1999 MIE 7.4 MPI ECM Parameter's

[bud37]

We had some discussions on here about that module that is located under your dash console....do a site search, it may help you here...(not an expensive part)...that module takes signals from the engines to compare rpms.

[waterbug]

Update. Fuel pressure. Key on engine off.
STBD 40psi and steady
Port 40psi and slowly leaks down.
They both spike to 50psi when the pump turns on.
Where is the best place to begin? Fuel pressure regulator, injectors. Is this related to my loss of power issue or is this leak down a separate issue?

[Viper]

Have you checked fuel pressure under way? Really need to test it at that rpm under load to see if you're getting rated pressure still. The pressure loss in a static state can be one or more injectors, a line or fitting leak, or a faulty regulator where it's going through the by-pass circuit when it shouldn't. Also inspect the vacuum line going to the regulator. There is also a tiny round filter screen under the regulator that might be clogged. A pain to get at though if it's the unit I think it is. Do you have a Gen II Cool Fuel module?

If you shut her off and try starting after 10 minutes, does she fire up right away or is she sluggish to start?

[waterbug]

So this is what my fuel system looks like. Regulator on cooler. It is mounted below #1 cylinder beside oil pan. There is also an inline pump mounted before the spin on filter and something that looks like a solenoid before that. Not sure if this is factory or not.

[Viper]

Yep that is Cool Fuel II. Not easy to work on because of it's location, and OEMs usually don't take that into consider with some builds/models.
If you scroll through this, you'll see some perimeters for normal reading... https://d3gqux9sl0z33u.cloudfront.net/AA/AR/wetbristol/downloads/224953/Mercruiser_v8_7.4_8.2_litre.pdf

[Viper]

Source of the post ....There is also an inline pump mounted before the spin on filter and something that looks like a solenoid before that......

Can you post a pic of that?

[bud37]

Does the other engine have the exact same set up ? Like Viper says, a pic would be good.

[waterbug]

Did water test this morning for fuel pressure. Needle oscillates 10 lbs or so until about 2500 then starts to smooth out until 3000 then holds steady as can be at 42.5 psi. Was able to hit 4000 rpm on port and held relatively steady only dropping off slightly. Throttles are no where near even when both are at 4000 rpm. Port about 80% of travel STBD about 60% of travel. Bother even until about 2500 rpm. Checked tach vs. diacom and spot on again.

As far as getting engine to temp then shutting off for 10 minutes and restarting. (checking for leaking injector) It fires right away revs (1200 or so) then drops to around 400 then revs back to 1200 then smooths out.

The pics are of the inline pump before the spin on filter. It comes from the tank to the valve/solenoid? then to the inline pump SAEJ1171 then to the spin on filter then to cool fuel II. Both are set up the same way.

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20200322_100738.jpg

[bud37]

From what I can see there, it looks to me like this is something that has been made up to maybe overcome vapor lock or the pumps failed ????? Nothing in those pics looks factory original to me,(I did look at the Mercury parts manual), now that being said it is just my opinion and I am sure that Viper can speak to this soon ....perhaps there was a tech service bulletin back then.

On the throttle positions.....put them in the approximate positions they were in when you did the water test then remove the flame arrestor and compare the throttle plates to see if they are close to the same. Did you notice any timing differences or fuel flow between the two engines.

A reminder, try to avoid revving the engines at the dock excessively, damage can result.

[Viper]

Ya there's no way that's original. And it's poor wiring and routing practices, not good. Someone has added a pump and fuel solenoid valve. Now later application typically have electric fuel valves but that's not looking like a factory install. This must have been done to either correct a problem like vapour lock as bud mentioned, or a work-around for something else. It looks like a steel line coming out of the pump. Have you checked to see if the original pump on the Cool Fuel Module is hooked up and operational? I called up your serial number and I don't see a mechanical pump on yours but have you checked to see if there is a mechanical fuel pump attached to the raw water pump on the engine? Earlier models were done that way when GM stopped building blocks for use with mechanical pumps. It was Merc's work-around until they could get out an all electrical delivery system. The fuel pump is bolted to the raw water pump instead of the block. If yours had that set up originally and they ended up tossing the water pump after it failed($$$), they may have come up with this add-on to replace the primary/low pressure/lift pump if it was required in that build though I don't see that in the diagrams.

Is there a plastic cover covering your fuel filter?