Misfire after head replace

[McSpooney]

Originally Posted by blue62

I hate to say it but I think you still have valve train issues on bank 2.
A leak down test only tells you if the valves and rings seal (or not) when the piston is at TDC. It is a static test.
It can't tell you if you have weak valve springs or lifter issues, or worn cam lobes, or...

You could do a vacuum test. It is an operational test. It will tell you how well the cylinders are filling with fuel/air mixture. Which is affected by any type of valve train issue. If a cylinder or cylinders are not filling with fuel/air properly it causes performance issues.
If the test is done correctly (and that is very important). It should give you a very good idea as to if the valve train on bank 2 is an issue or not.

Another (possibly) important thing to know is:
What RPM range are the misfires happening in????
Does it misfire in just a certain range like idle? or mid range? or high RPM?
Or are the misfires all across the RPM range??

Why did the head need replaced in the first place???
Did you ever have a misfire issue on bank 2 before replacing the head???

Edit:
Just re-read your posts.
What do you mean in post #3 when you say you "swapped" valves????

Ahhh that's not what I wanted to read. I was kinda worried it might be a stuck valve.... but I the only test I saw online for a stuck valve was kinda simple and the car easily passed. Just holding a piece of paper up to the exhaust pipe.

Vacuum test seems like the key now! This same one that blue62 described? Teeing off a vacuum gauge into the intake plenum?

This is all happening at idle. Off of idle i don't think it misfires at all. Engine pulls strong too. The head was replaced because it cracked and started dumping coolant into the SAI port on the exhaust.

I swapped the valves from my old head onto the new one. Lapped them, did a leakdown test a few times since and it all seems alright. Rough inspection of the valve guides, valves, cams... nothing showed excessive wear... I really hope i didn't f that up.

[blue62]

Originally Posted by McSpooney

Ahhh that's not what I wanted to read. I was kinda worried it might be a stuck valve.... but I the only test I saw online for a stuck valve was kinda simple and the car easily passed. Just holding a piece of paper up to the exhaust pipe.

Vacuum test seems like the key now! This same one that blue62 described? Teeing off a vacuum gauge into the intake plenum?

This is all happening at idle. Off of idle i don't think it misfires at all. Engine pulls strong too. The head was replaced because it cracked and started dumping coolant into the SAI port on the exhaust.

I swapped the valves from my old head onto the new one. Lapped them, did a leakdown test a few times since and it all seems alright. Rough inspection of the valve guides, valves, cams... nothing showed excessive wear... I really hope i didn't f that up.

Swapping valves from one engine to another is not a good practice.
Just as swapping valves from one position to another in the same engine is not a good practice.

Your RAKT's show that one bank is running lean and the other is running rich.
So I would check very carefully for an exhaust leak before the O2 sensor and also at the O2 sensor bung weld. A pinhole exhaust leak can cause your issue.

when you do the vacuum test make sure the engine is fully warmed up.
An easy place to TEE in is where the vacuum line from the fuel pressure regulator is connected to the intake. Near the throttle body.

Put one leg of the TEE directly into the intake, one leg of the TEE into the vacuum gauge, one leg into the line to the fuel pressure regulator.

Just let the engine idle. DO NOT rev the engine. Let it idle for 2-3 minutes while you watch the gauge. record the readings. BUT the MOST IMPORTANT thing is what the needle does.
Record any action from the needle. Does it tick??? does it vibrate does it move in any way no matter how slight over a 2-3 minute period with the engine at idle???

[McSpooney]

Originally Posted by blue62

Swapping valves from one engine to another is not a good practice.
Just as swapping valves from one position to another in the same engine is not a good practice.

Your RAKT's show that one bank is running lean and the other is running rich.
So I would check very carefully for an exhaust leak before the O2 sensor and also at the O2 sensor bung weld. A pinhole exhaust leak can cause your issue.

when you do the vacuum test make sure the engine is fully warmed up.
An easy place to TEE in is where the vacuum line from the fuel pressure regulator is connected to the intake. Near the throttle body.

Put one leg of the TEE directly into the intake, one leg of the TEE into the vacuum gauge, one leg into the line to the fuel pressure regulator.

