Troubles after warmed up

I could really use some help on where to start on my trucks problem.
91, 2500 8 lug, 5.7, auto.
The truck runs fine when cold but terrible once warmed up a bit, it will make popping sounds under the hood on acceleration, act like it's running on 6-7 cylinders, (missing), when going down the road at a steady speed it will surge a bit.
I pulled the plugs when all this first started last week and found a bit of black fluff, (rich). Though I did check them after a short trip to the store and the engine was still a bit cold.
The injectors look to be spraying in a good patern, (no drips etc).
No codes are being thrown at all.
Since the problem changes with engine temp I figure it must be a sensor or the like but which one should I start on?
Since I'm getting popping thru the tbi under load mostly I was figuring the EGR, so which unit controls the EGR valve? MAP? if it were the o2 sensor I should be throwing a code, but then wouldn't a bad MAP throw a code as well?
I did stick my finger in the EGR diaphram area and the diaphram does move freely.
After the rain slows down today I was planning on disconnecting the vacume from the EGR just to see if this is the cause, but I'm thrown by the free movment of the diaphram.
I could really use some help on this one, am I on the right track or should I be looking elswhere?
I would appreciate any help, Thanks.

First thing that I would look at is the Engine Coolant Temp sensor in the intake manifold near the tstat housing. You can use a scan tool to see what temp it is reporting to the ECM or you can use a volt-ohm meter to read the resistance when the engine is cold and hot. High reistance is cold and low resistance is hot. The resistance table is probably posted somewhere or post the results and someone can tell you what the values are.

If you unhook the ECT sensor, and run a jumper wire between the two wires in the harness, this will tell the ECM that the engine is running warm and if the problem goes away, the ECT sensor is bad.

Another thing could be a clogged exhaust or cat. As the engine gets hot, the exhaust blocks and you can get a backfire or popping thru the TBI.

Also check the heat riser in the air cleaner housing. As the exhaust temp rises, the heat riser should close so that cold air enters the TBI. As they get old, the valve does not close enough and hot air enters the TBI. I doubt the heat riser is your issue but can hurt to check it.

//2000CAYukon

Thanks for the input Yukon, your right about the heat riser, it's not it I modified my intake some time ago and it's non-existant,
I replaced the CAT about 2 yrs ago with a highflow CATCO unit, (not to say that it's not going bad) though I also installed new exhaust and headers at the same time and have not noticed a change in exhaust pitch recently or since I started having this problem.
One thing for sure is that disconnecting the EGR did not stop the problem, so I guess thats ruled out.
I disconnected the vacume at the EGR diaphram and plugged the vacume line, with little to no imporvment after the engine warmed up.
I'm trying to get where your going with the temp sensor only in the idea that if the temp sensor were not working properly wouldn't the problem remain a constant? this is why I never even considered it,
Is it your thinking that the temp sensor malfunctioning could be sending a false reading to the ECM and the conflict in sensor input to the ECM is causing it to change timing etc.
The reason I ask this is because I have always thought and been schooled in the idea that the only time you get any pop back through the intake is when the valve train or timing is off,
This is why I'm so stumped on this problem.
I will check the temp sensor next and post back on it.
Thanks for the ideas Yukon I appreciate it.
I'm kind of in a pinch situation here and really can't do without my truck, it's the only transportation I have right now and I'm trying to get to work get kids to school and to top it off I'm in the middle of moving across town, ARGGGG!!

If the temp sensor is reporting a lower than real temp, the ECM will give it more fuel and too much fuel can cause it to pop.

A MAP that does not hold vacuum or a leaking vacuum hose to the MAP can also cause it to run rich (which can also cause the popping thru the TBI).

Good luck.

//2000CAYukon

I posted about this problem a couple of weeks ago but it has been buried because I moved and have not been able to get back online till today.
The truck is a 91, 5.7, 2500 over 8600 GVW, 4l80e.
The problem is that when the truck warms up it runs like hell, pops through the TBI, but only when warmed up and only when under a load "past 1/3 to 2/3rds throttle, at WOT it stops most of the popping through the TBI but lacks any real power.
I looked at some ideas that "2000 YUKON" had but they didn't pan out.
The CAT is clear and flowing well, , the temp sensor is operating properly, as well as the o2 sensor, "had spares" and tried them, the EGR diaphram moves freely with disconnecting and plugging the vacume to the EGR not helping the problem, "though it did set a (check EGR) code".
I checked my plugs and they have a little coating of black fluff on them, "rich".
In going through my Haynes book I noticed that the one item that controles both timing and fuel delivery is the MAP sensor, which could account for both of the symptoms I have noticed, "running rich and popping through the TBI".
Yet besides the EGR code "which I set" no other codes have set even through a variaty of driving conditions.
Shouldn't a bad MAP sensor set a code?
Does it sound like I'm on the right track?
Is there something I'm missing that controls both timing and fuel delevery?
I plan on checking the Map sensor but between the rain here in the wonderfull Northwest and working 6 days a week it's going to take a week or so before I will get a chance and was looking for other ideas of what to check.
Under light throttle there are no problems though I have noticed a some idle roughness at long stop lights lights.
Though I lean to the MAP sensor I have not noticed many reported Map sensor problems with these trucks on this board in the past couple of years I have been on here, and a search does not bring much up either.
I would really appreciate input on this.