Engine Knocks with Cold Starts

Joe, first problem is its a neon, just kidding, but it sounds like a wrist pin and/or a bad piston. a little sticky when you first start it, loosens up a bit with no lube, knocks a bit till the oil gets in there then goes away. anyway good luck and let us know what it is if you find out...

I would not start tearing it apart just yet. Any computer controlled engine I have worked on has some "artifical" signal generation that the computer used to start things working. Once the engine has run a little (15 seconds), they then are using the various signals from the sensors like oxygen sensor, mass air flow, throttle position, cam position, crank position,etc. These signals are used to constantly adjust the timing for firing the spark and it is the spark timing that is probably causing your knocks. Some of these sensors will start to show defective by being slow to work when cold. After 1996, all cars started using standard OBDII diagnostics and connections for reading them. If you haven't had the car to a shop in awhile, my guess is they can use the OBDII to find a weak sensor (if one is starting to fail). Worse case you might have to leave it with them to see it cold if the error hasn't been stored in memory. Most cars show a check engine light when an error has been stored, yours may not or the check engine light is burnt out. A few of the aftermarket auto parts stores/repair shops will help you look at the codes for free. Not trying to advertise but try autozone or advance. Okay, one other suggestion, since you didn't mention if the warm-normal operation had any other symptoms, ask the wife is the car has acted sluggish. If so, I would be also check the cat converter and expect that you maybe seeing two differnt failures at this point that have compounded to your symptom.

The sensors is a good possibility, Because the throttle body sensor died two years ago, it would cause a crazy high idle. And bought a new one, but it was a beast to try to change out. And simply un plugging it, cured the High idle. And the only performance effect seemed to be that the cruise control no longer worked.

But then about a year ago I re connected the connector again, and all is fine again with the High Idle aspect,

Soo bad sensor? Bad connector? either,, Both?

so Maybe as you suggest another sensor is going bad or connector..

Problem is I bet they'd have to put it on the tester first thing in the morning out in the parking lot. For simply driving it into the shop will rid the knock for that day already.

I wouldn't worry about it. Every vehicle I have owned (computer controlled) has done the same thing. I have never had any problems with the engines or gas milleage. You should however always let the vehicle warm up for a few minutes even when it is hot out so you do not damage the engine. Oil drains to the bottom of the pan when it sits and is redistributed to the top of the engine as it runs.

I have seen people start up a vehicle in mid winter and take off like a bat out of hell. That is the vehicle you would hope you did not buy from the car lot!

Steve

I would think it less likely to be a sensor and more likely to be mechanical. A lazy hydraulic tappet is a likely contender, try an engine cleaner and oil change. If it genuinely is knock, and that is possible, then it's most likely the engine has fallen outside the calibration due to eg: coked up a bit, partially blocked injector on one cylinder etc. The engine probably starts rich so it won't knock then, but a little time later leans out as the catalyst warms up. Cold is not the most knock prone condition and also just after start and at low rpm the knock system may not be engaged. Once it is, the system corrects spark advance and the knock goes. If so you're loosing a little mileage but probably no engine damage for a few seconds when cold. Good advice to treat it gently till it stops knocking.

The tappet (Hydralic lifter) I would think the knock would as they have always did in the past knock right after starting until they get pumped up.

But this is quiet and no knock after starting for 15 seconds or so, Then the knock starts, and does so for the 30 seconds or so, then goes away.

hmmm?

If possible, use a scan tool to observe the spark timing and the "severe knock" flag during this event. As other users state, the OBD-II diagnostics may be testing your knock sensor to verify its function. You will see the spark timing advance aggressively while the computer listens for knock via the knock sensor on the side of the block.

It is possible that the knock sensor check is occurring early in the cycle (right after cold start), but it is more difficult to make create the in-cylinder conditions for combustion knock (also known as end-gas detonation) - especially at idle conditions. I'd expect that the Chrysler calibration engineers programmed the knock sensor check for a warm engine with 80 C coolant and part throttle.

Other things to check:

1. is the knock sensor hooked up? wire damaged?

2. any other codes in Scan tool.

As others hear have suggested, I am wondering whether this is really a mechanical type of knocking sound rather than "combustion knock".

Good luck.

That was my whole question, I thought it only was mechanical,, but could not figure out a situation that would behave like this, and if a diagnosis was made if it is something to worry about.

Hmmmm ? Very strange .

What kind of " knocking " do you hear ? Is it a deep low knock or a high pitched knock ? Can you determine where on the motor the sound is coming from, you can use a simple hose by putting one end in your ear and search the motor for the location of the noise.

If your sensors where the problem you would have a " check engine light " on to alert you . If it seems to be oil starvation related , you might have a clogged or collapsed oil filter , change the oil and filter using cheap oil and filter , buy a can of engine sludge cleaner and follow the cans directions , this will clean the sludge from the inside of the engine and most importantly , the oil pump pickup screen . If this seems to help , do it all one more time then replace the oil with full synthetic and the filter with a synthetic oil filter , they are built to withstand the longer synthetic oil change intervals . Also check the egr system for a blockage . Let us know what you find .

I'll try to isolate to location,, and I'll try to make a recording and post it someplace to download, so you all can hear it too.

Joe

So how do you decide if it is a knock caused by an over lean mixture, or advanced ignition timing? Or is it a rod bearing, main bearing, wrist pin loose, Wrist pin too tight?

Just like you did on that 289, or 327. Get an insulated pliers, and pull a spark plug wire off one at a time till the noise changes dramatically. That will be the bad cylinder. But it will also tell you if it is mechanical, or combustion caused. If it is lean knock, it will stop immediately. If the sound just changes, It was mechanical. You may have to repeat the testing a few times to be sure, but at least it will give you some answers. I think your Neon has coil on plug ignition. This will actually be easier than having to move a high voltage wire. You just have to disconnect the low voltage wire to the coil pack to stop the cylinder from firing. Good luck, and let us know what you find.

I forgot to mention the possibility of the noise being rocker arm or valve related. If the noise is caused by something in this area, there will be no change in the sound.

Good luck.

G'day NSS...

One quick thing to try is an oil & oil filter change.

If it has been awhile since the last one this might be one reason. The oil may have lost it's 'oompf' & is lacking when cold. Try this first before any major strip downs.

Does the noise sound top-end or bottom-end to you? You mentioned lifters, the oil change should fix this to a certain extent as well...

If you have one, put an oil pressure guage on the engine prior to starting & monitor the guage when the noise is present... is it low or flucuating etc;...

Has the unit be using any oil of late or in the past?

sorry for all the questions..

cheers for now

LOWIQJO...

Hi Joe.Have you checked the timing belt tension? Ive heard belts rattling on the plastic cover when cold then becoming quiet as they warm up .