Hello again,
It's been a while but I have been hard at work on the old blazer.To refresh your memory I took a 90 s10 blazer and basically stripped it down to what ever was good then left it.I took a W engine from a 92 s10 blazer (CPFI) and rebuilt it with a twist.I have heard a lot of bad things about the CPFI system so I modified a manifold and put a TBFI system on it.Basically the engine is original and the throttle body has new guts.I installed it and got it running...after my wife painted it.While the engine was out I replaced all of the steering components.Mostly with Raybestos.Did all the body work and the wife painted it....since she did such a good job on the engine.Ok here is where it get squirrley.The engine fires up and runs fairly smooth,a lot smother than the Z.The engine is at 0 degrees TDC but want to hesitate and stumble during acceleration.The first trip out I noticed the temperature gauge was running cooler at higher RPM's then going past 260 at lower signaling the check gauges light.Shut the engine down with no overheating under the hood but it does affect power.It drops .I advanced the timing by ear to get back home.Checked it with a light.Where it wants to run good is about 6-8 degrees.Still overheats.I have replaced about everything and checked what has not been replaced to no avail.Another thing that has me stumped is the timing.Unplug the wire under the carpet and set the time to 0.Good and the mark is dead on with NO FLUCTUATION.
Plug it back in and the mark jumps all over the place.I have been using my 91 for an example.It does not do any of this jumping and it sets up at the top of the timing gauge.The blazer engine is about 6-8.Remember this has a new pump @12 psi running.New O2 sensor,knock sensor,distributor,cap,rotor,wires,plugs,heat sensors,injectors,went through 3 computers plus a whole lot more.I parked it up on a hill diagonally yesterday so the radiator (which is new also) cap was the highest point and ran it for about an hour with the cap off to burp it.Don't know if it made any difference because it didn't have enough power to drive with out hesitating and then stalling.Oh yeah to make things so much more interesting there are NO CODES.The computer is functioning because it will light up the dash light once you unplug the sensors except the knock and O2 sensors.Been over a year messing with this thing and well here I am asking for advise.

 

It does sound like it could be a coolant flow rate issue. Have you tried it with NO thermostat just to see what it did?

Never had a bleeding problem with our Blazer coolant system.

Congrats on all the hard work and having a wife that is a good painter. You will whip this thing into a good ride soon I expect.

 

Not sure if this is your problem, but when I did a 4.3 rebuild, my temperature was shooting up after starting the engine for the first time. I had topped of the radiator, but there wasn't coolant reaching the intake manifold to open up the thermostat. This caused the temperature to shoot up and light the 'check guages' light after just a few minutes of running. My solution was to take off the thermostat housing, pull out the thermostat, and pour coolant directly into the intake through the thermostat 'hole'... then replace thermostat and housing.

 

First off thanks to all for the reply's.I DO appreciate any help.
I installed a new thermostat.I thought I had goofed some how and installed the wrong one or maybe upside down.I do some stupid things when tired and cold so...it was possible.Checked and all was well.I am getting warm hoses on both sides of the heater core but not so much heat inside the cab.When I attempted the burping yesterday I noticed the antifreeze would drop down for several minutes then pop up and out ,never the flow I would expect like watching a creek or river.Also might add the pump is also new.While revving the engine up to heat it yesterday I noticed (while holding throttle study) the engine would rev itself up for a few seconds then back to normal.______^^^_____^^^.Kinda of like my grandfathers 2000 s10 when you turn the defroster on the compressor will kick on and off.Mine is disconnected so it is not that.Might add I have been taking parts off of my 91 like spar control and map ext to try on the blazer.Still no good.I do know one thing you cant use a computer meant for a cpfi in a tbfi without changing the chip.

 

Thought I'd throw in some information I have found so far.The first link is almost identical to my situation except I did not remove the cat converter.
Plus a few other odds and ends.
Hesitation and stumble on my 1988 4.3L - GM-Trucks.com

The next supports your theory about overheating .Maybe the manifold has an air bubble.
Engine Coolant Sensors
Will have to check into it probably tomorrow.It's funny I can stand out in the snow and freezing rain to tear this stuff down then spend months tracking down the proper parts not to mention the money....oh man the money to rebuild it properly with the proper gaskets and torque but I am just to lazy to go out and remove the thermostat housing.My excuse is it was to wet and foggy here in WV to see what I was doing...no that's a lie.I tried.Got my steering shaft for the 91 today.Winder how long it'll be till I get motivated to swap it out.Turn out they are from a jeep wrangler.
Oh well.Hope any of this info helps somebody else.

 

Ok guy's just got in out of the rain.Checked the manifold fir antifreeze and she was plumb full.Any other idea's ? Oh and by the way I tried to correct the word advise to advice in the title section of this but apparently was unsuccessful.

 

Well I went to take the hybrid blazer for a test drive but it still didn't act right.I once again checked the time 0 degrees...plugged the pc in and it was about 8-10 jumping up and down.You could hear a miss or surge with pc plugged in but not without.I adjusted it again by ear and checked it to find it was about 8 degrees tdc.Thought I'd try it for giggles.Took it about a mile and still has dead spot in acceleration about 1/2 down to 3/4 then hear we go with more power.The temp never went over 250 degrees F.Once we got into town it dropped down to 210.Shut the engine down and turned key on to see the gauge at 150.This was within about 30 seconds of shut down.The oil pressure it getting jumpy like my 91 so I am wondering if the instrument cluster is going goofy.What now?

 

Could there be a problem with the bigger cam not matching up with the TBFI since it was meant to be for 92 to 94 CPFI.I know there is a difference in cams from 94-95,95 is smaller with less power.Am I starving for fuel?Anyone know?

 

See the little box next to quote in posts you make?
That's what you use to post additional thoughts
__________________________________________________ ________________________

Think you may have multiple issues but first thing is to find the irregular spark advance problem.

Of the things can cause that, TPS and MAP come to mind. I would have suggested the ICM but you imply you've already changed that.
Since the base timing is steady, that rules out mechanical issues all the way to the pickup.

You may have some flaky wiring connections and/or bad grounds. Since you're running OBDI, the ECM is sorta dumb in picking up those sensors served by those ground points as 'out of range'.

 

Thanks pettyfog...hope I hit the correct button here.Not use to forum's.Love to read but about half scared to ask for advice or to advise.
Last thing I have checked was my 91.I popped the distributor off and rolled it around top TDC to check the marks on the harmonic balancer.Was told to use the second but found on my 91 it is DEFINITELY the 1ST mark you go by.I too am leaning toward wiring or connections.I'll give an example that may also help someone in time.My wife and I were in my 91 and the service engine came on and the engine started to die.This was only a flicker less tan a second.On the way home I noticed it was kinda stumbling a bit.I was thinking man the truck has almost 300,000 mile on it I suppose it's gonna die soon.Made a few stops,no problems.Told my wife to make sure we had what we needed from town in case it never ran again....HA HA.I thought.Got home shut er down(the truck) unloaded and went to move the truck and it wouldn't start.Man I should not have been joking.Thank you GOD for bringing us home.Checked for spar...good.Fuel....nea.Man the pump went out.Made arrangement to get back to town and pre ordered a new pump.My wife crawled under the dash.Hey honey do you remember smelling Bakelite.Now that I thing it...yeah.She pulls out this melted mangled fuse that had actually been on fire but hadn't popped.NO WAY.The fuse had been loose in the box for years and was corroded and the box melted and had been on fire.We cleaned and replaced what needed and an hour or so later it was running again.GM has had bad connections for years.Just have to find them.