15 replies to this topic

[motorsportelectronics]

Hi Chaps, heres one for you...

 

We have a customers mini MPI in after being bounced from another garage. The fault is the car has a misfire through range but not really noticeble at top end. IT drives OK. The inner two plugs richer than outer two.

 

The other garage has changed all sensors, and the car has come to us with same fault.

 

Also, perhaps related... Coolant fan comes on with engine running. Coolant gauge reads OK (seperate sender I assume?). This fan problem is intermittent though also. Sometimes its OK, sometimes not.

 

Car apparently had NS wing rebuild from accident damage, no other history known.

 

We scoped it with oscilloscope..

 

Found cam sensor signal not there. Changed sensor and now we have a nice waveform so that is working.

 

Scoped crank sensor to make sure it had the right reluctor, which was found to be a 32-4 (?) wheel  which seems OK.

 

Compression and V/clearances checked and OK.

 

New leads and coil, no effect.

 

Timing gun shows approx 6* at idle, but it seems to 'jump' around by 5-10* eaither side of this every now and then, which is most likely the misfre problem...

 

Any ideas...

 

We have everything to check with so no idea too silly! Rolling road, AFR, diags everything.. awaiting ideas!

 

Cheers,

Matt

 

[fattail95]

Perhaps the coil pack? Has that been changed? I know Nev Payne on here had some troubles with his MPi, changed the coil pack which solved his problem.

[motorsportelectronics]

Hi, as stated new leads and coil pack :) Thanks

 

It is a tricky one!

[FlyingScot]

Fan problem sounds like this one ! http://www.theminifo...t-fan-problems/ as few down in the list on the forum.

The change in timing could be the result rather than the cause, I would suspect one if the injectors isn't atomising or pulsing properly (2 cylinders running rich too...) the MEMS unit is sensing the misfire and adjusting the timing to keep the motor running possibly.....

Although normally with a misfire we are normally thinking ignition rather than fuelling.

As all the obvious things have been tried, I would see if you can borrow an injector to rule this out. Or see if you can test the injectors themselves (you have a scope to test the pulse) and if you have diagnostic gear you could even remove the injector and set it to test the component and measure and see if the injectors are working and producing similar volume?

FS

[motorsportelectronics]

FS,

 

Thanks for the info.

 

Since sorting the cam sensor the plugs have now evened up in colour which is a good start.

 

Will look at injectors next :)

 

Matt

[motorsportelectronics]

Ok spray pattern is good. On cranking with ijjectors out to check pattern, we get maybe 10 steady pulses then nothin then it comes back 500ms later.

 

I think it may be an anti flood method on the ECU, as injectors are also nit being told to fire. Is this normal? Or inidictive of a sync loss issue?

 

Regards

Matt

[Shifty]

Have you done the basics?

 

-Check the tappet gaps

-A compression test

 

I had a miss on mine and when I chucked on my acr code reader the map pressure was incorrect, I re sealed the inlet manifold and fitted new locating rings and its been fine since.

 

The coolant sensor(on the thermostat housing) signals the mixture as well, with this in mind is the thermostat ok?

 

Theres also a relay pack on the lefthand side of the engine (by the pedal box) that can fail as well.

[motorsportelectronics]

Shifty thanks for the info.

 

As per OP, have checked both of those and A-OK.

 

We need to get our hands on an ACR reader by the looks of things, as our stuff wont talk to it!

 

Will report back shortly :)

 

Matt

[motorsportelectronics]

Ok assumpotion kills me...

 

We thought it didnt have OBD2 it does. Snap On Solus picks up ambient air temp sensor short to ground, and in data it reads -240*C.

 

... So thats the next step..

 

Matt

[Shifty]

Good luck!!

[motorsportelectronics]

Ok,

 

Ambienbt sensor is NOT the IAT snesor as some people ay, as the IAT sensor is reading fine and increasing as itr should. I think this MEMs ecu has an input for iut but its not used on this setup, so I will ignore that.

 

HOWEVER:

O2 VOLTAGE (V) reads 1.96#70.. FAR too high (higher than I though an O2 sensor could produce!) and it also only drops slightly when unplugged...

 

Hmm...

 

Does anyoneopne else have an O2 voltage from a Snap On Soplus Pro reading?

 

Cheers

Matt

[Shifty]

This might help(or not?)

 

http://www.tmsmini.c...oper/sp_acr.htm

[FlyingScot]

Inlet air temperature and coolant temperature are measured, the ambient is a calculation from memory.
Pretty sure that your Solus will not be reading the right data as AFAIK only the old diagnostic gear measures the outputs correctly.
Lambda reading definitely suspect as it normall goes up to 800mv max and swings around quickly as the MEMS adjusts.
Could be with all the previous poor running it is clogged (worth a clean ?) or don't rule out wiring as people tend to forget the injection minis still had pretty poor wiring!!

FS

[jamesmpi]

This might help(or not?)
 
http://www.tmsmini.c...oper/sp_acr.htm

Think we should pin this page if it hasnt already been done

[FlyingScot]

Ah Shifty has posted the link to Terry's information (should have looked!)

FS