Trouble Code P0300, Multiple Cylinder Misfire Detected!

[jbry31]

Trouble Starting, Fuel Pressure readings are stated a few post down

Hard to start. Especially after setting all night. Had a P0300 Code but it went away after disconnecting battery and has not re-appeared. Read through and towards the bottom I state the Fuel Pressure information I gathered. Does not seem right to me.

Thanks, Josh

1996 Chevy Tahoe 5.7 Liter 4X4

 

[ccapehartusarmyINF.(ret)]

hot coolant smell +multiple cylinder misfire =blown head gasket maybe
any white smoke coming out the tail pipe?

 

[jbry31]

No white smoke out of tailpipe. Never has smoked since I have owned the truck, owner for over two years now. The SES light has not been on since yesterday. The truck finally started yesterday so I went to O'Reilly's and bought two cans of SeaFoam and filled the tank with 93+ Octane gas thinking I had possibly got bad gas. Drove around for little while, parked it and restarted it and it started immediately.

Today, after setting all night it took 8 to 10 attempts to get the truck to start. I would turn it over, let off the key and turn it over again. In between each try letting the fuel pump run until it stopped. I am beginning to think it is not bad gas. The only kicker is once it starts and runs for a few seconds it runs fine.

???????????????? I need some suggestions or advice here. Am i loosing prime over night? The fuel pump going out....? Anyone dealt with this experience?

 

[ccapehartusarmyINF.(ret)]

if it is the original fuel pump then id say replace it all these 2000 to 2006 tahoes seem be nortorious for failing fuel pumps

 

[jbry31]

I was debating on replacing the fuel pump because it has always been a little hesitant to start. Always been able to start it in one attempt but it would always turn over for a second or so before starting. By the way, it is a 1996 Tahoe with 199,000 miles.

 

[jbry31]

After deciding to go buy a Fuel Pressure Tester I have some results.

With the key in the on position the pressure rose to a peak of 55 PSI, immediately it started dropping. Within three minutes and thirty seconds the pressure dropped to 20 PSI. First question, is 55 PSI a good number for the key in the on position? Second, with the key on shouldn't the pressure hold constant?

Ok, now with the truck idling it held about 51 PSI. Revving the truck up lightly (nothing crazy) it read about 55 PSI. With the truck in DRIVE it still read about 51 PSI.

I hope this is enough information for someone to help me resolve my problem. THANKS!

 

[laredo1307]

From everything I've seen on this site I believe those fuel pressures are on par with what they should be. Hopefully somebody with more knowledge can chime in. When it comes to this stuff I always start with the easy things first. Remove you distributor cap and check that stuff, then check your wires for arcing or bad spots, and finally remove you spark plugs and see how those look.

The P0300 is saying that you're having a misfire so it could be corrosion under you cap which could also lead to a fouled spark plug. That's why i would check that stuff first, especially if all that stuff is original.

Fuel pump usually either works or it doesn't. I wouldn't replace it till it goes out. Just my opinion though.

 

[jbry31]

Should the pressure drop with the key on or hold constant?

---------- Post added at 09:08 AM ---------- Previous post was at 09:07 AM ----------

Will look at the distributor when I take it out to replace intake gaskets. Hopefully no spark plug problems, just replaced those and wires rescently. Did not replace rotor and cap

 

[makaveliwi]

When I had that problem with my 97 Tahoe, it turned out to be the distributor cap that was causing the random misfire. The hard to start problem turned out to be the poppets on the fuel injector being clogged. I upgraded to the new style injectors and replaced the intake manifold gasakets, and did a full tune up with new Delco plugs, cap, rotor, and wires. My truck runs like brinad new again. I have 133,000 miles on mine.

 

[jbry31]

How did you clean the intake when you pulled it off? Just replaced plugs and wires rescently. Will go ahead and out new cap and rotor while I have the distributor off. The random misfire code has not been on since saturday. Just really difficult to start. The fuel pressure is leaking off when the key is on and engine off instead of holding constant

---------- Post added at 04:50 PM ---------- Previous post was at 04:49 PM ----------

I can't afford a new injection system at this time so I'm taking a shot at the pressure regulator leaking.