P0300 Error Code + Progress
 

Replaced the main catalytic converter. I didn't realize the upstream bubble is a "Pre-Cat". (Trying to avoid the major job of replacing the whole Y pipe assembly.) Seemed to make a lot of progress. Now, I still get the P0300 at start up, but after the engine gets up to temperature, all codes disappear. Any suggestions??

Incomplete question
 

2002 Blazer LS, 4WD, 4.3L Cold start produces a rough idle, but if I increase it to 1500rpm, it smooths out, but the P0300 shows up. After warm up, and after cancelling the error code, it idles smooth and will not produce the P0300 error. Does this help or further complicate??

When the O2 sensors are cold the truck runs in "open loop" meaning the pcm/ecm is not yet using the voltage measurements from the O2 sensors to produce optimum air:fuel ratio (14.7:1). The pcm is kind of "assuming" and probably running a little rich (like in the old days when you would close the choke to start your car). Once the O2 sensors come to operating temp, they start sending the signals the pcm needs to get that right air/fuel mixture (closed loop). There are heated O2 sensors and unheated O2 sensors. My guess is your's are heated. P0300 combined with your symptons probably means the heater element in one of your O2 sensors is bad. You can check this with a multi-meter by measuring the resistance across the two black wires on your O2 sensor.

EDIT: The point of the heated O2 sensor is to get it hotter quicker so it can send the signals sooner then if it was only being heated by the radiant heat of the exhaust system itself.

Thanks ROCKP2. I already checked all three O2 sensors. One (upstream right bank) had an open heater circuit. I replaced it. Perhaps I need to check them again. I thought it strange that, when cold, it has a rough idle, but when I increase rpm's to 1500 and above, it smooths out. I will recheck them.

Further Developments
 

ROCKP2: I rechecked the three O2 Sensors. All three heating circuits tested OK. But, when I put my AutoTap Laptop tester while the engine was running, I found what may be the problem in the signals.


Bank 1 Sensor 1 varies between 85-855 mV (left bank)
Bank 1 Sensor 2 varies between 55-80 mV (right bank)
Bank 2 Sensor 1 varies between 75-870 mV (down stream)


The right bank sensor is way below the other two.


I had replaced the right bank sensor earlier because the heat circuit was open. The replacement is a Denso 234-4650 from Advance Auto and was a direct replacement "according to their book"


One other observation: When cold starting, something rattles. The exhaust connections are all tight. The rattling sounds like it might be coming from the "bubble" (pre-catalytic??) ahead of the regular larger catalytic converter that I replaced. The rattling disappears at 1500 rpm when cold and is non existent at any speed when warm. Spooks??

I think you have sensor locations out of order. I believe they are :

Bank 1 sensor 1 is left pre cat (left bank)
Bank 1 sensor 2 is post cat (downstream)
Bank 2 sensor 1 is right pre cat (right bank)

I have no experience with Denso or Bosch O2 sensors, but have read the AC Delcos are more reliable

Hope that helps

From my understanding, Bank 1 Sensor 2 (downstream) should hover around .5mV and should fluctuate much slower than the upstream sensors. I believe .45mV indicates a perfect mixture coming out of the cat ("not too lean, not too rich...just right" -Goldilocks). The upstream sensors will rapidly fluctuate between .1mV and .9mV But since the trucks smooths out when warm, it would make me think that the sensors are fine.

Since P0300 is the random misfire code, normally I would recommend what I learned from this forum and start with a fuel leakdown test, but I'm not sure if that is where to start since it seems to be only when it's cold. Maybe Captain Hook or one of the experts could shed light on that.

But I would take a look at a couple other things. If the EGR valve is stuck open, that can cause a rough idle. The other thing I would consider is my secondary ignition items. Are they in good shape? Is there any condensation under the distributor cap before the truck is started cold. Are the plug wires good (and are they AC Delco)? Methinks a tiny inner break in a wire could close as the wires heat up?

That's where I would start looking...just before I started pulling my hair out :)

EDIT: Also check for vacuum leak.

