Simultaneous MAP and TPS low voltage

[stanfiel]

I have got a 1996 Cavalier sedan 2.2L, VIN4.

The problem is it stalls while driving at any speed.

I have checked it with a scanner, when the fault appears the MAP and the TPS voltages get down to almost 0 volts, so the MAP low and TPS low fault codes are registered.

I checked the 5 volts reference voltage that supplies the MAP and the TPS. They come in different wires from the ECU but they have 0 ohms between them, so this 5 volts are the same for both sensors.

I connected a voltmeter to this 5 volts wires (GRAY on both MAP and TPS) and when the fault happens this 5 volts drop to almost zero volts.

So I can deduct that the problem is that the sensors dont get the correct 5 volt reference signal so they send incorrect signals to the ECU.

Does anyone has an idea as why this 5 volt signal is failing?

Any help would be grateful, I live in Venezuela where the cost of a new ECU is U$S 1360.
(By the way, the mininum wage here is U$S 83/month so you get the idea of how much this money represents in this country)

Best regards

Diego

[perna00]

i had a few problems for my cam sensor showing low voltage. i ran a wire w/ +12 volts to the cam and it fixed it. if you could find an already existing 5 volt reference wire you could splice it into both of the reference wires that need 5 volts and that should solve it. or if you want to, get a replay with only a 5 volt output to power the wires as references.

[perna00]

by the way, mine is a 96 also, they have a tendancy of the wires dry rotting and getting moisture in the pcm/wiring harnesses.

[Three_Fingers]

Originally Posted by perna00

i had a few problems for my cam sensor showing low voltage. i ran a wire w/ +12 volts to the cam and it fixed it. if you could find an already existing 5 volt reference wire you could splice it into both of the reference wires that need 5 volts and that should solve it. or if you want to, get a replay with only a 5 volt output to power the wires as references.

WTF!!? ( methinks dude needs to brush up on basic electronics).

Check the connectors to and from the sensors and ECM for fit and corrosion. You can make a test plug to backprobe the MAP sensor.
Just snag an old MAP sensor plug with some wire left on it from the junkyard and put some bullet connectors on the two outside wires. Leave the middle wire unplugged but connect the two outer wires tothe harness connector.
Ground the negative lead of your voltmeter and read the voltage off the middle MAP lead-it should change with RPM.
The MAP and TPS are just potentiometers, the actual lead to the ECM's MAP input terminal in the middle and +5v on one end and ground on the other. The ECM makes adjustments according to how close to +5v or ground the sensor is at any given time.

If the =5v reference voltage is too low-check all the connections/wires in the circuit and replace/clean anything that looks suspicious.

Cleaning and tightening the ECM grounds at the engine block also works wonders. Cavs are famous for crap ground connections.

[stanfiel]

I solved the problem, with an external solution.

I made a 5V regulated power supply, and feed the TPS and MAP with this voltage.

Still the car is not running 100%, has some backfiring on hard accelaration, but it rolls.

Thanks for the advice.

By the way, where is the ECU ground connection? I could not find it.

Diego