Ok Guys... I need your help on this one.... I am working on my brothers car... he has a 96 3.8 with about 75,000 miles on it. The car is very hard to start when the car sits over a prolong period of time..(about an hour). When the car starts it runs really rough and the check engine light starts to flash. Well I pulled the code from the computer and it read a P306-indicating a Misfire condition on cylinder 6. so i replaced the plug and wire..... still the same problem!!! next I replaced the fuel injector... thinking the fuel injector was leaking fuel into the cylinder causing a flooded condition... still the same problem..... next i swapped the coil pack for that cylinder to see if it was a coil issue... and nope... it continued to mis-fire.... I have run out of options and need some advise on what to do before i take it in to GM... I really don't have the $$Funds$$ to pay those guys to bench my problem... Also the I get a engine code P300.. (multiple cylinder mis-fires) but it varys between that code and the p306 code. Any Ideas???

 

Not to be a smartass or anything but the wire that you replaced, was it a new wire? I had a similar problem andfound that one of my wires has some small cracks in it. Now on a wild guess, are you running decent gas???? Let us know what you find out.

 

Yes Brand New Wire And Exxon 93 Octane Gas... Is it possible that something controling the coil pack is causing the misfire? Thanks for the reply BTW

 

I'm going waaaay out on a limb here, but what about the fuel pressure regulator? Have you checked the fuel pressure in the fuel rail? Possibly the fuel pump. What did the plugs look like? Black, brownish-red, white??? The check engine light has me stumped. With the car throwing a "hard" code for a misfire doesn't really narrow it down very well. You know as well as I do that could be any number of things...plugs, coil pack, wires, etc... I would start by making sure you're getting the correct fuel pressure after checking the plugs wires and coil pack. Like said before, make sure you try a new wire, and make certain you have them installed on the coil pack in the right firing order. Going from front to back it's 6.3.2.5.4.1
If you have a wire switched, you'll surely get a check engine light with the car running like CRAP!! Hope I'm not telling you things you already know....good luck.

 

I'm taking a wild guess but check your egr you might have some carbon build up making it stick

 

Just out of curiosity... Have you done a compression check? I know it's a pain in the @$$ in these cars, but it could be worth the time. It sounds like you've checked all the normal electrical systems that could be causing the misfires, but if there's a problem with your compression, you won't get the spark you need which could cause misfires and hard starts... Kahouna's right about checking your fuel pressure regulator and fuel pump as well... Good luck!

 

Thanks for the replies everyone... I am off for the next two days so i am gonna try out both the fuel pressure and the compression check. I'll respond back with what i find. THANKS AGAIN!!!!!

 

The number one suspect here is the fuel pump. The fuel pump has a check valve in it, so when you shut your engine off this check valve shuts so it holds fuel pressure between the pump and the FPR, fuel rails and injectors. Now when you go to start it you have fuel pressure right away. When this check valve (its really just a flapper valve) goes bad fuel pressure leaks back through the pump and into the tank. The fuel pump most likey has plenty of pressure when on, but does not hold pressure when off so when you go to start it takes a while to get pressure to all the injectors, only some will start to have enough spray pattern to start so it is missing on the cylinders with no fuel yet, it will be missing and take a while to get all cylinders firing and you will even take a miss-fire DTC. When you do your fuel pressure check, also shut the engine off and keep checking the pressure for up to 30 minutes. It should hold at least 27 - 40 PSI for it to start right. I hope this helps, I have seen this way to many times, and its real fun to yank the tank!! you have to drop your rear axle, then pull the heat shields off. Do yourself a favor and use a Performance LT1 or LS1 fuel pump, like a Holley, Warblo etc.. plenty of good ones to pick from, then you will have the GPH rating for future mods too!

kingslam

 

THE FUEL PRESSURE REGULATOR WAS THE PROBLEM!!!!!!

I went to the parts house and purchased a fuel pressure gauge. I installed it on the fuel rail and Turned the ignition "on"... the fuel pressure jumped all the way up to 49, then held for a few seconds.... and then started to drop!!!! I was STUNNED! I took apart the fuel rail once again to see what the problem was..... Here is what i found....

The Fuel Pressure Regulator was busted, Causeing fuel to leak through the vac. line into the intake manifold which was right above the # 6 cylinder....Causing the mis-fire condition and raw fuel smell!... I replaced the Fuel Pressure Regulator and the car starts, and runs like a champ!!!

THANK YOU EVERYONE FOR YOU REPLIES !!!!!

 

Just a quick note on this topic...... I too have a 96' 3.8L..... and I too had a mis-fire with the check engine light flashing..... and I was also pulling the same codes....... here's the good part... A while back GM released two documents stating that they were having problems with faulty spark plug wires. Causing the car to mis-fire. I don't have the document numbers off hand, but the shop should have em'. The best part is that any owner (regardless of warrenty) can take their car to any GM shop and they are REQUIRED to diagnose for free. Even if they find out that the plug wires are not the cause. So, if you bring your car in with those symptoms, it's a free diagnoses. I am NOT kidding. This is no bull.....