I have a '86 GMC Rally STX 1 ton with a 6.2 diesel. Within the last month the vehicle has become increasingly hard to start when cold. Once running and if the engine is warm it seems to start okay. I have read a number of posts here and I can say it doesn't surge at all when running and I even re-bled the injectors thinking I may have had some air in there. I have about 4000 miles on the fuel filter and the air filter is new. I have replaced 5 of the glow plugs but I can not easily get to the front two on the drivers side. I will get the front on the passenger side. When I pulled out the old plugs they were covered with powdery black carbon. since I have changed the plugs it seems now that sometimes even when its warm it takes awhile to start. It seems to be getting plenty of fuel thru the filter. I can start it sometimes on the second or third recycle thru and it will run then die then it takes forever to get it started usually cranking it for 10 seconds then shutting it down then doing the same thing two or three times. When it fires it is alright. Glow plug indicator works fine and I hear it clicking like it should be. Is there a possibility that my fuel pump may be causing the system to drain or that or it could be losing its prime? I don't know as I am stumped here. Checked the intake manifold bolts and that sort of thing and the batteries are two months old and the started turns nicely.
Any help would be appreciated.

First, test all of your glow plugs with a 12v test light. One end of light to Battery +, other end to spade on glow plug. If the bulb lights then the plug is OK. It is important that all 8 are working.

Next, get a short piece of clear 1/4 inch hose. Find the fuel return hose on the top of injection pump(has a 90 degree bend) remove it and replace with the clear hose. Crank engine and watch hose for bubbles. If bubbles are seen in the hose, then you have an air leak that needs to be repaired. The air leak can be as simple as a loose hose clamp on a fuel line. An air leak in the system will allow fuel to drain out of the filter and back into the tank, causing the engine to loose it's prime. Give it a shot.:grd:

I have heard this test method for GP's a few times now, and I have some questions, theories...

When the test light is used, will the glowplug actually be heating?

I was talking with a fellow MV guy (he has a M1028) and we were discussing making an indicator setup that would tell the status of each GP. Basically a series of 8 LED's somehow wired to show that each GP is functional. Any thoughts on a way to do this?

Mangus,

When testing the plugs using the method above the plugs wont start getting hot. The test bulb doesn't pull enough current to do that.

Do you keep the GP wires hooked up? If so, an LED could be wired (just like the test light) to each GP and powered when the key is turned on... (or maybe a test button pushed) hummmmmmmmmmm

You unhook each glow plug wire and then check that plug. You can also use an ohm meter. If the glow plug has failed then your test light will not come on and if using an ohm meter then you will not have any resistance (open circuit).

Yes, it is technically possible to monitor each glow plug, but there is a lot involved and I don't I don't think you would appreciate the cost. And I don't see any great advantage.

More of a curiuosity thing....

I have a 1983 suburbon with a 6.2 diesel. It lost most of its power so I hsd the pump, controller and cellanoid replaced. It has plenty of power now but its hard to start when cold or has not been started for a while.The glo plugs seem to be working fine. I let them cycle two times. It starts right up and dies. It will do this several times. I have learned to hold the fuel pedal down a couple of inches and it will start and run as long as I hold the pedal down.If I let up on it right away it will die. If I hold it down for a couple of minutes it will continue to run. It runs fine on the road and starts fine as long as it is warm. I dont know what to do. Any suggestions would be appreciated.

Thanks in advance

Buddy GRIGSBY

When the engine starts and then dies, it is usually caused by an air leak. Replace the 90 degree bent hose on the top of the injection pump that goes to the fuel return line with a piece of clear tubing. Attemp to start engine. If engine dies, leave key on so that fuel solenoid is energized and check the clear hose. If it is full of bubbles, your system has an air leak. It could be as simple as a hose clamp that isn't tight to a cracked fuel line. These can be a real pain to fix but this test MUST be done first to determine the cause.

