My 01' has thrown a misfire every once in a while over the last few months I've owned it. I've changed plugs, wires, coil packs, injectors and injector o-rings.

It's the second motor and the heads have been machined and gaskets replaced about 30k ago. So, I'm thinking a sticky valve or I just read about a valley gasket leaking oil in the cylinder. It did only happen at harder acceleration (never gave the truck full throttle) and I would tip back in the throttle and feel the shudder then see the code thrown. Now, it's frequent even at easy tip in.

Thoughts on testing for a sticky valve?

Thanks in advance!

 

I doubt it is a sticky valve but it could be.
What motor oil do you use and how often do you change it?

 

how about we start at the top.

any codes?

 

Old school, before all these exact on the money scanners, one tool in every shop was a vacuum gauge. Just attach it to a port on the plenum. It will have a reading, and you would like it to be steady. If it varies 3 - 4 inches (vacuum is measured in inches), that could indicate sticky valves.

Heres some info on using a vac guage.


ENGINE STATEVACUUM GAUGE READINGINDICATION
Steady idle (800-1200rpm)Gauge steady, 17-22Normal & healthy

Steady idle (800-1200 rpm)Intermittently drops several needle divisions Sticking valve or broken valve spring
Steady idle (800-1200 rpm)Steady, low reading, 8-14Small vacuum leak or valve timing off; could have low compression/worn rings (verify with a compression or leakdown test).
Steady idle (800-1200 rpm)Steady, low reading, under 8 Vacuum leak (check brake booster, vacuum lines, etc.)
Idle (800-1200 rpm)Needle drops sharply on a regular rhythm Burnt valve, or a valve with clearance too tight
Idle (800-1200 rpm)Needle drifts up & down, along with rpm drift Mixture off or small vacuum leak
Idle (800-1200rpm)Vacuum gradually drops Excessive exhaust back pressure (plugged muffler or catalytic converter)
Idle (800-1200rpm)Intermittent fluctuation Ignition miss; sticking valve
Idle (800-1200rpm)Steady, above 22 Ignition timing may be too advanced
Open & close throttle quickly Drops to about 2, jumps to about 25 Healthy engine
Open & close throttle quicklyDrops to 0, jumps to about 20 May confirm worn rings (especially if idle shows only about 15-20) Verify with a compression or leakdown test.

 

Touche, but my train of thought was if the PO spent that kinda money chasing a misfire, then hopefuly, He would have at least checked to see what codes he had.
I guess though, that might be asking too much.

 

The OP question about sticky valve diagnosis brought back stuff form the way-back machine. Vac gauge would certainly be sensitive to a sticky valve, as they are right there in the intake (well, one side of them). I guess it would be something that could be used to provide a "second opinion" of certain diagnosis.

And back in the day, many a Benz sported a cluster mounted vac gauge.

 

Most definately, but i wouldnt trust some techs I work with to use a vac guage, far less a DIYer (no offense)
Most of those golden oldies dont ever come to dealers. Unless the owners want to spend insane amounts on factory restorations which almost never happens.

 

5w30 every 3k

 

yep P0305 (cylinder 5) & P0300 (generic misfire)

 

Good info Savannah. Thank You. You posted some helpful info in the RAVE last year when I first saw this happening. I remember reading process of how the Rover determines misfire accurately down to one cylinder. It seems near impossible that it could but most people think it does it pretty decent.