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More 7th generation problems...ugh

3K views 35 replies 8 participants last post by  drewsk 
#1 ·
So my 05 3.8 has the dreaded p300 code. Vacuum is rock steady at idle and at 3k rpms, new oem plugs, cleaned maf and checked coils. Seems like air/fuel isnt right? Just falls on its face on load if I don't "baby" the throttle. Dont think converter with steady vacuum but....? I have a obd2 reader with live data stream but csnt find what all the readings should be? I've read a lot on this issue, but maf shows good voltage thruout the range? Frustrated is an understatement lol.
 
#2 ·
I'd look at the EGR valve and associated components/hoses/wires.
 
#5 ·
Hmmmm. But wouldn't it show which cylinder if it was a wire? They aren't very old, maybe 20k miles. Thought it was the MAF or TPS, but I don't have one to change it out and see without throwing cash. Feels like it isn't getting fuel, and when it first happened, it just sputtered out and stunk like converter. But it runs smooth as ever at 3k rpm with great vacuum.....as long as it isn't under much of a load!
 
#7 ·
Even if wires are new, look at them anyway. They like to go bad where they meet the connector, could be a bad crimp job on one of the connector pins also. I have seen bad crimps more times than I can count, why I don't like to use them myself.
 
#10 ·
So besides a water bottle....can't I check plug wires with an ohm meter? If so does anyone know what the resistance should be per foot? And wouldn't it be a constant miss or has anyone just had a random miss? I'm thinking out loud again aren't I? Thanks all!
 
#13 · (Edited)
If that don't work try disconnect battery for 10 mins and reconnect and let relearn. Had an issue very similar to this on an old sunbird. Turned out the cat was pooched. It had come apart and was all lying in the muffler. Filled a swear jar to overflowing on that one.
I take it no problem reaching max RPM at WOT and feeling like it's being held back or running out of fuel ?
 
#14 ·
Wide open throttle only have to increase throttle really slowly. If I accelerate too fast, It falls on its face. I tried unplugging maf, no change. Thought of fuel pump/regulator....but it will run at 3k rpm all day long as long as there's not much load!
 
#15 ·
You may be on to something there. More load will require more fuel. Try just pressing the pedal all the way to the floor and see how it will accelerate. I'm not saying dump the throttle all at once but a steady pressure to WOT and see if it will run all the way up. If it lays down you may have a regulator/pump/filter issue. You can pressure test the fuel rail with a gauge I believe. Cant recall directly what it should be but I am pretty sure it's on here someplace. I think between 50 and 60psi.
Have you checked the plug wire towers on the coil pack to see if any are corroded ? Use some dielectric grease on those.


I'm still kinda thinking plugged converter. Loosen it off where it connects and take it for a run. Don't have to take it all the way off but just loosen enough for a good leak to occur and see if it makes any difference.

Let us know.
 
#16 ·
Have you checked what your fuel trims are?
Have you checked what your a/f ratio is
I would also check for a vacuum leak around the intake manifold. There have been times a p0300 would come in and the intake manifold was leaking. Similar symptoms as you are describing.
Youre gonna get a bunch of check this and check that. What you might have to end up doing is biting the bullet and have it properly diagnosed before you rattle your brain too much. Who knows, it could all lead to a coil or module also
 
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#17 ·
On wot is stumbles hard until I let off the gas to about 25% and it smoothes out. I used dielectric grease on towers and plugs when I replaced plugs and etc. I haven't pulled converter loose yet, this weekend I will and see what happens! Still on the fence with the cat, vacuum never drops off and that stumps me..... Thanks for all if the feedback! I'm trying to stay GM for life!
 
#19 ·
Ok so with the converter disconnected, Its no difference. Thinking of changing crank and cam sensors, and tps and maf. Or take it to a shop and pay to have it figured out. This random misfire code doesn't help narrow it down lol!
 
#21 ·
I changed filter when I changed plugs and etc. I was really hoping plugged converter! Not sure if this will help or not but, at low speeds if I go wot, its as if I'm not even applying throttle and cel flashes. Can just feel it stumbling and light black smoke in mirror. It just runs flawless at cruising speed, thinking it has to be a sensor or tps. No code for it though.
 
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