Quote:
Originally Posted by BAD ASP
I have a 408w with a large turbo. The engine is FI using MSD ignition and coil. The distributor is a stock Ford and I'm using a Fast sequential bank to bank ems. The injectors are 83 lb.The problem is only between 2000 and 3000 rpm. The engine misses and hesitates but you can push through it. The problem is that the rpm range is right at cruise in traffic.When cruising the engine is breaking up and popping a little. It's much more noticeable to me but I had a techie riding with me checking my ems with the laptop and he says all is good. I've changed the plugs and they showed a little rich but not bad. The A/F is right at 13.5. My gut says its ignition because the fuel pressure stays at 60 lbs and I can hear the pump.... it doesn't break up at all. Could it be an injector not spraying at the rpm or is that in the ems.... This condition is somewhat intermittent but I'd call it 80%. It also doesn't matter cold or hot.
Any thoughts will be appreciated.
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This is problem is likely a driveability issue with the tune in your EFI system. First, does this happen under stready acceleration through the 2000 - 3000 RPM range or when you first step on the accelerator at an RPM in this range? Is you A/F ration at 13.5 at part throttle crusie or at WOT throttle under acceleration? Are you experiencing knock or detonation when the problem happens? Is the problem the same when the engine is cold vs. hot? When the outside temperature is cold vs hot?
I'd guess that your motor is experiencing a lean condition in this RPM range, possibly in conjunction with not enough acceleration enrinchment. These sort of "driveability" issues are pretty common when an EFI system is first installed in a car and driven on the street.
Since you are using a FAST system, I'd suggest you enable data logging in your ECU and capture (RPM, MAP, TPS %, ignition advance, Target AFR, Actual AFR, Injector Pulse %, Coolant Temp, Air Temp, O2 Correction %, and Battery Voltage) for starters. Drive the car, make the problem happen and then sit someplace quite and look at what was happening with your motor when the problem occured. Was it right after you hit the throttle? Where were you in the VE and Timing tables? Did the motor go lean (indicated by position O2 correction or actual AFR below target)? What was the target AFR when the problem happened? If you had just hit the trottle and you're still at 13.7:1 than you definitely went lean, etc. Its important that you have a clear picture of what is happening before you change the tune to correct the problem. You also want to see if the problem is at one specific RPM and load point in your VE/Timing tables or if you can make it happen for a range of cells. This will also determine what you need to do to correct the problem.
The folks at FAST can also help you if you send them this sort of log information if you don't feel comfortable making the changes yourself.