The Mitsubishi Pajero Owners Club®

THOMSONS · Newbie Joined: 21 Sep 2006 Posts: 3 Location: STOURBRIDGE

HELP PLEASE.
I HAVE A 3.5 V6 WITH A GAS CONVERSION. A WHILE AGO I HAD A BACKFIRE WHILE RUNNING ON GAS. I'VE SINCE HAD THE GAS SIDE SORTED OUT AND IT RUNS FINE, BUT THE PETROL SIDE IS SOMETHING ELSE. I'M FAIRLY SURE ITS THE AIRFLOW METER THATS SHOT. THE LOCAL DEALER SAYS HE HASNT GOT THE RIGHT CONNECTERS TO TEST IT AND YOU COULD HEAR HIM SMILE WHEN HE SAID THE PART COST NEARLY £520+VAT. Q1, IS THERE ANY WAY OF TESTING THE AIRFLOW METER. Q2, IS THERE ANYONE WITH A 3.5 V6 LOCAL TO ME THAT I COULD BORROW THEIR AIRFLOW METER TO TEST MY ENGINE. Q3, IF IT IS THE AIRFLOW METER, WHERE CAN I CAN ONE CHEAPER THAN £520+VAT. I'M REALLY HAVING TO GROVEL TO THE BANK MANAGER (WIFE) TO GET MY MOTOR FIXED. ANY HELP/ADVICE WILL BE GREATLY RECEIVED. THANKS STEVE.

Google · Sponsor

ahalton · Posted: Thu Sep 21, 2006 21:51 Post subject: LPG

Your probably right with the airflow meter, when you get a back fire it usually takes half inlet with it.

If you have a single point LPG kit installed, and bare in mind you shouldn't on the 3.5, the best bit of advise is to leave the jubilee clips loose on the airbox side of the inlet, it will probably happen again.

As for the airflow meter ask www.japarts.co.uk they can source parts.

They need all the usual info like chassis number, model, year, etc.

I guess I'm too far away for you to borrow mine, but if your passing more than happy to help, maybe I could borrow your PTU, to check something on mine Wink

Andrew

Ivor Green · ****** Joined: 07 Mar 2003 Posts: 1944 Location: Coventry

I was told by a gaz engineer to remove the aloy honycomb and this alows the odd pop back without dammaging the sensor, I hve also seen a sprung loaded flap on the oar box that works like a one way valve ,if it pops back the flap lifts and alows the pressure to vent to atmophere ,

more x 4 · Posted: Thu Sep 21, 2006 23:38 Post subject:

got two here at the moment you could borrow,but i guess i'm too far away too Rolling Eyes

Ivor Green · ****** Joined: 07 Mar 2003 Posts: 1944 Location: Coventry

James are yuo running a parts lending library ?

more x 4 · Posted: Thu Sep 21, 2006 23:42 Post subject:

looked like a mitsi dealers today,4 parked outside Laughing

wayne rang me back mate,all sorted i think Wink

Ivor Green · ****** Joined: 07 Mar 2003 Posts: 1944 Location: Coventry

what wayne ? oh my technician

more x 4 · Posted: Thu Sep 21, 2006 23:54 Post subject:

yes mate,welsh wayne. really nice guy Wink

ahalton · Posted: Thu Sep 21, 2006 23:58 Post subject: Welsh

Can you keep it on topic please, you'll get shouted at now your not green Rolling Eyes

Andrew

more x 4 · Posted: Thu Sep 21, 2006 23:59 Post subject:

like i care Twisted Evil

ahalton · Posted: Fri Sep 22, 2006 0:01 Post subject: What

Eh

I was careful - only two Crying or Very sad

Some welcome that is Shocked

Andrew

Ivor Green · ****** Joined: 07 Mar 2003 Posts: 1944 Location: Coventry

If James was about to be shot on a fireing quad yuo can imagine him saying " bring it on and only use blunt bullets i love the pain " yuo are mad as a fish but I love yuo mate .

Bush · Posted: Sun Feb 12, 2012 7:10 Post subject: Pajero 3.5L NM 2000 backfire on LPG

I bought this car in December and the owner did not tell me that it had backfire problem when running on LPG. (Suck and Learn!) So I am new to this problem. (Have had an automatic 1982 Mercedes Benz 380 SEL running on LPG without any backfire issue. It simply dies if on LPG when in slow traffic). Back to Pajero. The air filter box must have blown before I had the car because all the clamps are missing and the cover is kept down with a rubber strap with a hook at each end. The car runs fine on petrol (except for the consumption). It also runs very well on LPG on highway. The engine is very quiet. The backfire happens only when on LPG if the car feels 'under-powered', that is, it happens to be in a higher gear than the speed demands (e.g. slowing down suddenly in 3rd gear due to uphill slow traffic) and if the accelerator is pressed too quickly. Bang it goes! I am unable to check if there has been any damage to the sensor.

