Thread: rod knock or something else?

Hello. It's my first post. It's not that I have been avoiding you guys it's just that I never had a Pontiac Grand Prix before. But now I need your expertise.

I bought a car for my daughter. I knew that it had some engine problems but I liked the car so I bought it. It's a 1999 Pontiac Grand Prix GTP. The guy said that it had a rod knock. So I went and looked at it. When I started it at first there was no rod knock and then after a minute it started. It does increase as you give it gas.

I drove the car home and it drove well but would knock pretty load when taking off from a light. Then when it would shift at about 35 the knock would pretty much go away. it may have been there faintly but I couldn't really hear it. Then we I got closer to the house I got on it a bit more. No huge knocking or anything and the car accelerated well and ran good. Then as I got close to home the car really was not running real well and seemed like it wanted to quit.

I have no warning lights and my code scanner shows no DTC, temp is good. I out up some vidoes to see what your opinions are.

The car was maintained well and I have all the records. The car has 101,000 miles and the oil was changed regularly. The guy said it was his sons car who now works in D.C. and so the car has been sitting in the dads driveway for over a year. However, the dad would take it for a drive about once a month to keep everything going. He took it out one day and then he heard the sound. before that it ran great and they were going to drive it out to D.C. until this happened. I am ready to throw a new engine in it but first I want to get some other opinions.

It doesn't just knock but it makes quite a bit of noise. Sounds like metal or like a bearing on a pulley. Also I found a vacuum ose disconnected because the connector and rotted and split. I did put that back on but after that the cars seems to want to surge when it is ideling. It's also kind of hard to keep it running now when you pull it into the garage or out.

Trans fluid is full and looks good. Oil looks clean and was actually a nit over full. I drained some out.

So take a look at the videos and tell me what you think. If I have not put you to sleep yet

2011-08-27_13-41-06_330.3gp - YouTube

2011-08-27_13-41-59_623.3gp - YouTube

2011-08-27_14-27-25_218.3gp - YouTube

2011-08-27_14-27-58_825.3gp - YouTube

Fubar flexplate.

Thanks for the replies guys. Hippo Machine - Honestly I think that my third video sounded just like yours. I have that same squeeky/chipping should along with the knock. Also, after I got it home it started running like it was going to quit. It would run real slow and the oil light would flicker real lightly here and there.

When you put it in gear and let off the brake it wanted to quit so you had to two foot it just to back up and go forward a little bit.

I know that to even fix the flex plate I have to pull the engine. Is there anything else that you guys would suggest checking before I pull it?

On the back side of the engine I see a lot of oil. I can smell the oil burning also. I also smell coolant a little when the car is running.

Coming home there was no smoke or steam out the tail pipe even when getting on it a little bit.

Yes LOL. second to the last line of my OP. I checked it and it's clean. it was a little bit overful so I drained some out. Now it's right on the button.

Originally Posted by mainjet

Yes LOL. second to the last line of my OP. I checked it and it's clean. it was a little bit overful so I drained some out. Now it's right on the button.

Why was it overfull? I have a feeling coolant is getting in it and creating the overfull condition. This is of course assuming you do the oil changes and know for a fact you did not overfill it last time.

I visually inspected the flexplate the best I could from under the car. However, in my mind I would not see a crack that runs around the bolts holding the flex plate. So do you think that it would be a good idea to take the bolts off from the torque converter to the flex plate then see if I can get movement in the flexplate?

I know that in the end it will probably be a rod and I can deal with that. The thing that is bothering me is this -
1. The car was very well maintained and I have all the records of regular oil changes and maintenance. why would the rod go at 100,000? Could happen but seems unlikely.
2. The noise seems like it is coming from the area of the flexplate/transmission. At one point I thought -is it the trans?

And lastly, this has nothing to do with this problem but when I picked up the car it was almost out of gas so stopped and put regular octane gas in the car. I noticed in the manual it says to use premium. Do you guys use premium in these cars or what?

You could use Regular, but it honestly won't run as good as with Premium.

Originally Posted by bluegtp91

Maintenence meaning the Lower Intake Manifold gaskets? If they were never replaced with the metal replacements...and still used the factory ones and the dexcool was never totally flushed out of the system...then that's the issue.

Dexcool is a killer on plastic stuff.

At 96,000 the following work was performed:
Supercharger gasket
plenum gasket
lower intake gasket
heater bypass tubes
antifreeze

What do you mean "then that's the issue"? I don't quite understand what your saying.

I understand now. I appreciate the wisdom.

So far I have found most of the little rubber vacuum connectors to be dryrotted ad cracked. I am going to replace those so that the vacuum is tight everywhere. Then I am going to remove the belts so taht I have no accessories running and see if I hear any change.

If the above does not produce results then I will take the bolst out out the torque converter to flexplate and see if I can figure out if anything is wrong with the flex plate.

If again I get no results then I will pull that motor out and put in another one.

Originally Posted by bluegtp91

Well...in order to swap the flexplate either the transmission has to be dropped out...or the motor has to come out the top...so if your replacing the flexplate...you might as well swap the bottom end...and get headers...and cam it...and put a supercharger on it LOL

What about the paint and the interior? Should I do anything there since the flex plate is bad? Of course that is just going to make the siding on my house look bad and you can't side the house and leave the shingles like that. LOL