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General ChatChat about all things Blazer (and related vehicles). Off-topic stuff should be in the lounge, and all mechanical problems should be posted in the proper forum.
My 2000 2wd blazer is throwing the good ole p0300. Need some ideas on getting rid of it. Here's a story leading up to this. Parked it on a Sunday. It sat on Monday. Tuesday I get up to go to work and in similar fashion to a carburated vehicle I let off the key before it fired. Usually it fires up with no issues right away.[just let off too early]. I couldn't get it to start after that. It was acting like it was flooded. So I grabbed keys for another vehicle and off to work i went. Got home that night with a can of ether. Gave it a shot and it poofed back. Repeated the same situation 2 more times. Let it sit overnight and on Wednesday morning it fired up, ran rough and smoked a little till it cleared the cylinders. Threw the p0300 code. Put a new cap,rotor,plugs and wires on today the 19th. Still missing and running rough. I sprayed the ether around the plenum and vacuum hoses with no noticeable change in idle or harmonics, vacuum hoses were soft and pliable and secure.Im kinda stumped as to where to go next.Any help would be appreciated. TIA
Thanks for replying, when I sprayed the starting fluid it backfired I guess you could say out the throttle body as it it was cranking. I do have some freeze frame data as well. Hopefully it shows up here. Short term fuel trims are definitely outta whack. I am hoping to get a fuel pressure tester this weekend and verify pressure and leak down. Will report back on that.
Last edited by Lincoln9; Oct 23, 2025 at 03:34 PM.
I was able to check fuel pressure today and got a new code as well. Key on while pump primes 62psi. When pump stops priming holds about 60 psi.Turn key back off, 58psi holds for over 10 minutes no noticeable change after 10 minutes. 56 psi while running. I drove it down the road and the check engine light started flashing. It was like driving down a bumpy road felt it in the whole vehicle lol. I got back home and read the code again and got p0155 bank 2 sensor 1 Could an oxygen sensor be causing all this mess? Fuel pressure doesn't seem to be the "issue". The freeze frame shows the misfire problem starting while the fuel system is in closed loop. No freeze frame data for the o2 sensor code.
Fuel pressure is not the problem, but at least we ruled it out because its a common issue.
Your fuel trims do indicate a major fuel control problem
You mentioned closed loop. If you start cold and watch live data, does the truck start running crappy at the moment of transition to closed loop?
What cylinders have the highest misfire counts?
Do misfires go up dramatically after closed loop?
Do you know your value for CMP retard?
A bad O2 sensor can cause problems yes but your code is for the heater which means slow warm up and less likely to be the issue. That said can you graph the O2 sensors or at least look in live data to see if the front two are switching between 0.2V and 0.8v and the rear sensor is flat lined between 0.5-0.8v?
A flashing CEL means misfires bad enough to potentially damage the engine
Fuel pressure is not the problem, but at least we ruled it out because its a common issue.
Your fuel trims do indicate a major fuel control problem
You mentioned closed loop. If you start cold and watch live data, does the truck start running crappy at the moment of transition to closed loop?
What cylinders have the highest misfire counts?
Do misfires go up dramatically after closed loop?
Do you know your value for CMP retard?
A bad O2 sensor can cause problems yes but your code is for the heater which means slow warm up and less likely to be the issue. That said can you graph the O2 sensors or at least look in live data to see if the front two are switching between 0.2V and 0.8v and the rear sensor is flat lined between 0.5-0.8v?
A flashing CEL means misfires bad enough to potentially damage the engine
George
Thanks for coming back to the thread and the info. The light came on a few seconds after start up. Freeze frame showed closed loop. It came on while in the garage. Do they start closed loop then switch to open loop or vice versa, I can't remember. I can only see freeze frame with my little scanner. I'm hoping this week and friend will be able to come by with his Solus and we can watch live data. Will the better scanners show which cylinders are missing as opposed to my cheap one? Could there be an issue with the spider injection system that the computers wont pick up?
When the truck starts cold the truck is in open loop which means that the O2 sensors are cold and not yet controlling fuel delivery. Fuel delivery control is in speed density mode using sensors like ECT, TPS, MAP and MAF along with factory look up tables. As soon as the engine is warm enough the fuel is controlled entirely by the O2 sensors in closed loop except at full throttle.
Yes a better scanner will show you which cylinders are misfiring
Yes a defective spider can be involved in this and has no codes per se, we figure that out through other tests.
If your O2 sensors are behaving properly then we move on to other tests. In the mean time you can deal with that sensor heater problem. Its either the heater coil in the sensor or the 12v wiring driving the sensor. I can help you with that when your ready..
Heres some live data I was able to get off the Solus Ultra. Looks like cyl 4 and 5 are the culprits. I took pics of the screens, sorry if I doubled up on any.
Fuel pressure is not the problem, but at least we ruled it out because its a common issue.
Your fuel trims do indicate a major fuel control problem
Need all 4 numbers, one got cut off
You mentioned closed loop. If you start cold and watch live data, does the truck start running crappy at the moment of transition to closed loop?
Need this answer
What cylinders have the highest misfire counts?
This says there is a problem in both banks so not likely the O2 sensor. Check your ignition wire routing and connects at both ends. Mist the engine around the wires in the dark with water to look for arcing. Pull 4 and 5 in turn and check for 1" of strong spark with a regular cadence. If all that is good then its likely either mechanical trouble (need a compression test) or the spider
Do misfires go up dramatically after closed loop?
Do you know your value for CMP retard?
Need this answer
A bad O2 sensor can cause problems yes but your code is for the heater which means slow warm up and less likely to be the issue. That said can you graph the O2 sensors or at least look in live data to see if the front two are switching between 0.2V and 0.8v and the rear sensor is flat lined between 0.5-0.8v?
Need this answer
A flashing CEL means misfires bad enough to potentially damage the engine
P0300 need some ideas
