LPG Tuning

[bad4u]

I just converted my 86 chev 1/2 ton 350cid 4wd to liquid propane, 425 mixer, model E converter (no computer) I installed a 1 wire bosch O2 sensor, connected a digital volt meter and I can adjust the idle mixture to about .5v, but cruising down a flat road at 50-55mph It runs about .18 to .20v. Under excelleration voltage jumps up to .90v. From my research I understand that it should be at approximately .55v for optimum air:fuel ratio. Shouldn't the air:fuel voltage be aprox .50v at 50-55mph cruising speed? Seems to run really good, but being the perfectionist that I am, I really want it RIGHT. I would appreciate any information anyone has to offer.

Timing spec. 10deg initial 28deg total

 

[franzh]

Disregarding the specifics of your application, and due to the O2 sensors designed voltage output, you will never read .550 steady volts. The shift knuckle starts around .400 up to around .600 where it levels. Running at .18 to .20 at cruise means you are running lean, while at load .90 is rich. The fact that it shifts back down means that the airvalve profile is about correct. Due to the mechanical nature of the parts, you will never get the same readings twice in a row. That system is very sensitive to fuel blends, temperatures, and ambient conditions. That is why open loop fuel systems will never meet modern emission regulations.
Franz

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[bad4u]

Thanks for your reply. How do I remedy the lean condition at cruising speed? Can I reshape the cone inside the mixer? What are my options? also, does the converter mounting position have anything to do with it. As of now it is horizontal over the top of the right hand valve cover.

 

[franzh]

The vaporizer position has no effect. There are three gas valves you can select, the stoich model, a lean model, and a rich closed loop model. Contact your propane supplier.
Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rdd48856]

You should upgrade to closed loop...

 

[bad4u]

what is involved in a closed loop system ?

 

[franzh]

Locating an electronic fuel control unit, installing an oxygen sensor and related wiring connections, tuning the system for proper mixture control.

Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[marcdeluca]

I have put closed loop systems on a few GMs. go to

http://www.autotronics.com,

read about the 5952 controller. They work great. You set it a bit rich, then the controller leans it out according to the O2 sensor. It uses a pulse width modulated solenoid to control vacuum on the atmosphere side of the regulator diaphragm. You can put an analog voltmeter across the solenoid and watch the module adjust the mixture for you. I leave the meter on the floor so that I can watch it whenever I want. I have this controller on my '72 Impala.

 

[btrueblood]

Marc,

your link takes me to a "carnav" site - any idea how to get to autotronics.com?

 

[franzh]

Try

http://www.dualcurve.com.

The name Autotronics has been sold when the company was bought out about a year ago.

Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.