2001 Blazer back/misfiring, P0300
 

Hi guys,

Replaced the entire rotor and shaft (the old one had badly worn gears) about 6 months ago. At that time it ran great.

The truck sat over the winter, and is now causing all sorts of problems. It starts up fine and idles while cold, but once hot it starts backfiring/popping in the exhaust. It throws a P0300 code.

What can I do to start diagnosing this problem? I do have a scan tool with live data.

Thanks!

To add a bit of additional info, I took a look at the live data.

SHRTFT1 and LONGFT1 are 0.0

SHRTFT2 and LONGFT2 are variable, but are roughly +20 and +25.

What am I looking at here, a vacuum leak maybe?

Positive fuel trims indicate a lean misfire. Either too much air, (vaccum leak is a possibility), or not enough fuel, (inoperative injector, low fuel pressure or volume are possibilities).

Start by checking fuel pressure and leakdown at the service port and at the fuel filter outlet. There is a How to thread at the top of this sib forum. Post all 4 readings and we can analyze them for you.

Will do - you're awesome, thanks. I will have to borrow or purchase a fuel pressure testing kit - in the meantime is there any other obvious tests I can do?

What can I do to eliminate a vacuum leak as a possiblity?

As noted I will be replacing the fuel filter today on the off chance that it is plugged.

The fuel pressure tests are the obvious ones you need to do. All you symptoms point to a fuel pressure related problem.

With the fuel trims at +25, if it were a vacuum leak, it would most likely set a lean DTC on one bank or the other. Low fuel pressure may or may not set a DTC, but if or when it does, it's almost always P0171 & P0174 simultaneously. Here's the link: https://blazerforum.com/forum/2nd-ge...eakdown-88305/

I haven't seen P0171/4 or a lean DTC, just P0330.

I did see P0341 - Camshaft Position Sensor etc. but it was after some trouble getting it started and I haven't seen it since.

P0330 is a knock sensor issue. The P0341 will set if the ignition is in the RUN position and the camshaft position sensor is unplugged, whether the engine is running or not.

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