need help with strange 7.4MPI problem
#21
Banned
![](https://www.offshoreonly.com/forums/images/icons/gold_member_star.gif)
Join Date: Aug 2002
Location: IL
Posts: 5,660
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
Glad to hear you figured it out. We have been chasing an issue on a friend 7.4 for over a year. Can run fine all day on inland lakes connected by channrls, but get it on Lake Michigan where it can run at high RPM for longer periods of time and it appears to go into limp/safe mode. Turn the key off for a few seconds, restart and runs fine for a while.
We've checked codes - none stored, flowed injetors and changed out bad ones. Cant figure it out!!! Soemthing must be getting hot, shorting or grounding and making the computer go into limp/safe mode.
Or maybe its the computer itself.
Glad your issue is solved, because this sucks.
We've checked codes - none stored, flowed injetors and changed out bad ones. Cant figure it out!!! Soemthing must be getting hot, shorting or grounding and making the computer go into limp/safe mode.
Or maybe its the computer itself.
Glad your issue is solved, because this sucks.
#22
Registered
#23
Registered
Thread Starter
Join Date: Apr 2009
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
As I said earlier, even with this issue, nothing would ever make me go back to a carburetor and mechanical ignition advance.
Tom
Last edited by tomtc; 05-10-2009 at 04:12 PM.
#24
Registered
Join Date: Aug 2005
Location: sint maarten
Posts: 1,491
Likes: 0
Received 0 Likes
on
0 Posts
#26
Registered
Join Date: Jul 2009
Location: west of chitown, il
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
I know this is an old post but what did you find? I'm dealing with a similar issue like this as well on a 98 7.4mpi. After 45 min of run time I lose power bad, the fuel pump is louder than sh!t. If I let it sit for a bit I can run for awhile before it happens again. I have replaced the injectors so far(had 3 that tested bad) and now i'm going to order a new pump and regulators.The injectors helped getting on plane but the 45 min problem is still there. I am really confused on this one. Whats up with the fuel pump whining so loud?
#28
Registered
Thread Starter
Join Date: Apr 2009
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
At all RPMs below 4,000, it occasionally starts running VERY rich and power and rpm drops way off. It will do this sometime for just a few seconds and other times for minutes. I have a Floscan and when the problem occurs, the fuel flow will jump way up. For example, at idle it will jump from about 1.2 gph to 5 gph or so. At 2,200 rpm (about the fastest it will run when the problem occurs), it jumps to something like 19gph. When the problem occurs, you can smell the strong odor of the unburned fuel. It does this both when the engine is basically cold and when it is fully warmed up.
If above about 4,000 rpm it runs just fine and the problem does not reoccur until I slow back down and the rpm drops.
This weekend, the problem took on a different nature. Now, the opposite is happening. The fuel flow is very low (lean) for the engine speed and load, and the engine is running VERY rough. For example, it is only showing about 5.5gph at 2,500 rpm, about the fastest it will now run under any circumstances. The problem is now also no longer intermittent and is occurring constantly.
The ECM on the engine is a computer and like any electronic device, it can develop a problem. In this case it appears it was the driver for one of the two banks of injectors. Since everything was fine as far as the computer was concerned (it has no way to know that one set of injectors was not firing properly - this was before the later versions which can do an injector test), no codes were set. It's rare for an ECM to fail but it can happen.
Tom
Last edited by tomtc; 08-03-2009 at 07:07 PM.
#29
Registered
![Default](/forums/images/icons/icon1.gif)
Merc had a problem with a bunch of bad ECM's on the 7.4L MPI early in it's run (1998 & 1999 models). I bought a used 1999 Crownline in Sept. of 2002. In April of 2003, I was having hard start problems. My Merc tech sent the ECM into Merc and even with it being well out of warranty Merc shipped back a new ECM free of charge.
#30
Registered
Thread Starter
Join Date: Apr 2009
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
Merc had a problem with a bunch of bad ECM's on the 7.4L MPI early in it's run (1998 & 1999 models). I bought a used 1999 Crownline in Sept. of 2002. In April of 2003, I was having hard start problems. My Merc tech sent the ECM into Merc and even with it being well out of warranty Merc shipped back a new ECM free of charge.