Glow plug problem!

[Animal]

I have a glow problem when it gets cold out works fine hot, replaced the controller & ignition switch no help, any ideas.

Thanks

[libtec]

Move closer to Fairbanks, get away from Delta. Just kidding.. Seriously. It sounds like you are facing the same problem I have been working on on my rig. If your 90 Suburban is the diesel you are having trouble with then maybe I can help, I have a 90 6.2 1/2 ton with around 130K on it. How familiar are you with diesels? I'm new to them up to six weeks ago and I have had to do a crash course in self teaching to get mine going. I just bought my rig in the early fall with a starting problem. Was your glow controller bad? what was it doing to make you want to replace it? Mine cycled just fine for five seconds then it would chatter in the controller, it worked but I replaced it anyhow. Are all your glow plugs operating? did you pull them out and check each one across the battery terminals? have you checked each glow terminal with a meter to make sure the plugs are getting power? You can pull each plug, leave its lead hooked up, ground it to the frame using a test lead and actually check operation using the key and glow system. Is the starter cranking the motor fast enough? I had to replace mine after the batteries, alternator and glow plug controller simpply because my cranking rpm was too low to build heat in the cylinders. What is the cold PSI cylinder pressure of the motor? 400 is great, 300 useable but not great, 200 marginal but only good in warm temps and for basic transportaion. My father in-law nursed his 82 on for a couple of years on 250 PSI in all 8, but cold weather starts were only possible after plugging in for a while and warming the block up. You say the warm weather starts were good but cold is rougher? Even when the 82 had good pressure, at a very younger age, plugging in even at 20 above was still needed for an "easy" start. I have noticed mine being very stuborn in the cooler temps our area has been seeing in the last two weeks, I'm running a range of 400 on the front two, 380ish on the middle four and 320ish on the rear two. To bad one of the past owners forgot to keep up on the oil changes. Having two well matched, high amp batteries is a must. Like I say, I'm still figuring out my truck. I still want to check my fuel system for air leaks and anything else I can do as I learn more. Like I say I bought it not long ago and current situations as they are have left me very little time to learn, trouble shoot and fix a truck that I need to rely on for the winter. Write back with more info, maybe I can help some. If not watch friday's paper, I'm selling my 78 blazer. Good luck! Watch out for those Deltoids..

[smcghan]

An easier way to check the glow plugs is with a simple 12 volt test light. Disconect the wire on the plug, put the alligator clip on the pos. post and touch the blade on the plug. If it lights up the plug is good. No light it's bad. The timer duration should depend on how cold it is outside. In the 40's here I get obout 8-10 sec. When it gets to 10-20 its usually 12-15. I hope you both get the start problems fixed before the cold. Steven

[Animal]

The plugs are fine, the controller isn't energizing, it started this the end of last winter so I purchased a new controller to install this fall. The glow system worked fine all summer until the temp got down to 30, now it's not energizing again. I replaced the controller and no help, installed a new ignition switch and no help. If it is around 30 I can bump the starter two or three times and the controller will engage but if it's colder than 25 it will not. Starter is good, plugs are good, and if I use a jumper to heat the plugs it starts.

Is there any other relays or connections that it may be?


Thanks

[libtec]

The Haynesdiesel engine repair manual has a basic diagram of the glow system of an 85-93 type 6.2-6.5 motor. There is a "glow plug inhiobit temp switch" that feeds into the "c" terminal of the five pin connector that plugs into the glow contoller. The inhibit switch allows a voltage to the center pin (pin c) when the motor is cold that tells the controller to turn the plugs on. In other words, 12 volts at the center pin with a cold motor is a good thing. If there isn't twelve volts then the contoller isn't going to turn on. This is what the book says and it is something I've seen when troubleshooting my truck. There is also a motor starter wire on pin "b" (the wire furthest from the ground). This wire ties into the the starter solenoid and it sends a signal to the controller telling it when the starter is spinning and to send power to the plugs. This might explain why yours works when you bump the starter. The five pin connector has four wires to it one space on the end should be not used, the opposite end is the ground. So imagine this order of pins and what is hooked into them. 1- ground (one end of the five) 2- ignition switch, 3- glow plug inhibit switch, 4- engine starter input, 5- not used. I hope this helps. Go to Napa and get the Haynes diesel engine book, it has some usefull info. The digram for the glow system is on page 2-74 and the theory info is on the next page (system 4). Unfortunantly the book concentrates a bunch on the 6.5 and also has half it's pages covering ford diesels, but it's still a good reference to get ideas on where to start looking for problems. Good luck, let us know how it's going.

[libtec]

Sorry about all the grammar errors. I've been reading blue prints all day and my mind went numb about 6 hours ago. Nothing like having to redesign something the engineer says is perfect... Good luck!

[Animal]

libtec,

Thanks for the help. Do you know where the inhibit switch is located in the engine bay?

