I followed my persistent #5 misfire and found a plug wire problem on that cylinder and that got rid of the worst of it. I am still looking to get a better idle so next I am doing an injector balance test. For me fuel pressure is good at all operating levels so no problem there.

A few things on misfire. First it is the detection of a momentary change in crankshaft velocity so it can be fuel, ignition ... Also, sometimes the counter gets the cylinder wrong. Lastly some inconsistent misfires on your live data is normal.

Do you know if spark is strong?

To be certain that your vacuum problem is solved look at fuel trim. If it is positive at idle (adding fuel due to a lean condition) and gets better at 2500 rpm then you may still have a vacuum issue. If so you can inspect, do a smoke test or the water bottle test. Also you should do the fuel pressure stuff found in a sticky here. A good test without a fuel gauge is get your scanner on live data and look at one of your B1S1 O2 sensors (ahead of the cat). Watch it swing above and below 0.5V at cruise or idle. Then floor it in first gear and see if the sensor pegs at 0.8V. That indicates the rich condition that the ECM goes for at WOT and shows that your pump can deliver the maximum required output. The gauge is still required to check leak down and pressure regulator level though.

You should also make sure that compression is good. If you did not check it when you did plugs, disconnect ignition and crank the engine. If you get a wavering cadence to the cranking process you may have a compression problem.

Also, look at pending codes on your scanner.


Theres more. Post back.

George

 

Great info! Thank you very much. I will get this thing on a live scanner, soon. I am just upset that I spent all this money and time and didn't
fix the problem.

 

Don't spend anymore money until a test teslls you that you have a problem. Les further back in this thread made a great suggestion for an inexpensive and advanced scanning tool. I bought a used android tablet, bought the BAFX bluetooth module on Amazon and Car Gauge Pro. The whole thing was under $100 and does a lot. Once your set up we can walk through some tests tofind out what wrong.

In the meantime there are tests that you can do without a full tilt scanner. You can check spark with a gap tester or a grounded test probe, you can check compression with the crank test above and you can do a drop cylinder test with a grounded test probe focusing on your misfire cylinder. Also you can check for vacuum leaks on your new intake gaskets and elsewhere with the water bottle test.

George

 

Well....I did compression test today on #6.....60 lbs! 180 on #4 and 170 on #2 cylinder. Decided it must be a head gasket...so I am tearing this engine down. AND what fun I am having!

 

Nice work getting to the bottom of it with analysis. Good luck

George

 

I found a comprehensive list of causes for a rough idle for the 4.3L engine from a repair data base:

Throttle position sensor voltage
Fuel trim
PNP switch
Poor fuel
Fuel pressure (pump/filter/regulator/injectors)
Injector balance (test)
Exhaust restrictions
PCV
Compression
Spark output (plugs/wires/distr cap/coil/ICM)
Knock system spark retard
Ignition timing
Idle speed
IAC
EGR
Power Steering Pressure Switch Circuit

Hope this helps those who are struggling with a difficult rough idle challenge. I am currently getting ready for a fuel injector balance test.

George

 

Sounds like George has you covered for good advice. I just wanted to add that it has been determined that Car Gauge Pro works only in Generic Mode on 1996-1997 Blazers (presumably because the PCM is different). But Dash Command does CMP Retard on 1996-2004. Either one uses the BAFX Bluetooth OBD2 adapter.