New member... and my first post is a long one. I've had a misfire on cylinders 2&4 since November of '09 on my 1997 Legacy Outback 2.5 DOHC Manual Trans. with about 155k miles. The misfire persists despite the work done below.

 

I have replaced the following in the last 3 months or so:

-Plugs

-Wires

-Coil

-Headgaskets

-Timing Belt

-Tensioner

-Water Pump

-Seals

-Header Pipe

-EGR Sensor

-Igniter (used)

 

I have had the following services performed in the past 3 months:

-BG fuel system cleaner

-Seafoam in gas tank, PCV valve & motor oil

-Throttle body service

-Reset TPS & IAC

-Leakdown on all cylinders (no problem)

-pressure test on all injectors (no problem)

 

My next step is to replace the ECU. I pulled an ECU from an automatic '97 Legacy Outback but my car is a manual '97 Legacy Outback. The VIN's are below. Is the junker ECU compatible with mine? I'm open to any other suggestions that may fix my misfire problem, too. Thanks for any help.

 

My Car: 4S3BG6859V6611396

Junk Car: 4S3BG6850V7622314

 

-Sean

To quote myself from an old thread:

 

There are certainly a few possible causes, but there's a simple one to investigate. Verify that the injector connectors for #2 and #4 are in the right place (not reversed). The engine will start and run with them swapped, just not very well. There should be a piece of identifying tape around the harness right at each injector connector; it's white on the front cylinders (#1 and #2), and black at the rears (#3 and #4). If the tape is missing, you can check the wire colors.

One more thing -- in looking over your list of things done, I don't see any indication that valve lash (clearance) was checked or adjusted. It can be a less-than-obvious cause of misfire if out of spec enough.

I ran out and checked on the injectors. White on the front and black in the back. Not sure about the valve clearance. Wouldnt that be ruled out by the leakdown test?

 

Any thoughts on the auto/manual ECU transplant?

[...] Not sure about the valve clearance. Wouldnt that be ruled out by the leakdown test?

A leakdown test can reveal if the valves are sealing well when closed, at the temperature the engine happens to be at when the test is done. However, there could still be excessive or insufficient clearance during actual running conditions, especially when taking into account metal expanding/contracting with temperature change. Subaru lash is typically speced with a cold engine so that it remains within tolerance when hot.

 

 

Any thoughts on the auto/manual ECU transplant?

I believe that there's a particular pin on the ECU that determines (by it being grounded or not) whether it "thinks" it's in a car with auto or manual. How do the part numbers on the two ECUs compare?

So an auto versus manual ECU swap should be plug and play assuming all else is the same. My car must have the ground wiring going to the transmission pin. Reconnect everything to the new ECU and I should be set. I'm not sure about the part number for my ECU; I'm waiting for the snow to melt to pull it. The junker ECU has these numbers on it:

 

DF7 5N, 22611 AD000, JA18000 DF7, and 6X29.

 

I'll compare when I pull mine out.

Also, I'll keep the valve clearance idea in mind. First, though, I'm gonna try this "new" ECU. It may have problems of its own, but they'll probably be different problems. This way I can be sure before I spend $300-$500 on a new ECU.

So an auto versus manual ECU swap should be plug and play assuming all else is the same. My car must have the ground wiring going to the transmission pin. Reconnect everything to the new ECU and I should be set. I'm not sure about the part number for my ECU; I'm waiting for the snow to melt to pull it. The junker ECU has these numbers on it:

 

DF7 5N, 22611 AD000, JA18000 DF7, and 6X29.

 

I'll compare when I pull mine out.

 

from : https://www.chaplinssubarugenuineparts.com/oe_parts_cat.html

 

 

 

 

item Number...... MSRP ..........Core.......... Price Price

22611AD001..... $549.07 .......$0.00 ........$468.91

 

Electrical - Ignition system - Ecm - 2.5 liter

All 1997

Edited February 8, 201016 yr by johnceggleston

...so it would appear, at least from the parts catalog, that the auto/manual ECM's are interchangeable. Awesome.

I've swapped auto/manual ECU's before in older Subaru's so I'm not surprised it's still the same.

