'76 300D won't start

Indicator lamp stays on. 10.5vdc at #5 glow plug. Wondering what steps to take next.

Thanks!
Nicole

Forums

Chassis Model Number

W115

More information needed

What are your voltage readings at the other glow plugs? Do you still have the original style series glow plugs?
Any evidence any of the glow plugs or resistance wires are getting hot?

Sorry to take so long, Kent.

Sorry to take so long, Kent. Had to get the car towed out of the employee parking garage. Amazing how quickly one can test glow plugs in proper light!

Series glow plugs. #5 reads 11.5, #4 reads a few hairs less than that, and #3, #2, and #1 read 0. I'm guessing the resistance wire between #4 and #3 is shot? Glow plugs only 6 months old.

Number three glow plug may be burned out or the resistance wire shorted against the plug. I would highly recommend you upgrade to the fast glow plugs that we offer on our website. When you install parallel plugs and one burns out your engine will still start!

Thanks - I bought the

Thanks - I bought the parallel plugs off the site and plan to do the upgrade tonight. It just seems like a waste to replace 5 glow plugs that are barely 6 months old!

Caution

Be sure to follow the instructions very carefully when installing these new plugs. You do NOT want to ground the front plug (like the originals) or you will burn out all your new glow plugs! We have had a couple of customers give there plugs to a mechanic to install and they failed to read the instructions.... Bad!

Back to original problem

Don't worry, I installed them myself, and did NOT ground the front plug.

My car started up, but I'm back to the original problem before the series system failed - hard start, indicator lamp does not come on.

Suggestions?

Troubleshooting

Be sure to follow the complete testing sequence as outline in my Pre-glow Systems troubleshooting manual. You could have a bad relay, loose wiring, or light burned out. Use the proper test equipment to ascertain all five glow plugs are heating up.

Don't forget hard starting is a function of engine compression and proper fuel delivery as well as a proper functioning pre-glow system. Have you adjusted your valves, checked compression, inspected fuel injectors, etc.

Pre-glow relay issue

Your pre-glow troubleshooting manual has been a lifesaver!

I suspect the wiring to the pre-glow relay is shot. It was so stiff that I could barely maneuver it when upgrading the glow plugs, and all the manhandling probably did it in.

Finally got the panel off to check the relay (had to drill out a screw) and saw that it was upgraded at some point. Couldn't see any identifying markings, but I think there were 12 pins. Did lots of online searching but can't identify this relay. When did this 12-pin style come into play?