3.9EFI running bad on petrol good on lpg

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gooselogan

gooselogan

New Member
Posts
96
Location
Minehead, Somerset
I've just got a new 3.9 V8 disco1 that had starting problems, which I've now solved and it starts on the button everytime.

But, it runs very badly on petrol, smoke coming out of the exhaust, sounds rough and won't really rev past 3000-3500rpm.
However as soon as I switch to lpg it runs lovely and as it should.

I've replaced dizzy cap, rotor arm, leads, checked all spark,dizzy gaps etc. and also replaced the coolant switch. The correct fuel pressure is there and it's fresh petrol aswell.

And now I'm at a loss at what to do now. :( Anyone have any ideas what it could be?
 
We are having the exact same problems with our V8.

How did you cure the starting problems?

When you turn the key on ours it just seems to whine and whine on and eventually it will start then stop. Put it on gas and its perfect
 
i would start with the temp sensor as it is the most coman.
have the ecu fault read as well
could be a faulty afm too as the gas does not use it.
is it a mono gas of multi point gas system?
 
I've already replaced the temp sensor so I would guess it isn't that.

I've done some reading up on AFM problems, will try a few of them tomorrow.

And it's a mono gas system.
 
On the 14 cuz system the ecu holds faults thus changing parts alone will not cause the fault to go away that is why a ecu parameter check is worth the test and a fault clear
Disconnecting the battery will clear faults leave for 1/2 hour before reconnecting but this route is expensive as you will not know what is causing the fault
 
It does have a smaller petrol tank, as in no more than 25 litres, and 4 large LPG tanks so it's clearly biased towards running on LPG. None the less it should still run fine on petrol surely for starting and warming the engine up?

Thanks for the info vogue, I don't have access to fault reader at the mo, by my understanding would disconnecting the battery mean that the fault code would clear and if the cause of the fault was sorted it would sort itself out?

I have had a quick look at the AFM plug and it's pretty loose and doesn't have the clip that normally holds it in place.
 
I'm now back to square one, it isn't starting again, due to me messing about with it.

I had to take the dizzy off and dismantle it to get the bob weights all moving again which they do now, but I rubbed off the marks I had made for the timing so set it all up using the marks on the engine and a screw driver in the cylinder to make sure, so I'm pretty sure it will be firing when it should be.

I also took the AFM off and gave it a quick clean just using some spray cleaner into the hotwire hole. The battery was also disconnected.


There is defiantly fuel there as the plugs were black and wet, so took them out and cleaned them and let the cylinders air to make sure it wasn't flooded. There is also a nice big blue spark when I checked. So I'm now unsure on why it won't start.

Will the air gap for the module in the dizzy make a difference to starting?

Is there something I have likely done without realising that has stopped it from starting?
 
If you are getting fuel at the plugs then the dissy pick up is ok I would be inclined to reset the static timing ensure you are on number one tdc and set the dissy to number one remember the dissy is a scue gear so set it one tooth back to install
 
gooselogan said:
Will the air gap for the module in the dizzy make a difference to starting?
Click to expand...

YES.

Do a search, I have posted a method for setting this before. As mentioned, you will also need to check and set your static timing - this csn be a bit if a faff because of the skew gear but hey ho we all do it!

Have you checked the setting of your Air Flow Meter - again do a search there is info on what to check and how to set.
 
Thanks for the replies, I'm inclined to think its the timing aswell. I shall check it again at the weekend. I did set the air gap according to haynes but I will check that again aswell

For the AFM setting do you mean the screw on top at the back of it? If so yes and I have adjusted it to give out the volt readings that I found on g33 website.
 
Last edited:
rmember the voltage reading is for setting the afm is for idle only after that the afm and ecu control the fuel enrichment so do not set too lean at idle 1.0% on co at idle or 300 ohms resistance when setting the afm with a multi meter on the outer two pins
 
You do not set the afm with the igniton on you do it with the ignition off and disconect the afm plug
Then set to 300ohms resistance on the outer two pins
 
Oh right okay, I followed the guide on RPI engineerings website, I shall do it your way tonight. Will also play again with the dizzy to try get it starting again.
 
Good news is that I've got it running again. Whipped the dizzy out, set the air gap using some paper, put it back, made sure it was set to TDC at no.1 cylinder and it fired up. :D

Also managed to set dynamic timing quite happily so that's all sorted. I also adjusted the AFM. Seems to run slightly better on petrol but still won't rev past 3500, can't see if there is smoke coming out of the exhaust cos its dark. But doing a white paper check behind the exhaust, no sooty crap seemed to be coming out which is alot better than before, will double check tomorrow.

So I'm wondering if an injector is blocked, sound plausible?


I'm not so worried about it running on petrol now cos it starts straight away and the majority of the time it will be run on LPG but it would still be nice to get it running properly on both fuels.
 
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