Now, Emissions, was: Conundrum: Pressurized air in fuel rail. How?
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Originally Posted by Bill Ball
Argh. MAF, O2 and cats and no better. What else can cause a very lean condition?
Poor fuel flow
All eight injectors misbehaving in the same exact way.
The Evil Eye....
What else?
A gross intake air leak would be another possibility but it should cause idle issues. Still, looking for things like the breather line falling off the right side of the MAF boot, or a hole in that line, would be worth checking.
It's not clear whether the air/vapor in the rail was a red herring. I think someone already asked if you found the same thing on a cool engine, which would make that more interesting.
Originally Posted by 928saregreat
Guys, are you using the same test facility each time? Could there be a problem with their equipment? It might be useful to get an independant check to be sure. Especially if the fuel economy is improving.
Originally Posted by ZEUS+
It is possible that the high flow cats are not getting hot enough to lower NOX. Some high flow cats are good from a performance aspect, yet not totally emission efficient.
#48
Burning Brakes
To reduce the NOx the cats need to see a rich mixture, that is why the A/F is suppose to swing back and forth between rich and lean. The emission results seem to indicate that the cats are working, just they are only working on the oxidation side (getting rid of the HC and CO) and not on the reducing side (to get rid of the NOx). Is the air pump putting to much air into the exhaust resulting in a "lean" exhaust mixture even though the combustion chamber is not really leaner than intended? This may have all been covered but I just thought a new voice in the mix might open a new thought process.
#49
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Dave:
You can borrow the LH out of one of you cars. Any of them should work fine in the 87. Heck, you'd even gain the ability to use a Spanner.
I'd attach your A/F meter first and see if the A/F mixture is cycling as it should. You probably know it won't do this until the sensor warms up - just a couple of minutes. But then it should cycle from rich to lean extremes about once a second at idle or cruise. If it's not cycling, then I'd swap the brain.
It would be worth running the car for a short while and see if you still get the air/vapor in the fuel rail without heating the rails much. Since the smog test is done with the hood up, I can't see the rails getting heat soaked, so you have to see this vapor phenomenon at lower temps for it to be a factor in the test.
You can borrow the LH out of one of you cars. Any of them should work fine in the 87. Heck, you'd even gain the ability to use a Spanner.
I'd attach your A/F meter first and see if the A/F mixture is cycling as it should. You probably know it won't do this until the sensor warms up - just a couple of minutes. But then it should cycle from rich to lean extremes about once a second at idle or cruise. If it's not cycling, then I'd swap the brain.
It would be worth running the car for a short while and see if you still get the air/vapor in the fuel rail without heating the rails much. Since the smog test is done with the hood up, I can't see the rails getting heat soaked, so you have to see this vapor phenomenon at lower temps for it to be a factor in the test.
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Originally Posted by ZEUS+
Cats usually need a short break in period to become familiar with the gases. Usually after the smell is gone they become efficient.
Originally Posted by Bill Ball
You can borrow the LH out of one of you cars. Any of them should work fine in the 87.
What I don't have is a known good MAF except in one of my cars. My spare is core worthy only. Apparently rebuilt MAFs are as scarce as honest politicians right now.
Heck, you'd even gain the ability to use a Spanner.
I'd attach your A/F meter first and see if the A/F mixture is cycling as it should. You probably know it won't do this until the sensor warms up - just a couple of minutes. But then it should cycle from rich to lean extremes about once a second at idle or cruise.
Anyway, in my test I did see the voltage (multi-color LEDs if you've not seen the ARM1) cycling from almost-full-lean to almost full-rich. I noted that the cycle time seems to be proportional to RPM; Slower cycle time at low RPM and dancing along at 3k or so. Display shows full lean during overrun (throttle off engine braking) and full rich at WOT. So, I think it works. I can see how the a/f ratio is related to what I'm doing with the throttle.
It would be worth running the car for a short while and see if you still get the air/vapor in the fuel rail without heating the rails much. Since the smog test is done with the hood up, I can't see the rails getting heat soaked, so you have to see this vapor phenomenon at lower temps for it to be a factor in the test.
If it's not cycling, then I'd swap the brain.
In essence: how can you distinguish between the a/f ratio being constantly too lean (except at WOT) and a brain with a fried o2 control loop? With a bad LH will the output be nearly-constant? And with too lean dancing around degrees of lean?
