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Old 09-26-2010, 01:05 PM   #1
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Default Poor idle with A/C and headlights on :(

FMII Hydra 2.5
RC 550 Injectors
Walbro 190HP

Without additional loading, the car runs great. My AFRs are between 14.7 and 14.8. A rev to 3k rpm yields a cushioned and predictable return to idle.

With headlights on, the car runs as if there were no change to 'unloaded'.

With the A/C on, the car complains only slightly. AFRs are between 14.6 and 14.8. A rev to 3k rpm yields a fast drop to idle RPM minus 75, followed by a quick return to idle rpm.

With the A/C on, AND the headlights on, idle AFRs immediately richen by a ratio of 1. (Between 13.6 and 13.8). The car does not run any differently than with just A/C on, and actually stays in the same load/rpm cell as A/C only. (Switching headlights on/off with A/C on yields no noticable difference, only a change in the AFR being reported by the Hydra WBO2.) A rev to 3k rpm yields a fast drop to about 250 rpm, where the car stumbles only briefly before stalling. It's repeatable during post start and fully warmed up.

Any ideas?
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Old 09-27-2010, 09:32 AM   #2
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Does the Hydra have a battery voltage compensation table to compensate for injector opening time increasing at low battery voltage? It sounds like that needs some adjustment.
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Old 09-27-2010, 09:38 AM   #3
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It does IIRC and that's exactly what it sounds like to me as well.
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Old 09-27-2010, 11:08 AM   #4
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Thanks, I'll look into it
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Old 09-27-2010, 11:12 AM   #5
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Check your dashpot
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Old 10-05-2010, 08:46 PM   #6
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Default Do I need to replace my alternator?

This is the second time I've heard "dashpot" mentioned on this forum. Wikipedia only leaves me more confused. My understanding is that a dashpot simply resists motion - a shock damper is an example. How does a dashpot relate to idle / low rpm response?

I found the setting for low voltage injector compensation in the Hydra. "Control 1 - Injector Response" I did a graduated increase from 10 to about 11.2 volts. 10% at 10 volts, 8% at 10.3 volts, 6% at 10.6 volts, and so on. It helped a good bit. I then added another graduated 10% on top of that so total would be:
21% at 10 volts
17% at 10.3 volts
etc.
etc.

This seemed to help a good bit again, still getting the idle dip, but it is far less ferocious than before.

I then added another 20% to the 10 volt cell to more or less be a 'last line' of defense against stalling.

End result is the car doesn't die from a rev drop with A/C and headlights on. It also happens to be much more "stoplight friendly" where before I was tapping the gas by habit to get the rpm up before engaging the clutch at a stoplight in order to keep the car from bogging/stalling. I can now engage the clutch at idle engine speed and comfortably accelerate out of a stop.

I was looking at my battery voltage indicator, at idle with no accessories, it shows about 12.1 volts. With the headlights on, I drop to about 11.6 volts.

If I rev the engine without any accessories on, I show a more or less steady 13.5 volts from about 1250 rpm on up.
With just the headlights on, I barely make it to 12 volts at 1250 rpm, this continues to increase with rpm to about 13.5 volts somewhere above 3k rpm.

At cold idle, my "battery" light is barely lit - can only see it if it's dark out and no lights on. With the headlights on, it gets the tiniest bit brighter. Can see it with outside lights on. I'm under the expectation that the battery light shouldn't light under idle circumstances ever; assuming a properly functioning electrical system.

The battery is a westco, about 2 months old.

I tore the alternator apart during the rebuild to refinish the alternator case. Don't know if I may have damaged something? Didn't make any alterations while I was in there.

Do I need to replace my alternator?
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Old 10-05-2010, 11:39 PM   #7
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Dropping fast from 3000 rpm to 250, stumbling and dying could be the dashpot because the dashpot operating correctly will slow the final closing of the throttle so that the ECU can get a chance to correct the air/fuel mixture for the load. Once it hits 250 rpm, it can almost never recover.

The dashpot catches the throttle and eases it closed.
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Old 10-06-2010, 09:31 AM   #8
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Quote:
Originally Posted by fooger03 View Post
Do I need to replace my alternator?
When my alternator was bad, when I'd turn on my headlights the voltage would drop from 13.5v and dip into the low 12s...then it would gradually lower the longer I sat at idle. Now with a new alternator, the voltage stays at 13.8v at most conditions and drops to 13v with all accessories on.

I'd say yes. Like you, I started using the voltage dwell correction table as a bandaid until I figured the alt was the problem.
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Old 10-06-2010, 06:46 PM   #9
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Thank you!
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Old 10-12-2010, 09:23 PM   #10
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Last Tuesday: Ordered alternator from mazdamotorsports.
Monday: While out shoping, alternator gave up the ghost. Started the car at one point during the day and got a funny seatbelt buzzer, looked at the dash and the charge light was fully lit.
Today: Drove the SUV to work today, alternator was on my front porch when I got home. Went to install the alternator. If it wasnt for the additional work of removing the undertray and getting around my intercooler pipe, there would be nearly no work at all, holy **** it was easy. Easiest alternator replacement I've EVER done. Started the car.

14V at idle now, SWEET! Poor low-rpm performance is gone. Car no longer even thinks about dipping below idle with headlights and A/C compressor on. Drops down to about 1200 RPM, slows dramatically, and settles down to 850.

Again, thanks for the timely input!
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