Misfire under load on single turbo
 

right where do i start with this.

it will drive fine in vacuum and anything below 0.4bar of boost at any throttle position but as soon as the boost starts climbing more throttle it will just misfire/splutter.

running hks twin power
apexi pfc
rewired ignition direct to battery
new magnecor 10mm leads
new plugs
tried different leading coil
all pressure/vacuum sources checked
TPS adjusted

need some input guys, im now starting to think that it might be fuel related. fuel filter was only changed around 6 months ago as well.


cheers

karl

it do the same thing with the hks removed?

could be the beginning signs of fuel pump failure - although that's purely a guess. It'll get worse if it is that.

i havent tried it with the hks disconnected?? why do you think that would be causing it??

the fuel pump is also only 6 months old, 044 wired direct to the battery as well.

Sounds like you might have a stuck/clogged secondary injector. What injectors are you running? Has the car been sitting for any period of time?

If you have a spare injector connector, you can test them by applying 12v & ground or you can ground each injector at the ECU end and have a friend listen for a click

im running 1680's no it doesnt really sit for longer than a couple of days without running. at what stage do the secondaries open, i thought it was around 4000rpm??

dont think i have a connector kicking around but will try it at the ecu end.

What are your AFR's at the miss?
Can you give us a log of the run?
Maybe you should be asking this in the PFC section.
Barry

the thing is i havent touched anything for the misfire to occur. the AFR will be all over the place when its misfiring because either its not getting enough air, fuel or spark. or maybe like you say, some sensor or wiring but they all look fine.

i carnt log the run :(

on another note, just before i realised it was misfiring it started to hunt at idle between 900rpm and 1400rpm. i seem to have cured this now though.

Do you have resistors soldered in or the FJO driver?

Connectors would have been soldered or crimped on to run the 1680's, check that a wire has not come lose.

The secondaries are controlled by multiple inputs not just RPM, load and TPS as well. For instance you can free rev the car to 7K without function secondaries, but put the car under load and it will fall flat on its face the second boost kicks in. In the same example you can ease a car to 6K by not applying full throttle and keeping the boost low.

no resistor or FJO driver. they have been soldered on, i did all the work. i have checked the wiring to them, even stripped back all my heat shrink and all is ok.

ah right, that does makes sense yeh. i really hope its not the injectors.

That is a bit of a problem. The PFC controls high impedance injectors and the 1680's are low impedance. This has been known to fry the secondary injector driver in the PFC or the injectors themselves. This is why resistors or the FJO are installed.

What boost level and injector duty cycle were you running the car at prior to the problems starting?

never heard of that before, could be my problem then :( im sure i have read/seen other people not run them with no effects.

running boost at .9bar and unsure of injector duty, never actually run that on the commander as i thought it would never get high, next time i take the car out i will keep an eye on the duty and report back.

Start by testing the injectors by one of the two methods that I previously posted.

There are literally hundreds on threads covering resistors installations and the FJO driver for low impedance injectors in high impedance systems.

Yes, there are people that report not running resistors, that say they have not had any problems. Why take the risk of frying the PFC or the injectors over resistors that are only a few dollars? The PFC is not designed for low impedance injectors.

yeh, i will get the injectors tested.

really appreciate your help with this. i will take your advise and get some resistor's fitted too.

the car has been running the injectors like this for over a year and a half now but i suppose it could just fail.

did the car ever run right with the current setup?

oh yeh, its been fine, always has.

Scope the injector drivers first to see if that is your problem. Log AFRs can help alot

what do you mean by scope?? inspection? what would i be looking for??

just checked the injectors, they are clicking away nicely. so it must be something else.

Oscilliscope, -vital piece of equipment for finding electrical faults as it draws a picture of the voltage trace to really see whats going on in a circuit.

when thinking about it ,
it sounds like a igntion misfire, recheck the coils and all the secondary side of the ignition again.

You may have to take the car to your tuner or mechanic if you dont have the equipment or knowledge for fault finding. (NO offence intended)

i'd try it without the hks, just to rule it out. to me it sounds like a spark issue. the hks alters the spark time ( it doesn't make the spark stronger... I believe it lengthens/delays/advances it).

just bypass it and see. it's an easy test. then you can at least rule that thing out.

This is true, you can just unplug the HKS twin power and see if anything changes.

You have confirmed that the injectors have the ability to spray, now you need to make sure you do not have an issue with the PFC. Any friends that are willing to let you borrow theirs for a test?

Oscilliscope, i see. all the ignition side of things have been check and re checked, rewired, and replaced. i thought it was ignition related to start with.

yeh i will try it without the hks next.

i also think it might be something with the pfc, been out in the car today and when i put electrical load on the engine it starts hunting again at idle. ie lights, ac. as soon as i turn them off it will idle normal??

no one local to me with a fd let alone a pfc haha

the AFRs won't bounce around that much if you have ignition misfiring. sounds like a secondary injector issue to me.

had a similar issue with a T78 third gen that had the front secondary wired into the smog pump clutch circuit... the connectors look close but really? lol

well pfc checked and all is ok. twin power disconnected and still there.

could it be an earth problem?? where are they all??

all earth are fine, you guys always mention earth's to the coils but there isnt any?? only in the actual loom that connects to the coils.

also when the car is running it will idle fine, as soon as i put the headlights on or press ac for fans etc as i dont have ac it will hunt really bad. tps is fine etc etc so what would cause that, maybe thats my problem??

new map sensor and still the same. adjusted the idle so when the headlights are on it will idle fine when warm, as soon as i turn them off it will start hunting again.

maybe blocked injector(s)??