1984 Chev one ton military pickup truck w 6.2 diesel engine

We have this truck which had a badly leaking fuel tank. We replaced the
tank and have been able to get fuel up to the filter but we are not certain if it is getting any further. We opened one of the injector
lines while the engine was cranking and did not get any air or fuel out
of it. I was told that we should open all the lines to bleed the system
of air. How important is it to do this? Will the air eventually be pushed out intio the cylinders if you don't? And when bleeding, do you do this one line at a time or all together? We are hesitant to try to open a number of these lines because they are so badly rusted I'm afraid we may break them off. Is there any other way to do this, perhaps by pulling the glow plugs? Will that bleed the air out of the lines? Also could someone please tell me something about how this injector pump works, and how to confirm if it is working properly independant of wether or not it will start the engine? I understand that it is something like a distributor which runs off the cam but instead of distributing spark it distributes fuel? I think I have alot of blow by because the oil gets very dirty and thin
very fast. I also think the glow plug controller is operating off the breaker system which is a backup because of voltage readings from last fall told me that it wasnt working the way it should but still worked off the backup. The truck wont fire up. I have pulled the glow plugs and I dont know if a problem with the fuel not geting to the cyclinders
or compression? Maybe the glow plugs are not working enough to heat it up. Maybe the batteries are not strong enough to turn the engine fast enough because it doesnt seem to crank very fast at all even with 3 batteries fully charged and the block heater plugged in for hours it still did not crank fast. Does it need to crank fast to start? Thanks in advance. Lenny
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Greetings,
You seem to have quite a few questions concerning your truck. My first suggestion is to go to www.thedieselpage.com and dig around there as they are a great source of info for GM light duty diesels both old and new.
To answer a few items, one of the most problematic issues with older diesels is air in the injector lines. Newer models have a primer pump that lets you evacuate the air from the lines, but older ones needed to be done manually one line at a time (it will not prime itself). If you have air trapped in the lines, it will compress but not be able to open the injector so you won't get any fuel to the cylinder. Pulling the glow plugs will not prime your system. You should also have replaced the fuel filter when you replaced the tank, and bled off the water in the fuel/water seperator before trying to start it as a clog in either one of these will also starve your motor of fuel. You will need either an owner's manual or a service manual to tell you how to do this on a truck over 20 years old.
On this motor you will have an all-mechanical fuel injection pump, probably the DB2 but I'm not quite positive. Along with a properly functioning FI pump, you will also have to check what is known as the lift pump (aka transfer pump) that moves fuel from the tank to the FI pump. The FI pump by itself cannot draw fuel from the tank and through the filter, hence the need for a lift pump. The lift pump is easy to test (open up a downstream connection, turn on the key and see if it pushes out fuel), but I don't know the procedure for testing the FI pump itself.
There is no "back up system" to power the glow plugs or controller. They have a single power source and either work or they don't. The controller was a notorious item on the 6.2L diesel so it's quite possible that you need a new one, but you will have to test both the controller and each plug to verify. Sorry, but I'm not privy to the procedures.
Slow cranking speed is an indicator of a weak starter. Diesel starters need to generate a lot of torque because the compression ratio in the motor is so high. Pull and test the starter, but don't be surprised if you need a new one - but don't just use one from a gas motor. It won't be able to turn over the diesel.
On an older diesel like what you have your oil will probably get black after one lap around the block after you change it. I had a similar problem with my old 6.5L turbo diesel, but was able to help alleviate the problem by using a can of Restore engine treatment with every oil change (3000 mile intervals). It took several changes for me to finally see the difference in the oil, but it was working and the 6.5 had a compression ratio of around 21:1 so blow-by was a factor.
Good luck - Jonathan

