Problem with 2000 Mitsubishi Challenger 3.0 V6 LPG

Howdy,

Was hoping to glean from some experience.
Recently, the challenger has been 'backfiring' on LPG not from exhaust but through the cold air intake box. No issues with vehicle apart from this and went fine on petrol as well.
The first one blew out the honeycomb gauze from the maf sensor and loosened the clips holding the air box together.....
No biggie, all still worked fine. The LPG install is fairly recent but I don't suspect anything there as it's done over 10,000 kms since install with no issues.
I hoped it was a one off..... but no. Funny thing is there was no apparent further damage occuring.... it is an issue i need to fix. I took the engine cover off and realised what a job it is to get to the plugs and leads..... the plugs (double platinum) were supposed to be new from a repco service 20,000 kms ago and they fitted new leads too. That service was just before I bought the car but I have the service report.
Another issue now also is it hunts on petrol- idles and drives eratically. On petrol, it seems to test drive ok with the maf sensor unplugged with only an occasional struggle.
So, I need to fix both issues, the petrol one I suspect has been caused by the backfires.

Cheers.

G'day FF

I won't be much use to you here, but my thoughts are, your gas is runnen a tad too rich, there should be an adjustable knoby thing for lean/rich on your gas unit!
you may find that the air box boom screwed the filter? try taken the filter out and take it for a quick run?? if the symptoms have gone Just replace the air filter!

Restricted air flow is a common problem!

Cheers
Chris.

To run on petrol don't you have to retard the distributer by 10 deg?

G'day FF I had a similar problem with my old V6 fouruner. The gas ring was fitted before the sensor. What we ended up doing was to get a new gas ring to fit at the inlet manifold so gas is entering strait into the manifold. No more backfiring... Hope this helps... PS mine actually blew up the air box-final straw...

Cheers.

Mike.

If i could get a hold of the mechanic who installed it, I am sure he would say "electrical'

Howdy Mike, Gas collar is right up near (before) the throttle body. Had issues in another vehicle after 120,000 perfect kms on LPG, turned out was the leads. Had changed the sparks and then had an issue 300km later so thought was a dodgy spark plug, after changing sparks again then tried the leads.... all fixed! The mechanic had said then most likely electrical, start with plugs... then leads and so on.... costly and a bugger!

I suspect the backfires are electrical again but they were all changed 20,000 kms ago.... maybe a bit of carbonisation on sparks after being a full time petrol going to mostly LPG with only a brief run here and there on petrol.

Cheers Someday, but it runs fine on LPG (apart from the chitty chitty bang) and i suspect the maf sensor as it' seems to run nearly right when the maf is unplugged. It does need a new air filter from the scorchings but air flow doesn't seem to be retricted due to running ok on LPG and Petrol with no maf.

ARK, all electronic, has its own gas computer which switches off when on petrol.

With platinums and expensive leads.... and a painful place to install.....
I was happy with the vehicle till now, not like holdens being easy to work on....

Cheers all, FF.

No expert here, but I have had LPG vehicles for over 30 years now.
Sounds like you're talking about pre-igniting there. Backfiring is in the exhaust section, pre-igniting in the intake section. Common causes are unburnt fuel in the intake section that ignite, causing the filter box to blow-up. The explosion can cause the maf sensor to blow, which will only effect the petrol side and not the LPG side. Unburnt fuel in the intake can be caused by fouled plugs and tired leads. If you can get to the leads, stick an ohm-meter across them and wiggle them. They should have anywhere from 2k to 20k resistance and not be effected by the wiggle. Incorrect timing can also cause pre-ignition. Rule of thumb is to increase the timing by approx 10 degrees for LPG but sometimes this makes the petrol ping under load, and also gives bad petrol performance, so it's a bit of a trial and error to find what best suits your needs. Vaccum leaks and rich/lean mixtures are also possible causes. It's a process of elimination so start somewhere and hope that you find the culprit.
Cheers

Hi FF
To solve the problem if you like the car just get gas injection fitted.Ive had this issue on a couple of cars.Check you dont have an air leak around the intake manifold and hoses etc causing misfire.Your Maf sensor has been damaged take it out and check visually causing it to run badly on petrol.
The taxi drivers with Vn's used to fit a section of wetsuit arm after the Maf sensor which would prevent damage to their air boxes and sensor it was a common problem mostly ignition leads.They need replacing every 50,000 on LPG vehicles with special ones designed for LPG.Gas plugs should also be fitted.
Steve

Only going on my own experiences, and I've had a few boom air box's runnen on gas!

It was always caused by the gas running too rich?? spose to be air in the filter, not a build up of gas fumes!
Was never a problem with the old style gas units with there separate air filter!
Can't see how a dodgy lead or plug could be the cause? a hot spot on a valve would have better luck!