Any luck? I'm curious to know how you make out.

rockp2......Any luck?.........A little
 

2002 Blazer LS, 4WD, 4.3L


First of all, let me explain. In a former life, I was a tool maker, so "I think" I can fix anything. But, when I put on my "mechanic's hat", I know otherwise. Second: All of my dumb questions "are intended to be "informational" and not "argumental" (no such word).


I can not find an EGR valve. One google answer said there was not one on the 4.3.


What is inside the "bubble" between the Y pipe and the catalytic converter? Another google search says it is a "Pre Cat". There is still a rattle in the bubble at a cold start. It rattles for about one minute and then quiets down. At 1200rpm it quiets down and disappears at warm up. The rattle comes back a little at deceleration from 1200 to idle speed @ 720.


One other observation from my AutoTap analyzer:
Short term fuel trim bank 1 = 0-2.3%
Short term fuel trim bank 2 = 0-3.9%


Short term fuel trim from O2 bank 1 sensor 1 = 0-2.3%
Short term fuel trim from O2 bank 1 sensor 2 = 99.2% (doesn't move)
Short term fuel trim from O2 bank 2 sensor 1 = 0-2.3%


I don't really want to do it, but my inclination is to replace the whole Y-pipe exhaust system from the exhaust manifolds to the muffler flange with the one piece version. This would replace the suspect "bubble". Presently, I just replaced the downstream catalytic converter.


I certainly appreciate everyone's patience and help. Joe

Also
 

Should have added: Still getting Service Engine Light, and P0300 Random Misfire on Actron CP9580A. But, no P0300 error on my AutoTap analyzer???

Here is a link to what your EGR valve looks like: Duralast/EGR Valve EGR1067 at AutoZone.com - 1 reviews

Use this link to see how to test it using a 9v battery: http://econtent.autozone.com:24999/z...sheet_egr1.pdf

Where??
 

All the pictures I can find, show it near the front of the valve body, to the right of the alternator. There is no EGR valve there, only the thermostat cavity and pipe. I know what the valve is supposed to look like. I need to know where it is located. Some sites say there is no EGR on the later 4.3 engines.

I did a search for an EGR Valve on Autozone's website for a 2003 and one didn't come up so I assume what you're finding is correct, about later 4.3L not having them. I'm assuming that the build date of your truck is after 6/02?That learned me something, so I guess you can scratch that one off the list. I don't know what's going on in the "Pre Cat". The next one I would try is checking for vacuum leak when the engine is doing that rough idle. One other question, have you done any work on the truck that would have required the Crankshaft relearn procedure?

Other repair work
 

I replaced a bad head gasket on the RH side. It involved removing the intake plenum, intake manifold, distributor, then the RH head. Before starting this repair, I put the engine on top dead center on cyl #1 and was very careful to replace the distributor in exact position. It starts and runs smooth above 1200 rpm. I drove it down the road and up to 50mph with no problems. At the destination about 3 miles away, I stopped, cleared the error code, drove it back home and there were no error codes. Only after it set for awhile and cooled off and restarted did it have a rough idle and P0300. Strange???

If the crankshaft position sensor was disturbed in anyway, you need to do the CKP Relearn Procedure.

But I would start with vacuum and secondary ignition. what kind of wires are you using? Check under the cap for evidence of condensation. If the wires are old, when you first start it up (do this at night) spray a fine mist of water over the wires and see if you see any arcing.

Progress
 

Same old 2002 Blazer LS, 4WD, 4.3L
Latest developments: I finally decided to replace the "Y pipe-pre cat-catalytic" assembly to find the rattling noise. Here is a picture of what I found inside the Pre-Cat. No wonder it was rattling!! I still wonder why it quieted down when warm. Needless to say, the rattling stopped. I drove a short distance. Noticed a lot of pickup and it seemed to run fine. No Service Engine Light. However, when I plugged my Actron Code Reader in, there was the dreaded P0300 "pending" code. The last advice given was to check the spark plug wires & distributor at night with some water misted over them. I will do that tonight. I just bought the 14 year old beast so I don't know if the distributor cap & wires are Delco or not.


