Any Techs Want To Take A Shot At This DTC45?? UPDATE--PROBLEM FOUND!!

[mosesburb]

Here's what I've got:

92 S10 Blazer 4.3L "Z" M/T 4wd
-Intermittent MIL
-DTC45 Stored
-Runs Rough at idle (often times it could be described as really rough--sometimes, not so bad)
-Vehicle bucks while moving when engine is in "float" (between power and decel) at most any speed and intermittently under decel conditions--creating nasty manual-trans gear slap!!
-Normal power
-No Smoke of any color
-No rich exhaust odor

-Fuel Pressure = 12.75 psi with normal flow
-MAP values normal (3 MAP sensors give same readings--bypassed original hose asm) Applied artificial vacuum to MAP with no discernable difference in performance.
-New HO2S (O2 values do fluctuate, but not like they should--usually in the 750mv to 900mv range--very low, if any crosscounts especially at idle--usually zero at idle) Sensor was clean--not sooted from excessive fuel
-TPS sweeps smooth (.78 @ idle)
-CTS within 2-3 degrees of actual (Raytek laser thermometer)
-Both Block Learn and Integrator are usually low (sometimes as low as 108--not always this low, varies a fair bit), but strangely Block Learn seems to change rapidly while the Integrator moves much slower. In this unit Block Learn is volatile so it resets when the key is cycled so no long term trends can be observed.
-625 RPM idle speed
-All grounds verified
-18" vac at idle (steady needle)
-Air Filter is clean
-ThermAc unit in air cleaner housing pegged open
-TBI unit re-sealed relatively recently--no seepage
-No injector drip/leakage
-Fuel pressure regulater replaced recently--no seepage
-Pickup coil ohms out at 932
-Recent ignition coil
-Recent cap, rotor, wires
-New Delco CR43TS plugs--plugs looked even and normal, not sooted from excessive fuel
-New muffler and tail pipe


-Swapped TBI unit off another (identical) 4.3L "Z" M/T truck and experienced same symptoms--no change
-O2 values go to 447mv when disconnected get good crosscounts also--Truck actually runs quite well with O2 disconnected. Still bucks when in "float" mode though.
-CKT 453 is not open
-Grounding CKT 412 drops O2 readings down to about 10mv
-Canister is not fuel saturated
-Oil changed to eliminate possibility of fuel contamination


Problem started some time ago. Been checking things out when time prermits (and when the vehicle is stationary.....Wife's truck) Nothing seems to make a difference worth noting. This is starting to get a bit aggravating as I have dumped more time than I would care to remember into trying to figure out what is going on with it.
At this point, I'm open to most any ideas.

 

[84zz4ss]

What is you egr actual value?
How long does block learn stay near or below 108?

Pm me for more.

 

[cgassett]

I'm not at work to check the books, but does that motor have a crank sensor? I dont think it does, but from what you're describing, it's acting like the vortecs when the crank sensor does'nt communicate with the ecms? Is there any arching inbetween the plugs and wires around the boots or water anywhere. Have you manually tested the plugs top see if they're good or have you just visually inspected them? I check stuff like that late at night so you can see any arching easily when it's running. I don't know, it sounds like ignition to me. All your fuell looks good from what you've told us. I guess, break out the test light and check each plug and wire one by one at the cap and at the plugs. or switch out the ecm with the person you used the tbi unit from.

 

[mosesburb]

What is you egr actual value?
How long does block learn stay near or below 108?

Pm me for more.

I haven't seen an egr actual value on the scanner, so I'm not sure what it would correspond to on my scanner (Snap-On MT2500)
Block Learn will linger down there quite awhile especially at idle. It might increase a little bit for part throttle cruise.

 

[mosesburb]

I'm not at work to check the books, but does that motor have a crank sensor? I dont think it does, but from what you're describing, it's acting like the vortecs when the crank sensor does'nt communicate with the ecms? Is there any arching inbetween the plugs and wires around the boots or water anywhere. Have you manually tested the plugs top see if they're good or have you just visually inspected them? I check stuff like that late at night so you can see any arching easily when it's running. I don't know, it sounds like ignition to me. All your fuell looks good from what you've told us. I guess, break out the test light and check each plug and wire one by one at the cap and at the plugs. or switch out the ecm with the person you used the tbi unit from.

Nope, no cam or crank sensor.
No noticable arcing anywhere. As far as the plugs go, I hadn't changed them in a few years, so I figured that it would be the easy thing to try first. So I changed them and noted the condition of plugs removed (worn, but still decent) installed the new ones and problem sysmptoms stayed the same.

Swapping ecm not an option. The TBI actually came off my truck and it uses a different style ecm (VCM).

 

[cgassett]

Go ahead and do a compression check just to cover the bases. I dont know, it's weird. I checked everything at work and verified your readings, which are within acceptable limits and it should run fine. But, just thinking about it; if it bucks when the motor is floating down from decel, I think valves for some reason. Good luck

 

[mosesburb]

I was going to do a comp test, but I figured with the steady needle on the vac gauge I was fairly safe. I took my liquid oscilloscope (79 cent leaky spray bottle filled with water) to my secondary ignition system and got a decent light show out of both the wires and coil. I decided to replace them as they were both warranty-able items. Did that and fired it up to find no change in anything, Started poking around looking for something real stupid like a screw through the firewall poking into a harness or something to that effect. Found nothing--of course. So there I stood, staring at the motor looking for anything to try or re-re-re-try as the case was. I decided to re-route the plug wires on the right bank. Re-routed them over the heater hose instead of under it, got in, fired it up and everything is perfect. Block learn is running anywhere from 122-125, integrator bounces around from low 120's to mid 130's depending on conditions, o2 bounces around beautifully, no more bucking/surging--everything works great. This thing has never run so smooth--stack the wine glasses kind of smooth. The wires were run in close proximity to the main engine control harness that runs up the right side of the intake and I guess, even with new wires, enough RF was getting into the injector circuit to jack with the pulse width creating my rich condition.
I guess I have you to thank for making me think twice about the ignition system. I figured the system was cool as the oldest parts were the plugs that I had initially changed out. Even though *technically* it wasn't the wires, it was related to them in the end. What a weird one. Thanks for the time .