Just my opinion

Cheers
Chris

Howdy Deutran,

Will consider injection down the track, can't quite afford it at the moment unless i sold the magic wand....
i blew up around 3 airboxes on the VY and have a reverse dent in the bonnet cause of it....
wetsuit arm good idea- no hard points like the occy strap to damage bonnets with.....

On further inspection, found a leak on the intake at the back, seems a hose is missing from the rocker breather outlet to in pipe just before gas collar. I don't know whether that was missing from the recent gas install (around 20,000 km ago....) or whether it blew off with the first backfire.
Do you think that would cause any issues? ... why is it so, in cadbury chocholate's mad professor accent?!

Can't see any damage to maf sensor but it is basically only a resister sticking out in the airflow
Tried to get a 2nd hand MAF today, but wreckers had none. For the record, a 3 litre V6 magna maf sensor is a different size and different plug..... have to wait to get to the big smoke in the new year.
Have heard of gas plugs- just loading a lpg bosch catalogue now. Standard oem plug is already double platinum around $22 each x 6

The leads shouldnt be tired after only 25,000 k but once i manage to get to the plugs, it's all getting changed as it looks like a job i don't want to do again shortly.

Will keep you informed.

Cheers all for the help and wish you a happy new year.
FF

someday wrote:Only going on my own experiences, and I've had a few boom air box's runnen on gas!

It was always caused by the gas running too rich?? spose to be air in the filter, not a build up of gas fumes!
Was never a problem with the old style gas units with there separate air filter!
Can't see how a dodgy lead or plug could be the cause? a hot spot on a valve would have better luck!

Just my opinion

Cheers
Chris

Cheers Chris, was the leads with the VY. The VR always was risky putting the foot down a little fast..boom, was the same with the VY, a bit of foot or in most cases the cruise control grabbing too quickly after a spped zone change off the highway...
Mechanic checked the gas sytem and exhaust levels with sniffer and said was all ok.


While I can't get back to mechanic at the moment and i am sure he is on holidays anyway, it's all ecu computer and solenoid controlled

hi FF we had a xf ford that would back fire then one day it blew a hole in the air intake hole and the lid of the air filter box took it to my mechanic and after much time searching he found it was a dusty computer relay i think you would say the size of a rego sticker that i never new the car had replaced and fixed the problem cheers Terry

FF,

The cause of your backfires could be any one of several reasons, not always easily recognised, your vehicle has an ignition system using coil packs involving a wasted spark factor...not unknown for this to cause backfiring if a coil develops a problem.

H.T leads can contribute to this if damaged (high resistance), even if leads are run parallel to each other a spark can be induced between the leads (bit like the operation of a transformer) nice and tidy but a problem source.

Rough idle problem on petrol would have been caused by the breather pipe from downstream of the MAF to crankcase being blown off by the original backfire...common problem with GM V6s on LPG.

Suggest you don't fiddle with it but get it back to your mechanic ASAP, he can run the scan tool over the vehicle for both LPG and ULP computers (they both operate off the same engine sensors) and nail the cause quickly, but if you start goosing around with the system you could raise a number of fault codes not associated with the true defect. This will set him off in the wrong direction until he can work out what has happened and what you have done to confuse the issue.

He will have to clear the fault codes and try to get the defect to recur on the road to raise the appropriate fault code/s, if the backfiring is intermittent he may not even experience the defect for himself.

All of this will cost you money, even if you did marry his daughter.

Like him I also have problems with the wanna be's messing about in the hope of saving a bob or two, then whinge when they get a bill amplified by their efforts, incidentally they never admit to fiddling with it first.

Most faults can be quickly located and rectified provided the vehicle is presented as is and not when all else has failed.

Yep! one of the reasons my Nic is "Cranky"

Cheers and Best wishes for the New year to All

back in my day......years ago now. i used to run a colder plug and set a slightly smaller gap than the spec. used to have backfiring problems under load, and sometimes when starting. this fixed my issues, but it was an old carby'd commodore. i would be getting the mixtures checked for a start.as said,there could be many reasons for this, but after mixtures, i would be looking at leads/plugs/coils, then possibly manifold leaks.

cam

dont bring that heap up here coz it will stay broken down--no one up here will work on gas--

Bad enough changing the timing belt and spark plugs on Pajeros-take a third of the motor apart--absolute bullshit and extremely bad engineering..

Get a Diesel and not a mitsubishi..u rarely have problems--sorry

Regards
oneday69

Yep cranky, at least your in good spirits about it.
Taking it back to the mechanic is the last resort as it's a big hike to get there and then get back.... twice...if not thrice.