Just let the engine idle. DO NOT rev the engine. Let it idle for 2-3 minutes while you watch the gauge. record the readings. BUT the MOST IMPORTANT thing is what the needle does.
Record any action from the needle. Does it tick??? does it vibrate does it move in any way no matter how slight over a 2-3 minute period with the engine at idle???

Yeah, I know swapping valves is not ideal. Like I said though. They were lapped and tested working... I guess that may not mean working in all states per your previous point. I took this as a 'no-no, by the book', but lots of people do with no ill effect. Porsche says the part numbers are the same and the fitment was spot on to the valve guides. Finish on valve guides and valves looked perfect at install. FYI I only swapped exhaust valves. Intake valves all looked great and have never showed signs of problems (leakdown check with both manifolds off and no air ever came form the intake valves, but a lot of air came out the exhaust).

The RKAT values are within 1 point of each other. Isn't that good enough for a beautifully running motor? I'll double check for an exhaust leak this weekend though. Last time I put my smoke tester on the exhaust and saw nothing before the o2 sensors. I figure 1 point could just be from o2 sensor variation, thus why I've got extra o2 sensors on order too. (But I've swapped the o2 sensors from side to side too)

The exhaust was full of coolant at one point before the head swap. Literally I put a heat gun on the muffler then smoke and coolant smell came out the tailpipe. I was worried that all this burning coolant may have had an ill-effect on the o2 sensors or the SAI system or even the cat.

The vacuum gauge is on order... will get to play with it next week. Thanks so much for the help. I'll update once I've done the vacuum testing and looked for exhaust leak.

[blue62]

Your RKAT's as per post #3...... I read as a -1.4 and a .8

Coolant in the Cat's will destroy them rather quickly.
A plugged up cat could cause your issue.
So I will tell you how to test the cats for restrictions with the vacuum gauge.

AFTER YOU DO THE "IDLE" VACUUM TEST.

Take the RPM up to 2000-2500 hold it as steady as you can.
Hold that RPM for 1 and a half to two full minutes.
Watch the needle on the gauge if it slowly falls over time your cats are plugging up.


I forgot to mention:
Very important... make sure your A/C, heater, lights, radio are off when you do the tests.

you can use your Durametric to see if the Cats are "Catalyzing" (working) correctly by observing pre and post cats O2 sensor signals under the right conditions.

I can describe how to do that for you but lets see what the vacuum tests have to say first.

Make sure you hook the vacuum gauge up and run the tests the way I described, or the tests will be meaningless.

[McSpooney]

Originally Posted by blue62

Your RKAT's as per post #3...... I read as a -1.4 and a .8

Coolant in the Cat's will destroy them rather quickly.
A plugged up cat could cause your issue.
So I will tell you how to test the cats for restrictions with the vacuum gauge.

AFTER YOU DO THE "IDLE" VACUUM TEST.

Take the RPM up to 2000-2500 hold it as steady as you can.
Hold that RPM for 1 and a half to two full minutes.
Watch the needle on the gauge if it slowly falls over time your cats are plugging up.


I forgot to mention:
Very important... make sure your A/C, heater, lights, radio are off when you do the tests.

you can use your Durametric to see if the Cats are "Catalyzing" (working) correctly by observing pre and post cats O2 sensor signals under the right conditions.

I can describe how to do that for you but lets see what the vacuum tests have to say first.

Make sure you hook the vacuum gauge up and run the tests the way I described, or the tests will be meaningless.

So I think it failed the vacuum test. I guess googling this test makes me think its a sticking valve and or bad valve guides... but maybe It would be best for you to see the video. The needle starts out a little wobbly... then goes crazy flying back and forth from 22 to 16 in hg... eventually stabilizes. It seems to do it when the car is idling very low... at 680 per durametric, with a target idle at 680. One caveat though: I ended up tapping into the right behind the throttlebody where it branches off for the AOS and that fuel tank purge valve. I have never seen a fuel pressure regulator on my car so couldn't really tap there. Keep in mind mine is 2003 3-chain, doesn't show a regulator in the katalog.

