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Discussion Starter #1
1985 S3 - L-Jet.

I have been running the car with very rich mixture, I suspected the reason was a faulty Fuel Pressure Regulator. I replaced it along with spark plugs, new vacuum hoses...etc. At this point my Cat glows really red hot, and the car buck. I what thinking of using Lucas Fuel Inject cleaner... to possibly help the fuel injects and the rest of the engine, before i replace the Cat Converter.

What do you guys think about the Cleaner??
 

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I use Techron on occasion but more as preventitive maintanence than trying to fix anything.

The Lucas stuff probably won't hurt but not likely to help, either. A glowing red cat is likely partially plugged - restricting exhaust flow.

If the O2 sensor is of unknwon vintage I'd replace it & make sure the mixture issue is fixed then replace the catalytic converter (otherwise the continued rich mixture will poison the new cat).
 

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Injector cleaner does work to some extent, but I doubt it's going to fix your problem.

The cat converter glowing is just a symptom of rich running, not the cause. You need to fix the root cause problem. If you replace the cat now, all you're going to do is burn out the new converter.

The simplest cause for what you're experiencing would be one of your cylinders not firing. If that's not it you need to figure out why it's running so rich.
 

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Discussion Starter #4
I use Techron on occasion but more as preventitive maintanence than trying to fix anything.

The Lucas stuff probably won't hurt but not likely to help, either. A glowing red cat is likely partially plugged - restricting exhaust flow.

If the O2 sensor is of unknwon vintage I'd replace it & make sure the mixture issue is fixed then replace the catalytic converter (otherwise the continued rich mixture will poison the new cat).
Understood!!...I did replace the O2 sensor with a bosh unit. The only think i can think of doing at this point is to deal with injectors. So that is why I thought it could be a quick start.

I ran the car for few mile and the CAT gets very glowing. However I checked the new Spark-plugs and do not seem to build up the carbon on them.

I am so troubled.....i can't figure out the problem. Grrrr!!!
 

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Discussion Starter #5
The simplest cause for what you're experiencing would be one of your cylinders not firing. If that's not it you need to figure out why it's running so rich.
I will check on that, but based on the spark plugs, they all show very similar burn marks. Actually they seem better than before (less Carbon buildup).
 

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I had the same problem. Although the CAT on my Alfa was cut out and replaced with straight pipe. I found that #4 cylinder was not firing. Fuel Injector was completely shot. Also a vacuum leak was causing it. The Vacuum sensor located behind front passenger seat near the ECU. I removed it, and capped the hose at the intake plenum.
 

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Discussion Starter #7
I had the same problem. Although the CAT on my Alfa was cut out and replaced with straight pipe. I found that #4 cylinder was not firing. Fuel Injector was completely shot. Also a vacuum leak was causing it. The Vacuum sensor located behind front passenger seat near the ECU. I removed it, and capped the hose at the intake plenum.
What did that do? Can you give me more details on the fix you found for your problem? Where is this vacuum sensor by the ECU (I know of the altimeter sensor).

In my case all 4 spark plugs show same black buildup....amazingly identical. so i think they are all firing....
 

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After 30 years, it is about time to have all the injectors rebuilt and re-hosed. Cruzin Performance in CA did mine at a cost as I recall of about $130.00 a couple of years ago. OK Injuction will also do this rebuilding. If you send all the injectors in for a rebuild/rehose, they will tell you if you have any which need to be replaced entirely. If you make this invesment and replace all the other fuel hoses you encounter while you are in there, it will be a great future investment in safe and quality motoring in your Alfa.
 

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Discussion Starter #10
After 30 years, it is about time to have all the injectors rebuilt and re-hosed. Cruzin Performance in CA did mine at a cost as I recall of aboout $130.00 a couple of years ago. OK Injuction will also do this rebuilding. If you send all the injectors in for a rebuild/rehose, they will tell you if you have any which need to be replaced entirely. If you make this invesment and replace all the other fuel hoses you encounter while you are in there, it will be a great future investment in safe and quality motoring in your Alfa.

Thanks for the suggestion, I had my done as well about 18 months ago.


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If your injectors/fuel rail was recently rebuilt, you can probably eliminate that. We are having several issues with our '85 spider abd considering a Weber conversion. These cars are 30 years old and given the number of sensors and connections, it does not take much for the system to be out of spec. I'll bet when the L-Jet system was new it was unbeatable for a stock "sporting car", but just like us, we wear out.
 

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The vacuum sensor is located under the carpet on the side near the wheel well. it has a vacuum line and a plug. Unplug it and cap the third hole(the one on bottom) of the intake plenum facing the rear of engine compartment. Not saying it will cure your woes, but helped me with erratic idle issues and vacuum leaks
 

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Discussion Starter #14 (Edited)
Could the flywheel sensor be the reason my car is running rich? Following the l-jet document, I notice that the Flywheel sensor (gray color) is measuring 39 M ohms ( see picture).

Could this sensor (gone bad) affect the fuel mixture ? Somehow??

Any inputs from the experts???

ImageUploadedByAG Free1428178310.762731.jpg

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Discussion Starter #16
I agree with you. However before "investing" $100.00 on this sensor I wanted to understand its function as it relates to my rough engine run. I am trying to understand why my car is running rich.



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An expert I am not, but have done much research regarding our Bosch injection systems. From what I understand both flywheel sensors are "switches" that tell the ECU the timing (position of #1 TDC) and engine speed. I would probably think your rich condition is not caused by either flywheel sensor.
 

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Discussion Starter #18
What I am thinking is that, if the sensor has a timing function related to the firing spark, it could be off timing just enough to create an un-burned fuel mixture.... I could be reaching here (that is why I am hoping someone could provide me some details).


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A flywheel sensor does "NOT" need replacing. They either work or they are busted and the car would not run if busted. If the car runs they are fine. It's just a transformer, your meter may be giving you bogus readings. If the cat is original maybe it time for a replacement FLOWMONSTER http://flowmonster.com/search.html?q=415200 Got one in my 82 and it's the smallest and fit under the heat shield. The other thing you can look at is your AFM and see if it was messed with. It's the only unit that can be adjusted for fuel mixture. I've been checking a bunch in my Milano for a friend of mine and adjusting them to make the car run smooth.
 

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Discussion Starter #20
Alfarule...clearly the reading on the sensor shown in the pic is an indication of a sensor gone or going to be gone shortly. The meter I used in the second sensor in the car measure 1005 ohms. So the meter is good and the sensor is bad. My question relates to the affects of the nearly or gone bad sensor in the fuel mixture.

I thank you for your input.



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