As for the hope of saving a dollar.... it's a neccessity not a choice.
I know in your eyes, being a retired? motor mechanic that i am just another wannabe that is goosing around, but hey, with the dozen workshop manuals or so for various cars over the years and paying bugger all to mechanics over the years, why would I start now?
I had a 'partial' apprenticeship from my diesel engineer father from around the age of 5. This way i learn something and the bill is all mine. Usually only charge myself a few beers

As for the "rough" idle, the breather pipe doesn't seem to be making a difference to that as it is 'hunting' which is from my understanding the ecu trying to balance out the mixture program due to hopefully the maf sensor being buggered. If i unplug the maf sensor, there is no hunting occuring.
Also the engine light never came on during all the issues, it only came on after i unplugged the maf for testing.
It is my understanding ecu error codes are only generated if the engine light comes on.

I am planning on plugs and leads and a 2nd hand maf and new air filter.... and see how we go eh?

So as for colder plugs, the standard plug for this engine is PFR6J-11, is PFR5J-11 a colder plug? (or does it go the other way...)
The lpg install mechanic recommended a 0.1 reduction in gap size for lpg used plugs. Bosch recommend about the same.

Thanks oneday for the heads up. If i travel outback it would most likely be in a diesel patrol or cruiser, used to brew some bio but being in a alpine climate, it gets hard in winter, literally....

oh biodiesel, being a mechanic, cranky your gunna love that

being a diesel mechanic in alpine area's during cold snaps with folk using non alpine fuel is awesome! sit back an chillax till noon
Yup the diesel should be flowen through the filters again by now

FF with your MAF sensor disconnected, that should just have your donk runnen in bland mode.

As for plugs? a comp check while there out would influence your choice of plug to go back in! good comp all round, you could go one colder for gas but I wouldn't bother! stick with standard plugs, there not the culprit there made out to be! 50k know wuckers!! Had me El-XF XE fords on gas, 100k on the same plugs not an issue!

Cheers
Chris.

hmmm, always wanted a compression tester
it may have to come before compressed air.

yep the old vr, when she pre ignited, it used to pull the power wire off the lpg mixer, pull the map plug out of the sensor, blow up the air box etc
As for plug life though, i find the electrode wears out pretty fast and the vr was pretty fussy about the gap size..... was running 1.3mm v groove plugs standard was 1.5 Tried to go back to standards one day as was all i had and it ran like a dog on lpg.
Put the 1.3's back in till i got new ones. the mechanic said change em every 20,000 on gas. i have found they last up to around 50,000 but then they start running rough.

So what did you put on the bill for "chillaxing till noon" waiting for the diesel wax to melt? Especially as you have all morning to write the story

A lot of challengers have 265/70r15 tyres--problem tyres in the country.

i would change them to 31x10.5r15 more common size tyre...(change all tyres)

just a thought

regards
oneday69

FF,

Wot' me retired, not ruddy likely. Why walk away from an industry that presents a new challenge every day many of my peers that threw in the towel, retired and went fishing are now resting comfortable with an earth doona over them.

Nuh, still reading up, attending study and training courses trying to keep up to date...getting harder though just as I get the hang of something some smart a...rse upgrades the mobile lounge room with more gadgets and I'm off to the races again.

Yup, I try to remain positive about the wanna be's efforts...Hey they make it harder to fix....they make the bill bigger!

Biodiesel....Can't see anything wrong in producing fuel from vegetation sources if done in a properly controlled professional establishment....with chemical additives at production it could be a great alternative.

Biodiesel, sometimes the term applied to running used fish and chip oil through a dunny roll or two and bunging it in your tank......there I have reservations, while the engine may run on the stuff it was never intended to do so. If you would not eat fish and chips fried in diesel fuel why expect your vehicles fuel system to tolerate used oil from the chippy.

I could go on like the old fart that I am expected to be at 75 and a bit years but that would move off topic and would not help with your immediate problem.

Cheers Cranky

So,
Finally changed the plugs and leads. Lead ends on plugs were a bit oily from a previously fixed rocker covers oil leaks.
So all is good now, with a new air filter and a cleaned MAF sensor and a reset ecu and reset TPS.

Performance now is better than ever since i have owned it and I am starting to like it again.

Cheers all for the help.

PS; I would reccomend a toyota or nissan over these as they are easier to work on....

G'day FF

Pleased to hear you have mastered the beastie at last....from my experience when properly sorted out this vehicle can be pleasure to own and drive......Hope everything stays good for you.

Being a bit of a pessimist I feel duty bound to remark upon the recent problems of accessing and changing the Plugs and H.T Leads which would be walk in the park when compared to the fun in store should you have to replace the water pump and/or timing belt.........Thats the catalyst for becoming the owner of a Nissan / Toyota in short time.

Cheers Cranky