The dreaded PO300 CAUTION LONG POSTas123
Login  | |
|
The dreaded PO300 CAUTION LONG POSTas123 - 10/7/2007 9:01:18 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Greetings all,
I will try to make a long story short, but I'm afraid that it's not going to turn out that way. But here goes anyway. First things first, I am attempting to locate the cause of a DTC #PO300 (Random/Multiple Cylinder Misfire). I know, it's the absolute worst code to diagnose but it's the hand I've been dealt.
The vehicle in this case is a 2001 s-10 Blazer 2wd with a 4.3 (W) 5 spd (NV3500) with 103000 miles. My wife bought it new just before we met so I know the complete history of this vehicle. About six months ago on the way to work it suddenly started to buck and surge and then just died. It felt like a fuel delivery issue, like the pump quit. It would crank fine, but would sputter and die and wouldn't rev over about 5-600rpm. trailered it home and started looking for the problem. Turns out it was a bad ignition module and a weak coil. (no codes and the pump tested fine) Replaced both along with the spark plugs, cap and rotor (all ac delco parts) and plug wires (msd) Figured while I was at it might as well change the fuel filter.
About 4 months ago I started to notice a slight intermittent miss (no codes) from then until now it has gotten progressively worse. Now I have a serv eng soon light, and the missfire can be quite severe at times, but it seems to happen mostly under part/light throttle conditions, and not so much if at all under acceleration, or idle. It was a little sluggish from idle to about 1000 rpm but would pick up from there all the way to red line. But at cruising speed (55-65 mph, 1900-2400 rpm) you could feel a surge, almost like a cylinder dropping out then refiring. So Thinking maybe the fuel system was getting dirty I changed the filter again, ran some fuel system cleaner through it (3times with a filter change in between each) and got no improvement. Given the fact that I live on the gulf coast where humidity is a real BIG issue I also ran some HEET (water evaporater) through it as well.
That didn't cure the problem (not that I REALLY thought it would) that would be too easy.
I have checked the following as well, the TPS, MAF, and MAP sensors I replaced the IAT sensor thinking that be cause the problem was more pronounced at a lower ambient air temp it might help,....NOPE!
This weekend I upgraded to the MFI Spider (THE BEST THING I HAVE DONE TO THIS TRUCK THUS FAR, BAR NONE!!!!!! THANKS BLAZER FORUM!!!!!!) No I haven't checked my fuel pressure yet, (can't find my guage) but with the cost to have the injectors etc. pro cleaned, plus parts I figured I'd be money ahead.( Was it necessary,......WELL, I won't argue with the end result, It runs better than it ever has!) The throttle responce(sp) is incredible,....got the old girl sideways last night, WHOO HOO! Anyway the part throttle misfire is still there. Cleaned pcv and the EGR valve and tube (not that it needed it, was really quite clean actually) No improvement, as of yet I have found no vacuum leaks (BTW don't vacuum leaks SUCK?! ;p I pulled the spark plugs and they looked ok, (minor amount of high speed glazingn ,not bad but I will replace them)
So I'm thinking I either have a unlocated vac leak or may be a bad O2 sensor or two. It seems that after the initial warm up,....for the O2 sensors (couple of mins) the missfire starts,but as I said it's only at part throttle/ cruise rpm, not under accelleration. I'm assuming (Ya, I KNOW) that the truck is going into open loop in reasponce to bad O2 sensor(s). How often should they be replaced I mean is there a scheduled replacement interval, or is it a replace at failure deal. Speaking of which how can I test the sensors with a multimeter ( I didn't have much luck earlier, not my strong suit sorry to say) Please correct me if I'm wrong but If I were having issues with fuel pressure or volume wouldn't accelleration be affected more so than part throttle/ cruise? I gue
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/8/2007 5:09:38 AM
|
|
|
swartlkk
Posts: 14308
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
|
Looks like you've got a lot of experience trouble shooting vehicles! You've done pretty much everything right. I would have inspected the O2 sensors before replacing the spider, but with 103k miles on the clock and your justification (I did the same thing), the new spider was money well spent.
