ULTM8Z

I’m helping out a thirdgenner with some tuning and we’re trying to trouble shoot BLM’s pegged at 108.

Car is $8D with a ZZ4 and only has minor mods like headers (certainly nothing that would drive the BLMs down like that). Accel 24# injectors which we have the injector constant and correct voltage offsets from Accel put into the bin.

A quick experiment by putting the injector constant at 28 lb/hr had no noticeable effect on the BLMs, which means this is reading extremely rich. All other data looks ok, except for system voltages, where there's a large voltage reading difference between the two reported system voltages.

Here’s the thing... we seem to be getting confused on what seems to be very inconsistent nomenclature between TP and the bin file. I’m using the S_AUJP adx file.

The TP data says the “keyed ignition voltage” is 13.4V at full operating temp. However, the “fuel pump voltage” is only 12.2V.

However, when he checks the voltages with a multimeter at the ECM terminals C16 and B1 for the battery voltage, as well as terminal A6 for keyed ignition, he gets the full system voltage.

The injector “battery voltage” offsets are based on the keyed ignition voltage, unless you flip the flag switch to have it base it off the battery voltage.

So the question is, within the TP domain, what is considered the “battery voltage”? Is it the keyed ignition voltage? Or is it the “fuel pump voltage”.

Also, is the ECM sensing the true keyed ignition voltage off of terminal A6? Or from somewhere else?

ULTM8Z

So I "think" the keyed ignition voltage in SAUJP is the battery voltage here.

When I look at his data with the standard $8D adx file, it lists the two voltages as battery voltage and fuel pump voltage. Assuming the two fuel pump voltages are the same in both standard 8D and SAUJP, that means the keyed igntion voltage in the SAUJP adx file is the battery voltage in the standard $8D adx.

ULTM8Z

As I'm thinking about it....

Using the voltage offset table, the offset for 13.4V is .79 ms, whereas the offset for 12.2V is 1.07 ms.

So if the injectors should be firing at a pulsewidth per the 13.4V offset value, but the ECM is mistakenly firing them according to 12.2V, that's an error .28 ms.

The BPW's I'm seeing are on the order 1.2 ms where this 108 BLM is being recorded. So that's a significant percentage error, like almost 30%.

84Elky

Every AUJP ADX file prior to the latest version of S_AUJP said "battery voltage". That was incorrect (thanks to RBob for the explanation), thus the description was changed to "Keyed Ignition Voltage" to reflect the actual voltage seen and used by the ECM with the key in the Run position.

The ECM reports voltage at the ignition switch because it is representative of the voltage in the system. Battery voltage is well above ignition switch voltage due to voltage drop caused by the car's wiring.

It would seem in your case that ignition switch voltage should be used for injector offsets. But also, it would seem the wire to the fuel pump is too small resulting in the large voltage difference. Both ignition and pump voltages really should be 13.5-14.0v+ assuming 14.3-14.5v at the battery when engine running. And running would be somewhat above idle if the alternator does not have a sensing wire.

But none of the above should have any effect on the BLM issue. Something else of significance is causing that problem. Send me a log file and I'll be glad to look at it. You should have my email address.

ULTM8Z

Thanks Elky.

Tunercat still has the "battery voltage" nomenclature in it, so then in reality it means keyed ignition voltage.

84Elky

Yep! Only voltage after switch is in Run position is reported.

Can prove it by starting to log with key off and you'll see that no voltage is reported (will generally report 0.4v). Turn on key and will see voltage reported. Measure voltage at battery at this point while not running and ECM voltage will be lower due to wiring voltage drop. Start cranking and you'll see cranking voltage until it starts and when running, keyed ignition switch voltage will be reported. This simple process shows key-on voltage drop: battery .vs. across wiring, while not running and running. Desirable always that the difference be as small as possible.

Can also prove it's ignition voltage by placing volt meter across battery terminals while running at 1500 RPM. Should see 1+ volt higher than reported by monitoring software that looks at and reports what the ECM is seeing at the switch. HTH.

ULTM8Z

So the injector offset vs battery voltage table actually defaults to the "fuel pump voltage" then.

in tunercat you have to flip the switch to make the ECM look at the battery voltage, or I guess its the the keyed ignition voltage now.

But in the absence of a solution to his voltage drop issue, I flipped that switch in his calibration to get around that problem.

he has yet to report back on the results. I'm hoping that it has a significant effect on the BLMs.

84Elky

The factory calibration defaults to using fuel pump voltage for injector offsets from table at 0x3FA. But as you know the voltage used can be changed by bit 6 of Switch 0x016:
... 0=Use fuel pump volts
... 1=Use keyed ignition switch voltage
Generally want to use the higher of the 2 voltages to minimize the correction because the correction is added twice to BPW:
... when cranking, during AE, and when running normally
Minimal correction when voltage >= 12.2v

It's unfortunate all the older ADX files used "battery voltage" which leads to much confusion. Again provable it's NOT battery voltage per post #6 above.

Not sure what you mean by flipping the switch in Tunercat. I assume you mean flipping b6 referenced above.

ULTM8Z

Yeah, the b6 bit as you describe above.

On my car, I have it set to run off the "battery voltage", although my two voltages are still within 100mV of eachother.