1991 Mercury 200 EFI fuel pump issue maybe ecu?

[ChuckC]

My 1991 Merc 200 EFI is having an issue. I think it's the ecu but wanted some advice first. Last week I went to take the boat out and wouldn't start. I turned the key to the on position and couldn't hear my high pressure pump come on. Ran a ground wire and it started running. Went out for a spin and it never ran that good ever! On the way home it stumbled a couple times. I think I may also have a fuel delivery problem as running it the engine will just die. It will fire back up every time, sometimes I have to crank it a bit, but it always fires back up. Also it will from time to time have no power. Full throttle and maybe get 1,200-1,500 rmp and then it will "snap" out and take off. Talked to a local guy that owns a shop and he said he's never seen an ecu go out on them. Could the ecu be causing all of these issues or do I have multiple gremlins running around? Thanks in advance for any help!

[CharlieB53]

Check the entire fuel system. Install a temporary clear hose from the pulse fuel pump to the VST, run the motor, watch for any air bubbles indicating air sucking into the system somewhere before the pulse pump. Be SURE to REMOVE that clear hose once finished testing, it is not recommended for fuel use.

Check fuel pressure at the high pressure port, make sure pressure remains steady at WOT.

As you have already installed a groundn wire you need to check fuel pressure and compare to the ECU running the pump or your ground wire running the pump. If your ground wire improves pressure then suspect the pump driver within the ECU.

If pump pressure varies using your ground wire then suspect the pump or regulator.

Edit; Do you have the FACTORY Service Manual?

Send me a PM with a good email address if needed.

[ChuckC]

Thanks Charlie! Sent you a PM. I will try this out today and tomorrow after work.

[mn808gade]

b4 starting HP fuel tests,verify lift pump functions.most square liftpumps need a rebuild kit installed (if not serviced already)-th.

[ChuckC]

Thanks for the help! Got it down to the ECU. Going to send it to Simon.

[TEXAS20225]

if its a analog ecu i dont think it can be tweeked as in a 1994 down models does it have the pig tail on it for ddt plug in? it may have been changed

[ChuckC]

Well back for more help =) Had the ECU redone late last summer and worked like a champ. For about 5-6 times having it out. I replaced all the fuel lines, filters why ecu was out. Now it ran good or the first few days and now I can only get some RPM after putting it in natural and wrap it out a couple of times. Get on plane and then can only get about 3/4 throttle and it starts to stumble and bog down. Lift a little and it comes back. Could ECU be acting up again? Any suggestions? Thanks in advance!!!

[wired247]

Sounds like fuel delivery. Low pressure pump, high pressure pump or regulator. Get a cheap analog fuel pressure gauge, a long hose and a schraeder valve adapter and you can watch the fuel pressure when you get to the point where it cuts out.

[ChuckC]

Sounds like fuel delivery. Low pressure pump, high pressure pump or regulator. Get a cheap analog fuel pressure gauge, a long hose and a schraeder valve adapter and you can watch the fuel pressure when you get to the point where it cuts out.

Thanks! Will try to do that asap!

[KOMotion]

Could it be a bad throttle position sensor?