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what causes knock?

 
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  #1 (permalink)  
Old 26 Dec 2011, 11:26 am
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Default what causes knock?

I mentioned earlier in a previous post that I was having interminent what I assumed where mis-firings and the vehicle acting like I was basically a new driver and learning to drive stick.
but no codes showed when preforming the key dance that appeared related to the jerking action.

I just got home from the holidays where I drove the interstate 8 freeway east from san diego to El centro and back a round trip of roughly 200 miles give or take.

on the leg up I kept the vehicle mostly in 5th gear since it was all freeay and a very slight incline (on return trip sign says 6% grade)
during some of the more strenuous up hill portions the car started bucking again and seemed to get worse the more gas I gave it....slowly adding more gas until WOT. and usually by this time the peak would be reached and I could left off the gas slowly and the jerking would subside. only a few times did I down shift into 4th to maintain speed or pass. the whole trip I was traveling between 55-70 mph....think I hit 45 once when I came up behind a truck and was thinking of drafting behind it then decided screw it I'll maintain the 60mph speed I was enjoying....which was probaly my average speed most of the time.

no bucking occured on a decline or a straight away.

on the return trip there is a significant uphill into the mountains I was actually able to keep it in 5th most of the way up the hill maintaining a speed of 50-60 mph. with little bucking till I reached the top and then there was some minor bucking and I decided to drop into 4th gear.....no bucking there.

one a portion of the leg back I needed to speed up to get in front of merging traffic and noticed the same feeling of bucking...but not as harsh as in previous cases...and on a flat portion of freeway....but something new happened....the check engine light started flashing for a few seconds then stoppped and just stayed on.
I've currently had the check engine light on for a while due to a thermostat code (p0128), which despite having the part I havent had the time to replace yet.
anyways pulled into parking space and home and decided to do the key dance to see if anything new popped up and low and behold code p0325 PCM knock Sensor circuit
along with the p0128 coolant thermostat
and p0522 oil pressure sensor voltage low...I also have this part but I have difficulty seeing the sensor let alone getting to it and if I run some seafoam in the crackcase before an oil change and reset pcm the code disappears for a time.

The Gas I use is Chevron unleaded octane 89....from the same two gas stations I always get gas at (theres one near my home and one near my work depending on which one I am closest too determines which one I go to, but have been going to these two stations for years)

from what I remember in my automotive days knock otherwise known as pinging (I didn't hear any pinging but my wheelbearings howl like no tomorrow and my radio is almost constantly on) is usually caused by....
premature ignition of the air/fuel mixture....which can be caused by...
high compression
timing off
something in the combustion chamber too hot (ie carbon build up or spark plug tips)
lean fuel mixutre

can anyone think of any other potential causes?
maybe point me where I should start looking first?

The timing belt was replaced before I bought the car(recently before I bought to be more specific) and the owner had receipts. at the time of purchase mileage was around 99,900....mileage is now 123,551 and the jerking as been a relative new occurance maybe starting around the 118k mile range but happened very rarely and no check engine code/light. until recently starting more often....and then the issue happening this morning on the drive home.
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Old 26 Dec 2011, 12:25 pm
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Default Re: what causes knock?

I can tell you this: I have a 2006 5 speed. I use 5th gear frequently when I'm on the highway, or in town with light traffic to maintain speed. But 5th gear has no noticeable pull in the N/A unless you're going over 55 or so. On the freeway, I'll shift down to 4th to pass at up to about 70 mph. 5th is basically overdrive as far as I can tell on our little crusiers. On any of our trips on any kind of long uphill, I always drop to 4th gear. It's not always necessary, but I believe it's kinder to the engine and the transmission. I've had 5th gear in at as low as 40 mph, but it has no pull, and will barely keep the car moving on a level.
If your car is a turbo, I have no clue how the gearing sets. Someone else might help though.
Have you replaced the plugs and wires yet? I think every person here will tell you the factory wires are crap, and the plugs aren't much better. If the last owner had the car dealer serviced, they probably use the same gear when they replace it. Even if they have been replaced in the past 30k, look into some good plugs and wires. Those seem to account for about 90% of the running isues on our cars.
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Old 26 Dec 2011, 12:37 pm
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Default Re: what causes knock?

