Help wanted to diagnose Impreza Turbo'97 problem
 

Out of the blue, the number 3 cylinder on my '97 Impreza Turbo has stopped firing, regardless of engine speed.

I've had the car from new, it's done approx 40k. miles. No mods. or any work has been done on it (so far) apart from oil changes, service etc.

I pulled the sparkplug lead and ran the engine - it gave a strong spark...

I connected those 2 black connectors under the dash, turned ignition on.
Engine warning light just gave a steady even, continuous flashing, which I understand means no errors.

Question: if injector was blocked or faulty would this give an error code?

Any input would be appreciated.
Thanks

I would think a faulty injector would throw a code.
Have you taken the spark plug out to check if it's not just a broken plug?

As said by ossett2k2 pull the plug out. hopefully its still in one piece. ull also see if fuel is getting in there as it should be wet with fuel if its not firing and fuel is being injected. Have a look to see if the injector plug is plugged in firmly. Loss of compression is another option.

unplug injector and start car, if the symptoms are the same then you have your answer.

Had this only yesterday on a hawk wrx...no injector fault code just po304 cylinder 4 misfire detected.
compression good,spark plug and coil good, checked injector for power: no power at injector.
traced the fault to corroded and broken terminals in the 16 pin brown plug behind the battery,
repaired wiring now running sweet as.

Thanks for your reply. I will be having another look at it tomorrow and will remove the plug for inspection .

Thanks for your reply.
I hope it turns out to be just the sparkplug.

I'll check that also, thanks.

I'm puzzled though , as I said, I don't get any error codes at all... the #3 cylinder is not firing at all.

A cracked or burned out or unseated exhaust valve would cause the same symptoms cant fire when the fuel is rammed into the exhaust unburned.

My car often stands 2, sometimes 3 weeks between runs, and usually they are very short trips.
Could this have a bearing on the cause of the misfire? I'm thinking fuel supply, injectors etc. rather than electrics.
(OK, I have removed the plug and it appeared to be fine - insulation and general condition are fine, and it sparks OK.)
Any opinions about relevance of car infrequent usage?

As per JDM mentioned, unplug no.3 fuel injector and start your car.

That is not going to help. The car is not running on that cylinder. Unplug the injector and nothing will change. You will really need to remove the plug and compression check.

Do a compression test if all ok Use a test light on that injector plug if that flashes (with car running) then the injector is getting a feed and if the spark is good then only thing it can be is faulty injector

Thanks for your reply - things have changed though. See my next post.

Update on the situation... now it's #4 cylinder misfiring!
Without me doing anything, the misfiring (not firing at all when idling) on the #3 cylinder, the problem just disappeared by itself, and all was fine for several days. I ran the car around, did several trips of about 5 to 10 miles each day and all was fine.
Day before yesterday, started the engine and the misfiring has come back. Obviously, I assumed it was #3 cylinder, but no, this time it's #4 !
( I verified this by pulling the spark plug leads - pulling #3 nearly stops the engine, pulling #4 nothing happens)
I listened to the injectors on #3 and #4 by pressing wooden stick against the injector body and to my ear, got quite a distinctive loud ticking corresponding to the solenoid functioning of the injector.

If anybody's got any ideas , please post.

PS I checked the MAF (by running with it unplugged it's worse)
I checked for vacuum leaks etc - nothing found.
When driving along at approx 15% - 20% throttle, if I move the accelorator just 1/2" back and forth, I feel the engine suddenly pull on all 4 cylinders, but it's only momentarily.

does the 97 have the ignition igniter on the top of the manifold ?

Its under the boost solenoid like the earlier cars. 97 is a wasted spark system, so each side eg 3 and 4, will spark at the same time even when not required. If you swap the leads on the coil for 3 and 4, the car can/will run normally. If you switch them as your car is now, and the missfire swaps to the other cylinder, you have a coil problem. If no change go back to the ignitor.

Thanks for this info. I didn't know about the wasted spark system.
I just tried what you suggested, but I was rushed, and I'm not satisfied that #3 fired normally using the lead from #1 (although it seemed to do so)
I will try again tomorrow.

However, I noticed that there's a strong spark coming from both #3 and #1coil connection holes (where the spark plug leads push in)
I ran the engine on just two cylinders.
Having pulled the #3 and #1 leads from the coil, the spark arcs between those two sockets and the manifold, so I would assume the coil is working OK ??

Edit: I should have put cylinder #1 not #4. Now corrected to read #1

I have found the culprit, it was the spark plug on that cylinder.
I've replaced it and the car is now working great.
As a matter of interest, the plug looked fine after cleaning.
However, testing with the multimeter showed a hidden leak or partial short-circuit of approx. 3K ohms resistance between the body and center eletrode.https://cimg7.ibsrv.net/gimg/www.sco...1a90653c4c.jpg

Mighty gap your sporting on that plug!

Yes, it looks big, but just measured it and it's 0.72 mm.