Tuning large injectors, Siemens Deka 80 lb, 7427 $0E, Turbo 383 MPFI

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.

you're likely experiencing a phenomenon of closed loop O2 operation.... you have injectors that are able to deliver over twice as much fuel as what you were running previously with good results. I would dig into the O2 PI/PID tables and cut them in half to start.

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Originally Posted by RobertISaar

you're likely experiencing a phenomenon of closed loop O2 operation.... you have injectors that are able to deliver over twice as much fuel as what you were running previously with good results. I would dig into the O2 PI/PID tables and cut them in half to start.

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Ahhh...proportional fueling...duh. I guess I was suspecting something else due to it idling good and only having the issue while driving. I will play around with those tables and see what happens.

Well I gave up and put the old injectors back in. I lowered the proportional gain to where the 02 sensor would not even swing anymore. That was really about the only way I could get rid of the surge. I played around with all the PID parameters I could find and was just not getting anywhere. I did notice that the I only got a surge when the 02 would swing consistent like a saw tooth shaped wave. If the 02 was slow to switch there is no surge. The truck runs extremely well on the Bosch injectors they are not big enough though.

Did you try open loop and just tuning with wideband?

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Originally Posted by brian617

Did you try open loop and just tuning with wideband?

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No, I did not try that. I would like to keep closed loop tuning for better gas mileage if possible. Its weird because the tunes are pretty much identical other than the size of the injectors, short pulse adder, and battery voltage. You can watch the injector pulse width almost double when the surge happens. I originally thought it was the short pulse adder, so I zeroed it out. Still did it. The LS guys complain about the same thing with these, but none of the tuners want to give up any secrets on them, because thats how they are making their money.

http://i105.photobucket.com/albums/m...pscneti9nl.jpg

Only reason I suggested OL was to eliminate O2 correction as the culprit.

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Originally Posted by brian617

Only reason I suggested OL was to eliminate O2 correction as the culprit.

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I may give it another shot when I can come up with a good game plan on getting them tuned. I have been looking through a lot of bins to see the differences in the 02 correction tables. They seem to be all over the place.

I just watched my datalog again and noticed a few things, for one the battery voltage the PCM is seeing is showing 10.4 to 11 VDC. Also my desired AFR is showing 11 as well. Ever since converting to $0E I have not been able to get the desired AFR to work. The battery voltage has me concerned though..

For what its worth, I use $OE and didnt have any problems getting desired AFR instead of batt volts. Just followed the instructions in the XDF.