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Old 12-29-2018, 03:58 PM   #1
61_FL_Apache
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01 Blazer p0300 code

It seems like this issue came on kinda slowly. It started out as the engine was taking longer to start. Once started it ran fine. That lasted for a few weeks then it got worse. There were no CEL's at the time.

Once my daughter said she broke down when trying to leave a store, we went an rescued her. I was able to start it up and get the car home. I put a code scanner on it and first got a p306 code and started down that road. I replaced the cap and rotor to start and nothing changed. I was no longer getting the p0306 but it switched to p0300. I looked at the #6 wire and plug and the spark plug was firing.

After some research, many people pointed to a worn dist gear. This car has 114k on it, but who knows. I pulled the distributor and it looks like new. Someone had replaced not that long ago. The gear looked great and there was no play from top to bottom.

Some have suggested the crank position sensor and that's likely what I will throw at it next.

I would like some feedback from you guys if you have had this issue.

Thanks in advance for your help!
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Old 12-29-2018, 04:47 PM   #2
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Re: 01 Blazer p0300 code

So its not the crank sensor. I happened to have one from my Tahoe which takes the same one. It was hitting the crank and had some wear on it, but changing it didnt help.
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Old 12-30-2018, 12:59 PM   #3
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Re: 01 Blazer p0300 code

Ruled out Plugs and Wires.
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Old 12-30-2018, 04:30 PM   #4
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Re: 01 Blazer p0300 code

Checked the fuel pressure, injectors, compression, did you use di electric grease on the cap and rotor, they can go bad prematurely when they dont have any applied on them
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Old 12-30-2018, 07:12 PM   #5
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Re: 01 Blazer p0300 code

Fuel pressure is 55psi. The injector spider was replaced last march with the multi-port model. I dont have a way to do a compression test. dielectric grease was not applied when I installed the cap and rotor.
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Old 12-30-2018, 08:44 PM   #6
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Re: 01 Blazer p0300 code

I would pull it back out to see if there is any corrosion on there
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Old 12-30-2018, 10:41 PM   #7
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Re: 01 Blazer p0300 code

Quote:
Originally Posted by 61_FL_Apache View Post
It seems like this issue came on kinda slowly. It started out as the engine was taking longer to start. Once started it ran fine. That lasted for a few weeks then it got worse. There were no CEL's at the time.

Once my daughter said she broke down when trying to leave a store, we went an rescued her. I was able to start it up and get the car home. I put a code scanner on it and first got a p306 code and started down that road. I replaced the cap and rotor to start and nothing changed. I was no longer getting the p0306 but it switched to p0300. I looked at the #6 wire and plug and the spark plug was firing.

After some research, many people pointed to a worn dist gear. This car has 114k on it, but who knows. I pulled the distributor and it looks like new. Someone had replaced not that long ago. The gear looked great and there was no play from top to bottom.

Some have suggested the crank position sensor and that's likely what I will throw at it next.

I would like some feedback from you guys if you have had this issue.

Thanks in advance for your help!
I see no "0306" trouble code for GM OBD2 ECMs. However, I suspect the ignition module is the problem.

I recently started having intermittent stall at idle and intermittent no-start on my '89 S10 Tahoe. It has the ODB1 ECM and no trouble codes were stored. I found that the two contacts that connect the ignition module to the field coil (both parts are inside of the distributor on my truck) were very rusty. After removing it and scraping the rust off, it tested good, but I decided to replace it anyway.

I suggest you start by checking the contacts that connect it to the field coil for corrosion. This one plug does not have a weather seal on it (and in my case the contacts did not have any dielectric grease to protect them). If they are rusty, scrape the rust off and retest or replace the ignition module.
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Old 12-31-2018, 09:52 AM   #8
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Re: 01 Blazer p0300 code

I removed the cap and noticed something new. Two of the six contacts are perfectly clean like there was no arcing there at all. This happened to cyl 3 and 6. The other 4 has oxidation on them. The pin at the bottom of the pic is one of the 4 that seem to be firing. The top one is either cyl 3 or 6.



I also pulled the plug on the ICM and the pins look clean. I removed and installed the plug several times to clean them more and it didnt make a change.