1. Don't use 5th gear under 2,000 RPM, cruising. It'll lug or buck. If you need to accelerate while cruising in 5th at 2,000 RPM, downshift. Giving it more gas in 5th will make it worse. When driving in the pass between El Centro and San Diego, you probably need to stay in 4th.
2. The 'bucking' you describe is called 'lugging' (technical term) and it is bad for your engine. It reduces fuel economy, increases wear to to the constant thudding on the parts and it will also cause premature wear on the main and rod bearings of the engine. I have seen bearings destroyed by persistent lugging and it is not pretty. Lugging can also cause overheating.
3. What shape are the spark plug wires in? I would suggest that you need a new set. I suggest MSD cables designed for a PT Turbo. They will fit fine, and I use them on both of mine. Be sure to clean the coil towers with 400 grit sandpaper and also use the dielectric grease on the boots. I also recommend new spark plugs. I use iridium plugs, but other list members have had success with a wide variety.
4. I can't explain the problems with the 'check engine' light. Replacing the sensors is probably not going to solve the problems.
5. Unless your car is a turbo, 87 octane (as marked on the pump) or heavily carboned-up will be adequate. Engine knock is caused by what you describe. Since about 1987, cars have come with knock sensors that adjust timing to stop engine knock. Back before knock sensors, lugging your engine would have caused severe engine knock that you would have heard over the bearing noise, for sure.
6. What is the coolant level in the system? If it is too low, the sensor may not be reading accurately. What kind of coolant is in the car? Is it Chrysler-approved HOAT (Hybrid Organic Acid Technology) or Dex-Cool? If it is Dex-Cool, you have a bunch of expensive repairs coming, including clogged radiator, hardened water pump seals and maybe bad head gasket. [I really harp on this because the previous owner of my 2001 had the car serviced at Midas. They used Dex-Cool, so when I bought the car, it had a clogged radiator and needed a water pump, thermostat and housing.]
7. The oil pressure sender in my 2004 is cranky. On cold mornings, it tells me that the car has low oil pressure. I turn off the car and restart it, and the sender wakes up, telling me that all is well. Oil pressure senders are a known "feature" of PTs.
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Old 26 Dec 2011, 12:46 pm
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Default Re: what causes knock?

^----Yeah, what he said!
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Old 26 Dec 2011, 12:55 pm
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Default Re: what causes knock?

I forgot to mention: lugging can also break engine mounts.
And . . . What CreepyPT said!
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Last edited by Matt42; 26 Dec 2011 at 12:59 pm.
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Old 26 Dec 2011, 04:07 pm
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Default Re: what causes knock?

I understand what you are saying but at the sametime it does add up 100% to me.

I know about plugs and wires, just for financial reasons and time reasons I have yet to actually get a set of either and do the replacement.....which I do want to do.


as for coolant it is topped off and thus far I have no known issues with the coolant itself.....only the thermostat.....and from the paperwork I have the water pump was replaced with the timing belt.
as to teh type of coolant I unfortuntately do not know.....it was done at a dealer so its probably not HOAT.....another cooling system feature problem I have that is common on the pt's is it seems the high speed part of the fna wont come on.....thus far no over heating has occured.
under heating thanks to teh constantly open thermostat has occured quite frequently.

as for the oil sender unit....samething
sometimes but not always. turn vehicle on oil light stays off turn off and restart all is well. (I also make it a point to check and top off my oil (if needed) when I get gas) and I did that before heading to el centro and when I got back as well.

I seemed to have no problems pulling in 5th gear....while on the freeway.
the run between san diego and el centro is a speed limit of 65-75 depending on which section you are in it. It seems like those speeds keep the engine around 2-2.3krpm. I didn't really notice any power problems other than the bucking. and for the most part I was only maintaining speed. there are a few hills that are steeper than the rest and for those I just wanted to add more gas to maintain speed....as I said there was only about one time I truly tried to pass which was the truck going 45mph(pretty sure I down shifted for that one) and even on the grade into el centro I took my foot off the gas completely and just kept the car in 5th all the way down.
it was instereing on teh return trip up the grade the vehicle seemed to do fine until around the top.
the bucking seemed to happen at 50% throtle and beyound.

