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EJ25 doesn't run well after engine swap


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11 replies to this topic

#1 grossgary

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Posted 06 June 2007 - 02:58 PM

swapped a 1997 Legacy GT EJ25 into my 1998 Legacy GT (manual trans) and it's not running very well. check engine light doesn't come on. car will start, rev up high (3,000 rpm) and then eventually just die. if i give it gas it barely goes..bucks and kicks and will eventually die as well. the engine is good, because it came out of my 1997 Legacy GT and ran great just before i pulled it.

first issue - i pulled the O2 sensor wires out of the plug. the plug wouldn't come apart and it didn't take much before the wires just came out. when i reinstalled them...there were 2 white wires and one black wire. i got the black wire dead on, i compared it to my other legacy. but the whites i took a chance it didn't matter which way they were plugged in. could that make it run bad? do i need to double check those and how can i tell which white wire goes to which plug? should it run fine if i disconnect both O2 sensors? i know the older soobs run fine without the O2 sensor connected.

second - i played with some vaccuum hoses. the 97 i installed had a different solenoid in the passengers strut tower..really the exact same solenoid, but it had one additional vaccuum hose fitting. so i swapped solenoids as well so i plugged right up. solenoid connector was identical and everything dropped right in perfect. pretty sure that won't matter, actually i can't imagine it would matter at all.

anyone know if there are any wiring differeneces from 97 to 98? maybe i need to swap the ECU as well?

#2 Legacy777

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Posted 07 June 2007 - 09:33 AM

I'd try unplugging the O2 sensor and see how it runs. If you're not getting a code, chances are it's ok.

You may need to swap the ECU. Was the 97 a MT as well? It could be a slew of things......never know what got tugged on during the swap, etc.

#3 nipper

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Posted 07 June 2007 - 10:29 AM

it almost sounds like a collapsed or clogged cat Any rags stuck in the intake anywhere?


nipper

#4 grossgary

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Posted 07 June 2007 - 10:48 AM

both engines from a manual trans vehicle.

it should run with both O2 sensors unplugged? could crossing the 3 O2 sensor wires up ruin the sensor? i'm not familiar with what those wires are all for. since i guessed which pin they go to, chances are good that at least one, if not both are wrong. but i would have expected a CEL if they were.

funny you mention the cat nipper......i had to remove the entire exhaust as an assembly, angle it and flip it upside down by myself. and before that i was shaking and jarring it vigorously. i dropped a tool into the exhaust manifold! oh the fun that was. none of the exhaust bolts will come out, i tried that first to get the tool out, so i can't just disconnect it to see if it runs right. guess i'll have to cut them off.

check O2 sensors
check catalytic converter

thanks guys, i'm headed out of town so i'll check it out monday.

#5 porcupine73

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Posted 07 June 2007 - 11:07 AM

It'll run without the o2 sensors. It only uses the front o2 sensor to refine A/F ratio control in closed loop operation after warmup, and even then only at certain 'cruising conditions', like not under heavy throttle. Not sure about the wire colors, but one wire has to be the output, one wire is for the heater, and the other is probably a ground as the heater can take up to maybe 10 amps.

#6 grossgary

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Posted 07 June 2007 - 11:37 AM

oh right, O2's don't do anything until the car is warmed up. so i guess they can't be the cause of this since it's right at start up. but i need to check that wiring, can't be good to have them backwards!

#7 nipper

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Posted 07 June 2007 - 11:39 AM

with no 02 sensor the car will run fine in the driveway, you would throw a code once the car warms up enough. It would affect gas mileage, but not that you would see under these conditions.


Can you throw a vacume gauge on the car and tell us what it does?


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#8 grossgary

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Posted 07 June 2007 - 11:49 AM

with no 02 sensor the car will run fine in the driveway, you would throw a code once the car warms up enough. It would affect gas mileage, but not that you would see under these conditions.

just like the old school soobs, sounds good. i'll unplug them at least until i fix them right.

Can you throw a vacume gauge on the car and tell us what it does?

i don't have one nor do i know how to use one, but i'm not against learning if other things don't pan out.

#9 nipper

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Posted 07 June 2007 - 12:32 PM

just like the old school soobs, sounds good. i'll unplug them at least until i fix them right.

i don't have one nor do i know how to use one, but i'm not against learning if other things don't pan out.


Not hard to learn. They can tell you if the exhaust is restrictive, low compression, sticking valves etc

http://www.classictr...cts/vac/uum.htm


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#10 grossgary

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Posted 16 June 2007 - 01:00 PM

i removed the exhaust (at the exhaust manifold) and unplugged the O2 sensors and it ran exactly the same as it did before. so the exhaust and O2 sensors shouldnt' be the problem.

i used a 97 GT intake manifold in a 98 GT vehicle. slight vacuum line differences and the 97 had the charcoal canister lines that the 98 did not have. it all seemed to go together right, but i'm hoping the problem is there since that's easy enough to do. so i'm swapping manifolds right now so it has the stock 98 GT set up on it.

#11 brandoncrone

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Posted 16 June 2007 - 02:27 PM

i removed the exhaust (at the exhaust manifold) and unplugged the O2 sensors and it ran exactly the same as it did before. so the exhaust and O2 sensors shouldnt' be the problem.

i used a 97 GT intake manifold in a 98 GT vehicle. slight vacuum line differences and the 97 had the charcoal canister lines that the 98 did not have. it all seemed to go together right, but i'm hoping the problem is there since that's easy enough to do. so i'm swapping manifolds right now so it has the stock 98 GT set up on it.


Did you hook up the fuel lines backwards. You can swap the pressure and return lines without realizing it.

#12 grossgary

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Posted 16 June 2007 - 03:00 PM

everyone say together "brake booster vacuum hose". at least it was simple. i should have went with nipper vacuum testing, i probably would have used that port!

yep, checked the fuel lines, my wife has an outback sport with identical fuel lines...now why did i double checked some things and not others??




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