Subaru Forester is leaving me baffled

I have a 2000 subaru forester, 190k mi on it, owned it less than a year. when i bought it the head gasket needed to be replaced which was done. a few months later it started hesitating, like it wasn’t getting enough power from time to time. shop said it was exhaust problems (it was badly rusted and leaking). There were also some codes that came up, knock sensor, ignition coil and a vent solenoid. I replaced all of those things including my entire exhaust and the plugs and wires myself. car ran for a few weeks and then totally died on the highway. the engine will idle (poorly) but won’t go and dies when you give it gas. A friend and I looked the thing over, knock sensor code is still coming up, compression is fine, timing is off very slightly. he’s thinking it’s possible it could be the timing? maybe a bad fuel filter? i really want to figure this out before throwing more parts at it and super don’t want to replace the timing belt if i don’t have to. help!

How do you figure the timing is off very slightly?

The compression is defined as “fine”. What are the numbers?

A knock sensor code does not mean the knock sensor is bad; only that there’s a fault in that area.

Offhand, I’d say connect a vacuum gauge to an intake manifold vacuum source and see what that reveals.
I’d also say that you should not dismiss the timing belt because if it breaks the engine will suffer damage and everything becomes moot points.

the knock sensor before was cracked but with the new one i figured it was something else and there is a knocking in the engine now. When we looked at the timing we took the cover off, lined it up with zero and then looked at the marks which were not at top dead center, but like i said was only off a bit. i want to change the belt but also want to get to the bottom of this problem plus it’s snowing now i have to do the work outside. Honestly at this point i don’t remember the compression reading but it was within the specification range given in my manual

You might try replacing the MAF sensor going from what you describe about the trouble.

Sometimes , paying for a professional diagnosis is money well spent, even if you plan to replace the parts yourself. To be fair to your mechanic, you should tell him up front your plan.

Oh, I thought you meant the ignition timing was a bit off. If the ignition timing is only 2-3 degrees off, that wouldn’t cause this symptom. With that you might get some pinging if advanced, or loss of power if retarded, but that’s about it.

But if you mean the valve timing is off, that’s a problem that needs to be addressed before spending time and money assuming the problem is something else. The valve timing has to be spot on anytime you are doing an engine diagnosis. Mechanics rarely find engines with the valve timing off, so its not usually an issue. But in your case, suggest as first order of business to correct the valve timing problem. It might fix all your symptoms.

It’s usually possible to set the valve timing without replacing the timing belt, which should save you some $$$ in labor.

You were correct to replace the rusty exhaust system. Modern engines are designed to be air-tight contraptions from the air filter to the tip of the exhaust pipe. Any leaks will usually cause difficult to diagnose drivability symptoms. Along these lines, make sure all the intake path, including the various boots and vacuum lines are in good condition and not leaking. It’s always a good idea to check the PCV with symptoms like this too.

I’m with oldtimer on this. I’m reading guesses, but no diagnosis. Things like fuel pressure and much more can be tested rather than guessing.

I liked OK4450’s suggestion too (I almost always do :smile: ). A vacuum gage used correctly can tell you a great deal, and there are some good pamphlets on how to use one… there’s probably even a pamphlet on how to do so in the box that the gage comes in. A kit with fittings will cost you probably less than $50, and it’ll be useful forever.

I commend your willingness to do your own work. Learning some diagnostics will, in the long run, save you a fortune and make working on cars yourself far more gratifying.

Oh, and exactly what “knock sensor code” are you seeing? If your code is suggesting a bad sensor, that’s one thing, but if your “known” slightly advanced ignition is causing signals from the knock sensor, you could be damaging your engine. Long term unresolved pinging or preignition can do serious damage. This problem needs to be resolved.

Thanks everyone. I just put in a new MAP sensor, car is idling better but dies when i give it gas. The knock sensor is new, i replaced the old cracked one months ago. I was going to check the PCV valve next and check the fuel pressure. problem with the mechanic is i already replaced everything they said was wrong with it at this point. thought about taking it to the dealership but they charge an arm and a leg just to look at it

Did u replace the cats? 1 or more could be failed/ restricted.

It seems that the engine isn’t getting the fuel pressure it needs. If the fuel filter hasn’t been replaced that would be my next step along with verifying the fuel pressure of the pump and to the injectors. The fuel pressure regulator may be bad.

Join and post at this site. They know Subaru’s.

im actually on that forum, they have been really helpful. The cats were replaced and the O2 sensors (along with the rest of the exhaust actually). i’ve been trying to solve this problem for months. it started slow, it would hesitate from time to time but now it just won’t go at all. i have not changed the fuel filter yet, i might try that next. it doesn’t appear to have been changed

Here is how to use a vacuum guage.

i gave up and took it to the dealership but now they can’t figure out whats wrong either! extremely frustrating although i do feel a bit better about my diagnostic skills

I’m all in favor of checking other sites but one thing should be kept in mind and it applies to other sites; not just the ultimate subaru site.

Some of the “Subaru experts” on that site are very misguided to say the least. I base this on the complaint from a guy who posted here some years back about a rough idle. He was told by (?) on some other site that this may be caused by bad ring/pinion gears in the transaxle.
That of course is utter BS and I told him so. He chose to argue the point…

A few days later he had posted on that subaru site and ripped me a new one over what I said here.
Some of the long time “experts” on that site were in full agreement with the Subaru owner that I was an uninformed doofus…

Needless to say, I have to question the mechanical acumen, or sanity, of the Subie experts who agreed with him.
I try if at all possible to avoid crude language but if I were going to go with the crude version of the above I’d say those Subie experts are effin’ clueless twits for even considering a line of thinking like that.

You towed your car to a Subaru dealer, they can’t diagnose the problem and you must tow the car elsewhere, is this the case?