C36 lumpyness, closer to a solution.

[kris30]

Hi there, thanks for all your ideas, I have now managed to work out a rough idea as to the problem.

The problem was, a sooty spark plug, and diagnosis following that....

So, traced the problem to the no 3 cylinder, used a volt meter to measure the voltage at the injector electrical connectors, all about 1.2 volts at idle (on removing the plug the engine note changes as expected) with the exception of the no 3 connector, which shows open circuit, now, from what Dieselman said about how the transducer works, I think a wiring fault is causing the injector to stay open causing a very rich mixture, sooting the plug and causing a rough idle, So, question is...

Who agrees with me? who doesn't? as usual all ideas welcome

 

[Dieselman]

A better way to test is with an LED and resistor. You will see the led flash with the duty cycle varying with regard to fuel delivery.

If the return line was shorted out you would see 12v across the injector.

I don't think the problem is the wiring because when you removed the injector conector this should have closed the injector. The engine note didn't change so it can't be the injector as that has already been changed.

Carry out a compression test and a leakdown test. Is the plug simply black with dry soot or is it oily.

 

[kris30]

hmmm

I'll do a more comprehensive electrical check tmro on the connector or cable, I've seen the LED 'things' but havn't got access to one, I have done a compression test and alls ok, 12bar plus, havn't got the kit for a leak down test either. I'm just a bit confused by the volt meter readings, the one and two cylinder read 1.2 volts, but the number three, no voltage reading at all, not zero volts or 12v, just a '1', indicating to me a definate differance from the 'norm' of the 1 and 2 cylinder. The plug is dry soot not oily. I think what i might do also is try the gunsons test tune kit to check the flame colour.
Cheers again, Kris

 

[Glenn Smith]

I haven't experience with this engine, but usually the injectors have 6volts positive all the time, the on off being effected by earthing the negative side through the ecu, some systems fire all injectors at once, others (called sequential) fire individually, so to hold the injector open you would need full voltage at the plug. I'd swap injector for another cylinder (don't rule out a faulty new one) and take a look at the ignition sytem>

 

[kris30]

ideas

thanks for that glen, I'm going to have another check this arvo. I've already done the injector swap, no differance, i had a chat with an autoelectrician friend earlier, got a few more checks to do, I'm still swaying towards a fretted cable, or corroded connection somewhere... I'll keep posting

 

[kth286]

kris30

If it's any help, do you know that if there is an ignition fault on any cylinder the injector signal will be cut and no fuel to that cylinder.

Also, the control system has the ability to selectively retard individual cylinders if there is a fault on any particular cylinder - it doesn't retard all the cylinders, ie the whole engine.

Have you got a mate with same car to do an ECU swap in case it's ECU related.

 

[Dieselman]

I'll do a more comprehensive electrical check tmro on the connector or cable, I've seen the LED 'things' but havn't got access to one, I have done a compression test and alls ok, 12bar plus, havn't got the kit for a leak down test either. I'm just a bit confused by the volt meter readings, the one and two cylinder read 1.2 volts, but the number three, no voltage reading at all, not zero volts or 12v, just a '1', indicating to me a definate differance from the 'norm' of the 1 and 2 cylinder. The plug is dry soot not oily. I think what i might do also is try the gunsons test tune kit to check the flame colour.
Cheers again, Kris

How are you metering the voltage? It sounds like you are metering the voltage across the injector but you should be measuring the feed and signal lines seperately and with respect to ground. One side will be a constant feed voltage and the other a variable signal.

 

[kris30]

ahh, I see Right!

Thanks for that, that is a big help, I'll check that as soon as i get time. There still must be something wrong there, because the number 3 cylinder is different to the rest. this should help me to decide if its feed or return.

Next Q', if it comes down to changing a cable, how important is it to replace it with the same gauge of cable, ie, I work with aircraft engines, if I find something similar that we use on the loom, will that do, or will it have to be the exact same type/gauge of wire, because of any voltage drop?

Cheers, Kris.

 

[Dieselman]

The cable won't be critical as long as it can carry the full voltage when under load then it'll be Ok.

Kris, I've just noticed you are in Scotland. If you are struggling with this contact member jgevers. He has an auto diagnostics business and appears to know his stuff.

 

[kris30]

more info leckie wise

Thanks again dieselman, I'll look into that.

I've done a bit more investigation into the fault, going on what you said last time.

I checked the voltage at the injector connector on the 1 and 2 cylinder both sides were roughly 12v, plus or minus 1 volt. I checked the no3 cylinder, 12v on one side but only 1.2 volt on the other pin, so there we have it, only had time to do one more check, a resistance check from a cable plug to the injector connector all ok, so the problem must be futher back, hopefully not all the way back to the ECU!!

Cheers Kris.

 

[Dieselman]

Disconnect the engine loom at the firewall and do a continuity check of bot hthe wire and wire to engine.

 

[kris30]

I'm on it.... soon Cheers Kris.