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Air/fuel ratio won't richen under boost

Old 12-20-2009, 10:13 PM
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Originally Posted by Lignite View Post
Sniper Special Forces tuner (software and flash box as I understand it). Truck was idling good, and even better now with new coils (Screamin Demon). Running a blow-off valve to atmosphere (but with the manual trans I am thinking the bypass system would be more useful?).

And for ZRX, I think I said that wrong. My understanding of the Explorer PCM (please correct me if I'm wrong!) is it uses three fuel tables, low medium and high power. I believe my tune is set up to use about stock fuel table for low power, start adding more fuel in the medium table, and really dumping fuel in the high table. I was told this is done for fuel economy's sake. It does add more fuel for boost conditions, but not as much as for high power boost conditions. This is probably oversimplified, as I don't know if I completely understand all of the PCM parameters that were modified to add more fuel, but it does (or was) working quite well according to the A/F and boost gauges before my problem developed. I'm thinking the 'miss' is not allowing the PCM to utilize the high power fuel table, and therefor I'm not seeing the safer (lower) A/F ratios I need to in boost. Just my theory, so far all my theories have been wrong!

I got new rearend under it and front wheel bearings in and took it for a drive today, but no bed, no 4 wheel drive and no brakes (wrong front gear ratio and brakes need a bleed) and its snowy everywhere here, so I can't get enough traction to even get into boost yet.

I'm hopeful that the new coils may have fixed my problem, it seems to be running very healthy, but I need to finish my drivetrain overhaul before I dare to really get into higher horsepower stuff. Whew, got a little long winded there. sorry.
Thanks for the explanation of the low, med., high, fuel addition, It is my bad. I assumed wrong.I wish you the best of luck at correcting your problem.It is probably something simple, that has been my experience over time. Have a great Christmas!!! zrxlover
Old 12-21-2009, 05:13 PM
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Ford uses one fuel table (for open loop fueling) but most tuners modify it several ways to accomodate different driving conditions. In closed loop, it will maintain stoich, 14.64, and utilize short term fuel trim to add or take away fuel in closed loop. In open loop the fueling is based off of a table (Load vs. RPM), which will add more fuel at higher loads and/or engine speeds in certain cells.

If you got the datalogging software with your tuning software then you can log and read some engine info and see what's going on with it. If not, I believe you can still get it for around 100 bucks.

Some simple things to eliminate is the tension on the blower belt and making sure your inline pump is coming on when it is supposed to, and any type of vaccum leak after the air meter.
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