v6 petrol running rough.need to eliminate possible causes

[hogggman]

hi all,
since probably the beginning of the year,my v6 has been running a bit rough.not always,here are some symptoms:

`hunting`or `missing`on tickover(tickover when first started is about 1200rpm,dropping to about 800 when warm)

hesitant,or`bogging down`at 2500 rpm/50mph.when i put my foot down there`s nearly always a muffled`pop`from under the bogo,then it`clears`and over 55-60mph all is well again.

emissions were way out at mot in february(mot guy passed it`because it`s on the v5 as a motorcaravan,and emissions don`t apply )

it feels as if it`s `holding back`,not as smooth as it once was.

and this is what i`ve done so far:

new sparkplugs

oil/filter

fuel filter(from 1.6 mazda,but same size/fitment etc)

new air filter

cleaned maf sensor

removed/cleaned distributor cap and contacts

removed/cleaned/replaced all plug and coil leads

replaced lambda/oxygen sensor with ebay universal one

generally cleaned electrical connections,tested vacuum pipe connections etc

one thing that may be worth noting is that my heat sensor on the cat is broken off and missing.i plugged the hole with a small bolt.the heat light still comes on/goes out when engine is started.i have seen these on ebay for 125 quid,but folk on here have said that they are not essential.
i know people like apole and cheffy have been through similar things,but before i start shelling out for distributor cap,rotor arm,plug leads,coils,or even heat sensors or new cat,does anyone have any suggestions?as people may point out,i may have a worn engine as it`s quite tappetty,but it was the same for the mot before,and sailed through the emissions that time,i have done only a few thousand miles and taken care of the engine in respect of servicing,so hopefully it`s not down to engine wear.
any ideas or suggestions?
thankyou
jamie

[kelv]

If your car had an old fashioned carburretor, considering what you have already ruled out, I would have said "air leak " weakening the mixture without a doubt.
Not sure if that is as relevent with injection systems though.
Maybe a cautious spray aroundthe manifold with brake cleaner might show up a change in engine note, confirming an air leak.
That's what I did to a carburated car once, highlighted a leak in one of the gaskets, which , when changed, cured the problem.

[francophile1947]

As kelv says, it does sound like a weak mixture, but I have no idea how a fuel-injected petrol engine regulates it (presumably ECU) What did the plugs look like before you changed them? - they should be sort of coffee-coloured in the middle and black around the edges. If there was no black, it would indicate that the mixture is far too lean.

[apole]

Hi,

You've changed quite a few bits there. Things I can think of:

Can you get the fault codes read anywhere, this will tell you if there are any known errors, say sensors not working etc.

What colour are your plugs after a long run, this will give an idea of how rich/lean engine is running and if any of the pots are not firing properly for some reason.

Outsider but have you ever changed your fuel filter, I did hear a of V6 running badly and the dealer tried loads of things, turned out to be that in the end which was not what they had thought it would be.

If an air leak, there are many hoses on the V6 engine, some of which are quite well hidden. Can you get hold of a stethoscope, that is useful for finding these things.

You can measure the output voltage of the lambda sensor, easy to do, do a google search, the reading should be all over the place but you can see an average.

Has the engine got a good earth connection, maybe the earthing wires are a bit corroded and not helping things.

I'd be leaning towards the HT side of things initially from what you say but have a look at the above things and let us know what you find.

Andy

[kelv]

There was once a gadget called a colortune, which was a transparent plug that screwed into the sparkplug hole alowing the colour of the burning mixture to be viewed.
Depending on what colour it was, you could adjust the mixture to give the right air/fuel strength.
One of those may be useful for diagnostics on a problem like this one.
Don't think they make them anymore, but they only cost a few quid when new, maybe evilbay might turn one up.

[helen&tony]

Hi
Jamie
I presume the Bongo is electronic ignition..can you confirm?...I may have a couple of ideas
Cheers
Helen

[mikexgough]

There was once a gadget called a colortune, which was a transparent plug that screwed into the sparkplug hole alowing the colour of the burning mixture to be viewed.
Depending on what colour it was, you could adjust the mixture to give the right air/fuel strength.
One of those may be useful for diagnostics on a problem like this one.
Don't think they make them anymore, but they only cost a few quid when new, maybe evilbay might turn one up.

They still make 'em http://www.gunson.co.uk/item.aspx?item=1822

[francophile1947]

There was once a gadget called a colortune,

I used to have one of those - great little gadget
Still don't know how you adjust the mixture on a fuel-injected engine though

[apole]

Hi,

Yes the bongo is electronic ignition.

