Engine Stalling at Temperature: Development of a MAP Sensor failure
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Joined: Aug 2007
Posts: 668
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From: Austin TX
Engine Stalling at Temperature: Development of a MAP Sensor failure
I had created a couple of posts requesting help in a couple of different heat related issues in my LT1 that resulted in the replacement of the Manifold Absolute Pressure or MAP Sensor.
It started out as a stall or cough, “one time”, at approx. 180-181*F coolant temperature as the engine was warming up. This was in September, at approx. 90*F ambient temperature. This was happening every day. At this time, I was not getting any SES Service Engine Soon lights.
Reply’s on the Forum were pointing to the Opti and low resistance in the fuel injectors. Fuel injector tests were good and having my Opti checked would have been my last resort.
As the ambient temperature in Texas dropped to below 50*F, the symptom’s changed. Five seconds after starting the engine in the morning, I would get a SES light on the display. The engine would run rough and would sputter at 1300RPM’s. When the coolant temp would reach 122*F, the SES light would go out, the engine would stall, and then the engine would run great all day until a cool down overnight. Then the episode would repeat.
A check of the codes revealed a code 34 indicating a low signal sent from the MAP sensor to the ECM. Initially, the input, output and ground of the MAP sensor tested good. Troubleshoot Charts indicated an issue with the ECM, low compression, or low fuel pressure. Since it seemed to be a heat related issue, I tried heating up the ECM with a heating pad in the morning for about 30 minutes with no effect in symptoms, thereby eliminating an ECM issue.
I moved the heating pad to the MAP sensor and applied heat for about 30 minutes. I found as long as I kept heat on the MAP sensor up and past a coolant temperature of 123*F, the SES light would not illuminate. I rechecked the MAP sensor at 38*F and observed an input voltage of 5.2VDC and an output of .03VDC. While my meter was still hooked up to the MAP sensor, I heated the sensor with a heat gun. The result was that at some point in heating it up, the voltage jumped to 5VDC. Seems the sensor needed to be at a stable 122*F or above to pass the voltage, which would indicate a intermittently failed MAP sensor.
I replaced the MAP sensor and the problem was solved. It turns out to be the evolution of my failing MAP sensor.
It started out as a stall or cough, “one time”, at approx. 180-181*F coolant temperature as the engine was warming up. This was in September, at approx. 90*F ambient temperature. This was happening every day. At this time, I was not getting any SES Service Engine Soon lights.
Reply’s on the Forum were pointing to the Opti and low resistance in the fuel injectors. Fuel injector tests were good and having my Opti checked would have been my last resort.
As the ambient temperature in Texas dropped to below 50*F, the symptom’s changed. Five seconds after starting the engine in the morning, I would get a SES light on the display. The engine would run rough and would sputter at 1300RPM’s. When the coolant temp would reach 122*F, the SES light would go out, the engine would stall, and then the engine would run great all day until a cool down overnight. Then the episode would repeat.
A check of the codes revealed a code 34 indicating a low signal sent from the MAP sensor to the ECM. Initially, the input, output and ground of the MAP sensor tested good. Troubleshoot Charts indicated an issue with the ECM, low compression, or low fuel pressure. Since it seemed to be a heat related issue, I tried heating up the ECM with a heating pad in the morning for about 30 minutes with no effect in symptoms, thereby eliminating an ECM issue.
I moved the heating pad to the MAP sensor and applied heat for about 30 minutes. I found as long as I kept heat on the MAP sensor up and past a coolant temperature of 123*F, the SES light would not illuminate. I rechecked the MAP sensor at 38*F and observed an input voltage of 5.2VDC and an output of .03VDC. While my meter was still hooked up to the MAP sensor, I heated the sensor with a heat gun. The result was that at some point in heating it up, the voltage jumped to 5VDC. Seems the sensor needed to be at a stable 122*F or above to pass the voltage, which would indicate a intermittently failed MAP sensor.
I replaced the MAP sensor and the problem was solved. It turns out to be the evolution of my failing MAP sensor.
