Im lost! 1986 S10 Blazer ..

[SLO_GTO]

Hello. So heres the story.
1986 Chevy S10 Blazer/ 2.8L TBI V6 / 5spd / 4x4 ..

Truck starts, runs, and idles somewhat smoothly at approx 800RPMs.
According to my OBD scanner, the following is happening with truck @ idle:
Throttle sensor : .88v (voltage rises as accelator pedal pressed)
MAP sensor is reading around 2.6v
Oxygen sensor is reading around 450-500mVolts. When engine warms up, the O2 sensor does not fluctuate, from high to low, yet fluctuates somewhat
The ECM is staying in open loop.
Rich/Lean flag: Instead of switching back and forth, it reads Lean constantly. However, tailpipe its running very rich, leaving tailpipe black on the inside.
ECT sensor is reading functional.

When I rev up the engine, it seems minorly hesitant. When I try driving it, Im forced to rev high, and slowly let out clutch to get it moving. Once its moving, when I press accelator, it bucks, and Im hearing popping from intake.

I have tried swapping out ECMs from a good working truck, and no change. New plugs, new fuel pressure regulator. I tried replacing the oxygen sensor, but believed it to be faulty, as it was constantly reading 475mVolts (which I believe is a set value from ECM), and was more static in readings, then old one. Fuel pump and both injectors was replaced not long ago.

Im stumped and grabbing straws.

edit: new MAP sensor, not more than a couple weeks old. Also, there is no valve on fuel lines to check for fuel pressure. I plan on checking spark timing tomorrow.

[pocket-rocket]

Popping in the intake would tell me you have an intake valve open when it's not supposed to be. I would start looking at your cam timing. You also might be right with the O2 sensor since it's running rich but the ECM says it's lean.

[SLO_GTO]

Update: Just put timing light gun on, checked out OK.
Installed another O2 sensor as well.
The engine is internally mechanically fit. I believe the popping may be do to lean mixture? The tailpipe is coated in black (carbon im assuming) and smells like fuel. (yes, I know that sounds contradicting)

I really wish I had a way to connect fuel pressure gauge.

Does anybody know how to adjust the TPS? Im unsure of what voltage its suppose to begin with. The car is MAP equipped. Would a car buck due to bad TPS setting, or would it buck under load due to lack of fuel.
Reason I ask, is I was fooling with it, and now I get a SES light, code 13. O2 Sensor failure, which could be somewhat connected to TPS.

Thanks

edited to change some details

[robertisaar]

o2 and TPS are related?

[pocket-rocket]

You could have your cam timing off, yet have the dizzy turned enough (or off a tooth on the gear) to compensate giving a correct spark advance with a timing light.

Was this something you bought that was like this from the get go, or did it just start doing it one day.

[SLO_GTO]

Just started the other day. This truck belongs to a fellow work colleague. I took his truck home from work one day, to install some exhaust hangers and fix a small leak. I did the exhaust repairs, and when I pulled it out of my garage bay, the truck cut off and died.
The diagnosis began there. First thing, I checked for fuel. Fuel was there, but faint. Unplugged one of the injectors, got it run for a bit. Turns out, it ran out of fuel.
Added fuel, about 3 gallons. Truck cranks, and starts now, but under load (trying to drive it), Im getting not enough fuel, which is causing the pops in intake.

As of right now, I adjusted the TPS to .50 volts for idle. I am getting no SES light.

Robertisaar- According to my Haynes manual, a code 13, it says: "Oxygen sensor circuit: Check for a sticking or misadjusted throttle position sensor."

[robertisaar]

god GM, can't make up your mind what to label trouble codes....

i'd look through the source to see the exact conditions for it, but it isn't a priority anymore...

[pocket-rocket]

I wonder if one of the fuel injectors is stuck shut. I've had vehicles that had bad fuel pumps have injectors get stuck shut till I took them out and banged them into the side of my bench some because the owner kept trying to start it with no fuel pressure. What stumps me though is it running really rich (where you can smell it and it's coating the inside of the tail pipe black) meaning it can't be injectors stuck shut... Now, I am just thinking and typing what I think instead of erasing it. Maybe this will get some more minds turning on the problem. Has the owner ever had a problem like this before?

[SLO_GTO]

Update again (plus a free bump ) :

Just road tested, with my scanner hooked up.
First off, both injectors are working and spraying accordingly.
After letting it sit @ idle and warm up, I noticed a few things:
The computer finally entered Closed Loop... the O2 sensor voltage was switching High to Low like its suppose. It was switching from Rich to Lean every 2 seconds are so. I have set the TPS to .50v.
IAC meter seems to be working (however, somewhat unrelated).
The road test seemed to of went somewhat fine, maybe only one "pop" happend. However, I noticed the computer kept switching in and out of open/closed loop. The Rich Lean check, it wasnt switching back and forth so often, more rich then lean. And while driving, the O2 sensor seemed to of stayed at around 700+ mVolts.

My road test only consisted of maybe 1/2mi drive, I live on a small street that dumps into a 45mph street, so I didnt want to take it on a main road.

[robertisaar]

you also have a C3 ECM that only pushes out a full stream about once a second...

that could be why your rich/lean flags seem to stay rich more often than lean...

as for open/closed loop. it probably switches to open at low throttle and then goes closed when you are on throttle. if it goes closed/open at a steady speed, something is wrong.

EDIT: also, most if not all C3 ECMs add spark in ALDL mode. in both $42 and $4E its 8*. not sure why they chose to do this but.... whatever.

did you happen to look at your knock counter during this?

[SLO_GTO]

Also, just got off phone with owner. Here what I found out:
When I picked it up, the MAP sensor was unplugged. He says, when its plugged in, it would start, idle would drop, and cut off.

When I was trying to figure out its issue (when it ended up being out-of-gas) I noticed a vac line unplugged, that led into charcoal canister.

Maybe this leaked caused something to occur with his stalling issue, I dont know, but as of now, the MAP is plugged in, and Im getting no codes thrown out, and the truck idles just fine.

I replaced the cat-back exhaust not too long ago.

[SLO_GTO]

Knock sensor was saying something around 20

[robertisaar]

did he drive it with MAP unplugged? that would explain why the O2 was acting funny...

[SLO_GTO]

Yes, drove it with MAP unplugged.
I just installed a brand new O2 sensor (that makes 3 in total I have tested on this truck).

I drove it to my house, about 23mi with this unplugged, you could definatly feel the lack of power, but on the drive home, I was still able to make it, besides lack of power, and god awful smell of rich mixture.

I tried unplugging the MAP and the other vacumm line, just to see if I could let this truck drive back to where I got it, but no dice.

This is not my truck, and it needs to go, I got too many other projects (twin turboing my GTO, repairing rust on my truck, and fixing problems on my 93 GTP).
I live @ home with my parents, and they wanted this truck off our property few days now, LOL. Im thinking I need to tow it back to where its from, and let owner worry about it.

However, was hoping theres something Im missing here, and unfortanly, I feel this burden was left on me. The owner is a good guy, but if somebody borrowed my vechile, and bought it back all busted, I wouldnt be a happy camper neither!
So .. back to the discussion!

[robertisaar]

unplugging the MAP, the ECU goes into a worst-case scenario mode and richens the mixture a LOT. thats kills O2 sensors almost as fast as leaded gas...