FAST system: voltage drops/inj duty cycle doesnt move

[Spooled231]

Hey Guys,

I ran into a slight problem at the track on the last run. The voltage has always been a constant 14.0 to 14.3 at all times, idle and WOT. On the last run at 5600 rpms in 2nd gear, voltage drops like a rock to 12.2 at the top of 2nd 6200 rpms. As I go into 3rd gear, it was at a constant 11.8-11.7 volts until I let off the throttle then procedes to jump back up to 14.1 going back to the pits. One thing that is really weird....the injector duty cycle didnt change at all stayed at 75 to 80 percent at all times during the entire turn and the A/F ratio was at its target of 11.5 What puzzles me if the voltage drops...the inj duty cycle should have gone up. I know that for a fact cause it costed me a motor a couple years ago before I had the adj volt regulator. The car didnt lay over at all during the run so I couldnt feel anything. If yall want to see the log, I can email it out.


Thanks
John Martin
10.98 @ 121.7
6.93 @ 99.11

 

[Louie L.]

"What puzzles me if the voltage drops...the inj duty cycle should have gone up. I know that for a fact cause it costed me a motor a couple years ago before I had the adj volt regulator. The car didnt lay over at all during the run so I couldnt feel anything. If yall want to see the log, I can email it out"

Spooled 231,
From what u describe it appears that the Voltage correction feature in the ecm kicked in corrcting the voltage and maintaining a steady Inj DC. I would look into the electrical system, battery and possibly a + bat wire making contact at WOT.

 

[Craig Smith]

I agree with Louie. the only problem I gather is a charging system problem. If nothing else changed other than voltage, the ECU worked perfectly.

It doesn't always work this way. A lot of it has to do with the injector opening time and how a particular injector responds to variations in voltage. I would say that the opening time you have programmed, as well as the correction curve built into the ECU, are perfect for your injectors.

 

[bruce]

Originally posted by Spooled231
One thing that is really weird....the injector duty cycle didnt change at all stayed at 75 to 80 percent at all times during the entire turn and the A/F ratio was at its target of 11.

The injector correction for voltage is a time based correction. We're generally talking in the .000x range. So at a 8 msec duration pulse width you'd hardly see it, if at all. Now at idle is a whole nuther matter. Duty cycles are a VERY course measurement.

 

[Spooled231]

Craig,

If the serpentine belt slipped, that would cause the drastic change in voltage. Right? I am going to look at the position of the belt and tensioner. The belt is only a year old and is a GM.

THanks
John Martin
10.98 @ 121.7
6.93 @ 99.11

 

[Eric Stage I]

John,
I had problems with voltage drop during a run. It would go from about 13.9 down to 12.9 at WOT. I found that the wire from the alternator to the battery was badly corroded inside (10 ga. I think?). It was under the insulation so I couldn't see it. Ever since I replaced that wire, I have consistent high 13's for voltage at WOT.

Eric