LPG and Exhaust Backfiring - Please Help!

Submitted: Tuesday, Oct 14, 2003 at 09:03

ThreadID: 7807 Views:5049 Replies:5 FollowUps:7

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Gordon

Hi all, Just recently moved out to this great country and bought an 88 Pajero (278k KM's) to run around the countryside with the kids, however I'm having some bother with the LPG system that came fitted to the car. The engine runs as smooth as you like (when running on LPG) however the exhaust makes a 'bubbling' sound whenever I take my foot off the accelerator. When I switch over to petrol the car initially picks up nicely and runs for a about 3 minutes before there is a loud pop from the exhaust.

Within the engine bay it appears that someone has disabled the emissions components. For instance, there is currently no hose from the Air Injection Valve to the vacuum Outlet (this is the thin hose with the one-way reed valve). Also, the 4-Port Thermal Valve (located in the Thermostat Housing) only has one hose attached to it - the others are open! Is there a requirement to modify the emission control hoses when fitting LPG or has a previous owner 'fixed' a more serious underlying problem? I have taken the car to two mechanics however all they seem to do is adjust the timing and charge me a small fortune!

Should I rewire the vacuum hoses? Could my problem be due to the EGR (and other components) being disabled? Any help would be much appreciated as the weather is starting to pick up and we want to go camping!!!!!

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Reply By: Kiwi Ray - Tuesday, Oct 14, 2003 at 09:29

Tuesday, Oct 14, 2003 at 09:29

Hi Gordon
I am no expert on LPG but do know that the ERG needs to be dis abled on LPG powered engines.
If the engine is trying to backfire on the over run on LPG it would suggest that the idle mixture is too lean
Ray

AnswerID: 33701

Follow Up By: Gordon - Tuesday, Oct 14, 2003 at 11:40

Tuesday, Oct 14, 2003 at 11:40

Thanks Ray
I just rang the mechanic who did the last tune-up and he assures me that the 'bubbling' (or gurgling) sound is to do with the exhaust pipe and not the LPG set up (or re-ignition of unburnt gas in the exhaust). Furthermore, he says that the backfiring whilst running on petrol could be due to the carb needing some work done on it as the LPG system is switched off whilst the car operates in petrol mode (this I can understand).

I guess being a new user of LPG I just want to very certain that there are no safety issues surrounding the use of my car.

Gordon

FollowupID: 24219

Follow Up By: GaryInOz (Vic) - Tuesday, Oct 14, 2003 at 18:31

Tuesday, Oct 14, 2003 at 18:31

Just a word of warning, when you are on gas DO NOT start the car with your foot on the accelerator pedal, just let it turn over until it fires up. If you have your foot on the accelerator it can allow ignited gas back into the lpg vaporiser causing a very loud explosion tearing the diaphram membrane inside it. It will be the loudest (like a gunshot) and most expensive ($300-500 repair) backfire you have ever heard....

FollowupID: 24252

Follow Up By: Gordon - Tuesday, Oct 14, 2003 at 18:53

Tuesday, Oct 14, 2003 at 18:53

Thanks for that mate, I'd better brief the wife before she scares herself silly!!!

FollowupID: 24254

Follow Up By: GaryInOz (Vic) - Tuesday, Oct 14, 2003 at 20:18

Tuesday, Oct 14, 2003 at 20:18

Yeah, it's about the easiest way I've seen to give yourself a "seat lift"!!!

FollowupID: 24264

Reply By: Member - Wherethehellawi - Tuesday, Oct 14, 2003 at 11:31

Tuesday, Oct 14, 2003 at 11:31

Is the car still under used car warranty from Car Yard (if you got it from car yard) If so take it back and get them to fix it. It is illegal to disable emission unless you can prove the car meets the standard with it disconnected.Wow! am I cute
If yer ain't fishing, Yer ain't livin
Richard

AnswerID: 33721

Follow Up By: Gordon - Tuesday, Oct 14, 2003 at 11:46

Tuesday, Oct 14, 2003 at 11:46

Richard
I did get it from a car yard and that will be my next stop. However, the car underwent an ACT State Inspection, which it passed, prior to me taking ownership. I presume the State Inspection includes emissions testing? Assuming the car did pass the emissions test will disabling the emission controls affect the car, ie cause it to backfire or is the problem elsewhere do you think?

Gordon

FollowupID: 24220

Reply By: Member - Bob - Tuesday, Oct 14, 2003 at 13:01

Tuesday, Oct 14, 2003 at 13:01

Gordon,
I'd contact the people who did the conversion if they aren't too far away and are still in business. Are you in the ACT region?Bob

AnswerID: 33732

Follow Up By: Gordon - Tuesday, Oct 14, 2003 at 14:55

Tuesday, Oct 14, 2003 at 14:55

Bob
Unfortunately I have no paperwork relating to the LPG conversion and can't tell from the hardware who the manufacturer or installer was. I have managed to find a reputable (albeit expensive) LPG mechanic who is going to look at it for me. The car yard that I bought it from are doing their best not to get involved.

Gordon

FollowupID: 24229

Reply By: Andi - Tuesday, Oct 14, 2003 at 16:45

Tuesday, Oct 14, 2003 at 16:45

Hi Gordon,
Not sure about the specifics but my 60 series cruiser can also do all sorts of weird things (Run on specifically and occasional backfire) on Petrol when hopping about town, no probs on long runs. Once again no expert but I had a "balance pipe" added between the converter and the carby in my vehicle by the LPG guys who I had my old XC falcon converted by years earlier. I have no clear understanding of how this operates but I certainly noticed the overall idle and accelaeration changed for the better after they had done this. Aparently it should have had one all along. All my vaccuum hoses and emission control equipment is still connected and working fine so I guess an LPG specialist who can at least give you 10 minutes of his time to tell you what is wrong, could not possibly charge you too much. But we are dealing with doctors, I mean mechanical technicians here :))
Andrew T

AnswerID: 33756

Follow Up By: Gordon - Tuesday, Oct 14, 2003 at 19:04

Tuesday, Oct 14, 2003 at 19:04

Thanks Andi,
I've got the car booked in for another check-up in a couple of weeks so I'll see what that uncovers (and costs!). In the meantime I think I'll service the ignition system as I understand this can cause problems if not correctly set up. Wish me luck!
Gordon

FollowupID: 24255