Regulator before MAP sensor??
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From: Elverson, PA
Regulator before MAP sensor??
OK - here's my problem. I put a low pressure air regulator in the line before my map sensor and I'm still getting the ses light. I used my air compressor set to about 35 psi to set the regulator to right around 20-22 psi - so that's all the map should see. Now since I'm still getting the light I'm assuming that the gauge on the regulator is off a little and it is still seeing enough boost to trip the light. Now my question is - will it hurt the performance if I set it too low and the map sensor would never see boost over, say 15 psi?? I'm not real clear on what the map sensor actually does or controls?? I don't want to set it too low and mess something up. Thanks!
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From: Cabot, Arkansas
The MAp sensor can trigger the SES light at anything abouve 4.7 volts. Usually this equates to 24 psi, but can occasionally be lower. The stock fuel map supposedly tops out at 16-18 psi, so as long as you can get the light off between 18-24 you should be ok.
The other possibility is that you are not getting the SES light from overboost, but rather from excessive backpressure. It triggers the light in exactly the same fashion as boost.
The other possibility is that you are not getting the SES light from overboost, but rather from excessive backpressure. It triggers the light in exactly the same fashion as boost.
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From: Elverson, PA
Thanks Cookie - I never heard of the excessive backpressure before - I didn't know there was such a sensor. Does that mean a problem somewhere or is it like the map sensor setting the light? Is there a way to get a round that too?
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From: Cabot, Arkansas
I never heard of the excessive backpressure before - I didn't know there was such a sensor.
If that is the problem there are a couple of approaches. The first is to remove the sensor and clean the carbon off the end, and clean out the sensor's tube with carb cleaner and compressed air. If that dosen't work then replace the sensor....but it is stupid expensive for no more than it does. The third is to eliminate the sensor. There is only one source for the sensor elimnator that I am aware of. SP Diesel click on "exhaust backpressure" in the left hand menu.
I had a similar problem a while back, kept getting the SES light through the valve. Put a mini regulator and the backpressure switch eliminator on at the same time and haven't had a light since.
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Thanks for the help Cookie - I'm off work today for rain so I had a chance to pull the truck into my shop and play with my regulator. I turned it down a little and took it out for a run and didn't get the ses light anymore without any performance difference, so I guess I found the sweet spot on the reg. I couldn't run it too hard on the wet roads but I guess if I start getting the light again I'll know its the backpressure sensor. A quick question - what does the backpressure sensor do or control? Is it just another input to the computer? And what would it do if that would be setting the ses light?? Sorry for all the questions but like I said before I never even knew about it!! Thanks again for the help!
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The Exhaust Back-Pressure sensor is a variable capacitor sensor that is supplied a 5-volt reference signal by the PCM and returns a linear analog voltage signal that indicates pressure. The Exhaust Back-Pressure sensor measures the pressure in the RH exhaust manifold. This sensor is used in conjunction with the exhaust back-pressure regulator to form a closed loop exhaust back-pressure control system.
The exhaust back-pressure is controlled by the PCM to provide more heat to the coolant for cab heating when ambient air temperature is below 7°C (45°F) and engine oil temperature is below 75°C (167°F) during low load, low speed operating conditions.
An open or short in the Exhaust Back-Pressure sensor wiring will result in a low out of range voltage at the PCM, and the PCM will disable Exhaust Back-Pressure control.
The exhaust back-pressure is controlled by the PCM to provide more heat to the coolant for cab heating when ambient air temperature is below 7°C (45°F) and engine oil temperature is below 75°C (167°F) during low load, low speed operating conditions.
An open or short in the Exhaust Back-Pressure sensor wiring will result in a low out of range voltage at the PCM, and the PCM will disable Exhaust Back-Pressure control.
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