Ditto. I bought a little bag w/ 5 of the white plastic Schraeder valves from an auto tools specialty shop in Atlanta decades ago. The springs are very weak. I expect you could find such today on ebay or Amazon. No internet then. And also please verify that you are using the proper thick spacer collar on the injector adapter.

Fwiw, I just used my HF diesel compression tester and got accurate readings, it worked great! These Chinese things are luck of the draw it seems..

Used on a 602T, got 400psi across all 5. Had to test through the glow plug holes with the adapters provided. Put some Teflon tape on the threads of the adapter.

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H.F. Diesel Compression Tester
 

You needn't use Teflon tape, there's copper sealing rigs you're supposed to use .

When lost Brake Supply Shops and maybe Plumbing Supply Shops will have them .

Many times my new H.F. tools are broken or not threaded etc. right out of the box, typical Chinese / Brazilian co$t cutting by not having any quality control .

Every H.F. store *except* the Pasadena, Ca. one simply exchanges the broken tool for a good one, the manager in the Pasadena store is an ******* who thinks he's saving the company $ , not realizing I just buy my tools at a different store now .

Any chance his name is "Sheldon"?

I don't know, he's just your basic jerk .

Sorry, joke. "Sheldon" is the persnickety Physics professor at Cal Tech on The Big Bang Theory. Thought he might have 2nd job.

Had the same problem with my hf kit. I bought mine there many years ago. It was a bigger kit than the one they have now. It costed me more too but I forget the number. Anyhow it read 100psi and it hissed at the chrome quick release. I put some o ring lube in there and I got numbers in the low 300s.

Measured through glow plugs.

I never really figured out if that was my real compression. It was disappointing.

My car doesn’t smoke and it starts easily, although it won’t start without glowing.

I’ve always suspected that gauge. I’ll look into replacing it with another 500psi gas gauge.