7.3 controller glow time.

[Black dawg]

Any body played with different wire/cable size to the gpc to alter glow time?

On my truck I get a full 20 seconds (this morning at 20 deg) first cold start. Havent checked voltages or voltage drop to controller, but in theory the factory wiring must be tired, causing volt drop at gpc and long glow times. It has been this way a long time with glow plugs lasting as expected.

I would like to add a battery cable from battery to gpc to hopefully shorten glow times, but seems like I remember doing that to one of my trucks and it shortened glow plug life.

 

[The_Josh_Bear]

I added an auxiliary wire once and it didn't change anything for me. Took it off after a year and no difference. How cold was it this morning? 20 seconds is the upper limit for the controller but if very cold not a problem.

 

[Thewespaul]

The feed side of the relay shouldn’t affect glow time, but the output side does. I offer replacement harnesses that will last much longer than the factory design, generally see less cycle time with them and a quicker glow.

 

[Black dawg]

So, less resistance to the plugs = faster warm up = voltage coming back up quicker = shorter on time?

 

[Thewespaul]

Correct, with less resistance in the harness, more energy is reaching the plugs so they heat up quicker. As they heat up resistance drops which the controller reads as the plugs being done cycling. It’s supposed to function so that once warmed up they don’t cycle at all, but resistance in the harness and connectors throws that reading off. I prefer to do away with the rather poor design and go with a manual control but it’s nice not having to have another button/switch/gauge added in the cab.

 

[Black dawg]

Guess I should have measured voltages before I started messing with it. The harness that I had from the controller to the plugs was pretty small wire. I had (about 10 years? ago) used the harness off of a 6.5, because I had converted to a different style plug needing spade connectors, and manual control. After that I went back to zd9s with the factory controller and just put a connector that matched the zd9s on the gm harness. So yesterday I dug up a really nice 7.3 glow plug harness and put it on.....now the plugs are on 21-22 seconds at 20 deg.

I would be fine with that long of a cyle if this truck started on the first try.....but usually doesn't, and the second cycle of the plugs is 15 plus seconds. Just seems like they are cycling too long to me. Another 7.3 truck here in the parking lot (same glow setup, and new berus yesterday) glows about 15 seconds at the same temp, and the second cycle is well under 10.

Going to check voltages/drops, if it all checks out I have a new controller to try on it.

 

[Thewespaul]

Thats odd, check your voltage drop and go from there, if nothing seems out of place maybe try swapping the controllers?

 

[Black dawg]

So, had 2 full volts of voltage drop from battery to controller. Added small cable, now almost no volt drop and much shorter cycle. Will know in the morning how much shorter.

Tested against the other truck, with all factory wiring it had less than a 1/2v drop from battery to controller. Neither trucks show more than a couple 10ths through the relay.

It is funny, on my truck repaired the connector where the glow plug feed wires usually melt, and on the other truck the connector looks partially melted. Maybe I did a crappy solder job......was almost 20 years ago.

Maybe this old **** will start better.....doubt it. Never has been an outstanding starter. I remember this truck with low miles (original owner lived near me) smoking out the neighborhood when he would finally get it started.

 

[Thewespaul]

Interesting, well a good starter makes a hell of a difference.

 

[franklin2]

Correct, with less resistance in the harness, more energy is reaching the plugs so they heat up quicker. As they heat up resistance drops which the controller reads as the plugs being done cycling. It’s supposed to function so that once warmed up they don’t cycle at all, but resistance in the harness and connectors throws that reading off. I prefer to do away with the rather poor design and go with a manual control but it’s nice not having to have another button/switch/gauge added in the cab.

As the glowplugs heat up, their resistance rises. The only way I know this, is less current through the z-bar makes the glowplug controller glow time shorter.

Less current must be because the glowplugs resistance is rising up. Verification for this is when a glowplug goes bad, that is that much less current flowing through the z-bar, and it short cycles.

 

[Black dawg]

Cold start at 20 degrees now gives me 15 second initial glow time, and if it doesn't start on the first try, gets about 5 seconds on the second cyle. Seems about right to me.

As a side note. During this messing around I had 1 plug removed but grounded so that I could see how hot it was getting before and after fixing the voltage drop issue. The controller would shut them off right as the glow would just reach the seat of the glow plug, before and after fixing the voltage issue.