Troubled 175 EFI

Burstie

Cadet
Joined
Sep 7, 2002
Messages
6
Hello<br /> First time user, sure hope you can Help. Have a 1998 Mercury 175 EFI been having problems with it for the past two years. On my most recent trip to Canada the engine ran poorly, very poorly. I always thought I had an electric problem since the engine would run well first thing in the morning when the outside air is cold, once engine gets to normal operating temperature it starts to miss and cough, I also will get a drop in RPM's. A friend had me check fuel pressure and I have 38 PSI during the initial 30 seconds the pumps starts and runs. Once the pump shuts down I lose pressure. First thought was that I was losing it through an injector, or that it was blowing pass a split o-ring so when I got home I removed the injector assembly from the motor. I found no leakage either in the injectors or o-rings. I found out the fuel is draining back into the pump. While I had the injectors open I preformed a spray test and found # 1 and # 2 injectors are not firing. Swapped wires and they will fire. Service manual states the problem is with the trigger, stator or inner switch box, which controls the firing of the injectors through the ECU. So the two questions I have are: are there any additions test I can perform in order to pin point the injector problem/switch box problem and why is the fuel draining back into the pump/bowl?<br /> Additional information:<br />* Checked fuel pressure while running 20 PSI.<br />* Checked fuel pressure with regulator disconnected 38 PSI with a good flow.<br />* Voltage to pump is in accordance with manual requirements.<br />* Rebuilt manual fuel pump last year.<br />* Fuel bulb is hard.<br />* I do have a blue spark to all cylinders, using the Mercury Spark Gap Tester.<br /><br />If you need any addition that may help please email.<br />Any and all suggestions you may have will be greatly appreciated.<br /><br />Thank you,<br /><br />Burstie :confused:
 

ODDD1

Lieutenant Junior Grade
Joined
Jan 23, 2001
Messages
1,054
Re: Troubled 175 EFI

mike, I can narrow it down for you...if you have a solid spark on all 6, something that will jump a 7/16" gap, you can pretty much rule out ignition....20 psi running is tooo low, with regulator on you need 30+ psi minimum....these pumps will bleed off pressure after shut down, with a gusge on it aveage loss I see is 10 psi in the first few seconds, then stabilizez and creeps down over next few minutes.....to verify that you have a wiring problem and not a [gasp] bad ecu, check your manual for the proper pins to perform an ohms test across the 3 injector pairs at the large ecu disconnect...all three should be fairly close, if not, a wiring problem exists...otherwise you are looking at a bad ecu injector driver.....if you can find a sympathetic tech with a spare ecu [beer helps] try it to verify....<br /> so what do I think is wrong?<br />after running the motor with the negative side of the pump grounded aside from the ecu and getting the same low readings as before, I would change the pump.<br />after checking for the wiring faults I would retest with a diffent ECU to verify failure of the old one.<br /> I would have some one familiar with mercs efi set all throttle linkage, idle timing, and tpi voltage to 'normal' specs....this should take care of your 'hot to cold' change in drivability....
 
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