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Tractor Talk Discussion Forum

6.2 Diesel starting help

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JCSinGA

02-18-2008 14:53:47




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I'm having trouble cold starting a mid 80's 6.2 Diesel. I know the majority of cold start problems have to do with the glow plugs and/or circuitry.

The truck owner put glow plugs in a few months ago and the light stays on a good 10 seconds so I believe the system is functioning properly however I have not checked the system otherwise. What should a good plug ohm out at? And what voltage should be going to it?

When cold cranking it acts like it has lost it's fuel prime, it tries to run but its hard to get it to stay running. I have installed an electric fuel pump that was no help. After it decides to run it runs good until it has the opportunity to sit for half a day then the whole process starts over, dont see any major fuel leaks, engine oil is not overfull, the pump solenoid is getting power.

Also he had the injectors and injection pump rebuilt about 2 months ago. If I can get some glow plug info I'm going to look at again tomorrow and probably do a compression test as well. Thanks for any help or ideas

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jdemaris

02-19-2008 05:43:54




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 Military 6.2 service bulletin - cold starting in reply to JCSinGA, 02-18-2008 14:53:47  
As RayP(MI) mentioned, the 6.2 trucks are prone do getting suction air-leaks near, or at the fuel tank. When this happens, since it's a fuel suction line, there's no leak on the ground, just air being sucked in. I've got over twenty 6.2 diesel trucks, and I live in the rust-belt in New York. Most of them have gotten rust pin-holes in the both the fuel lines going to the tank, and also in the fuel-pickup assembly itself that is attached to the tank. Easy way to diaganose is to hook a small fuel tank, small engine, outboard motor, etc. directly to the fuel-filter assembly. Start it, run the air out of it - and then let it sit overnight. If you find it now starts much better -well then you know it's a perforated fuel-line issue. Here's the military bulletin on the other air-in-fuel issue.

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RusselAZ

02-18-2008 21:07:33




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
Another important part is the cold start solonoid mounted on the rear of the passenger cylinder head. It advances the pump timing for help in cold starts and reducing cold run smoke. I think it opens at about 95 degrees engine temp. There are also the related fuse and relay which are on the wiring diagram.

Also, the way the drive for the engine is built there is a lot of room for wear between the crankshaft and the injection pump drive.

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Bob

02-19-2008 19:49:26




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 Re: 6.2 Diesel starting help in reply to RusselAZ, 02-18-2008 21:07:33  
The thing in the CYLINDER HEAD is a thermally operated SWITCH, NOT a solenoid!



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Goose

02-18-2008 18:17:38




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
I once had an '85 GMC conversion van with the 6.2 diesel. It developed approximately the same problem.

I found out there was a vacuum relay behind the right cylinder head that disconnected the glow plug electrical circuit after the engine started and vacuum came up. It had failed, so the glow plugs never got power, regardless of what the light said.

GM's practical solution in the field was to simply bypass it, as it was totally unecessary. By the time the engine starts, the glow plugs have timed out anyway, so why would it need a vacuum relay to disconnect them? I plugged in a short bypass wire, solved the problem, and drove it another 50,000 with no problem.

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Bob

02-18-2008 19:57:38




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 Goose... in reply to Goose, 02-18-2008 18:17:38  
A "vacuum relay" involved in the glow plug circuit? LOL, Goose, you REALY have NO idea what you're posting about, do you????



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jdemaris

02-19-2008 05:24:29




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 Re: Goose... in reply to Bob, 02-18-2008 19:57:38  
I don't know what he's referring to either - but GM DID use a "glow plug inhibit switch" on most of the pre-1990s 6.2s. It's just an electric sensor that screws into a coolant port. It loses continuity when the coolant gets warm and prevents the glow-plugs from working. For that, a common fix IS to bypass. I think he's got his circuits and solenoids mixed up. The C-code,light-duty 6.2s DO have several electric-to-vacuum solenoids hooked to the fuel injection pump and vacuum pump, but they have nothing to do with the glow plugs. They control converter lockup and emissions-controls. Also, GM diesels in LUVs and S10s use a fast-idle control on the injection-pump that is electric solenoid to vacuum controlled via an electric coolant sensor. But, those GMs have 2.2 Isuzu diesels, not 6.2s, and it still has nothing to do with the glow-plugs.

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RayP(MI)

02-18-2008 18:14:22




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
Been having trouble with mine too. First of all, see that the relay is really passing current. Mine was bad. Sounded, worked OK, but current not reaching glow plugs. Finally figured that out, and replaced relay. Even with 5 plugs working, starts pretty reliably. Bypassed the self timer with a simple switch, couple years ago. Those timers aren"t long lived, and they want a fortune for them. I can count to 8 seconds as well as a timer can, then I switch it one for a couple second bursts while starting, and the first minute or so of running. I have found the most reliable way to test glow plugs is with a 12 volt test lite. Connected between the + battery terminal, and the spade terminal on the glow plug (unplugged from harness.) Light lights, glow plug is good. I had a nightmare a few years back. Air kept collecting in fuel filter. Mine has aftermarket filter - looks like a small version of a gasoline storage tank filter, plastic globe, centrally mounted filter element. Finally traced it to the intake unit in fuel tank. Never did find what was leaking to allow air into the line. Replaced intake line, fuel guage unit, finally solved the problem.
If you don"t have electrical engine heater, you should get one. When temps are in the 20"s or lower, may mean the difference between starting and not starting. Mine is 550 watts, in block unit. three hours, and the thermostat housing is warm to the touch. Makes a heckova difference.

