ok i got a 6.2l 91gmc diesel and it dosent like to start to easy in the morning, even it isnt that cold. after that in the day it fires right up no problem, should i check my glow plugs?? what does a bad one look like compaired to a good one. what kind is good if i have to replace them?? should i do all of them if only a few are bad? like i said before the truck fires right up if it has been running earlier in the day. its my first diesel so im new to all this, thanks

First off, how long is your wait to start light staying on when the engine is cold? Next, take a 12v test light and connect one end to the + battery post, now remove one glow plug feed wire at a time and touch the test light probe to the spade on the glow plug. If the glow plug is good the light should light up. P.S. before testing this way test the probe to a good ground to make sure light works. If light does not light and light is known to be working, replace that glow plug. If more than 3 are burned out, I would replace them all.

Now for glow plug types, Kennedy sells some good fast heat replacements, AC 60g's are also good. Don't waste money on brands that you don't know the specifics about. What you are looking for is a dual core self regulating glow plug that will not swell if it burns out. They should be stamped in tiny letters, 10.5v or 11.5v. Early glow plugs like 9g's were a 6volt plug that would heat very fast and burn out even faster!

ok i will try that, thanks for the info i will let you know the results, you think i should go for the ac 60g's??
thanks

the light stays on for about 5sec about when its cold

5 seconds isn't long enough when it is cold to get enough heat into the combustion chamber and will cause hard start. Until you get it fixed, try cycling the glow plugs 2 or 3 times before turning engine over. I am not sure if your ecm controls glow plug cycle time on a 91 or not. I will try to research.

sorry i checked how long today, its more like 8-10 i guess, im going to pull them and check tomorrow. someone told me beru glowplugs are good?? thanks again

D. Camilleri has given good advice. Do not use the Delco 9 or 11G glow plugs or the Champion glow plugs and do not mix them, especially Delco 60G's. I have been using the Delco 60G glow plugs since they came out and I have never had a problem. I had some of the first three types burn out, but never a mushroom (I was probably very lucky!!!). I have a manual switch for my glow plugs and when the temperature is below 20 F degrees then I leave the plugs on for 30 seconds. If it got below 10 F degrees then I would probably go for a minute, but you can only do this with the Delco 60G's. I have never used the Kennnedy glow plugs so I don't know their qualities.

ok well im going to pull them tomorrow, what do i do if one of them mushrooms?? i wont be able to get it out will i? what should i do if i stumble onto one?

Before you pull them, test them. I have run beru's and they were good, just like 60g's. There are some quick heat glow plugs being advertised on ebay that seem like a good deal. They have a 2 year warranty which I believe was the same that kennedy had, though I don't remember about his for sure.

When a glow plug fails like a 9g, they will sometimes get a little bump portruding and it makes for difficult removal from cylinder head because of the close tolerance of the hole. I have removed stuborn ones by loosening until threads are free and grabbing with vice grips then start engine and let the compression hammer the plug out. If this doesn't work, pull the injectior for the bad glow plug,bring that piston to TDC, grab the tip with mechanical fingers after unthreading, break off outer threaded part, say a couple of prayers and fish out rest of glow plug. If you drop it, and it goes down the precup you get to remove the head.:eek: good luck and hopefully they will all come out easy. P.S. sometimes they fell like they aren't coming but they are only held by carbon.

i was told that testing them with a test light isnt always the best way cause sometime they say you have power and everything, but the glowplug could be heating from the treaded end instead of the other end (the tip) so plling them and giving them power to see what end they light up from is the only real way of knowing

That statement is only partially true. First, when checking glow plugs with a test light, if the test light glows when connected to the spade of the glow plug, the glow plug is at least partially functional. If the light does nothing, the glow plug is burned out. The best case for pulling glow plugs and bench testing them is if they all test OK with the test light but engine still doesn't start well. Then by bench testing and watching the tip it can be determined if the glow plug is just weak. Another thing to check is that you have a solid 12v coming to each glow plug wire when the wait to start light is on. Again this has to be performed one wire at a time.:cool: I always use the test light approach before trying anything else and it usually solves the problem.

