Chasing a misfire that I can't solve. Help!

[G_Raw]

Well there goes that idea...

I'm not sure if power braking is the correct term. What I do is firmly press the brake with one foot, shift to drive, then apply some throttle. You should be able to "load" the engine up to cause the not sealing valve to struggle and hopefully cause the vibration you are feeling without moving at all. I wouldn't recommend doing this for more than a few seconds at a time as it creates a lot of heat in the torque converter causing transmission temps to rise pretty quick.

Yes it will vibrate but I have to hold it at 2200 rpm and it's not as strong of vibration. Likely due to it being in one spot as opposed to moving at speed.

If you want to know what it sounds like...

https://www.youtube.com/watch?v=eakveE-C2tE&feature=youtu.be

 

[Bad Luck]

Yes it will vibrate but I have to hold it at 2200 rpm and it's not as strong of vibration. Likely due to it being in one spot as opposed to moving at speed.

If you want to know what it sounds like...

https://www.youtube.com/watch?v=eakveE-C2tE&feature=youtu.be

That tells me that the vibration you are experiencing is from the misfire. That is definitely one loud valve!

 

[Takeo77]

Had this same set of symptoms, in my case turned out to be a headgasket in danger of imminent failure. Unfortunately I didn't catch it, it overheated, cracked both heads, needed and engine swap.

 

[G_Raw]

Had this same set of symptoms, in my case turned out to be a headgasket in danger of imminent failure. Unfortunately I didn't catch it, it overheated, cracked both heads, needed and engine swap.

I'm worry free knowing I've secured a motor being built up the way I want it. So if this one goes no biggie. I don't drive daily by any means in the rig. It's the adventure rig so those unfortunately are halted for snow season. Thanks for the input.

 

[G_Raw]

While making sure I didn't miss a crack in my intake manifold I did another compression check for fun. All cylinders are 200 to 190 except cylinder 6 which was at 180 when I first started chasing this...today 160. The valve is getting worse. I noticed cause I filled up the tank. I was averaging 10.8 to 12 mpg at the start of chasing this misfire. Most recent fill up was 8.7 mpg.:gun5:

 

[LittleCaesar]

So when will the motor swap occur? Pulling the heads on these engines isn’t too terrible but a built engine as you see fit is probably the better road to take no doubt.

 

[G_Raw]

So when will the motor swap oc cur? Pulling the heads on these engines isn’t too terrible but a built engine as you see fit is probably the better road to take no doubt.

Yea Bay Area prices for heads to be built put me close to the same cost as Yota1 rebuilt motor with their black Friday sale. So a combo of shit luck at good time I suppose. Plus Yota1 will gap piston and such to accommodate forced induction better.

So Yota 1 is building the motor for me...as I don't have time or care to take that part on. They are back logged with Covid and holidays. So motor sounds like it won't be till mid February at this point. I have till mid January to let them know if I want the motor built to better accommodate forced induction. So if someone has a deal on a SC let me know!

Good news is the San Jose guys just did a video on this swap so thanks [MENTION=120071]mtbtim[/MENTION] and [MENTION=102606]infamousRNR[/MENTION]

 

[SunyDe]

Hey folks

Piggy backing on this thread cos I'm having a similar issue.

Intermittent P0300 that would clear on it's own due to some intermittent electrical issue. This has been happening for awhile and required me to Hot Smog it when I had to renew registration last year.

Last week started running like crap and threw a P0306 and P0303 to boot.

I replaced the spark plugs and wires with NGK and cleaned up the contacts on one of the coils cos it had something on there not sure if it's old dialectical grease or what but it was the only one that did so made it look like the others.

It's running better but threw a P0300 on cold start up. Once cleared and test drive it didn't come back.

However I think the ultimate issue is fuel related. Since it's had a issue starting in that it seems like it's not getting enough fuel on startup (sometimes) and will just die if I don't give it some extra throttle.

It's not the filter cos I changed that in December.

Ordered a OTC fuel pressure kit and a Russel/Edelbrock banjo bolt, 1/8" NPT 90 and Schrader valve to check to see if it's fuel pressure related so will be checking that later this week along with compression.

Figured y'all might have some insight. Thanks in advance for any replies.

And super big thanks to [MENTION=120071]mtbtim[/MENTION] and his youTube channel for giving me the confidence to DIY instead of paying a mechanic to do the bare minimum. Slowly aquiring all the tools and know-how. Maybe one day I'll swing down to the southbay and show you a trick or two for your newly acquired welder.





