merc 140 tach problem.

[jenny1671]

We tested the engine with a Digital Engine Analyzer. After reaching 1500 rpm We could not get a stable reading It reads up and down and then after 2500rpm the reading drops to 1000 or less. We are not getting a proper reading. all electrical conections are new and tight. Boat runs well but rpm reading tops 3000 should be at 4600 Reading off the distributor is unstable. New wire from distributor to coil. No difference. Can anyone help?

 

[jeff13601]

Re: merc 140 tach problem.

Do you have a brown wire that goes from the tach to the coil and then to the dist? And what year is it?

 

[jenny1671]

Re: merc 140 tach problem.

There is a grey wire that goes from the tack to the coil and then to the distributor. It is an 1986 merc cruiser 140hp. 3.0L

 

[jeff13601]

Re: merc 140 tach problem.

You probably need to check the continuity in that wire. If I remember you should also have a white 12 volt wire from the water temp gauge to the tach. If those are good maybe the problem is the tach

 

[jenny1671]

Re: merc 140 tach problem.

Digital Engine Analyzer is supposed to measure rpm of the engine to see if the tachometer is working properly. After reaching 1500 rpm We could not get a stable reading. It reads up and down on the analyzer and then after 2500rpm the reading drops to 1000 or less on the analyzer. We are not getting a proper reading. all electrical conections are new and tight. Boat runs well but rpm reading tops 3000rpm and should be at 4600 Reading off the distributor is unstable. Replaced new wire from distributor to coil. No difference

 

[jeff13601]

Re: merc 140 tach problem.

Are you using the digital anilyzer because you dont trust your tach? Think the analyzer could be faulty. Is a mechanic doing this or is their a poss that you are not hooking it up properly?

 

[jenny1671]

Re: merc 140 tach problem.

No we don't agree with the tach. It reads 3000rpm at WOT. It should be reading 4600rpm at WOT The analyzer is brand new. We are hooking it up as the instuction say; Black wire of the analyer to good ground and the red wire of the analyzer goes to the negative side of the coil.

 

[jeff13601]

Re: merc 140 tach problem.

There are a lot of other reasons that you could only be topping out at 3000 rpm's. Are you grounding the analyzer right to the battery?

 

[jenny1671]

Re: merc 140 tach problem.

we are grounding it to the negitive battery cable at the engine block. Engine analizer is set at 4 cylinders.<br /> We belive the engine is running at WOT 4400-4600rpm the boat tach only shows 2900at WOT. <br />Could the distributor be sending a irratic rpm reading?

 

[jeff13601]

Re: merc 140 tach problem.

I ground mine right to the terminal. I wire brush the terminal first so their is no doubt on the ground. If their is paint or rust you wont get a good ground. Do you have anything else that you can test to rule out the meter? The meter you have should also test point dwell.

 

[jeff13601]

Re: merc 140 tach problem.

I wish you would reply back and let us know whether you got the problem taken care of. I have a 120 and I got wondering about these analyzers, and I got jealous because all I have is a cheap dwell meter, so I went to Sears today and let my wife buy me a new one for Fathers Day. LOL. I will let you know if I have the same problem

 

[jenny1671]

Re: merc 140 tach problem.

I did not get my problem solved yet with the RPM I did however buy myself a Megellan GPS SportTrack color at costco for $249. It will tell me how fast my boat will go if I dont trust my speedometer and get me home in a fog. LOL Still learning how to use it. Both the tack and speedometer were replaced five years ago by my ex because he could not see the numbers without glasses. I dont know if he hooked them up right. so That is why we need to know the reading is true.

 

[jeff13601]

Re: merc 140 tach problem.

A few years back I bought a Lowrance LMS350A and I never looked at my speedometer again. I still do not understand why the analyzer didnt work