I know i have another thread or two open on this vehicle but im posting this one specifically in engines since now I have narrowed down the issue but not resolved it.
It is a 1987 TBI 350 rebuilt 41K ago replacing a retired 6.2L and mated to a non lockup TH350 replacing the 700r4
My issue is now with the o2 installed and working, once the system enters closed loop which is usually by 110F-120F depending on ambient temp. Idle is fine besides the one issue i will address later. I can rev to a little more than 5000RPM in the driveway and while street or mud racing. I used to be able to reach 6000RPM before i replaced the dizzy, however i DID install my working 369 module.
FP i do not think is a issue as I could tow 11,500lbs/18,000 GCVW, AND go 80MPH into a 35MPH direct headwind during a storm trying to get good footage. No hesitation no lack of power
I tried the timing at exactly 0 BTDC and o2 unplugged, i get a "kick in the pants" about 2000rpm up to about 3500rpm, my tach is a elcheapo so it has lag. i am assuming that is the 369 module since its hardly noticeable if at all with the 048 module installed.
I am currently at 3 BTDC. I get the best overall response this way, I originally timed it by "ear" and with my vac gauge to find maximum vac then back down approx 1inhg and that put me between 3-4BTDC because i cannot believe that it was a stock rebuild seeing as a 1987 block with TBi was stock limited to approx 4800RPM redline and I was hitting 6000 on a daily basis.
With o2 unplugged it will not enter closed loop but it runs just perfect at cruise and all other RPM.
With o2 plugged up ONLY at cruising throttle i.e. 5%-40% it seems to bog down, and im 99% sure it cutting fuel out thinking its rich some how but i do not have access to a scanner i can drive around with for a while. I am sure its not timing since i would think it would backfire if the timing was just being backed off then brought back to normal when i push the throttle harder.
The exhaust reeeks when this happens and even at idle, not like raw fuel but really nasty. I have verified 3 working o2 sensors all do the same thing, 1 wire OEM GM, 4 wire OEM GM, and a 3 wire Bosch all known to be good, all show the exact same values on the live readout on the MODIS snap on scanner, so i know its not the sensor.
The only issue i can think might be possibly related is a slight pitter patter out of the exhaust that sounds like an exhaust leak but i just put different mufflers on and its more "hearable" now and even more so with straight pipes, I did the dollar trick and it pulled and pushed it out very steadily not intermittently like a miss but matching the engine rpm and not variable. im thinking maybe sticking valve because i cant hear "ticking" under the hood.
What can cause this?
Is it trying to enter highway lean mode and failing horribly?
The VSS is off by about 10mph because of the new axles but it doesnt matter what speed im going.
TPS is good and smooth
CTS is good
EGR is good but currently bypassed
NEW platinum plugs, wires, cap rotor and oil 4000 miles back
Tried a brand new coil but no change
150A alternator charging at 14.5-15V for the audio system
grounds have ALL been cleaned inspected and reconnected including to T-stat housing
PCV brand new
SES light burned out but i never ever get any codes when i plug into the MODIS or MODUS i cant remember what its called
no play in throttle shaft
no vac leaks using propane or brake/carb cleaner.
17inhg at idle
MAP is good and smooth readings
knock sensor is working
NO slop in dizzy that i installed
exhaust runs right to 2 nice throaty glasspacks and dumps out so no restrictions
video readout on my youtube here:
https://www.youtube.com/watch?v=IZn_I7HXOMo this was 2 weeks ago but pretty much everything should be accurate
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