Regarding the colourtune I remember those, they were useful. I'm not sure it would work on the bongo though as the spark plugs are very deeply recessed in the engine and the plug connector is consequently a very deep tube.

Andy

[kelv]

There was once a gadget called a colortune,

I used to have one of those - great little gadget
Still don't know how you adjust the mixture on a fuel-injected engine though

You probably don't ( not without a special tool or an injecti computer or something equally expensive and impractical ) but at least it would show if the mixture was weak
If , of course the recess wasn't to deep to read the colourtune. Mine had an adaptor for recesses, and a tube and mirror kind of set up for hard to view engines.
I used it on a Rover V8, so maybe there is hope of it working on a V6 Mazda, but I have never seen the depth of the recess so perhaps best to go borrow one if poss rather than buying and finding it don't fit.

Pleased to hear they still make them .

[hogggman]

thanks guys,i will go over everything at the weekend and see what i can find.
thankyou
jamie

[hogggman]

hi,
thanks to all who have offered advice,especially mikexgough.i now have an idea what i`m looking for,and need to work through things methodically.
now........does anyone have any pics showing the locations of the tps or crank sensor on the v6?
thanks again
jamie

[missfixit70]

This may help - http://www.lushprojects.com/bongopartsm ... mgno=.html

[cheffy34]

hi all,
since probably the beginning of the year,my v6 has been running a bit rough.not always,here are some symptoms:

`hunting`or `missing`on tickover(tickover when first started is about 1200rpm,dropping to about 800 when warm)

hesitant,or`bogging down`at 2500 rpm/50mph.when i put my foot down there`s nearly always a muffled`pop`from under the bogo,then it`clears`and over 55-60mph all is well again.

emissions were way out at mot in february(mot guy passed it`because it`s on the v5 as a motorcaravan,and emissions don`t apply )

it feels as if it`s `holding back`,not as smooth as it once was.

and this is what i`ve done so far:

new sparkplugs

oil/filter

fuel filter(from 1.6 mazda,but same size/fitment etc)

new air filter

cleaned maf sensor

removed/cleaned distributor cap and contacts

removed/cleaned/replaced all plug and coil leads

replaced lambda/oxygen sensor with ebay universal one

generally cleaned electrical connections,tested vacuum pipe connections etc

one thing that may be worth noting is that my heat sensor on the cat is broken off and missing.i plugged the hole with a small bolt.the heat light still comes on/goes out when engine is started.i have seen these on ebay for 125 quid,but folk on here have said that they are not essential.
i know people like apole and cheffy have been through similar things,but before i start shelling out for distributor cap,rotor arm,plug leads,coils,or even heat sensors or new cat,does anyone have any suggestions?as people may point out,i may have a worn engine as it`s quite tappetty,but it was the same for the mot before,and sailed through the emissions that time,i have done only a few thousand miles and taken care of the engine in respect of servicing,so hopefully it`s not down to engine wear.
any ideas or suggestions?
thankyou
jamie

Late i know forget the heat sensor not controlled by the ecu , simple loop wire thingy when it overheats brakes the circuit lights the bulb to highlight cat prob(which could mean other issues) only fitted on the older ones same as the old mx5s and other jap imports only:roll: can't see how it could be cat if it's hunting i have ideas but ! not that brave, if it missing for example an itermittent quick blip in the revs i'd look on "mine" towards the coil pack knowing that i'd been to the rest already but what the hell do i know Apole is right look for fault code, i looked at mine with a volt meter with some success and it still works and it has passed emissions with no exceptions for being a camper gives me an idea tho if it ever does and i can't get to the root of it I'm lucky my mate is a mechanic i kick his backside if i get stuck but it still me that gets me hands dirty aswell even tho i'm paying him Maybe Mr Preeeeetender will have some wise ones


Catch you on the flip side as i'm working like a bitch at mo for all the folkies


Dar


ps when you say a muffled pop do you mean like a backfire

[hogggman]

hi all,
i intend to spend more time on this over the weekend,but had a quick look last night.found the tps but not sure about the crankshaft sensor.the pop that i get from underneath is just like a backfire,but very muffled.this can happen when putting my foot down,and when going uphill.it`s a shame i don`t have someone with a v6 locally to `borrow`the plug leads or coil etc to eliminate problems,or pinpoint them,then i could purchase parts knowing that they were actually needed.
i`ll let you kmow how it goes tomorrow.
thanks
jamie