For me, it's easy to take a look at the sensors and what the vehicle is doing while the misfire occurs, but I have a scan tool capable of showing me whatever it is I want to see. For this type of problem I would look at the O2 sensor trace, cross counts, as well as long and short term fuel trims. This information would tell me if a sensor has become lazy to a point of affecting performance/efficiency or maybe point me in another direction.
Without a scan tool capable of delivering this data, your choices are really quite limited. AC Delco O2 sensors aren't exactly cheap, but in my experience with O2 sensors for GM vehicles, there isn't another that beats it. At 103k miles, the O2 sensors very well could be the culprit.
Hope this helps!!
_____________________________
Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/8/2007 10:41:03 AM
|
|
|
Hanr3
Wheels & Tire Moderator
Posts: 3476
Joined: 5/11/2005
Status: offline
|
Boy does this thread seem familiar. 
My P0300 turned out to be cap, rotor, and plug wires. All replaced within a year of the problem. Don't rule them out. Still got the old wires, swap them and see what happens. Pull the cap off and look for corrosion. Try spraying the cap with water while the engine is running, see if she purrs differently.
I need to do some research into the MFI change thingy. Anybody got a link to a thread on it?
_____________________________
"Some people spend an entire lifetime wondering if they made a difference.
The Marines don't have that problem."
-President Ronald Reagan
'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
'00 S10-Blazer 4x4x4 - My
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/8/2007 3:45:32 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Thanks for the quick reply,
Just for giggles, if I were to disconnect the O2 sensor(s) (upstream of the cat; for diagnositic purposes only) would that tell me if I had a bad or marginal one? I.E. force the computer to stay in open loop. Short of taking it to a dealer to diagnose them and not being sure exactly how to test them with a multimeter am at a loss. I really don't want to through money at the problem until I stumble on the cure.
Just a straw to grab
Thanks again,
Gator
Thanks,
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/9/2007 5:40:17 PM
|
|
|
Hanr3
Wheels & Tire Moderator
Posts: 3476
Joined: 5/11/2005
Status: offline
|
yea, you could disonnect the O2 sensor. The puter only read the sensor after the engine is up to operating temp. Once up to temp it reads the sensor and makes adjustments to the air/fuel ratio to hit that perfect ratio. If the O2 sensor is disconnected teh puter will stay in open loop, trip a code, and go into some default programming. If it runs smoother, your O2 is at fault. If nothing changes, you haven't found the problem yet.
Disclaimer: with the O2 disconnected the engine will get horrible gas mileage, and if you let it go long enough it could plug up a cat.
_____________________________
"Some people spend an entire lifetime wondering if they made a difference.
The Marines don't have that problem."
-President Ronald Reagan
'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
'00 S10-Blazer 4x4x4 - My
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/9/2007 7:58:50 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Thats what I was thinking, and yes I am aware of the adverse effects of disconnecting the sensors. I would only disconnect them to rule them out as a possible cause for the current condition. But as I'm sure you are aware O2 sensors ( AC Delco) aren't CHEAP. I'm wondering though in order to make it a valid test I have to disconnect all (3) at once correct? If it clears up how do I determine which one is the culprit,...replace two of them, buy a third and just keep changing it's position ? Or should the smart thing to do be just bite the bullit and replace them all at once. Gee that was a STUPID question !!!! (Tripping over dollars to save nickels)
Thank you so much for pointing out the detrimental effects of disconnecting the sensor(s) as I realize that others who may not know also read these post! I'm am so greatfull to everyone on this site for their help. As soon as I can figure this mess out I will most definately post the results so that others may benefit as well.
Please keep the ideas coming.
Thanks again,
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/9/2007 8:16:56 PM
|
|
|
swartlkk
Posts: 14308
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
|
Only the upstream (B1S1 & B2S1) sensors influence fuel delivery and these sensors are located before the catalytic converter. The post-cat or downstream sensor B1S2 is a catalyst monitoring sensor only and should only be replaced if a code is present and repeatable (ie. comes back if you clear it).
So since you are experiencing an engine drivability concern, the only sensors of interest would be the upstream sensors, B1S1 & B2S1. You can disconnect them independant of each other. Driving around for a day with an O2 sensor disconnected should not significantly impact the life or performance of the catalytic converter.
