MyE28.com

I have read a few posts that talk about tweaking the IP, removing smog related equipment and advancing the timing to get more power and more importantly higher fuel economy.
I have only had my TD for a little while now and my average fuel economy on the highway averaging 70mph is right at 32mpg. Is this normal? I have read that many people get upper 20s in the city and low 30s on the highway. Some people have posted that after minor tweaks they get close to 40 on the highway.

I have searched and read every post I can find but I have not been able to find what people have changed to improve performance. Could someone please post a how to on tuning the 524?

Thanks

Firefly

When I first got my car, it was really-REALLY slow. But it averaged 40mpg on my trip back to San Diego from Texas, and there absolutely no smoke coming out of the back.

I joined the Yahoo 524td site and they have some resources there on tuning the Bosch VE injector pump (IP) in the 524td that is very similar to the one in the 1st gen Cummins TD truck. My car had a freshly rebuilt IP and it turns out it was set very conservatively and the timing was slightly retarded as well as it was very hard to start, even when it was warm and all of the glowplugs working. I did a series of adjustments on it very similar to what "seattletd" did. These adjustments changed the off idle power enrichment, the rate on how fast more diesel is added and the total amount of diesel added to the entire throttle operating range. The car performed to where I would it expect it to be in stock form, but it now was only getting low to mid 30s mileage. From my perspective this is considered typical for the car, and your 32mpg @ 70mph is considered normal.

I then developed an exhaust leak and my mileage went down and the smoke went up until I fixed it. After that, I realized my EGR and the entire vacuum line routings were wrong and redid them to factory specs. My mileage went down to high 20s to low 30s and I could tell the power was stifled just a bit at part throttle. So I plugged the EGR valve vacuum source and everything went back to before. Lastly, I realized my internal wastegate actuator spring was weakened with age and limiting boost to 9psi. I bought a cheapie manual boost controller to set the max boost level back to 13.5 psi. The smoke went down, the power and mileage went up slightly so that now I was getting mid to high 30s mpg consistently.

From there, I fabbed a custom cold air intake for my 524td. I didn't just simply add a tube with a high-flow cone air filter, but I also routed so that the filter was outside of the engine compartment. I used a K&N off of a Dinan CAI. Mileage and power went up again and smoked went down. I also love the turbo whistle that sounds very similar to my slightly modded Dodge diesel. Also, I advanced the IP timing about 4 degrees so that it would start right up with all cylinders firing, but wasn't rattling too badly, and mileage was pushing 40mpg at that point. Lastly, I removed the EGR valve and replaced it with an external wastegate setup. Smoke went down alot and power went up at full throttle, mileage increased only a smidgen at best.

MIleage in general depends on how much you put your foot into it , what speed you drive at, and how much smoke you have coming out of the exhaust. If you're sending a huge screen at back at full throttle like one 524td I test drove, then you tuning down the IP will give you mileage benefits. It's desirable to send a good puff of smoke when throttling off idle to then go to just a haze at full throttle for the rest of the rev range.

Currently, I just added this higher stall torque converter, and I'm finally having a blast with my 524td. I had my first kill yesterday of a late model BMW 325 sedan!!! (it must have been an automatic though) I also like to hear the turbo whistle go up and down when the torque converter locks up so I'm sure my current mileage isn't great. However, if I'm chillin' on a road trip, I usually get right around 40mpgs.

Chris H.