Former VWDieselParts.com Forum

1.6 diesel jetta its a 91 wont start unless engine is plugged in and warm or still warm from driving runs good once started the glowplugs are new and tested Ω with multimeter there is also voltage before and after glowplug fuse how do i troubleshoot problem from here

Just to be sure check for voltage at each glow plug. It's always possible to have a weak, corroded, or loose connection at a crimp connector. It's a long shot but a good thing to eliminate. Also make sure the block has a good ground connection to the battery. At 40+ amps current draw a bad connection becomes a huge voltage loss.

Low compression can behave the same... a compression test will tell a lot.

As noted above, all GPs working together will initially draw ~ 48A, then decrease when heating. If you initially see a fraction of 48V, one or more GPs may be bad.