[Alfa-Born]

I finally replaced several hoses on my 1985 S3 and it appears that the rich condition as gone away....cat no longer glows. Also despite the reading on the flywheel sensor, the car starts right up...no hesitations.

However today as I was test driving the car I noticed that the car when reaches 2900rpm it cuts off or it seems to stall (or choke). If I stay under the 2900 the car cruises awesomely. I was thinking fuel pump (s) but at least the main Pump feels that it kicks strongly to the touch...when the key is turned.

Can you guys give me some input?

Thank You!


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[Gubi]

So that red glow was your cat converter seriously overheating. Unfortunately one of the things that can happen when you dump a lot of fuel into the cat converter is that the internal substrate can melt and block off exhaust flow. In bad cases you can even get chunks of converter clogging the exhaust downstream of the cat. So it's entirely possible you need to replace the cat converter (and maybe clean out the exhaust too) at this point.

If this does turn out to be the problem, make really, REALLY sure you've solved the rich mixture problem before replacing the cat. Otherwise you'll just nuke the new cat converter same as the old one.

 

[Alfa-Born]

Gino thanks for the heads up, I am not ready to pull the trigger at a new cat until the car runs normal. However I am prepared to make those upgrades.

Do you know what could be the issue with this RPM cutoff?? It's repeatable to the mark at 2900 rpm.


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[Gubi]

Yes, the tachometer could be really far off and you could be hitting the rev limiter. You can verify with an external tachometer.

I had assumed this was a new issue after the cat problem, but if it was doing it before it could very well be the tach.

 

[Jim G]

If you remove the cat and you look down the hole and it doesn't look like a really fine honeycomb then the cats bad. You can gut the cat. ie take out the material in the cat and put it back on and see how it runs.

 

[Alfa-Born]

Would a clogged cat allow the car to be driven to a certain RPM (say 2900)..??? I think it may be more a fuel issue or electrical, but I do not not for sure. I know that this car has two pumps and maybe one is not working.


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[Jim G]

Would a clogged cat allow the car to be driven to a certain RPM (say 2900)..??? I think it may be more a fuel issue or electrical, but I do not not for sure. I know that this car has two pumps and maybe one is not working.


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Yes it can because its creating a blockage in the exhaust. Also with the cat glowing red from the mixture being to rich is how they get damaged inside.

 

[miami592]

Fuel pumps/filters/strainers?

Are your fuel pumps making any noises like humming? Have you changed the fuel filter as of late?

The reason I ask is that I've been having similar issues with my "89 S3.

I replaced the in tank fuel pump, which had no strainer attached and replaced the fuel filter as well, which contained something that looked more like brake fluid than gasoline.

At that point it ran much better, but still has a drop in power after 2000rpm once warmed up. My in-line pump is still humming so I have a new one on order, thinking that is the next logical step.

Hope this helps-M5

 

[Alfa-Born]

Issue Solved...YEAAAHHH !!!!

The Cat. is fine, the car now run very well. I replaced the RPM sensor on the transmission Bell Housing and the car did not cut off (as it did consistently at 3100 rpm).

On a day like today, I will wash the car and go for a spin on my Alfa Romeo.

Thank you all.