Low compression on cyl #3

1997 v6 with 341k mikes on the odo. On cold start, engine misses a little, and occasionally a little white smoke from exhaust. After it warms up, it runs fine for the most part, unless getting on the freeway, in which case it stutters a little. Code shows misfire in cyl #3. Wet and dry comp test confirmed low compression (133 psi compared to 155 psi in all other cyls). Pulled the cylinder 3 spark plug for inspection. Plug looks good, no signs of excessive oil fouling. Inspected the cylinder with borescope to check for any coolant or anything abnormal. No coolant in cylinder. Visual checks OK. Engine has 341k on it but was maintained very well by prev owner. Have not done a leak down test yet. I have heard that 133 psi should not be low enough to cause a misfire and that it could be coil pack or spark plug? But it seems like that has been ruled out? Some say I will need to replace the head or get a new engine. Don’t know what to do.

 

I would rule out the coil pack by swapping it to a different cylinder to see if the misfire moves. Any other codes?

 

Does the borescope have side camara? You want to check the intake valves for carbon deposits. Sometimes if there's too much, it wont shut properly. It's worse on EGR models.

First things first, swaptronics, swap coil pack, fuel injector etc.

 

thanks. No, no other codes.

 

No carbon deposits

 

If the #3 cylinder passes the leak-down test, incorrect valve lash has been shown to yield low compression in the 3.4L V6. Check the MTX records to see when the valve lash was last checked, if ever. My '97 V6 Taco with 133K has 190-195 PSI in all 6 cylinders & runs like a scalded dog for a stock original 3.4L V6. I wish my much newer 3rd "turd" Gen TRD 3.5L V6 engine ran like my 26-year-old 3.4L V6.