(The last time I tried to attach a photo on another Thread, it was very small, so someone please tell me how to resize.) Maybe, just click on it and it will increase in size?

We've been discussing P0300 in 2nd gen forum in more than one thread. Please take a look there. General info and strategy applies to you as well. Verify no vacuum leaks, verify ignition system per instructions, verify fuel system per instructions. Don't assume anything. Then start worrying about P0300. You will need scan equipment that will do live data for cam sensor retard and fuel trim, a fuel pressure gauge, and other equipment noted in the fuel pressure testing thread at the top of the 2nd gen forum. Again, don't skip or assume anything is OK.

Since you removed the distributor you will need to hook up a scanner capable of giving real time data (mostly cam retard) readings and see where that is at. I removed mine and reinstalled exactly how it came out and still could not get it to run proper until I was able to read the cam retard. It has to be at "0" +or- 2 or you will never get it to run proper all the time. Mine was out at like -10 or something so I ovalled out the hold down bolt hole so I could make adjustments to the distributor while watching the cam retard and getting it within spec. Now all is well and no more issues:)

"2nd gen forum"
 

Please excuse my ignorance, but specifically what is "2nd gen forum"? I have been searching with "P0300" and found a wealth of information.

The last time I was just "experimenting", I erased the P0300, the engine was warmed up. Setting still in Park, I then held the accelerator down to about 1200 for a couple of minutes and the Check Engine Light did not come on and there were no error codes. Sounds like it first appears with a cold engine and at idle speeds.

The forum dedicated to the 2nd generation of the s10 blazer... 1995 to 2005

the 2nd gen forum is here - a different sub-forum of this site. Some of us tend to hang out in different places. 2nd Gen S-series (1995-2005) Tech - Blazer Forum - Chevy Blazer Forums

Avoid any threads that don't instruct you to first check for vacuum leaks and verify fuel system and ignition system before trying to chase a PO30x in earnest. A lot of mis-information on the Internet. You will need a scanner capable of reading cam retard, a fuel pressure gauge, and some misc fittings to block the fuel lines. Get loaner pressure gauge from local parts store, an inexpensive scanner that will do cam retard is Car Gauge Pro for Android with BAFX Bluetooth OBD2 adapter from Amazon - about $35, and the sources for fittings required are listed in the testing fuel pressure sticky at the top of the 2nd gen forum.

Hint: A vacuum leak from pulling hose off vacuum storage cannister inside rear of driver's inner fender during removal/reinstallation of the intake manifold seems to be a common recurring problem. You might want to check this before you get started.

Thanks Les Myer for sticking with me!!
 

I just downloaded Car Gauge Pro on my new smart phone that the kids gave me for my birthday a few days ago. I have the BAFX Adapter ordered and should get it by next Tuesday. I did the misting test a few minutes ago and found no sparkies. I took it for a 5 mile 50mph test drive this morning and no service engine light came on. I hooked up my Actron CP9580A and it had P0300 "pending". I thought it ran really good. No hesitation, plenty of pep. I feel I am getting closer. Thanks again. No more news until Tuesday.

Good choice, the ability to read CMP retard will help a lot! Let us know when you get it. It doesn't sound like your misfire is very severe, so I think that is a good sign that setting the CMP retard might just fix your P0300 problem. Still we will need to check the distributor gear for wear and other things, especially if the CMP retard is off significantly.