I also did the vacuum test to see if the cat was the culprit... vacuum didn't seem to drop when holding 2k rpm. I also visually inspected the cat... with a little boroscope though. It looked fine.

Putting in a link to a video of the vacuum gauge. The needle starts freaking out at around 25 sec, but eventually calms down at around 3 minutes. Engine was warm already from previous running, but only on about 1 minute before i started the video.
https://www.youtube.com/watch?v=jzao8NScuJE

I'm a little confused if this is a valve issue. I really hope it isn't. But I roughly felt each valve as I installed... clearances felt consistently good at install. Unless this is an issue with the intake valves, but those appeared to never have been bent and just seemed to be 100%

I'm actually a little familiar with verifying cat function. I would typically look for the post-cat O2s to see if the wave function flat-lines after the cats get to temp and I'm cruising. Right now I'm using my desktop for durametric though lol. I'll have to devise a way to check the sensor reading while the car is moving. The exhaust smells pretty bad btw. Makes me think cats aren't doing so hot, but also makes me think maybe the injectors.

I replaced the ignition coils... and as expected... that was a waste. Car runs exactly the same. Maybe fuel injectors?

[blue62]

Originally Posted by McSpooney

So I think it failed the vacuum test. I guess googling this test makes me think its a sticking valve and or bad valve guides... but maybe It would be best for you to see the video. The needle starts out a little wobbly... then goes crazy flying back and forth from 22 to 16 in hg... eventually stabilizes. It seems to do it when the car is idling very low... at 680 per durametric, with a target idle at 680. One caveat though: I ended up tapping into the right behind the throttlebody where it branches off for the AOS and that fuel tank purge valve. I have never seen a fuel pressure regulator on my car so couldn't really tap there. Keep in mind mine is 2003 3-chain, doesn't show a regulator in the katalog.

I also did the vacuum test to see if the cat was the culprit... vacuum didn't seem to drop when holding 2k rpm. I also visually inspected the cat... with a little boroscope though. It looked fine.

Putting in a link to a video of the vacuum gauge. The needle starts freaking out at around 25 sec, but eventually calms down at around 3 minutes. Engine was warm already from previous running, but only on about 1 minute before i started the video.
https://www.youtube.com/watch?v=jzao8NScuJE

I'm a little confused if this is a valve issue. I really hope it isn't. But I roughly felt each valve as I installed... clearances felt consistently good at install. Unless this is an issue with the intake valves, but those appeared to never have been bent and just seemed to be 100%

I'm actually a little familiar with verifying cat function. I would typically look for the post-cat O2s to see if the wave function flat-lines after the cats get to temp and I'm cruising. Right now I'm using my desktop for durametric though lol. I'll have to devise a way to check the sensor reading while the car is moving. The exhaust smells pretty bad btw. Makes me think cats aren't doing so hot, but also makes me think maybe the injectors.

I replaced the ignition coils... and as expected... that was a waste. Car runs exactly the same. Maybe fuel injectors?

So a couple of things.
First you should really hold the gauge in you hand or find a way to isolate it from the car. I know you laid it on the car so you could video but the needle will pick up vibrations from the car and skew needle action.

Second: video or post a picture of your hookup so I know it is correct.

Third: It is great the way you tested just letting it idle and giving me a good long view of the gauge.
Your probably the first person to do it correctly. LOL

When you research vacuum testing info on the web (youtube) you have to remember most all info is for testing "single cam" engines.
The Boxster is a four cam so needle action (if any) is going to be a little different and much harder to interpret.

So the bad news:
Looks like you have a valve train issue.
Possibly one or more lifters acting up.
I think I hear a ticking sound in your video but not sure.
The reason I think you have lifter issues is from the needle action.
If you watch the needle it is moving in a very specific way.
it is not bad at first just drifting between 20-21 that is not bad.
Then it goes crazy as you say but in a very set way.
Then it settles down again after a while.
Like a lifter or valve sticking.
Then correcting itself.

Please remember all this is an educated "guess" at best.
Diagnosing issues remotely is very very difficult.
But what I am seeing points to valve train issues.

You could do the test again with the Durametric hooked up and see if your misfire count comes and goes when the needle on the vacuum gauge starts acting up.

