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 My car is running rich

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Chevy freak '91

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PostSubject: My car is running rich   Fri Nov 03, 2017 5:20 pm

During tech inspection, I found out that my car is running very rich. I smell gas when my car is idling. My car starts ok, runs great, acceleration is fine. So, what do I need to check or replace first?
Or must I buy a OBD1 scanner? Does anyone wich scanner works best? There're several for sale on Ebay.
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Fred Kiehl

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PostSubject: Re: My car is running rich   Fri Nov 03, 2017 9:31 pm

You can cross the two leads in the under dash connector, and it will produce the codes with the SES light. It blinks 1, 2, twice, than the codes in two digit numbers. Follow the instructions in the FSM.

If it is electronic, it could be your O2 sensor, or the ground at the right of the thermostat adapter.

It could also be the fuel pressure regulator. None of these, except for the O2 sensor would throw a code.

If you buy a code reader, it will short the two pins when you turn it on. A couple of alligator clips on a wire will work just as good, and cost a lot less. [You must be registered and logged in to see this link.]
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sat Nov 04, 2017 4:50 am

Thanks for the tips. One of my friends has a OBD1 scanner and we are going to check my car tonight. Hopefully this will makes clear why my car is running that rich.
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Fred Kiehl

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PostSubject: Re: My car is running rich   Sat Nov 04, 2017 9:15 am

Do not drive it very much or you will ruin the cat.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sat Nov 04, 2017 11:25 am

I don't have the cat anymore, so no worries. Is there way to just adjust the mixture, so that will not run that rich anymore? Or is that not possible with our type of engines/carbs?
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sat Nov 04, 2017 6:05 pm

So, I've scanned my car tonight. Scanner didn't work so I used the paperclip methode.
I got two codes: number 12 and number 23.
Number 12 is: 'Electronic `brake Control Module (EBCM) fault. I have to check this one but it doesn't relate to the rich running of my car.

Number 23 is: 'Left front outlet valve fault' and that does fits my symptoms of running rich. I have to figure out what this means or needs to be replaced.
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Fred Kiehl

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PostSubject: Re: My car is running rich   Sat Nov 04, 2017 11:06 pm

12 means it works, and is not an ABS code. 23 is the IAT sensor. The Intake Air Sensor is located on the toaster on the passenger's side. The wiring may be at fault, or it could be the sensor. Check the wires from A on e sensor connector to A11 on the ECM (ground), and B on the sensor connector to C12 on the ECM. You can also check for 5 volts on B, and ground on A. Those are only active during RUN. You can also check the sensor (if you can get it out of the toaster). Temperature of 210F 100C (boiling water) will give you 185 ohms, 160/70 450 ohms, 100/38 1800 ohms, 70/20 3400 ohms, 40/4 7500 ohms (approximately refrigerator temp), 20/-7 13500 ohms, 0/-18 25000 ohms, -40/-40 100700 ohms.

You should also check all of your vacuum hoses for leaks. You might even replace all of the vacuum hoses as a preventive measure on a 26 year old car.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 5:38 am

Thanks for the tips and info. I'll go and check. If the sensor is broken, is the one I need to order?
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Just doublechecking, because when I search on Google images, I get a lot of different sensors.
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Fred Kiehl

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 8:32 am

Here is the Rock Auto part, it is the same for the 5.0 and 5.7: [You must be registered and logged in to see this link.]

You can use the code on the forum to get a 5% discount.
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lakeffect
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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 8:39 am

If the IAT is not functioning, by default, the ECM assumes it is -40, and therefore adds lots of fuel since atomization at -40 is so bad. In other words, it thinks it needs to choke the hell out of the engine by adjusting the ail/fuel ratio from 14.8 down into single digits, like 5 .

The old sensor is easy to test with a multimeter set to ohms. The reading will vary with temperature. Simply attached the meter leads to the sensor. Note the reading at first. Pick it up, Your hand heat will change it. So will an Icecube, or a cup of hot water..

I am having the same issue. The sensor is Fine, but the ECM is not seeing the signal.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 1:04 pm


Just to make sure, because I see several sensor at Rockauto.
Do I need this one:


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Last edited by Chevy freak '91 on Sun Nov 05, 2017 1:07 pm; edited 1 time in total
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 1:06 pm

Or do I need this one:
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Chevy freak '91

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 1:13 pm

And this is the one I need to replace, right?

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Fred Kiehl

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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 1:51 pm

That is the correct one, but you may or may not need to replace it. Check it for operation before you buy one. It could be the wiring.
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lakeffect
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PostSubject: Re: My car is running rich   Sun Nov 05, 2017 3:39 pm

Like I wrote above, all you need is a ohm meter to test a change in resistance as it warms or cools. Probably one of the simplest test that could be done.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Mon Nov 06, 2017 4:27 pm

Ok, but if want to replace the sensor. Do I need to reset the ECM? And how do I do this? Or will my car automatically resets itself?
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Fred Kiehl

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PostSubject: Re: My car is running rich   Mon Nov 06, 2017 11:31 pm

The ECM will read the new part, and if it has the right output, the computer will use the information. You should clear the codes before using the car. You can unplug the computer fuse, and wait 1-2 minutes. If the condition still persists, the part was not the problem, and you wasted some money. If you do not unplug the computer fuse, the code will persist for about 20 restarts, unless the ECM still sees the issue.

It makes sense to check the operation of the sensor, especially an easy one like this.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Wed Nov 08, 2017 4:28 pm

I've replaced the sensor just to rule this one out. I did what you told me about resetting the ECM.
But now I've code: 32 when I ran the diagnostic. [You must be registered and logged in to see this link.]

This code can be 32 and has also the symptom of rich running...
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Fred Kiehl

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PostSubject: Re: My car is running rich   Wed Nov 08, 2017 11:45 pm

That may be your real problem. The MAP sensor is not expensive, and it is easy to replace.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Thu Nov 09, 2017 5:40 pm

The code 32 says:

Baro Sensor Circuit Error (Carburetor only)

EGR circuit Error

Map Sensor Signal Open


So, what do you think? The MAP sensor? Maybe a stupid question, but does my '91 Chevy Caprice with a 305 V8 has a caburator? (That would rule out the Baro sensor Circuit sensor)
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Fred Kiehl

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PostSubject: Re: My car is running rich   Thu Nov 09, 2017 8:53 pm

The car has a TBI. The MAP sensor is on the edge of the cowl. Two screws, and a vacuum hose removes it. The vacuum hose may be cracked/broken as well, or even a fitting.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Mon Nov 13, 2017 3:55 pm

Ok, I've ordered a new MAP sensor and hopefully my problems are over. So, you don't think that it's the EGR or Baro sensor?
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rauldelp

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PostSubject: Re: My car is running rich   Mon Nov 13, 2017 7:03 pm

I think in our case the MAP sensor "is" the Baro sensor. It basically tells the computer the load on the engine.

EGR has always thrown a code for me. Or if it causes a vacuum leak it runs terrible at idle or idles at 1500+rpm.

Easy way to test would be to unplug the MAP sensor electrical plug (not the vacuum line, that'd cause other issues) and see if the car runs the same. If it runs the same, the MAP sensor is shot.
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Chevy freak '91

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PostSubject: Re: My car is running rich   Mon Nov 13, 2017 7:31 pm

Thanks, I did that test. I unplug the MAP sensor and my car just kept running so It was a good idea to order a new MAP sensor.
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