Stumbling, shaking; even on coast-down?

[James614]

Been driving my EJ20G around for the first time, and its not acting too happy. Initially I was using a Robtuned ECU that has suspected circuit board damage. The car idled roughly, and was rough if you blipped the throttle. Driving is way too rough to even leave my development. On decel in gear it was just as rough. I pulled the codes and got 31 and 45. Tested the TSP's resistance and it seemed fine. So I threw on a spare, unmolested EJ20G ECU and it the codes went away (had a code 44 until I remembered this one isn't tuned, so I threw my dropping resistor in there which fixed that issue). Feeling hopeful, drove it again but she acts the same, no codes this time.

Kinda feels like a bad misfire, but what really gets me is that it doesn't smooth out on decel at all. It still occasionally bucks on decel too. Makes me think its probably something internal to the engine. Thoughts?

[Alphius]

I would start by checking compression/leakdown on all 4 cylinders.

[mjc1310]

I faced similar issues but with my ej22. Have you looked back over your timing to make sure you aren't ever so slightly off?

[James614]

I'll check compression this weekend. I doubt its the timing, it shouldn't be knocking around off throttle if that were the case I'd think.

[ride_child]

have you tried checking any of the other ignition components? i know a lot of people on here had hesitation issues and it wasthe alternator, coil pack or both. being lazy and not checking those other threads so i dont know if its the same hesitation, but its probably worth checking out

[Alphius]

With a warm engine and decelerating above 1500 RPM the injectors are turned off for Decel Fuel Cut. Any fueling/ignition issues would not be causing an issue under these conditions.

[James614]

Okay, finally got , compression numbers:

1 160
2 162
3 165
4 150

4 is lower, but the spec for the UK WRX EJ20G is 132- 165ish so its not "low". All the spark plugs looled normal.

[James614]

Would something on the bottom end possibly cause my issue? I cant hear any audible knock or piston slap.

Im positive I didnt, but ill ask since I heard it mentioned somewhere: would mistakenly swapping the intake and exhaust cams on one head possibly cause an issue like this?

[cj91legss]

Do you remember looking at your cam shafts when you were installing them? Each camshaft is labeled. When I get home ill look at mine and see if theres a physical difference. Im sure there is and I would guess the car wouldn't run at all.

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[James614]

I saw the labels, and like I said I'm certain they aren't switched. But its something I touched on the engine so I figured I'd just see if its plausible given the symptoms.

[James614]

Okay, I got brave and took it on a longer and faster test drive tonight. Got a better idea of how its behaving.

- Noise/vibration from propshaft or rear diff. This was definitely contributing to what I thought was roughness in the engine. Because of it I don't want to drive it over 30mph. I think this may be related to me using a high-mileage JY rear diff.

- Occasional bubble in the overflow. Bad head gasket? Even so, shouldn't be causing drive ability issues.

The engine is less rough than I thought, the main issue is its sorta low on power (this is my first time on a 2.0, and car wont go fast enough to build boost so I'm not sure what it should be really) and falls flat if I give it any sort of real load. But the shaking seems to be from the drive train.

I checked for spark on each coil. I'm kinda leaning towards the knock sensor or its wire being damaged during my swap at this point.

[Alphius]

Yes, sort out any drivetrain issues before focusing on the engine. Are you absolutely certain that your transmission and rear end are the same ratio?

[James614]

Pretty sure they're the same. The early WRXs were almost all 4.11, and that's what I found from multiple sources checking the code. The rear diff is suppossedly from a 91 MT Legacy and has 4.11 stamped on it.

I'll start with checking the diff fluid. How common is it for drive shafts to be terribly unbalanced in these cars?

[James614]

Holy fucking simple batman. Okay, the roughness was just my exhaust rubbing the axle, nothing major. I just kinda ignored it because of the bigger problems with the engine. The cutting out, hesitation, etc? The AT/MT identifierpin. God dammit. I'm so happy and so pissed right now. Quite possibly the stupidest and longest reason a car of mine has ever been not up to DD status.

[James614]

Im running waste gate boost on a stock WRX wagon ECU right now, and its already faster than my 22T with a TD04 at 13psi. Can't wait to crank it to 15 and stick my rob tune in there

[Legacy777]

Glad you got it sorted out.....it's always the little things