Thanks guys for the suggestions! They are greatly appreciated. I will definately check the fuel pressure. Is there already a procedure written up on this? I guess there is a port on the fuel rail that allows a measuring gauge like other GM cars? Where is the best place to get a gauge? Also, I replaced the fuel filter that is on the passenger side, right in front of the wheel just recently and saw no change - is there a secondary filter somewhere else that I need to be aware of?

Using the picture below, you'll see a port on the fuel rail that has the black cap on it. That'* where you test. The cylinder with the vacuum hose is the fuel pressure regulator.


This thread shows how to test the fuel pressure.
http://www.bonnevilleclub.com/forum/...ic.php?t=85138

Also, check the vacuum line to be sure there is no gas, or smell of gas, in it.

While you're testing things, you may as well test your coils per this procedure in techinfo.
http://www.bonnevilleclub.com/forum/...e=article&k=33

Sorry, I missed that you said that you had replaced the fuel filter in your original post.

..

Has anybody mentioned the coils?

Similar sysmptoms on my 97 were the result of a bad coil. And when replaced with a "new" one from NAPA, it lasted 3 months.

Replacing THAT with one from Canadian Tire has solved the problem for more than a year now.

Okay guys, just got through testing all the coils - all three of the coils measure almost the same thing - just over .5 ohms on the primarys, and almost 6 k-ohms on all three secondaries. I also tested them while they were hot, from running the car to full operating temperature, to see if they would get out of specs while hot, but they still tested in range - about 6.33 k-ohms on the secondaries, and almost .6 ohms on the primarys. These are still the coils the car came with from the factory; and I guess they wouldn't all three be bad, right? I will try to find some time this week soon to test the fuel pressure; I'll need to buy a fuel pressure gauge from somewhere; any suggestions on that? Thanks!!

Depends on where you are, I guess. Autozone sells an Actron fuel pressure gauge in the USA for about $36 (last I checked). Sears sells the same one for around $40. Ebay is cheaper (sometimes), but you'll have to wait for it to ship to you.

Just make sure you get the one for fuel injection, not mechanical fuel pumps. You're looking for around 40 psi, not the 5-7 psi that an old mechanical fuel pump puts out.

i have a 1998 gmc yokon w a 5.7 vortec engine w a trouble code of p0304 wich is a cyl 4 misfire. i kno its nt the misfire due to plugs n wires. i took the manifold off n shanged the vortec spider fuel assembly n still no change in the way the engine is running. im thinkin it is due to a spring n rocker arm n lifter but nt sure. mind u im a mechanic n love chevy'* but this one is bout to get blown the f^%k up..lol. anyone kno wat to do before i rip into the engine that i really dnt wanna do

Umm this thread has been dead for just shy of 4 years...If you like you can start a new thread and put the link to this one in it to better help us with what you've seen as far as diagnostics goes and not work so we can come up with a better Answer for ya Thanks!!!

I would suggest that you check/change your plug wires. I had a problem with a 96 SE with 115k miles. I had changed the wires but one of them was bad/damaged and it would cause what felt like shifting problems when I accelerated hard. I was sure it was the transmission, I even put an additive in the trans to help it shift smoother didn't work..then I found the bad wire. It never thre an OBDII code, I guess because it only happened briefly when pushing it hard like to pass on the expressway.

Umm this thread has been dead for just shy of 4 years...!!!