Running Rich
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Heel & Toe
Joined: Sep 2004
Posts: 19
Likes: 0
Running Rich
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? 
Thanks for any help.
Mike
Thanks for any help. Mike
Racer
Joined: Aug 2004
Posts: 379
Likes: 170
From: Buffalo Grove IL
When you had the AutoXray on the car, did the fuel injection go into closed-loop mode, e.g. did the O2 sensor start "sweeping" back and forth from low to high voltage and back? Also, were you able to check the BLM values with the AutoXray?
I could definitely see the MPG reading being optimistic if the previous owner installed bigger injectors and didn't reprogram the ECM or adjust the fuel pressure down some; when I installed smaller-than-stock injectors on my 'Vette, the MPG readout was 2 MPG too low. Now that I've bumped the fuel pressure up to roughly match the stock injector flow, the MPG readout is more accurate.
The good news is that once the car gets in closed-loop mode, the ECM will read the O2 sensor and adjust the injector pulse width to get the correct fuel/air mix. So, the car would just be running rich during warm-up and full throttle.
Ben
I could definitely see the MPG reading being optimistic if the previous owner installed bigger injectors and didn't reprogram the ECM or adjust the fuel pressure down some; when I installed smaller-than-stock injectors on my 'Vette, the MPG readout was 2 MPG too low. Now that I've bumped the fuel pressure up to roughly match the stock injector flow, the MPG readout is more accurate.
The good news is that once the car gets in closed-loop mode, the ECM will read the O2 sensor and adjust the injector pulse width to get the correct fuel/air mix. So, the car would just be running rich during warm-up and full throttle.
Ben
Drifting
Joined: Mar 2005
Posts: 1,923
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From: GA
Originally Posted by MDsbch
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?
These ECM's can only do so much with a system that has been tampered with, without doing PROM work.
Can you see any casting/stamping numbers on your injectors?
Here is another biggie...If the prev owner replaced "some" of the injectors and didn't put in the correct ones.... 1985 used 24# injectors running at 36PSI...the 86-91's had 22# running at 43PSI...you CAN NOT mix and match them and if you do you'll see all sorts of crazy sheite.
Last edited by Morley; May 8, 2005 at 03:13 AM.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi.
I have an 85 4+3.
First I have heard that a leakage in the cold start injector may gmake the engine go rich. The same with the other injectors. The test is to have a pressure gauge on the valve on the fuel rail and see if the pressure falls after you have switched engine off. Then you can either overhaul the injectors or buy new ones.
The other thing is. You are talking about the Auto xray. I bought one but it do notperform and show the parameters as they are. It should be difficult to let it show the right values. For instanse it shows a water temp that is constant and totally wrong also in relation to my gauges and to other professional tools. I am very interested in hearing what you have done to get it to work all right.
I have an 85 4+3.
First I have heard that a leakage in the cold start injector may gmake the engine go rich. The same with the other injectors. The test is to have a pressure gauge on the valve on the fuel rail and see if the pressure falls after you have switched engine off. Then you can either overhaul the injectors or buy new ones.
The other thing is. You are talking about the Auto xray. I bought one but it do notperform and show the parameters as they are. It should be difficult to let it show the right values. For instanse it shows a water temp that is constant and totally wrong also in relation to my gauges and to other professional tools. I am very interested in hearing what you have done to get it to work all right.
Advanced
Joined: Apr 2005
Posts: 85
Likes: 0
From: San Diego CA
My dearly departed '86 had a litany of these problems. More often than not, it's not the MAF. First thing is to check your Throttle Position Sensor voltage; this is huge. Check Haynes or Chiltons for the range. Also, try disconnecting the 9th injector clip- this may cure it right off the bat. The relay on the 9th can go bad and fire it constantly, which leads to rich run and hard starts. Also, if you're using an aftermarket MAF, be very careful- some are not calibrated well. I would also check your coolant temp sensor (also huge) and check all of your injector connections as well. Carefully trace all wiring related to the injector rail and MAF / TPS - any shorts here can cause a nightmare.
Any burning electrical smell?
Chris
Any burning electrical smell?
Chris
