Help please M400 constant misfire

[Fixanything]

Out cooking around the M25 yesterday in me M400 and after about 60 miles a constant (some times for a few seconds it felt like it corrected itself, but not certain) misfire started most noticeable below 3000rpm, just sounds/feels like its not firing on 1 cylinder and not as smooth as normal, power is reduced a bit and easy to stall, no other indications. I have just changed the plugs no difference, I have put oscilloscope probe across each of the coils and can't see any significant differences in waveform, I have put a screw driver on each of the injectors and all sound like they are making the same noise !

The only other thing I did noticed is that the Fuel pump noise became noticeable, quite loud in the cabin I don't normally hear it. However today after changing the plugs the fuel pump sounded fine but misfire just the same.

Any suggestion, things I could try ?

Many thanks
Mark T

[TuxMan]

Hi Mark , sorry plugs did not help :-(
Fuel pump gets noisy because it is hot and yesterday was bloody hot !!!!

Wonder if it's a ecu issue , they get very hot because of the M400 mounted cooler in the side pod !!

Probably a trip to Yellowshed or Jetstream is needed :-(

Tux

[Gadgeroonie]

can you read the ecu with the noble software ?

could be the pipe to the map sensor has come loose

[R0162]

The Ecu do not suffer thermal shock but still better to move it out of the side pod.
Could be a blocked injector or you could be losing fuel pressure? if so Check ARV and check fuel filter, and as others say plug it in for diagnostics if you can.
It could also be caused by fuel evaporation, i used to get this on hot days until i modified the system, sounds like a fuelling issue to me.

[Fixanything]

Got some advice from Skip (Very helpful)here's the investigation so far:

With engine running I removed each coil connector in turn, which clearly indicated that cylinder number 3 (rear, kerbside) was doing nothing (ie absolutely no change in RPM).

I then removed both the coil & injector from that piston and swapped it with number 4 cylinder (front drivers side (easy to get to)). Started no change, problem still with number 3 cylinder !!!!

My gut feel right now is the ECU injector driver electronics or cable, Why ?, if it was rings/piston I'd get chuffing ! from the oil filler cap, which there is absolutely none, in fact pressure wise its absolutely neutral without any sign of smoke. If stuck valve I would have thought some sort of mechanical noise, with fuel smell from exhaust.

If the injector was injecting I would have thought you would smell the un-burnt fuel from the exhaust, there is no smell of fuel at all.

The next check is to conduct a compression check on #3 and #4, if that's OK I intend to connect some flying leads to the injector and measure the signal with an oscilloscope from the ECU to the injectors Good & Bad cylinders.

I've not connected to the ECU yet, good idea, will do that before compression check.

I my gut feel is right, where do I take a faulty ECU for fixing ?

If anybody can think of any other easy checks it would be much appreciated.

Cheers
Mark T

[daddysumo]

Plug a noid light into the plug of the injector that is suspect...

[D_G]

Fixanything said:

Got some advice from Skip (Very helpful)here's the investigation so far:

With engine running I removed each coil connector in turn, which clearly indicated that cylinder number 3 (rear, kerbside) was doing nothing (ie absolutely no change in RPM).

I then removed both the coil & injector from that piston and swapped it with number 4 cylinder (front drivers side (easy to get to)). Started no change, problem still with number 3 cylinder !!!!

My gut feel right now is the ECU injector driver electronics or cable, Why ?, if it was rings/piston I'd get chuffing ! from the oil filler cap, which there is absolutely none, in fact pressure wise its absolutely neutral without any sign of smoke. If stuck valve I would have thought some sort of mechanical noise, with fuel smell from exhaust.

If the injector was injecting I would have thought you would smell the un-burnt fuel from the exhaust, there is no smell of fuel at all.

The next check is to conduct a compression check on #3 and #4, if that's OK I intend to connect some flying leads to the injector and measure the signal with an oscilloscope from the ECU to the injectors Good & Bad cylinders.

I've not connected to the ECU yet, good idea, will do that before compression check.

I my gut feel is right, where do I take a faulty ECU for fixing ?

If anybody can think of any other easy checks it would be much appreciated.

Cheers
Mark T

Get a noid light on the injector connector and see if it flashes. If not check it has a 12v supply (ignition live), if so then either ECU or an open circuit between the ECU and injector connector. If the noid light flashes then resistance check the injector or swop it over with another cylinder.

[sundance002]

IMO get the ecu checked, as if it starts to run lean it can cause major probs, they are affected by heat but don't always show there is a problem, miss fire was the first symptoms I had, not saying yours has the same prob but def needs checking just so it can be eliminated.

[Fixanything]

D_G said:

Get a noid light on the injector connector and see if it flashes. If not check it has a 12v supply (ignition live), if so then either ECU or an open circuit between the ECU and injector connector. If the noid light flashes then resistance check the injector or swop it over with another cylinder.

"noid light" good gadget may get a set, but can probably do with Multimetre or Oscilloscope that I have. I have already swapped injector & coil around, problem stays with the #3 cylinder.

Many thanks for the advice

Cheers
Mark T

[sjc]

Although you di new plugs. the gaps can commonly be set wrong.
Have you had the fuel pump wiring mod?

