Misfires P0300, P0302, P0305 Help
05-01-2013, 05:04 PM
#1
Misfires P0300, P0302, P0305 Help
I know there are a number of other posts on misfires, but before I posted this, I did a decent amount of work and I am now at a loss and looking for some answers from those in the know.
So I have a 2000 Boxster S with e-gas. It was running great. I was driving it and the CEL came on. It wasn't running right and had minimal power. I had it towed home. I started it and read the codes, I believe on first read there was only P0300 and P0305. But my memory may be wrong.
I pull all the coils and plugs. And #5 did look a little blacker than the rest. They all looked good btw. I buy a replacement coil. I put it #5 and there is no change. I replace the spark plug. No change. I move coils around, no change. I remove the #5 coil from the engine and put a spark plug in it and there is visible spark. It was also showing P0302 from time to time. But P0305 is most common. So it shows #2 and #5 most of the time, so it isn't just on one side.
So I was concerned that the IMS bearing went out and the timing jumped. I changed the oil and looked for metal. I did see some flakes. So I believe the ims bearing is dying. So I pulled the cam caps and checked the cam timing. It is good! What a relief. But I still have to replace the ims bearing. But I don't want to do that until I fix this not-running issue.
While I am doing this diagnosis, the car started to also show code P1502. And sometimes it would not rev at all. So I look up the code and it didn't make sense it was a fuel pump code. But after some research, for the e-gas cars, it is a bad throttle code. So with the engine not running, but the key in accessory mode, the throttle should work. Sometimes it did, sometimes it didn't. But more so it didn't. So I bought a new throttle motor assembly. That problem fixed. Throttle works and it is not showing a P1502. I did do the calibration routine btw.
But I was thinking this would solve all my problems, that it was in limp home mode because of the bad throttle. And that the limp mode was causing the misfire codes. Nope. It is still misfiring. And still barely running.
There are no other codes, and other sensors look good. Data from all four O2 sensors looks good. MAF values look good. Temp values look good. I disconnected the maf and reset codes and it didn't affect anything.
SO... Whats up, this is puzzling.
Generally you think one thing breaks. So we know the throttle broke. And we know it is now fixed.
Do you think the throttle broke because of the misfires?
Because of a backfire?
Does the car go into limp mode due to the P1502 code?
Could the car still be in limp mode? If so, how do you clear it? I only have a generic, basic scanner. I did disconnect the battery for a day to see if that would clear it - nope.
What else would cause the misfires and not other codes? Vacuum leak? Fuel injectors, fuel side of things? What is most common on this car.
It almost seems like the DME is bad. What are the chances of that?
Since it showed #2 in addition to #5, it doesn't seem like there was a valve failure on #5. I am hoping a valve didn't fail. I don't hear any major bad noise other than the very rough engine. So I think the engine is mechanically sound (except the ims bearing). I think this is an engine management issue.
Any other input would be appreciated.
So I have a 2000 Boxster S with e-gas. It was running great. I was driving it and the CEL came on. It wasn't running right and had minimal power. I had it towed home. I started it and read the codes, I believe on first read there was only P0300 and P0305. But my memory may be wrong.
I pull all the coils and plugs. And #5 did look a little blacker than the rest. They all looked good btw. I buy a replacement coil. I put it #5 and there is no change. I replace the spark plug. No change. I move coils around, no change. I remove the #5 coil from the engine and put a spark plug in it and there is visible spark. It was also showing P0302 from time to time. But P0305 is most common. So it shows #2 and #5 most of the time, so it isn't just on one side.
So I was concerned that the IMS bearing went out and the timing jumped. I changed the oil and looked for metal. I did see some flakes. So I believe the ims bearing is dying. So I pulled the cam caps and checked the cam timing. It is good! What a relief. But I still have to replace the ims bearing. But I don't want to do that until I fix this not-running issue.
While I am doing this diagnosis, the car started to also show code P1502. And sometimes it would not rev at all. So I look up the code and it didn't make sense it was a fuel pump code. But after some research, for the e-gas cars, it is a bad throttle code. So with the engine not running, but the key in accessory mode, the throttle should work. Sometimes it did, sometimes it didn't. But more so it didn't. So I bought a new throttle motor assembly. That problem fixed. Throttle works and it is not showing a P1502. I did do the calibration routine btw.
But I was thinking this would solve all my problems, that it was in limp home mode because of the bad throttle. And that the limp mode was causing the misfire codes. Nope. It is still misfiring. And still barely running.
There are no other codes, and other sensors look good. Data from all four O2 sensors looks good. MAF values look good. Temp values look good. I disconnected the maf and reset codes and it didn't affect anything.
SO... Whats up, this is puzzling.
Generally you think one thing breaks. So we know the throttle broke. And we know it is now fixed.
Do you think the throttle broke because of the misfires?
Because of a backfire?
Does the car go into limp mode due to the P1502 code?
Could the car still be in limp mode? If so, how do you clear it? I only have a generic, basic scanner. I did disconnect the battery for a day to see if that would clear it - nope.
What else would cause the misfires and not other codes? Vacuum leak? Fuel injectors, fuel side of things? What is most common on this car.
