Misfire under load
 

Hi everybody,thank for taking the time to read this.

I have a bog standard 2000 on a x imprezza turbo classic with a misfire under load,it has been code read and came up with the lamda sensor,this has been repalced with a know working 2nd hand one,all the leads,plugs,air filter,fuel filter etc have been changed.

I have also changed the wastegate actuator,checked all vac pipes etc,any ideas please?

take it to a specialist and get them to have a look.

I was hoping for some inspiration from here tbh.

NPS maybe?

newage cars have this problem under big torque or when a nps is on its way out. hth

Rob

not realy sure what to sugest tbh, you;ve already chased it round the engine bay with no luck, is it def a misfire? or is it hitting boost cut?

Whats the nps please?
I have had a boost gauge on it today,under load in 2nd and 3 rd the psi drops when it does it,it is more like a boost cut now you mention it.

ah right.... thought the Neutral Position Switch might be faulty. The ecu on the newage flashes up with a misfire code when the car is reving high with a faulty NPS as the ecu think the car is in neutral so it gives off the OBD2 misfire code.......HOWEVER:wonder: Im under the i impression this doesnt alter the performance, but i can not vouch for the classic... just a thought.

ie: my car running a brand newly built engine on a standard TD04 was fine, no ECU issues. Now engine running in with a complete overall inc 3" decat, STI pinks and VF30 etc has now started offering up the misfire code frequently due to the torque pushing the NPS out of sync on the gearbox. The gearbox litteraly twists slightly under load. Im getting a new NPS fitted next week (£50)

HTH

Rob

Ah ok,there is no check light or codes stored in the ecu,it literaly just farts for a second,it has also had a 2nd hand good working maf sensor,all the 2nd hand bits have been tried on my mates one and are fine.

Snowy Guildford

What was wrong with the inspiration that Tidgy gave you? On the basis of what you've told us, getting your car looked at by a specialist would be a perfectly legitimate way forward.

You can forget about the neutral position switch btw. If this was a factor you'd get an error code when you checked the memory.

What's your boost gauge reading when you get the "misfire"? How, if at all, is the car modified?

It has been into a scooby main dealers for them to diagnose,they told me the lambda was faulty,this has since been repalced and has been re-diagnosed,they said there is no faults showing.

As above, what is the boost gauge holding/peaking at?

Agreed with Splitpin :thumb:, its not the NPS (i was under the impression on the original post that the engine check light was on)

As the location is on here now it wont tale long for someone to tell you where to go. Im up North so im no help with my contacts :wonder:

The boost is peaking at 15 psi,the car is totaly standard
sorry,should of said it wasnt on

Forgot to say,it is a uk spec car.

Thank you for your help.

have you tried the fpr,i had the same problem on mine changed it to a after market one and problem solved:)

Whats the fpr please?

Fuel pressure regulator

Thank you again,I might put the fuel pressure gauge on it and go for a drive,someone suggested it may be the throttle position switch?

Any idea what the the fuel pressure should be?

Just been out in it again,it hunts on idle,it is almost as if it has an air leak,I have changed the pipes that operate the actuator for ones off another one,I made sure the restricted one was in the right place.

There isn't much opportunity for air to leak past the idle speed control valve on a 99-00 - although it is worth checking the inlet tract for loose pipes - for example the return from the charcoal canister or, possibly, the joint where the dumpvalve recirc pipe joins the inlet.

Hunting idle points to, among other things an airflow sensor issue. If your reading of c.15psi is accurate, that suggests you are not experiencing overboost and fuel cut. While there are still any number of possible explanations, one of them may be a failing airflow sensor and corresponding very lean on-boost mixtures (and probably very serious detonation).

You would therefore be well advised to take Tidgy's advice and get it looked at by someone able to diagnose the car properly. You need to know what's wrong with it ASAP, as it sounds like there's enough of a fault to be doing your engine long-term damage.

Incidentally - someone who doesn't know better might be along in a bit to tell you about a test which involves unplugging the airflow sensor with the engine running and seeing if the engine stalls, with a stall meaning that the "sensor is good", and a lack of stall meaning the sensor is "bad". This "test" is a myth based on complete bullsh*t and, as described above, can give dangerously misleading results, don't bother doing it.

What might be worth trying is unplugging the airflow sensor with the engine off and then starting it up. If the idle magically stabilises, that adds further weight to the theory of a damaged sensor, but is not, in itself, conclusive.

Oh - if you've changed the boost control pipework, one presumes that the "new" pipes have the correct size restrictor in them?

The pipework came off another car,so all pipes are genuine,so therfore pressuming the restrictor is the right size.

Now this is the thing,when you do a cat test,the co and hc's are fine.

The plugs are a nice browny colour,so that would suggest all is ok on the mixture,could it be wrong plugs? what should it have in there?

The maf sensor was changed,I bought a 2nd hand one of grade a,we also tried this on my friends classic.

I am in Guildford or down on the south coast,anyone recommend someone I can go to please?

And? Your car obviously isn't under boost/load when an MoT cat test is done. Therefore this test tells you nothing about the on-boost mixtures.

Again this tells you next to feck all as far as on-boost mixtures are concerned. As your car will spend most of its time under closed-loop mixture control, the plugs will superficially look "okay". Did you look closely at the tips to see if there was any sign of damage?

Aside from anything else the 99-00 MAF has a failure mode in which its output momentarily disappears due to fractures in its internal wiring causing bad connections - with the duration of the drop-out getting longer and longer as the sensor degrades. In practice this under-read on the airflow input causes the ECU to under-calculate the fuel mix for the duration of the drop-out. Depending on how bad and how long the drop-out lasts, the symptoms can either be undetectable (and undamaging) to undetectable (but cumulatively damaging) to detectable and seriously damaging. You need to know which, if any, of the above apply.

Doubt it's wrong plugs. Should be NGK PFR6B with 0.65-0.7mm gap on a standard car.

The tips all looked ok.

I'll just have to bite the bullet and take it in,anyone recommend anyone near to guildford,southampton or portsmouth please?

New thred required mate:

"Reputable garage required near southampton or portsmouth"

That ought to work mate.

Cheers
Rob

Edit- And put it in the Southern section https://www.scoobynet.com/southern-england-22/ ;-)

Anyone recommend anyone good please

sorry if im hijacking the thread here,

i have a newage wrx and keeps throwing faults when i boot it in 4th gear mainly. the cel comes on and when i get the codes read its showing missfires on all cylinders so im asuming after changing all the plugs etc etc its the nps switch am i right???

thanks phil

If the car pulls fine then I would say NPS mate (£50 seems to be the going rate).

There are two switches on top of the gearbox, 1)reverse swtich and 2)NPS, so if doing it yourself get the right one. Personaly im taking mine to Scoobyteknx in fleetwood.