2G Cam sensor reading too high voltage

[lapointebrett]

Hey guys I've been having a no spark, no fuel injector pulse issue that randomly came up recently. To my knowledge the crank sensor is responsible for spark and the cam is responsible for injector pulse. I've tested the crank and cam sensor, the crank sensor is reading correct voltage but when testing my cam sensor it is reading between 11-13 volts on the signal wire which I know is way too high.

I've checked the harness side with it unplugged from the sensor and it reads the normal 5 volts so it seems like its gotta be the sensor. I ordered a new OEM Mitsubishi cam sensor from xtremepsi and just put it in today and tested it but I'm getting the same issue with the voltage being too high, anyone might know whats causing this?

Any input at all would be appreciated as I am completely lost at this point as to whats going on. thanks.

 

[Justin DuBois]

Hey guys I've been having a no spark, no fuel injector pulse issue that randomly came up recently. To my knowledge the crank sensor is responsible for spark and the cam is responsible for injector pulse. I've tested the crank and cam sensor, the crank sensor is reading correct voltage but when testing my cam sensor it is reading between 11-13 volts on the signal wire which I know is way too high.

I've checked the harness side with it unplugged from the sensor and it reads the normal 5 volts so it seems like its gotta be the sensor. I ordered a new OEM Mitsubishi cam sensor from xtremepsi and just put it in today and tested it but I'm getting the same issue with the voltage being too high, anyone might know whats causing this?

Any input at all would be appreciated as I am completely lost at this point as to whats going on. thanks.

What year CAM sensor are we talking about? CAM sensor tells the ECU which injector. Crank sensor is used to trigger WHEN for both spark and injector.

Signal should be 0v and 5v square wave. Sensor power is +12v - When do you get "normal 5 volts" with the sensor unplugged?
Can you power the sensor outside the car, and manually test it with a chunk of metal in proximity to the tip of the sensor?

 

[lapointebrett]

What year CAM sensor are we talking about? CAM sensor tells the ECU which injector. Crank sensor is used to trigger WHEN for both spark and injector.

Signal should be 0v and 5v square wave. Sensor power is +12v - When do you get "normal 5 volts" with the sensor unplugged?
Can you power the sensor outside the car, and manually test it with a chunk of metal in proximity to the tip of the sensor?

It's a 97 gst and yes it gets 5v when the sensor is unplugged just overvolting when plugged in but ill see what it does manually testing it outside of the car, I guess the crank sensor could be a culprit but the voltage seemed fine so not sure how that would make sense

 

[lapointebrett]

My ECU is reading injector pulsewidth, does that mean that the cam sensor is sending signal to the ECU?

I'm also getting rpm reading, which means I'm getting crank sensor readings as well right? Just trying to make sure because I'm getting no spark and no fuel injector pulse tested via noid light.

Really confused here as the other day I randomly stopped getting both of them at the same time. Any ideas?

 

[Justin DuBois]

It's a 97 gst and yes it gets 5v when the sensor is unplugged just overvolting when plugged in but ill see what it does manually testing it outside of the car, I guess the crank sensor could be a culprit but the voltage seemed fine so not sure how that would make sense

Ah!

I may not have the right understanding on the ECU vs Sensor signal voltage. What you describe - 5v on the signal wire from the ECU compared to ground - (without the sensor connected), would be correct in a "pull down" sensor, where the sensor pulls the ECU signal voltage from 5v to 0v when triggered.

The other way sensors work is with a "pull up" approach where the ECU signal wire compared to ground is 0v, and then when the sensor is triggered, it supplies the ECU 5v, pulling the ECU signal up.

Honestly I don't know which way this one works... but you need to know this to diagnose your results. 11-13v on the signal sounds wrong.

 

[steve]

I don't quite follow how this might be going on if you have a new sensor unless there is some way the connector is shorting the pins and I would expect this would happen with or without the sensor connected.

As mentioned the sensors get battery voltage (from the MPI circuit) to power them and the signal lines are pulled up to +5 inside the ECU. To answer Justin's question the sensor then pulls those signal lines down to ground to do the signaling back to the ECU.

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Note that this diagram shows +5v pullups to the cam and crank sensors but a battery voltage pullup to pin 91 which the harness either pulls to ground or not depending on ATX/MTX.

I'm not aware ATM of any case on a DSM where a sensor provides a battery voltage to the ECU directly. That's usually a solenoid, relay or other device where the ECU grounds the signal to activate it. (like the ISC/IAC or the injectors)

 

[Drewpy Dawg]

Tach signal comes from the ignition transistor.