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jdemaris

02-19-2008 05:50:56




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 Re: 6.2 Diesel starting help in reply to RayP(MI), 02-18-2008 18:14:22  
I've heard for years about the early failures of timers in both GM and Ford diesels. I've got two Fords (6.9 and 7.3) and over twenty GMs with 6.2 - and I've yet to ever find a bad timer. For the 6.2s, that includes the early separate relay versions, and the later unitized versions. I suspect they are often blamed for problems they did not create. With the older setups, the glow-plug inhibit switches and relays are usually the culprits. Regardless, new controllers can be bought for $55 if you shop around. As far as the manual button goes - they are fine except when it comes to lending the vehicle to someone else and trying to explain it's function.
The OEM timers do not cycle properly with the newer burn-out-proof dual-coil glow-plugs. You have to change one resistor to make it work properly - which costs around 75 cents.

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jdemaris

02-18-2008 17:15:58




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
6.2 has two different glow-plug systems, depending on the year. You said mid-80s, but the system changes in 1984. Since you're getting 10 seconds of glow-plugging, seems the controller is OK. You don't need an ohm-meter to check. Just see if they are drawing any current. They will draw 6-8 amps each when tested with 12 volts. There is only one correct glow-plug for the 6.2 now - and that's a 10.5 volt dual coil self-regulating plug. If you use Delco, it's a AC60G and its 10.5 volts, NOT 6 volts. If you use Wellman it takes a GO50. When GM changed over to the AC60G plugs (made by Beru in Germany), it throws the timer off a little then don't cycle quite as long as needed. The remedy is - to install a manual over-ride - or change one resistor inside the controller that makes it run four seconds longer. Here are the specs on the only plug sold for the 6.2 now (been that way for 5 years).
12-14 seconds gives the best heat.
The Wellman plugs heat much faster.

AC60G (Beru) plug for 6.2 and 6.5 diesels
2 seconds - 10 volts, 8.6 amps and 807 degrees F
5 seconds - 10 volts, 8 amps and 1145 degrees F
9 seconds - 10 volts, 7.3 amps and 1545 degrees F
12 seconds -10 volts, 7 amps, and 1716 degrees F

Wellman GO50 plug for 6.2 and 6.5 diesels

2 seconds - 10.2 volts, 13.6 amps and 1500 degrees F
5 seconds - 10.3 volts, 11.7 amps, and 1560 degrees F
9 seconds - 10.3 volts, 9.66 amps, and 1905 degrees F
12 seconds - 10.4 volts, 8.6 amps, and 2000 degrees F

Now, it sounds like your 6.2 is getting air-bound when parked which is a common problem. The military has a lot of trouble with it in the 6.2s. So did Ford with the early 6.9s. It is caused by any of the following -

Hole in fuel line back by the tank.

Bad check valve in the fuel pump - regardless if mechanical or electric.

Bad housing-pressure-regulator on the injection pump which also serves as an anti-drainback fuel valve.

On Fords only - a leaking Shrader valve on the fuel-filter housing.

In regard to the electric pump you put in, hopefully you mounted it back by the tank?

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nw_bearcat

02-18-2008 18:17:47




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 Re: 6.2 Diesel starting help in reply to jdemaris, 02-18-2008 17:15:58  
sounds more like a fuel issue than glow plugs. dad has an 85 that seems to loose prime and starts hard if it sits overnight. he uses a clamp to pinch off the rubber line between the fuel filter and the motor when he parks it for any long period, not perfect, but kinda works.



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El Toro

02-18-2008 16:42:56




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
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I would install an engine coolant heater to preheat the engine. You can get them that will plumb into the heater hoses. Hal



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HeyPigFarmer

02-18-2008 15:43:08




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 Re: 6.2 Diesel starting help in reply to JCSinGA, 02-18-2008 14:53:47  
A common problem with the glow plug IDI engines from GM(5.7L & 6.2L) and IH/Navistar(6.9L & 7.3L) is that with age, the temeprature sensor starts going bad and they usually short cycle the glowplugs which makes them hard to start when cold. The sensor is in the water jacket part of the intake manifold, screws in about a 3/4" hole, and has about 4 or 5 wires coming out of the plug. It determines the temperature of the coolant and times the glow plugs running time based on the temperature.

These engines run 6 volt plugs on 12 volts so they will heat faster. It the glow plug sensor or the relay sticks it will fry your new glow plugs.

Hard cold starting is usually related to glow plugs or low compression. These engines are very hard to start if all the plugs don't work or they don't stay on long enough. I woud start there and if that doesn't work check the glow plugs themselves, if he used cheap plugs they will go bad in no time.

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jdemaris

02-18-2008 17:21:34




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 Re: 6.2 Diesel starting help in reply to HeyPigFarmer, 02-18-2008 15:43:08  
Cheap plugs will go bad real fast, as you said. But, there hasn't been a 6 volt plug recommended for the 6.2 in years - at least not from GM for any civilian 6.2s. Military versions are different. The dual-coil AC60G is the correct plug and it is rated at 10.5 volts. Also, some of the early glow-plug systems, e.g the Ford 6.9 up to the end of 1986, do not use a separate coolant sensor.



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