Erratic OBD codes

[Clifford Pope]

1992 240, LH 2.4, LPG conversion with mixer.

I think I have now mastered the various vaporiser adjustments, and have got the car running well on gas and petrol. Idling is reasonably smooth even on gas, and seems to "catch" reliably when pulling up.

So I cleared all the old OBD codes, and out of interest checked again after a run. It showed;

1:3:3 = No signal from Throttle Position Switch
1:2:1 = No signal from Air Mass Meter
1:1:3 = = No signal from fuel injectors

I cleared the codes, and after the next run read them again:

2:3:1 = System compensating for rich, or weak, mixture
1:1:3 = No signal from fuel injectors

After again clearing and rechecking:

2:3:2 = Compensating for rich, or weak, mixture
1:1:3 = No signal from injectors.

These seem to be completlely erratic. Obviously the fuel injectors are working, because the engine runs well on petrol and idles evenly.
I cleaned and re-adjusted the throttle body and stop, and checked the switch was clicking at the right point and giving the correct electrical readings at the contacts.
The plugs look perfect - no evidence of rich or weak mixture, and the earlier AMM "fault" appears to have corrected itself.

So is all this merely confirming the statement that the engine light always comes on with LPG, and is meaningless, or is does it indicate some underlying fault?

[classicswede]

If you think about the fuel injectors are not working - well when you are running on gas anyway. My guess is with the botch dutch conversion they have just used a relay to cut the injectors. If so Idealy you will need to fit a pitagora unit. If it does have a pitagora emulator then you will need to chnge the combination of teh two buttons unit it stops coming up with the injector code.

The mixure issue is no supprise as the petrol system is not intergrated with the gas and non of the petrol ecu adjustments have any affect on the gas fuel mixture. If you had a closed loop gas system then the errors would be minimal. In an ideal world and intergrated injection system is the best set up for this spec car. What you can do is fit an ecu reset relay to clear the errors when you switch off.

[Clifford Pope]

Thanks very much for that detail. It's as I suspected - a basic system that just turns off the petrol is bound to throw up spurious errors.
The previous owner simply removed the bulb, so I was curious to know why.

I suppose the advantage of clearing the codes after every run on gas is so that it gives it an opportunity to show any genuine "petrol" codes that might indicate real faults.

How would I fit an ecu reset relay? Doing it manually needs a procedure of pressing the button, waiting for the indicator to come on, then holding it again until the light goes out.
Perhaps not really worth it. I'll just accept that it's a rather primitive conversion, but it works, so I'll leave it at that.