I feel stupid, but while towing a 9000# trailer, I decided to manually shift me AT down while going down a hill, thinking I would use the engine to slow me down instead of relying so much on the brakes.

Well, for about 4 seconds( I don't think it was any more) the engine spiked the RPMs to about 4500!!!!!!!

I didn't realize this could happen, but it did. Any chance of damage to the engine that is not yet noticeable? I had to get it into the shop, as it was smoking white, couple days later it was smking REALLY bad, got it into the shop, and they replace ALL of the injectors. It still smokes white on start up, and blows black smoke when I punch it( it never did that before)

Power feels fine, Econo is good(18.2mpg at 70), should I be worried about anything.

Again, thanks for the response.

 

Most common thing would of been to drop a valve seat due to valve float. Since it is not knocking, all is well. Did they adjust the valve when they did the injectors. This might be the cause of the black smoke.

 

How would you drop a valve seat from valve float? Generally when you get valve float on any engine you risk the chance of the piston coming in contact with the valve head.

 

And that's what exactly can happen when you overrev, you can slap the piston. That can happen past 3500rpm without springs in many circumstances. I would think revving to 4500 rpms for and extended amount of time would definitely drop some valve seats. But if you're lucky snowmanx, you didn't do any strenuous damage.

 

Auto tranny

 

Yeah. I agree.

You other guys care to explain how over revving can drop a seat? A dropped seat and a bent valve are NOT the same thing, so what am I missing??

 

you got lucky run it and youll be fine just dont do it on a regular basis!

 

LOL...no DOUBT!

 

All right I have to ask the question.

If the Ratios of a 48RE are

1st = 2.45 to 1

2nd = 1.45 to 1

3rd = 1.00 to 1

4th = .69 to 1

Then in third gear if your RPM's were 2,000 your rear driveshaft is spinning 2,000 rpm. In 4th gear your rear driveshaft is still spinning the same speed, but RPM's would drop because of the lower gear ratio to say 1,380 (I'm not a expert, just basic numbers) since a .50 would be half 1,00o rpm. (this is assuming you stay the same "speed"

So if you were doing 2,000 rpm in 4th and down shifted, it should have only went up to say 2600-2700 rpm. if it went up to say 4500, you either pulled it down to 2nd, or 1st, that's a lot of RPM's

 

I agree with TAS05CTD610. I have an extreme grade I regularly go down and after warping many rotors I shift down one and my rpms only go from about 2000 to 2600 rpms. Have done this prolly 100 times in 80,000k and never one trouble. Are you sure you only went down one gear?

 

John is absolutely right, He could have reved the motor to 8,000 and has nothing to do with dropping a valve seat. Valve seats are rings that are pressed into the cast iron head and can only fall out if the press fit becomes loose, a prime cause of this is running very high EGT's for a prolonged periods of time.

 

Remember, this is an automatic tranny, I shifted from drive, and after just looking, to 2nd gear. I was in overdrive while I was going down hill I was travelling at about 75 mph.....like a said, I feel stupid, but it was also stupid! LOL

Anyways, seems like all is well.

Thanks again.

 

You guys can preach all you want too. We had a fellow on here that did this during an emergency stop situation to help create back pressure for his exhaust brake. He had an auto also. What happened???? He dropped a valve seat. How????? Don't know, don't care. Valve float is not when a valve hits the top of a piston. It is when it never fully closes due to overreving and bounces on the valve seat.

 

This is poor information to be posting about valve seats falling out of their pressed fitted pockets in the heads which is very common due to over reving the engine. Care to guide me to a scorce of information explaining this?

 

I would think overcompression could generate enough heat to cause one to drop.