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94 Chevy K2500 6.5 Multiple Codes Present

Okay. Here's a pic of how mine is. Not getting power to the negative side of the relay. No power to ECT either.received_736455160108864.jpeg
 
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Not trying to insult you but I'm going to try and explain how the relay and system operate. So to start with the big red wire is the power wire and it needs to be big as the glow plugs draw around 155amps. The stud right next to it separated by the little plastic wall is the wire with the fusible links which goes to the glow plugs. The small wires in the plug in terminal are the control wires for the relay. The pink wire should be hot when the key is on, the black wire is a ground wire, the yellow wire is grounded by the PCM to activate the glow plug relay. When the relay gets activated it makes the loud click you hear and then the small wires, with the fusible links on them, will be hot.
 
Okay that makes sense now. Was referring to the two gray fusible link wires as the negative side. I'm not getting power to my glowplug fuse or my crank fuse. All my other fuses have power. Tried putting in new fuses and still nothing. Not sure how old the glowplug relay is. Wish I knew more of what the previous owner did to this truck. Whenever I stick my test light on the fusible link wires even with key on, it doesnt light up. I did also ground the PMD harness to the injector pump last night where it's supposed to be. Just went and started the ol girl up. Its 32 degrees outside, glowplug light came on for about 10 seconds and then went off, then a few seconds later briefly flashed again then went off. It dodnt cold start as bad as it normally does and there was little to no white smoke. Check engine light was still on though. It comes on every cold start and then goes away after a few minutes once the truck is warmed up.
 
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When the GP light is on this relay is working. You will only have +12v for 10 seconds on the blue wires. The blue wires are fusible links and can break from age. Put your test light on a glow plug connector wire. Run the test light on the wiper so you can see it from the driver seat. Key on, GP light comes on: test light should be on. Test each "bank" as they are split driver and passenger side. Each GP has a fusible link and some may be bad as well.

The real PIA here is if the relay only works some of the time due to internal arching aka wear out.

Listen for the relay to click: it's unmistakable and loud. If the GP light doesn't come on every time it clicks (rather "bangs" on) you have a problem. Warm or hot engines may not call for GP use on start and this is where the temp sensor wiring may be messing you up to smoke cold.

gp_pic.jpeg
 
Okay. Yeah I put a test light in the glowplugs with the connectors still connected, have not tried them unplugged yet. The light did not come on at all when I did that though.
 
Okay. Water pump took a crap on me over the weekend. Or at least, it was the cause of the pissing coolant. Replaced that, and then it was leaking out the hose connecting the water pump to crossover. Replaced that, now leaking at heater hose connector and passenger side thermostat crossover. Never ending! I did also fix the engine ground at the back of the block and it didn't change any of my issues I've been having. If anything it made it worse. Lots more smoke now on startup and rough idle at startup for several seconds while smoking and SES light on entire time. I replaced the water pump with an OEM Napa unit. Before any of y'all say I should've done the HO unit, I have reasons as to why I didn't.
 
YUP. what He said /\. LOL
I went with the NAPA coolant pump on My truck, mainly because it is My daily driver and I have no other transportation when it is broke down. I need it and I need it NOW. LOLOLOL
 
Yeah it was affordable and convenient at the time. I filled her up with green coolant too. She's still smoking white on startup and still getting glowplug relay fault code and injection pulse width timing long code. Heard a slight buzzing coming from injection pump at idle while inspecting something else. Fixed the engine ground on passenger side at back of block and grounded PMD to injector pump. Should I try replacing glowplug relay and see what happens? The connector to the glowplug relay seems to not want to stay on well either but just slightly. Would I be able to replace that and the fusible links easily?
 
Must be a slip on terminal end on the GP relay, I do not remember how things gets connected to the relay, been a quit a while since I had to mess with one. If it is a slide on terminal it might be able to be tightened up by squeezing in the appropriate positions with a set of pliers. IE, look inside the plastic protector and squeeze on the terminal where the barrel or female blade connector would squeeze on the connector when plugging it back onto the relay.
Okay, I think its time for a rest. LOLOLOL
 
Be careful You dont take them down too far, sometimes they can be a bear to get spread enough to get them to fit back on.
And, it was not uncommon to have to change a GP relay on the 6.5 trucks that the state owned, I think I had changed out three relays, there were five mechanics in the shop. I dont know how many the others had to change out.
 
Oh okay so they do go bad often then? Were they pulling a glowplug relay code everytime? Mine is pulling a GPS relay fault code but in getting power to it and it looks fine on the outside. Maybe bad parts on the inside?
 
YUP, that relay operates much like a starter solenoid with heavy duty contacts on the inside that moves the large amount of electricity.
A relay is a device that takes a small amount of voltage to engage a set of contacts that enables it to move large amounts of amps without burning up ignition switches and having the ECM try to control those large amounts of voltage.
IIRC, I think that the GP relays on the units I worked on had totally failed or were running on a real short cycle so that the engines would not start. I dont remember there being a code posted in the ECM, too much bridge under the water between then and now. LOL
 
Yeah mine has thrown the code 29 since I bought it. The relay that's on there currently seems to be of decent quality, says Made In USA. Would a Standard Motor Products relay be okay to put in there? Could that also be the cause for it wanting to smoke and cold start even when it's not very cold outside?
 
The Standard Motors products that I have used seemed to be of good quality.
I do believe in using orifinal equipment and components as much as possible.
Yes, a shortened GP time can cause hard cold start issues and excessive smoke.
 
Okay I'd be that's my issue then. Starting to get longer crank times and more smoke. So the relay can still be bad even if it clicks? It's not super loud though but it does make a click.
 
Put a volt meter on the post that has all the glow plug wires attached to it, and use the battery negative.

If it powers up ( same voltage as battery has) when you cycle the key on it is ok.
If not, make sure the ground to it is good by removing and cleaning contacting points.
If still wont work, then yes replace it.

If it does power up- suspect bad glowplugs first (use AC Delco 60G) and glowplug wires second. It’s a good idea to remove and clean wire connections before condemning wires.
Remember that the wires are not normal electrical wires, they are actually fuseable link wire. Better aftermarket one is available.
 
Where is the ground for the glowplug relay? If it's the ground at the back of the intake on the passenger side, I've already cleaned and fixed it.
 
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