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1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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Discretesignals
Ultimate Carjunky
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May 29, 2013, 7:45 PM
Post #26 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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It appears the MAP sensor is working properly and it does have vacuum to it from the intake manifold.
You could test the TPS sensor signal with your meter. The TPS works almost the same as the MAP sensor, but it uses a potentiometer that is connected to the throttle shaft to change the voltage output signal.
The range is usually 0.5-1.0 volt at closed throttle to 4.5 volts at wide open throttle. I believe the signal wire is dark blue.
You want to back probe the TPS connector with the your meter the same way as you did the MAP sensor. With the key on slowly open the throttle. The voltage should rise without any drop outs in voltage as you get to wide open throttle. You have to do it slowly to catch dead spots using a digital volt meter.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 29, 2013, 7:48 PM)
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ericthegr8
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May 29, 2013, 8:10 PM
Post #27 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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I got .7 to 4.35 and its not skipping or jumping at all
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Discretesignals
Ultimate Carjunky
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May 30, 2013, 8:11 AM
Post #28 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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So the TPS sensor checks out. Take a reading at the engine coolant yellow wire. Same thing back probe and turn the ignition on with your meter connected . The voltage at the sensor with the engine at operating temperature should be around 1.7 volts. The voltage goes down as the engine coolant temperature increases.
You can also compare the ECT sensor signal voltage with the engine cold with the IAT sensor signal voltage (tan wire). They should be fairly close to each other.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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ericthegr8
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May 30, 2013, 4:30 PM
Post #29 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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I tested ECT and IAT cold they both came up with 1.5
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Discretesignals
Ultimate Carjunky
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May 30, 2013, 5:43 PM
Post #30 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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Now with the engine at operating temperature the ECT voltage should be around 0.5 volts. Does the voltage go down as the engine warms up?
Sorry about that. I think it was a typo in the service information.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 30, 2013, 5:49 PM)
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ericthegr8
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May 30, 2013, 7:48 PM
Post #31 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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No problem I checked it and it read 0.3 at OT
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Discretesignals
Ultimate Carjunky
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May 31, 2013, 4:15 PM
Post #32 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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Ok, so the coolant sensor signal is checking out.
You could monitor the O2 sensor voltage using your meter. You can see what kind of oxygen content is in the exhaust to determine if the engine is running lean or rich. The O2 sensor on this one isn't heated, so it doesn't get active until there is enough exhaust flow across the sensor to get it hot.
Back probe with your volt meter to the purple wire of the O2 sensor harness and other lead to the battery negative. If you unplug the connector, you should see about around 0.5 volt with the ignition turn on on the engine harness side of the connector. When the sensor is operational as the engine is running it will cycle between 0-1 volt. If the voltage from the sensor is less than .5 volt, that means there isn't much oxygen in the exhaust, so the engine is running lean. If the voltage is more than .5 volt that means there is high oxygen content in the exhaust, so the engine is running rich.
Make sure you don't have any exhaust leaks before the sensor because that will mess up the readings. Also make sure the sensor isn't covered with oil or mud and the connector is free of oil or other contaminates.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on May 31, 2013, 4:19 PM)
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ericthegr8
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Jun 2, 2013, 11:32 AM
Post #33 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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Got it fixed, the ECU had a bad seal and the circuit board was all corroded, in '94 and '95 GM mounted the ECUs in front of the wheel well (bad spot for electronics if you ask me) but I picked one up at the local junkyard for $40 and its running like brand new.
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Discretesignals
Ultimate Carjunky
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Jun 2, 2013, 11:48 AM
Post #34 of 34
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Re: 1994 Chevy lumina euro 3.1 liter 140,000 won't rev up past 2000 rpms
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Good catch!
Most of the time us technicians will eliminate all possiblities before condemning an ECM because an input, output, power feed, or power ground problem can cause driveability problems and make it appear the ECM is the culprit. Plus most modern ECUs are expensive, so using deductive logic is very important. I'm going to say that the older ECMs in those that had the removable calpacks and EPROM were kind of problematic. You really don't run into too many modern ECU problems.
Glad to read that you got it figured out and it was physically apparent the ECM was no good.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 2, 2013, 11:51 AM)
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