My check engine light came on about a month and a half ago. Pulled the codes and had a misfire in each cylinder with a multiple random misfire code. I cleared it and it came back after a week or so. Since then, it comes on for about a week, goes off again for about a week, and repeat. .. the car seems to drive normal throughout. I have 95k miles and is a 6mt. I will admit, I did mis shift a downshift once before, but it was 6 months ago and I hit the clutch once the tach hit 7000rpm for a split second. Light never came on, and no change in driveability. Just before the light came on about a month ago, I seafoamed because I noticed surge/hesitation symptoms. Seafoam helped that issue, and a couple months later am having this issue. Any ideas or fixes?

 

Time for a valve adjustment.

 

^^^^prolly more like a valve replacement

 

I forgot to add that the light always seems to come on at idle just after a cold start when I let the car sit to warm up.

 

Check your spark plugs and wires down to the 02 sensor, you could have a faulty sensor somewhere that you'll have to find.

 

i bet it was over revved

 

OP tells us he over-revved.

 

ill just go ahead and say he bent all his valves.. get a leak down test done. but you might as well start looking into new heads now op.

 

I'd say screw the leak down/compression test
and just dig right into the heads.

 

It was overrevved but the light didn't come on til 6 months later. Never noticed a change in how the car drove

 

get a leakdown test man. im sure the heads are toast if its missing in all cylinders.

 

How is a leak down test done as opposed to a compression test? I've done a compression test before but not a leak down.

 

You can do a compression test first. If it comes out good then do a leak down. If the compression test is bad no need for a leak down.

A leak down test is just that, you put a metered amount of air in a cylinder through the spark plug hole and measure how quickly it leaks down. It's much more accurate than a compression test but it won't turn up things like. Bent rods like a compression test does.

The reason it took a while to get the misfires is you only slightly bent the valves at the time of the overrev. The valves cool themselves by fully closing and transferring heat into the valve seat and ultimately into the heads. Yours were not closing uniformly and it led to burned valves which is why you have the misfire. The other reason is if they're slightly bent they're weakened. When you figure they open and close 7 times a second at idle and 58 times a second at redline you can see how they can fatigue and get even more out if shape.

Compression problems show up more at idle and less as the rpms come up so you probably run into more problems at idle.

 

I did the same and my car had to have both heads rebuilt. I have a guy who is a master tech at Honda of Enfield in Ct if you're not to far from there that will do the job for a good deal

 

these motors burn valves so easy. I burned all the valves in my wrx running 25 psi and it still ran strong for 10,000 more miles then i could start the feel the misfiring. Swapped the whole motor considering it had 190k on it and 90k of those miles were big turbo and high boost. . So im not surprised your not feeling any misfires, YET.

 

How did you burn them in the first place? Do the suburus use Inconel or some other high temp exhaust valve? I tried the Manely "severe duty" exhaust valves in my turbo car since the factory inconel are hard to come by and they were fine until I started jacking up the boost. It also didn't help when I had a bout of very retarded timing for a few days.

 

i just think high boost and over revving bent the valves up. plus all that boost over time in an aging motor takes a tole on the valve train. im surprised i got 90k out of the big turbo set up IMO. good tune i suppose.

 

i have the same problem, had a valve adjustment, leak down test down and all didn't fix the problem, i have a small lost of compression on cylinder 1 but all other cylinders are fine. yet my check engine light tells me all six are missfiring. my next guess is a burnt valve or something along the ECU..let me know how you make out

 

i think it has something to do with mapping, my car runs GREAT sometimes, check engine light goes away. then a few days later the car will randomly run awful. if it was mechanical problem wouldn't the car run poor all the time?

 

Just wanted to update everyone since I started this thread. I did a valve adjustment myself and I think that was the fix. Its been running strong for about a month and a half with no issued or CEL. In fact, I feel restored power, and better fuel economy. She was due for some lovin. Now to continue mods....custom magnaflow exhaust is next with 3rd cat delete. Any suggestions on the setup?