[R0162]

it has to be the wire or the plug that goes to that injector..could be a hard fault like a wire come loose from the plug or it could be the wire is broken at some point on the way to the ECU, all the wires run past the front downpipe..mine got melted so i re-routed them.

before you said up to 3000rpm its misfiring?..i assumed over 3000rpm it was ok thats why it sounded like a blocked injector, running on 5 clyinders is a different matter, are you now saying its constant on 5 cylinders, so the problem has got worse?
First post you said injector appered to be working but now its not, definitely you have found the problem, its just whether its the plug, wire or the ECU leading to it.

Edited by R0162 on Friday 29th June 19:49

[Gadgeroonie]

any workshop with an oscilloscope can see the pulses from the injectors / coils and should be able to tell where the problem is

have you plugged in the ecu software and had a look ?

[Fixanything]

R0162 said:

it has to be the wire or the plug that goes to that injector..could be a hard fault like a wire come loose from the plug or it could be the wire is broken at some point on the way to the ECU, all the wires run past the front downpipe..mine got melted so i re-routed them.

before you said up to 3000rpm its misfiring?..i assumed over 3000rpm it was ok thats why it sounded like a blocked injector, running on 5 clyinders is a different matter, are you now saying its constant on 5 cylinders, so the problem has got worse?
First post you said injector appered to be working but now its not, definitely you have found the problem, its just whether its the plug, wire or the ECU leading to it.

Edited by R0162 on Friday 29th June 19:49

I think the air con cutting in and out may have made me think it was intermittent (i.e. you don't tend to notice the air con cutting in and out above 3000 rpm), what ever it is, its clearly rock solid now that cylinder #3 is not firing, so yes I think it is constant and only running on 5 cylinders.

The reason I thought the injectors were all working is that initially I used a screw driver on the top of each injector and listened for pulse activity, I subsequently believe this not to be a good test as all you are listening to is the noise on the fuel common-rail and not each individual injector i.e. they are not isolated from each other (May be if you could get to the body of the injectors it may be a better test).

Like you, I'm almost convinced its an injector loom plug, cable or ECU driver problem, just need to do some more measurements.

[Fixanything]

Gadgeroonie said:

any workshop with an oscilloscope can see the pulses from the injectors / coils and should be able to tell where the problem is

have you plugged in the ecu software and had a look ?

With my oscilloscope I can see the coil is working as it radiates HT energy all over the place the same as the working cylinders however, the injectors are LT/12v solenoid so you have to be connected to the connector when running which is under the inlet manifold, that's why I need to some how extend the injector lead/plug from so that I can get the probe on to it.

The next thing I will do is plug in the ECU SW and have a look, probably be Sunday afternoon now, still fitting mother-in-laws kitchen !

Thanks to all the help and advice, keep it coming.

Cheers
Mark T

[Fixanything]

sjc said:

Although you di new plugs. the gaps can commonly be set wrong.
Have you had the fuel pump wiring mod?

Replaced plugs and gapped as recommended by Yellowshed NGK's with .6mm gap, I think I have discounted Plug's and Gap's now.

Yellowshed post: "Since then, NGK have offered the BR7EFS which fits, doesn't have a protruded electrode and comes at 0.6mm gap which is absolutely fine for a turbo engine."

I believe the fuel pump mod was done by the factory or the main dealer before delivery, regardless its done and I don't think I could see a way for the fuel pump mod or not causeing no fireing on #3 cyliner only.

Many thanks
Cheers
Mark T

[Gadgeroonie]

might be worth getting the injector(s) cleaned in case you have a blockage

simple test is to swap the injector with another one and see if the problem goes with it

[R0162]

Gadgeroonie said:

might be worth getting the injector(s) cleaned in case you have a blockage

simple test is to swap the injector with another one and see if the problem goes with it

lol mike he already did that above.. tahts how we know its the electrical signal to the injector

[Gadgeroonie]

inside the ecu is a set of injector drivers which are actually a mosfet (type of transistor)

if you can find the part number you can repair it yourself they only cost a few quid each!

alternatively SBD should be able to repair it

[Fixanything]

Gadgeroonie said:

inside the ecu is a set of injector drivers which are actually a mosfet (type of transistor)

if you can find the part number you can repair it yourself they only cost a few quid each!

alternatively SBD should be able to repair it

You seem quite certain, have you had the problem before ? do I still need to bother compression testing or checking for pulse at the #3 injector connector.

Cheers
Mark T

[Adrian W]

Fixanything said:

With my oscilloscope I can see the coil is working as it radiates HT energy all over the place the same as the working cylinders however, the injectors are LT/12v solenoid so you have to be connected to the connector when running which is under the inlet manifold, that's why I need to some how extend the injector lead/plug from so that I can get the probe on to it.

The next thing I will do is plug in the ECU SW and have a look, probably be Sunday afternoon now, still fitting mother-in-laws kitchen !

Thanks to all the help and advice, keep it coming.

Cheers
Mark T

The injectors are pwm so if you have a scope you should see something sensible , I would have thought anything that looks like a duty cycle would mean the ecu is ok