P0300 and weird readings
 

I was having intermittent misfires, usually when driving up a hill, so I just recently replaced the whole distributor because the bearings were totally worn out to the point where there were plastic chunks missing on the rotor and one of the rotor hold down screws was missing. But now with the new distributor it is at the point where it happens anytime the Blazer gets above 65 MPH, even on a level surface. Has no power above 80 MPH.

This 99 Blazer ZR2 also has been converted to MFI with AC Delco Iridium Plugs and Wires and a fresh fuel filter, the fuel pump is a Delphi that was replaced about 2 years ago. The transfer case was also recently replaced only to find out there is no power to the front wheels with the new case.

I think the new distributor may be off a tooth, but I did line up the pointers with the old position before replacement. My code reader can't show me live data but here is a freeze frame:

DTC That Caused Freeze Frame: P0300
Throttle Position: 42.7%
Engine RPM: 2357 RPM
Load Value: 30.9%
Air Flow Rate: 47.30 GR/SEC
MAP Sensor: 82 kPA
Short Term Fuel Trim1: 7.8%
Long Term Fuel Trim1: 11.7%
Long Term Fuel Trim2: 9.3%
Short Term Fuel Trim3: -86.6%
Long Term Fuel Trim3: 90.6%
Short Term Fuel Trim4: -11.6%
Vehicle Speed: 73 MPH
Fuel System 1: CLSD
Fuel System 2: CLSD

Any suggestions what to change next?

Lack of a code P1345 indicates the distributor is not a full tooth off.

Borrow a fuel pressure gauge from local parts store and look at fuel pressure when misfire takes place (duct tape the gauge to your windshield or somewhere you can see and drive it).

If fuel supply is OK - get a capable scanner and ensure CMP retard is 0° ± 2°.

If these two things don't reveal your problem, get back to us for more. Don't be a parts changer - diagnose it.

p.s. for a 1999 blazer - an Android phone, BAFX Bluetooth OBD2 adapter, and Car Gauge Pro or Dash Command with Enhanced GM PIDs for your vehicle will do the trick. $30-$40

Thanks! I just ordered a better reader so it should arrive in a few weeks and I will know more then.

Make sure that whatever you get will read the CMP retard (cam sensor retard) as live data - most of the ones under $150 won't. You need this on a 1996+ Blazer.

Ok I did a the relearn procedure and things did calm down a bit but seems to misfire in cylinders 2 and 3 when above 65.

At idle I have spark at anywhere from 15-20 degrees, typically steady at 18.
I do see spark go up to 40 degrees at times.

The two spark retard readings go between -1 and +1 while driving and both stay close to 0 at idle.

In an interesting turn of events I just discovered a pinhole leak on the transmission cooling lines. Not sure if that is spraying transfluid up into the spark plugs on the passenger side or not.

Please advise what relearn procedure you did and what scanner you used to do it? Is the SES light flashing or coming on above 65mph - or are you just reading misfire counts on the scanner?

Timing advance seems normal.

A CMP retard between +1 and -1 is just fine.

What about the fuel pressure testing?

GM Tech 2. Relearned from the menu while sitting parked, press brake pedal and rev up to 4000 RPM until fuel cut out occurs.

Misfire sets P0300 with a blinking SES light, And I saw the misfire count accumulate in the counters for cylinders 2 and 3. The total count was about the same for both cylinders in the 14200 range after it was done.

Not sure if I can do a fuel pressure reading with the Tech 2 or not, not sure where my gauge for the test port went.

OK - sounds like relearn was good and the misfire count is definitely significant. I guess I would check the fuel pressure during the misfire to rule out that being the problem. Have to use a gauge - Tech 2 won't do it.

Problem was with a Prestone radiator flush fitting that the plastic dissolved over time. It was presumably leaking down on to one of the cylinders and was right next to the coil so presumably spraying in to that as well.

Also I'd like to take the time to let people the fitting exploded in my face with hot antifreeze during inspection after noticing a drip on the driveway.

Here is a picture of the fitting in question: