Will bad guides throw misfires and rough idle?
05-01-2005, 12:33 PM
#1
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Will bad guides throw misfires and rough idle?
I decided to start a new thread from my previous one regarding my chasing a misfire code. (see https://rennlist.com/forums/993-forum/191242-chasing-the-elusive-misfire-code-any-suggestions.html)
Here is were I am now. I am still getting persistant CEL's and the **phut**Phut** type noise from the exhaust even with new caps/rotors/wires. Its hard to go much further without any rear diagnostic tools so I took it to a independant shop that does a lot of work for local Porsche club members. I give him a couple of hours of shop time and told him to see what he could find.
He ran test drove the car (of course had a hard time to get the CEL), ran a 4-gas analyzer on the exhaust, check the vaccum leaks, injectors, and O2 sensors. Vacuum is strong and steady, sensors are fine and everything appears to be OK. His ODBII reader read the same and additional codes than mine, all related to emissions failures and misfires, not related to SAI though. The 4-gas tester showed high hydrocarbons in the exhause, especially on cylinders 4-5-6.
So what was his conclusion on the cause the **phut** **Phut** and the CELS? He suggested that I had worn valve guides that were getting bad enough to cause the valve not to seat properly, and this would cause the misfires and rough idle. This kindof makes sense to me but the question I will post to the list...has anyone seen worn valve guides cause misfires and rough idle?
He may be right given:
1 - My 993 is a 96 which seems to be prone to the valve guides problems.
2 - The car has 75,000 miles on the original engine.
3 - The PO left the engine tray on so the engine had the first 60,000 miles with the tray on and drove the car daily in Toronto which has bloody hot and humid summers.
4 - The car does use oil, on the high side of consumption, but I have not tracked it precisely enough to say xxx km/litre. Definitely not 2500 miles/quart like some others. Is likley closer to the consumption limits as speced by Porsche.
My goose may be cooked here but the mechanic was not 100% sure it was the guides. We did not remove the valve covers and check...I had only booked a few hours. That could be a next step.
The cost of having a mechanic replace the valve guides is just nuts...it not proportional to the dropping value of these cars. Either I have to sell the car with disclosure, get the cash out and take the hit or take on the job on myself. I can't afford to pay someone to have it done. It would be interesting to do the top end myself, and still quite a bit cheaper even if I factor in taking Bruce's rebuilding class. Might make an interesting DYI. I am leaning that way once I am sure its the guides.
Who thinks its the valve guides?
Cheers,
Mike
Here is were I am now. I am still getting persistant CEL's and the **phut**Phut** type noise from the exhaust even with new caps/rotors/wires. Its hard to go much further without any rear diagnostic tools so I took it to a independant shop that does a lot of work for local Porsche club members. I give him a couple of hours of shop time and told him to see what he could find.
He ran test drove the car (of course had a hard time to get the CEL), ran a 4-gas analyzer on the exhaust, check the vaccum leaks, injectors, and O2 sensors. Vacuum is strong and steady, sensors are fine and everything appears to be OK. His ODBII reader read the same and additional codes than mine, all related to emissions failures and misfires, not related to SAI though. The 4-gas tester showed high hydrocarbons in the exhause, especially on cylinders 4-5-6.
So what was his conclusion on the cause the **phut** **Phut** and the CELS? He suggested that I had worn valve guides that were getting bad enough to cause the valve not to seat properly, and this would cause the misfires and rough idle. This kindof makes sense to me but the question I will post to the list...has anyone seen worn valve guides cause misfires and rough idle?
He may be right given:
1 - My 993 is a 96 which seems to be prone to the valve guides problems.
2 - The car has 75,000 miles on the original engine.
3 - The PO left the engine tray on so the engine had the first 60,000 miles with the tray on and drove the car daily in Toronto which has bloody hot and humid summers.
4 - The car does use oil, on the high side of consumption, but I have not tracked it precisely enough to say xxx km/litre. Definitely not 2500 miles/quart like some others. Is likley closer to the consumption limits as speced by Porsche.
My goose may be cooked here but the mechanic was not 100% sure it was the guides. We did not remove the valve covers and check...I had only booked a few hours. That could be a next step.
The cost of having a mechanic replace the valve guides is just nuts...it not proportional to the dropping value of these cars. Either I have to sell the car with disclosure, get the cash out and take the hit or take on the job on myself. I can't afford to pay someone to have it done. It would be interesting to do the top end myself, and still quite a bit cheaper even if I factor in taking Bruce's rebuilding class. Might make an interesting DYI. I am leaning that way once I am sure its the guides.
Who thinks its the valve guides?
Cheers,
Mike
05-01-2005, 03:31 PM
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Mike,
Have you had a leakdown test done? If you do have a guide problem, this could be used to confirm/isolate the problem.
Hope a top end rebuild is not needed as I know how much you love your car.
Have you had a leakdown test done? If you do have a guide problem, this could be used to confirm/isolate the problem.
Hope a top end rebuild is not needed as I know how much you love your car.
05-01-2005, 04:34 PM
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Hi Kelly,
I thought a leakdown test will not confirm wear in the valve guides but show if the valve is not sealing with its seat...which could be from wear, carbon or perhaps a bad guide? My inclination is to do the screwdriver test on the valve stem which will involve taking off the valve covers, removing the rockers because of the lifters, and then testing the play. I would expect some play but then it comes down to experience...how much play is too much?
It also comes down to a fundemental question : Will bad guides throw misfires and a rough idle?
Cheers,
Mike
I thought a leakdown test will not confirm wear in the valve guides but show if the valve is not sealing with its seat...which could be from wear, carbon or perhaps a bad guide? My inclination is to do the screwdriver test on the valve stem which will involve taking off the valve covers, removing the rockers because of the lifters, and then testing the play. I would expect some play but then it comes down to experience...how much play is too much?
It also comes down to a fundemental question : Will bad guides throw misfires and a rough idle?
Cheers,
Mike
05-01-2005, 04:51 PM
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Mike,
Yes, you are correct. My suggestion for a leakdown test (and possibly a compression test) was made to help you isolate and troubleshoot the problem instead of working from the assumption that the valve guides are your problem.
I know RL member Adrienne has recently had her guides redone. Perhaps you can PM her and ask what her symptoms were.
Good luck... hope it's not what you're suspecting.
Yes, you are correct. My suggestion for a leakdown test (and possibly a compression test) was made to help you isolate and troubleshoot the problem instead of working from the assumption that the valve guides are your problem.
I know RL member Adrienne has recently had her guides redone. Perhaps you can PM her and ask what her symptoms were.
Good luck... hope it's not what you're suspecting.
05-01-2005, 05:21 PM
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Good point! Its better to be open then assume its something specific. I will contact Adrienne and see what she says.
Cheers,
Mike
Cheers,
Mike
05-01-2005, 07:09 PM
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Mike,
Had to chime in as this sounds all to familiar to my scenario. Although my car never had the CEL illuminate and ran just fine, I was experiencing high oil consumption, sans clouds of smoke. Similar history, first 60K with the engine tray on in southern FL. (only to add to the high temps; no doubt hastens the valve guide wear issue)
Can't help you on the evaluation side of the coin, next to the wiggle factor of the valve guides, I really don't think there is any test that is conclusive.
I recently had to address this issue (top end rebuild) and chose a well known and respected professional. Although my approach was not "budget friendly" I intend to have the car for a long time and did some upgrades that I felt were reasonable given the nature of what was already being done. That said, to approach this from a min cost direction, I think you have some alternatives. In addition to the Bruce A. class, which I agree would be satisfying, you could also drop the engine, remove the heads and send them to out to be done. This would leave the assembly and cam timing, etc. for you to accomplish.
If your happy with the car I would be hesitant to get out of it. Do whats necessary to get back to "right" and just make a long term commitment to your car. Unless your moving up in car, I honestly don't think theres anything out there that compares to the 993, after the top end rebuild, you'll be back to "bulletproof" car (if there is such a thing) and you'll have a great car that is on a slow depreciation curve.
PM me if I can provide more info!
Jeff
Had to chime in as this sounds all to familiar to my scenario. Although my car never had the CEL illuminate and ran just fine, I was experiencing high oil consumption, sans clouds of smoke. Similar history, first 60K with the engine tray on in southern FL. (only to add to the high temps; no doubt hastens the valve guide wear issue)
Can't help you on the evaluation side of the coin, next to the wiggle factor of the valve guides, I really don't think there is any test that is conclusive.
I recently had to address this issue (top end rebuild) and chose a well known and respected professional. Although my approach was not "budget friendly" I intend to have the car for a long time and did some upgrades that I felt were reasonable given the nature of what was already being done. That said, to approach this from a min cost direction, I think you have some alternatives. In addition to the Bruce A. class, which I agree would be satisfying, you could also drop the engine, remove the heads and send them to out to be done. This would leave the assembly and cam timing, etc. for you to accomplish.
If your happy with the car I would be hesitant to get out of it. Do whats necessary to get back to "right" and just make a long term commitment to your car. Unless your moving up in car, I honestly don't think theres anything out there that compares to the 993, after the top end rebuild, you'll be back to "bulletproof" car (if there is such a thing) and you'll have a great car that is on a slow depreciation curve.
PM me if I can provide more info!
Jeff
Last edited by jnor10; 05-01-2005 at 08:03 PM.
05-01-2005, 08:20 PM
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I would suspect that if your valve guides were worn enough not to allow the valves to seal properly, your oil consumption would have increased substantially. if you are using no more oil than usual, then I would look elsewhere before tearing the engine apart.
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07-22-2005, 09:02 AM
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I have a 1997 993 with about 42k (it's only been mine for the last few thousand). After a short trip around town the CEL came on with P0300, P0304 and P0306 (multiple misfire codes). The CEL came on just after backing out of the parking space, not at speed. I have a relatively low idle and the small **phut** sound from the exhaust on the passenger's side -- both go away when the A/C's on. I don't have any smoke at start-up or on deceleration at speed (other than an occasional gray puff when I start the car after it has sat for a number of days).
The car was already scheduled to go in for regular maintenence next week so I'm going to add this information to what I tell the service manager when I take it in.
Any other diagnosis would be handy.
The car was already scheduled to go in for regular maintenence next week so I'm going to add this information to what I tell the service manager when I take it in.
Any other diagnosis would be handy.
07-22-2005, 09:56 AM
#9
Nordschleife Master
Originally Posted by Mike J
...<snip>...
The cost of having a mechanic replace the valve guides is just nuts...it not proportional to the dropping value of these cars. Either I have to sell the car with disclosure, get the cash out and take the hit or take on the job on myself. I can't afford to pay someone to have it done. It would be interesting to do the top end myself, and still quite a bit cheaper even if I factor in taking Bruce's rebuilding class. Might make an interesting DYI. I am leaning that way once I am sure its the guides.
Who thinks its the valve guides?
Cheers,
Mike
The cost of having a mechanic replace the valve guides is just nuts...it not proportional to the dropping value of these cars. Either I have to sell the car with disclosure, get the cash out and take the hit or take on the job on myself. I can't afford to pay someone to have it done. It would be interesting to do the top end myself, and still quite a bit cheaper even if I factor in taking Bruce's rebuilding class. Might make an interesting DYI. I am leaning that way once I am sure its the guides.
Who thinks its the valve guides?
Cheers,
Mike
07-22-2005, 10:41 AM
#10
Burning Brakes
Mike...I had similar symptoms to you and it turned out to be arcing plug wires. I know you replaced the wires, caps, rotors etc...But (and I apologize if this sounds too obvious) did you check the dual distributor belt too?
My experience with worn valve guides in past 911s (not my 993...yet) has been that there was no performance degradation, just smoke and excessive oil consumption.
In my admittedly unqualified opinion, your problem just doesn't sound like worn valve guides...
My experience with worn valve guides in past 911s (not my 993...yet) has been that there was no performance degradation, just smoke and excessive oil consumption.
In my admittedly unqualified opinion, your problem just doesn't sound like worn valve guides...
07-22-2005, 11:59 AM
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Originally Posted by Matt Davies
Mike...My experience with worn valve guides in past 911s (not my 993...yet) has been that there was no performance degradation, just smoke and excessive oil consumption.