It almost seems like the DME is bad. What are the chances of that?
Since it showed #2 in addition to #5, it doesn't seem like there was a valve failure on #5. I am hoping a valve didn't fail. I don't hear any major bad noise other than the very rough engine. So I think the engine is mechanically sound (except the ims bearing). I think this is an engine management issue.
Any other input would be appreciated.
05-01-2013, 06:39 PM
#2
Instructor
phild328 When I got my first Boxster S a 2005 last year. I changed the spark plugs
and new coils connected everything and got the misfire message. Car drove just fine but unable to get rid of error message. Changed coils to different spots, still error message. After two days of trying to figure out what the problem was, reluctantly made a appointment with the dealer. Took the car to the dealer and they said the problem was that the plugs were not correctly torqued down. I could not believe what they said this car is more sensitive than my 951. This is just a thought hope it helps.
and new coils connected everything and got the misfire message. Car drove just fine but unable to get rid of error message. Changed coils to different spots, still error message. After two days of trying to figure out what the problem was, reluctantly made a appointment with the dealer. Took the car to the dealer and they said the problem was that the plugs were not correctly torqued down. I could not believe what they said this car is more sensitive than my 951. This is just a thought hope it helps.
05-02-2013, 10:00 AM
#3
Thanks for the reply. That reminds me that I forgot to mention that #5 does have oil leaking into the spark plug tube. Will replacing the tube generally seal up the leak? Is it easy to do, or does it ever turn into a nightmare?
But I cleaned the oil out and I don't think that is the issue.
My engine is not just throwing codes, it is really badly misfiring. It runs really, really rough.
It runs like it is down 2 cylinders. Which I did try to disconnect various cylinders to see which ones would make a difference. But at the time, the throttle was bad, so it didn't make sense. So I may go back now and do that.
But I cleaned the oil out and I don't think that is the issue.
My engine is not just throwing codes, it is really badly misfiring. It runs really, really rough.
It runs like it is down 2 cylinders. Which I did try to disconnect various cylinders to see which ones would make a difference. But at the time, the throttle was bad, so it didn't make sense. So I may go back now and do that.
05-02-2013, 12:09 PM
#4
Race Director
Thanks for the reply. That reminds me that I forgot to mention that #5 does have oil leaking into the spark plug tube. Will replacing the tube generally seal up the leak? Is it easy to do, or does it ever turn into a nightmare?
But I cleaned the oil out and I don't think that is the issue.
My engine is not just throwing codes, it is really badly misfiring. It runs really, really rough.
It runs like it is down 2 cylinders. Which I did try to disconnect various cylinders to see which ones would make a difference. But at the time, the throttle was bad, so it didn't make sense. So I may go back now and do that.
But I cleaned the oil out and I don't think that is the issue.
My engine is not just throwing codes, it is really badly misfiring. It runs really, really rough.
It runs like it is down 2 cylinders. Which I did try to disconnect various cylinders to see which ones would make a difference. But at the time, the throttle was bad, so it didn't make sense. So I may go back now and do that.
The question is not which cylinders but why.
No real time to analyze this now so I'll throw out some things for you to consider...
If the plugs and coils are "old" that's always a good start if you want to throw parts at the misfires.
Be very sure you install the plugs and the coils correctly. The connection at the plug is important but so is the one at the coil/wiring harness connector.
Anything recently done to the car, particularly the engine?
Has the car sat a while, thus the misfires are due to bad or stale gas perhaps? Long shot I admit.
Any chance rodents could have been at the car while it sat? Don't laugh. Those buggers can wreck havoc on a car in no time. And engine troubles is often the first real clue the car has been inhabited by mice or rats.
I do not think the misfires could have damaged the e-Gas hardware.
More later...
05-02-2013, 05:26 PM
#5
The car did not sit for any period of time. It is one of my daily drivers. It was a very sudden event. It was running great. It went out while driving, probably 50-60mph.
Only thing to note is that about a year ago the air scoop flap under the engine came off on the drivers side. I did not get to put it back on since I need to source a new one. It doesn't seem critical as there should still be good airflow around the engine and I am not in a super hot climate. It was not hot the day this went out. Maybe 50 degrees.
Since it went out, I replaced the ignition switch. People have had such weird issues with them, I thought it wouldn't hurt to try. It did not change anything.
A misfire code is not necessarily a misfire. I read that it determines a misfire by a change in rotation speed of the crank.
I am have tempted to pull the accessory belt off to make sure nothing is slowing down the crank. But this doesn't make too much sense since it keeps pulling a #5 code. I am guessing most accesories are not in a whole number ratio to the crank (in other words they might make 1.3 rotations per crank rotation). So if they are not in sync with the crank, than it would throw random misfires. Though it does give the P0300 code, which is multiple random.
Though an accessory that is binding you would think would make noise, I don't hear noise. Also it runs poorly through the rev, not just at idle. Above idle engine power should easily overcome accessory load. So I am talking myself out of that.
I did replace the one coil and plug on #5. And it does have spark. No change in running.