Use the CMP Retard with the single asterick after scanning the PIDs for your vehicle under Powertrain. You can save the scan to a file so you don't have to scan them each time, and so that all the Powertrain PIDs can appear when not connected to the vehicle (useful for building custom gauge screens). Here is one custom gauge screen that I have. CMP Retard, a misfire counter for each cylinder, coolant temp, rpm, & MAP sensor as digital gauges. I wish the digital gauges were smaller and not round with just only the digits and label so they are easier to place on the screen, but that's the way they are in Car Gauge Pro. Still useful to watch them all at once. Note that 20 scans/sec with 10 gauges on a screen will give you a refresh of 2 times/sec on all things including the misfire counters (so they can seem a bit jerky if counting up rapidly and cycling back to zero) . If you want things faster, you need to reduce the number of things monitored, or increase your refresh rate. OBDLINKMX bluetooth will get you 30/sec but think that will not be very noticeable. The pricier Windows software with USB OBD2 adapters are in excess of 100/sec if I remember correctly (light speed in comparison), but I find them much less convenient to use (I only drag them out when I need them).

https://blazerforum.com/forum/attach...ine=1444752438

http:// http://i1260.photobucket.com...pshshwtrwa.png

lesmyer...AMAZING TOOL
 

Got the BAFX adapter. Disappointed that there is no user manual available. At 81, I stumbled through and found the Cam Retard is 5.8. I am not sure what it should be. I did discover the misfires are all coming about equally from #3 & #4. There were more at idle than at higher rpm's. I suppose this means I should replace the plug wires and/or distributor cap?? I can't believe all the info I can now get for $33!! I haven't mastered getting the gauges on the screen. I was able to watch all 6 cyl misfires at the same time.


I said earlier the vacuum lines were intact. After checking again, I found the elusive line that you mentioned going to driver's side vacuum storage canister. I had not done any work on the left side and this short line was hanging under the ledge and concealed. I didn't notice any difference after hooking it back up. I think some of the lines need to be replaced. Some are soft and some are brittle.

Cam retard HAS to be "0" + or -2. Get that in spec and I suspect your po300 will be gone.

Glad you like the app. Yeah it sucks that there is no user guide at all. Actually I'm (independently) working on writing up a Car Gauge Pro user guide for Blazers because I think it's such a good deal for us. Hopefully enough info to get a person up and monitoring PIDs and making/saving custom screens and PID lists/profiles as well as understanding what it will and will not do on our particular vehicles.

You did use the CMP Retard PID labeled with the single asterisk? If so adjust your distributor to 0. Typically CMP retard values are off in the negative direction, presumably due to wear on distributor gear and stretch/wear of timing chain. Probably you will need to do some modification on the distributor hold down in order to do any adjustment. It is locked in place if never modified. Also fix any vacuum leaks or bad vacuum hoses and then see if the PO300 disappears.

A few misfires will be observed on the counters now and then in a normal system, but if not enough to trip a pending misfire code and it runs good then consider it fixed.

Plug wires and distributor cap can cause misfires, but probably not to be really worried about unless setting cam retard doesn't fix your problem. New ones don't hurt, though if you feel like replacing them. Use only AC Delco cap and rotor. Plug wires can be removed and inspected inside both boots at both ends for carbon tracking, the length of the wire inspected for burns and breaks - then checked with an ohm meter to be less than 2000 ohms. Should have some dielectric grease on the terminal at each end of each wire. Also watching at night is a good way to subsequently judge spark plug wire condition.

Did you say that you are 81 years old? If so, I hope to be like you at 81. My hat is off to you.

Let us know how things turn out or if you have any additional questions.

Les

Thanks to all.
 

81 is correct. I dont always act it. A big thanks to all for your good help. I am on a different errand of mercy now. I will get back to work on the Blazer later today. This vehicle is planned for a destitute family member. I think it can be saved.with a little more work.

I did use the cam retard with the single astrisk.

Almost there
 

I had to elongate the hole in the distributor clamp. Some said there was 15 degrees of movement available, but not so with this one. Anyway, the Cam Retard is now -0.5 I thought the car was running pretty good before this adjustment, but it now has more pep. I still get a few misfires on #3 & #4 when idling. If I increase the rpm's to 1200, they disappear. Also, the Service Engine Light flashed when idling, but when I took it for a test drive, the light went off within 1/4 mile and stayed off during the six mile trip. I still need to inspect the vacuum circuit. I would like a diagram to make sure I get every line. So far, I have not found one for this vehicle (2002 Blazer LS, 4WD, 4.3L). Perhaps I should now give everyone a break. Thanks again to all and especially the clue about the cheap Car Gauge Pro and BAFX adapter (can't believe only $34). Any other clues are still appreciated. Joe

What are the misfire counters getting up to (highest value observed?)