In my admittedly unqualified opinion, your problem just doesn't sound like worn valve guides...
In my admittedly unqualified opinion, your problem just doesn't sound like worn valve guides...
07-22-2005, 12:49 PM
#13
Burning Brakes
Mike, I went back and read your previous thread and was REALLY surprised that nobody suggested you check the dual distributor belt. If that's broken, it could cause the symptoms you're describing.
Also, you mentioned a "glow" coming from somewhere... As you know, that is an arc, and you would be shocked (okay, pun intended) at how much havoc can be wrought on the normal function of your ignition system by rogue electrical currents...It caused really bad misfiring on my car.
Good luck!
And if you do eventually need to do a valve-job (with your oil consumption, you might be looking at that fairly soon..), you could do what my independent has suggested for me when the time comes,
which is we drop the engine together at his shop, and I do the valve rebuild myself, under his supervision. Minimal labor costs (and with less chance of f-ing it up) make it not such a scary future proposition...Sometimes the glass is 1/8 full!
Also, you mentioned a "glow" coming from somewhere... As you know, that is an arc, and you would be shocked (okay, pun intended) at how much havoc can be wrought on the normal function of your ignition system by rogue electrical currents...It caused really bad misfiring on my car.
Good luck!
And if you do eventually need to do a valve-job (with your oil consumption, you might be looking at that fairly soon..), you could do what my independent has suggested for me when the time comes,
which is we drop the engine together at his shop, and I do the valve rebuild myself, under his supervision. Minimal labor costs (and with less chance of f-ing it up) make it not such a scary future proposition...Sometimes the glass is 1/8 full!
07-22-2005, 08:28 PM
#14
Burning Brakes
Mike-
My 993 was making a "ticking" noise that was first heard only at idle becoming progressively louder. My mechanic thought it was a dead lifter & replaced all of them. Still ticking - valve guides. When the engine was dropped down, a large amount of debris (leaves, sticks, etc) was blocking the furthest forward cylinders creating an overheating problem which inturn trashed the valve guides.
Oil consumption was unknown - I had just purchased it.
It had 48k miles with the tray in place and it came from Fla. The car has been repaired and now has 51k miles - running great. Do what you can to get her fixed as selling will only lead to regret.
Good luck!
My 993 was making a "ticking" noise that was first heard only at idle becoming progressively louder. My mechanic thought it was a dead lifter & replaced all of them. Still ticking - valve guides. When the engine was dropped down, a large amount of debris (leaves, sticks, etc) was blocking the furthest forward cylinders creating an overheating problem which inturn trashed the valve guides.
Oil consumption was unknown - I had just purchased it.
It had 48k miles with the tray in place and it came from Fla. The car has been repaired and now has 51k miles - running great. Do what you can to get her fixed as selling will only lead to regret.
Good luck!
07-22-2005, 11:06 PM
#15
Rennlist Member
A leak down test would be a good test for a burnt valve. If you have compressed air escaping into the exhaust, then you have a serious problem.
Definitely check the dual distributor drive belt. They were a real problem for the 964, but have not heard so for the 993, but check it anyway. If the belt is deteriorating it can jump a cog and you will get misfires and loss of power. Good call Matt!
The CEL is not a good sign. Seems carbon build up might be the cause and worn guides can produce that issue.
It also worries me that you are consuming oil. That is not good and it must be going somewhere. Bad guides and seals will increase consumption, so will leaks. Do you see evidence of oil leaking on the floor or engine?
Given all of the symptoms you should have the car rechecked for valve guide wear. A car with excessively worn guides is a ticking time bomb.
Definitely check the dual distributor drive belt. They were a real problem for the 964, but have not heard so for the 993, but check it anyway. If the belt is deteriorating it can jump a cog and you will get misfires and loss of power. Good call Matt!
The CEL is not a good sign. Seems carbon build up might be the cause and worn guides can produce that issue.
It also worries me that you are consuming oil. That is not good and it must be going somewhere. Bad guides and seals will increase consumption, so will leaks. Do you see evidence of oil leaking on the floor or engine?
Given all of the symptoms you should have the car rechecked for valve guide wear. A car with excessively worn guides is a ticking time bomb.