A/F goes rich at idle with high electrical load

[clemsgn]

I've got a Buick turbo T with 72 lb injectors, WB O2, that is running well. Charging system is fine at 14.2 avg. measured at the battery or alternator terminal. When it's at idle (825 - 850 RPM) and I turn on most any electrical item (lights/heater fan etc.) the actual A/F goes richer as each item is switched on. My target A/F at idle is 13.5, but it ends up at 10.8 with all accessories on !! The battery voltage on the dashboard in the FAST program shows around .3 volts less than at the battery due to normal losses through the wiring etc. but it doesn't drop much lower than 13.6 with everything on at idle. Why is the A/F going so rich with an electrical load at idle ?
I've read that a voltage drop, at idle can effect larger injectors more than smaller ones, but this much ? The car will still idle at 10.8 A/F but it's a bit rough. Even though the voltage shows 13.6 on my laptop, it still is around 13.9 - 14.2 at the battery when all this is happening. Someone also said somthing about a firmware update that may help, but I don't know ? My ECU says Firmware Rev. GM204C with a date of 1/12/98. I also checked voltage at the back of the ECM terminal M1 (Batt 12v) and at L3 (switched 12v) with the engine off, and it was the exact same as the voltage at the battery.
Anyone have any ideas ? Thanks for any help !

 

[norbs]

Is your wb o2 wiring from the sensor to the ecm, near any sources of high current? ie altenator wiring, ignition wires, battery cables? I' dont know any other suggestions at this moment!

 

[10SV6]

With the firmware date you gave, if the box hasn't been updated, it should be. One of the issues the later revisions took care of was a voltage correction deal that wasn't right.

I've got a SpeedPro box from 9/20/99 in front of me now that has the Firmware Rev. listed as B2BGN4.

 

[davekusa]

Check you map vs AE. There was a post about that same problem. Do a search. The change in MAP when the cooling fans come on (load on the engine)

 

[norbs]

Good thinking dave!

 

[clemsgn]

Thanks for the suggestions guys.

10SV6 I thought I read something on the firmware issue. I'll try calling FAST this week.

Norbs My wiring is not near any of those sources you mention as it runs along the A/C evaporator/ heater core area.

Davekusa I know what you're getting at, but my problem only occurs when "I" switch on lights/ fan etc. I have my dmap noise threshold set at 2 and it will idle fine and stay at 13.5 A/F as long as I (or the computer) don't turn any electrical items on. If the fans kick on, I would imagine the A/F would go richer, but it still has to do with electrical load and not the fact the dmap noise threshold is set too low or to zero. I bet the firmware needs an upgrade. I'll keep you updated on this.

Thanks again

 

[bobc455]

I had the same problem. I got a firmware update, and that helped considerably.

Then with some re-wiring, I got the voltage to 13.8 as indicated by FAST (14.2 at the alt), and that helped the rest of the way. I don't see the problem any more.

I still would like to see some way to make the voltage comensation adjustable, because different vehicles have different voltage charachteristics. Unfortunately, it's fixed in the box.

-Bob Cunningham

 

[clemsgn]

Well I recieved my ECU back from FAST after they updated the firmware. The A/F still goes waaay rich at idle with a large electrical load. The Voltage is not falling off that much on the dash starting at 14.5 and dropping to 14.1. The A/F goes to 10.6 - 10.9 from a start of 13.8 and drops each time I turn an electrical item on. Anybody have any ideas ? I will call FAST tommorrow to see what they say. Thanks for the help

 

[turbosam6]

Does the "bubble" stay in the same cell on the fuel map when the fans or whatever are on? Like dave said, increased load will change things, maybe you could tune it out? I know when my fans kick on, it places a hefty load on the charging system and the engine definitely bogs down. I'm too lazy to check the A/F when this occurs.

 

[bobc455]

What does the dash show for your batt corr%? I found that even 1.6% would make my car irritable.

I'm still not convinced that the FAST has the correct formula for low-voltage enrichment. My car has 36# inejctors, and if yours are bigger, I bet the problem gets even worse.

It almost feels like they are adding 1.6% to the duty cycle(i.e. from 2.0 to 3.6%) instead of multiplying the PW by 1.016 for that enrichment...

-Bob C.

 

[Lonnie]

I can guarantee the voltage offset is not correct as every injector brand/size has a different opening characteristic & the FAST box has only 1 canned setting.

I sincerely hope the next version has an adjustment table like the Gen7. The present FAST system has caused me grief on 2 tunes so far due to voltage correction. I wasn't thrilled buying a $300 alternator to fix a problem caused by a $2000+ computer. Lets see if they can take a hint.

 

[bobc455]

That was definately highlighted in the other thread about improvements that could be included on the next version of FAST. Which, by the way, anyone have the inside scoop how far away that is? It was originally supposed to be done in April 2003 (I think), has the whole project been shelved?

-Bob Cunningham (who probably should have put this in a seperate thread)

 

[davekusa]

I was at PRI last year and they still didn't have it ready for testing. They were talking summer for testing. I think they're having issues.

 

[bruce]

Not to be too obvious, but injectors operate on magnetic fields, and the strenght of those fields and the weight/enertia of the injector components are all critical issues.

Here's a typical table from oem application. The *normal* operating range corrections are critical for having good all around manners. Not to mention that if you sling an alt belt it's nice to not have the engine immediately flood, or go extremely rich.

Also, another good reason for running those nasty volt boosters. While they don't help at idle, they make for reliable/repeatible injector behavior when under load.


*------------------------------------------------------
* F33B TABLE -
* INJECTOR OFFSET VS BATTERY VOLTAGE (ADBAT)
*------------------------------------------------------

F33B0 FCB 16 ; USE 17 VALUE TABLE

FCB 255 ; 0 VOLTS
FCB 255 ; 1.55
FCB 255 ; 3.10
FCB 255 ; 4.65
FCB 255 ; 6.20
FCB 108 ; 7.74
FCB 66 ; 9.29
FCB 49 ; 10.84
FCB 35 ; 12.39
FCB 27 ; 13.94
FCB 21 ; 15.49
FCB 18 ; 17.04
FCB 15 ; 18.59
FCB 15 ; 20.13
FCB 15 ; 21.68
FCB 15 ; 23.23
FCB 15 ; 24.68


Just for grins a second one....

F92:
;Fuel Injector Off set vs Battery Voltage
FCB 16
FCB 37 ; 0
FCB 37 ; 1.6
FCB 37 ; 3.2
FCB 36 ; 4.8
FCB 35 ; 6.4
FCB 33 ; 8.0
FCB 31 ; 9.6
FCB 29 ; 11.2
FCB 24 ; 12.8
FCB 18 ; 14.4
FCB 17 ; 16
FCB 17 ; 17.6
FCB 17 ; 19.2
FCB 17 ; 20.8
FCB 17 ; 22.4
FCB 17 ; 24
FCB 17 ; 25.5

I just wonder by the time the aftermarkets get them really good how close they'll actually be to not being the *easy answer*.

Simplicity is great so long as it's complex enough.