#51
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If the O2 is cycling above and below .5 volts it is usually doing its job. Computers are always shooting for stoichiometric efficiency. In a perfect world we would always see .5 volts. Sensors can be lazy and not respond quick enough. A false signal from the 02 could force lean or rich conditions. You can try focing the system lean by creating a large vacuum leak. 02 should have low volts, .1 to .2. Then try forcing the system rich by spraying carb clean in a vacuum hose. 02 should have high volts .8 to .9. 02 should respond quickly to these tests. Just an easy 02 test.
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Originally Posted by ZEUS+
You can try focing the system...
So, I'm thinking that if, with this '87, I can get some positive indication, as you describe, that the 02 sensor (should be new) is doing anything then:
1) Any periodic cycling of the a/f reading would indicate that the LH is trying to do something. If the a/f is cycling in the lean range (0.0 to 0.4 volts) then the motor's running lean.
2) If I see no cycling then the LH is suspect.
In this case, it will be a good idea to test, on the failing '87, continuity and resistance from the 02 connector black wire to pin 24 of the LH itself.
3) If I see normal cycling of the volts and indication of 'centered' cycling around 0.5 volts then I shoot the motor in the head...
Observations will of course be made with the car driving down the road under light to moderate load that recreates something like the dyno environment.
#53
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QUOTE :What I don't have is a known good MAF except in one of my cars. My spare is core worthy only. Apparently rebuilt MAFs are as scarce as honest politicians right now.
>>>>>>>>>>>>
Hi Dave,
928 Intl carry my rebuilt MAFs . They have stock.
>>>>>>>>>>>>>>>
Quote:
Heck, you'd even gain the ability to use a Spanner.
Theoretically yes. Since the 87s have the 7-pin (IIRC) connecter, my spare '91 LH would give a little help.
>>>>>>>>>>>>>>>
12 way recatngular.....
Your idea to check out the O2 loop is good. O2 loop is only active after engine gets to normal water temp.
>>>>>>>>>>>>
Hi Dave,
928 Intl carry my rebuilt MAFs . They have stock.
>>>>>>>>>>>>>>>
Quote:
Heck, you'd even gain the ability to use a Spanner.
Theoretically yes. Since the 87s have the 7-pin (IIRC) connecter, my spare '91 LH would give a little help.
>>>>>>>>>>>>>>>
12 way recatngular.....
Your idea to check out the O2 loop is good. O2 loop is only active after engine gets to normal water temp.
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Originally Posted by John Speake
928 Intl carry my rebuilt MAFs . They have stock.
Your idea to check out the O2 loop is good. O2 loop is only active after engine gets to normal water temp.
#55
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Yes, if 02 is getting extra voltage there will be the false signal forcing it lean as I suggested. This just would not coincide with the emission test results HC will be higher.
#57
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It's unlikely there would be a small "leakage". Either the wires touch so O2 output shorted to ground or 12v. To have a high impedance path to have a reduced voltage needs something to give the high impedance path between the two (bare) conductors.
You would need something burnt (i.e. carbon deposit) or some conductive gloop or other to achieve that...
If no LH cycling, knowing O2 sensor is new, and wiring to LH proven as OK, then yes, LH is suspect.
You would need something burnt (i.e. carbon deposit) or some conductive gloop or other to achieve that...
If no LH cycling, knowing O2 sensor is new, and wiring to LH proven as OK, then yes, LH is suspect.
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Originally Posted by ZEUS+
This just would not coincide with the emission test results HC will be higher.
The way it makes sense to me is: Let's say the 02 sensor is reporting 0.5 volts (stoich) but, because of a partial short (say 0.2 volts for discussion's sake) through the damaged harness the LH is seeing 0.7 (rich). Then the LH will drive the mixture leaner until the 02 sensor reports 0.3 volts (lean) and the LH sees 0.5 volts (stoich.) So because of the postive voltage offset the LH is controlling the mixture to a lean condition rather than stoichiometric.
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Originally Posted by John Speake
It's unlikely there would be a small "leakage". Either the wires touch so O2 output shorted to ground or 12v. To have a high impedance path to have a reduced voltage needs something to give the high impedance path between the two (bare) conductors.
You would need something burnt (i.e. carbon deposit) or some conductive gloop or other to achieve that...
You would need something burnt (i.e. carbon deposit) or some conductive gloop or other to achieve that...
If the pin 24 of the LH is shorted to 12 volts rather than the 02 sensor's signal then the LH will most definitely believe the motor is running rich.
#60
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Yes, if burning is evident, then leakage is possible. But you only mentioned bare copper - abrasive damage ?
I would thing the screen on the signal wire is more to protect against interference signal pickup. But yes, it is a sensitive signal wire.
Let us know what you find.
I would thing the screen on the signal wire is more to protect against interference signal pickup. But yes, it is a sensitive signal wire.
Let us know what you find.