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Jonathan did a good job on the info. I'll just throw in a few things I learned about my 82 6.2 diesel which may help you.
I replaced headgaskets on my truck several times which requires removing all the fuel lines and ran the truck out of fuel once. Each time the engine would fire up without needing to bleed the injectors. This surprised me due to my expectation of it being necessary to do so because of my experience with HD truck and construction equipment diesels. So it may not be necessary to bleed the injectors if you are lucky.
I rebuilt the starter every fall or it would fail in the winter (northern Ontario, Canada). If you are in a cold area these engines need a block heater to start when its very cold. These starters are longer and heavier than a standard gm starter. Make sure the bracket on the non drive end that supports the end of the starter to the block is in place or eventually you will crack the starter drive housing which is aluminum.
IIRC the glow plug controller cycled the glow plugs on for 9 seconds for the first shot then 3 seconds on after that. I don't remember the length of the off cycles. Don't bypass the controller with a switch, or the glow plugs burn out if left on too long. You can test the glow plugs with an ohmmeter.
Good luck with your truck.
Scott
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I have been learning a great deal from everyone. I really appreciate all the responses I've gotten to my long winded questions. I've been trying to understand as much about this system as I can so that we may successfully (hopefully) troubleshoot it, and have a working plow truck this Winter. I have been likening this injector pump which apparently is cam operated to a distributor that distributes fuel to each cylinder at, (and i'm guessing here, the bottom of the compression stroke?). Is this a fair analogy? Also when I turn the key on, if my wait light is coming on for the 9 seconds and I have 12V present at the plugs during that time then I'm assuming that the controller is working ok then? My son had added the part in the original post that he felt the plug circuit was working off the breaker but I was not sure what he meant by that. If it was would it just heat the plugs until the overload popped the breaker? If so how long would it allow the plugs to run? I guess what I'm getting at here is that I would want to be certain that the controller is in fact working. How would I determine that the controller is knocking off the plug power and that it isn't being knocked off by the circuit breaker tripping instead? Thanks, Lenny.
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Greetings,
Here is the basic misconception of diesel injection timing - the fuel is not injected into the cylinder at the bottom of the compression stroke then compressed with the air on the upstroke like in a gas motor. In truth, the air (and air only) in the cylinder is compressed on the upstroke and then the fuel is injected into the cylinder which ignites immediately upon leaving the injector nozzle and starts the power stroke. When fuel is added to the cylinder is the chief difference between a gas motor and a diesel motor (yes I know there are other differences, so please don't anyone belabor this point!). If fuel were mixed with the air then compressed, you wouldn't need injectors or FI pumps that could generate 15-30,000+ psi.
If you have your FI pump timing set wrong, you will never get your motor to run.
Just because you have 12v to the glow plugs doesn't mean the plugs are functioning. You need to remove each plug and test with an ohmeter. If the controller is giving power to plugs for 9 seconds on cold start then the controller appears to be functioning properly. As the motor warms up, if you need to restart then the controller sends power to the plugs for 3-6 seconds on repeated start attempts. When the controller shuts off power to the plugs, you should hear/feel the relay open because the controller only controls the relay and it's the relay that acutally sends power to the plugs. This is why you can eliminate the controller completely and replace it with a manual switch if you need to (NOT recommended - too easy to burn up your glow plugs). From what you describe, it sounds like the controller is working OK but you need to check the glow plugs. Hey, if they are the originals I'd suggest springing for replacements - you got your money's worth out of them after 21+ years!
Cheers - Jonathan

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Your analogy is pretty good. The injection pump is similar to a distributor but instead of distributing spark to each cylinder it distributes a shot of fuel near TDC of the compression stroke for each cylinder. It also greatly increases the pressure of the fuel which on the 6.2 is supplied from a lift pump on the side of the block.
I am not sure what you mean by "breaker". AFAIK there is no CB only fuses protecting this vehicle.
You should hear a clicking noise coming from the controller which switches the 12v current on and off to the glo plugs. After the initial turn on, approximately 9 secs on, then off for a few secs then on and off approx 3 secs each cycle and so on. If this is happening your controller should be OK.
Scott
On 17 Nov 2005 04:49:18 -0800, snipped-for-privacy@yahoo.com wrote:

