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Persistant miss-fire
clairetoo - 6/10/12 at 11:39 AM

One thing I thought I would have a problem with at the MOT was emissions - and they were a mile out
Mainly due to a constant missfire ). Driving gets lots of spitting and popping , as if its very weak , but the AFR reading is rich (12 to 13)
So it seems to be both rich and weak , which has got me stumped ?

matt_gsxr - 6/10/12 at 03:47 PM

Blocked injector? Are the plugs all similar looking?

clairetoo - 6/10/12 at 03:58 PM

Well......I've just swapped the complete throttle body setup from my Fury , including the injector harness (right back to the megasquirt) and its still there
I've been sat in the car changing the fueling manually , and it does seem to be getting better - the next step seems to be to copy as close as I can the maps from my Fury - the problem there is the Fury is Ms1 , the Mx5 Ms2..........

I'm beginning to think the fueling is so far out that tuner studios auto-tune cant cope , and un-burned fuel is causing unreliable readings from the Lc1 .

daviep - 6/10/12 at 06:01 PM

Do you know what the HC, CO and Lambda were at MOT? This will help work out whether it is rich or lean.
High HC will be caused by any misfire, if the CO was also high then it might be too rich, CO low and HC high would indicate a lean misfire.

Cheers
Davie

matt_gsxr - 6/10/12 at 06:07 PM

Translating maps from Ms1 to Ms2 is a real pain. I ended up remapping. The problem is that the fueling equation isn't quite the same (from what I remember), also some of the defaults may differ (multiply MAP in the fueling I think is unique to Ms2, but not 100% sure). Basically translating is too difficult.

Miss-fires certainly upset the LC-1, as super-lean looks like rich, but I'm not telling you anything you don't know.
Are all the cylinders doing approximately the same thing?


There is a theory that most fueling problems are actually spark problems. (just covering the bases here)


Matt

austin man - 6/10/12 at 08:46 PM

Had a problem on a zetec changed injectors, pump, coil pack, leads, loom etc, no change, fitted a larger swirl pot and problem solved

BaileyPerformance - 7/10/12 at 03:32 PM

quote:
Originally posted by clairetoo
One thing I thought I would have a problem with at the MOT was emissions - and they were a mile out
Mainly due to a constant missfire ). Driving gets lots of spitting and popping , as if its very weak , but the AFR reading is rich (12 to 13)
So it seems to be both rich and weak , which has got me stumped ?


Hi Claire,

I would do the basic tests first to make sure the engine is sound, such as compression test.

Another good thing to do is with the engine at idle, disconnect each injector plug in turn (in no particular order) to check the engine RPM falls by the same amount. (normally around 150RPM on a V6). If you find a cylinder what has no effect (or very little effect) on the engine RPM you know you have a problem with that cylinder.

If you have an infer-red hand held temp sensor (mind was from Maplin) its worth noting the exhaust header temps of each cylinder - if you have a low one you have a problem.

I assume you have throttle bodies? check the balance again as it maybe something simple like one weak cylinder due to poor balance. Have you got a lambda in each side of the engine or just one measuring the total exhaust gas??

clairetoo - 7/10/12 at 03:47 PM

I think the problem was injector wiring - pulling one of the injector plugs had no effect on tickover , so I swapped the injector but no change . I put a meter across the plug , and it was showing just milliamps - so maybe a dry joint .
So rather than muck around with wiring , I swapped the complete throttle body assembly off my Fury , and got an improvement - but still not drivable .
So.......next step was to sort the mapping - the Mx5 is Ms2 , but the Fury is Ms1 - so tonights fun is to copy the fuel table as close as possible , one step at a time

I didnt get that done today - while ticking over on the drive yesterday , the heater matrix burst........so today has been spent pulling the dash out and sorting that

BaileyPerformance - 7/10/12 at 05:36 PM

quote:
Originally posted by clairetoo
I think the problem was injector wiring - pulling one of the injector plugs had no effect on tickover , so I swapped the injector but no change . I put a meter across the plug , and it was showing just milliamps - so maybe a dry joint .
So rather than muck around with wiring , I swapped the complete throttle body assembly off my Fury , and got an improvement - but still not drivable .
So.......next step was to sort the mapping - the Mx5 is Ms2 , but the Fury is Ms1 - so tonights fun is to copy the fuel table as close as possible , one step at a time

I didnt get that done today - while ticking over on the drive yesterday , the heater matrix burst........so today has been spent pulling the dash out and sorting that


Humm, you should not attempt to measure current at an injector plug as this will short it, did you mean millivolts?

One side of the plug should be 12v other side grounded by the ECU. I normally have a spare injector to plug in as a quick test - hold the injector in your hand (with engine running) and you should fell it click. Another way of doing it is to use a low wattage 12v lamp, this puts a load on the wiring that mite show a dry joint. (hard to see with a meter dues to high input impedance)

No point at all in transposing maps, if i was you i'd check the engine first, then set fixed ignition timing of say 10deg, then manually change the VE values at idle to get the fuelling right (13.5-14AFR will do) When you have done this do the injector RPM drop test again. The AFR should go leaner with an injector plug off.

Did this engine ever run right? (new build) or has it been running OK and developed this problem??

clairetoo - 7/10/12 at 08:00 PM

I tried with a spare injector on the one cylinder that seemed to be at fault , and no clicking at all .

I'm going to try and re-write the map as I know my Fury works and runs , and the only thing on the Mx5 setup that is unproven is the mapping.......... It is a fresh build , but I have no reason to suspect a mechanical problem - no smoke or rattles , and the odd occasion it has run well , it has run very well

BaileyPerformance - 7/10/12 at 09:47 PM

quote:
Originally posted by clairetoo
I tried with a spare injector on the one cylinder that seemed to be at fault , and no clicking at all .

I'm going to try and re-write the map as I know my Fury works and runs , and the only thing on the Mx5 setup that is unproven is the mapping.......... It is a fresh build , but I have no reason to suspect a mechanical problem - no smoke or rattles , and the odd occasion it has run well , it has run very well


If you tried the injector test and it did not click in your hand you have a wiring fault, nothing to do with mapping - as you know the MS has 2 injector outputs, normally output A for drive all three injector on the left of the engine, output B would drive the injectors on the right. As you only have 1 bad cylinder the MS outputs or mapping is not at fault.

You said "the odd occasion it has run well , it has run very well" - mapping does not change, it would run OK all of the time or not at all, intermittent faults are electrical or sometimes mechanical.

No point putting a map from another engine (even if it is identical) as there is always some small difference, it sounds like you have already proved you have a wiring problem.

As you have said the AFR is on the rich side, i would say adding more fuel in the VE table may have cause it to go VERY rich as 1 missing cylinder will give you a false lean reading - making you think its lean and so adding more fuel (this is the case with autotune, which is naff anyway without a fault present making it think the engine is lean)