Also when the needle starts ticking go to your exhaust and listen you will probably hear a difference in your exhaust.

So run a fuel trims scan with your car fully warmed up and lets see your RAKT and FRO's FRU's what ever your other fuel trims are.
Do the RAKT at idle.
Do the other fuel trim at 2000 RPM.

For Cat function you need to get the car good and warm like a 20 minute drive.
Then hook up the durametric and just hold your RPM at 2200-2500 for 60-90 seconds and watch the post cat voltage. if everything is good post cat voltage will stay above .450mv best to see it around .750mv mostly a flat line on the graph as long as you hold the RPM steady.

[McSpooney]

Originally Posted by blue62

So a couple of things.
First you should really hold the gauge in you hand or find a way to isolate it from the car. I know you laid it on the car so you could video but the needle will pick up vibrations from the car and skew needle action.

Second: video or post a picture of your hookup so I know it is correct.

Third: It is great the way you tested just letting it idle and giving me a good long view of the gauge.
Your probably the first person to do it correctly. LOL

When you research vacuum testing info on the web (youtube) you have to remember most all info is for testing "single cam" engines.
The Boxster is a four cam so needle action (if any) is going to be a little different and much harder to interpret.

So the bad news:
Looks like you have a valve train issue.
Possibly one or more lifters acting up.
I think I hear a ticking sound in your video but not sure.
The reason I think you have lifter issues is from the needle action.
If you watch the needle it is moving in a very specific way.
it is not bad at first just drifting between 20-21 that is not bad.
Then it goes crazy as you say but in a very set way.
Then it settles down again after a while.
Like a lifter or valve sticking.
Then correcting itself.

Please remember all this is an educated "guess" at best.
Diagnosing issues remotely is very very difficult.
But what I am seeing points to valve train issues.

You could do the test again with the Durametric hooked up and see if your misfire count comes and goes when the needle on the vacuum gauge starts acting up.

Also when the needle starts ticking go to your exhaust and listen you will probably hear a difference in your exhaust.

So run a fuel trims scan with your car fully warmed up and lets see your RAKT and FRO's FRU's what ever your other fuel trims are.
Do the RAKT at idle.
Do the other fuel trim at 2000 RPM.

For Cat function you need to get the car good and warm like a 20 minute drive.
Then hook up the durametric and just hold your RPM at 2200-2500 for 60-90 seconds and watch the post cat voltage. if everything is good post cat voltage will stay above .450mv best to see it around .750mv mostly a flat line on the graph as long as you hold the RPM steady.

So I got some time to work on it... but not a lot. I had tried holding the gauge in my hand and also resting it on the car... didn't seem to make a difference, so I just filmed it as you saw. Attaching image of the setup... hopefully you can make it out... its on the hose that leads to the AOS. Probably hard to see with the shifter cables in the way.



I ran the engine at idle 2 more times and drove it for like 20 minutes the other day. Honestly it's just been idling, so i don't think that the other fuel trim values are up to spec yet. After that 20 minute drive though, I checked o2 sensor responses and the cat on the side of the new head does not seem to be working... Honestly back when the head blew, it was running for like 20 minutes (between having to move it around and trying to diagnose the issue) while it was pouring out coolant smoke out of the exhaust. So maybe the cat is dead. I think I'll try and test the cat for blockage again after driving it around then maybe swap back in another set of cats I have.

So I'll and drive it again before I give you fuel trims, buuuut... the vacuum gauge drama out not seem to correlate to the misfires. I got the misfire counter to run up to 27 on cylinder 4 (sometimes one cylinder, often 4 or 6 will just shoot up in count) but the vacuum gauge was very steady. I also had the gauge freaking out and the misfire counter was barely moving. I'm hoping that's good news.

I also want to note that when i drove it around... it drove great. Felt smooth, had decent power. I think maybe off throttle it seemed to burble a little... that's about it. I think I hear it burble sometimes at idle, but it's super hard to tell. The burbling does seem like maybe its connected to the vacuum gauge drama, so that ain't great.

I think I'll try one of these engine cleaners soon.