80 series 4.5 petrol/lpg missing on petrol

[jiffjaff]

hi my 80 series vx auto 4.5 petrol with lpg conversion has started missing quite badly on petrol and seems low on power when running on both but sounds to be running on all 6 on gas anyone have any ideas on what this could be ?

 

[karl webster]

Think my mate had same issues and quite sure it wa the lamba sensor on the downpipe.

 

[jiffjaff]

hi thanks for the reply
is that a case of remove and replace or clean up and replace ?

 

[karl webster]

For the sake of 60pounds id just replace it. By the time you have got the old one out cleaned it up if you can do that.Then refitted it to find no better the time would be better save by doing the job once. See if anyone else comes up with anything but that was my mates issue. He had swapped a few other bits before that but it stayed the same.

 

[jiffjaff]

also do you know if there is any easy power increase for these motors and is it worth removing the cats as running on lpg ?

 

[karl webster]

I really wouldnt know. They may do a power upgrade. Jon w may know on here.

 

[jiffjaff]

ok thanks .. do these lamba sensor's normally come out ok or are they usually an ass to get out ?

 

[OG.]

I've never had a problem removing them. Just use a decent quality ring spanner (22mm from memory)

 

[jiffjaff]

I've never had a problem removing them. Just use a decent quality ring spanner (22mm from memory)

thanks og do you think this will be the prob with missing and power loss ?

 

[OG.]

Quite possible. Could also be the MAF. Had that issue on a Volvo. Easy checked by unplugging it and running with it disconnected. You may get an engine management light on doing this.

 

[jiffjaff]

MAF what is that when its home ? and location ?

 

[karl webster]

Air flow sensor? on the intake. If you want to try that first as my mate did i could send one out if you cover postage to test it. Was lamba with mate though.Easy to take out.

 

[jiffjaff]

ok mate will have to take it out can they be cleaned and replaced or need to be a new one ?

 

[karl webster]

Ive sold second hand ones a few times. Think they are fairly expensive new. Cant be cleaned i dont think.Not up on the petrols at all. Deisels far easier and very simple

 

[jiffjaff]

is there no way of overide them or disable them to see if its the fault ?

 

[karl webster]

Now im guessing here so someone jump in if im wrong. The Mass Air Flow sensor is there to pic up the amount of air going into the engine and i expect it tells the ecu what full needs going in to run right.Wrong mixture = rough or poor running.

 

[OG.]

As Karl said the MAF tells the ECU how much air is entering the engine. They work in a couple - some work by having a vane which is sucked by the engine against a spring. The distance it roates is the amount of air being drawn in. The more recent types work on a hot wire which is cooled by the air flowing over it. If the signal is bad teh ECU thinks it has more or less air than is really there. It then compensates by adjusting the mixture which if it goes too lean or rich will cause a misfire and reduced power. If it doesn't get a signal from the MAF it uses air temp and a default value to 'guess' the air being used. As the guess is usually pretty reasonable the engine will run better without a faulty MAF than it runs without one at all. Of course the engine knows it has no signal from the MAF and will post a warning light - not a problem if you have a way to reset it. The light will usually go off after a number of good restarts and driving.