Serious issues - Need help!
 

EDIT: The car is 100% stock, 124K

Over the past couple months I have had a cel briefly come up 3 times for random misfire. I changed my spark plugs after it came up twice, and i had no issues for nearly a month. The light came up again for the same issue a week or two ago.

I took my car to have the clutch done at a local shop that was recommended by lots of socal s2k owners, and while it was there i asked him to pull the code and check around to see if he can figure anything out.

Before he did any work he pulled the code, and it came out "random misfire cylinder 3 and 4" (I've have all cylinders already before)

When the car came it, it ran and drove fine, you can take it to 9k no issues, only rarely it would idle somewhat unsmooth.

The shop changed the clutch and flywheel and called me to pick it up. When I showed up, he was replacing my coils with spares he had in the shop. He had switch coils 3 and 4 with 1 and 2 to see if the code would come up for 1 and 2 to pinpoint bad coils. He took it for a test run and it drove fine until suddenly it was cutting out on him at 2-3K rpm. He switch to 4 different coils, and I went to drive it around the block, and as soon as I got out of the driveway, i couldnt get the car above 10 mph, it feels like a fuel cut at 2 or 3K rpm. It also idles like it has a big cam in it.

We let it run, pulled codes and reset about 5 times, each time it came up with random misfire, all cylinders (1399 i think it is) except one time we pulled high o2 voltage.

More info:
Restarting the car allows the car to run fine, it seems like closed loop has no issues, sometimes as soon as it goes into open loop, its idling/running terribly, sometimes it runs fine for a while.

Based on research and possibilities, we replaced the following with parts:
Coils (used spares in the shop)
injectors (known good)
MAP (brand new)
o2 sensors (spare used ones he had in the shop, unknown condition)
Checked every connection and censor and they looked good.

The tech was convinced it needed a valve job, otherwise hes stumped. I told him that makes no sense, the issue is obviously electric due to its randomness. Sometimes its there, sometimes it isnt. Restarting the car cures it briefly.

I just ordered a pre cat o2 from the dealer and will have that installed when it comes. The closed loop operation, o2 code, and the fact that the issue seems to be electrical lleads me to beleive its my first step at this point. (even though we tried a used o2 he had int he shop.

After this, I am absolutely stumped and really need help.

BTW, the new clutch feels excellent. ;)

hook up a fuel gauge, see fuel pressure dorp when the engine stall,

what would that tell me?

the fuel pumps has a check valve builded in to it, if the check valve is bad, gas would bleed back to the tank (not enough fuel pressure to the engine) cause engine to stall, misfire..etc etc.. Just another thing you can check before throwing more parts in it.

How do you know the injectors are good?

Misfires are usually caused by: plugs, coil packs, injectors. Very rarely, valves may be the problem. A leak down test will tell if the valves are the culpret.

On s2000 , misfires usually cause by mishift/ over rev. bent valves or cracked retainers. IMO. thats 9 out of 10 s2000's i see had misfire code.

[QUOTE=negcamber,Jul 20 2008, 05:30 PM] How do you know the injectors are good?

Misfires are usually caused by: plugs, coil packs, injectors.

How long have you had the car?

So you replaced old plugs with used plugs?

Buy new OEM plugs gapped at .044-.046 and change all 4 at the same time.

I replaced with brand new OEM spark plugs. (updated)

I bought the car in the beginning of april and only have about 6,000 miles on it.

(edit: since buying it USED)

huh 6k miles? you might just have some bad gas in the tank