Misfire after head replace

[ike84]

If your coils are cracked they all should be replaced. Generic ones are ebay are cheap and I've been running them for a year without issue. I would start there.

The injectors can fail. Most commonly they get stuck open. A sign of this is if your oil smells like gas - just pop open your fill tube and take a whif. If you replace them, swap them all. The ef-1 style Bosch injectors for 03-04 are cheap. Kinda pita to swap though with the air box and sai in place.

You may want to do a vacuum test to make sure it looks good. Smoke tests are not always reliable. Blue62 has written some great posts about doing this type of test.

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[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????

[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?

[McSpooney]

Originally Posted by ike84

If your coils are cracked they all should be replaced. Generic ones are ebay are cheap and I've been running them for a year without issue. I would start there.

The injectors can fail. Most commonly they get stuck open. A sign of this is if your oil smells like gas - just pop open your fill tube and take a whif. If you replace them, swap them all. The ef-1 style Bosch injectors for 03-04 are cheap. Kinda pita to swap though with the air box and sai in place.

You may want to do a vacuum test to make sure it looks good. Smoke tests are not always reliable. Blue62 has written some great posts about doing this type of test.

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Ahhh... i guess I'll drop the cash... I just try and take pride in not 'throwing money at the problem'.

The fill oil fill tube smells very oily... no gas for sure. If it were stuck open... I think I would see it in the O2 or RKAT values on durametric?

I'll prep for a vacuum test tho.

[ike84]

Originally Posted by McSpooney

Ahhh... i guess I'll drop the cash... I just try and take pride in not 'throwing money at the problem'.



The fill oil fill tube smells very oily... no gas for sure. If it were stuck open... I think I would see it in the O2 or RKAT values on durametric?



I'll prep for a vacuum test tho.

Not necessarily. The injectors tend to stick open. Your may see rkat deviations but not always, depending on how bad the leak is. You can use the durametric to test each injector, turning them off 1 at a time while the car is running, and see if it makes any changes. The logic here is that a functioning injector will shut off when told to do so and make the engine run rough, an injector that is bad will not respond/effect any overall change in engine behavior when it is good to turn off.

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