No start and code P0300

CHEVY4LIFE89

MEMBER
2004 CHEVROLET BLAZER
4.3L
V6
4WD
AUTOMATIC
220,000 MILES

Hello, I am currently having some issues with my vehicle. It was running pretty rough for a couple weeks engine light was on and it was reading p0300 random or multiple misfire. And the other was one of the o2 sensors cannot remember code. While driving it would idle crazy, sometimes idle down until it stops running, but always started back up. Then it started losing power while on highway. I would pull over shut it off and on it started. Later that day I shut it off for a few minutes then tried starting and no start. I first thought was fuel pump so replaced it still no start. Ran a wire drone battery to fuel pump. Pump kicked on tried to start it still nothing. I put starting fluid in throttle body truck started but died immediately. Tried it again and the throttle shot a flame and popped loudly. So now I am not getting fire. Fuel pump only turns on when wire is ran directly to battery. Also, getting fuel at valve pressure test was around 60 psi.

3 Replies

STEVE W.

MECHANIC
13,379 POSTS

The initial problem sounds like a crank sensor failure. Very common on the 4.3 (I keep a spare in mine with dedicated wrenches because it is so common)

Loss of pump control -
Check ECM B Fuse (20A) as it is pump power.

Next would be fuel pump relay or relay socket. Another common point. The pump pulls more power as it ages, the relay contacts get pitted and fail. I have had one melt the shell because of the heat.
The last is the pump circuit itself. If you get the pump to run with a direct feed. Try powering it through the bypass prime connection in the fuse box next to the fuel pump relay, or pull the relay and jump power from the orange wire to the gray wire. If the pump runs it is a bad relay or relay control signal loss. To check that go to the PCM, connector and find pin 9, It is a dark green with white trace. Hook a test light to ground and probe that wire while turning the key to run. It should show voltage for about two to three seconds as the pump prime signal.

Reply back with results or more questions.

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Friday, January 29th, 2021 AT 11:21 AM

CHEVY4LIFE89

MEMBER
2 POSTS

Replaced the crank sensor and still nothing no power to coil still. I'm at a loss don't know what to do.

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Friday, January 29th, 2021 AT 11:21 AM

CJ MEDEVAC

MECHANIC
11,004 POSTS

Different Guy,

Owns 2 Jeeps one 40, the other 70 years young!

Much more Manly and adored by women! LOL!

I'm following along, not familiar with your rig.

I am sorta Jeepin' along on your map (on your engine performance wiring diagram, "VIN X", in "Prodemand")

I followed your coil's hot wire back to ECM I FUSE 15 AMP (Prodemand says it's in the under-hood fuse block).

The wire looks to be a straight shot coil to fuse with nuthin' else in it.

Is the fuse good?

Is there power to one leg of the fuse's socket (key on)?

The Medic

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