4.8 with no compression on all 8 cylinder

XJ96 · February 3, 2012

Good day

I owned a 2009 gmc sierra with the 4.8l this morning I start the engine and when I engage the transmision on revers the truck stall and it wont start any more. after cheching the compression the pression is betwean 80lbs and 60lbs ??? on all 8 cylinder.

any idea ????

sorry for my bad english I'm french canadien

ps the truck stall a couple of time sinc i bought it in 2009 ( when I engaged the transmision the rpm just drop until the engin stop)

gmtech4 · February 4, 2012

you have warranty left ????

here is the proceedure and the specs

take it in if you have warranty !!

1. Charge the battery if the battery is not fully charged.

2. Disable the ignition system.

3. Disable the fuel injection system by removing the injector fuse or removing the injector electrical connectors.

4. Remove all spark plugs.

5. Turn the ignition to the ON position.

6. Depress the accelerator pedal to position the throttle plate wide open.

7. Start with the compression gauge at zero and crank the engine through 4?compression strokes, 4?puffs.

8. Measure the compression for each cylinder. Record the readings.

9. If a cylinder has low compression, inject approximately 15?ml (1?tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and record the reading.

10. The minimum compression in any 1?cylinder should not be less than 70?percent of the highest cylinder. No cylinder should read less than 690?kPa (100?psi). For example, if the highest pressure in any 1?cylinder is 1?035?kPa (150?psi), the lowest allowable pressure for any other cylinder would be 725?kPa (105?psi). (1?035?x?70%?=?725) (150?x?70%?=?105).

• Normal — Compression builds up quickly and evenly to the specified compression for each cylinder.

• Piston Rings Leaking — Compression is low on the first stroke. Compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil.

• Valves Leaking — Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.

• If 2?adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders

GMC Tech · February 4, 2012

I'd suspect it broke the dowel pin in the end of the camshaft and bent the valves due to the camshaft bearing seezing on the cam and then trying to spin in the block. If you have any warranty left on the truck, its time to take it to the dealer. Also since GM is standing behind the powertrain for 5 years or 100,000 miles, if it s out of warranty, call GM and ask for assistance.

XJ96 · February 4, 2012

Thanks

And yes the truck still under warranty.

Can you tell me if GM can find I try a programmer (superchip) for less then 30mins 1 1/2 - 2 years ago?

Silverado4x4 · February 4, 2012

Thanks

And yes the truck still under warranty.

Can you tell me if GM can find I try a programmer (superchip) for less then 30mins 1 1/2 - 2 years ago?

What do you mean? you have a programer? If you do then GM will find it and then your screwed. Bye bye warranty.

markw8 · February 4, 2012

Take it in and see what happens.

Mark

XJ96 · February 4, 2012

Thanks

And yes the truck still under warranty.

Can you tell me if GM can find I try a programmer (superchip) for less then 30mins 1 1/2 - 2 years ago?

What do you mean? you have a programer? If you do then GM will find it and then your screwed. Bye bye warranty.

no i just try it for 30 min 1 1/2 -2 years ago