Col79

Hey does anyone have any idea what might be wrong or how to find out what is wrong with my engine? I have a 1999 GMC Sierra w/ a 4.8 V-8 Vortec. The problems I am having with it is that the #7 piston is missfiring and its hard to start weather its cold or hot, kinda like its not getting fuel. I changed out the spark plugs and still no change, but when I pulled out the #7 plug I found oil on it. There was not any water in there though. All I can come up with is that I might have a blown headgasket, the piston rings might be shot, or there is something wrong with the fuel injectors. If any one has suggestions or know whats wrong please let me know.

Col

PappyDan

iTrader: (4)

time to run a compression test, could also be a hole in the piston, any way you look at it, your still looking at tearing it down to find out what it is.

budhayes3

iTrader: (19)

Yea, definitely start with the basics...spark, fuel, compression. I've actually read of a few people having misfire issues on the #7 cylinder and it turned out to be the injector. Upon removal, the tip actually looks rusty. I thought there was a TSB about it, but couldn't find it when I just checked.

budhayes3

iTrader: (19)

Ah ha, found the TSB:

EVAP - MIL ON/Engine Misfiring & DTC P0300 Stored

File In Section: 06 - Engine/Propulsion System

Bulletin No.: 00-06-04-024

Date: June, 2000

TECHNICAL

Subject:
Engine Misfire, Water in Fuel, Service Engine Soon Lamp illuminates, DTC P0300 Set ( Replace EVAP Canister Vent Hose Asm/Replace EVAP Canister If Necessary)

Models:
1999-2000 Chevrolet and GMC C/K Pickup Trucks (Silverado and Sierra) Built Prior to August 31, 1999

Condition
Some drivers may comment about the Service Engine Soon lamp illuminating. The Powertrain Control Module (PCM) may have stored a Diagnostic Trouble Code (DTC) P0300, Engine Misfire Detected. The engine may be exhibiting a misfire, possibly in the # 7 and # 8 cylinders. This condition may also affect the six cylinder models. This condition may be more prevalent in areas with high amounts of rainfall.

Cause
Diagnosis of the fuel system may reveal the presence of water, possibly in the fuel rail near the # 7 and # 8 fuel injector. Water entering through the evaporative emission (EVAP) canister vent solenoid may cause this condition. Because of this, an engine misfire may develop.

Correction
A new EVAP canister vent hose assembly, P/N 15759042, that includes the valve and the solenoid has been developed to correct this condition.
The new solenoid has a revised mounting bracket and a sealant has been applied to the top lid seal surface of the solenoid to address water intrusion. Use the procedure and the part numbers listed below.

If standard diagnostics do not lead to the resolution of the misfire, do the following steps:

1. Remove the fuel rail at the # 7 and # 8 fuel injector from the engine and drain the fuel into a suitable container. Inspect the drained fuel for the presence of water. Refer to the Fuel Rail Assembly Replacement procedure in the applicable Service Manual.






2. If the presence of water is detected in the fuel rail, remove the fuel tank and inspect the fuel for the presence of water. Refer to the Fuel Tank Replacement procedure in the applicable Service Manual.

3. If water is present in the fuel tank (other than from a water enriched fuel fill), replace the EVAP canister vent hose assembly. Refer to the EVAP Vent Valve Replacement procedure in the applicable Service Manual.

4. Disconnect the EVAP canister line connections and remove the canister. Inspect for the presence of water at the canister line connections and inside the canister. If water is present, replace the EVAP canister. Refer to the EVAP Canister Replacement procedure in the applicable Service Manual.

5. Flush and clean the fuel system. Refer to the Fuel System Cleaning procedure in the applicable Service Manual.

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From what I remember, injector replacement was necessary also

RyPkr_99

I have a 99 chevy with a 4.8 and I had somewhat similiar problems. It was hard to start when the engine was warm and threw a SES code that was multiple cylinder misfire (can't remeber the actual number sorry). I did some research and it turned out the fuel pressure regulators on these things are very prone to failure. I was like $60 and 2 minutes to fix.

Check - On the driver side of the engine I believe coming out of the fuel rail theres a little nub thing with a metal retaining clip. Theres also a small vacuum line running up under the intake manifold cover or somewhere up there. Once the truck is warm shut it off and pop that line off at the regulator. If there is any moisture in there whatsoever it's no good. This is probably not your problem but for the 10 seconds it takes to check you might as well.