5th gear is an over drive gear.....almost all 5th and 6th(where applicable) gears are over drive gears.

the engine mounts are already shot on this vehicle. again its a part I haven't had the financial capabilities to fix....probably going to have to bust out the credit cards soon though.

and your right 87 octane is what I use not 89. use the cheap stuff LOL. but I do unfortuntely like paying for the chevron name.

now here's the part that doesn't 100% add up.
the lugging will also happen in the lower gears, both at part and wot. normally it happens when merging onto the freeway.
but I have had it happen starting from a stop (in 1st) on a level road as well....and the rpms were above 2k in those instances. and I try not to drop the clutch so it shouldn't be from engaging the clutch and engine too fast.

I have been wanting to do the spark plugs and wires for a while now, I'll probablyjust have to put it on credit.
and since the thermostat issue has come up I have been wanting to flush the system and replace the coolant when I do the thermostat replacement. and I wanted to get coolant from teh dealership when I did....I have paid at least a little attention on this forum LOL.
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Old 26 Dec 2011, 04:14 pm
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Default Re: what causes knock?

Have you tried replacing the Cam Shaft positioning Sinsor? I had problems with that if you reach 2500 rpm's and it jerking that's the cause.
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Old 26 Dec 2011, 08:43 pm
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Default Re: what causes knock?

Quote:
Originally Posted by srebik View Post
I understand what you are saying but at the sametime it does add up 100% to me.

I know about plugs and wires, just for financial reasons and time reasons I have yet to actually get a set of either and do the replacement.....which I do want to do.


and from the paperwork I have the water pump was replaced with the timing belt.

Good.


as to teh type of coolant I unfortuntately do not know.....it was done at a dealer so its probably not HOAT.....

I'd be surprised if the dealer put in the wrong coolant. Really surprised.



5th gear is an over drive gear.....almost all 5th and 6th(where applicable) gears are over drive gears.

the engine mounts are already shot on this vehicle. again its a part I haven't had the financial capabilities to fix....probably going to have to bust out the credit cards soon though.

now here's the part that doesn't 100% add up.
the lugging will also happen in the lower gears, both at part and wot. normally it happens when merging onto the freeway.
but I have had it happen starting from a stop (in 1st) on a level road as well....and the rpms were above 2k in those instances. and I try not to drop the clutch so it shouldn't be from engaging the clutch and engine too fast.

I have been wanting to do the spark plugs and wires for a while now, I'll probablyjust have to put it on credit.
and since the thermostat issue has come up I have been wanting to flush the system and replace the coolant when I do the thermostat replacement. and I wanted to get coolant from teh dealership when I did....I have paid at least a little attention on this forum LOL.
What you describe could be engine mounts, spark plug wires, spark plugs or all three.

Quote:
Originally Posted by BIGROB21172 View Post
Have you tried replacing the Cam Shaft positioning Sinsor? I had problems with that if you reach 2500 rpm's and it jerking that's the cause.
I've never experienced problems with this part, so I can't say one way or the other. Sounds right, though.
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Old 27 Dec 2011, 12:36 am
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Default Re: what causes knock?

I'd get a tube of 3M windsheild Urethane (~$12), a set of Standard Motor Products wires, least expensive champions (Copper Plus or whatever) and order a Stant t-stat & gasket.

You can fill the torque arms, replace plugs & wires, and get your coolant situation figured out for a few $.

I'm not sure what to tell you about codes.

after '01 PT went to the .72 5th gear, it's pretty tall, especially with the 15" and 16" tires these came with. ('01 came with .81, huge difference)
Don't be afraid to drop down a gear or two, rev's won't hurt this engine.
Someone did 12's in a Neon with a stock 2.4 lower end with radical cams-
must've done some crazy revs

Finish fixing what's known faults, knock sensor could be mislead by thumping from broken mounts
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Old 27 Dec 2011, 11:30 am
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Default Re: what causes knock?

I agree with Uptown Sport. Even the least expensive spark plugs and Standard Motor Product's wires will be a big improvement. Standard Motor Products items are pretty inexpensive and very good for the price.

As for the windshield urethane, I can't say. But I can think of 101 other things I could use it for!
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