Help? Crank position sensor 5.7 MP 340hp

[Majr808]

Does anyone have experience changing their crank position sensor on a 5.7 MP v drive? I've read some other posts about it causing revs to bounce all over.

I believe this is the correct part: https://marineenginedepot.com/crank-position-sensor

[freeheel4life]

It'sboat possible. May explain your no start issue.

It's down low behind the harmonic balancer on the port side

[Majr808]

Yeah I’m pretty lost right now and haven’t been able to use my boat for over a month…

Timeline:
The issue started as an engine that revs on its own in neutral or drive and flutters at speed. Heard a loud “can popping” noise at speed once while it was acting up really bad.

Replaced a ton of parts which never changed anything. (Throttle body, plugs, wires, relays, cap, rotor, tac module, potentiometer, coil, fuel injectors, fuel pumps). Checked all connections I could find. Checked all grounds etc. Fuel & pressure are good.

Had a diagnostics ran and got a bunch of TAC faults. MP told me based off this it’s either throttle body or ECM. Since I already replaced the throttle body they sent me a new ECM.

Now my engine won’t even start with the new ECM which wasn’t the case before. It would start fine with my old ECM. I verified that I have spark at the plugs.

My old ECM is in their hands while they are running a diagnostics on it.

If my crankshaft sensor was bad wouldn’t it have been flagged as an engine trouble code in the diagnostics?

This was my can retard, which I don’t know if it is normal or not.
Cam Retard...................... 62.48 DEG


I found the crankshaft sensor by the harmonic balancer. Do I just unbolt, pull out, and pop in the new one?

sorry for the lengthy message… I’m loosing my sanity over here

[freeheel4life]

Yup. Unclip harness plug, remove the holding bolt and remove and replace sensor

[freeheel4life]

I have a hard time keeping all the different timing specs correct...

Pretty sure the 5.7 you have can still set timing with the crab cap. I'd look at the attached chart and hit it with the timing light.

Feel like I remember boatwakes saying he's seen distributor gears wear out....

[Majr808]

Pulled the sensor out like you said and it looks good.. but I'll replace it since it's a relatively cheap part.

Timing is a little over my head sad to say. I'll report back if the new crankshaft position sensor fixes anything.

[freeheel4life]

Timing light at harbor freight. Clip it to #1 plug wire at point it at the harmonic balancer/crank pulley. Be sure to cutting hair and don't wear anything baggy....

but all in all it wouldn't explain your surging issue.

Would explain your new complaint, with new ecm....

Theres a lot of data you've provided at this point but 1 and 1 are adding up to 2 in my head

[Majr808]

Thanks for trying to help me diagnose. Checking timing doesn't look too bad after all.

[Majr808]

I’m guessing this is my pointer arrow, and this line on the harmonic balancer is 10° for neutral timing?

[Majr808]

My plugs were wet w/ fuel from trying to start. Changed them out & tried to start.. acted like it wants to start but when i let off the key it dies quick. White smoke came out of the intake manifold via the throttle body. I think I can see some gasoline in the very bottom of the intake manifold in a tiny puddle. Maybe this new ECM was on a different timing sequence than my original and that's why I'm having the issues with it.

[Majr808]

Thanks gumby. I followed your directions and found cylinder 1 was set to fire via rotor @ distributor at compression when the balancer's line was in line with the pointer on the block.

My next step is talking to MP because it looks like something isn't right with the ECM they sent since my old one wasn't giving me this issue just days ago.

Appreciate all your guys help very much.

[boatwakes]

Hello Majr, sorry I've been absent, had to fight the vid but won without issue. Im up to speed on your issue but have some questions:
1) When did it run correct last and how long have you owned the boat?
2) When did this issue start and was there a service or something changed in the boat or on the engine preceding the issue?
3) I see you've changed fuel pumps but has a fuel pressure gauge been installed to monitor while cranking?
4) Has the boat taken on water at any point to cover the crank position sensor?
5) Since replacing the ecm has spark been checked during cranking?

First, a crank position sensor will not always set a code so to answer your question, no. If the CPS saw water, I've seen the wire harness connections fail and cause the same issue. Additionally, those engines run the crab cap distributor which only needs to be within 15-20* of correct timing for the engine to run, the computer takes care of the rest. However, being off a tooth on the distributor causes the engine to run fine at idle but fall flat on its face above around 2200-2400rpm.

To keep up with freeheel's statement about the distributor gears, it was actually the distributor shaft seals which failed and caused oil to migrate up the shaft and into the distributor causing all kinds of havoc. If you pull the distributor cap and find oil or oil residue, you'll need a new distributor to fix the issue. Answer the above for me and lets see if we can figure this out.

[Majr808]

Glad to have your help boatwakes... I just got an update from marine power on my original ECM and the issues I'm having with the new ECM that they sent me.

They finished the diagnostics on my original ECM and they told me it's toast. This would explain the surging I've been chasing.. with my original ECM the engine still started fine and worked well sometimes, but randomly the surging would get crazy. The ECM was still capable of being scanned at my buddies shop and pulling codes, so I thought there was a chance it was good.. but apparently not.

The new ECM they sent me would not even let the boat start.. which was the new problem. They got back to me today after some digging and told me that the ECM they sent me was programmed without a certain hidden file.. and that this would cause a no start issue. So, they are sending me yet another Mefi 4 ECM with the included programming that I apparently need.

Hopefully this is the answer to my surging issue and also explains why the new ecm I got wouldn't function. It's been a really rough and expensive 1-2 months of summer during my first year of boat ownership!

If this new ECM does not fix everything, I'll report back and answer all of your points. Thank you again for your time.

[Majr808]

Issue has finally been resolved. ECM was failing and I was able to get a new ECM in today and water test it. Everything is great now. Thank you to each of you for your help.