_____________________________
Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/9/2007 9:30:57 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Thank you so much for clearing that up for me. I'll try it and see if it helps.
I did run across onther post in a different section that sounds carbon copy to my situation, that I will reinvestigate (i.e. TPS) I did check it but I might have missed a flat spot. HUMMMM come to think about it my rolloff truck (MACK) did the same thing and it was the TPS. I'll get back to you
Thanks again,
Gator
P.S. Nice reply to goat6500 : )
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/10/2007 8:33:26 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Nuts,
Disconnected all (3) O2 sensors, 1 at a time and,.........no change. Oh well, I guess it's not all bad. I haven't found the problem,............yet, but at least I don't have to spend big$$$$ on O2 sensors. The battle continues.
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POSTas123 - 10/11/2007 5:10:32 PM
|
|
|
Hanr3
Wheels & Tire Moderator
Posts: 3476
Joined: 5/11/2005
Status: offline
|
quote:
ORIGINAL: blazeofglory
Nuts,
The battle continues.
Gator
I feel your pain.
_____________________________
"Some people spend an entire lifetime wondering if they made a difference.
The Marines don't have that problem."
-President Ronald Reagan
'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
'00 S10-Blazer 4x4x4 - My
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/19/2007 8:41:55 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
The battle continues,.............and I'm still fighting but not making much headway.
Changed the TPS and the MAP sensors today, the throttle response has improved but the code and the random miss is still there. All the parts I have tested and or replaced have helped the overall drivability to the point that it runs better than it ever has( bought it new from the dealer)
I've reached the point where I've run out of altitude, air speed and ideas. I could change plugs, cap and rotor again ( but the problem occured BEFORE I changed them the first time) so I don't really think changing them again is the answer.
Tomorrow I will go through all my grounds again, so far all the wiring and electrical componants have checked out fine or have been replaced. Everything I have done up to this point has helped but not cured the problem, and is found in previous post.
I have in the past taken this vehicle to more than one dealership ( under warranty) but in most cases they could never find the problems ( things like a siezed throwout bearing, 2 sticking rear calipers etc.) that were
discribed. So I'd come home order the parts and repair the problems myself, and up until now I've been pretty sucessful. Is it just me or do dealerships really hate to do warranty work? Its not like they have to do it for free (correct me if I'm wrong, but dosen't the factory reimburse the dealer for warranty work?)
Sorry,...... my train of thought derailed. (Somebody call the NTSB)
I would really like to solve this problem, without removing the radiator cap and driving a new truck under it.
I'm open to any and all suggestions even if they have been covered in this post before. I'm missing something,.........somewhere,.......and I'll bet it's so simple that it's easy to overlook. The question is what.
Thanks in advance,
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/19/2007 9:06:28 PM
|
|
|
thegr81
Posts: 2621
Joined: 1/16/2007
From: PHOENIX,AZ
Status: offline
|
what about the distributor itself in general maybe its slipping gear thats the only suggestion i haven't heard yet and so maybe thats causing the misfire check that out you never know
_____________________________
2001 2wd 4.3 vortec v6
"I'm not fat, I'm a minitrucker"
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/19/2007 11:32:27 PM
|
|
|
Hanr3
Wheels & Tire Moderator
Posts: 3476
Joined: 5/11/2005
Status: offline
|
Man does this post sound familiar.
I too pulled out my distriburtor, it wasn't the problem.
Got a test for ya.
Turn off the lights in the garage, start the truck and look for arcing from teh plug wires to surrounding metal. Also verify that your plugs are on al the way, and in the correct locations. At this point, start with the basics and run through them again.
Can you get a to the data stored in the puter? See if you can get the readings whent he code was set. I am drawing a blank on the technical term for them. Howver when a fualt code is triggered the puter stores the engine readings at the exact moment of the fualt. Post those up.
One other thing. Bang on your cat, under the truck, does it rattle?
_____________________________
"Some people spend an entire lifetime wondering if they made a difference.
The Marines don't have that problem."
-President Ronald Reagan
'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
'00 S10-Blazer 4x4x4 - My
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/20/2007 8:36:46 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
The battle still wages on,.....and I'm short on ammo.