 

[steve]

My ECU is reading injector pulsewidth, does that mean that the cam sensor is sending signal to the ECU?

The ECU doesn't "read" injector pulsewidth. It reads the air entering and decides how much fuel is required and then fires the injectors for that long to provide the fuel. What ECU reports as injector pulsewidth is what it computed as a value to get that amount of fuel.

Please try to stick to one thread even if your questions change so we don't rehash everything.

 

[lapointebrett]

Does anyone think it could be the ECU causing too high of voltage and somehow be affecting fuel injector pulse and spark and how I would check to make sure the ECU isn't the culprit?

I haven't been able to figure this out for months because no fuel and spark out of nowhere. It doesn't make sense to me seeing as it was just running at the tuner and I bring it home and now this happening.

I'm so close to finishing this car finally after 2 and a half years any help of any kind would be greatly appreciated.

 

[DSMPT]

Another possibility.

By any chance, didn't you remove and install the cylinder head recently? If so, you should check the sensor wiring just for in case. I have seen a couple of times that the wires get pinched between the block and cylinder head when install the cylinder head, and that damages wires and causes a short.

It would end up causing some weird issue.

 

[jed344]

Not having spark or injector pulse is something i have not had to deal with. Years ago we spent a ton of time figuring out some issues and i think my idea of how this all works is somewhat correct. Everything worked fine then one day it lost spark and fuel? From my experience it is not so simple as crank does spark and cam does injector pulse. A 97+ i have never seen have a cam sensor go bad. Like said you can test the sensor side and also test for 12v and continuity on the harness side. This would show if it is a cam or crank sensor or a wiring issue. Then on the off chance all test's good then it would have to be a ecu issue.

 

[steve]

Does anyone think it could be the ECU causing too high of voltage and somehow be affecting fuel injector pulse and spark and how I would check to make sure the ECU isn't the culprit?

I wouldn't expect so but you can eliminate the ECU from the picture, unplug it. You'll then need to turn on the MPI/MFI power manual by grounding the MPI relay's coil (pin 2). Then measure the voltages at the CAS and CKP. There shouldn't be any voltage on pin 2 of either sensor since the ECU isn't pulling it up to 5v or shorting it to 12v.

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[lapointebrett]

Another possibility.

By any chance, didn't you remove and install the cylinder head recently? If so, you should check the sensor wiring just for in case. I have seen a couple of times that the wires get pinched between the block and cylinder head when install the cylinder head, and that damages wires and causes a short.

It would end up causing some weird issue.

It's not that I've looked in every corner of this engine bay for any apparent wiring issues like that, and all the sensor wiring checks out how it should it's just the cam sensor that overvolts from 5v to like 12-13v when the connector is plugged in

Not having spark or injector pulse is something i have not had to deal with. Years ago we spent a ton of time figuring out some issues and i think my idea of how this all works is somewhat correct. Everything worked fine then one day it lost spark and fuel? From my experience it is not so simple as crank does spark and cam does injector pulse. A 97+ i have never seen have a cam sensor go bad. Like said you can test the sensor side and also test for 12v and continuity on the harness side. This would show if it is a cam or crank sensor or a wiring issue. Then on the off chance all test's good then it would have to be a ecu issue.

It's definitely odd because the car was running at the tuner (not perfectly because the map sensor stopped working) but it's just weird that the ECU could start having an issue randomly like that, also sucks because my tuner mostly tunes evos so I swapped to an Evo 8 ecu to get it tuned by him and they aren't easy to find if I do need another one

 

[lapointebrett]

Just an update for everyone, I have spark again now, not sure what made it come back I may have bumped a wire when I was under the dash but I will figure that out later at least its back.

Now it's just down to the cam sensor and injector pulse. I've put a new sensor from eBay which I'm assuming is a generic Dodge sensor but it did work because the car did have injector pulse when I took it to the tuner before whatever this issue is happened. I ordered a new OEM Mitsubishi cam sensor off of STM Tuned and tried that out and that is overvolting as well.

It is weird the eBay one reads 11v on the signal wire only with the connector plugged in and the Mitsubishi one reads 10v while plugged in. I know both are too high and I tried to test both of them via swinging a piece of metal in front of them with it out of the head and the voltage does not change at all, I even tried using different metals to see if it would make a difference. I'm starting to think it is a possibility although highly unlikely that both of the cam sensors could be bad because if it were the ECU or a short in a wire then it would be having an issue on the harness side when not plugged in but I'm ruling that out because it reads 12v for the red wire, 5v for the blue wire, and no voltage and it has continuity on the ground wire.

Gonna order one more cam sensor just to see if it will fix this mess.