multiple p0300 and ocasional p0141 codes.notice misfires when wet or damp out and under load.changed to ac plats , bosch wires and duralast gold brass insert cap and rotor last spring. fine until now. any thoughts ?? 97 blazer 130,000 miles.

 

P0300

If the Misfire Index indicates that one bank of the engine is experiencing misfire, the HO2S for that bank may be malfunctioning (i.e. Bank 1 Sensor 1 or Bank 2 Sensor 1). If the Misfire Index indicates that paired cylinders (i.e. cylinders 1-4, 6-3 and 5-2 for V6 applications and 1-6, 8-5, 4-7 and 3-2 for V8 applications) are experiencing misfire, inspect the CKP sensor reluctor ring for damage.
The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring.
Many different conditions could cause an intermittent misfire.
Check for the following conditions:
Check the spark plug wires and the coil wire for the following conditions:
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Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.-
Check the wire routing in order to ensure that crossfiring is not occurring.
[ol][align=left]if the misfire occurs when the weather is damp, the problem could be due to worn plug wires. In order to test for this condition, spray the wires with water. With the engine running, watch for a spark to jump from the wires. If a spark is visible, replace the wires. [/align]Check for contaminated and a low fuel level and the following conditions:
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Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition.
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If the fuel level is low, contaminants in the bottom of the fuel tank could enter into the fuel metering system. P0401Heated oxygen sensor or wiring problem
•
Check for a poor connection or a damaged harness. [align=left]•
Inspect the harness for the following conditions:-
Backed out terminals-
Improper mating [/align][align=left]Broken locks-
Improperly formed or damaged terminals-
A poor terminal to wire connection-
A damaged harness [/align][/ol]

 

I am having the same code P0300 after replacing my intake manifold gasket. I didn't mark the distributor correctly before removing it. So after replacing the manifold gaskets I set the distributor back to the original settings. On the forum people mention setting the distributor to the #1 cylinder, but the repair manuals says to set the rotor to a mark indicated by #6 located on the rotor distributor housing. I tried both and managed to get the engine running when setting the #1 cylinder to TDC and pointing the rotor towards the #1 cylinder. Now I get the P0300 and P1345 codes. Checked wires, spark plugs, and the timing marks on the crank. When I opened the distributor cap again I noticed the rotor now points to the #6 mark on the rotor distributor housing when at TDC - how did it do that? I have never had this much difficulty setting timing on an engine before - in fact it was easier to get the timing on a VW TDI after replacing the timing belt where you have to get the diesel pump lined up with the crank when at #1cyl TDC. The engine ran fine before but since I did the intake manifolds I replaced the plugs, wires, cap and rotor. Now this is irritating.

 

Been through this one twice on my 99. First time was the fuel pump not holding quite enough pressure and the last time was my Duralast Gold distributor cap which had all of about 200 miles on it.Never could see what the problem with it was because it looked fine but that definitely fixed it. I also have a 90 Camaro that I put one on and that one only lasted 6 months so I'm done with those.

 

all is well, problem fixed. first i used a "car chip" data module and read trip after trip of p0300 codes and no p0141 codes. went to friend who has a good updated "snap on" code reader(he is a damn good independent mechanic) he searched the car computer and determined the cam sensor in the distributor was bad. when he pulled the cap and rotor they were gray with misfire arcing (he had never seen one that bad) he dropped in a new distributor, cap and rotor and ac plat plugs.cleared all codes (found 2 that weren't showing on my car chip oran acton code scanner -- one for an abs problem and one for the fuel guage. fixed them in the computer) this vehicle has never run so well.

now the distributer, i read on another blazer forum about distributors that weren't clocked right and mechanics including GM shop have had to drill the mounting plate to allow the dist. to be rotated so the engine would run. the first dist I supplied would not run, he pulled it and it was clocked wrong. the second dist. matched the original and was clocked about 15 or so degrees different from the first replacment. interesting if you drop a new distrbutor in match it up to the orignial lay it on a bench andlook at the "keyway pin" at the gear end. withthe top rotor plate alined the pins should match. be aware as i wounderif the distribtoris made for two different 403's maybe the w and the z???engine.