2000 350 MPI Fuel Delivery Issue

[Randy Dive]

Hello guys, I am having issues with my 2000 Mercruiser 350 MPI MIE. When I hit the start switch, it shows 40+ psi fuel pressure, then immediately drops to around 20 psi. I had a mechanic look at it and said its the fuel pump. This motor has the Cool Fuel system (Gen I) and is mounted under the motor. Any suggestions that might help me avoid pulling the motor would be GREATLY appreciated, as the engines sit amidship and I need a tele-extender just to pull them. Additionally, the engine has new injectors and a new fuel pressure regulator. Thx...

 

[alldodge]

No need to pull motor to replace FP, its mounted on the port motor mount, and while may be hard to get at, it can be removed and replaced.

Tell us more about the the issue(s) and what happens when?

Serial number of motor?

 

[Randy Dive]

Oh boy, here we go!! The motors were both just replaced. The original motors were Horizons, but had no serial plates. We determined the serial range to include OL302199, which seems to match the parts we were needing during the refit. These motors are in a 2000 Luhrs. 350 MAG MPI, with the old-style intake manifolds (1-pc). I originally thought it was getting no spark, but the mechanic found that to be inaccurate. He pressure tested the fuel system and determined the system spikes 40+ psi then immediately drops to around 20. According to him, this is not enough pressure to fire the injectors, which is why I have a no start situation. Battery is fully charged (and new), we have 12.9v going into the injectors. The motor only has about 3.5 hrs on it, it was running, shut it down and the next time I went to fire her up, nothing. Fuel filters are new, and I replaced the fuel pressure regulators in the Cool Fuel system because they were rusty when the motors were out. As an aside, the mechanic who installed the motors is not the same guy who is troubleshooting her now (looooong story) Also new cap, rotor, plugs, wires, coil, ignition sensor inside distributor. Please let me know if there is any more information that would be helpful. And thank you for the assist...

 

[Randy Dive]

Additionally, I was told that these particular motors were only built for about 3 years, from 1999-2001. Allegedly they have the the Mercruiser intake as opposed to the standard GM intake, and after 2001 Mercruiser stopped using their own intake setup and went to the GM 2-pc intake manifold. Also, the distributor is the round one, not the square top. Don't know if this will help any, but I figured the more info, the better.

 

[alldodge]

motors were both just replaced.

Both motors where replace and neither will start, did I rear that correctly?

Your pressure should be at 30 psi, so it being able to build to 40 is either a restriction on the return side or maybe a gauge issue. This would not be why it wouldn't start.

When motor is cranking, does the tachometer show at least 300 rpm?

0L320199 is a 7.4 but 0L320200 is a 350 and first SN in series of Horizon MIE

The injectors start firing if the ECM can read a signal from the distributor. Being a Horizon I would assume it has a TBV dizzy. If your not seeing rpm check for spark.

 

[Randy Dive]

Yeah I wasnt sure about the serial #, only that the first gen number series allowed us to get the correct parts. The port engine runs perfectly. The issue is only with starboard. The tach does not move when cranking, and I have already tried disconnecting the gray wire from the tach as described in other threads. We checked for spark... we have spark at the cap, and at 6 of the 8 plug wires we checked (all checked but the 2 forward outboard wires due to inaccessibility). I am n ot sure of the make of the dizzy, so I cannot answer that one... but I would imagine youre correct. As an aside, the tach on the port motor does not work, but the hour meter that is built into it does. Not relevant I know, just throwing it out there.

 

[alldodge]

If its a TBV then it can be tested, and it has usually 2 wires (Red/White and Green/White), but if the pickup coil has been replaced it may have one additional black ground



It its the EST distributor will have 2 connectors on it as shown

 

[Randy Dive]

It is the TBV unit. The re/white and the green/white wires, plus the additional black ground wire.

 

[Randy Dive]

As mentioned, we are getting voltage to all of the plug wires, so I dont think the distributor is an issue. The 40 psi fuel pressure is literally less than a 1/2 second, then it drops to around 20. I just dont want to become a parts replacer, and accidentally fix the problem while spending much unnecessary cash.

 

[alldodge]

Under no time should the pressure come up and drop quickly to 20, or any other number. It should come up and when pump turns off prior to cranking, it should hold, and could go down really slow.

So there is a leak between pump to regulator. Can be anything from pump, lines, injectors, and reg. Even with 20 psi it should fire, but probably run like crud

To find out if injectors are firing, but not enough fuel, use a NOID light.

In first post you said motor has new injectors, if these came from ebay or the like, they may be junk. Only way to know if they are good is if they came from Merc dealer or they have been cleaned and flow tested by a reputable marine test facility

 

[Randy Dive]

Hmmm ok, I will check out the injectors. What are the odds that all 8 are bad? Wouldnt 1 or 2 cylinders at least try to pop off? Yoyu may be closer in thinking theres a leak that is preventing fuel from getting to the injectors in the 1st place.

 

[alldodge]

Hmmm ok, I will check out the injectors. What are the odds that all 8 are bad? Wouldnt 1 or 2 cylinders at least try to pop off? Yoyu may be closer in thinking theres a leak that is preventing fuel from getting to the injectors in the 1st place.

Unknown without more testing, but would think not all injectors would be bad. I'm thinking the injectors are not being turned ON by the ECM, so need noid light