Crankshaft position sensor replacement

[lvecch]

Hello guys, I have a Mercruiser 350 Mag MPI. I do not know the serial number because the engine block was put on acid to be cleaned and the acid corroded the serial tab. But I am sure it begun with 0W... some of the earlier. I have the crankshaft sensor position bad. My engine do not use sensor in the distributor. I bougth one Chevrolet Bazer crankshaft position sensor here in Venezuela, were i live, and phisically it looks identical but it does not work. I am electronic engeneer, so I tested the failed one (it fails only at relatively high RPM) and the new one in my little home lab and discovered the following. The original sensor (failed) everytime I pass a piece of iron close to it, there is a pulse in the output pin. But the new one, one time I pass the iron, and it output a pulse, but the next pass do not output a pulse. I mean every two passes of the iron it output a pulse. Of course my engine does not work wjth this. The next thing I did was to buy another sensor on ebay, what is suppose to be a replacement for the 864297001 that is the original part number, and when I receive it, it works like the one I bougth in Venezuela, one pulse every two passes. So, now I am afraid of keep buying more sensors. I do not know what sensor to buy. Does any one have some knowledge about it and can help me? Here is the link of the sensor I bougth on ebay:

https://www.ebay.com/itm/PC123-For-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Additional info.: The original sensor has stamped this number: 12562910, and the one I bougth on ebay has 12596851

Thanks in advance for any help.

 

[alldodge]

Are you getting a code for CPS showing bad, or just think that ?

Unable to say if you should get one or two pulses, but was the reluctor wheel installed correctly ?

The GM numbers 12562910 and 12596851 are the same part, just from different times of manufacture. There are many other cross numbers from Delphi, Masterpro, Kemparts, others

 

[scoflaw]

Buy the Merc OEM part, they're on Ebay for $105.

 

[alldodge]

Test procedure

 

[Fun Times]

Watching some videos (linked below for you) it sort of seems that they weren't getting an "continuous" output pulse reading by hand either probably/possibly because of the required gap that's supposed to be between the sensor and crankshaft reluctor wheel... 'Plus their by hand motion?...But when they touched the sensor it would pulse ever time...Did yours seem to pulse ever time the sensor was touched?

https://www.youtube.com/watch?v=AAbSwQlczDU

Skip ahead to the 4:50 second mark, https://www.youtube.com/watch?v=pkwaqydbtas

 

[wrench 3]

The sensor is a square wave generator. With +5 volts on terminal A and a negative ground on terminal B, The output on terminal C should be high when iron is close to the sensor and low when no iron is present. The best way to test them is with an oscilloscope if you have one. If they spike instead of going square they really mess up the running but usually don't set a code.

 

[QBhoy]

Hi

quite unusual for these to fail. Perhaps an intermittent error that could have been reset ??
if not, I’d be taking it out and cleaning/testing to make sure. Like most of the sensors on these mpi...it’s a simple 5v signal you’re looking for.
Good luck. Ps...I’d just buy the genuine part if you need to.

 

[lvecch]

Ok I am going to send a video of what I see on the sensor output. But, by now, has anyone has installed a Chevrolet car crankshaft position sensor on a Mercruiser 350 with no camshaft position sensor?

 

[alldodge]

Many use the GM (Delphi) part and have no issues. Others use the GM part and have issues. Mercruisers has sensors made for specific areas, but this is not one of them. You can get a bad sensor even from GM or anyone else you buy from, If you buy from a legit source there is a better chance of getting a good part.

We all know that electrical parts are not returnable. I bought a Delco part for my car and installed, the car still had an issue, so I take it to the dealer. The dealer replaces the same part and problem is fix.

So right now you believe the CPS is the issue and there are no other problems?

 

[scoflaw]

Many use the GM (Delphi) part and have no issues. Others use the GM part and have issues. Mercruisers has sensors made for specific areas, but this is not one of them. You can get a bad sensor even from GM or anyone else you buy from, If you buy from a legit source there is a better chance of getting a good part.

We all know that electrical parts are not returnable. I bought a Delco part for my car and installed, the car still had an issue, so I take it to the dealer. The dealer replaces the same part and problem is fix.

So right now you believe the CPS is the issue and there are no other problems?

