Alloytec Misfire- Mechanic and Autoelec MUST read.

[2005vzute]

g'day all,

very sorry about a wall of text, but i think this could turn out to be a great thread if you take the time to read

so i've been thinking for a while why nearly every alloytec i've driven always has a rough idle...to my car i have done absolutly everything practical except for oxy sensors and ignition coils, you name it, vacuum leaks, filters, maf cleaning, ultrasonic injector cleaning, spark plugs etc, rough idle still there

so although i'm pretty sure it's got something to do with ignition coils i don't wanna go spending hundreds to possibly got an end result of nothing...the problem with these engine's im finding is misifre at idle right? not under load, not at certain revs..just idle...and it's a majority of alloytecs..so im not entirely convinced it is the ignition coil itself, but possibly something to do with it...surely every igniton coil isn't going to shit itself in these engines right? so it got me thinking maybe there has been a stuff up from factory, not entirely to do with quality of parts, but maybe the design of wiring and where it has been placed..

my ute is currently out of action till later this week, in which my dad needs to use it anyway so i can't go investigate this straight away but it's a theory and it could possibly be causing our misfires.

so here it is...anyone that knows a thing or two about the CAN bus system will know that the CAN high and CAN low (twisted multiplexing wires) wires use signals...the reason these 2 wires are twisted together is why? to reduce interference...could it be possible that wires somewhere along the line are getting an interference? possibly causing a distorted signal? possibly causing igniton coils not to be as fully functional as they should be? maybe the interference is coming from the wires being to close to a power cable? an electromagnetic field distorting the signal?

i think i am going to investigate every wire from the twisted multiplexing wires to the igniton coil wires for anything that may cause a distorted signal that may cause a misfire..this could also possibly mean a distorted injector duty cycle signal...the possibilities are endless to where interference may come into it? but is it possible, i think so.

to those that understand what i'm talking about PLEASE share your thoughts and comments about it..i could be way off the mark about a simple misfire, maybe not

cheers everyone

[mattsv6]

It's not that expensive to replace your coils.

The fixed the misfire issue I was having.

[Paul13pp]

I'd be thinking that the designers would have stipulated shielded(and maybe earthed at each end) wiring for anything important that could pick up noise and disrupt the computer and idle.
Might be handy to have some spare coils lying around anyway.

[azazeldeath]

I understand entirely where you are coming from, but I am afraid to say that is appears to me that it is rather the leads and coils themselves that are flawed in the Alloytecs. I know numerous Commodores, Crewmans and anything with the alloytec in it really that gets the same problem eventually.
I need to do more searching for an aftermarket system for it. Or atleast replacements that arent OEM or Bosche.
The shielding on the wiring should be fine, if not think of what your BCM would be doing? It would be going nuts lol.

[heyitsEnricoPallazzo]

Well thats one theory.

I still maintain the reason for the occasional rough idle is the purge control solenoid operating during idle. My understanding is this solenoid should not operate at idle.

Also the supersoft hydraulic engine mounts would only exacerbate the problem.

[2005vzute]

someone understands...depending on what part of the mulitplexing cable could be affected could cause the rough idle...im trying to get my hands on a wiring diagram for the igntion coils to see what the 5 or so wires are there for at the connector...im assuming positive negative and signal so far, maybe there is only 3 and im thinking of th maf sensor connector, i needa investigate...but could it be possible that the signal wires from the ignition coils would bundle into 1 wiring harness somewhere, and possibly get interference and causing the misfire...wish i had an oscilloscope handy hahaha

[heyitsEnricoPallazzo]

You do realise the canbus signal is only connected to the PIM, PCM, ABS and steering wheel angle sensor (ESP) via ECU.

See pics below for coil, throttle and purge schematic.

[heyitsEnricoPallazzo]

Just thinking. Could it be the purge control (PCS) signal causing interference with the coil or injector signals?

[2005vzute]

it runs between all the control modules true?what if injector signals are interfering with coil signals:Sthey could be running wires closely together? who knows...tell me about this purge control n what it does please=]...haven't heard of it before, unless i've heard it called something else or just didn't know the name haha

[heyitsEnricoPallazzo]

It takes petrol vapours from fuel tank via charcoal canister and then releases this into manifold air stream. Controlled by PCS and ECU.
It should have a 10% duty cycle @ 3000 rpm (see below). However you can hear it working at idle on occasion.

[2005vzute]

hmmm, i will have a look into that to understand it abit betterer, i get the part about putting petti fumes in the engine, what doesn't go in the engine these days:/ exhaust, petti fumes, crankcase fumes, whatevers floating around in the air....psht, gayyy haha, im off for now, i'll check in tomorrow arvo after work, might talk to some of the tradies at work n see what they know about the pcs thingo haha, peace bro