04 Trailblazer LL8 4.2 tune for E85

[gui67]

Hi,
I have just purchased a MPVI2 to tune my 04 trailblazer for E85.
I am used to MS3 tuning, and the parameters here are different, so I don't really know where to start.

I was thinking about changing the injector sizing in the tune, to increase the opening time. So the AFR could be correct. Is this a good way? (Injector const. in Fuel/General)

I am looking for a way to increase the cranking fuel and cold start corrections. But I don't find the parameters to change.

Let me know if you can help me understand a bit the logic in this ECU.

Thanks in advance
Guillaume

[5FDP]

Injector data can not change, it's a set and forget table. You can't just start changing values out of the blue.

If you know the exact alcohol content of the fuel you can change the stoich value to represent that. Then start adjusting the MAF/VE tables or just the VE tables depending on how that computer operates.

Some computer are very limited on what you can change. Very possible that there are no cranking fuel or cold start corrections that you can make. Just be sure you are in advanced view under the EDIT tab to see all tables.

I'd be watching your injector information in your logs, the factory injectors may not be large enough for the 20-25% increase that E85 usually requires.

[gui67]

Thank you for your answer,

Unfortunately, it was already in Advanced mode.

For the Ethanol content, it is 72%.

I did not find any Stoich value or table to adapt. I have an Injector contant in [Liters per Gram per Second]. I imagine it combines the displacement and injector flow, but i am not sure

Are there some explanations in a manual about the fuel calculations, how VE, PE... are taken into account to calculate the injector opening depending on RPM, MAP,...?
The ECU is a P10.

[ScarabEpic22]

P10 PCMs (what you have) were never offered w/FlexFuel capabilities, so you'll have to create a separate tune specifically for E85. If you want to run regular 87/89/91/92, you'll need to flash another tune file in as the PCM can't compensate via a wired or virtual FlexFuel sensor.

On a non-P10 platform, follow what 5FDP said: tune VE then change the Stoich table to match the fuel you're using. It won't be 100%, but it'll be pretty close. Downside here, the P10 doesn't have a stoich table (at least that HPT has mapped).

You may have to hack the IFR (what you were suggesting), but it's definitely not the best way to do it. Unfortunately, you're playing with limited functionality with this PCM so may be the best approach. Make sure you've got your Wideband O2 hooked up and monitoring, then start making small changes.

Have to ask, why are you going E85, is this a boosted application? Otherwise it may be a lot more headache than it's worth, but also could be fun to figure out!

[gui67]

In fact, I would like to switch to E85, because I am in France. E85 costs 0.70€/liter and gas cost 1.70€/liter. Even with the lower mileage, it saves a lot of money.

I have an adjustable fuel pressure regulator to increase fuel pressure. I will also decrease a bit the maximum RPM to avoid injector saturation.

It seems an easy way to increase the opening time of injector is the Injector constant. I will try that and follow AFR. There is a kind of cranking VE table, I will try to adjust it even if it seems that it is already at the maximum value in the stock tune.
However, I still would like to have more precise explanations about how the fuel calculations are done, in order to understand fully the logic between all the tables and parameters and not randomly change values without knowing all the consequences.

[mikequad]

Bonjour Guillaume, je poss?de un traiblazer de 2003. Je suis ?galement int?ress? par l'e85..... Quel r?gulateur de pression r?glable avez vous mont? ??.
Merci