This ^^^^ Spend the money and get the OEM Merc part

 

[lvecch]

Ok, why I am almost sure I have a bad crankshaft position sensor? Since I have the failure on my engine, I changed the Spark Plugs, the spark plug wires, the rotor and the cover of the distributor, the ignition module, the ECU was sent to a place were fix it and they said there is no failure in it. A scanner was put, and there was an error on the ignition module, so it was replaced an the error went out, so now there is no error. The connections between the Ignition coil, the ignition module, the ECU and the sensor was tested by myself together with a mechanic. 5V from the ECU to the sensor is OK. Ground connections are all oK. The engine start very difficulty, with throttle mid way. Once started it does not maitain idle, and make explotions thorough the exaust. Taking the spark coil HV wire out of the distributor and placing it close to an engine iron (ground), then cranking the engine, we can see the spark that is not continuos, I mean you hope to see a spark every equal period of time, but in this case some of the sparks are missing. Then, analysing the sensor with the osciloscope I see the same behaviour, at a very low speed you can see every pulse, but as the speed increase, close to the equivalent to 600 RPM some pulses become to erase. So I think the failure is at the origin of the pulse, that is the sensor. So I bougth a replacement sensor that is for cars. It did´t work on my boat engine. Analyzed it with the osciloscope and see that only every 2 touches of an iron the output goes high ones. I bougth a second one and it works the same, so I do not believe both are bad. And I cannot think is possible that a failure can cause a memory inside the sensor to memorize that one pulse was sent to inhibit the next one. So, definitively those sensors I bougth are different that the original from my engine. So now, here in iboats there is one sensor that "Replaces the OEM", how can I be sure is the one I need? I say that, because there are some Mercruiser engines wich uses a camshaft position sensor, those engines maybe works with car sensor (the one that goes high every two touches). If I cannot solve this uncertanty i will be forced to buy the really OEM, hoping it will work. Another question, the original sensor works on every mercruiser engine? having or not having the distributor sensor? Isn´t there any other special sensor for some Mercruiser engines?

Sorry, I wasn´t able to upload the video.

Thanks a lot for your help.

 

[alldodge]

The CPS is the same part number for both motors that use a Cam sensor and ones like yours which do not.

Backfiring and having trouble to idle would have me also looking at timing, IAC and distributor cap. You mentioned that the distributor cap was replaced, and if the motor has the same issues prior to replacing, then I would not do it again currently.

Is the distributor positioned as shown?



Double check the plug wire connections.
What was the motor doing prior to developing these problems?

 

[wrench 3]

What were the ohm readings on the 5v and ground circuits to the CPS?
Did you check the tension on the terminals in the plug for the sensor? To make sure that they are getting a good connection to the pins on the sensor.

 

[hughesy1]

Ok, why I am almost sure I have a bad crankshaft position sensor? Since I have the failure on my engine, I changed the Spark Plugs, the spark plug wires, the rotor and the cover of the distributor, the ignition module, the ECU was sent to a place were fix it and they said there is no failure in it. A scanner was put, and there was an error on the ignition module, so it was replaced an the error went out, so now there is no error. The connections between the Ignition coil, the ignition module, the ECU and the sensor was tested by myself together with a mechanic. 5V from the ECU to the sensor is OK. Ground connections are all oK. The engine start very difficulty, with throttle mid way. Once started it does not maitain idle, and make explotions thorough the exaust. Taking the spark coil HV wire out of the distributor and placing it close to an engine iron (ground), then cranking the engine, we can see the spark that is not continuos, I mean you hope to see a spark every equal period of time, but in this case some of the sparks are missing. Then, analysing the sensor with the osciloscope I see the same behaviour, at a very low speed you can see every pulse, but as the speed increase, close to the equivalent to 600 RPM some pulses become to erase. So I think the failure is at the origin of the pulse, that is the sensor. So I bougth a replacement sensor that is for cars. It did´t work on my boat engine. Analyzed it with the osciloscope and see that only every 2 touches of an iron the output goes high ones. I bougth a second one and it works the same, so I do not believe both are bad. And I cannot think is possible that a failure can cause a memory inside the sensor to memorize that one pulse was sent to inhibit the next one. So, definitively those sensors I bougth are different that the original from my engine. So now, here in iboats there is one sensor that "Replaces the OEM", how can I be sure is the one I need? I say that, because there are some Mercruiser engines wich uses a camshaft position sensor, those engines maybe works with car sensor (the one that goes high every two touches). If I cannot solve this uncertanty i will be forced to buy the really OEM, hoping it will work. Another question, the original sensor works on every mercruiser engine? having or not having the distributor sensor? Isn´t there any other special sensor for some Mercruiser engines?

Sorry, I wasn´t able to upload the video.

Thanks a lot for your help.

Did you ever get to the bottom of this?