Merc 3.0 not getting over 3200rpms

[jbooher83]

Ok i have never posted on here before so i will list techinical data first. 1986 19ft sunrunner. Has merc inline 4 3.0 with volvo penta sx outdrive ratio 1.85. Upgraded est ignition not coil. Has been compression checked, new coil, ignition control module, timing set correctly thru base timing mode. Holley 2 barrel carb recently cleaned and rebuild

the problem is when i take it out on the water boat only gets between 3000 and 3200 rpms not matter what size or dia prop i put on it. This boat has had this problem for 2years now. I inherited the problem from a buddy. Fun times i know. I have checked fuel pressure and the pump is a year old and puts out a steady 3psi. I have changed the gear oil in the drive and also tried switching to counter rotation with no change. Revs find on dry land with great throttle responce. I have tried a counter rotation 15 x 13 prop and a regular rotation 14 3/4 x 19 and 15 1/2 x 15 prop. Stays in same rpm range everytime.

Somebody tell me the one thing i have not checked lol its driving me nuts!!

 

[Don S]

Re: Merc 3.0 not getting over 3200rpms

Well, since Volvo didn't have the SX in 86, and they darn sure didn't use a Mercruiser engine. I'm kind of scratching my head and wondering what you do have.
What do you mean when you say "est ignition not coil" ? You have to have the EST coil for the ignition to work properly.
If it is a Merc engine, that formerly had points ignition, do you still have the resistor wire in it?

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

DON, its a cross breed of some sorts. the merc engine number applies to a 86 with points. along the way someone upgraded to est ignition. i ment to say est and not points. its got a coil on it a new one in fact. idk if the changed the drive out but it is a volvo penta sx drive tag say prod#3868035 type sx ratio 1.85 and a hard to read number underneath it. and what resistor wire are you talking about? is it he wire off the ignition control module and coil?

 

[Don S]

Re: Merc 3.0 not getting over 3200rpms

Here is a wiring diagram for an 86 Mercruiser with points. You can see the resistor wire in the diagram.
If you do have one, you are cutting the voltage to the coil down to around 8 volts. Not much for the EST.
Without seeing your wiring, I can't tell you where to check exactly. But if you wiring is like that diagram, then you need to disconnect the plug from the coil and with power OFF the engine, take an ohms reading between the purple wire pin on the coil plug and at the purple wire connector at the choke or alternator.

View attachment #10 GM 4 Cyl 85-89 212.pdf

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

ok don i dont see a wiring diagram attachment. also i know the choke is not hooked up and there is only a red wire to the battery on my alternator.

 

[Don S]

Re: Merc 3.0 not getting over 3200rpms

Oops, forgot to put it in. Try it now.

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

i got it now don. i know i have the purple wire on the plug in the coil but i will have to look where i goes to bc i know it is not on the choke or the alternator.

 

[Don S]

Re: Merc 3.0 not getting over 3200rpms

i got it now don. i know i have the purple wire on the plug in the coil but i will have to look where i goes to bc i know it is not on the choke or the alternator.

And you wonder why it doesn't work. :facepalm:

You have what I call a "junk yard dog". Just a mix of parts and previous owner changes that no one can see or help you troubleshoot. Color codes means nothing, only experience and having the boat in front of you can find problems like you have.

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

yeah i know thats what i figured don. but i figured i try what i could first and go from there. hopefully i find this wire!

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

i also work in a service department for a car dealership and :facepalm: this face i have given to alot of customers

 

[bruceb58]

Re: Merc 3.0 not getting over 3200rpms

Post a picture of your distributor and coil so we can see what you have.

Add a picture of your outdrive while you are at it so we can tell you what you have there too.

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms




theses are the pictures i took. i found the purple wire don told me about i followed it and it goes into the engine disconnect harness and the up to the front.

 

[Don S]

Re: Merc 3.0 not getting over 3200rpms

theses are the pictures i took. i found the purple wire don told me about i followed it and it goes into the engine disconnect harness and the up to the front.

Should go to the I terminal of the ignition switch.

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

yes i looked it does go up to I terminal on the ignition switch.

 

[jbooher83]

Re: Merc 3.0 not getting over 3200rpms

i do have a question though. when i tested for spark i used a inline spark tester and it had spark but it was not as bright as when i use it on a car engine. is that normal or should it be about the same?

 

[achris]

Re: Merc 3.0 not getting over 3200rpms

Spark should be fat and blue, and draw at least 1/2", just like a car. If it's not, it will not fire a mixture.

Chris.........
R.I.P. Don S.
I post here in memory of you. This thread contains your last post.
Farewell my friend.