Hard start/ no start after glow plug resistor bypass mod

[twomorestrokes]

I've never had any issues with my truck or the starting until the glow plug resistor bypass mod yesterday. the truck was starting fine but has 1 bad glow plug on the right bank so I did the modification so I can nurse the other glow plugs along. now the wait light stays on longer and it is on for about 20 seconds before hearing the relay clunk. Than the light goes off just a few seconds later but the engine starts hard after that. This afternoon it almost did not start. After about 6 or 7 attempts it fired. Until then it just cranked but when it fired, it started right up like normal. I'm assuming the relay is now sticking and needs replacement but its odd that it just started happening now. Also, my gen 2 lamp now stays on after starting but goes off after driving down the road about a mile or two then the gauge goes to the top of the green again. Just coincidence or does this sound familiar to anyone?

 

[doghead]

Replace your relay.

Here's one of the threads you missed when you searched before posting this thread. http://www.steelsoldiers.com/showthread.php?91039-Resistor-Bypass-now-won-t-start
or this one, http://www.steelsoldiers.com/showthread.php?100959-glow-plug-resistor-by-pass-mod

 

[Warthog]

Many guys are reporting that the GP relay needs to be replaced when the GP resistor bypass is done. The 12v isn't strong enough to overcome the carbon buildup on the internal contacts of the GP relay.

 

[twomorestrokes]

Thank you very much! New relay tomorrow as that's what it sounded like anyway out in the quiet snow listening to what it was doing. I'm confused also though as it should not have been seeing 24v at the relay before with the resister. Oh well, that's gotta be it. The Gen2 light issue must be unrelated? So far it always starts charging after a few minutes/ miles. I'll post again after the relay replacement tomorrow.

 

[antennaclimber]

Your relay may look like this inside.
Measure the voltage when it's closed on both sides and report back.

 

[alburms311]

Many guys are reporting that the GP relay needs to be replaced when the GP resistor bypass is done. The 12v isn't strong enough to overcome the carbon buildup on the internal contacts of the GP relay.

I will report this as well, and replacing the relay resolved my issue.

 

[scottladdy]

New relay here as well after the bypass. All is well for 6 months now since.

 

[760gamemaster]

Me to same thing replaced relay no problems.

 

[twomorestrokes]

The new ST85 relay worked for me. Thanks again!

 

[MarcusOReallyus]

I'm confused also though as it should not have been seeing 24v at the relay before with the resister.

Yes, you should.

In the stock configuration (24v) when the glow plugs are NOT operating, you will see 24v at the input to the relay. This is AFTER the resistor.

????

But I thought the resistor drops the 24v to 12v????

Yes, it does. WHEN THERE IS A LOAD ON THE CIRCUIT. Not otherwise.

If you measure voltage at the input to the relay while the glow plugs are turned on, you will measure 12v.

Once the glow plugs are turned OFF, the voltage will rise to battery voltage (24 volts).


When there is no current flowing, the voltage will be the same on both sides of a resistor. You only see the difference when there is current flowing in the circuit.