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Old 12-08-2012, 10:57 AM   #1
chris124816
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Member#: 47413
Join Date: Nov 2003
Chapter/Region: MAIC
Location: Burlington, VT
Vehicle:
1999 impreza obs
black

Angry Misfire p304, stumbling, poor gas milage,

1999 impreza outback sport 2.2
173,000 miles
no major mods
previous history
new gas filter 5000 miles ago
new front o2 sensor 30000 miles ago
new rear o2 sensor 40000 miles ago
new pcv valve recently

The car has had a slight stumble occasionally for the past year with no cel's.
1. I decided to change the plugs and wires.
2. Installed NGK plugs with new spark plug tube seals.
3. Installed a new muffler at the same time.
200 miles later I get a blinking p304 while going uphills on the interstate in 5th gear. If I would stop, downshift or reach the top of the hill the blinking p304 went off.It is now overusing fuel.
4. removed plug boots and installed dielectric grease. there was no improvement.
5. Removed most sensor plugs, cleaned and reinstalled with dielectric grease.
Still no improvement.
6. Tested resistance between opposite coil pack leads (where the plug wires connect), they are within SOA parameters.
7. Installed new crank shaft position sensor with a new one
Still no improvement.
8. I know I need a new catalytic converter so I thought the exitsing one was clogged. I do not have the money for a new one right now so I gutted the existing one to asses if it was in fact causing the problem.
9. Now it runs worse with the same problem
10. It stopped throwing p304 misfire codes
11. Checked timing belt, it is in its proper position.
12. Adjusted valve clearance. #4 exhaust was a little snug but not that bad.
Still no improvement.
13. As per a recommendation from an experienced mechanic. I poured a can of BG 44k power enhancer into the gas tank and drove 50 miles.
Still no improvement.
14. Took plug wires off the coil pack individually. All 4 were firing strong because they were jumping all over.
15. Took out the map sensor, plugged the hole and applied a vacuum to the sensor while it was running. a change in vacuum effected the idle so I think the MAP sensor is fine.
Still no improvement.
16. Installed new windshield wipers and kicked all 4 wheels in anger.
Still no improvement.
17. Listened to all 4 injectors with a long screw driver stethascope. All 4 are clicking, But that only tells me that they are getting the proper open signal, not that they are actually opening.

Update -15 testing hours later and lots of forum searching and message replies
18. Compression test on all four cylinders showed good compression 175-190 ish
19. tested knock sensor for resistance. tested good.
20. borrowed a friends coil pack to see if there would be an improvement...No change.
21. Switched injector #2 and #4 !!!!!!!!!!!!
THe p304 moved to p302 cylinder misfire
PROBLEM Faulty fuel injector originally on #4

FIX Buy a new fuel injector and install it.

I previously owned a 97 impreza outback sport that had a similar problem and I replaced the MAF sensor to solve the problem. But this can does not have a MAF, it has a MAP

The mechanic suggested that I switch #4 injector with another one and watch if the P 304 code changes to another cylinder but it has stopped throwing the code so this will not be able to tell me anything.

ARGghh, any suggestion? I do not have a lot of money so I can not afford to go buy all new sensors, but there is a junkyard close to my house with 8 of the same cars.
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Last edited by chris124816; 12-12-2012 at 09:40 PM.
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Old 12-08-2012, 11:25 AM   #2
yarrgh
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Why'd you ask for me?

How about a PCV valve? I can't see it doing much on an NA car, but it's a part of maintenance. I didn't see it, so I gotta ask - how's the air filter? I doubt 50 miles on BG is going to do anything, it might take a couple of tanks of using cleaner.

Do a compression test, come back w/results. Did you check ALL valve clearances or just #4? How clean are your grounds?

I think you've beaten the spark path to death, sounds like it's time to focus on other areas. I can't imagine how removing a cat would make a car run worse. Have you reset the ECU at any point in all this? Have you checked out the knock sensor? Do the resistive tests on it and see if it's in spec.
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Old 12-08-2012, 12:56 PM   #3
chris124816
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I will do compression test tonight.
Pcv is 300 miles old
Checked all vacuum lines for cracks.
I Will also check knock sensor resistance tonight.
All grounds were cleaned this summer. I put on a couple extra body-battery-engine ground wires on last summer.
Checked all valve clearances and made very small adjustments.
Air filter is not that old and I blew it out last month.
I did a 30 minute battery ecu reset after the plugs were installed.
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Old 12-08-2012, 05:08 PM   #4
cal_look_zero
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I've gone through all of the same issues and had minimal positive results. I get a flashing misfire about once a week, p0304 every time, get horrid fuel mileage, and have a notable stumble below 2500 rpm.
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Old 12-08-2012, 09:17 PM   #5
mod maniac
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Change holes with your injectors and see if it moves if you haven't already.
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Old 12-09-2012, 10:17 AM   #6
chris124816
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Quote:
Originally Posted by cal_look_zero View Post
I've gone through all of the same issues and had minimal positive results. I get a flashing misfire about once a week, p0304 every time, get horrid fuel mileage, and have a notable stumble below 2500 rpm.
CAL Look Zero
Yours is most likely the MAF sensor if it is on your 97 obs.
I had all these same symptoms on my 97 obs and it was the maf.
I wish my 99 obs had a MAF sensor so I could just replace it but it has a MAP which seems to be working in correct order.