Checked / cleaned and reinstalled all the grounds (execpt pass side head to body,........I'll add one from the engine to frame before I tackle that nightmare!) They all looked as good as the day the factory hooked them up. (no change) I guess i'll throw some more money at it tomorrow ( cap, rotor, and plugs) even though I don't think it will make any difference. Plug wires checked out fine (multimeter) and no signs of arcing to ground by sight or sound (checked last night)
All the wife's cats are inside so I had to wait for the neighbor's cat to walk under the truck before I could (bang on it) it didn't rattle,.........it just hissed.  (NOTICE TO PETA,...........IT'S A JOKE!) I love cats,......(They taste like chicken) (NOTICE TO PETA,........SEE ABOVE)
Sorry it's been a REALLY long day.
As for the distributor I inspected it while it was out during the MFI spider upgrade and it appeared to be fine, nothing worn, cracked, broken etc.standard production tolerences (excessive shaft end play, corrected with a moroso shim and a new roll pin) I haven't checked the ignition pick up yet ,.......hmmm, I wonder..... ( I'll check that tomorrow) I don't remember is it a magnetic or hall effect style?
Any other ideas?
Again thanks to all the wonderful people on The Blazer Forum!
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/20/2007 10:12:17 PM
|
|
|
thegr81
Posts: 2621
Joined: 1/16/2007
From: PHOENIX,AZ
Status: offline
|
deffinitly check the pickup coil and see if thats bad that could be possibly the problem its one of the few last things on the check list. Dont worry about ammo we got a surplus of it!!!
_____________________________
2001 2wd 4.3 vortec v6
"I'm not fat, I'm a minitrucker"
|
|
|
|
|
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER - 10/21/2007 4:15:11 PM
|
|
|
blazeofglory
Posts: 50
Joined: 9/30/2007
From: Navarre Fl
Status: offline
|
Anyone got any rope?,.....cause I'm about at the end of mine! Spent this morning replacing vaccum lines as some were starting to deteteriorate. As luck would have it it didn't help. Replaced the pick-up in the distributor, and as I feared,..... no change.
I have never in my life had this much difficulty in diagnosing a problem. Stupid me for thinking I was intelligent enough to fix this myself! !@#$%! I'm really starting to hate late model stuff! Nothing is easy, or cheap! I could dam near rebuild anyone of my big blocks for what I've spent trying to fix this misfire (ok I'm exaggerating somewhat,........but right now it doesn't seem like it!)
Don't get me wrong, everything I have done to this point has helped. The difference is almost night and day, and except for the missfire it runs great. I haven't just thrown money and parts at it hoping that I'll somehow figure it out, but it sure seems like it. Every part I have replaced has made a difference how ever slight, but it to this point it still hasn't corrected the issue that I was attempting resolve, (PO300)
I'm so tempted at this point to rip out the 4.3 and stuff a 383 that I have built in to it! (with a carb and a magnetic distributor) I was planning to do that anyway but I'm not ready just yet and I was wanting to use factory F.I. instead of an aftermarket system. (stealth factor, avalibility of replacement parts etc.) I felt if I didn't solve the issue before I performed the conversion then it would come back to haunt me. Now a large portion of the budget for the conversion is gone, and I'm no closer to fixing the problem than when I started.
Should I have taken it to a shop (dealer, independant, etc.) hard to say. Past dealings around here have proven less than fruitful. (If someone knows of a really good shop in NW Florida I'd love to hear about it)
I can honestly say that I have learned alot during this adventure, and have had the pleasure of talking with some really great people on the Blazer Forum !!!! Thanks so much.
Have I given up,.......NO WAY! Now it's personal!!!!So where do I go from here?
Thanks again,
Gator
_____________________________
2001 s-10 Blazer LS 4.3 5 spd 2wd
2004 Kawasaki ZRX1200
1986 K-5 Blazer 4x4 420ci 700r4 4in lift 33's
1979 c-35 1 ton dually 505 4L80E
1971 ElCamino SS 496 6 spd 4.56 posi
|
|
|
|
|
Printable Version