Removal will be easier if you use some aluminum anti-seize on the threads before installation.

ok i will do that, i forgot my tester tonight so i will do that tomorrow. i have electric fans on a switch so i think with me having them on might be part of the problem
thanks

D. Cam's right. I use a test lead with alligator clips. I clip one end on the glo-plug terminal, hold the other end and lightly/quickly "scratch" it on the positive post of the nearest battery. If I get a hot, blue flash, the glo-plug is shorted internally. If I get a light, barely visible yellow spark (like a July 4th sparkler makes), the glo-plug has proper resistance. If I get no spark, its open circuit. If they all give that light yellow spark and it still doesn't start, I pull them, heat them and observe where the heat is on the probe. Just a quick check that works for me.

ok guys heres the stuff. i used the test light and had power to each glow plug, and it got power when the glow plugs lite up. i even pulled on glow plug and turned the glow plugs on and it heated up, not red hot but the motor was a little warm so they didnt stay on that long. i also used a volt meter and it is reading 12.6 going into the relay and 10.2 at the glow plugs. i thought it had something to do with the relay and the glow plug light isnt always coming on. i am sure that this is my problem cause the glow plugs look good. there AC's in it right now. do you guys think that the 2.4v i am loosing is enought to cause trouble?? i should replace it before i do any of the plugsright? or do you think it could be something to do with my injectors?? when the glow plug light comes on for the first time it stays on for about 8-10sec then they seem to cycle after the truck is started , its like the come on then turn off like one sec later. it will also do that when i cycle them and dont turn the motor over. do you think that the relay isnt giving enough power to the glow plugs to get them hot enought?? thanks

If you have a voltage drop across the relay, you will have to replace it to get an accurate handle on whats going on with the timing of the glo-plugs. Eight seconds is long enough to properly heat the 9G/11G plugs but not long enough for the 60G's.

Any voltage drop on a circuit is bad. If you are reading the voltage under load (glo-plugs on) and you have a 2.4 volt loss, that's enough to upset the heating of the plugs. Correct the volt drop problem and you may solve the starting problem without replacing the plugs. Let us know.

do you know how much the relays are for a 6.2l?? once again guys thanks you have helped me out lots with everything. :ro)

ok i replaced the relay and it was taking more volts, but still wasted that good at starting in the morning so i put in a set of new plugs and it fired right up after sitting for 2days. didnt need to cycle them or anything. it was about -17 today also. the plugs that were in it were the ac delco 10.5v, are those ones junk? so everything is good now thanks

At -17 you are pushing the envelope. New glow plugs will be a great help because they heat faster. If your old ones said 10.5v at least they weren't 9g's because they say 6v's. Keep your old glow plugs for spares. One day if you get bored, take out one of your new plugs and hook it up to a 12v power source for a predetermined amount of time and then do the same with one of the old ones. You will probably see that the new ones glow bright red faster than the old ones. And that is why I like manual glow plug switches, just hold the button longer:D

i hooked the old ones to a batt. charger, they didnt heat up as fast as the new ones. they were about twice as slow

This scenerio shows us just how important each individual piece of the puzzle really is. If everything is right, it starts. Good deal, glad it worked. You might consider using the block heater when it gets that cold. It will help lessen the load on the electrical system, which is already working hard.

i have one i just wanted to make sure i had it fixed, thanks

cougarjohn,
You mentioned a manual glow plug switch - does this mean you are not using a glow plug timer at all? This is interesting because i have heard that the glow plug timers tend to wear out often, and i would like to not have to rely on it especially while on a road trip or something. I wouldn't mind just having a manual switch if this is possible. But i am not very knowlegeable about all this, just got my first diesel 7 months ago and still learning. Please let me know if i have this correct, if you have a moment. Thanks!
Paul

chech out the resistance, it shoud be at .8 ohms brand new 1 ohm is ok but higher indicate probleme is on the way even if it still working
:)