I would like you to confirm that the misfired detection system is working properly by inducing a dead miss in a different cylinder than 3 or 4. You can do this by removing a plug wire and grounding the distributor terminal so spark doesn't jump around inside distributor. In Car Gauge Pro you should be able to see the misfire counter for that cylinder count the misses. If it can't count the induced misses, then your other detected misfires are probably not real and the misfire detection system needs repair. My own Blazer had false misfires when seemingly running good, and I chased misfire issues around for a while in the wrong areas until I did this simple test.

If misfire detection is good, since you have already fixed the vacuum leak caused by the line being off of the vacuum reservoir - please post live short term fuel trims and let's throw the MAF sensor reading in there too while idling. Also same readings at 2000RPM steady in park. Should be able to confirm or deny any remaining vacuum leak severe enough to cause a misfire.

I think that's enough for now, but depending on what is found we will then continue with verification of the ignition system, followed by the fuel system.

Having connection problems
 

Having connection problems with the BAFX adapter. I emailed their trouble line to get help.

First make sure bluetooth has not been turned off in your phone. Unpair OBDII in your phone settings/bluetooth and then click on OBDII in available devices to pair again. Is it successful? If it pairs again, then communication between the device and your phone is OK. Also, sometimes rebooting a phone can solve problems.

If you are trying to connect with various modules in the software other than Powertrain and are getting a connection message, remember what I said about them not being filtered by year and vehicle. Most of them won't work with the Blazers.

It would be helpful if you would describe your connection problem.

p.s. I've had mine for a year and it has worked flawlessly with two different Androids and three different softwares (originally used it with Torque Pro and also connected with Scan XL Pro and a Windows Laptop for the heck of it).

If you want to check if the Car Gauge Pro app or the app settings is the problem, you can download Torque free version and see if it connects to your vehicle OK using the BAFX adapter.

If a verified to be paired BAFX device will not connect with either Car Gauge Pro or Torque Free, only then does it suggest that you may have a problem with the device itself.

BAFX is working now.
 

Maybe it just needed a reboot. It is OK now.


MAF = .886 lb/min or 6.7 gm/sec at 700 rpm
MAF = 2.06 lb/min or 15.6 gm/sec at 2000 rpm


CMP* = 0.0


Short Term Fuel Trim
Bank 1 = 0-3.1
Bank 2 = -0.8-1.6
O2 Bank 1 Sensor 1 = 0-2.3
O2 Bank 1 Sensor 2 = 99.2
O2 Bank 2 Sensor 1 = 0-0.8
These Short Term Trim numbers jump around a lot.


Misfire check. Something screwy here.
I grounded #1 plug wire (left front according to my book). The misfire is identified as #2.
I grounded #2 plug wire (right front according to my book). The misfire is identified as #1.
Another screwy result: While doing this, the previous misfires at #3 &#4 were less frequent than before this test.


I need to leave on a mercy taxi service for the evening. Will check back late tonight. Thanks again for your patience. It means a lot.

Are you doing this at the distributor or at the spark plug?
#1 is drivers side front.
#2 is passenger side front.
terminals cross within the distributor cap - might want to check to make sure is wired exactly this way.
https://blazerforum.com/forum/attach...ine=1444856169

Fuel trims are well within normal ranges. Yes they jump around a lot. Are they negative or positive can't really tell by your description. For example, a reading of +3.0 would mean the system is adding 3.0% additional fuel to the factory calibration in order to get the correct O2 sensor reading (computer thinks engine was running lean 3.0% and needed more fuel). a negative fuel trim means that computer thinks engine was running too rich and needed to lean things out a bit. -10% to +10% is considered normal. Outside that is definitely indicating a problem.

