1993 Chevrolet Blazer running thread

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Originally Posted By: RF Overlord

It's also possible when they put in the new motor they somehow damaged the O2 sensor wiring...check that before you waste $70 on a new sensor.


Good idea but IIRC there's a seperate "no signal" code. Yet OBDI can be pretty dumb.

Also if grease etc clogs the part of the o2 sensor where the wire goes in it can ruin its "Fresh air reference".

But remember, because the o2 indicates lean exhaust, that could be a legit report from a good sensor of problems in the upstream fuel metering or air intake.
 
Originally Posted By: eljefino
Originally Posted By: RF Overlord

It's also possible when they put in the new motor they somehow damaged the O2 sensor wiring...check that before you waste $70 on a new sensor.


Good idea but IIRC there's a seperate "no signal" code. Yet OBDI can be pretty dumb.

Also if grease etc clogs the part of the o2 sensor where the wire goes in it can ruin its "Fresh air reference".

But remember, because the o2 indicates lean exhaust, that could be a legit report from a good sensor of problems in the upstream fuel metering or air intake.


But his emissions test showed the opposite: that the exhaust was actually rich.
 
Originally Posted By: TechnoLoGs
The car runs so good with the paperclip in.. aside from blinking SES light, it ran almost as if it was fixed! Why?


Placebo
 
Originally Posted By: TechnoLoGs
The car runs so good with the paperclip in.. aside from blinking SES light, it ran almost as if it was fixed! Why?


It stays in open loop with the terminals jumped.
 
Originally Posted By: Warstud
Disconnect the battery and leave it disconnected for a half hour.


Disconnected 4:30PM.

What does this accomplish?

And.. open-loop?

I seem to notice that it doesnt rev up as much, and the RPMs are more in sync with the transmission, feels more power.. !!! The SES light just blinks a lot, and sometimes shuts off...

I will Google it too, but, what does Open Loop mean? I left paperclips jumpered. May be onto something until I can go places to get it checked out and 02 sensor changed..
 
Wait a minute.. it bypasses the 02 sensor when it does.

Quote:
Closed loop mode means the engine control module (ECM) measures the A/F (air/fuel) ratio and uses this information to maintain the A/F ratio at a certain constant value. This mode uses feedback from an (oxygen) O2 sensor to close the loop. The A/F that the system tries to maintain is 14.7 to 1. The reason is that a 14.7 A/F ratio allows a catalytic converter to reduce exhaust emissions most efficiently. Engines don’t necessarily run the best at 14.7 at all times, but they produce the least emissions with a catalytic converter at this ratio. Also, it just so happens that the standard O2 sensor is most accurate at 14.7 A/F ratio, which gives a good feedback signal.

The bottom line is that the ECM control logic tries to maintain a 14.7 A/F ratio during normal conditions. Normal conditions are a fully warmed engine and other than full throttle. Because of closed loop, engines can run for thousands of miles and the EFI system will compensate as the engine wears to keep fuel delivery consistent.

Open loop mode differs from closed loop in that the O2 sensor is ignored and the engine can be managed to run at A/F ratios other than 14.7, usually richer or lower than 14.7. The ECM controls the fuel injectors without getting any feedback that the calculated fuel delivery rate actually matches what the engine received. Without feedback, the loop is open, hence the term "open loop". A good example of open loop is when the engine is first started on a cold day. It requires a rich mixture to start a cold engine since a lot of the fuel doesn’t reach the combustion chamber. This is because a portion of the gasoline doesn’t vaporize and pools inside the manifold until engine heat vaporizes the fuel. Another reason that engines run in open loop when cold is that O2 sensors don’t work until they reach about 6008 F, so it takes a few minutes in cold weather for them to begin functioning. Open loop is sometimes used at idle conditions since some engines idle better with a rich mixture. In open loop, the ECM commands an A/F ratio that is determined from a table of A/F vs. engine coolant temperature. The open loop A/F is also adjusted to run richer as MAP increases.


Open loop mode differs from closed loop in that the O2 sensor is ignored

I see the light. Also smelling less exhaust!

http://carprogrammer.com/Z28/PCM/FAQ/How GM Electronic Fuel Injection Works.htm
 
Originally Posted By: bullwinkle
Might want to take a look at RockAuto-your $70 Denso O2 sensor is under $27 + shipping there.


