My stock 91 T/A lb9/700r4 has failed emissions 4 times due to HC and CO indicating a rich condition(?). I had changed plugs (AC Delco), wires(cheap), cap(cheap), rotor(cheap), pcv, o2(Bosch), oil(Mobil 1) and cleaned the k&n prior to the first test. The next test I had only changed the EGR valve and it was worse on the CO and slightly better but still not passing on the HC. In my attempt to fix it, I set the timing. I unplugged the wrong wire and screwed it up royally. After that test I reset the timing to the factory 6* base and re-tested. I have since reset the base timing from the stock 6* to 12*. By placing the timing to 12* I got better SOTP throttle response and better overall driveability.
I would rather try and fix this myself than take it to someone. I have nothing that indicates a vacuum leak (brakes are normal heater controls all work etc) and don't have a fuel pressure guage to see if I have an injector going bad or to tell you what my fuel pressure is.
Can anyone help me decipher the data? I have the whole spread sheet up on my web site http://members.***.net/swgathering/GM011701.xls in MS Excel format.


Emission test results:

1
HC 2.33 (<1.00 to pass)
CO 13.71 (<12.00 to pass)
NOX 1.92 (<2.50 to pass)

2
HC 1.84
CO 15.66
NOX 1.95

3 (screwed up timing)
HC 1.78
CO 39.44
NOX 1.52

4 (Base timing 6*)
HC 1.44
CO 21.59
NOX 0.85

TIA!!!!!:hail: :hail:

 

Are those the Firehawk rims? How much did they go for?

Nice ride BTW...

 

Yep, Ronal R-15 Firehawk's, 17x9.5. I paid about 1300$ for them, painted, from Ronal direct. They really dressed up the car. The WS-6 centercaps really helped too. Thanks for the compliment!

 

Man I want a set. Those rims make a mean Firebird look even meaner!

Pricey but definitely worth it.

 

While this will not tell you if the injectors are clogged (not likely anyway unless you fill it up with italian dressing IMO), the most common injector failure mode on 3rd gens is shorting. So, beg/borrow/steal a DDM or something that can check resistance to current. Our injectors are suppost to be around 16 ohms (I don't remember the exact figure), unplug and check resistance between the terminals on each injector. When some of mine went bad the bad ones were like 2-4 ohms. If any vary more than 10-20%, they're bad!!! I have heard from from a few people that IF A FEW ARE BAD, CHANGE THEM ALL. Two reasons--first, since all TPI cars are batch fire, the faulty injectors' cylinders will run lean and the oxygen sensor will catch the lean 'wofts' from that/those cylinder(s) and the computer will try to trim it back to normal by increasing the duty cycle and possibly beyond the injectors' capabilities and thus damage the rest of them. I heard if you exceed factory injectors rated duty cycle you do damage. Second, its nice to have a matching set of injectors, and buying individually (like I did before I was aware) can get expensive and troublesome. I think Hawk's or Thirdgenresource has sets of 8 priced under $300. When I found a few bad ones, I just changed those. Then more went bad, changed those, and finally A FEW MORE went bad, and I finally changed all the rest. Of course this may not be the problem but I hope this helps.

 

Forgot to mention, when I had 2-3 bad ones it wasn't real obvious in terms of driveability--the only SOTP difference I felt was a bit of occasional SLIGHT hesitation.

 

Not that this is solved by any stretch of the imagination, but it appears the injectors aren't clogged, but rather leaking. With the key on I'm running the standard 45# of pressure, but within 1 minute of key off, I'm down to 10#. New injectors should be here tomorrow (Accel 19#) and I'll have a better idea.

I am seeing slightly better results on my scans with a Fram (shudder) air filter and the stock 6* of timing over the k&n and 12*.

Thanks for answering the un-asked question of wether or not to change all the injectors. This board rules in regards to the technical data and assistance!

 

Well I got the injectors done last night. I ran the scanner this morning and the lowest blm registered for the entire trip was 113. I'll definitely be seeing the emissions tester this afternoon.

Thanks for all the help!