94 mercruiser magnum EFI problems

"Have a 94 ski sanger w/mercru

"Have a 94 ski sanger w/mercruiser magnum 350 EFI boat has ran perfect since new till now. It won't go over 3400 rpms and starts to hesitate at full throttle. It has been in the shop for over a month and they are frustrated. The computer,distributor,cap,rotor,plugs,plug wires,injectors,fuel filter,map sensor have all been replaced. Timing chain has been checked and mercury says all the read outs are right where they are supposed to be. It keeps fouling 4 of the plugs and is running rich at idle. Compression check is fine. They are down to checking every wire in the wire harness. Any help would be appreciated."

Did they clean the throttle bo

Did they clean the throttle body and idle air control (IAC)? Test the throttle position sensor (TPS)?

Yes..they are currently in the

Yes..they are currently in the process of isolating every wire in the wiring harness and checking each one. They think a spike in voltage caused the ECU to go bad. They said the vaccum pressure is at 15 which he said he thinks is low but mercury says it is w/in the perameters. So far havent found a vaccum leak. He says 2 cylinders are off 37% but says that is not a big enough problem to cause this issue

Also after replacing all the p

Also after replacing all the parts mention above they took it and lake tested it and ran no problem at 4600rpm w/out a hiccup. We pick it up and right away have an issue

Nate
Are the 2 cylinders that

Nate
Are the 2 cylinders that are "off" next to one another? If so may be a head gasket problem. 37% is too wide a range to dismiss as "not a problem" IMHO
Bert

How long was the lake test; 15

How long was the lake test; 15 min.? Did you go with them?

Give me a "good carb"

Give me a "good carb" any day.

Bert I am not exactly sure abo

Bert I am not exactly sure about the 2 cylinders being next to eachother. The guy doing the work has been a boat mechanic for a long time and seems to not be to worried about that part. I will find out tho. I was thinking the same thing. They say it is blowing out black exhaust smoke also. Guy as far as the lake test goes I am not sure how long the lake test went for I was not w/them.

Is it TBI or MPI?

Is it TBI or MPI?

Did they check for a missing e

Did they check for a missing exhaust shutter (they fall into the Y pipe and cause an exhaust restriction)?

"If it's MPI, you could ha

"If it's MPI, you could have several dirty injectors.
Have you tried some injector cleaner?
How many hours on it?

Rod"

""Give me a "good carb

""Give me a "good carb" any day."

Guy, you aren't serious, are you?

Just kidding; the last thing I want to do is start a huge heated debate about the relative merits of carbs and MPI.

When a carb is working as intended all is well. Gee, that's just like MPI I guess?

Rod"

I've seen Bad ignition coi

I've seen Bad ignition coils do similar things.

"Rod:

No debate from me. C

"Rod:

No debate from me. Carbs are high maint. considering needing to be rebuilt every few years. But the rebuild is simple for a duece. What I like about MPI engines is as you have stated. But, as seen here in discussion, there appears to be a need of add'l training of employees in the field on MPI service.

Look at the number of MPI repairs where the dealer has just swapped nearly the entire fuel management and ignition system and the engine still is not working 100%. That bothers me. I'm half tempted to get the necessary MPI tech. training and go back to work.

Parts swappers are not marine techs. They are there to get the boat in/out quickly while making the dealer the most profit in the shortest time--nothing wrong w/a business making money while serving their customers.

A good tech. has the training, experience, systems knowledge and most of all the ability to logically think problems through to complete the repair. MANY times electronic problems are intermittent which is the nature of the elec. beast. Two major enemies of electronic systems are heat and corrosion. The GREAT tech knows it and is able to recreate the problem w/a heat gun or circuit chilling spray and how to find the corrosion problem.

In my opinion, mfgrs. NEED to use higher quality military grade tinned copper wiring and sealed plug connectors to prevent corrosion failures a few years after purchase. These changes will cost a bit more but I am willing to pay for it.

From a sales standpoint dealers w/a lower retail cost make more sales/profit. In the end, MONEY always talks last and loudest."