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I also did fuel pressure check and was good. Also changed map sensor. Engine revs fair in neutral with mild misfire but put in gear and add load to engine and misfires severly! just turning on a/c in neutral loads engine and causes severe random misfires. Taking any suggestions I am at my witts end with this thing! please help! I suspect fuel injectors but a near by auto parts store ran a diagnostic and said if it was injectors it would pull up a code and not the generic random misfire code that keeps popping up. Any help greatly appreciated! Thanx!

Oh yeah and before anyone

Submitted by whitetailjedi on Thu, 06/02/2011 - 21:30.

Oh yeah and before anyone gets on to me for auto neglect i changed the oil twice. Its the old ladys daily driver and she found quite a puddle to play in and is putting tons of unwanted miles on my new truck so pleeeeze help!

The misfire could be do to

Submitted by Big Block 409 on Fri, 06/03/2011 - 02:43.

The misfire could be do to alot of different things. Is code PO300 set, or is it a cylinder specific code, like PO304 for example? Posting the results of a compression test and a cylinder leak down test will help narrow down some of the possibilities. Sounds like you might have replaced the ignition cables as well. If you didn't, then you should. If you did, are you sure you didn't accidentally mix up the firing order? Alot of folks don't know that vacuum leaks cause misfires, so making sure there aren't any vacuum leaks is another thing you gotta do.

Yup the code was po300. And

Submitted by whitetailjedi on Fri, 06/03/2011 - 06:50.

Yup the code was po300. And yes I had a vac leak at the fuel pressure regulator but that was resolved with a new MAP sensor and a new tube that runs from the sensor to the regulator. And yes I replaced the wires with new ones when I replaced the plugs and I double checked the order when installed and have rechecked since hoping that was a possible cause but to no avail. A friend is coming up this weekend to help take a look as I am shade tree all the way and most of my exp is from bikes and atv's but I can swing a hammer and strip a bolt with the best of em. I will see what I can do about a comp test and repost when that happens. Could you elaborate on the cylinder leak down test, that is def not somthing that I am familiar with. I do appreciate the post and am certainly willing to chase down what I can but as u may have guess funds have dwindled with all I've done so some things may have to wait till pay day again. Thanks so much I will see what I can do about the suggestions asap!

the misfire probably is

Submitted by bfree on Fri, 06/03/2011 - 12:21.

the misfire probably is caused by a faulty Ignition Control module[ICM], (the part that the ignition coils bolt to).

Use a spark tester to check for a spark at each spark plug wire (one at a time). When you find the wires with no spark the likely cause is the ignition coil not producing voltage (don't replace the coil yet!)

If you find a coil which isn't producing a spark, swap it with one which is producing a spark and retest the non-firing spalk plug wire, If the wire now fires the coil is bad (repalce it).
If the wire still isn't firing then you know it is an ICM problem (repalce ICM). Can buy a used one from a salvage yard dirt cheap compared to a new one.

I bought a new icm a few days

Submitted by whitetailjedi on Fri, 06/03/2011 - 13:29.

I bought a new icm a few days ago after taking the coils in and they all tested in spec. It made no change in the misfires or the code. But I think I may have found my problem. There are three connections to the icm and one of them I didn't replace the wire harness protective sheath or it fell off. But it has melted through to bare wire touching the header shroud coming out the back of the engine. It was just down far enough I didn't see it. I actually found it by feel when I was replacing the plug wires on the rear of the engine. I will splice them back together later and let ya knw. GOD I hope this works! If not I will run and do a comp test and post the findings. Thanks sooo much guys having help means everything!

If it doesn't work, and you

Submitted by Big Block 409 on Fri, 06/03/2011 - 16:17.

If it doesn't work, and you wanna learn more about a cylinder leak down test, simply "Google" the term. it's also possible that you have more than the vacuum leak you found. The most effective way to find a vacuum leak is with an "Engine Vacuum Pressure Tester".

As Willy Nelson said, On the

Submitted by whitetailjedi on Fri, 06/03/2011 - 16:53.

As Willy Nelson said, On the road again! Man I can't belive sumthin like that causes so many headaches! I do appreciate the help. This is def my new first stop for car issues and will recommend to friends for sure. Thanks for yur help Big Block, I will google the leak down test for future ref. I got an idea what its about but knowledge is power they say and maybe I can pay it forward one day. Thanx again!

you may have a bent

Submitted by mws919 on Fri, 06/03/2011 - 16:59.

you may have a bent connecting rod causing misfire, it's the most common damage with water lock.
compression test?

You're welcome man. Glad I

Submitted by Big Block 409 on Sat, 06/04/2011 - 04:20.

You're welcome man. Glad I was able to help. Here's a few things that will set PO300.

Problems with spark plugs
Problems with ignition cables
Problems with ignition coil pack
Problems with ignition module
Problems with one or more oxygen sensors
Problems with one or more fuel injectors
Problems with fuel flow (PSI) rate
Burned exhaust valve
Problems with one or more catalytic converter.
Stuck (due to carbon) EGR valve
EGR passages all carboned up
Problems with camshaft position sensor
Defective computer