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rattle/ping/knocking at high RPM?

Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
I've put about 200 miles on the Vette since getting it back last week, including some higher RPMs. Noticed something that might be a problem...

Sometimes (but not all the time - maybe 50% of the time) when the engine is above 4-4.5k RPMs I hear a distinctive rattle from it. Sounds like when I was having problems with my old turbo car and it was pinging under boost. I feel no appreciable loss of power, like I did then, but the noise is a bit worrisome. The engine is fairly high-mileage (132k mi) and I'll be doing some work on it this winter but wasn't planning on tearing it down yet (just plugs/wires/distributor-sort of stuff).

Anyone have any thoughts on this? Compression is supposedly OK (tested by mechanic before purchase) and it's not really burning oil.

Thanks...
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
HI there,
Well, honestly, I would suggest, due to your mileage, first, check your fuel pressure, then a decarbonization of the cylinders, before attempting anything else.
I am assuming that you do not have a check engine light on, and that you find nothing else out of the ordinary.
1050002 is the top engine cleaner that we use at the dealership. Basically, we split 2 cans between the 8 cylinders, and add the cleaner into the spark plug holes, and allow the engine to soak over night. This is to break up all the carbon in the cylinders. When carbon is removed, you lower the compression ratio, therefore, the chance of knock.
These are just suggestions, and the car should be correctly diagnosed.
Please keep us posted, besttoyou, c4c5:hb
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
I had the same thing.....

When you nail it, it sounds like Carmen Mirandas rythym section. And the hotter it gets the worse it is, right?

Yes it will have carbon in the top.... BUT

Try the following....

Pull the electrical connection for the MAF sensor & drive it..

Mine was sending the WRONG info to the ECM and the Mix was WAY to lean. But not enough to throw a code.

Trust me on this.... what do you have to loose?

Now if this works...you will have to replace your MAF & Relays( for good measure )

175.00 rebuilt MAF @ Kragen
25 bucks for relays

But, you will be sounding like a Z Max infomercial testmonial.


Mike
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Thanks, guys. These sound like good simple solutions and I'll try them. Any idea where to get 1050002 if you're not a dealer? I've used BG's 44k injector/deposit remover before with good results, but it's a bear to find retail.
[RICHR]
 
C

c4ever

Guest
Mike,
I agree with what you say. Since installing my stage II chip I've had slight detonation on FOT particularly in hotter conditions. Base timing is right and car runs great. My first line of thought is to relocate IAT sensor as that will allow a richer mixture due to cooler air info to the ECM. I did remove the sensor only to find out Eckler sent me the wrong connector so haven't gotten it done yet. Any thought on this working. My second plan is the fuel pressure.

Carlo
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
The problem with mine....

The re-man MAF's look completely different internally then the old style. My old one had a little fin sticking up the middle..... that was covered in GOO!

I believe it is a precision capictor to help in the calc of the sender.

I cleaned mine up and it helped a bit...

But the NEW one made a 75% improvement.

The new ones have an inverted wishbone assy with a piece of wire running across it... which is not the Hot Wire.

When I first had my problem, I replaced & tried EVERYTHING... this FIXED the problem.

And it's an easy test.. remove 1 connector and BINGO! either it works or it dont.


Mike
 

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