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LPG going out of tune 

 

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 Post subject: LPG going out of tune
Posted: Sat Jun 23, 2007 7:41 pm 
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Hello people,

I am just wondering if any of you learned folks can explain to me WHY an LPG setup with an ECU, stepper motor etc would go out of tune.

I ask becasue I have noticed that my pajero, after 30000kms on LPG is now starting to slowly consume more fuel. I keep detailed records and it fuel consumption has started to incrementally creep up over the last 500kms with the exact same driving. it uses the OMVL r90 and AEB electronics and

I know I can adjust the convertor but I just don't get why it would need that becasue the ecu reads of the 02 sensor and tries to maintain stioch ...I mean it controls the stepper motor to try to acheive the air/fuel ratios programmed. If that's the case why would any physical change in the actual convertor make any difference e.,g. changes in the diaphram from age etc. Even if the convcertors was oversupplying , shouldn;t the stepper motor compensate for the increase by decreasing fuel flow as it would suddenly detect a rich mixture?

The stepper motor is basically the valve that controls the flow and its activated by what the ECU reads of the 02 .....I don't get why it would ever go out of tune. 02 sensor is only 30000km new too. plugs/filters/leads are all good.

I am about to fiddle around with the sensitivity screw does anyone have any suggestions?

thanks in advance
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Posted: Sat Jun 23, 2007 9:38 pm 
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I also have an au fairlane , which has recently been converted with a gastec system. It has also exhibited an increase in consumption since the day of installation, however I am yet to take it in for the first service.
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Posted: Sat Jun 23, 2007 9:40 pm 
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o2 sensor may be buggerd

 

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Posted: Mon Jun 25, 2007 1:47 pm 
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They do tend to go out of tune, i'll be tuning my Fairlane this week but i'm pissing the stepper motor off.
I done it once before and found i can get more power and better economy by running a straight power valve.
To be honest, i don't really trust stepper motors, my EF went better without it so i'm taking it off the AU.
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Posted: Mon Jun 25, 2007 5:34 pm 
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How would you tune it with just a power valve? A powervalve's restriction to gas flow is constant is it not? How would you determine which setting is adequate?

Dyno? Wideband sensor? you have an OMVL r90?
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Posted: Mon Jun 25, 2007 10:09 pm 
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Your stepper motor could be stuffed (read stuck) or the diaphram has stretched (normal) or has a hole in it. First I would check for problems. Pull the stepper out with the wiring still connected and turn the ignition on. The stepper should cycle all the way in (to find a base line) then out ready for startup.

Assuming OK, pull the rear brass looking cover off the convertor (r90 type). Careful, there is a spring that may want to launch into space. Check the diaphram for pin holes/tears.

Assuming OK, get a pen and paper and count exactly how many turns each adjustment screw takes to seat lightly. Now we can fiddle.

The new school of thought from OMVL is to never use the idle bypass (the small screw). Unscrew the larger (10mm) screw out at least 5 or 6 times until the vehicle will start and run. Now adjust in (or out) until the revs settle, keep going until the idle falters. If you were screwing in this is lean best, if you were screwing out it is rich best. Find the middle of these for a good starting point.

Take it for a drive. Try some full power hill climbing. Try turning in 1/4 of a turn until you start to lose power then turn back out to the best setting. For me this is about 1/2 turn in from the middle setting. If you feel you are running lean, turn out from the middle setting.

Better yet get a dyno turn. But this gets me the same mileage as when it is professionally tuned.

cheers
Scott

 

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Posted: Sat Jun 30, 2007 11:59 am 
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thanks scott,

Some useful information here. Just wonder, when you say to not touch the bypass screw, do you mean leaving it screwed all the way in and just focusing on the sensitivity screw?

I am going to tune this thing tonight.
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