Something is going on with cyinder #4. I wouldn't call the plug fouled (I see someone on your IMGUR made comments about oil fouling), but something is keeping the cylinder from firing consistently and getting hot enough to burn the carbon off the porcelain - that is the black you are seeing. This is evidence of your misfire and it points directly to #4. Also of note is your findings in post #11 when disabling the injector for #4. Both are good observations.

I'm sure you will find the gaps to be proper, but you should check them as planned (also inspect porcelain inside/out for cracks and look up inside the spark plug boots to make sure terminals on end of wires are shiny and don't look black or burnt).

Static compression readings are consistent enough, but they do seem a bit high for a stock engine. Maybe the gauge is off some. Irregardless, we are looking (and will continue to look) at relative readings - so there will be zero issues with compression gauge accuracy. Good work so far. Progress has definitely been made. Please continue with the running compression testing and add it to your existing data.

 

Thanks! Unfortunately need to get some school done tonight so no direct updates. Hoping to make the time Friday or definitely this weekend. In the mean time had a couple quick questions:
-For the remaining tests does the engine need to be at operating temp?
-I found a 96 4wd with bad trans but a lot of good parts including the engine and talked the guy down to $550. Let's say bad turns to worse and mine needs engine work/I just want to say "F" it and swap a good engine in, will I be able to do so without any modifications from a 96? Overall I'm considering it for a ton of other parts (radiator core support, front fenders/bumper, ect as mine has front end damage) regardless but if the engine will work I'll pretty much 100% pick it up as then I'll have a spare one just incase.

 

If you need to use it, the 96 engine will work nicely in your 98. You might have to change intake/exhaust manifolds depending on any differences in your AIR system and EGR but the rest will work great. You would want to change intake gaskets anyways on a used engine.

 

Yes, always test compression at operating temp.

If you need to use it, the 96 engine will work nicely in your 98. You might have to change intake/exhaust manifolds depending on any differences in your AIR system and EGR but the rest will work great. You would want to change intake gaskets anyways on a used engine for insurance (was a common problem with these engines and result of gasket failure is coolant in the oil which ultimately results in bad bearings).

 

Les is directing you to very good diagnostic tests, especially the cam retard and the cylinder compression tests, all valuable. I also learned something new about the fuel injector cylinder balance function in that scanner. I agree on plug 4, the question is, is it compression/mechanical, rich fuel or weak spark? #2 might also be running a little rich.

I would offer some additional thoughts on fundamental ground that you can cover and would help rule out a bunch of possibilities. I will leave the quarterbacking of your issue to Les but here are my thoughts:

I didn't see a fuel pressure test

Look under the distr cap for carbon trace arcing.

When the engine is running crappy, pull a plug (#4 is a good choice) and check for 1" of strong blue spark with a steady cadence. You can also do an ignition drop cylinder test by pulling and grounding each plug while watching rpm and listening.

Fuel trims may cut the possibilities in half.

This can be a sensor problem without a code. You can look at the values in live data and compare them to ambient/operating conditions. This includes ECT, MAP, MAF, TPS. Example, at key on engine off does the MAP sensor read ambient pressure?

Do the O2 sensor graphs make sense?

As Les would say, there is more but ... I'll let Les prioritize your approach but will assist if needed. I have some articles in my signature that may be helpful since you want to learn.

Good luck,

George

 

Sounds good will do.

Currently out in my garage about to start the idle and static tests and I read this step (read the guide multiple times and never really thought about this one):
4. Disconnect the injector for that cylinder on a port fuel injection system.
Is this true for the 4.3L V6?? If I'm disconnecting it, where will the fuel intended for this cylinder go? Just wanted clarification before I move forward and make a drastic mistake...

I would say yes as I upgraded to an Multi port fuel injection system but am nervous what exactly to do with the disconnected injector...

 

George, nice to make your online acquittance and thanks for the response!

As I wait to get some feed back on the specifics of the compression test above I figured I'd reply and take a look into what you've mentioned.

When I was working with a mechanic on my installation one of the things we checked was fuel pressure. Per his knowledge, it was correct. With that being said; I'm willing to do it again under specific guidance to the engine if need be. But as far as I'm aware I trust his input on this.

I have and have posted pictures here. To my eye, seems fine but would love to hear thoughts. Something I did notice some play in the rotor cap, both side to side and up and down (if this is normal never mind me), video .

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If I'm not mistaken I believe I tried something to this effect per Les' advise during the "Cylinder Power Balance" tests, or would this be different?

What do you mean? Could you elaborate?

I'll check all this out next, just wanted to post a reply as I'm not sure when I'll be able to complete.

Honestly, I don't know. My knowledge base is limited as I am still learning, some insight as to what should make sense would be very helpful.

Again, thanks for chiming in. As I've said I'm doing this to learn about engines and how they tick. All the help and patients with my ignorance has been seriously appreciated.

 

There is a procedure in a sticky in the gen 2 forum. The key is to maintain 55psi at the shrader for 10 min.

Don't know on the rotor play, I have always looked at gear wear. My guess is that its normal. If I remember you have a dead nuts 0 CMP retard. If thats true and it doesnt jump around then I think your good.

I am suggesting an ignition cylinder drop test, iow pulling ignition wires. I think Les was suggesting an injector balance test.

Look at fuel trims in live data at idle and at 2500 rpm. You need 4 values: LT and ST for both banks

I forgot to add the IAT sensor for checking the static values

If you have graphing capability your two upstream sensors should oscillate between around 0.15 and 0.85v at around a 1-5 hertz rate with around a 140ms rise and fall time. This might be helpful:



I have some articles in my signature that might help you.


George

 

Not practical to disconnect an injector on a Blazer because of the spider configuration. Fuel will go where it does during a misfire - Out the exhaust. I have done this test before on a Blazer without disconnecting the injector. It's not a problem but do ground the spark plug wire for the cylinder you are working on.

 

George, he has identified the misfire/rough idle as cylinder 4 by injector balance test and a visual of the spark plug. He has a new cap/rotor/wires/spark plugs. I'm trying to follow a logical train of diagnosis and not throw out a bunch of stuff (all at once) to check that can cause misfires. Yes we may get into one or more of the test that you mention, but we don't want to overwhelm or confuse him right now. Please let him finish the compression tests before we go on.