Running Rich

[mdsbch]

I'm still fighting a problem with my 85 running rich. I have replaced several components - MAF Sensor (because I was getting code 33), EGR, MAT, O2, Rotor/Cap/Plugs/Wires, and even a vacuum line that was leaking. I did notice when checking the gas mileage that the MPG coming from the ECM computer is showing 22 to 23 MPG, but when I divide it out it is only 18 to 19 MPG. Could it be possible that a previous owner installed larger injectors but didn't re-program the ECM? Could this cause more fuel to be injected into the cylinders than the ECM thinks it is injecting, causing it to show a higher computed MPG and also running rich or would the ECM automatically correct for this? I've also hooked it up to an autoxray and monitored the O2 sensor and it is around 600 to 800 most of the time and the rich/lean flag reads rich most of the time. Am I correct in my thinking here or has the ECM gone bad? :confused Thanks for any help.

Mike

 

[Moonunit 451]

How do you know it is running rich? Not trying to be silly, just curious. Are you running the original wheels? If you've got 17's that could explain the milage difference, also your speedo will be off

 

[Vettefan87]

The on board dash average mile thing is not accurate unless you reset it at every fill up. Mine gets about the same in the city as yours. Pull a plug and see if it is wet, if it is you are running rich. If your ECM was bad I don't know how your car would run. The milivolts on the O2 is fine, but I am not sure about it running mostly rich. Mine did that when I hooked it to a scantool, then twenty minutes later it went from rich to lean under driving conditions, but at idle stayed mostly rich.

 

[mdsbch]

I am assuming it is running rich because of the following: When it is idling it has a strong smell that sometimes causses your eyes to burn a little, I replaced the mufflers in the fall and ever since the insides of the tail pipes have been black, and the catalitic converter got red hot over the winter, so I replaced it and trashed the new one in about 5 minutes after I started it the first time. I checked the injectors for leaks as per the Helms manual and they held pressure, so I don't think I have any leakers. I ran three cans of BigRed fuel injecter cleaner through in three consecutive tanks of fuel to see if it would help and it didn't. I am however; running 17" wheels, but would this make that much of a difference in the gas mileage difference. Right now I am running with a test pipe in place of the converter, but would like to put a new one back on to be legal, but am afraid to until I am sure it is not running rich. :confused

Mike

 

[Jeb]

I would have thought that a lean condition, not a rich one, would fry the converter.

Also......how's your base timing?

 

[mdsbch]

Timing is at 6 BTDC and the TPS is right at .54 volts at idle. When I returned the Cat to try and get another under the waranty they told me that I had a fuel problem because it reaked of gasoline and wouldn't honor the waranty. This is also what makes me think it is running rich.


Mike

 

[Edmond]

It's possible that you're having injector issues. If they are the originals, they are 20 years old and they're bound to have problems. Many members here have had their injectors rebuilt or have replaced them.

 

[Vettefan87]

Yeah a real rich condition will fry the cats. When you said you checked the injectors did you check the resistence? That is what you need to check then go from there.

 

[Edmond]

I also believe that when you're running rich and if you pull the plugs, they will be very black in color.

You'll have to pull each plug individually to check them.

It is possible that the injector(s) could be staying open longer than they should.

I believe Rich Rubel used this place to rebuild his injectors: www.cruzinperformance.com I hope I got that site right. If I did get it right, check them out, their website is quite detailed. I think it's $12-15 to clean/rebuild an injector?

TPIS: www.tpis.com also works on fuel injectors.

 

[WhalePirot]

Could it be possible that a previous owner installed larger injectors but didn't re-program the ECM? Could this cause more fuel to be injected into the cylinders than the ECM thinks it is injecting, causing it to show a higher computed MPG and also running rich or would the ECM automatically correct for this? I've also hooked it up to an autoxray and monitored the O2 sensor and it is around 600 to 800 most of the time and the rich/lean flag reads rich most of the time.

Yes, all of that is true. A cam change can also cause rich running, as can other things that lower manifold vacuum. The easiest would be to ask the previous owner what was done to the car. Do you have normal vacuum at idle? Is the fuel pressure set at stock specs? I'd not get into the injectors beyond what you've done. The ECM will reduce fuel as much as it can, but it has limits. Your's may be 'bottomed out'.

has the ECM gone bad?

A bit early for that conclusion. You are right to do the basics and troubleshoot before throwing parts at it.

I doubt the fuel economy display is all that accurate anyway and hardy a good troubleshooting tool. Do you really care if it's right on?
mike

 

[WaveDoggie]

Check fuel pressure and MAF relay.