V6 Missfire

[bongoblue]

My V6 with LPG conversion runs great while warming up but starts to run lumpy once fully up to running temp. This happens both on gas or petrol. The plugs are new and clean.
Is there a sensor that would typically cause this?

[apole]

Hi,

There are many things that could cause this.

I'd check the following:

Distributer cap and rotor arm.
All plug connections/leads including coil.
What colour are the plugs, too dark and it's running rich, too light lean.
Any air leaks anywhere.

What is the service history like and has it had a good one recently with new air filter etc.

Can your LPG fitter read any fault codes from either the LPG or car ECU's, that may help.

I don't think it could be the O2 sensor as if this doesn't read then the car runs a default fueling map.

Regards

Andy

[cheffy34]

Typically the leads etc are more prone to break down if they are old and worn when up to running temp, i also doubt it lambda. Mine is sometimes lumpy if he been stood for a couple of days but improved greatly when i changed the leads and plugs, i'd have my plugs out and see what they looking like, i'd edge my bets towards a lead etc but what do i know I would say is it anything to do with your lpg but i know nout really



Dar

[bongoblue]

Hi Guys,

Many thanks for the help. It's running better today. Must be the positive vibes from the bongo community!
My local "Bongo friendly" mechanic ran some diagnostics last week. He's really a diesel bongo mech and this is the first V6 LPG he has dealt with. He said that he cleared all the fault codes except one which came up as VRIS. Any thoughts on that?

The other thing I've done for sure is cook the Lambda sensor when the plugs were knackered. It's now disconnected to get rid of the red light.

I've got some cleaning spray to clean the MAF in case that helps.

Much appreciate all the advice.

Tim

[apole]

Hi,

I'm pretty sure if you just disconnect the lambda sensor the car will run a default fueling map. This will most likely mean your fuel consumption will go right up so it would be a good idea to first test it. Easy to do with a digital multimeter:

Important for this test you must leave the sensor connected to the ECU!
To ensure the engine is fully warmed through run the engine at fast idle until the cooling fan cuts in. If all is well the voltage shown on the meter should flicker up and down the scale changing at least twice a second between about 0.1 and 0.8 volts -- the average reading should be about 0.4-0.5 volts but it should never be steady at this voltage. Flick the throttle open and the voltage should flicker, rise for a second or so then fall again, this indicates the ECU is receiving input from the sensor and is responding properly.

A steady voltage of between 0.4 and 0.5 V is a sign that the ECU is running in open loop mode --- either the engine is not fully warm or it may indicate a bad connection or a faulty water temperature sensor or an ECU fault.

More info here, the above is a cut and paste of another post:

http://www.picoauto.com/applications/lambda-sensor.html



I would not leave this disconnected, you can get a new universal 2 wire one.

[bongoblue]

Hi,

It sounds like a disconnected Lambda sensor could well give me the symptoms.
If I replace the lambda will the overheat red light clear automatically?
Where can I get a universal sensor, and who makes them?

Many thanks again,

Tim

[apole]

Hi,

Firstly we may not be taking about the lambda sensor here, it depends on what year your car is. Newer models just have a lambda sensor, this looks a bit like a spark plug and is in the exhaust just in front of the cat on the passenger side of the car.

On the older models they also have a heat sensor, looks similar and it's in the cat itself. This sensors job is to warn if the cat is overheating.

Check which one you are talking about first as the heat sensor plays a different role and is alot more expensive (cheffy would know more but I recall a figure of around £100).

Have you tested your lambda sensor yet with a multimeter?

If you need a new one, these guys are good:

http://www.lambdasensor.com/main/muniversal.htm

This is the part you need:

250-22000 Universal 2 Wire Zirconia sensor £46.00

[bongoblue]

Hi Apole,

You are way ahead of me (not difficult).
I just discovered that the sensor which was isolated is the heat sensor, not the Lambda. I reconnected it and have the red "heat" caption back on the panel.
I cleaned the MAF also.
Still got the missfire.
My Bongo seems to suffer from the wet like some others - could this point to the distributor or leads being the problem?
Sorry I can't check the output from the Lambda as that's beyond my technical expertise.

