Woah... my cheap Harbor Freight vacuum gauge gives me 17-18 "hg(increases from 17 to 18 on a cold start as it warms up). The gauge holds rock steady.
So I did the conversion and that is 57.5 to 61 kpa. I am read a consistent 35kpa at idle. I pulled the MAP and applied some non hardening silicon to the seal in case it had a vacuum leak. No change.

So, even a cheap gauge can't be that wrong. I'm going to start with a new MAP sensor and see what happens. That totally explains misfires causing it to retard timing as well as running rich.
As soon as the part shows up I'll post up what happens. Troubleshooting and diagnostics is my major weakness with vehicles so this is a big help.
I hope my struggling can help someone else with their future diagnosing.

Edit:
So I did some reading and was disappointed. Someone said the sensor is based on absolute and a gauge is atmospheric. So after factoring that in my readings are not that far off. That brings MAP readings up to 19.6 inHg and gauge reading the 17-18. So now I might go ahead and pick up the wires and see what that does. I almost got a new MAP sensor but now I'm not sure if that is the problem. Sure explained a lot if it was.

Edit:
Wire change does not seem to change anything. The old ones were in rough shape though.
I disconnected battery cable following wire change and watched timing advance during startup. It dropped right to -20 degrees "timing advance". It actually measured lower engine vacuum following this so maybe that will come back as soon as it settles in with fuel trim. I did not recheck with the gauge to verify.
Now I only wish I could see knock counts.

 

Well I think I better break down and start with the fuel system testing. I'm sure that's what the smart guys on here are waiting for. I've been in denial up to this point and maybe thought it didn't make that big of a difference.
I found a thread with the same timing issue in a 95 Blazer on another site but it ended with "problem solved, I traded it off for something else."
I thought that guy was wise beyond his years except he got a 95 Suburban instead. Doh!

 

Since it's staying cold I'm going to start with just dumping injector cleaner in the system and see if it gets any better. I was starting to think about replacing the ignition coil but now I'm starting to think either the injector or poppets are sticking open at times.
I've been thinking about it today and I am wondering what has kept anyone from putting the old style TBI intake on these crappie CPI engines?
MAP sensor can be reused.
Distributor is kept.
TPS would need the connector replaced as well as the IAC.
EGR would be the holdup but there are ways around that.
The TBI uses 2 injectors and I am not sure the PCM driver can handle that. A driver could be made to use the original signal to run two injectors.
Finally the pump would need replaced or another regulator to step down the fuel pressure.
Sure putting in a new spider is easier but the new setup would be bulletproof.

I dumped in a home brew of Seafoam, acetone and naphtha into the tank so I'll see what idle quality does after this tank gets run through. Weather is below 30 for the next 2 weeks so it has to at least make it another month.

 

Well, this thread might be closing earlier than I thought. Started up great at 4* this morning and idled smoother than ever when it's this cold. Tomorrow at -5* will be the next test.
There were maybe half as many coughs/misfires and I could hardly hear them.
Exhaust volume was noticably quieter as well. I have found that in rich conditions the exhaust volume will increase. Might not be in 100% of all cases but so far it's been that way for 2 of my vehicles.

I'll let this tank run through and see what happens. I added 4oz. of Seafoam, 2oz. of Acetone, and 2oz. of Naphtha to a just filled tank. Let it idle for a minute and shut it off.

 

Sounds interesting, keep us posted.

 

Startup at -3* was pretty good. It did go back to it's old ways for a short time during warmup.
So far it has had mostly just idling and short drives. The coughs/misfires are not as harsh but overall it's better. I might try changing out the ignition coil next. I pulled the coil off my TBI car because it's the exact same thing. If it works I can pick up a new one for the car. After that I either need a new spider or pull this one out and see if there are any obvious problems.

 

Fuel pressure test at filter: pressure went to around 90 and dropped to 65 after 10 minutes.
I also disassembled the CPI spider injector which is such a simple thing. Everything seemed pretty clean but I'm not sure about the spray pattern from the poppets. I put 60 lb of air to each one and it looked like a stream of fuel instead of a spray. Of coarse it's different when it's not pulsing though.
Hopefully it starts this morning since I never tried starting it after doing all that.
If its not better I'll just pick up a spider since that's about all it can be.

EDIT:
Cold start off-idle hesitation is gone. Startup and drive at 25* was smooth and it did not hesitate once. Idle was smooth but it did throw a code probably from trying to start with an empty spider injector.

If I ever take the spider apart again I'll get pics and make a writeup. I suppose cleaner could be run through individual poppets by means of a syringe and some tubing to connect them.
Overall it is in rough shape but I'm not going to call it quits until it quits. Considering the price of a new injector and each individual part I can see how they run $150-$300 for a new assembly. I found that it was mostly covered in the brown fuel varnish and I just cleaned it up as much as I could with Naphtha. I don't think the plastic liked it very much though.

 

Blegh. Not 100% fixed. I give up. Good enough I guess.

 

TZFBird These are the clips you need.


Kent Moore J 34730 230 Poppet Nozzle Test Devices 6 Six New Testers | eBay


Jeff.


If this guy does not come through let me know. I have twelve.

Self addressed stamped envelope and I will send the # you need, just don't suck me dry. There hard to find.

 

So how do they work? I'm not understanding how to watch them if they are inside the manifold. I guess it would be possible to kill the ignition but that just causes flooding.
It's getting better no doubt about it. I still have an exhaust leak most likely before the "cat".
The hesitation feels like lean tip-in which one poppet leaking would cause a lean condition on the other 5. If it does not get better after a couple more tanks running more cleaner I'll think about ordering some of those to help with troubleshooting. It runs 100% better now than when I bought it a couple years ago though. Every time I fix one thing another problem shows up.
Sometimes I wish I knew what how a Blazer should run so I have something to compare it to.

Maybe I should disconnect the battery to clear fuel trim with the dirty poppets so it can start over.