Is it possible this ICM is the issue with only firing 4 cylinders?
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Old 12-31-2018, 10:25 AM   #9
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Re: 01 Blazer p0300 code

I just so happened to have my 97 Tahoe in the driveway and it uses the same ICM so I swapped it and no change. I also had a spare coil and tried that too.. No change.
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Old 12-31-2018, 06:41 PM   #10
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Re: 01 Blazer p0300 code

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I just so happened to have my 97 Tahoe in the driveway and it uses the same ICM so I swapped it and no change. I also had a spare coil and tried that too.. No change.
I assume you made sure the '97 Tahoe runs before trying the ignition module and coil from it, LOL.

Not sure why some of the electrodes on the distributor cap have corrosion while others do not, nor whether it means anything. Looks like your ignition system is fully electronic, though, based on the round electrodes. My S10 has a "hybrid" system that still uses a rotor to distribute the spark to each spark plug. Not sure how yours works.

Did you try clearing trouble codes from the ECM, then retesting to see if it is actually trigging the "0300" trouble code right now? Sometimes people forget to do that, so worth asking. I found this other page that DOES list the 0300 trouble code (https://repairpal.com/obd-ii-code-chart) that has this info about it: https://repairpal.com/obd-ii-code-p0300

Quote:
What Does OBD-II Fault Code P0300 Mean?
OBD-II Code P0300 is defined as a Random, Multiple Misfire Detected

P0300 Symptoms
  • Check Engine Light flashing
  • Rough running, hesitation, and/or jerking when accelerating
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power (especially during acceleration), and a decrease in fuel economy

Common Problems That Trigger the P0300
Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)
Incorrect ignition timing
Vacuum leak(s)
Low or weak fuel pressure
Improperly functioning EGR system
Defective Mass Air Flow Sensor
Defective Crankshaft and/or Camshaft Sensor
Defective Throttle Position Sensor
Mechanical engine problems (i.e.ólow compression, leaking head gasket(s), or valve problems
...so the trouble code does support your assertion that there is a misfire condition or even non-fire condition on some cylinders. It's a long list of possible causes. If the misfires always occur on the same cylinders, I should think it more likely that the ignition wires and/or spark plugs on those cylinders are suspect. On the other hand, if the misfiring is not always on the same cylinders, I'd look for a more central cause.
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Old 12-31-2018, 07:06 PM   #11
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Re: 01 Blazer p0300 code

Yes. My Ho runs great!!

I did clear the codes many times and 0300 was the only one to return. I only saw 0306 once.

So from this checklist here, This is what I have covered so far.

Common Problems That Trigger the P0300
Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable) Changed all
Incorrect ignition timing - Computer does this, I dont think its adjustable. I know the dizzy is in a fixed position
Vacuum leak(s) - No visible broken vacuum lines
Low or weak fuel pressure - 55 psi when tested
Improperly functioning EGR system - have not checked this
Defective Mass Air Flow Sensor - have not checked this
Defective Crankshaft and/or Camshaft Sensor - changed crank sensor.
Defective Throttle Position Sensor - have not tested this.
Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems - these have not been checked.
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Old 12-31-2018, 07:49 PM   #12
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Re: 01 Blazer p0300 code

Quote:
Originally Posted by 61_FL_Apache View Post
Yes. My Ho runs great!!

I did clear the codes many times and 0300 was the only one to return. I only saw 0306 once.

So from this checklist here, This is what I have covered so far.

Common Problems That Trigger the P0300
Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable) Changed all
Incorrect ignition timing - Computer does this, I dont think its adjustable. I know the dizzy is in a fixed position
Vacuum leak(s) - No visible broken vacuum lines
Low or weak fuel pressure - 55 psi when tested
Improperly functioning EGR system - have not checked this
Defective Mass Air Flow Sensor - have not checked this
Defective Crankshaft and/or Camshaft Sensor - changed crank sensor.
Defective Throttle Position Sensor - have not tested this.
Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems - these have not been checked.
The order of steps you have taken to identify and fix the cause is the same as what I would do, and you have ruled out a lot of causes. Kind of surprising you have not nailed it already. :-\

Here is some of my personal experience with the remaining possible causes that may or may not be of use to you:

Throttle Position Sensor: When mine went bad, I got a specific trouble code for it. I believe I damaged it accidentally by spraying carb cleaner on it while cleaning the TBI (did not realize this part was still attached and sensitive to chemicals). According to the Haynes manual, a problem in any of the TPS circuits will set a code 21 or 22. Once a trouble code is set, the ECM will use an artificial default value for TPS and some vehicle performance will return. Unfortunately, no test procedure is provided.

Mass Airflow Sensor: My S10 has a MAP sensor, which I recently replaced (did not help engine run better). The only MAF sensor I've had trouble with was on an '87 Buick 3.8, and in that case, the ECM stored a trouble code specifically for it. I tried cleaning it, but it did not help, so replaced it, which fixed the problem.

