Missing or 'Coughing'!

#1 10-16-2004, 06:00 PM

Hi Guys, just done the head gaskets on my svx, well worth it as it drives well now!

Just 1 annoying problem left - when the engine is warm & idling, it 'coughs' just a small miss, like 1 of the injectors forgets 2 fire?

I had a listen under the bonnet (hood for the usa! lol) and it sounds like the injectors on the left bank, 1 will make a 'louder' click when the engine misses! all 3 have done it, but nothing from the right bank!

I dont think it's any of the sensors under the intake manifold, pretty sure it's the injectors making the noise, but only 1 at a time!

I'm running it on 'normal' unleaded fuel at the mo (due 2 the cost in the uk of super unleaded), but surely that won't make THAT much difference? I've run cars which specify 'super' before on 'normal' & i've only noticed a slight drop in power, not missing or bad running!

I've checked the connections & they seem ok, will try some 'Injector Cleaner' in the fuel, & then some 'super' unleaded, but it does seem 2 be electrical rather than actually the fuel itself!

Anthing else worth checking?

Thanks,
Phil.

NikFu S. · #2 10-17-2004, 10:10 PM

I had this problem while driving, and I'm extremely worried that it might be viscosity, or friction due to inadequate oiling.
My pump is due for a change.

It would make sense that this would happen at low rpms, but you seem to have a good idea on whats wrong.

Being that mine only does this in motion I can't diagnose anything.

I figured it could be anything to injectors or sparks missing, to the brakes engaging (abs failing), as there would be negative G's on the pad (aka a sharp slowing down feeling).
I did get a good listen and the exhaust actually gets louder at that point even though rpms drop slightly (slightly as in 100r).
Check that out.

Amazonparrot · #3 10-19-2004, 10:47 AM

I had a similar problem with my car. Now while this may not be the solution, it was found to be the solution to my problem when I took it to the mechanic. Check the left banks coil packs, and you might find that some of the rubber? insulation has been deteriorated, causing the spark to arc across the cylinders and cause misfires (this is not my explanation, only the mechanics, which i trust, since it fixed the problem) If this turns out to be the case, you might just need to replace one or two of those coil packs, until the car runs properly. Hope this helps!!

-Andrew

#4 10-19-2004, 03:27 PM

Thanks Andrew, i'll take a look at them! Sounds like a good possiblity as i can hear them clicking louder when it misses!

Phil.

RojoRocket · #5 10-19-2004, 05:32 PM

Good advice there. After replacing one in early summer that flat failed, with a used part my Subie guy had on hand, I developed a similar "shudder" at idle a month or so later. After looking at vacuum lines, TPS and a dozen other possibilities(myself) my tech put it in the air and determined that 2 more were failing/arcing. Just bit the bullet and bought a new set ( $500+

) and the car is purrrrring again!!! Sure glad I took care of it before the wet weather hit! Examining the 2 in question the insulation had definitely failed after 11 years.

Glenn

#6 10-20-2004, 03:11 AM

how do you tell which coil packs are playing up? my brothers has a similar problem i am going to buy the new ones for him and as you guys know they are different for the front /middle and rear coils left and right are the same but i dont want to get the wrong ones they are too dear for that

so does the computer tell you?

cbx-man · #7 10-21-2004, 01:25 PM

I know a guy that had similar intermittent missing. Couldn't figure it out.

Turned out to he put (too much) anti-seize on the spark plug threads. Poor connection = no spark

Some opinions (from spark plug mfgs) these days say that anti-seize is no longer necessary on aluminum heads.

RojoRocket · #8 10-21-2004, 01:32 PM

Quote:

Originally posted by camosuba
how do you tell which coil packs are playing up? my brothers has a similar problem i am going to buy the new ones for him and as you guys know they are different for the front /middle and rear coils left and right are the same but i dont want to get the wrong ones they are too dear for that so does the computer tell you?

If it's a regular miss rather than intermittent it's easy to unplug one injector at a time, noting any worsening/or same(ah ha!) of the idle. My tech put the car on the rack and observed closely the noise of the external arcing. Maybe a layperson could drive up onto ramps, slide under the idling car and have someone turn off the lights?

Glenn

#9 10-25-2004, 04:03 PM

is the insulator on the coil pack a seperate part or do you have to change the whole unit?

RojoRocket · #10 10-25-2004, 06:24 PM

Quote:

Originally posted by camosuba
is the insulator on the coil pack a seperate part or do you have to change the whole unit?

The insulation is where the trigger wiring meets the coilpack and is part of the entire magilla. Take a look here, a new coil, but you can see what I'm referring to.

http://www.subaru-svx.net/photos/fil...cket/21852.jpg

Glenn

#11 10-25-2004, 07:41 PM

I thought it was the piece where the coil met the sparkplug that might be faulty it looks to be rubber , would this make it short/miss also would having a cam cover leak in this area cause it to play up if the oil was contaminating it?
regards camo

Ps I am trying diagnose a car that is 2000km's away ,but it looks like my brother is going to fly me there to fix it ! lucky me! I think i'm cheaper than the dealer!

RojoRocket · #12 10-25-2004, 08:31 PM

camo, I see exactly what you mean, and it makes sense that the high energy spark at the "business end" of the coil-pack would be the area arcing/snapping to the head if the boot were deteriorated. I just took a look at the old packs, and a couple of the "boots" are stiff, cracked, etc and it follows that those would be the trouble-makers. However, the wiring insulation in the trigger-wire input area is also gone, with bare wire on both input wires, hence my comment about wet weather, as that end is exposed to "splash/mist" when running in the rain.

The interesting part though, is that the rubber "boot"endcaps are exactly that, caps that pop off the pack, and would be an easily replaceable part if Subaru found it in their heart to sell only that part. Couldn't be more than a $2 part if available separately!

Glenn

#13 10-26-2004, 11:17 AM

Surely as a quick fix to check if this IS the problem, couldn't u use a silicone sealant to seal the tops again? & the bottom rubber covers 'look' like the rubber boots u find on spark plug leads?
I may give that a go 1st, b4 i buy a few coil packs!

Phil.

#14 10-28-2004, 02:01 AM

i've checked here and you can only buy the whole unit so we'll have to check them out . Would i be right in the assumption that the coils are the same as each other but the wiring lengths are different ? which is why there are 3 different part numbers? are the plugs different as well?
regards camo

SilverSpear · #15 10-28-2004, 06:05 AM

Quote:

Originally posted by Notall There
Hi Guys, just done the head gaskets on my svx, well worth it as it drives well now!

Just 1 annoying problem left - when the engine is warm & idling, it 'coughs' just a small miss, like 1 of the injectors forgets 2 fire?

I had a listen under the bonnet (hood for the usa! lol) and it sounds like the injectors on the left bank, 1 will make a 'louder' click when the engine misses! all 3 have done it, but nothing from the right bank!

I dont think it's any of the sensors under the intake manifold, pretty sure it's the injectors making the noise, but only 1 at a time!

I'm running it on 'normal' unleaded fuel at the mo (due 2 the cost in the uk of super unleaded), but surely that won't make THAT much difference? I've run cars which specify 'super' before on 'normal' & i've only noticed a slight drop in power, not missing or bad running!

I've checked the connections & they seem ok, will try some 'Injector Cleaner' in the fuel, & then some 'super' unleaded, but it does seem 2 be electrical rather than actually the fuel itself!

Anthing else worth checking?

Thanks,
Phil.

did u try the spark plugs? their wiring? if averything is ok, try to switch the injectors with the right bank, and see if the problem persists