Alright DF crew...im stumped. see if any of you can help me solve.
Customers car: 2003 corolla type s 4 cyl.

Crank, no start. Engine free spins as if you take the plugs out and crank. No compression across the board. Timing marks all line up. All 4 pistons move with the crank. Setting each piston at tdc than pressurizing cylinder with shop air. Cylinder holds psi. No air coming from radiator, dipstick tube, intake or exhaust.

Cranking compression shows 0 on 2 different testers. Verified testers on shop air.

Wtf!?!?!

 

Sounds like the valves are stuck open. The shop air is enough psi to force them closed, whereas compression from pistons is not. Broken cam? Is cam gear permanent to cam or mounted with slot and key? Check to see if rockers and lifters are operating.

 

Dohc, no lifters or rockers. Cam gears are bolted to cams. Doesnt appear to have any camshaft, chain, or cam gear problems.

Maybe shop air is slamming them shut...hmm. Toyotas have preset "cup" shims between the cam lobe and the valve spring. I did notice they rotated by hand at tdc..wonder if applying shop air would tighten them up, pushing the valve up into the cam lobe....guess the heads coming off

Edit: or!? If slowly applying shop air via ball valve would allow me to hear if air is escaping?

 

Thats a tough one. Does it have that variable valve timing? Either it's going out the valves or by the rings. This must be a fluke anyway, I've been told by many Toyota owners that they never break down.

 

well thats like scooter owners telling you they keep up with street bikes...

Couldnt be slipping past rings or id hear air coming from dipstick tube.

 

Have you watched the cams rotate? Years ago my truck left me on the side of the road far from home. Shop told me no compression, cranking fast, and that my timing chain was in good shape (V8). So I paid a fortune to tow it home, pulled the timing cover off and right off the bat noticed the shaft key had been sheared. New key and it was fixed.

 

Yes both cams rotate and timing marks stay lined up after cranking. I'm leaning torwards valve issues. Customer gave the ok to pull the head so here goes nothing. Lol

 

For the valve clearance check, shouldn't 8 of the buckets rotate at piston #1 TDC and the other 8 at #4 TDC? The buckets that aren't being pushed by the cam lobe and still spin would mean that there is still some valve clearance. If none of the 16 rotate on either TDC then the valve clearance is used up and they're all sticking open which I can't imagine happening.

Since the timing marks all lined up then I'm puzzled. I can't think of anything else right now. All that comes to mind is that the timing belt jumped. Of course, this would most likely mean death to the valves because it's an interference engine, right?

 

Cody, have you pulled the valve cover? In my experience, verifying rocker placement, valve lash (or lack iif, if lifters are hydraulic), etc. Also, if the reason shop air lets the cylinder hold pressure, you would see the valve stems move once applying the air.

If the timing belt jumped off, then the cams would not turn. If you skipped a tooth, or two teeth, then the timing marks would not line up, and there is no way you would see compression with shop air.

 

Btw. Its a timing CHAIN engine so slipping a tooth is near impossible and would yield catastrophic timing gear failure...im stumped. It is an interference engine so most likely my diagnosis to the customer is engine failure. They can keep dumping time and money into diagnosis but a new engine would be cheaper at this point.