confused
 

Hello, I have a '99 Blazer 4x4 with a 4.3l. It has 170k miles on it. Here's my trouble: engine is sluggush, it surges or misses going uphill/ under a load & my fuel consumption is terrible.
There are no codes stored.
I have a '98 blazer 4.3l with 310k & it runs way btr than the '99. Any ideas or suggestions please?

Start with a fuel pressure and leak down test. It sounds like you may have a leak in your fuel spider somewhere. Also look through the throttle body into the plenum and see if there are any washed out spots generally it tends to be toward the rear driver side but not always.

I took a fuel pressure test with key on: 60 psi with no leak down after key was shut off. & as far as I can tell, I didn't not have a leak in the fuel spider ( but still have terrible fuel mileage & it doesn't seem 2 have near the power uphill that I think it should.

Sounds like ignition control module is starting to fail.

not getting anywhere
 

So far I have changed the throttle position sensor, ignition coil, air filter, idle air control sensor & mass air flow sensor. it STILL feels horribly sluggish/ no power uphill, it almost feels/.sounds like it's got a few dead spots in the throttle ( step on the gas & NOTHING happens for a couple-3 seconds.
thus vortec is NOT impressing me at all. My '98 has 310k miles on it & it was fast as hell & unlimited power.

replace the icm. Everything you state is symptoms of a bad icm

Another thing worth checking is the catalytic converter. It isn't that difficult to pull one of the upstream sensors (remove it from the exhaust and disconnect it from the wiring harness). It's basically a free test as it takes only time (unless you break something in the process). This will leave the O2 sensor port open to allow exhaust gasses to bypass the catalytic converter. An open exhaust leak like this will be loud.

If it runs better with the sensor out, then the catalytic converter is clogged. If there is no change other than the noise level, then the catalytic converter likely isn't the cause of your issues.

This will set a code for the O2 sensor, but that code should go away when you reinstall the sensor.

What are you referring to by replace the icm?

ICM == Ignition Control Module

It is located on the same bracket as the coil.

I changed that yesterday. I've almost come to then conclusion that it's missing ( low compression in a hole, bad injector etc, etc. That would explainyour poor milege, no power etc. Any ideas?

Another question- can these blazers be de-tuned in order to comply with emissions or anything like that? My '99 is still sluggish uphill, feels like it's either surging or missing & feels as though there are "dead parts" in the throttle

I read your post and feel your frustration on having a problem and not knowing what part to replace. Here is a helpful site which is specific to GM Vortec 4.3 L V6 and tells you how to test parts rather than replace $$ them. It is Troubleshootmyvehicle.com and you then go to GM and then to 4.3L, 5.0L, and 5.7L for the Vortec engines. There you will see a index of articles for the 4.3 V6 Vortec engine. One article you may like is how to test the ICM on 95-05 4.3 engines. It also covers head light switch , the TPS test, the ECT sensor, how to test the blower resistor, the misfire by the Spider, MAP sensor test, and so on. If you read this forum, you have heard many of these complaints.

Part 1 -GM 4.3L 5.0L, 5.7L Index of Articles