I have acquired a 'backfire protection valve' on eBay. It is a spring loaded flap that will open to release the back pressure.

I ask: Has anybody installed such a valve? Where is it installed? Can I install it in the top centre of the air filter box cover (where the back pressure tends to lift the cover off)? Should I use some kind of rubber gasket with it? And the last question. Is it safe to do so? I mean, the release of back pressure would not be a fire risk? Thank you.

Bush · Posted: Sun Feb 12, 2012 7:15 Post subject: Pajero 3.5L NM 2000 backfire on LPG

I should also mention that the local mechanic (not a LPG mechanic) says that the left exhaust manifold has a crack in it. Can that contribute in any way to the backfire problem? I plan to replace both the exhaust manifolds with extractors but do not have a budget yet (A$800). Has anybody installed extractors on their Pajero? Any gains or pains?

Pajero Stue

HI all,

So I have been reading everything I can about an NM Pajero LPG vapor mixer backfire. I have had the car for a while and ever since the timing belt was done by the previous owner, it would blow up the air box many times a day. It is a 6g74 Exceed.
This was mainly when accelerating under load. Normally taking off from a roundabout of after a right angle corner etc.
I thought I had better get to the bottom of the problems. I am doing this so someone in my shoes someday can stop pulling their hair out and rectify a very frustrating issue.
Having back fires / front fires like this shows there is an issue somewhere. A mixture of gas and air in to an engine is a simple process that really cant have too much go wrong with it. Rich or lean is about the only thing that changes. My car has a OMVL R90/3 mixer, and a Gastec FP32 controller.
Anyway, this is what I did.
I checked the compression. I cant remember the values but they were all similar.
I replaced the spark plugs - numerous times with different varieties. - Still backfired
I looked at the leads at night and could definitely see cross firing between the plug leads. I changed them with new NGK leads and thought this is obviously the issue. - Still backfiring (although less I think)
I wrapped the leaps in EPDM rubber of about 1.5mm thickness - Still backfiring
I took the head off as I thought it may be the valves leaking. I re-seat the valves and redid the timing belt to go back to square 1. I also did the valve stems seals while I was there. - Still backfiring!
I changed the crank angle sensor - still backfiring
I bought the 5mm lead holders and spaced the leads so they were not touching each other or any metal by at least 1.5mm. My plugs were re-gapped to .9mm as most people recommend as I thought the path of least resistance would be through the plugs. - Still backfiring (although less I think)
I rebuilt the OMVL mixer with new seals and diaphragms as I was thinking that a lean mixture in a hot engine may be the cause. - Still backfiring
I re-programmed the Gas controller - Still backfiring

Now, I was close to giving up but thought that the gas/air mix shouldn't spontaneously combust. Even when hot. It would need an ignition source. After re-seating the valves and fixing the cross fire, I was struggling to see what it could be. I started thinking it may be the throttle controller or something like that giving off a spark. This is like looking for you missing phone in the fridge as you MAY have put it in there. We have all done it, and I bet it has NEVER been in there...

My last resort was then to go back in to timing (thinking it may be too advanced). Also replace the O2 sensor.
My airbox at this stage was half plastic, half silicone and an OKY strap. The aluminum honeycomb in the MAF sensor resembled a ball of Alfoil, which made life very hard in seeing how the engine was running. I was constantly trying to straighten it out as best I could. They always run rough without the comb to change the air from a turbulent flow, to a laminar flow across the diode.

I only had a few booms left until the airbox was no more.

Before I looked at the timing again, , I went and bought the cheapest set of plugs I could find and I re-gapped them to .7mm. I was clutching at straws at this stage. (Autolite 3924)
Anyhow I put them in and the backfiring stopped. Well it stopped for about a week and I had 2 booms in this time. I had found something that had a very obvious change.
I then re-gapped the platinum plugs I had in previously (Autolite APP3924) to .6mm and have been backfire free for a couple of weeks now. It starts on gas and runs fine.

Now I dont know why the plugs need to be gapped from 1.1mm all the way down to .6mm but it seems to have solved my issues. The only thing I want to do now is replace the O2 sensor which is coming via ebay.
The car has over 350 000 kms on it so the engine is tired.

I hope this helps someone one day. As everyone says, start with the leads and plugs. 90% of the time, this is the issue. Don't be scared to re-gap the plugs down to .6. I dont know if there is anything detrimental in this, (or even lower), and someone please chime in if you can see anything.

Good luck