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Just a few observations I've made with my 1983 6.2 diesel:
I have not had Scott's luck with not having to bleed the fuel lines. If I run out of fuel, my truck absolutely requires bleeding. So it would seem that YMMV.
When my starter was beginning to fail, the first symptom was that the cranking became slower despite having a good charge in the batteries. So I would suggest you check your starter.
The previous owner of my Suburban replaced the glow plug controller with a manual switch, and sure enough the plugs weren't lasting more than 6 months that way. So try to save your controller. In my case, I found it cheaper to switch to Toyota glow plugs, which have taken the abuse without any problems for two years now. (I don't care for Toyota, and I don't like bastardizing my engine. But their glow plugs do indeed last longer than GM's, at least in my engine.)
You might also want to take a look at your injectors. When I got mine, it still had the original 20 year old injectors. They worked, but were due for replacement.
Breaker? I'm not familiar with the military version, but as far as I know there should be fuses only.
Once you get it fixed, I hope you find this motor to be as reliable and almost indestructable as I have. It is worth fixing.
--
Warren Post
Santa Rosa de Copn, Honduras
  Click to see the full signature.
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We worked on the truck over the weekend. I found that the last owner of the truck, (The state of New hampshire) replaced all the glow plug wire terminals with poorly crimped on ones. Most of these were badly rotted and loose. We replaced four glow plugs and I soldered new terminals to those wires. The plugs on the other side of the engine didn't look as bad as the ones I replaced so we left them for the time being. One battery wire was burned and loose in its connector. We cut off the connector. tinned the battery wire with good solder and installed a replacement connector. One glow plug though, the one closest to the firewall on the passenger side had a broken terminal and was so badly rusted that we could not get a wrench on it so we had to forgoe replacing it for the time being. We also replaced the batteries with two Optima dry cells which have a CCC of 1000A. and without bleeding the lines I wasn't expecting much. I put a voltmeter on the batteries and read 12.6V. We turned on the key and that dropped to 11.5V indicating that the glow plugs were on. The wait light went out after about 10 seconds but the voltmeter stayed at 11.5 V. This was puzzling but we cranked the engine and noted that the battery voltage dropped to 10.2V, (a far cry from the 8.4 V the other batteries read while cranking), and although cranking seemed slow, lo and behold the truck started! It sputtered a bit at first but soon began to run very well. After about almost a minute there was a loud "clunk" sort of sound the the battery voltage came up to about 12.2V indicating that perhaps the glow plug circuit was off. I will put a meter right on the plugs next time to confirm this but there seems to be something not right with that whole scenario. It would seem that the excessive battery load should have dropped after the glow plug timing period of nine seconds shouldn't it? The other more obvious problem is that at 12.2V running voltage the batteries do not seem to be charging. I'll have to look into that too. This truck was apparently modified from 24V I'm told. The alternator has a bat terminal a single small guage wire connected to a single terminal; and a two wire connector also. Does this alternator sound like a common one? Does anyone know where I might find a schematic diagram of the charging circuit used with this? I'm an electronics technician so I'm not too concerned with troubleshooting electrical problems if I can find suitable documentation. There is however one other issue ( besides the brake line that popped when we finally moved the truck). There is engine oil slowly leaking out from an area around the upper rear passenger side.of the engine. We thought that it was one of the engine oil cooler lines at first. I got underneath and you can see the two enginge oil cooler lines and they do not have fresh oil on them but its crowded up in there so its hard to tell. It does not seem to be one of the lines. It seems to be coming from the top left side of the engine. I'm wondering if perhaps from sitting for 7 months could it be that the very back area of a valve cover gasket just dried up? What else up in that area would ooze oil out and down that back left side of the engine and drip on the exhaust pipe? I can't imagine that it could be a cracked block but if it is a valve cover gasket it looks very difficult to get at. I wonder if running the truck up to operating temperature may soften up the gasket, that is if this is whats happening and somewhat seal this leak up. We never had a leak there.before. Any further thoughts on this saga especially the leak would be most sincerely appreciated. Lenny Stein.
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The 12.2v running voltage is too low, the batteries are not being charged. You should have about 14.5v when the engine runs.
The truck when built had the two batteries in parallel, never heard of one with the batteries in series for 24v. Transport trucks use 24v (24v at start, switch to 12v when running) but they use huge batteries. The idea of the dual batteries on the light duty trucks is to supply enough amps without using a single battery of sufficient capacity which would take up a lot of room under the hood.
Is your engine oil leak coming from high up on the block, if so it is most likely the valve cover gasket. If not it could be the rear seal.
Sounds like you are making progress
Scott
On 21 Nov 2005 13:27:03 -0800, snipped-for-privacy@yahoo.com wrote:

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Hey, congratualtions on getting the truck started! Now replace your alternator - it's dead as a rock. If you remove it and take it to a reputable auto parts place, they should be able to match up the numbers on the casing and get you an exact duplicate.
If you are looking for schematics, you should still be able to get a Chilton's or Haynes manual for this truck. I know many military vehicles were 24v, but you will have to verify this as I don't recall if any of the regular civilian trucks that the military used (like your pick-up) used 24v. I am under the (possibly mistaken) impression that they were kept 12v. Your truck did have two batteries originally, but in parallel for 12v and a lot of CCA but not in series for 24v. They still used a certain amount of electronics back in '84 that would make converting your truck from military 24v to civilian 12v economically unwise, so I suspect it actually was 12v originally.
If you're truck hasn't been running for 7 months, dump a dose of diesel fuel treatment into the tank even though you replaced the tank anyway. Your oil leak does sound like a valve cover gasket, which under normal circumstances wouldn't be too much of a problem but on a lot of these light duty diesels you have to remove all of the high pressure fuel lines to the injectors to remove the valve cover. Again, if it sat for 7 months then I would expect leaky gaskets and seals.
The clunk you hear after a minute of running is a mystery. It should not be the glow plugs or the contoller for them because 1) it doesn't clunk, and 2) a full minute of power to the glow plugs will most likely burn them out. Keep a meter on the batteries and after the motor starts pull the relay for the glow plugs before you hear the clunk and see if the voltage comes up. If it does, then replace the controller (which are notorious on these motors anyway). If the voltage doesn't come up then it's something else. I'm suspecting a partially sticky solenoid on the starter or something of that order, or maybe the AC compressor clutch releasing. Starting should be much easier when you get all of the glow plugs and connectors replaced.
Cheers - Jonathan

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Jonathan wrote:

    All CUCV, CUCM & other Military Versions of Civilian light duty 4x4 trucks that might be considered combat vehicles were 24 Volt Electrical Systems.
    As For Economical, GM has a Seperate line to build Mil-Spec 6.5's. just like they did for Mil-Spec 6.2's. In fleet sales the US Armed Forced are GM's Best Customers. Nasa and the NSA are the largest pruchers of Hugh's Aircraft products ( a devision of GM).
    Hell all us Civies could stop buying GM's and the Goverment alone could keep the company alive. Unlike in civie sales, Govement sales make them a profit. Charles BTW: Neither Haynes or Chiltons covers Military Vehicles, their electrical or mechanical systems.
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There may be a gov't field manual covering the 24v versions.

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