Making the 2007-2008 HHR flexible fuel with a software update
New Member
Joined: 06-08-2015
Posts: 27
From: New Mexico
Flex fuel
I thought the injectors and O2 sensors were different. Stoichiometric for gasoline is 14.7:1 and the O2 sensor being narrow band is tuned for that alone. Stoichiometric for E85 is 9.7:1 and must flow at a higher rate. The higher flow rate required, I believe, can't be met with the gasoline injector even with longer pulse. Are you saying just use a flex fuel ECU and it takes care of this?
Senior Member
Joined: 05-29-2015
Posts: 542
From: Cleveland, OH
Sub'd, definitely on my long list of things to do. Soon as I've got HP tuners, I'll be doing e85 tuning. Also going to change over to the opel injectors and rail. Not necessary but they're 135# instead of 120#.
Last edited by Dbeluscak; Jul 21, 2015 at 01:43 AM. Reason: Can never get the text size right!
Thread Starter
New Member
Joined: 10-19-2011
Posts: 12
From: Monument, CO
Naturally there is labor involved to remove the fuel pump, fuel tank, and swap out the o-rings. Takes me 30-45 minutes currently. But that was on methanol, which we have to buy by the 55 gallon drum. Ethanol is fine, remember, cars have been designed to run ethanol since 2001. I've taken the injector rail apart several times, no flaking or visual damage to the hoses.
2007 definitely comes with smaller injectors than the 2009; however, we've run E85 with and without the 2009 HHR injectors. Here's what happens. If we're on the 2009 FFV injectors, the vehicle fuels and matches the demanded air to fuel ratio. If on the 2007, at full power, the injectors are driven over their duty cycle, which causes them to stay open (no time to close). That leads to a much richer burn, which is safer for the engine, but horrible for fuel mileage. Remember, that's only during WOT, 99% of driving it wouldn't matter for.
Oxygen sensors have the exact same part number, no difference. The FFV 'virtual sensor' in the ECU is what takes care of things.
If fill with >3 gallons, the ECU goes into a fuel relearn procedure.
If Short Term Fuel Trims (STFT) >10% with at E10 [14.2 AFR]. It will jump to ~E20 [~13.# AFR]. It will continue to do this for about 10 miles until it sticks around E60-E75 no matter if you're running E70-85.
Just don't use the ethanol timing tables from GM, give yourself 4 degrees of advancement in the flex fuel spark tables for a proper drive and fuel mileage.
2007 definitely comes with smaller injectors than the 2009; however, we've run E85 with and without the 2009 HHR injectors. Here's what happens. If we're on the 2009 FFV injectors, the vehicle fuels and matches the demanded air to fuel ratio. If on the 2007, at full power, the injectors are driven over their duty cycle, which causes them to stay open (no time to close). That leads to a much richer burn, which is safer for the engine, but horrible for fuel mileage. Remember, that's only during WOT, 99% of driving it wouldn't matter for.
Oxygen sensors have the exact same part number, no difference. The FFV 'virtual sensor' in the ECU is what takes care of things.
If fill with >3 gallons, the ECU goes into a fuel relearn procedure.
If Short Term Fuel Trims (STFT) >10% with at E10 [14.2 AFR]. It will jump to ~E20 [~13.# AFR]. It will continue to do this for about 10 miles until it sticks around E60-E75 no matter if you're running E70-85.
Just don't use the ethanol timing tables from GM, give yourself 4 degrees of advancement in the flex fuel spark tables for a proper drive and fuel mileage.
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Lone Ranger
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Dec 23, 2008 08:20 AM