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[spartacus]

Ohm out the injectors (13 to 18 ohms.) and compression test should also help narrow down the issue.

 

[Skulking]

Hey folks

Piggy backing on this thread cos I'm having a similar issue.

Intermittent P0300 that would clear on it's own due to some intermittent electrical issue. This has been happening for awhile and required me to Hot Smog it when I had to renew registration last year.

Last week started running like crap and threw a P0306 and P0303 to boot.

I replaced the spark plugs and wires with NGK and cleaned up the contacts on one of the coils cos it had something on there not sure if it's old dialectical grease or what but it was the only one that did so made it look like the others.

It's running better but threw a P0300 on cold start up. Once cleared and test drive it didn't come back.

However I think the ultimate issue is fuel related. Since it's had a issue starting in that it seems like it's not getting enough fuel on startup (sometimes) and will just die if I don't give it some extra throttle.

It's not the filter cos I changed that in December.

Ordered a OTC fuel pressure kit and a Russel/Edelbrock banjo bolt, 1/8" NPT 90 and Schrader valve to check to see if it's fuel pressure related so will be checking that later this week along with compression.

Figured y'all might have some insight. Thanks in advance for any replies.

And super big thanks to [MENTION=120071]mtbtim[/MENTION] and his youTube channel for giving me the confidence to DIY instead of paying a mechanic to do the bare minimum. Slowly aquiring all the tools and know-how. Maybe one day I'll swing down to the southbay and show you a trick or two for your newly acquired welder.





Sent from my Pixel 3 using Tapatalk

To me with a P0303 and P0306 I would immediately suspect the ignition coil since cylinders 3 and 6 share a coil.

 

[Bad Luck]

I agree on coil being suspect. You could try swapping coils around, but unless you are getting a specific cylinder misfire code or can view live misfire data that's not going to be any help.

 

[G_Raw]

I also suggest the coil swap. You have the same codes I did ( although I've gotten my engine tune and running at mpg and vibrations under load I have avoided throwing codes for a month ).


Like others mentioned coil 3 feeds cylinder 6 for spark. Since you are dealing with 300,303, and 306. That's the easiest and free thing to test for the codes. Put coil 3 in spot 5. See if your codes change to 302 and 305. I choose spot 5 instead of spot 1. Since 1 feeds 4 and 4 is adjacent to 6( one of your problem cylinders). I've seen hidden HG leaks follow coil changes from time to time( I think this is purely coincidental and based off one coil giving a stronger spark signal then the other).

If it follows buy new coil. If it doesn't compression test. Look for a greater then 10% difference between values. I believe the lowest acceptable for 5vz is 175 psi. But if 5 cylinders are in the 195 to 210 psi range and the sixth is 175 to 185 while acceptable is more then 10% different then rest of your cylinders and should be looked into further.


Update on my end...I think I'm two weeks out from picking up my motor!! Pretty tired of the under load vibes and the 10mpg.

 

[Bad Luck]

Cylinders 3&5 are next to each other. There's no way to swap coil packs and avoid being next to a previous misfire.

 

[G_Raw]

Cylinders 3&5 are next to each other. There's no way to swap coil packs and avoid being next to a previous misfire.

Right which is why I suggested the swap the way I did. Coil pack 3 is unfortunately between 1 and 5. If he swapped coil 3 for coil 1 then cylinder 1 is next to 3. And 4 is next to 6 so no separation of offending cylinders. Coil 5 feeds 2 so at least he can separate 4 and 6 in diagnosis process.

 

[G_Raw]

Alright folks. It's back up and running. Due to time and work constraints along with only having 1 vehicle I had Yota1 do the install. Here is what they found...a random bolt in my in cylinder 6 intake valves. No one knows how it got there or where it's from. Obviously it dropped in at some point. I hadn't had the intake open to do any recent work prior to this whole issue starting so I cant think of how or when something would have dropped in. The motor always had a valve tick over cylinder 6 since I acquired the vehicle out right from the in laws...so idk if it had been there for years before causing this issue. But either way I'm happy to say I'm back on the road! Yota1 was great to work with and communicated well through the process. And I'm currently typing this from my phone pulled over on the freeway doing my 30 minutes on 30 minutes off break in drive...

Just a reminder... cover the intake manifolds!

 

[HiLife]

Yup. Most make it an overkill to cover the intake holes (when lifting the intake) with a covering to prevent that sorta thing. That tiny oversight took down a perfectly good working motor.