I have a 2000 Toyota Tacoma, 4X4 V6. I was on my way home from work today, pulled out from the intersection and sped up, then I got a very loud knocking noise. I pulled over to the side to investigate. I shut it off and checked the oil, all was well. I started it up and the noise was still there, when I reved it up the noise was in sequence with the rpm's. It sounded like a broken valve or something. Then the noise started to cut in and out as I drove it home. The truck started to miss and sputter. By the time I got home the noice was gone, the truck idles perfectly smooth, but when I drive it, it has a bad missfire. I was thinking timing chain, but came to find out it has a belt. Does anyone have any idea as to possible problems... The loud knocking noise has really threw me for a loop.

 

check pulleys/pulley bolts...

and NEVER rev your engine to "diagnose" an engine problem

 

thanks for the reply, I've checked the pullies and bolts, belts, all is good. But I don't think that should contribute to the missfire anyways would it?? Any other ideas??

Thanks, all help is greatly appreciated..

 

Just wanted to post the solution to the problem I was having. Figured I'd change the plugs as an expensive first choice. Turns out one of the plugs had broken into and the bottem leads had shattered cause them to drop down on the piston..I.E. " the knocking noise I was having " and explains the miss fire. Replaced the plugs and the truck is up and running like new again...

 

ahh, good job I forgot about the simple checks first

and yes, a loose lower crank pulley bolt will cause the pulley, and the lower timing belt cog behind it to slide a little out of position on the crank. This will mean the sensor reading the engine off of the timing belt cog will not work, causing a misfire. These pulleys seem to slide out of position at high RPM's, and return to position at lower RPM's and at idle. Revving, or going too long without fixing it can eventually cause your timing belt to rub enough it may fray and break.