1996 Mercury 175 EFI - Occasionally Doesn't Start

I have a 1996 Mercury 175 EFI that occasionally starts for about two seconds then dies and then refuses to start for a few hours. It turns over but does not fire at all until some time later when it will starts normally. Has only done this a couple of times this year. Of course when I take it to my mechanic it starts every time and everything is checking out fine. He did say it runs a little rich and could possibly be fouling plugs so I started carrying a set of plugs and a spark plug socket to try next time. Both times it failed to start I had made two 1 mile runs and fished for about an hour before trying to head to the third spot. It normally cranks easily and never dies so when it starts and dies immediately I know I'm in trouble.

Anyone had or have seen a similar problem.

When it happens, have you been able to pull a plug or two and see what it looks like? When a plug fouls, they usually don't clean themselves. I'm wondering when it happens if you have a good spark.

Sounds like the fuel pump driver in ECM is going out. Have you noticed if you can hear the fuel pump running when the key is first turn on it will run 5 seconds then shut if it is not running during your no start problem that is more than likely the pump driver. That has to be sent off for repair. I used to use Brucato but they do not repair anymore. Simons Mottorsports in
California is the only place now that repairs......OPTI

Thanks Opti, I'll check that next time. Could that be a temporary condition where the pump driver in ecm comes back on line?

rb7764, I haven't had the problem since I started carrying new plugs and a wrench. I hope to check that out next time also.

pretty sure Simon has quite doin' "anything".. don't know of anyone else.. lotsa folks lookin' for someone ta do ecu work..

I added a temporary ground wire under the cowling that I can use to test the fuel pump when it fails to start again. I plan to remove the ground wire from the fuel pump that goes to the ECU and replace it with this temporary ground. If that fixes the problem then I plan to use the temp ground plus I also installed a temp hot wire from a switched power source (used the purple switched wire near the starter solenoid) to get back to the ramp. For a permanent fix I plan to wire the fuel pump directly to the battery using a relay that is triggered by the switched wire from ignition.

I was checking some of the wiring and connections and was surprised to discover that the positive side of the fuel pump is hot even with the key off. I removed the ground wire from the pump that goes to the ECU and used the temp ground and the pump ran but did not stop in a reasonable time (about 20 seconds), it normally stops after about 10 seconds. So i see why the power to the pump has to be tied in to the switched ignition if you bypass the ECU.

The only concern I have is that it appears that the kill switch does not cut the switched ignition power so the pump would continue to run if the kill switch was activated.

wired thru a relay or direct it will not shut off like when controlled by ground from ecu... go here for choices if needed.. i pretty much used "painless" exclusively.


https://www.summitracing.com/search...cending&keyword=fuel%20pump%20relays

some might say you need a way to kill tha pump circuit jus like tha ign. kill circuit switch.. your choice.. if you decide ya wanna kill pump and ign. with one lanyard ya gonna need a different "kill" switch.. i've done it both ways but never had a problem by not using a combination ign/pump kill switch lanyard ...............

OK, wired the fuel pump through a relay and the boat has not failed to start. Now I have a new problem where the motor bogs down for a second or two and then kicks back in at full power. I don't have to restart. I asked Simons if they tested this ECU and they replied that they could but that this ECU normally has intermittent failures that are hard to detect with the test. They said in their experience the fuel pump driver and the 5&6 injector drivers are the most common problems found in almost 100% of the these ECU's they receive. I had not told them what problems I was having, I just asked if they tested them. Their description certainly fits my recent problems.

I'm going to check the ECU connector and ground but if they check out I am considering the $600 refurb.

OK, just to close this one out. My motor was bogging down more each trip so I finally sent in the ECU to Simons and had it rebuilt. They said the fuel pump driver and several of the injector drivers needed repair. One week turn around and $625 plus shipping and tax so over $700 total. I've taken it out for a couple of all day fishing trips with none of the original problems plus it starts quicker. Since they fixed the fuel pump driver I took the relay out that I had installed to wire around the ECU and re-hooked the original wiring.

Thanks Opti, your 2 for 2 on diagnosing problems on this motor.

Your welcome sir glad i could help