Your O2 sensor readings don't seem to be voltages.

I'll check on mine and let you know what the values are or if there is something screwey with Car Gauge Pro.

Found the misfire counter problem is definitely a bug in Car Gauge Pro. I could duplicate your results. In Torque Pro no problem with the misfire counters. I'll contact the developer again and see if he will fix it.

I'm convinced your misfire detection system is working fine.

This link is garbagehttp:// http://i1260.photobucket.com...psts2et2nm.png

Fuel Trim and O2 sensor readings on my Blazer at idle in drive and at 2100 RPM in park. How do these compare to yours? Note the min and max value for each.


https://blazerforum.com/forum/attach...ine=1444866574


https://blazerforum.com/forum/attach...ine=1444866428

Latest info
 

cancel this

Try again
 

Double checked distributor to plug wiring. It is correct.
When checking for misfire, Igrounded at the wire end, not at the distributor. I stuck a 1/4 bolt in wire and grounded it with a patch cord.

I didn't take the time (I amnot sure I could yet) to duplicate your fancy gauge pictures. Here are my numbers compared with yours.

[email protected]
STFT B1+1.2 (-.04 +4.3)
STFT B2 +0.4 (-2.7 +4.3)
HO2S B1S1 +0.15(+.05 +.81)
HO2S B1S2 +0.78(+.77 +.78)
HOSS B2S1 +0.19(+.09 +.82)
MAF +5.44 (+5.39+12.64)

[email protected]
STFT B1+1.2 (+.4 +2.7)
STFT B2 -2 (-3.5 +1.2)
HO2S B1S1 +.84 (+.83 +.86)
HO2S B1S2 +.84 (+.83 +.86)
HOSS B2S1 +.42 (+.05 +.85)
MAF +6.3 (+6.26 +6.46)



[email protected]
STFT B1-2 (-10.6 +7.5)
STFT B2 -5.9 (-12.2 +6.7)
HO2S B1S1 +0.65 (+.03 +.9)
HO2S B1S2 +0.75 (+.75 +.92)
HOSS B2S1 +0.24 (+.06 +.88)
MAF +16.42 (+4.95 +124.03)

[email protected]
STFT B1+3 (-2.7 +4.3)
STFT B2 +2.7 (-2 +5.1)
HO2S B1S1 +.71 (+.07 +.84)
HO2S B1S2 +.45 (+.44 +.46)
HOSS B2S1 +.47 (+.11 +.85)
MAF +14.75 (+13.67 +14.75)

Joe, please advise if the O2 sensor voltages in red below are swinging up and down across 0.45 volts during extended idle in drive or are they stuck above or below a certain voltage for an extended period of time.

[email protected]
STFT B1+1.2 (+.4 +2.7)
STFT B2 -2 (-3.5 +1.2)
HO2S B1S1 +.84 (+.83 +.86)
HO2S B1S2 +.84 (+.83 +.86)
HOSS B2S1 +.42 (+.05 +.85)
MAF +6.3 (+6.26 +6.46)

Maybe try each O2 sensor in graph mode. Here is mine swinging from <0.12 to >0.75 - time lapse for graph is 10 seconds and resolution is 20 points/sec (with the BAFX). My Blazer seems to do about 3-3.5 complete cycles up/down past 0.45 volts over 10 seconds. Both O2 sensors seems to swing about the same voltage amount back and forth. got to be careful about instantaneous readings with some of this stuff that cycles, like fuel trims and O2 sensor voltages.

p.s. I figured out during lunch that the misfire counter bug we identified is that only cyl 1 and 2 are switched. I tried all the rest and they are correct. So I'm convinced that yours is truly an intermittent misfire on 3 and 4 if that is what is reading and you can feel a miss happening. What is the misfire counter maximum during a misfire time period. That will tell us how bad it is. Bet you have noticed that the counter starts over periodically.

https://blazerforum.com/forum/attach...ine=1444931110

https://blazerforum.com/forum/attach...ine=1444931110