Misfire......possibly...

[terzoman]

Right, my car is an 1998 Impreza Terzo.

Its been running well until earlier today, apart from the fuel pump failing a couple of months ago.

It had an original Subaru fuel pump still, so I have replaced it with a Walbro 255 pump.

 

 

It was running perfectly, with plenty of power until earlier today :(

 

 

Accelerated up a hill after ~10 miles of twisty road having fun, and all was fine.

Pulled away from the roundabout at the top of the hill, accelerated hard, only to suddenly around 4k rpm have the car spluttering and coughing badly, boost gauge would bounce up and then drop back each time.

 

Obviously fuel pump was replaced recently, so that should be fine.



it now misfires at anything over say 1/4 throttle, but it will keep revving through the misfires which suggests it can't be anything too serious (hopefully!!)


I have checked the coil connector and it seems clean and OK, the leads all are plugged on tightly. (will look properly when cold)

I disconnected MAF while car running and car stalled instantly which I believe means the MAF is working OK?




So suggestions? things to look at?

Thanks!



EDIT:

Also, where is best to get a new coil pack?

[Nevell]

Sounds like plugs or leads to me mate.......or a loose connection ....

[terzoman]

Will check the plugs and leads today and see and lok for any loose connections.


I did plug the 2 black connectors under the steering column to check fault codes, but there arent any stored.



It just seems strange how it suddenly started to do it, literally after slowing down for a roundabout....

[quit]

Leads are common failure on these

[Rick 2014]

This happened to me the other week.And number 1 ht lead failed

[terzoman]

Right, I have put new spark plugs in to eliminate them.

the leads arent very old by the look of them, and they are good silicone ones :/


Wouldnt the lead failing/failed cause it to misfire continuously?

 

 

Because mine will sometimes rev up to 4krpm and then misfire, other times it will at 2krpm!
its not entirely throttle dependant either it seems.

 

Oh and I can't get any misfire in neutral.....


Could it be a failing MAF sensor?

 

 

EDIT:

Also it sometimes wont pull at all so your stuck at 3k rpm for a few seconds regardless of throttle.......




no knocking from engine and its using no water etc.....

[Rick 2014]

They don't always misfire all the time mine was every now and again.It can happen at idle just standing there.You can hear it in the exhaust standing at the back end of the car

[terzoman]

is there a way to test the leads?


I might replace the coil and leads asap just to make sure........



What sensors could cause it out of interest?

MAF unplugged the car stalls
unplugging the timing sensor is the same.

the sensor/device on the top of the manifold (with a pipe that links back into the intake pipe post MAF), unplugging that causes the idle to increase to ~1,200rpm.
Not sure what that sensor/device is?

[terzoman]

update....

 

with new clean plugs 2 spark plugs (back cylinders) are showing signs of sooting on the insulator (as I would expect)
front passenger plug shows a slight hint, but very clean

front drivers......thats wet with fuel and sooty which looks like poor combustion.
have looked inside plug cap and it looks corroded.....


So will get a new set of leads (Magnecor 8mm or 8.5mm) and might get a new coil at the same time, simply as its probably original as well......

[Rick 2014]

If you have unplugged the maf and it stalls it working mate.i went through all this the other week.It wouldn't hurt to clean the maf sensor with electrical contact cleaner though mate.Ive used the spray my self and does a good job.Also if your starting the car and your getting a spark from the coil pack when removing the lead then its ok.Did you buy the right plugs as well?How long have the leads been in the car for as well? im thinking its the leads or at least one of them.Can you get a video up of whats happening

[Ash007ks]

Wait you said it ran better with the maf unplugged >? surely this is showing you that the maf is broken.

[terzoman]

If you have unplugged the maf and it stalls it working mate.i went through all this the other week.It wouldn't hurt to clean the maf sensor with electrical contact cleaner though mate.Ive used the spray my self and does a good job.Also if your starting the car and your getting a spark from the coil pack when removing the lead then its ok.Did you buy the right plugs as well?How long have the leads been in the car for as well? im thinking its the leads or at least one of them.Can you get a video up of whats happening

the coil is definitely sparking, have checked that, the plugs are PFR7B gapped at 0.7mm I think....

looking at the leads they are date stamped 1998, so are old!

and yeah, unplugging the maf stalls the car instantly so am ruling that out for the moment :P

will order some new leads and see from there :/

definitely thinking the lead is at fault as the car doesnt run much worse with it pulled off!