Thanks

[diesel65]

On the 90 it should be on the thermostat housing crossover pipe, on the passneger side of the truck.
If not then look at the back of the engine on the passenger side, screwed into the water block off plate for the cylinder head.
It will be a two wire connector.

[yeti]

Just learning this myself. Would this make it start hard? My truck is an 82 and early morning or after sitting for several hours my truck will act like it is out of fuel. After cranking for about 20-30 seconds it will start and will run rough for about 10 seconds.

[libtec]

Hi again! The only temp switch I have found on my 90 is on the passenger side head towards the back. It has a green wire coming off it (forgot the color of the other wire) that runs into the group of wires over the valve cover on the left side. I'm guessing it splits into other wires inside the harness where I can't see it because the switch controls the IP cold advance and the high idle solenoid, I don't see why they wouldn't use it as a temp sensor for the control module as well. Anyhow, it is easy to find and see if the wires are hooked up. You could check if it is good using an Ohm meter across the terminals when the motor is cold to see if the switch is shut, it's a normally closed unit. I haven't found a wiring diagram for the motor yet, another reason I'm sort of disappointed in the Haynes manual, or else I'd be more confident in my advice. Is the motor starting okay when it's plugged in? When my father in law was helping me get my rig running this fall (after sitting for two years) we got it to start with the glow plug leads disconnected (compression only). Not like this helps but I was sort of amazed because I never new the heat came from compression, I always thought the glow plug stayed glowing from the combustion and continued igniting the next charge. Ya learn somthing new every day. Write back when you know more. good luck!

[Jgreemo]

Boy you guys started this thread in the nick of time. My rig didn't have any glow plug operation this morning. Took a good thirty seconds of cranking/pausing to get it going.

I did notice that when the glow plugs come on, it starts right away. If you drive it for a bit, warm it up, then let it sit for a few hours, it would be hard starting with no glow plug activation. I remember them coming on before even if the engine was a bit warm (~100*). Now for the past few weeks when starting first thing, the glow plugs were chattering on/off before coming on steady, or there would be a long pause after the key is turned before they would light up.
Anyways, I replaced the glow plug controller as of June this year and it was working great until recently. The old one was leaking and had several of the little internal heaters rusted through. I will check out the inhibit switch to see if that might be the culprit, but any other ideas would be appreciated. Keep up the good work guys!

Best regards,
Jon

[cschneider]

To reiterate my comments from Jon's question, there is no inhibit switch on the 85+ systems. The actual wiring remained until about '86 or early '87 but the switch didn't actually do anything if it was on the truck. The glow contoller has an internal temp sensor that performs relatively the same function as the temp inhibit switch did on the earlier system. Take everything you read in the Haynes manual with a grain of salt, these trucks are complicated and the model differences are significant especially in this area. The factory shop manuals are the only resources really worth having besides this page.

[Jgreemo]

Hi guys, I just checked out my GP system and it's looking like a bad relay. I used a meter to check for a signal at the relay from the controller, that being the small red wire. With ingition off, no voltage present. There is a constant 12 volts to the relay from the battery. With the ignition on, there is 12 volts to the relay, but the relay does not close, so it seems the new controller is working, but the relay is shot.

Thanks for the reply csschneider, but just curious, why the inhibit switch on these models if it's just an artifact now? I have one and it's connected to something (two green wires) and the meter is showing closed when cold. Does this work with the cold advance switch?

Napa is asking $88 for the relay and I just want to be sure before dropping the dough.

best regards,
jon

[cschneider]

The 85's, like mine, are kind of problematic. There may be a working switch in there but it is does not really perform a function. Why don't you try jumpering around it and see what happens? I had this same problem when I did a injection pump and injector rebuild on my truck and I did a lot of research on these systems because the shop I took it to really had no idea. They cut out the switch as I remember and couldn't figure out why it wouldn't fire hot. That's when I found some block diagrams of the controllers and saw the internal temp sensor. Like clockwork when the temp would go below 115 it would fire right up but anything above that and no glow. My problem actually ended up being a compression problem and I replaced the engine but I learned quite a bit about these systems from the experience.

[Jgreemo]

Well, I checked it again and the relay closed. With the relay closed, I disconnected/reconnected the inhibit switch and the system turned off/on. So it looks like the inhibit switch does pass a voltage to the controller. I haven't driven the truck at all today, so I believe the relay just decided to work (or since my girlfriend was turning the key, it decided to work for her). As far as I can see, it's original and those high current switches tend to go bad over time, so i'll just replace it.

I wonder if the inhibit switch is just a touch of overkill to completely shut down the system when it's warm.

Thanks again guys,
Jon

[cschneider]

The switches do work but they don't serve a real purpose. Overkill is right but they do it at the expense of system reliability. My choice and what seems to be the consensus is to eliminate these from the wiring and let the controller do the job it's supposed to.