Stupid car, why is it running rich at idle

Really need some help here.
My 92 348 is running rich at idle, very rich, it stinks pretty bad at idle.
Here is what I have done

- I am %100 sure there are No vacuum leaks
- my fuel pressure regulators where leaking, I changed those (both) and the smell has been cut in half. That's not saying much it was just killer before
- two new bosh direct plug in O2s
-195f/90c thermostat.
-tested the evap solenoids both are fine.
-no check engine lights, I did get a slow down light for 5-8, but it's running so rich I am not surprised. ( I am also sure it's killing the cats, hell they may already be toasted)

- previous owner did, plugs, wires, fuel pumps, fuel filters, coils, injectors. He was trying to fix the hard start when hot issue., but that's was fixed by the new fuel pressure regulators.

The car starts, idles, revs, drives perfect other than the smell.

I went to tune the MAFs by using the voltage from the O2s, but no matter what adjustments I make to the MAFs I see zero change on the O2s. the readings I get are 750s for one side and 850s for the other. 450 is stoich, 900 is rich. This leads me to believe the car is stuck in closed loop idle, trying to richen up the mixture for some reason.
The fans work properly, come on and off as needed, to me this means the coolant temp sensors as working fine, no?

So what the hell, why are the ECUs dumping fuel? This car is really pissing me off!

 

Are you positive the injectors are spraying correctly? It would be advisable to pull them and test each one for a given time period and measure the amount of fuel from each one.

Also, put a fuel pressure gauge on the rail and pull the vacuum line to the regulator. pressure should increase by 5-10psi.

Only thing I haven't seen you do is replace the MAF or even switch them side to side. You should see one or even both cats extremely hot if it truly dumping fuel.

 

Bad maf.
Read plugs.
Swap mafs.
Replace bad one.

 

Thanks, I will check the fuel pressure.

I am not convinced the injectors or the MAFs are the problem because when I try to tune the MAFs by unplugging the O2s and measuring voltage, it makes zero difference what I do to the. MAF ( both MAFs are set to 385, and the values change when I turn the screws)To me that means the ECU is stuck in open loop.
The car has two coolant temp sensors, is one used to trigger the fan, and one used to check coolant temp for the ECUs? Or is one used for each ECU for coolant temp ?

 

Will one bad MAF cause both banks to run rich?

 

No. Have you looked at the spark plugs?
A bad maf can still read correct ohms.

 

No, very MAF is connected with it's side ECU.
How do you know both banks are running rich?

There are 2 coolant temp sensors located under the intake plenum. They send coolant temp readings to it's side the ecu. If one or both are going bad and sending wrong readings, your ecus will not know what temp the engine is running, and the ecus could rich or lean the A/F. There is another coolant temp sensor that controls when the radiators fans turn on and off, and it has nothing to do with the others.

As I supose that you reset the ECUs by disconnecting the battery for some minutes, I wonder if the ECUs could have stored the codes when the FPRs were leeking (and maybe the car was running lean, so ECUs tried to rich up). I really don't know if this codes use to be stored, but you could try pulling the codes, and deleting if you find them.

 

I had the same issue and found a purposely installed obstruction (round plastic piece with a pin hole in it) where the fuel return line connects to the fuel block.

 

Cool thanks for the info! I going to pull the plugs today. I will also trying unplugging both MAFs start the car and see what happens

 

Awesome thanks! So even though the fans are working those temp sensors can be bad
I bought two yesterday, that is job one today!

I did reset the ECUs already, I should have checked for codes first. I also let the car idle through 2 fan cycles without touching anything so it could relearn

As for knowing how both banks are rich, I followed this procedure
http://www.ferrarichat.com/forum/348-355-sponsored-bradan/202083-how-set-maf-screw-accurately-motronic-2-5-a.html

And both O2s are reading high 700s low 800s when 900 is rich and 450 is stoich.

 

What! Awesome I will check that! Thanks!

 

Car won't start with mafs unplugged

 

Doh haha

 

Where abouts is that?
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Jeff has a 355. It's different.

 

Ah cool, rats thought he was onto something!

 

A few things to consider here.

1)
At first start up the ecu's will go to full enrichment. This is to get the cats to "light up" faster. It stays in full enrichment until the coolant temp gets over 140ºF. Secondary enrichment is between 140ºF and below 176ºF. The Motronics will continue to enrich the air fuel ratio, be it at a lesser value, until the car gets up to full operating temp. Once the engine gets constantly over 176ºF THEN it goes to normal mapping.

So......if you are trying to adjust the MAFs BEFORE the engine has gotten to it's full operating temp you are just beating your head against a rock. Let the car get up to full consistent operating temp before you try to make any adjustments.

2)
Based on the above comments, if your coolant temp sensors are worn/going bad the Motronic ECUs won't get the correct values, and thus won't be able to correctly adjust the fuel mapping.

3)
What condition are your catalytic converters in? If your cats are worn out, or if you are running straight pipes, it will stink something nasty. There is nothing to clean up any remaining fuel that didn't get burned up in the combustion process.

4)
Your cam timing will affect the low/high speed mixture. If your cams are setup with more over lap that can cause some of the incoming mixture to get into the exhaust stream. The cam timing for cars with cat has 22º of over lap, while Euro non cat cars have 23º of over lap, and the Competiziones have 24º of over lap. Then, are your cams advanced or retarded? What kind of ignition timing is the mapping in your ECUs running? All these things affect not only how power is made, and what rpm the power comes on at, but they also affect the emissions of the engine. If your cams, and ignition, are timed for power higher up in the rpm band, chances are down low you aren't gonna be running as clean.

That's my 5¢ worth.

 

Awesome
Info thank you!

1 - after installing the new thermostat the car sat at a constant 90deg, I let it go through 4 cycles of the fans. Sucker was hot when I checked the O2s. Oil was also at normal temp


2 - I really hope that's all it is! I have two sensors and will be tackling it shortly

3 - really not too sure how the cats are. If I can get the O2s to show anywhere near 450 I will try the etest again and see what the numbers are.

4 - really not too sure how the cams are setup. I am going to do the engine out this winter. I'll try a bit more messing around to get it to pass, otherwise out she comes for a complete overhaul and I'll try the etest again next spring

 

Which thermostat did you go with?

 

He said he went with a 195ºF t-stat.

 

https://www.rockauto.com/catalog/moreinfo.php?pk=100542&cc=1284993

$7 from rockauto, $20 locally eesh.
From a 1980 VW rabbit. It says 54mm in diameter which is the same as the x19 one. I saw a post from Ernie that said 54mm was too small, it was a smidge loose in the ferrari gasket but she seems to fit and work fine, so it might be a bit bigger. Could not find my callipers to measure.
I did have to drill a 1/8 inch hole on it, as it does not have one.
Here are a couple of pics
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Pic
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Another, sorry on my phone. Was going to make a separate post for it once I took a test drive
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I think the coolant temp sensors did it
Also the new thermostat makes a huge differnece too. The car drives so much better now that it sits at 90deg all the time. Even tonight with the outside temp being 10c it stuck right at 90.
Going to try the etest again tommorow and see how it goes.
Will report back with numbers
You guys are awesome !!!

 

Thanks Rob! Good to hear she's running well again.