Flashing cel light p300 multiple cylinder misfire

[Dapainter]

So my 96 blazers cel started flashing and the truck started running extremely rough. I changed the catalytic converter and the o2 sensor that is in the pipe. Made no difference. So I knew my intake manifold gasket has a leak so I changed the gaskets and put knew bolts in. I wasn't thinking and took my distributor out and forgot to mark the timing. So played like heck getting it in timing again. Took a bit cause I didn't realize there was two timing marks. So got it started again was running really rough so thought 180 off turned it nothing. So put it back started it up still running very rough and flashing cel so put a new crank sensor and cam sensor in and a ignition coil in. No dif still. Could it be the egr or ECM?

[old_master]

P0300 is almost always caused by a fault in secondary ignition: Spark plugs, plug wires, distributor cap & rotor and ignition coil. Low fuel pressure and incorrect camshaft retard can also cause it.

These engines are very fussy when it comes to ignition parts, especially the plugs, (need to be AC Delco 41-993 with a gap of .060") and the distributor cap & rotor, (also need to be AC Delco).

Most auto parts stores rent/loan/sell fuel pressure testers. The tester connects to the service port just to the driver side of the distributor. When the ignition is initially turned to the RUN position, (engine off) the fuel pump is activated for ~2 seconds and then deactivated. This time frame is referred to as "pump prime" and this when fuel pressure must be tested, (while the pump is running). Pressure must be 60psi to 66psi and it must remain above 55psi for at least 10 minutes after the pump deactivates.

Were there DTC's in memory that specifically instructed you to replace the cam and crank sensors? If not, you spent money needlessly and created more work for yourself: 1) If the crankshaft position sensor or timing cover are moved, removed, replaced, or disturbed in any way, the crankshaft position sensor relearn MUST be performed with a capable scan tool, (the el cheapo $500 jobbies can't do it). 2) If the distributor or cam sensor are moved, removed, replaced, or disturbed in any way, camshaft retard MUST be checked and adjusted with a capable scan tool, el cheapo's can't do this either. If either or both of these are not done, the engine will probably start and run, but not very well.

[NHRA]

im dealing with somewhat the same thing on my 2000 blazer and it may turn out to be the timeing chain waiting on shop to confirm<<<<<<<<<<<<<

[old_master]

Timing chain issues are almost unheard of with the 4.3L

I hope they're not disassembling it to check it, you can check it very quickly & easily without disassembly.

[NHRA]

Originally Posted by old_master

Timing chain issues are almost unheard of with the 4.3L

I hope they're not disassembling it to check it, you can check it very quickly & easily without disassembly.

well i have it at auto shop and he drove it and timing keeps changing like 7 deg the computer keep compisating back and forth i was told it had a tesioner on the timeing chain
and could be the prob? i bought it in thinking it needed a new scpi unit and thats the news so far ....thanks

[old_master]

No chain tensioner, unless it was added during a TSB, (technical service bulletin). Common things that can cause timing to be erratic are worn distributor gear, worn distributor shaft bushings and incorrect camshaft retard.

Edit: No matter how much the timing chain is stretched, if there is a load on the engine, the slack is always on the passenger side of the engine so the timing will remain constant.

[NHRA]

Originally Posted by old_master

No chain tensioner, unless it was added during a TSB, (technical service bulletin). Common things that can cause timing to be erratic are worn distributor gear, worn distributor shaft bushings and incorrect camshaft retard.

Edit: No matter how much the timing chain is stretched, if there is a load on the engine, the slack is always on the passenger side of the engine so the timing will remain constant.

hum well now im hopeing hes not blowing smoke up my ass.............
his other comment was he thought it was internal mind you he only looked at it
a little bit and told me he hasnt had time to go in detail with it ....so we'll see....thank you <<<<

[old_master]

If he tells you he has to disassemble the front of the engine to check the timing chain, take it someplace else. No engine disassembly is necessary to check the slack. Post back here what his diagnosis is before agreeing to anything.

[NHRA]

Originally Posted by old_master

If he tells you he has to disassemble the front of the engine to check the timing chain, take it someplace else. No engine disassembly is necessary to check the slack. Post back here what his diagnosis is before agreeing to anything.

will do and thank you!

[Rick Norwood]

I had a 2001 S10 Blazer 4.3L. The Distributor shaft bushing and shaft were so worn that there was almost a 1/2 inch of side to side wiggle on the shaft, and it ultimately broke the pointer off of the Rotor.

Old Master is spot on right with the timing chain. Take your distributor cap off and try to wiggle the shaft side to side.

The easiest way to check to see if your timing chain is bad is as follows:

1. Remove the distributor cap.
2. Using a socket wrench on the big nut on the Harmonic Balancer, rotate the engine
in the proper direction to remove any slack.
3. Mark the position of the Rotor on the distibutor housing and also mark the location
of the Harmonic Balancer.
4. Using the same Socket Wrench, rotate the engine in the opposite direction until
the rotor begins to move, then stop.
5. It may take several tries to get this down, but the Harmonic balancer should not move very much when the direction is reversed, however, it will move a little. If it moves about an inch or more, the timing chain is worn and stretched, but, As Old Master Said, this doesn't mean the timing chain is bad.

See, No Tear Down Required. Don't let them overcharge you for this simple test that you can do at home.

[Tech II]

If you are dealing with the same problem, a misfire, that they are starting their diagnosis with the timing chain....

[Rick Norwood]

P0300 codes from my experience are almost always Distributor and/or Cap. If this distributor shaft has too much wiggle, it could be the culprit.

[NHRA]

mine turned out to be the mass air flow sensor>>> strange but true!
thanks all <<<<<<<<<<<<<