[Rick 2014]

I paid £21 for a set of leads from euro car parts and its done the job great

[terzoman]

Ordered a new set of leads and just to make sure I have bought a new coil as well.....

If it turns out the coil is ok, well I have a spare for the future :)



Fingers crossed the leads/coil cure the problem :) 



I checked the resistance of the lead and it measured 11k which I know is quite high, new leads are around the 6k mark.....



IF the coil/leads doesn't cure the misfire, I will compression test each cylinder (will have to do it cold but will still see if one cylinder is low).

what are the cylinder compression psi figures meant to be out of interest?

[quit]

Sometimes can feel the leads pulsing when they are failing

[terzoman]

Brand new coil and leads fitted, sparkplugs were new a couple of days ago.....

Still misfiring.......



I have reset the ECU and will pull the plugs in a minute to see if there is any signs of something wrong......not happy though :(

also checked crank sensor, it looks clean....

[terzoman]

Just done a compression test.

Engine had cooled down for about 30 minutes (oil temp was 75 degrees celcius).


Presuming I have cylinder numbers correct:

Cylinder 1 (drivers front) - 102psi
Cylinder 2 (passenger front) - 125psi
Cylinder 4 (passenger rear) - 122psi
Cylinder 3 (drivers rear) - 110psi

(Thats the order I did them in, so engine temp had dropped a bit by the time I got to the final cylinder test, cylinder 3)



Now to me, that looks low across all cylinders especially cylinder 1 at 102psi :(


However, seeing both cylinders on that side are lower, could it be a head gasket or something? it doesn't lose oil or water......

[Nevell]

Maybe fuel pump if happening at high revs ... Or injectors

[terzoman]

Fuel pump is fine, is only a couple of months old, and it primes perfectly.

injectors possibly, but I'm more worried by the 102psi cylinder reading! :(

[terzoman]

Can't see the injector causing low compression :/ 


Really need some decent advice on best course of action please! :/

[terzoman]

Could it be a failing headgasket?


No water in oil, no noticeable water loss, but the coolant does have a slight smell to it :/

[savage bulldogs]

Scoobs do tend to pressurise the coolant (rather than mix oil n water) due to the large waterways in the block around the bore sleves.

A coolant sniff test would out rule headgasket

Couldn't tell you if that's a lower than average compression reading I'm afraid (give it a google maybe)

I'd double compression check the weaker bank (as you well know) the plugs a pain to get to

Have you checked the timing belt /tensioner condition ?

It might have slipped a tooth on a cam on that bank .

hope it's something that's not to costly , best of luck fella

[terzoman]

OK will see about a coolant sniff :/


120psi seems to be the lowest 'ok' compression before problems start....

the 102 is borderline misfire from low compression alone :(

I don't know whether to simply replace the head gaskets (they are composite ones I believe) and see how it goes....or simply chuck a good known running engine in for similar money :/



My car is a 1998, but if I got a 1999/2000 engine (different coils, MAF, etc), and then fitted my coil, MAF etc would it be fine? basically are the engines themselves identical?

[savage bulldogs]

Do you know what version yours is ?

As it might fall into the v4 or v5 dates

V5/v6 (late 98 till 00) have a different inlet pattern to earlier scoobs but ,im unsure about the engine loom sensor plug compatability.

I know that 93 (v1) to early 98 (v4) engine's heads share the same inlet stud pattern .

So you just fit the loom ,ecu inlet/auxiliaries maf ect .. of the version scoob the engine's going into

As the plugs for maf , idle control valve ect .. and the fuel rails/ inlet phase are different from v1/v2 to v3/v4

Head gaskets are a engine out job so I'd either fully rebuild it or source a good second hand v1 to v4 long engine .

As you'll be miffed if the bottom end goes after you've done the 1 headgasket and put it back together .

[terzoman]

Pretty sure mine is a V4 :/ Coil in centre of inlet manifold
Its the 8S ECU model (so can't be remapped without daughterboard)


Hmm so will look for a good engine.....