When an engine has a air leak, the engine will start and then die. The reason is that the air leak has allowed the fuel in the fuel lines to return to the fuel tank, leaving the lines empty, so when the engine dies, it has essentially lost it's prime and is now air locked. Any leak in a fuel line from the injection pump back to the tank will cause this problem. One way of finding an air leak is to pressurize the fuel tank to about 10 psi and then look at every fitting for leaking fuel. Also, don't rule out the fuel pump and the fuel filter as leak sources.:grd:

I TRIED TO REPLACE THE FUEL LINE ON TOP OF THE FUEL PUMP BUT HAD A REAL PROBLEM. you have to take off the manifold to get to the pump.There are about a dozen different things to take off before you can get to the pump. I had everthing loose except for the last bolt on the left side. I tried everthing but could not get to it so I had to put everthing back. Needless to say I killed about a half day without accomplishing anything. I think you are right about the air leak but could not check it out. I did thghten everthing I could get to but it didn't heip.It will start if I hold the gas pedal down about half way. If not it just starts and dies.

The injection pump sits in front of the manifold, the fuel line I am refering to is right on top of the pump, very easy to get to. I believe you were trying to get at the fuel feed line. You want to install the clear tubing on the fuel return line. Hope this helps.:grd:

Another thing to try the owners manual states to push the accelerator halfway when cold and all the way when really cold i have found that this helps mine. Also i have replaced the starter and have no trouble at all starting. Whereas before it took forever to start when cold because the starter would not quite crank the engine fast enough without giving it more fuel.

D Camilleri Thank you for replying to this post I have a follow up question, How and where do you pressurize the fuel system to 10 psi

grhcucv, I went through your prob about 6 months ago, D Camilleri is right on the money, I had an air leak at the primary filter - the drain cock had a buildup on it and wasn't sealing completely. To eliminate the need to prime the filters after a change and to pressurize my fuel system I installed a frame mount electric fuel pump - works fantastic makes me smile every time I fire it up. You may want to remove mechanical fuel pump to eliminate any chance of later problems.

Rim, Thanks for the reply, yeah the electric pump, but still i would like to pressurize the system to locate the leak. My drain cock on my M1028 is slightly leaking and that fuel filter assembly was superseeded by a unit which is different then mine. I put the "drain cock packing" in silicone and brought it back, so I'll install it this weekend. What electric pump did you use? Model number, where did you get it? Thanks Greg

Some of us are making this harder than it should be. Dave's testlight check is a quick and accurate way to determine if the glo-plug has continuity. The second test checks for air in the system. All a diesel needs to start and run is heat of combustion, intake air and fuel (without air entrained in it). These tests help determine the problem with a minimum of time and effort.

If you use these quick checks and don't find a problem, move on to a more detailed but time-consuming check. Test the glo-plugs with an ammeter (20 amp scale). Each plug should pull 8-12 amps. If that fails, take the plugs out and heat them up across a battery and see if they glow white-orange in 7 -10 seconds. (longer for the 60G's)

[ What electric pump did you use? Model number, where did you get it? Thanks Greg[/quote]

Greg, I picked up an E8090 pump from NAPA for $99.00 cdn, it is listed for use in a 7.3, so delivers all the fuel I need.

I can't say enough about the starting improvement.:)

Good Luck

Ceasefire. they are talking about 2 different tests for the glow plugs. In the first test a volt meter or circut tester is used to check to make sure there is power to the glow plugs. Find a good engine ground for the circut tester or volt meter. Unplug each glow plug lead and check that you have voltage to that lead while the "wait to start" light is on. If you have power to all of the leads go to the next test.

The second test determines the health of the glow plugs. Use an ohm meter, unplug the glow plug lead again and attach the meter to a good engine ground. Then with the other meter lead touch the post on the glow plug. If the glow plug is burned out it will show an open circut, 0.0 ohms. If it shows ohms it needs to be within a certain range. Sorry to say I can't recall what those number are and my book isn't here at this moment. Someone here will know and post them, I'm sure. Mike