p0303 misfire... scratching my head

9

995spdgt

New Member

Mar 16, 2018

19

1

3

May 19, 2019

#21

• May 19, 2019

• #21

Use a hose as big as you can go but small enough to fit the hole and either duct, masking, or whatever tape the hose to the shop vac.

Until you said you had 40 psi in cylinder 3 I was thinking we might have the same problem! My ‘99 had p0303 and just a slight misfire sound at idle but seem to run good and rev well in neutral, felt good under load and otherwise. But cylinder 3 for me was 145 or so and other cylinders 160-165. I’m starting to think my problem is something malfunctioned on just that cyl/piston before I got it or debris got sucked through cylinder 3 at some point.

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 19, 2019

#22

• May 19, 2019

• #22

Got it out with a couple straws taped together and put a filter in it so I didn’t suck it in my mouth lol. Didn’t help the problem though... took a video of the valve working and to me it looks fine but it’s not sealing. I put air on it again with the camera and I can see the fluid moving around and still feel the air... check out the videos

Cyl 3 action
View: https://youtu.be/hhkMD6xGdoQ


Cyl 3 air
View: https://youtu.be/1hHbxxhOtUs


I suppose next step is to pull valve cover and check for issues there unless you guys notice something I don’t... thanks for the help

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 21, 2019

#23

• May 21, 2019

• #23

Ok so I got all the valve cover bolts off but I can’t seem to get the cover off all the way... the dipstick for the trans fluid is in the way. Not sure how to get it off, any advice?

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

514

204

Houston Texas

May 21, 2019

#24

• May 21, 2019

• #24

It is possible to remove the transmission fill tube. However the bolt that holds the tube is kinda hard to get to.

 

9

995spdgt

New Member

Mar 16, 2018

19

1

3

May 21, 2019

#25

• May 21, 2019

• #25

Comes out on a 5 speed car! As far as ease of going back on I can’t tell you. I ended up pulling the engine and figured ill just put it back on before the engine goes back in.

Oh and I believe you have to like roll the top toward the strut tower to get it over the cams caps or something. From what I remember seemed like it could only come and go one particular way.

 

Last edited: May 21, 2019

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 24, 2019

#26

• May 24, 2019

• #26

OK I have more info and I did find an issue. Got the valve cover off and pulled the rocker arm and lifter out. Put air on the cylinder and IT SEALED!! So that gave me hope that the valve is OK. I noticed when putting it back in, that my valve lifter was higher than all the others. Pulled it out again and it is stuck up all the way and will not collapse(its seized). So at least I found that I have a bad lifter and I thought that was the problem. I put a new lifter in and reinstalled the rocker/roller. Compression test again, and it is still leaking through the intake valve. Take the rocker/roller off and it seals and I have compression. I tried swapping rocker/roller with another position that is working and same result. What else can I try. I may have a weak valve spring? Do i need to get the motor running for the lifter to work properly and get the proper oil pressure on it to work? Any other ideas or tips would be appreciated!

Thanks all and have a wonderful holiday weekend!

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

514

204

Houston Texas

May 24, 2019

#27

• May 24, 2019

• #27

Suggestion. Look down inside the valve lifter bore to see if there's any debris or sludge that might be preventing the lifter from seating all the way down inside the head. Also look for any burrs or other metal defects around the edge of the lifter bore.

Your motor has metal shavings inside that came from somewhere.

Some pictures might help as well.

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 24, 2019

#28

• May 24, 2019

• #28

I think the valve lifter bore looks ok I’ll post pictures... I can’t see anything bad but I’ll post pictures and get your opinion

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 25, 2019

#29

• May 25, 2019

• #29

Hey guys I want to replace the valve spring but I can’t find any that match the Haynes manual specs. Is the Haynes manual wrong? The pressure called out in the manual is much higher than any I can find...

The valves that I see online call for 198 lbs open and the manual says to get ones 433 lbs. way different

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

May 31, 2019

#30

• May 31, 2019

• #30

So I thought replacing the valve components would lead to a fix... replaced the spring and retainer, the lifter/lash adjuster. Also replaced the rocker roller. Replacing all this made it worse. Now instead of 30-40 psi compression, it’s now 0. Still boggles my mind that when I remove the rocker roller the valve seals. Don’t know what else to do now other than new heads or possibly cam shaft... any ideas?

 

wackinwallaby

Member

Mar 11, 2019

20

2

13

Ohio, US

Jun 21, 2019

#31

• Jun 21, 2019

• #31

So I wanted to give an update. I ordered a new cylinder head and installed. Fixed the issue and it runs great now. I looked at the old head but nothing was obvious so I may have a crack somewhere that I cannot see. Thanks to all who gave me advice!

 

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