502 Problems FIXED
 

You may remember I have been having to feather the throttle to get my EFI 502 to start, once started, she is fine. (since new SM exhaust, plugs, cap, coil, all factory parts.)
Today, water test;
She ran great the first 20 minutes, up to 4500 RPM, then a loss of higher RPM, TACH IS ALL OVER THE PLACE, so we limped back at 2000 RPM.
She starts fine, but that is it.
HELP

I will our club mechanic look at it, ideas?

I think distributor and timing?
Bryan

Maybe water in fuel or carb. I would drain the carb an try again. Change the water seperator filter if you don't have use quichsilver dry fuel

LOL....hummm....it's a 502 EFI....check the basics...fuel, air, heat... at all cylinders...heat=spark and compression....then pin out the sensors....get a read on your TP at idle and wot.

Tach readings eratic indicates a problem with the distributor or wiring. Check to b sure no wires are chafed or cut, all connectors are tight. Check inside the distributor for corrosion, loose parts. If the tach is crazy, the problem is not fuel related.
Good luck!!!

uuh EFI "drain the carb":crazy: shame on me

All wires are brand new, new plugs, new cap and rotor (all merc stuff).
Prior to all this, she rocked for 2 seasons, 157 Hours.
Gas is all fresh, including seperator. All maitenance is done every 30 hours, very well maintained, I am very anal.
I think the cap and rotor is the culprit, we had to pry the old rotor off! Our Merc mechanic on the phone thought the IAC sensor was the reason for having to feather the gas to fire her.
Like I said, she ran great for 20 minutes, then the problem hit.
We should know soon, she is now clean and covered....
Oil Press perfect, temp perfect 175.
Thank God for warranties.
Bryan

Maybe your fuel pump doesn't work right.

Your problem is in the primary ignition somewhere. If you have fuel or secondary wiring (cap, rotor, plug wires...) the tach will remain stable. The pickup in the distributor could be the problem, but not likely.
The rotor commonly sticks unless you use anti seize on the shaft.

Lubed the new rotor, th eold was a bear to remove.
The old was factory installed, 2001 OM series 502 Mag.

BLOWN 1500, the tach is now way erratic, 1800 to 2400 bounce when etc...
Bryan

Check all your ground connections on the block! An erratic tach (and running bad) on a Merc EFI setup is a sure sign of a missing ground to the EFI system. There are several ground straps coming out of the harness that must be connected.

In addition to what was mentioned above, I would put a scanner on the motor to read all the sensor values and check for codes. If there is a stored code, it would most likely point to the problem.

I had a friend that had a mouse or a rat get in his engine compartment, chewed his primary lead going to the ignition coil almost in two, like blown 1500 said earlier, check you wires going to the coil [primary and secondary] also grounds on the motor
sure sounds like an ignition problem to me

Plugs look brand new.
ALL wires are clean and snug, all connections snapped firmly in place..
Dist Cap, one screw was hard ro remove, possibly it was binding, fixed.
Neighbors get 20 more minutes of sleep until I fire her off.

What actually gets reset from the red button breaker on the engine?
Bryan

don't waste time looking at plug wires, cap, etc.
Your tach gets its signal from the ignition trigger. If your tach is erratic, then it is going to be in the ignition trigger, its wiring, wires to the tach, or the tach itself.

You say that the tach is erratic. When the tach is being erratic, can you hear the misfiring in the motor? If not, then you may just be having a tach issue that is unrelated to your engine ills (coincidences do happen).

I did go reread your original post and it sounds like the engine is indeed running like h@ll. Like others have pointed out, wiring connections need examined and don't forget grounds...

Just fired her off, same symptoms, tach is still jumpy and she won't rev up, no missing sounds.
Bryan

Well, sometimes I am my own worst enemy and forget the saying of "don't fix what is likely not broke!"

Stuck the old coil on and FIXED.
Runs like a champ.

I still have the have to give it a tad of gas issue to start her. I will next see if any codes are in the ECU.

Thanks guys, Bryan

Glad to see you found the problem. Thanks for letting us know what it was.

It's Sunday, your neighbors needed to get up before 9:00 to go to church anyway.:D

Bryan, Glad you found the problem. I have the same engines.....2nd set (just replaced by Merc, Bad exaust.) they are 2000's. I have never had an engine so critical on voltage, If you are at all low 11 or 12 volts they will not start right. I have had to feather the throttle to get it to start also. The other thing is, if it is cold like 45* there is no choke on these motors, they really like the 70* air temp better. good luck, Mark

Thanks for the replies. It was odd why I even replaced the coil, it was a cosmetic issue believe it or not and I got it for free basically.

She is running rock solid now, I started her after each thing I did so I would be able to tell what I did that helped. All conections on everything looked great.
Bryan

Bryan - Glad to see that you have found your tach problem, but I am wondering about your having to feather the throttle to start on an efi. My buddy came over to the house today, he has a 27 Fountain Fever with a 502 Mag Efi in it and he said towards the end of the season last fall he had to feather the throttle to start it, and it was hard to start a couple of times. But every time he did have to feather the throttle. His boat it winterized now, but next weekend he is dewinterizing it. He was talking today that he talked to a mechanic about why he is having to feather the throttle. The mechanic was not sure, but he said it is not normal, and it could be with the sensors. My buddy was thinking about getting it looked at before the season goes into full swing. I was wondering what you found out with yours so I could tell my buddy, it was wierd because I read this thread last night, and then today out of the blue he showed up and told me about his delima and I told him someone just posted a thread about this problem.

It is a strange thing about the feathering. I could see where if it were in the shifter it could be the safety switch. The throttle though is a bit kooky. I would take a look at the engine cut-out switch on the throttle linkage on the motor. This is the swithc that momentarily cuts voltage to allow shifting in and out of gear. The actuator on the motor should be centered except for that momentary movement just as the shifter is engaging forward or reverse. Take a look without touching anything and see if it sitting centered. If so, move the shifter in and out of gear and apply throttle. Re-center then check it again.

It may not be the problem but it's a viable culprit. I've had two "older" carburator boats that had to be re-adjusted because of this. In fact one was so bad I couldn't bring it out of gear...

I could hear the sigh of relief from here Bryan.. Now how much better does that thing run after the exhaust change etc ?