misfire problems
 

Ok.. it's not a SVX, but it does employ direct ignition. It is however, a Subaru.. a '91 Legacy wagon GT Jspec, with the 2.0L turbo engine. I have been having a misfire for sometime, but only on occasion. Recently, it has been getting worse. Mostly happens when it is good and warm, and when I come to a stoplight and idle. Sometimes, when I floor it, I can feel one cylinder not firing correctly. The plugs and coils were replaced(yea.. thanx a LOT Subaru.. it DIDN'T fix the problem).. and I'm not sure what to look at, cuz I'm not used to direct ignition systems. Any thoughts on how to trace this down?

Long winded but hopefully helpful (so what else is new? ;) )
 

Don't rule out the possibility of a fuel injector going bad. They feel identical to a spark miss. While the engine is running and missing unplug one injector at a time to find the culprit cylinder. This doesn't tell you if the injector or spark is bad, but you'll know which cylinder to concentrate on. Check the spark plug for that cylinder, if it's good continue to next paragraph. If not, replace it and retest.

From here I'm not familiar with the ignition you have, is it like the SVX with a coil on each plug or is there only two coils? The approach to determine the cause depends on which system is used. If COP (coil on plug) you can remove the coil but leave the wiring attached. Place an extra spark plug (leave the one in the engine) in the end of the coil and place the pair on a metal portion of the engine, away from any potential fire hazards, and start the car. Check for a big bright blue spark. If there is no spark you'll want to use a test lamp and make sure there is a negative pulse (12v system) and a constant power (also 12v.) If there is a lack of power or pulse you'll need to check the wiring and the computer/ignition module (whichever is applicable.) If pulse and power are present you've found a bad coil (assuming the spark plug is good.)

If you only have two coils it's much easier. First off, were there two cylinders missing or only one? If two cylinders are missing, are they co-joined at the same coil? If so you probably have a bad coil, wiring or computer. If not you probably have a bad plug, spark plug wire or injector. Just place an extra spark plug in the affected spark plug wire and rest the plug on a metal portion of the engine (away from any potential fire hazards), start the engine and watch for a bright blue spark at the plug tip. If there is no spark and only one cylinder on that coil is affected swap the spark plug wires for that coil. If the problem moves to the next cylinder the wire is bad, if not check the coil tower for a crack leaking to ground. If you have a spark and the plug is good you probably have a bad injector and will need a fuel pressure gauge to check further.

There is a small chance that there is a mechanical problem, but highly unlikely. The only thing that comes to mind that would be intermittent would be a valve hanging or a loose valve seat and both are almost unheard of these days. Plus they tend to be constant rather than intermittent.

Beav

Each cylinder has it's own coil. All coils have been bench tested according to Chilton's manual, and tested good(I think slightly off what the specs were, but all coils were the same). I should also add, that it does this a LOT first start of the day, when it is cold. If I don't let it warm up, and I put it in gear and start to drive away, it will sputter, almost stall, then suddenly give me a burst of power, then sputter again.. basically making the car buck. For the past few months, it has been kicking into high idle when cold, and I let it warm up that way. The past week it has decided it doesn't need high idle, and therefore sputters down to a bare minimum RPM, shakes quite a lot. I can give it gas, and it picks up, but if I just hold the pedal steady, it will sputter again. To keep it from sputtering, I need to constantly increase the amount of pressure on the pedal. After about a minute, it is fine. It has stalled a few times on me, but on the whole, just runs like crap until it is warmed up.

What you're explaining now is more indicative of a fuel or control problem. Diagnosis from this distance is difficult, the best I can do without typing out an entire manual is to suggest a few directions. Does the car smoke (white) when first started cold, as maybe an injector is leaking down? Pull off the snorkel tube and inspect the throttle body and plates - if the plates don''t close properly it creates havoc with the controller and idle can be extremely erratic. Try cleaning the throtttle body with a good carb cleaner, and while you're at it do the same with the MAF sensor, if so equipped, just be very gentle with it.

If the problem still occurs check the temp sensor for proper values. I'm thinking that if this continues for very long you may risk your O2 sensor(s) if they're not already damaged.

Let me know what happens.

Beav

May be air leak.
 

Could be a air leak between the air flow meter and the engine. This would produce a lean mixture at idle and off idle pickup. As extra air is in the mixture that the air flow meter didn't tell the ECU about. Would not affect higher engine speeds.
All the best .
Harvey.

I don't think it is air, because that should affect all cylinders. And I know it is only one cylinder, and here's how:
(Also.. have not noticed any kind of smoke from it.)

Tonight I was driving around, testing out my new turbo meter. Let the car warm up about a minute, then started driving. Did a bunch of off-the-line runs to see how the boost reacts to that, and some floored-while-moving runs to see how it does then as well. After about 20 minutes, I did another off-the-line run, and noticed at about 50km/h, at high rpms, I felt a very slight jerking. It was the feel of a single cylinder not correctly firing. Don't know if it's a miss, but I don't think it is. It was very slight, the kind of thing you might not catch if you weren't feeling for it already. Nothing noticable on any of the car's guages. The last time I pulled the plugs, 3&4 looked the worse, with some carbon on them. 4 was the worse of the 2. So I suspect the problem is with #4. My best guess would have to be fuel at this point, because it has a new coil on it, with a new plug, and when these were replaced, it didn't change anything. And it feels like it IS firing, just not enough power(the only reason I say this is because I believe a complete lack of a firing cylinder would result in a much more noticable jerk in the rpms, as well as a CEL). So fuel injector problem?

What's in a name?
 

Hi Bagheera

An OT question about your name. Have you any interest in French Matra cars, or are you a Jungle Book fan?

Joe
[Bagheera owner]:)

Came from the Jungle Book.. what is a French Matra car?

Bagheera
 

history:

Matra are a French aerospace company[they make satellites, missiles, heavy stuff] who made racing cars in the 60's and 70's. They had notable success in LeMans same period as Ford were doing well with the wonderful GT40.

They had a number of road cars, including the D'Jet, the Bagheera and latterly the Murena, and they also designed the Renault Espace people carrier, before selling the motor assembly line to Renault.

The Bagheera is a really cute car, three seats abreast, mid engined, low and sexy, and designed in the French idiom, more for style than for outright speed.

Pic enclosed from a French website:

Joe:) :)
This is not mine. My one is black, with acid green velour seats, not yet restored.