mikenj73

My HC was 297 (limit 100) and my CO% was 4.83 (limit 0.50). What could cause this? My car is a 1991 Camaro with a 3.1 V6 auto and 161K miles.

MightyFirebirdG

Hi,
i have a similar situation with my 1990 Firebird (v6 automatic)

At idle the readings are perfect:
@720 rpm, CO% is 0.023 (limit 0.50)

but at elevated idle, the CO% readings are extremely high:
@2800 rpm, CO% is 3.350 (limit 0.30)

So, my engine is running rich at 2800 rpm, but not at idle?!
The engine runs fine. However, the idle is maybe a little bit rough.

I did a little TunerPro-Session:
@idle the oxygen-sensor produces a 0.2V - 0.9V - 0.2V - ... signal (maybe a little slow).
As soon as i rev the engine to approx. 2000 rpm and above the oxygen-sensor gets stuck at 0.9V until i let the rpm drop again.

Distributor cap, rotor, spark plugs and wires are new (less than 1,500 miles i guess).
The Exhaust is new too, except for the catalytic converter.
The oxygen sensor was replaced a few months ago.
Engine oil was changed and i checked the ignition timing.

I could really need some advice here. Thanks!

Mr Froman

Air filter? How is it. Definitely start at the cheap and easy problems.

I failed BAD eight times since march. The car has run terribly rich since I bought it in 09. I did my heads but I also did injectors while they were off and BAM. Passed. It's worth checking the injectors.

Also check the converter. The inlet temp. should be lower than the outlet temp.

MightyFirebirdG

The air-filter isn't that old, but i'll check it. thanks.

I'll check the injectors as soon as i get a set of plenum gaskets. The Haynes says the injectors should have a resistance of 11 to 14 ohms. Did you mean to check the resistance or is there another method to test if the injectors are good?

What do you mean by
How can i check the inlet and outlet temperature?


What i'm wondering about is, how the CO% can be perfect at idle, but excessively high at 2500rpm.

I just took a look at my TunerPro Log, and something is weird (to me, because i'm not really a diagnostic guru ).
The BLM and INT should be really low, when the o2-sensor reports a rich mixture, because the ECM cuts back the fuel supply, right?
Well, the log says, that while the o2-sensor reports a rich mixture (950mV to 1000mV), the INT is always between 122 and 128, and the BLM toggles between 116 and 102 !?

Can this be normal?

Edit:
Just checked some things (maybe not related with the problem).
- the air filter looks fine, almost like new,
- the EVAP purge valve seems to work (can't suck on the purge outlet with ignition on),
- the MAT resistance fits the ambient temp.,
- the Throttle Body could use some cleaning,
- I checked the resistance of the EGR => 2x 25 Ohm BUT 1x 13.7 Ohm
As i understand it the EGR is to lower NOx concentration, but could a defective EGR have damaged my ECM?

So long and thanks again!

P.S. I hope my English isn't too bad.

MightyFirebirdG

OK, first some theory, why my engine would run rich:

In open loop the ECM depends on 5 sensors:
CTS, IAT, TPS, MAP, Oxygen
Except for the Oxygen Sensor i can definitely rule out the rest of the Sensors (checked them).

A too rich A/F-ratio is caused by:
1. insufficient air supply because of a clogged air filter
==> check filter, looks like new
2. too much fuel
2a fuel pressure too high
2b defective injector(s)

Additional parts involved:
- Catalytic Converter
==> since the O2 reports a rich a/f-ratio and the emissions @idle are perfect i tend to rule out the converter
- A.I.R.
==> i'm not completely sure, how it works on a 3.1l V6, but as i understand it, the A.I.R. is only active during cold start. That means there is no difference whether the engine is at idle or 2500rpm.

Did I miss anything?


Well i wanted to get my fuel pressure tested, but apparently no repair shop here (in Germany) is able to do that


So, back to my considerations from above, the most likely causes for my problem are:
fuel pressure regulator, fuel injectors, O2-Sensor

South Bay Fuel Injectors offers these re manufactured injectors:
http://www.southbayfuelinjectors.com...8_3.1_TPi.html
Are they any good? I think i read somewhere, that those are Bosch 2's. Is there any difference between Bosch 2's and Bosch 3's, respectively a reason to prefer Bosch 3's over Bosch 2's?
For a price like this, i'm seriously thinking about replacing mine anyway, since they are most likely the original ones and in there for 125,000 mls.


I really appreciate the help of this board! Thank you!


Edit:
Sorry it took me so long to post the solution.

Once I disassembled the Intake Manifold, I measured the resistance of the injectors, and it turned out, one of them had only 8 ohms.
After replacing the injectors (Ford Bosch II's from South Bay Fuel Injectors) the engine runs perfectly and more importantly I passed the emission test without any problems!
I also replaced the fuel pressure regulator diaphragm (Standard PR10), since i wasn't able to find someone to check the fuel pressure.
While the manifold was off, i also cleaned it. Looks like new now.

I guess the defective injector (8 ohms) was the cause.

And how it always is, when one problem is fixed another one appears.
During the emission test my radiator blew! But that's another story ;-)

Tanks again for your ideas and hints!!!