Author Topic: 6.2L Starts up but idles rough  (Read 2093 times)

Offline LegalCT

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6.2L Starts up but idles rough
« on: July 17, 2017, 09:23:44 PM »
So my 6.2L diesel usually starts up fine. However, it also usually rough idles. Sometimes a light blip of the throttle will get it idling higher/smoothly, sometimes it does nothing.

Any ideas?

Offline Irish_Alley

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Re: 6.2L Starts up but idles rough
« Reply #1 on: July 18, 2017, 12:44:36 AM »
is this a cold start up issue or all the time?
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Offline LegalCT

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Re: 6.2L Starts up but idles rough
« Reply #2 on: July 18, 2017, 12:13:41 PM »
It happens all the time, even when the engine is warm.

Offline Irish_Alley

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Re: 6.2L Starts up but idles rough
« Reply #3 on: July 18, 2017, 01:52:34 PM »
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

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Offline Irish_Alley

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Re: 6.2L Starts up but idles rough
« Reply #4 on: July 19, 2017, 11:22:20 PM »
ok, sorry forgot about you. but for a diesel your idle is either erratic fuel delivery or sticky advance piston.

fuel delivery issues
air leak
faulty fuel pump issues
throttle linkage adjustment



read more on these pages
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Training/GM_STG_16015_05_1C_1987_The_6_2_Liter_Diesel_Engine.pdf#page=358
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Offline 1967KaiserM715

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Re: 6.2L Starts up but idles rough
« Reply #5 on: July 20, 2017, 05:06:05 AM »
Put a clear line on the return line front of injection pump to check for air bubbles.

You'll also want to verify lift pump pressure.

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Offline Irish_Alley

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Re: 6.2L Starts up but idles rough
« Reply #6 on: July 20, 2017, 10:25:41 AM »
do they have lift pumps? im used to working with my cummins not the 6.2
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Offline 1967KaiserM715

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Re: 6.2L Starts up but idles rough
« Reply #7 on: July 21, 2017, 12:54:44 PM »
Yes, fuel pump in same location as a typical gas motor.

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Offline Irish_Alley

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Re: 6.2L Starts up but idles rough
« Reply #8 on: July 21, 2017, 12:57:23 PM »
On the side of the block?
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Offline 1967KaiserM715

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Re: 6.2L Starts up but idles rough
« Reply #9 on: July 22, 2017, 05:18:09 AM »
Yeah. All diesels need some sort of pump to move fuel from tank to injection pump- typically always referred to as a lift pump. Your Cummins probably has the lift pump internal to the actual injection pump, just like some of the older Mercedes.

The 6.2 and 6.5 DB2 pumps need an external pump otherwise it puts extra strain on the injection pump, and ultimately leads to a shorter life.

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Offline VileZambonie

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Re: 6.2L Starts up but idles rough
« Reply #10 on: July 22, 2017, 06:43:02 AM »
COMPONENTS
The fuel system consists of a tank, fuel pickup assembly, fuel filters, mechanical fuel pump, fuel line heater, and an injection pump, injector lines and individual fuel injectors for each cylinder. On 1982---83 models, the fuel pickup incorporates a water in fuel detector, Fig. 1, primary and secondary fuel filters are used, and a water drain siphon valve is included in the system, Fig. 2. On 1984---87 models, a single fuel filter assembly is used, which includes the water in fuel sensor, water separator and drain, and the fuel heater, Figs. 3 and 4. In addition, 1984---87 models are equipped with a low pressure switch which illuminates a warning lamp should the fuel filter become clogged.

1984---87
Fuel is drawn from the tank by the camshaft drive mechanical mechanical pump. Fuel is then pumped through the fuel filter and heater assembly mounted on the front of the dash on C, K, R and V models or under the air cleaner on G and P models. In the filter, contaminants are strained out of the fuel, water is separated and the fuel is heated to prevent formation of wax deposits. From the filter fuel is delivered to the high pressure rotary vane type injection pump. The injection pump meters and pressurizes the fuel, then directs it through the injector lines to the injector nozzles. The eight high pressure injector lines are all of equal length, although their shapes may be different, in order to prevent any difference in injection timing between cylinders.

1984---87
The water separation system on these models is incorporated into the fuel filter assembly, Figs. 3 and 4. The fuel filter separates and traps water contained in the fuel, and when the water level reaches a point where it could be drawn into the system, the ``WATER IN FUEL'' lamp on the instrument panel is illuminated. In addition, the low pressure sensor on the filter outlet will also illuminate the lamp if the fuel filter becomes clogged
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