Last night I looked for vacuum leaks. At this time, I do not beleive it is vacuum related. I don't hear any air hissing noise and I put propane around anywhere I could get it and there was no response from the engine to it.
Maybe my ims bearing is really bad and even though the cam timing is correct when I turn the engine by hand, it is off while running due to chain play and shaft play? Though I wouldn't suspect it would throw the timing that much to make it run the way it is. Plus wouldn't an ims failure mainly affect the #1-#3 bank since those cams are driven off the back of the engine, at the ims bearing failure point. #5 should still be good.
Only thing to note is that about a year ago the air scoop flap under the engine came off on the drivers side. I did not get to put it back on since I need to source a new one. It doesn't seem critical as there should still be good airflow around the engine and I am not in a super hot climate. It was not hot the day this went out. Maybe 50 degrees.
Since it went out, I replaced the ignition switch. People have had such weird issues with them, I thought it wouldn't hurt to try. It did not change anything.
A misfire code is not necessarily a misfire. I read that it determines a misfire by a change in rotation speed of the crank.
I am have tempted to pull the accessory belt off to make sure nothing is slowing down the crank. But this doesn't make too much sense since it keeps pulling a #5 code. I am guessing most accesories are not in a whole number ratio to the crank (in other words they might make 1.3 rotations per crank rotation). So if they are not in sync with the crank, than it would throw random misfires. Though it does give the P0300 code, which is multiple random.
Though an accessory that is binding you would think would make noise, I don't hear noise. Also it runs poorly through the rev, not just at idle. Above idle engine power should easily overcome accessory load. So I am talking myself out of that.
I did replace the one coil and plug on #5. And it does have spark. No change in running.
Last night I looked for vacuum leaks. At this time, I do not beleive it is vacuum related. I don't hear any air hissing noise and I put propane around anywhere I could get it and there was no response from the engine to it.
Maybe my ims bearing is really bad and even though the cam timing is correct when I turn the engine by hand, it is off while running due to chain play and shaft play? Though I wouldn't suspect it would throw the timing that much to make it run the way it is. Plus wouldn't an ims failure mainly affect the #1-#3 bank since those cams are driven off the back of the engine, at the ims bearing failure point. #5 should still be good.
05-02-2013, 06:48 PM
#6
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Since your misfires are localised to two cylinders, and you can not get them to move by swapping parts, it is now time to actually test mechanics. Cranking compression is the easiest, so do that first. Follow these tests with leak down tests. The tools are easy to get, compression only requires the tester, leak down will require a compressed air source.
Do these on all six cylinders and see what you get.
Skoot
Do these on all six cylinders and see what you get.
Skoot
05-02-2013, 07:38 PM
#7
Race Director
While a compression and leak down test are often misused I agree with Skoot on this. I think it is time for a compression test. You already know at least 2 cylinders are weak but it is time to see if the compression numbers show something mechanically amiss.
If one or more cylinders have sub-par compression you can change coils and plugs until the cows come home but the engine ain't going to get any better.
I was thinking that maybe only one cylinder was "bad", that the misfire on one was triggering or causing a sympathetic misfire at the other but the firing order as best I can tell doesn't look like that is the case/could happen.
Well, I do note cylinders 2 and 5 are across from each other so -- just thinking out loud you understand -- so say a burnt valve in say cylinder 5 might upset the air flow into or out of cylinder 2.
Long shot.
See what the compression numbers are.
Suggestion: Do this compression test with the engine cold. If you do it with the engine hot as the engine cools the compression numbers from cylinder to cylinder can change.
Also, remove the fuel pump fuse and crank the cold engine some to get some oil flowing. You want each cylinder "wet" with oil so the compression is not biased by the 1st cylinder being "dry" while subsequent cylinders are "wet" with oil.
If one or more cylinders have sub-par compression you can change coils and plugs until the cows come home but the engine ain't going to get any better.
I was thinking that maybe only one cylinder was "bad", that the misfire on one was triggering or causing a sympathetic misfire at the other but the firing order as best I can tell doesn't look like that is the case/could happen.
Well, I do note cylinders 2 and 5 are across from each other so -- just thinking out loud you understand -- so say a burnt valve in say cylinder 5 might upset the air flow into or out of cylinder 2.
Long shot.
See what the compression numbers are.
Suggestion: Do this compression test with the engine cold. If you do it with the engine hot as the engine cools the compression numbers from cylinder to cylinder can change.
Also, remove the fuel pump fuse and crank the cold engine some to get some oil flowing. You want each cylinder "wet" with oil so the compression is not biased by the 1st cylinder being "dry" while subsequent cylinders are "wet" with oil.
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05-05-2013, 09:53 PM
#8
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I agree with the compression and leak down tests...
Keep in mind you need 3 things for proper combustion. Fuel, spark, and compression. Something is amiss, and you know you have spark.
Keep in mind you need 3 things for proper combustion. Fuel, spark, and compression. Something is amiss, and you know you have spark.
05-09-2013, 12:27 PM
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+1 on the leak down and compression tests. Have you looked at your fuel injectors for those cylinders? Maybe even though you can't hear any leaks, I would still perform a vacuum leak test as well. Just my 2 cents.
