mercruiser 7.4l mpi crank position sensor

[cnotecherry]

I just finished building a marine 454 out of a auto block and all mercruiser outer parts from a 1999 mercruiser 7.4l mpi my question is, there is no plug on the wiring harness for the crank position sensor on the underside of the timing cover does this model not use that sensor I have built small blocks before that use it and thought the gen 6 big blocks did as well I had it runing yesterday and ran great for the first fire of a brand new engine I didn't think they would run without it do they use one in the distributor or something or is my harness missing it somehow any feedback would be appreciated thanks

 

[alldodge]

I just finished building a marine 454 out of a auto block and all mercruiser outer parts from a 1999 mercruiser 7.4l mpi my question is, there is no plug on the wiring harness for the crank position sensor on the underside of the timing cover does this model not use that sensor I have built small blocks before that use it and thought the gen 6 big blocks did as well I had it runing yesterday and ran great for the first fire of a brand new engine I didn't think they would run without it do they use one in the distributor or something or is my harness missing it somehow any feedback would be appreciated thanks

:welcome: to iboats

The 1999 BB does not use the crankshaft position sensor. They started being used by Merc in 2001

 

[cnotecherry]

thanks a lot I wasn't sure i know gm started using them 96-97 so how does the ecm time itself? and advance with the rpms? or does it

 

[alldodge]

thanks a lot I wasn't sure i know gm started using them 96-97 so how does the ecm time itself? and advance with the rpms? or does it

The engine is put into base timing mode and then the distributer is adjusted. Once timing is set the ECM does the rest based on it's program tuning.

To set timing you need a data link connector (DLC) connector, Scan tool or jump a wire across pins one and two of the DLC connector. Below is a link and scroll down to the V8 section. Timing set to 8 degrees BTDC
https://www.perfprotech.com/blog/art...-engine-timing

 

[Fun Times]

If you don't have a scan tool or diagnostics tool like mentioned in the link, then below is a Volvo EFI diagram of how to achieve base timing mode using a jumper wire.....But keeping in mind that on your engine model, you do not have to rev the engine idle up manually, it will automatically rev it up for you once you place it into service mode with the engine running. The two wire pins to jump at the DLC are wire pins A & B. White/Black & Black wires.

 

[alldodge]

1800 rpm right?

 

[cnotecherry]

thank you very much you are obviously very knowledgeable with merc i guess i just hit the timing right on the money when putting it together because it ran great first fire i will still go through the timing procedure though thanks again

 

[Fun Times]

1800 rpm right?

If you have to set it manually, 16-2000 range 1800 being best. This is if he has the MEFI 1 or 2....

If he has MEFI 3 like I believe he should have (but the engine serial number should help confirm this) then it revs automatically to around 1200 RPM. He will know once he put's it into service mode. If the engine dies then he has to raise the RPM to 1800 before going into service mode.

cnotecherry, using the first link below, what does your ECM look like? long or short? Long is MEFI 1/2, short is 3.
http://www.mercruiserparts.com/Show...br=70&bdesc=ELECTRICAL+BRACKET+AND+COMPONENTS

http://www.boatfix.com/merc/bullet/97/97_15.PDF

 

[alldodge]

Agree, just clarifying because your previous post indicated 1000 rpm, it's all good

 

[Fun Times]

Agree, just clarifying because your previous post indicated 1000 rpm, it's all good

1000 RPM is a Volvo thing.

That's just a really good diagram showing how to jump the wire safely is all, Merc doesn't really show it as well as Volvo did.

 

[cnotecherry]

Wow you guys are awsome I have been a long time reader but this is my first question and it is amazing how knowledge able you guys are I hope to help people In the future like you have helped me I usauly figure this stuf out on my own but this saves a lot of time

 

[alldodge]

Were all glad to be of help. Hope to see you showing up in other threads with the rest of us soon

 

[cnotecherry]

I do have the mefi 3 serial is 0L6, so once i jump it it will automatically rev to 1200rpms? are the wires the same colors as volvo? once in service mode I set the timing 8 degrease. if I run the motor right now and it is at 8 degrease at idle should i even bother timing it?

 

[alldodge]

I do have the mefi 3 serial is 0L6, so once i jump it it will automatically rev to 1200rpms? are the wires the same colors as volvo? once in service mode I set the timing 8 degrease. if I run the motor right now and it is at 8 degrease at idle should i even bother timing it?

Yes, 8 degrees is at 1800 rpm, at idle it can and most often is different. Color wires are the same, but most important is the pins used to put it in base timing. As you said you have a MEFI3 so it should automatically go to 1200 rpm

 

[cnotecherry]

hey guys hope you will still read this thread. so I got my motor put back together after finding a crack in my intake manifold and going with an aftermarket intake, rails, and throttle-body anyway I went through the timing procedure like you guys have posted it only reved to about 1100 rpms in base timing mode according to my tac timed it to 8* btdc removed the wire it went back to idle it seemed to run worse put the timing light back on it and it was runing about 0* btdc at idle and bounces a little maybe 2-4* is this normal? it seems to run a lot smoother a little more advanced could my timing light be out a little it is a cheep one with advance is there anyway of checking a timing light? thanks for ay feedback

 

[alldodge]

hey guys hope you will still read this thread. so I got my motor put back together after finding a crack in my intake manifold and going with an aftermarket intake, rails, and throttle-body anyway I went through the timing procedure like you guys have posted it only reved to about 1100 rpms in base timing mode according to my tac timed it to 8* btdc removed the wire it went back to idle it seemed to run worse put the timing light back on it and it was runing about 0* btdc at idle and bounces a little maybe 2-4* is this normal? it seems to run a lot smoother a little more advanced could my timing light be out a little it is a cheep one with advance is there anyway of checking a timing light? thanks for ay feedback

Don't see any way the timing light can be off, cheap or expensive, they flash light when the spark plug fires. Your idle rpm for base timing should be 1800 and your tach can be off. Don't mess with readjusting timing after it was set, you have another issue going on. Could be IAC, MAP or something else, even a vacuum leak from a gasket or hose which was not put back on.

Put a vacuum gage on it and see what your pulling after you reset base timing

 

[cnotecherry]

thanks I think it is all good though I think it was just the ecu re calibrating itself or something after runing it for a while and reving it a bit it seemed to get a lot better but still running at 0* btdc at idle witch seems weird for any engine it does advance very quickly with the rpms though i know the IAC is functioning properly and i have a new MAP sensor what are you suggesting the vacuum leak or sensor is doing? it idles fine at 600 it just seems a bit smoother a few degrees more advanced and i think the mefi3 is only suppose to rev to1200 in service mode

 

[alldodge]

Your correct (1200) forgot yours is the MEFI3. Only mention vacuum because of your mentioning of it running rough. Idling at 600 sounds good. Vacuum should be 15-18 in Hg at idle and smooth. What kind of intake did you go with

 

[cnotecherry]

No Title

Im not sure it looks like a FAST but there is no markings on it baught it off my engine shop for $400 with everything including harness and ecu looks like an mefi2 but I used all my harness ecu and injectors seems to work good should perform better and is fraction of the wieght and I can take my valve covers off without taking apart half the engine

 

[alldodge]

Looks good and as you say could be a FAST or even a holly. They work real well when tuned in. You will loose some torque without the long intake runners but can get more HP. The gain and loss will not be much. Issue you may be running into is with original ECM programing. If you could get the ECM retuned to your new setup it should run even better