At this point, if you can find a shop with the necessary diagnostic equipment that is actually willing to USE it, I would do that.
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Old 12-31-2018, 08:24 PM   #13
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Re: 01 Blazer p0300 code

My daughters boyfriend has a 2014 Camaro SS and had the exact same issue with the misfire on Cyl 4 and random misfires. We changed some of the same parts as mine and it ended up being a broken valve spring. I didnt dig that deep into the issue, we sent it to a local shop that he chose which raked him over the coals. They are charging him $1100 for the repair. The only broken/damaged part is the spring and possibly the push rod. They pulled the head and thats where the costs doubled.

I will check to see of my MAF is the same from my tahoe and swap them tomorrow. I dont want to get into swapping too many things with my truck, I still need to get to work
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Old 12-31-2018, 11:15 PM   #14
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Re: 01 Blazer p0300 code

Quote:
Originally Posted by 61_FL_Apache View Post
My daughters boyfriend has a 2014 Camaro SS and had the exact same issue with the misfire on Cyl 4 and random misfires. We changed some of the same parts as mine and it ended up being a broken valve spring. I didnt dig that deep into the issue, we sent it to a local shop that he chose which raked him over the coals. They are charging him $1100 for the repair. The only broken/damaged part is the spring and possibly the push rod. They pulled the head and thats where the costs doubled.

I will check to see of my MAF is the same from my tahoe and swap them tomorrow. I dont want to get into swapping too many things with my truck, I still need to get to work
Been having a lot of (mostly original) parts go one after the other on my S10 too. It's 29 years old, so to be expected, I guess...

Yeah, not a fan of paying to have my ride fixed. Replaced the valve stem seals myself. Was a major PITA and took me 4 days, but saved a fortune and learned a lot about this truck/engine. Replaced the A/C clutch and front bearing (only the bearing was bad) for the cost of the parts, shop wanted $1100 to replace the compressor.

Happy New Year!
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Old 01-01-2019, 10:03 AM   #15
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Re: 01 Blazer p0300 code

Happy New Year!
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Old 01-02-2019, 06:04 PM   #16
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Re: 01 Blazer p0300 code

So from the picture above, I put a timing light on 3 and 6 to see what they spark like and they looked normal to me. I was hoping for some missed fires there.

Back to scratching my head.
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Old 01-05-2019, 02:43 PM   #17
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Re: 01 Blazer p0300 code

Well, it looks like the injection spider has failed. Gas is down in the oil pan and under the plenum was covered with gas when I opened it up. I will keep you posted. Im working on a replacement spider.
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Old 01-05-2019, 09:27 PM   #18
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Re: 01 Blazer p0300 code

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Well, it looks like the injection spider has failed. Gas is down in the oil pan and under the plenum was covered with gas when I opened it up. I will keep you posted. Im working on a replacement spider.
Glad you found the probable cause of the problem!
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Old 01-06-2019, 09:09 PM   #19
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Re: 01 Blazer p0300 code

Something I dont remember.... Is there two O-rings per tube going into the spider? I attached a link to the line im talking about. I know there is an O-ring down each hole of the fuel distributor but is there one higher up hear the crimp in the line?
https://www.ebay.com/p/F-Inj-Fuel-Fe...7142094&chn=ps
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Old 01-07-2019, 08:20 PM   #20
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Re: 01 Blazer p0300 code

Issue has been solved!!

Replaced the FI spider today and it started right up.. I only ran it long enough to make sure all was well, then did an oil change. There was 1-2 qts of gas in the oil and it came out real fast!! It blew white smoke for a bit till all the excess gas burned off. After a few minutes of that it cleaned right up! Runs like new again! I have a very happy kid to get her truck back.

Thank you guys as always for the assist and hopefully this thread will help the next guy down the road
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Old 01-08-2019, 09:46 PM   #21
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Re: 01 Blazer p0300 code

Quote:
Originally Posted by 61_FL_Apache View Post
Issue has been solved!!

Replaced the FI spider today and it started right up.. I only ran it long enough to make sure all was well, then did an oil change. There was 1-2 qts of gas in the oil and it came out real fast!! It blew white smoke for a bit till all the excess gas burned off. After a few minutes of that it cleaned right up! Runs like new again! I have a very happy kid to get her truck back.

Thank you guys as always for the assist and hopefully this thread will help the next guy down the road
Great news!
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