High NOX Smog 1977 Seville Ideas

[60FlatTop]

15 hours ago, Bloo said:

Cars of this vintage normally dump air in the manifold ports most of the time.

 

They weren't expecting air to be dumped into a 45 year old converter when they built it. I would take the time to test it without the extra air going in. Especially if I was grasping for a solution.

 

Just making a list of all the assumptions could be valuable.

[EmTee]

This is an excellent discussion.  I was just thinking the other day that it would be interesting (since it's not my car and I'm not spending my money ) to have an O2 sensor bung installed ahead of the cat in order to allow sampling the raw exhaust.

[Pfeil]

19 minutes ago, EmTee said:

This is an excellent discussion.  I was just thinking the other day that it would be interesting (since it's not my car and I'm not spending my money ) to have an O2 sensor bung installed ahead of the cat in order to allow sampling the raw exhaust.

I mentioned that earlier, but you don't need to do that if you have CO-HC analyzer. You just disconnect the Cat from the headpipe / exhaust pipe and test from there. I should buy one if I ever see one that come up providing I can get all the filters and sample gas to calibrate. 

[Bloo]

6 hours ago, 60FlatTop said:

They weren't expecting air to be dumped into a 45 year old converter when they built it. I would take the time to test it without the extra air going in. Especially if I was grasping for a solution.

I have to admit I don't follow this, although shutting the air off would have been part of my normal test procedure, and would have been done, so I guess I never thought about it in quite this way. The converter itself on this car I believe is a single-bed oxidation converter for HC and CO, and requires surplus oxygen to work properly. Air is supplied whenever it is practical to do so without melting the converter, typically idle and cruise.

 

6 hours ago, EmTee said:

This is an excellent discussion.  I was just thinking the other day that it would be interesting (since it's not my car and I'm not spending my money ) to have an O2 sensor bung installed ahead of the cat in order to allow sampling the raw exhaust.

Highly recommended, although possibly a little impractical for MarkIV. I've done this to my own cars in the past as a way of checking mixture while underway (using an 02 sensor). Taking the exhaust analyzer on the road would have been highly impractical. If you have the 02 sensor bung on a car not needing it for an 02 sensor, it's easy to make a plug with a hose connection for the exhaust analyzer.

 

5 hours ago, Pfeil said:

I mentioned that earlier, but you don't need to do that if you have CO-HC analyzer. You just disconnect the Cat from the headpipe / exhaust pipe and test from there. I should buy one if I ever see one that come up providing I can get all the filters and sample gas to calibrate.

Dropping the exhaust wasn't typically practical for me in a shop setting, but it does remove all doubt. I wish every carmaker gave you a factory test port under the hood like VW/Audi used to do.

 

[Pfeil]

14 hours ago, Bloo said:

I have to admit I don't follow this, although shutting the air off would have been part of my normal test procedure, and would have been done, so I guess I never thought about it in quite this way. The converter itself on this car I believe is a single-bed oxidation converter for HC and CO, and requires surplus oxygen to work properly. Air is supplied whenever it is practical to do so without melting the converter, typically idle and cruise.

 

Highly recommended, although possibly a little impractical for MarkIV. I've done this to my own cars in the past as a way of checking mixture while underway (using an 02 sensor). Taking the exhaust analyzer on the road would have been highly impractical. If you have the 02 sensor bung on a car not needing it for an 02 sensor, it's easy to make a plug with a hose connection for the exhaust analyzer.

 

Dropping the exhaust wasn't typically practical for me in a shop setting, but it does remove all doubt. I wish every carmaker gave you a factory test port under the hood like VW/Audi used to do.

 

I realize some cars have the Cats welded in place, but the two way Cat on this Cadillac and other cars are a bolt in and so easy to do.

[MarkV]

On 4/19/2022 at 7:01 AM, EmTee said:

Yes, I've seen this problem also.  One hint I had in the past was that my '89 Silverado (TBI system) 'lost' its cold fast idle.  The sensor was always telling the ECU that the engine was warm.  It ran fine when hot, but I had to feather the throttle until the engine warmed-up, since the mixture was too lean.  Also, since this was happening during the 'open-loop' portion of the ECU program (and the sensor output was within the normal range) there was no MIL indication.  Maybe MarkV can think about this for a minute and let us know whether he's noticed any such subtle performance issues recently.

A bad coolant sensor on this era seville will prevent the car from starting they should measure 1000 ohm. I replaced both several years ago.