Hi everyone I'm new to the forum but I'm not new to working on my cars, but this Blazer is kicking my (U know what) . Here's is what's going on . First I have 2 codes it's throwing up , PO101 MAFM and PO300 Multi misfires. The symptoms it's doing is once the motor gets up to about 2000 rpm it start to bog down and if tried to give it more throttle it bogs down starts miss firing and stalls . The signal voltage from the MAFM output is being pulled down from 5V to about 3,5v which I understand is what is suppose to happen because it is a pull down circuit . I have changed out the distributor cap and rotor because I noticed some corrosion and the contacts were pretty worn, even though I did a tune up last summer on it. Just for laughs and giggles I have replaced the MAFM , Both didn't solve the problem . My next steps are to do a fuel pressure check and possibly a compression check . But before I go there is there other suggestions or tests I can do . I have read that a clogged cat converter can cause these symptoms, but how do you determen that is the problem. Since there is no timing marks on the crank shaft pully I have no way to determen if the timing is off eather. The motor is a 4.3 L V6 Also How do I test the camshaft sensor on the distributer and if that can cause the problem I'm having ?

 

Let’s get you fixed up.

First, yes you must do the fuel pressure test in the sticky and report back.

second you are going to need a good scanner capability, read the scanner link at the bottom of my post for cost effective solutions

yes an exhaust restriction can cause this but so can many other things. The most definitive test for exhaust restriction is a back pressure gauge in one of the O2 sensor ports. If you tap on the cat does it sound crunchy? Also, you can try running the truck with an O2 sensor removed to se if that helps. Measuring vacuum under different conditions also helps to confirm.

once you have scanner capability with live data and CMP retard then we can go further if fuel pressure is ok. We would start with CMP retard, fuel trims and O2 sensor graphs and spot checking other sensor values

your MAF sensor outputs a variable frequency proportional to air flow. The ECM converts this frequency to air mass as read by your scanner.

George

 

Also, anytime you get a sensor code you don’t know what’s wrong yet. Is the sensor failing, the wiring failing, the ECM faulty or the parameter being measured is actually out of bounds? You can read more about that in my sensor link below.


George

 

Thanks George I'll let you know what I come up with , but first it needs to stop raining so I can get back to it.

 

This video will explain the MAF sensor output reading that you are getting with a voltmeter. Basically you are seeing a voltage average resulting from the duty cycle of an AC signal. He has some rule of thumb readings but the engine is not the same. The definitive test for MAF reading is a rough check at idle and then capturing the reading at the moment of gear shift under a full throttle acceleration and comparing the reading to the result of a VE (volumetric efficiency) calculator. His approach of looking for glitches and erratic readings applies to all vehicles.



George