Hi guys, some of you may have seen my MPFI turbo 383 build where I am using the stock 7427 and a 2 BAR MAP sensor in my 94 Blazer. The truck has been tuned and running great for over a year, other than destroying a 4L60E and going 80E. The problem is or was that the 34 pound White Bosch injectors were going static on 10 PSI boost at about 5000 RPM. So, I backed the boost off to about 7 PSI. I finally bought a set of 8 80lb Siemens Deka injectors and a Walbro 450 fuel pump. I got it all installed over the weekend. I have the truck starting and idling very good, goes into closed loop fine and BLMS at idle are very close to being in line. I used the Ford injector battery volts offset table I found online and set the base fuel pressure at 40-43 pounds. I am using a vacuum/boost referenced regulator, so at idle I may have more like 38-39 pounds of fuel pressure at idle which is what the Ford data is based off of.

The problem I am having is the truck surges at part throttle cruise, while going down the road. I see the injector pulse width make large jumps which is making it surge. As far as I can tell AE is not coming on when this happens. I have been playing with Async Short BPW Offset vs. BPW table, which seems to have a big effect on idle quality, but I am wondering if it is also causing the part throttle surge.

I had a good working tune with the old injectors before swapping them out to these. The LS guys use these injectors a lot in turbo setups, and searching around shows them having a lot of the same problems I am having. I have some injector data for these in the LS1 PCM, but the run 60 pounds fuel pressure. I tried setting mine to 60 and using the LS data, but the truck did not like that. They seem to like the lower fuel pressure and the way I have it setup now, as far as starting and idle goes. Looking for some insight on what might be causing the surge if anyone has any ideas.

http://siemensdeka.com/specsheets/FI114992.jpg

The Ford data .pdf is attached.