LPG misfire following MAF sensor exchange

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Stryda
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Joined: Wed Jan 12, 2022 5:25 pm

LPG misfire following MAF sensor exchange

#1 Post by Stryda » Wed Jan 12, 2022 5:38 pm

Hi all.
Mazda Bongo 2Litre Petrol/converted LPG.
LPG installed 2019.
Recently failed MOT emissions with 9.9 CO readings.
Garage diagnosed faulty MAF sensor and replaced, which brought CO emissions down to 0.03.
Following this the car misfires badly when run on LPG. Runs perfect on petrol.
Prior to MAF exchange petrol and LPG both ran fine, just poor fuel economy.
I have spoke to the LPG installer, who advised that if fuelling from petrol was wrong prior to MAF exchange, then as LPG was mapped off those petrol injector pulses, it would all need re-calibrating.
Unfortunately the installer is too far to take back to him.
I spoke to another LPG centre who advised this is absolute rubbish and that it sounds like it has lost it's map somehow.
Can anyone shed some light on this?
I think it is a Romano system, or at least that's what the vaporizer is.
In Leeds, if anyone can recommend someone!
Thanks

Brian_H
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Joined: Mon Jan 23, 2012 12:21 pm
Location: Milton Keynes

Re: LPG misfire following MAF sensor exchange

#2 Post by Brian_H » Wed Jan 12, 2022 8:39 pm

Simon - LPGC is in South Elmsall and would be able to fix it, though he has been quite busy recently. He may well post on this topic shortly, but if not his contact details are on the bottom of any of his posts on here (Username LPGC)

LPGC
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Joined: Wed Sep 29, 2010 6:01 pm
Location: Yorkshire
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Re: LPG misfire following MAF sensor exchange

#3 Post by LPGC » Wed Jan 12, 2022 9:53 pm

Thanks Brian, just read this. As you've said, I am very busy.

Given the circumstances there may be some truth in what the original installer said because the Mazda engines feature unusual fuelling strategies. But that said, if the MAF was bad when they calibrated it it may have been running in open loop mode, in which case they should have realised and informed you the maf was bad. If the maf was working during calibration then fitting a new maf doesn't normally mean it will need recalibrating.

I've got another Bongo to convert myself coming up again soon.

Is the system a Romano sequential system (and if so which one) or is it a mixer system? Or if unsure, do you need to switch it back to petrol yourself if you run out of gas or does it switch back automatically?
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Stryda
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Joined: Wed Jan 12, 2022 5:25 pm

Re: LPG misfire following MAF sensor exchange

#4 Post by Stryda » Wed Jan 12, 2022 10:56 pm

Thanks guys. I know little about the LPG system to be honest, but yes when gas runs out it switches to petrol by itself.
I could do with getting it looked at sooner rather than later, as the bongo garage may charge more to look at it following their work if I leave it too long- though with petrol running fine I'm fairly confident the issue is on the LPG side.
Sounds like you are familiar with Bongo's Simon, if you could find time to take a look it would be very much appreciated.
Brian, much appreciate the recommendation.

LPGC
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Re: LPG misfire following MAF sensor exchange

#5 Post by LPGC » Thu Jan 13, 2022 12:00 am

My best chances of getting available time are on Fridays, if I've converted my few cars for the week and I get ahead that's when I'm likely to get a bit of time but I continue to be so busy that I can't say which Friday I might get time and strictly speaking I'm otherwise fully booked until mid early/mid May. Probably not for at least my next few available Fridays that come up because I've already promised similar to others that want to see me. I recently fixed a BRC system for a guy who first came to see me in May, he worked shifts so he couldn't make a few times that I contacted him to say I'd be able to do it but from this you'll get an idea of how busy I keep.

I suppose you could say I'm familiar with Bongo's.. maybe to a greater extent with the V6 models... but I know just about all the engines and the fuelling strategies. I'll also be very familiar with your sequential Romano system. A Bongo expert probably isn't an LPG expert or fuelling expert and an LPG 'expert' not familiar with Mazda's might not realise the fuelling strategy or be able to set it up as well as the system will allow. Not so much an issue as it is with the V6 Bongo's though, the V6's really do have very strange fuelling strategy, almost the opposite to most Mazdas which are also strange. A lot of Mazda's switch between group injector firing (under high load) and sequential injector firing (lower loads) which is strange and unusual but kind of makes sense, but the V6's are stranger because they run multiple injector squirts per cylinder per intake cycle at low loads (more like throttle body injector strategy than group injection) and switch to sequential injection at higher engine loads, almost the opposite to most of their engines and doesn't seem to make as much sense (emissions at low loads etc) but may be beneficial to driveability and smoothness at low loads during the period between cold engine and warm engine.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

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