1987 TBI 350 wont enter closed loop EVER!!!!

[MuddiGGEr25]

Ok, so i think i figured out my issues after reading hundreds of more pages regarding the Integrator and BLM values, and yada, yada, then I went back to my recorded video of the live data output on the shop snap on scanner. i noticed the 02 only really varies 430-451mv, it is always in open loop even at 208F, the knock counts are ridiculous. my BLM and INT both stay at 128, which from what i have read is caused by the O2 not letting the PCM head into closed loop.  my MAP was saying 8-9in but my manual gauge is reading double that, i cant believe i didnt see that before. I am gonna try to find my other MAP I had extra around and then record the data readout again on monday after i punch out. But before I start on my data recording on monday.


1. Is it true that it cannot enter closed loop without the O2 sensor reaching a preset temp/mv reading? its not original exhaust and it is very possible that the sensor is cooled off by that point. I will check sunday afternoon to see if it is a lazy O2 or wideband. i thought i saw 3 wires but cant remember.

2. VSS input, the PCM/ECM whatever you want to call it, its got a spot for it, did the 700R4 in 1987 have a VSS for the ECM? and if so will that control the open/closed loop at all? and even if it does not, can I get a VSS module for my TH350 and eventually change out my dash with all digital speedo & gauges?

3. After I get it to enter closed loop, the A/F learned should switch to YES, and my knock counts should be almost gone after it "learns" the block correct?

4. If all above are corrected, then I should get 100% performance back from the PCM after a few drives? assuming my used pump is in fact good.

[a.graham52]

I may be wrong due to only having heavy experience in 2000 plus but.... can u flash any codes? What are your fuel trims? +-5 long term is a fair place. ASSUMING your knock is NOT caused by out of wack fuel trims fom a bad o2, bad knock could potentially keep ecm from going into closed loop.however I would suspect you o2 to bounce between 90 and 1000mv In or out of closed loop. Those o2s are wicked cheep, I would start there if it was me

[MuddiGGEr25]

I may be wrong due to only having heavy experience in 2000 plus but.... can u flash any codes? What are your fuel trims? +-5 long term is a fair place. ASSUMING your knock is NOT caused by out of wack fuel trims fom a bad o2, bad knock could potentially keep ecm from going into closed loop.however I would suspect you o2 to bounce between 90 and 1000mv In or out of closed loop. Those o2s are wicked cheep, I would start there if it was me

no fuel trims on readout, too old, its a 1987 data stream.  and i just looked around underneath and realised that the o2 has the wires ripped out and the nearest "plug" in the as shown below appears to be wired for a 3wire heated 02. but was not connected to anything

so im not even sure what o2 i should be looking for

[bd]

That image looks more like the TCC connector for a 700R4 transmission.  As delivered from the factory, the '87 used a single-wire, narrow band O₂ sensor mounted in the left exhaust manifold and connected to the harness via a single-wire Weather Pack connector.  If you have headers or modified exhaust, it's not a bad idea to upgrade to a four-wire sensor, so both the sensor and its heater have separate dedicated grounds.  The O₂ sensor needs to heat above ~600° F to function.  The further it is from the "collector" the less responsive and accurate it is, both because of cooling and time delay.

[jg1977c20]

correct it will not enter closed loop without a proper functioning o2 sensor

[frotosride]

If I get a chance to show you the O2 plug I will post a pic but it literally runs right behind the left bank head, down the bell housing. It will be very close. To the shift linkage and rod.

[brandon6469]

I went to a 3 wire sensor since I have long tubes and my truck wouldn't go into closed loop.  Put the old sensor back in and worked perfect again.

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[MuddiGGEr25]

just to end this thread, I did find the purple wire on the passenger side wire loom and just ran a wire right from the o2 to that and now after a little bit of idling it pops right into closed loop, even without the heater circuit. no idea what that harness is for though that i took a picture of, maybe AIR or A/C


I have a new problem now on a new thread now that i am in closed loop


here is a video of the readouts after i entered closed loop if it helps someone in the future:

https://www.youtube.com/watch?v=IZn_I7HXOMo