I recently picked up a 95 Impreza L coupe with an EJ18. From idle to ~2500rpm it hesitates, jerks, and misses. Once it is above that rpm range, it runs great. I have searched threads for two weeks and tried multiple "standard fixes" with no results. I'm tired of throwing parts at it and Any help would be appreciated. So far I've checked the plugs (newish but looks lean), repl wires, repl fuel filter, repl throttle position sensor. This engine does not have a knock sensor (not that I could find anyway).

What shape is your timing belt in? Not a similar car, but I once had an Nissan Pulsar that ran the way you describe when I bought it. We had a new timing belt put on (the old one was 14 years old!) and it ran great, so I figured the old belt might have jumped a cog or two on the sprocket.

I would also guess timing is off a tooth.

 

Ej18 I don't think had a knock sensor. If it did its in the same place as every other EJ block under the manifold. Look straight down between the throttle cable levers on the side of the throttle body.

 

Search for my knock sensor 101 thread for pics.

It does not appear to have a knock sensor. I will probably be dropping it at the shop to let them check it out this week. I'm just fed up and inching closer to finding the proper size rag for the gas tank. Thanks for the direction though. I will mention that when I drop it.

So I pulled the timing cover and it appears to be timed correctly. Any help is greatly appreciated!!! I'm not in love with this car right now.

Does it transition from running like crap to running good or is it like someone flipped a switch when you hit the crossover point?

 

Have you done a compression test? basic misfire location test (unplug one spark wire at a time (from the spark plug and place it close to a metal surface to arc to))? actually replace the plugs rather than just looking at them (They can fail without external signs, my last bike was like that. Every spring. ugh)?

 

Vacuum leaks? MAP sensor?

Does it transition from running like crap to running good or is it like someone flipped a switch when you hit the crossover point?

 

Have you done a compression test? basic misfire location test (unplug one spark wire at a time (from the spark plug and place it close to a metal surface to arc to))? actually replace the plugs rather than just looking at them (They can fail without external signs, my last bike was like that. Every spring. ugh)?

 

Vacuum leaks? MAP sensor?

It is more like flipping a switch at 2500rpm. Have not checked compression but did check the spark. It has a MAF. Would it have a MAP too?

Any chance you can post pics of the timing marks? 

 

MAF sensor could cause that sort of issue as well. If it s a MAP sensor it would be on the right strut tower. Some of the 95s had both MAF and MAP. Some just had a MAF. 

 

I'm just fed up and inching closer to finding the proper size rag for the gas tank. Thanks for the direction though. I will mention that when I drop it.

This may be something, are you missing a gas cap? If so I would inspect your fuel, its possible you have water contamination.

I would also check codes and check for vaccume leaks.

So far...

Had a Subie tech check the timing. It was off by a tooth and was corrected (at no charge other than a 12 pack).

Could not find any vacuum leaks

Yes I have a gas cap

Replaced fuel filter, crank sensor, throttle sensor, wires

 

Possibilities I could see causing issue....

MAF, O2 sensor, Cam sensor, injector...????????????

Maf is the most likely cuplrit in that list. O2 sensors rarely fail, cam sensors usually work or they don't, injector is possible but less likely that the maf.

 

I would try a used MAF sensors they are cheap and easy to get swap out.

I'm going to try cleaning the MAF to see if there is any change before buying another part.

 

I also have an opportunity to pick up an H6 from an SVX. Any advice on whether that swap would be a good or bad choice would be appreciated. I'm looking at other options in case I can't figure out this ej18.

MAF checked out. O2 sensor is the last ditch before I seriously start considering a swap as an option.

MAF checked out. I replaced the oxygen sensor today and gutted the cat (to ensure it wasn't clogged of course). Still runs like shat.

 

Updated repairs thus far-

Wires Repl.

Plugs Repl.

MAF Repl.

Fuel filter Repl.

Timing checked and reset

Crank sensor Repl.

Coolant temp sensor Repl.

Catalytic Converter "cleaned"

Checked for vacuum leaks

Throttle Pos sensor Repl.

 

I am completely confused by this. Nothing so far has made the slightest change in the misfire / hesitation.

Edited March 24, 201610 yr by Fubaru

Check the compression before you replace any more parts, because that is obviously not working. I am running into the same issue with my car, but it is completely random, so I am thinking an electrical issue on mine, but one of my next steps is to check the compression. 

I pulled the plugs and wires again and the plugs from cylinders 1-3 were torched white. I purchased new NGK g-power plugs and replaced all 4 plugs just to see if there would be any change at all. PROBLEM SOLVED! I feel dumb for not doing that before but after replacing the ones that looked bad originally, I didn't think it could be plugs. smh.

White indicates its running too lean. Were the plugs on the 2-4 side the same color?

If just the 1-3 side were white you could have a vacuum leak at the manifold gasket or the fuel rail o-rings on that side.

All plugs were white except the one I recently replaced. It looked good but may have been on it's way to being white also.

All of them looked very white except the one I had replaced last week. It looked like it may have been on it's way though.

Too lean would explain your stumble problem.

 

With all you've done so far, it would be good to check fuel pressure while its under load to see if pressure is dropping off.

Be careful running the engine with an overly lean condition, as it'll grenade a good engine easier than a rich condition.

 

Might want to get some type of spray fluid, and with engine barely warm and running (warm enough it's not in high idle and has settled to constant idle; but cool enough you don't get a flash explosion if it touches headers.), spray your vacuum lines down, their end fittings, move them around while spraying including the brake booster hose, and spray down the intake manifold flange areas, throttle body, etc. and see if it surges or bogs down. While not fool-proof, it can sometimes find the leak.

Edited March 26, 201610 yr by Bushwick