

Welcome to the forum Grader.

 

[JMJNet]

The negative sign is very important.
IIRC, the desired range is between -0.50 to -1.50.
Heath Diesel recommended -1.94 so I think that may be at the edge of the good limit.

So -0.70 is within that limit.

 

[dbrannon79]

@grader6.5td I think now that you have your timing in spec you should see better mileage. all things considered, different engine will result a different mileage. There are lots of other variables and slight differences between the old and new motors that can cause mpg changes including sensor readings the pcm sees on the new engine.

I normally average 14 1/2 or so mpg's on mine and have not found anything concrete that helps that. including fuel condition ( time it's been sitting in the tank), even different additives. Every additive I have tried always seems to degrade my mileage (Howes being the worst for me), I happen to stumble across hotshots secret everyday stuff on the shelf at wally world this weekend. I'm trying it out this week to see what it does.

 

[NVW]

@grader6.5td I think now that you have your timing in spec you should see better mileage. all things considered, different engine will result a different mileage. There are lots of other variables and slight differences between the old and new motors that can cause mpg changes including sensor readings the pcm sees on the new engine.

I normally average 14 1/2 or so mpg's on mine and have not found anything concrete that helps that. including fuel condition ( time it's been sitting in the tank), even different additives. Every additive I have tried always seems to degrade my mileage (Howes being the worst for me), I happen to stumble across hotshots secret everyday stuff on the shelf at wally world this weekend. I'm trying it out this week to see what it does.

Interesting, I've used it before but always attributed any drop in mileage to winter fuel and warmup times here. You have a very different climate so that wouldn't be your issue

 

[dbrannon79]

I've used the stuff twice, first time was back in the great Texas freeze when it got down to 16 degrees, I had to find something to prevent gelling just in case. I had double dosed my tank that time which could have contributed along with the longer warmup's and putting around town that whole week where ice was all over the roads! I didn't have the Fuelly app then but I remember my mileage was around 11 then! This last time was back in February, we were warned that it might freeze again. I only single dosed it, that's where I got my worst mileage recorded on Fuelly. With our weather here, I normally warm up the truck for about 10 minutes or so with temps under 50 degrees mainly due to old habits plus this old rig sounds like hell moving down the road if I don't do a warm up and just take off lol!