Last edited by chris124816; 12-09-2012 at 10:23 AM.
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Old 12-09-2012, 10:24 AM   #7
chris124816
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UPDATE
Compressions checked and is within SOA parameters.
Knock sensor resistance checked and is within SOA parameters.
It stopped throwing the p304 code so moving the injectors will not tell me anything.
All resistance readings on injectors are within SOA parameters.
I heard of a service bulletin that this could happen due to winter gas. I will try premium this afternoon.
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Old 12-09-2012, 01:00 PM   #8
Elbert Bass
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Burning premium is a waste of money and will degrade your fuel mileage unless you have built a high compression engine. I have seen burnt valves give in spec compression readings so you need to do a cylinder leakdown test to get the real picture. Drop you're exhaust manifold to see if you have a valve guide migrating.

As mentioned swap two injectors and see if the code follows the injector. When you replaced plug wires did you use OEM or aftermarket? If you used aftermarket I would check resistance in wires - I have seen some lousy aftmkt wires on cars.
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Old 12-09-2012, 02:30 PM   #9
chris124816
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Well, I wasted my money on $20 of premium fuel, No change : )
I will do a leak down test mid week and drop the exhaust.
What will a migrating valve guide look like?
Do you think I will be ok driving 50 miles to get it to a garage where i have a better work area including the compressed air for the leak down test?
After I put in the premium fuel I got the blinking MIL again, but when I pulled over to check it, There were no codes present.
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Old 12-09-2012, 03:09 PM   #10
cal_look_zero
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On mine, it's not the MAF. A big change in how often I got the CEL, was when I replaced the hacked up stock snorkus with a complete one from a junkyard car. Then again, that's mostly a MAF related issue, so I doubt that would help.

One thing worth noting is that these cars get their fuel 4-2-1-3-FPR, so if you have weak fuel pressure, it can starve out the #4 injector and cause a lean condition in that cylinder only>misfire.

If I were you, I would check your fuel pressure (rent the test kit from autozone or oreilly) and make sure you're within spec. If you have good pressure, you may have a volume issue which could be related to the fuel pump "sock"
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Old 12-09-2012, 03:32 PM   #11
Elbert Bass
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Quote:
Originally Posted by chris124816 View Post
Well, I wasted my money on $20 of premium fuel, No change : )
I will do a leak down test mid week and drop the exhaust.
What will a migrating valve guide look like?
Do you think I will be ok driving 50 miles to get it to a garage where i have a better work area including the compressed air for the leak down test?
After I put in the premium fuel I got the blinking MIL again, but when I pulled over to check it, There were no codes present.
When you look in the exhaust port on the head you will see the tips of the guides sticking out into the runner. You should only see the tip of the guide. One or more that has migrated/dropped will stick out farther. If you have one bad enough to cause a misfire it should be pretty obvious.

As with anything automotive - you might go 5 miles and you might go 50,000 miles. Unfortunately I can't guarantee internet diagnosis ;-)
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Old 12-09-2012, 03:57 PM   #12
Wills03rexwagon
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I would re check you o2 sensor for maybe an open in the system..if you can get a scan tool on it, check your resistance. If it reads 255ohms when its running, then there is something funny going on there...also I would check ur evap canister/ gas cap I know its crazy be I've seen it happen before
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Old 12-12-2012, 09:34 PM   #13
chris124816
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Problem diagnosed!
Well, I was planning on doing a leak down test, intake vacuum test, and a fuel pressure test, but I did not have the proper tools to do all that so I was waiting for payday.
In the meantime, I borrowed a friends coil pack and put it on my car which resulted in no change in the problem. Then someone suggested one of the plugs might be defective, knowing I was going down a dead end I moved the plugs around and no change.
Next free option, I switched injector #4 and injector #2 Went for a test drive and then I got the wonderful blinking CEL, but I was happy to check it because the misfire moved to cylinder #2 P302, which means I have a bad injector.

Thanks for all the help NASIOC!!
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Old 12-13-2012, 07:36 AM   #14
Charlie-III
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Hmmm....I may try that.

I've had 2 different engines, thus 2 different sets of plugs.
-Replaced ignition wires...no change
-Replaced crank sensor...no change
-Cleaned MAF...no change

I have a light flywheel (Exedy ~12lb), but it's been on for 60K+ miles.

Mine is a 1998 Legacy 2.5GT with a MAF

My PITA is it basically ONLY happens in 5th gear, 2800-3400RPM usually light load. I will pop a flashing CEL at other times, but the speed/gear/RPM is a fairly constant issue.
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