I watched a good vid on youtube for diagnosing before spending on parts bit by bit.
98 blazer 4.3
New plug in problem cylinder #5.

i did a spark test with an inline tester between plug and wire, got spark.

Next fuel pressure test at fuel rail, key on up to 60 then down to 56. Held 56 for twenty minutes with key off, no leakdown.

Nexi i took connector off from spider and used an led and checked each for power while cranking engine. All have power coming thru.

Aside from doing a compression test should my next step be to remove the plenum and check spider wiring for short or intermittent.

Please help.
Thank you

 

Did you install an AC Delco #41-993 spark plug with a gap of .060"?


An inline spark tester is fine for determining if there is spark, which you obviously have. However, it does not have the capability to determine if the spark breaks down under a load. That would require an oscilloscope.


Your 20 minute fuel pressure hold time to 56psi tells us the leakdown in the system is acceptable. The 60psi reading is either fuel pump maximum output pressure, or regulated fuel pressure, (whichever is lower). Either way, 60psi is the absolute bare minimum required. This link explains how to do the rest of the fuel pressure tests so we can accurately diagnose it. Post all 4 readings and we can analyze them for you: https://blazerforum.com/forum/2nd-ge...eakdown-88305/


LED testing: All injectors are supplied battery voltage continuously when the ignition is in the START and RUN positions. The crankshaft position sensor creates and sends a pulse to the PCM, and the PCM grounds each injector sequentially to fire them. Sounds like yours is OK, depending on how you had the LED tester connected.


A compression test is used for checking the seal between the piston rings, and the cylinder wall, and the ability to build pressure. A cylinder leakage test is used for testing the ability to hold the pressure, (valves). Both tests are necessary.


When is the last time an AC Delco distributor cap and rotor were installed?


Has the crankshaft position sensor, or timing cover been disturbed?


Has the distributor or camshaft position sensor been disturbed?

 

I will do the other tests you mention after it dries up outside a bit.
I have only owned this since december so i cant tell you when all was replaced, it did run perfect when i got it.
The new plugs i got are bosch platinum.

 

Did you have the misfire prior to replacing the plugs?

 

Is this a felt misfire, or a misfire being detected by the PCM with SES light on, or both? If you don't feel it missing but the PCM is detecting a miss, then I advise checking to make sure the misfire detection system is working correctly by inducing a miss on each cylinder and watching the individual misfire counters using a scanner.

 

yes

i can feel the miss very badly as if the cylinder is not even firing at all, basically i am running on 5 cylinders now. The ses light flashes and the code reader states its #5 cyl. I was considering pulling the plug wire off and run it for a few minutes to see if plug is wet. When i had a ford with the same running condition it ended up that the injector was not spraying but just dripping.

 

OK - just wanted to make sure the miss was real. Sounds like it is. Captain will get you through it! He's the resident expert. Please answer his questions and you will be on your way to a fix.

 

Thank you all for your help. After new plugs, wires, cap and rotor i have no more misfire or that code.
Now to find out what i did to get a p0446 code now.

 

Nice work so far!!

 

Good job! P0446 is an electrical problem for the EVAP vent valve. Possibly an open circuit in the valve itself, or the two wires that go to it. The valve is mounted to the frame crossmember, just aft of the rear axle. On a 4 door, you need to drop the spare tire. On a 2 door you can get right at it. Disconnect the electrical connector from the valve and check resistance with a DVOM between the two terminals on the valve. If it shows an open circuit, it needs replacement. Most auto parts stores either have it, or can get it.