What Glow Plug Voltage

[dhartley]

I am seeing only 10.5 volts at the glow plugs,even with the temp sensor disconnected Is this normal or could the controller give reduced voltage without complete failure? the batts are good and i have not checked volts at the controller as my wife has her sub at work right now and i checked the volts this am at5am before she left
thx Dana

[DmaxMaverick]

Welcome to the Forums!

If you are checking your voltage with the GP's connected, it's normal. The current load will show a voltage drop, but it's superficial. If you disconnect the GP's and check the voltage, it should be within .5 volts of battery. Are you having GP or starting issues? If so, which GP's do you have installed, and have you modified the system at all, other than disconnecting the sender? That aside, it would be helpful if you identify the vehicle we are discussing.

[dhartley]

Thx for the reply. the vehicle is a 94 suburban and voltage check was with the lead disconnected I am thinking the contacts in the controller could be burned? as i said i did a quick check at 5 in the morning i can do a better follow up when she gets home. blowing tons of white smoke on cold starts . i just replaced the injectors 180000 miles on them when i did i did a bench test on all the glow plugs they were all good the burb is completley stock except for a 3 inch exhaust. i also did a compression test when i did injectors, a little low 345 to400 but not to bad for 300,000 miles.

[DmaxMaverick]

It could be a relay contact, but much more likely a ground issue. Grounds are a pretty common issue, and can cause all kinds of things to misbehave. Good idea to check again under better conditions. Check the voltage at the relay input and output and compare to actual battery voltage, key on (glow cycle) and key off. Also, check each plug for continuity to ground. You could have some bad plugs.

[dhartley]

I will check grounds I have already checked the glow plugs i had them out when i changed injectors last weekend.

[dhartley]

I have12.5 at relay key off drops to 10.5 key on, 10.5 out of relay ,disconnect the wires to the glow plugs,and i get 12.5 in and out. i cleaned all the connections on the relay, batteries and engine grounds topside,to clean the ones on the frame i will need to remove the downpipe and fender liner. i will see what tomorrow morning brings and see if i need to try that Thx Dana ps this is only a cold start problem so it should rule out air in injectors dirty filter etc. it is not that cold here yet only about -28 f

[bl78ljb]

dhartley,
Where are you located??? It is only in the teens to 30s here in Maine.

[DmaxMaverick]

I have12.5 at relay key off drops to 10.5 key on, 10.5 out of relay ,disconnect the wires to the glow plugs,and i get 12.5 in and out. i cleaned all the connections on the relay, batteries and engine grounds topside,to clean the ones on the frame i will need to remove the downpipe and fender liner. i will see what tomorrow morning brings and see if i need to try that Thx Dana ps this is only a cold start problem so it should rule out air in injectors dirty filter etc. it is not that cold here yet only about -28 f


OK. Stop looking for something wrong. It's absolutely normal, and exactly as I described in the first post. As long as the voltage at the battery doesn't drop that much, it's fine. Less is better, but it's normal. The circuit under load will show less voltage, but the reading is superficial. If it were really dropping to 10.5 volts, it would stay there after you take the load away. Still a good idea to clean up grounds for any reason, at any time.

If you're having smokey, slow starts, look closer at the plug model and glow cycle time. If they're 60G's, you need to extend the glow time when it gets that cold. That -28°? Is that wind chill, or actual? Your truck doesn't care, and won't see wind chill, only actual. Seems a bit too chilly this early in the season, no matter where you could be....Siberia???

[Robyn]

Just a side note.
The 94 has an interesting routing of the power to the trucks systems.
The power to the truck comes off the RH battery via a #6 wire that is crimped into the main battery cable to the starter. The small cable snakes down and then up thye back side of the engine block and into the junction block on the firewall by the A/C evaporator.

The battery cables on these rigs ARE CRAP
The corosion cant be seen unless you cut the cables open.
What happens is the core of the cables gets coroded and this can cause issues. The cables can be repaired with new solder on ends and if the cable is fully soldered then its fine for max draw.
The grounds to the block are also defeicient in this same manner.
Now the charging system connects to the LH battery and then the crossover brings the power to the RH battery.
All these cables can and do go slowly south over time and need replacement.
If you have a poor ground on the LH battery then the charge from the Alt does not work correctly.
My 94 Burb had issues and not until I replaced and or repaired the entire cable set did all the issues resolve.
The 95 and later trucks are wired a but different and the LH battery feeds the truck and is fed by the ALT. But thye poor surface solder/crimped connectors still corode and will hang you out to dry.

If the cables are still factory at 180K they are for sure toast.
If you need reliabilty in cold weather this is a great place to spend some $$$ and a little time.
The routing of a new power feed to the junction box need not follow the old route but instead can be routed a much shorter path to the junction via the inner fender and behind the Coolant recover/holding tank.
Using a slightly larger cable with solid soldered ends and connected directly to the + terminal is a sweet upgrade.

Also installing a FORD starter relay up by the RH battery and then using the starter solenoid feed from the Ignition to run the relay and then run the main starter solenoid with power off the battery though the relay.
This will take a buttload of work off the Ign switch, make the starter solenoid and ultimately the starter too.

Now what you end up with is that main wiring harness voltage on the engine feed will remaina bit higher due to the fact that the starter solenoid is no longer pulling off the small wires of the harness and also the small contacts in the Ign switch.

I did this on 2 94's one that I sold and the one that we still have.
It works sweet and costs very little.
The wiring on the starter can be accessed easily by removing the RH front wheel and the rubber flap over the inner fender.
The large red wire (IIRC) is the feed to the solenoid.

Fixing these areas is $$$$ and time well spent and will improve reliability and overall performance of the electrical system.

The glow controlers can go away and the contacts can burn but I think as Dmax said, what you are seeing is about normal.

If you are having a starting issue I would be checking the glowsticks to be sure they are all glowing bright red all the way to the tip when hooked to a good source of power.

The other issue that will really make things sour is a set of injector nozzles that are low on POP pressure and the spray pattern is a pee stream instead of a nice fine cone of fuel.

Make sure your starter is a whippin that little oil rat over good too, if the cranking speed is down then the whole process is compromised.

If the starter has issues the voltage available to the rest of the sytem can suffer too.

Good luck

Robyn

[dhartley]

Im back Maverick i made a error going from c to f should be+ 28 f or so. Any way the truck started badly smoked and missed at that temp and later in the day at about+40 same thing. the voltage did drop to about 10.5- 10.75ish. Missy thanks for the info about the route the glow plug wireing takes , i traced it and cleaned the connections. i also ran a#8 gage wire [using a fusible link with it]from the driver side battery to the glow plug controller. i now have 11.25 volts at the controller. the weather dropped to-15 c [ dont know what that is f] the truck started much better but still was not what it once was. changed the fuel filter and i have my old truck back. thx to the both of you for taking the time to answer my questions . Dana Ps Missy the truck has 485000 kms on it 265000 of them by us and i did not change the batt cables. I will probably do that shortly .