Thanks again

Tim

[cheffy34]

Hi Apole,

You are way ahead of me (not difficult).
I just discovered that the sensor which was isolated is the heat sensor, not the Lambda. I reconnected it and have the red "heat" caption back on the panel.
I cleaned the MAF also.
Still got the missfire.
My Bongo seems to suffer from the wet like some others - could this point to the distributor or leads being the problem?
Sorry I can't check the output from the Lambda as that's beyond my technical expertise.

Thanks again

Tim

It sounds to me if you have just bought your van some clever dealer has disconnected the heat sensor as it is goosed if it lights up on your dash! probably caused by the missfire cos as far as i know if it takes a sudden missfire it will dump fuel down the exhaust which will cause the cat to over heat especially if you are driving it, thus killing the sensor and lighting the light i had the same prob when mine took on water in the dizzy cap the water sits on the the bottom of the cap and kills two to three cylinders top tip replace the gasket the dizzy cap is on a direct collision course with water if you hit large puddles at any speed it will come up through your scav fan bad design but i guess that why they have a gasket on the dizzy cap i have had no probs in heavy rain or deep standing water since i did the gasket i have not sorted the heat sensor not worth the outlay in my eyes just disconnect and it will light up on startup and go out after just as if it were working It is not ecu controlled, I would certainly get the cap off and see if it wet in there If you had heavy rain The prob is it could be any manner of things, took me ages to get mine running sweet with no blips

ps mine runs lumpy when i disconnect the maf are you sure it fully connected


Dar

[apole]

Hi,

There should be a black O ring between the disty cap and the disty, if that is missing water can get in so as cheffy says check that first.

Andy

[bongoblue]

Andy,

The heat sensor was disconnected by my local garage after they put new plugs in. The new plugs are apparently designed to run hotter to cope with the LPG temperatures. Prior to that it was running really rough and caused the cat to overtemp during a steep hill climb. I will disconnect the sensor again.
After the plugs and filters were changed the running improved 90%.

If the rain stops for more than 30 minutes then I will get to the distributor.
The west coast of Scotland is not a good place for bongos which dislike water!

Tim

[apole]

Hi Tim,

Once you have the O ring in there and good HT leads you should have no issues with damp, I haven't in 2 years.

BTW there are places that sell you expensive LPG specific plugs, IMHO they are not worthwhile. Just stick with the standard Denso or NGK's for £2 each and reduce the gap by 10%.

Your car should not run any hotter on LPG either, the cooling system should cope.
LPG is a hotter burn than petrol, so there are higher temperatures to consider. Under normal circumstances the cooling systems should be able to cope with this, especially when you consider the same system that's cooling your engine is also heating up the LPG!
The concern your mechanic had was probably around any effects to the valves, which a flashlube system should remedy. Mind you a guy on here has just written a post after doing 60k miles on LPG with no issues as yet.

If you are worried about the engine temperature, first find out what range it's running in by either getting a code reader and seeing what the coolant temp is, or a TM-2 or mason alarm. If it's running hot you need to find out why.

Let us know how you get on.

Andy

[Grahame at work]

Andy,

Following this in case I ever have a similar problem with my V6 - interesting.

BUT you said: -

first find out what range it's running in by either getting a code reader and seeing what the coolant temp is

I'm very interested in this - do I take it that you can get a coded reading from the diagnostic socket?
Or am I missing something here

regards Grahame

[apole]

Hi Graham

If you know a garage with a diagnostics computer that can read the ECU codes via the diags port, one of the readings you can get is coolant temp. This should be pretty accurate, unless of course the coolant sensor is faulty. It's also very useful to see if anything else is wrong.

Regards

Andy

[Grahame at work]

Andy on my original 95 diesel (without checking the book) I'm pretty sure that wasn't available from the ECU.

So is this a feature of V6 ECUs or just newer models (mine is 98)?

I know the Russian site has quite a lot of info on this so maybe I'll do some searching tonight.

Regards Grahame