Omg... IT SURE IS!!!

Emission : Oxygen Sensor
DENSO Part # 2343094 OE Style
[Flag indicates this part fits vehicles sold in the US Market. It does not indicate where the part was made -- manufacturers produce parts in multiple factories worldwide.] [Flag indicates this part fits vehicles sold in the Canadian Market. It does not indicate where the part was made -- manufacturers produce parts in multiple factories worldwide.] UPSTREAM
$28.79 1 $28.79
Subtotal $28.79

Buying now!!!!!!!!!!!

Oh,m and my battery resting voltage is 12.8V.
 
I don't believe it - you listened to advice, Googled for information and made an informed decision.
 
Okay, we have a confirmed code for lean exhaust.

Let's now look at several possibilities, and see what we can rule out:

First off, a bad O2 sensor can cause a lean signal.
You would need really expensive equipment to check the O2 sensor, and a replacement is cheap enough, it might not be worth trying to test if it's bad when it's easier just to replace the sensor.

Second cause of a lean code would be an intake leak.
Any point between the throttle body and the O2 sensor can contribute to a lean code. A lean code simply means that the computer sees more oxygen in the exhaust stream than it can adjust (richen) for.

Third cause of a lean code is an exhaust leak between the point where the exhaust manifolds attach to the cylinder head, and the O2 sensor.

Now, Technologs....

Does your truck have an exhaust leak?

If you answer yes to this question, you should fix the exhaust leak.
It will also help not poison you with exhaust fumes when you drive the truck, so it's like a two for one bonus.

BC.
 
Originally Posted By: Bladecutter
Okay, we have a confirmed code for lean exhaust.

Let's now look at several possibilities, and see what we can rule out:

First off, a bad O2 sensor can cause a lean signal.
You would need really expensive equipment to check the O2 sensor, and a replacement is cheap enough, it might not be worth trying to test if it's bad when it's easier just to replace the sensor.

Second cause of a lean code would be an intake leak.
Any point between the throttle body and the O2 sensor can contribute to a lean code. A lean code simply means that the computer sees more oxygen in the exhaust stream than it can adjust (richen) for.

Third cause of a lean code is an exhaust leak between the point where the exhaust manifolds attach to the cylinder head, and the O2 sensor.

Now, Technologs....

Does your truck have an exhaust leak?

If you answer yes to this question, you should fix the exhaust leak.
It will also help not poison you with exhaust fumes when you drive the truck, so it's like a two for one bonus.

BC.


His emissions test showed it was running rich. The ECM thinks it is running lean. That's a pretty good case for a baffed O2.
 
Quote:
Now, Technologs....

Does your truck have an exhaust leak?


This, I do not know. I did have a shop offer to do a "smoke test" to find out. (Since maybe it was running rich enough to smell exhaust on a normal system, as the windows were always down? It SEEMS maybe decreased since I did a gallon and a half of "water cleaning" through brake booster. Could be inaccurate, though. Though I *think* I smell less, and felt less woozy.)

And do we have a pretty good case for 02 sensor change?
 
You don't need some fancy smoke machine to check for exhaust leaks. First of all, you can usually hear a leak pretty easily. Is the exhaust loud at all or sound not-totally-muffled in any way? You can find a leak easily by just putting your hands near the pipe and feeling any gases escaping. I feel like I shouldn't need to say this, but I will: Do this when the exhaust is cold. Start the truck, crawl underneath, and start feeling the exhaust pipes, particularly the joints. If you feel gases blowing on your hand, there's your leak. Start from the exhaust manifolds and work your way back. And work quickly; you'd be surprised how fast the exhaust gets hot. But keep in mind you don't have to actually touch the pipe, just get your hand near it. Feel all around on all sides of the pipe.
 
exranger -- I just missed your post.no disrespect, but do you think it's wise to tell techno to crawl under his truck, while running, to check for exhaust leaks ? remember, this is techno.
 
Originally Posted By: RobertISaar
INB4: my oil looks like chocolate milk/mayonaise.


It does not, though some water seems to have come from mid-pipe?

I was just in it, I smell some exhaust at lights.

Head gasket is in order and it still has a slight misfire somewhere (again we think timing) but less surge/lope of an idle than before.
 
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