 

Buying a new ECU is insanely silly and overkill. The ECU's very rarely fail - I've never seen it happen nor do I really recall many on any Subaru board talking about it much. I'm sure it's happened.

 

This makes used ones next to worthless - there is zero demand. So that also means they're super cheap at junk yards. They're also so easy to replace it doesn't warrant the outrageous cost for a new one.

 

Chances of the ECU fixing your issue are small....although it is odd all the parts you replaced. But I would think you probably have a valve issue, that's more common than an ECU issue.

 

How much is the one at a junk yard - I (or someone else on here) can mail you one already removed for the same price. Post in the parts wanted forum.

Grossgary,

 

Good to know that Subaru has a history of making its ECU's interchangeable. I already went to a u-pull-it yard and got an ECU for $30. Pretty cheap and an easy pull. If it fixes the problem, hooray, if not I know the ECU isn't the issue.

 

If the ECU doesn't fix things, I guess it's on to the valves.

So I put in the "new" ECU today. I lucked out with part numbers. The only difference is the last 3 digits.

 

My ECU: DF7 5N 22611 AD000 JA18000 DF7 6827

Junker ECU: DF7 5N 22611 AD000 JA18000 DF7 6X29

 

Sadly, though, it didn't fix the misfire. CEL came after about 10 minutes of driving with the new ECU.

 

So, how much does a valve job cost? Would a valve job be covered in a port & polish of the heads? I tend to try and spruce things up a big whenever I get maintenance done.

edit: nevermind

Does that engine have mechanical lifters that need to be adjusted? If yes, adjust the valve lash before anything else. I can't remember, did you ask your mechanic about knock sensors? I'm not sure if these engines have knock sensors, but they could be causing misfires if they need to be replaced.

 

If you pull the heads off it may be worth it to have them inspected and/or rebuilt at a machine shop. A machine shop will be able to check every detail and specification of the heads that may cause issues. While you have it apart, it wouldn't hurt to send the injectors to be inspected/rebuilt.

 

Make sure you check and clean all of the electrical connections before reassembling everything.

 

Note: I just wrote a very long in depth post but when I clicked post it deleted it. If you have any questions about the above, I have a lot of information on the entire rebuilding process, I just don't feel like typing it all up again!

 

 

-Kevin

Edited February 10, 201016 yr by CaptEditor

Wrap the injector wires with extra tape.

 

Put corragated plastic loom around the Spark plug wires.

 

Seprate the sets of wires.

 

NGK only plugs if you haven't got them in there already.

Thanks for the input guys.

 

Gloyale,

The plugs are NKG and about a year old. Good thinking with the extra tape and corrugated plastic. That stuff certainly can't hurt.

 

CaptEditor,

I replaced my knock sensor on 9/14/07, well before any of this misfire stuff. I imagine it is still good. I'm not sure if my engine uses mechanical lifters. Anybody else know? It's an EJ25 DOHC. The mechanic tested the injectors and apparently the fuel pressure was to spec. I hope I don't have to pull the heads and all that... (sounds pricey) but I will if need be.

Have you found any other threads about this? Surely someone has had to deal with this before? I recall hearing folks talk about valves but I haven't seen that happen yet so zero experience. I wonder if GLoyale has seen similar before?

 

So I put in the "new" ECU today.....

Sadly, though, it didn't fix the misfire.

that's what i expected, i understated my thoughts even by saying this:

Chances of the ECU fixing your issue are small...

I suggest you clean the ground leads going to the engine to see if that helps clear this trouble. Bad grounding can lead to extra noise being generated in the wiring and costs nothing to try and fix except your time. Trouble due to higher than normal noise pluses is something that Gloyale mentioned also but in a different way. If that doesn't help then I would check the signals from the cam and crank sensors using a scope to what they look like. These signals are used by the ECU to determine a misfire problem.

Edited February 11, 201016 yr by Cougar

"I'm not sure if my engine uses mechanical lifters. Anybody else know? It's an EJ25 DOHC."

 

Don't know for sure but what I've read is mechanical have tear drop shaped spark plug boots and the other is oval.

 

hth

 

Doug