1992 240sx... getting worse MPG after install HHO - Fuelly Forums

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Old 10-07-2008, 07:48 AM   #1
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1992 240sx... getting worse MPG after install HHO

1992 240sx 2.4L with 2 cells injected after the air cleaner. In fact, it was inject using a T at the fuel vapor return line. originally, the fuel vapor return line is a 5/16" hose which get connected into the large plastic vaccumm pipe. So now I put a T there to inject the HHO.

Firstly, I wonder if that is the best place for it.
Secondly, I got 26mpg, a 25% increase on the first 60 miles try (used to be be 20mpg, without HHO).

NOW, I am getting very bad mileage, only 16mpg.

I have a MAF enhancer installed but not using it at test, because it is sluggish at every starts.

Can someone give me an idea of what I am doing wrong? I know there has to be something wrong and I am missing something here.

Thanks,
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Old 10-07-2008, 08:18 AM   #2
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Your initial result was fine, but once the computer got used to the new operating parameters of the engine it realized it was running lean, so it upped the a/f ratio to bring it back up to par.


Nothing wrong. That's why people running HHO have to fool all sorts of engine sensors. A common mod to even things back out is to buy some spark plug anti-foul adapers at your localauto parts store, and drill them out with a 1/2 " drill bit. Then remove your o2 sensors, and screw the modified adapters in the exhaust, then put the o2 sensor in the adapter. This holds the sensor somewhat out of the main flow of the exhaust and will make it read richer than it really is which will help with the HHO running.

Personally I haven't tried any of this yet, you need to take extreme care when leaning out an engine. Too lean and you risk blowing a hole in a piston.

-Jay
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Old 10-07-2008, 08:25 AM   #3
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Your initial result was fine, but once the computer got used to the new operating parameters of the engine it realized it was running lean, so it upped the a/f ratio to bring it back up to par.

Nothing wrong. That's why people running HHO have to fool all sorts of engine sensors. A common mod to even things back out is to buy some spark plug anti-foul adapers at your localauto parts store, and drill them out with a 1/2 " drill bit. Then remove your o2 sensors, and screw the modified adapters in the exhaust, then put the o2 sensor in the adapter. This holds the sensor somewhat out of the main flow of the exhaust and will make it read richer than it really is which will help with the HHO running.

Personally I haven't tried any of this yet, you need to take extreme care when leaning out an engine. Too lean and you risk blowing a hole in a piston.

-Jay
Yes, I forgotten to let you know that I have an O2 extender installed. So you are right. The ECU caught on to the "too lean" and make the a/f ratio rich again to get back.

Anyone with other suggestions? Please help.
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Old 10-07-2008, 08:44 AM   #4
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What's your normal mpg for your car without any mods? My wife's car is a 1992 240SX- see the gas log on the left.

It will get 34-35 mpg on the highway with 40 psi in the tires (no other mods). Town mpg is only 25-28 mpg.
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Old 10-07-2008, 08:50 AM   #5
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What's your normal mpg for your car without any mods? My wife's car is a 1992 240SX- see the gas log on the left.

It will get 34-35 mpg on the highway with 40 psi in the tires (no other mods). Town mpg is only 25-28 mpg.
Very impressive, I wish I get that kind of mileage. Without HHO, I am getting only 20mpg. Maybe there is something wrong with my car.

I calculate the mpg by topping off the tank, then drive, then top off again. mpg = miles driven / gallons of gas bought at top off.
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Old 10-07-2008, 09:00 AM   #6
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It still runs well- and has over 265,000 miles. The engine has never been taken apart.

Be sure that none of the brakes are dragging and that the spark plugs don't look black with soot (this means its running too rich). You might also want to check the spark timing.

Has your plastic spoiler wing on the hatchback rusted off yet? Mine was always garage kept, but it came off about 4 years ago.
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Old 10-07-2008, 10:12 AM   #7
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Not sure about that car, but did it come in automatic? If yours is auto and his isn't that could explain such a large discrepancy. Otherwise I'm not sure, that's a big difference. Definately jack up and give the wheels a spin and see how good they spin. Check your plugs to see what kind of A/F your computer is giving you now.

You may have to fool the ECU more with an EFIE. For now you could try unhooking the battery and waiting a few mins and letting the computer reset and see if it 'learns' better now. That was always something I thought I'd try after installing HHO.

You might also want to check your HHO, not sure what kind of catalyst you're using or how much you bench tested, but it's common for the electrodes to erode or the solution to change and not work as well. Make sure you're seeing just as many bubbles as before, etc.
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Old 10-07-2008, 12:29 PM   #8
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Not sure about that car, but did it come in automatic? If yours is auto and his isn't that could explain such a large discrepancy. Otherwise I'm not sure, that's a big difference. Definately jack up and give the wheels a spin and see how good they spin. Check your plugs to see what kind of A/F your computer is giving you now.

You may have to fool the ECU more with an EFIE. For now you could try unhooking the battery and waiting a few mins and letting the computer reset and see if it 'learns' better now. That was always something I thought I'd try after installing HHO.

You might also want to check your HHO, not sure what kind of catalyst you're using or how much you bench tested, but it's common for the electrodes to erode or the solution to change and not work as well. Make sure you're seeing just as many bubbles as before, etc.
Yes, mine is an auto. That would have explained the difference. However, a 2.4L I4 can hardly get anything in the high 20's, not to mention 30's. There is something else.

As for my 240sx, I thinking maybe my EGR valve needs a clean job.
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Old 10-07-2008, 01:26 PM   #9
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Yeah- the transmission makes a big difference- my 240 is a 5 speed. Gearing on the 5 speed is OK- about 2600 rpms at 60mph in 5th gear.

The rear wheel drive is a real pain in snow...
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Old 10-08-2008, 06:04 AM   #10
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The rear wheel drive is a real pain in snow...
Heh, try a 4k lb automatic RWD cop car. There's hardly any weight on the rear wheels and you can't slip the auto real well and 300lbft torque or so at idle and everywhere else just brakes stuff loose easily. I basically sit at the bottom of hills and go nowhere. One time I made the turn and there was a hill and if I stopped I know I'd not make it but if I gave more power I'd spin out. Some how it stayed angled at about 35 degrees to the road for 2 blocks as I scared lots of people trying to shovel their cars out. But I just concentrated on my foot and made sure to not give too much or too little and aimed the front a little in the other lane.

Man I miss that car.
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