lost!!!

Hello chevy guys, I've been a Ford tech for some time, but my new job requires that I work on just about every kind of car. I recently "acquired" a job that 2 other shops looked at. It is a 2001 2wd Blazer 4.3L automatic.
The first shop replaced the lower intake gaskets, the second shop updated the "spider", replaced water pump, map sensor, crank sensor, plugs and wires. When I got a hold of it, I did a oil change and scanned for
codes, the only code I haven't been able to fix is the P0300. I've replaced
the cap and rotor (AC Delco), ICM and coil, Cam sensor w/pigtail, temp sensor w/pigtail. It idles fine, but under load, the light flashes and then goes away...sometimes the scanner doesn't even pick up any codes while it's happening. I've even cleaned the MAF and EGR. Any ideas? Thanks in advance.

Forgot to mention, I already did the fuel pressure tests, injector tests and they passed.

My Blazer sat in my back yard for 2 years because the tranny needed to be rebuilt and I did not want to spend the money getting it fixed. Last year exactly one year ago I resurrected it and got it running. It had nearly a 3/4 full tank of gas, I'm surprised it even started, but it ran fine all last year. It sat again over the winter. When I started it up a month ago and drove it around I got the p0300 code. I replaced plugs, wires, and fuel filter and the code has not come back.
What all this leads to is that when I was doing research on the p0300 code it looks like some folks had issue's with the gear on the distributor wearing down or out. You may want to check out 'www.blazerforum.com' and do a search on p0300. Others here can comment on that, but that may be something to look at. I'm not a tech or anything just offering what I discovered.
Good luck!

Hello chevy guys, I've been a Ford tech for some time, but my new job requires that I work on just about every kind of car. I recently "acquired" a job that 2 other shops looked at. It is a 2001 2wd Blazer 4.3L automatic.
The first shop replaced the lower intake gaskets, the second shop updated the "spider", replaced water pump, map sensor, crank sensor, plugs and wires. When I got a hold of it, I did a oil change and scanned for
codes, the only code I haven't been able to fix is the P0300. I've replaced
the cap and rotor (AC Delco), ICM and coil, Cam sensor w/pigtail, temp sensor w/pigtail. It idles fine, but under load, the light flashes and then goes away...sometimes the scanner doesn't even pick up any codes while it's happening. I've even cleaned the MAF and EGR. Any ideas? Thanks in advance.

Good hot blue spark and proper fuel pressure and AC delco plugs and camshaft retard setting?

The chev engine is very sensitive to fuel pressure.
Does the scanner show any lean banks right or left or both.
Cam shaft retard setting off can stir up misfires to.
Should be within Neg or positive not over 2 and as close to ) as you can get it.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
If not you can have cold start problems and lean running and misfires.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.
And camshaft retard setting.

I never did the camshaft retard setting, how do you do that? Wouldn't the pcm throw other codes if this was the problem?

I don't know how much "play" is acceptable for the distributor gear, I think it's excessive, but my boss doesn't think so......when I monitor the misfires with the scan tool, #4 misfires a lot more than any other cylinder, but only under load. We know the cat is partially plugged, but my boss wants the P0300 fixed before we replace it. Would the cat cause this code? The fuel trims are normal and the o2 sensor fluctuate normal as well....

Camshaft retard readings have to be checked and readout with a engine capable scanner.
Should read 0 degrees - or + or as close as you can get it.
I have had saw them off and did not set code.

Side play does not affect the firing like old type dist did.
But could make camshaft retard flunciate.

Make sure good AC delco plugs and wire and coil spark good and hot.
And confirm good compression and valve opening and closing.
Also good injector plug in wiring at top of intake.

Cat being plugged some is not good.

Miss on no 4 cylinder rings a bell.
On a few years older one's there was a problem with water getting into the 02 sensor wiring by starter and running back to 02 sensor plug in that would case some 02 sensor feed back and a miss on no 4 cylinder.
Look for any green corrosion in wiring and 02 plug ins.

There should be a TSB a few years back on that.

Update-------I unplugged the ECT sensor and drove the vehicle for about 10 miles while monitoring with scan tool.....no misfires anywhere whatsoever...PCM issues?
It still went into closed loop after a couple of minutes by itself with no temp sensor
input, the scan tool read -38F, but yet, It ran like a champ, what gives?

By the way, this particular Blazer only has the one temp sensor on head between #3 and #5 cylinders, there's no sensor by the thermostat.

With coolant sensor unplugged it goes into a rich mode.
That may take out miss if engine is to lean normal running.
Does the computer tempt sensor read correct at all tempts on scanner readout?

Yes, the scan tool AND the temp gauge are normal......they read the same thing.

Make sure good fuel pressure up to specs and camshaft retard setting good.
Air intake tempt senser MAF sensor should be checked real close to.

Can you feel engine miss on road?

I cannot feel the engine miss while driving...the service engine soon light flashes a few times and turns off.

Sounds like a light part time miss.
Engine light flashes on a miss fire.

I aways like to switch plugs and wire on miss fire or missing cylinder.

If you have tsb list for older blazers like 96-97 check out no 4 misfire caused by 02 sensor wiring.
Good Luck

Well, I finally fixed it!!!!! I replaced the crankshaft w/bearings. Turns out the previous tech that replaced the "spider" flooded the crankcase with fuel and all that fuel cleaned up all the crap inside the oil pan and partially plugged the oil pump. #1 main bearing was pretty rough and it stunk like burnt oil. She runs fine now....

thanks for the update!