Mazda Bongo V6. Some slight issues

[Our Bonnie]

Hello, after posting in the ‘tell us your story section’ thought I would post the little ‘issues’ that we have.
It should be noted that our Mazda Bongo ‘Bonnie’ drives perfectly on petrol and all these issues happen in the heat of summer as well as the cold of winter.
Bonnie is a year 2000, 2.5V6 petrol with a Romano injection system 8, converted when we purchased from a well known installer, October 2015.
So:
An intermittent hiccup when driving at constant motorway speed, around 2500-2750 rpm. No problems around town or up and down dale.
Fuel economy down to 14.5 from around 18 mpg
Both of the above problems were solved by remapping. There was a couple of occasions after the remapping when we didn’t use Bonnie for a few days, and the above problems reoccurred. When this did occur, she wouldn’t change over to LPG, and the LPG fuel gauge would stay on for ten minutes, even if ignition keys were removed. Then, when we started her, would change over without any problems.
A loud hum if driving in stop start traffic for a while or climbed a hill quite hard. Goes the instant you switch to petrol, comes back when you switch to LPG.
Have uploaded a video to youtube, may need to turn volume up a bit. https://www.youtube.com/watch?v=vTCO2dhfdJ4
Not sure where it’s coming from…..
A very high pitched whine, sounds like it’s coming from the ECU in the passenger footwell….
The garage have been great but we are 2 ¼ hours away, so any help, very much appreciated.
After reading some other posts, realise that I'm not that technical when it comes to LPG...!

Best wishes and many thanks

Kevin

[LPGC]

The LPG gauge staying on for 10 mins will be due to the engine's petrol system electrical loom staying live for 10 mins after the engine is turned off, not really a problem. The LPG system is powered up whenever it sees 12v at the engine, on some vehicle models all power to engine electrics is turned off the moment you turn off the ignition, on other vehicles the engine electrics are still powered up for a while (or for a while under certain conditions) after you've turned the ignition off... just an aspect of the vehicle.

The humming noise will be coming from your LPG system pressure reducer under the bonnet. Some reducers hum, some don't, some that hum will stop humming with a slight adjustment to it's pressure setting. The noise from a humming reducer can become louder if it is fitted to a vehicle part that can act as a sound board such as a body panel, or quieter if the reducer is isolated by mounting on rubber bushes. If the reducer hums and is fitted without a rubber bush to the bulkhead (body panel / sound board), the noise can seem louder still as the bulkhead is close to the interior of the car. It isn't usual to fit reducers on rubber bushes, only a small minority of types of reducer come with rubber bushes, for other types it can be a bit difficult to mount them on bushes but there is usually no need.

Simon

[Our Bonnie]

Hello, many thanks for the reply, and very interesting. Regarding the gauge staying on, it only happens when she won't change over, so I'm wondering if something else is going on. Hmm.

I'll have a look at the reducer later. I think its under the front passenger seat, with the Bongo being a mid engine (!) car of sorts

Regarding the stutter and fuel economy which improves after remapping, could that be related to an ECU problem?

many thanks as always

best wishes

Kevin

[colin33]

Hello, many thanks for the reply, and very interesting. Regarding the gauge staying on, it only happens when she won't change over, so I'm wondering if something else is going on. Hmm.

I'll have a look at the reducer later. I think its under the front passenger seat, with the Bongo being a mid engine (!) car of sorts

Regarding the stutter and fuel economy which improves after remapping, could that be related to an ECU problem?

many thanks as always

best wishes

Kevin

I'd be interested to know what sort of performance you get while running on LPG Kevin? Is it un-noticeable when it changes over, or is there a slight drop in power?

[Gilbertd]

or is there a slight drop in power?

If there is, take it back and get it set up properly. The old wives tale about getting less power on LPG went out the window when singlepoint systems with a mixer causing a restriction in the intake were no longer being fitted. With a modern system, properly set up, you might notice a fraction of a second difference on a drag strip but you won't notice any difference under normal driving conditions.

[classicswede]

Fit a smaller gas tank if you want a better time on the drag strip

[Our Bonnie]

Well, its been a while since I was here last, but things have improved. Took Bonnie to a certain guy in Plymouth who diagnosed something about the RPM feed being taken from the wrong place, and disabled on the ECU anyway! Result is the stutter has completely gone! The hum apparently down to the reducer not quite hot enough when she switches over. This is only intermittent and doesn't cause any harm...
mpg is a resolute 16mpg..


so far so good!

[LPGC]

I just converted another Mazda Bongo 2.5 V6, runs well.
There are some unusual (Mazda type) aspects to the petrol injection system though, and the usual types of LPG ECU 'Mazda change of injection type leaning controls' don't work on this engine.

I posted this on the other Bongo V6 thread too.