175 EFI at my witts end...!

[Bartman39]

Ok here`s the deal... I have another engine which is a 150 EFI that was running perfect but I had repaired my 175 EFI and wanted it on the boat...

So... It would`nt run right bog at 2K rpm`s... Ok change the stator and hey it runs better but had a strange intermmitant miss...? Also became hard to start when cold...? Found a bad plug wire which I changed out and it seemed to also fix the starting problem... Next time out hard to start again and still had a miss (was on #4) so changed the coil no effect... Next swapped out the switch box for that bank (inside box) and still had the miss... Note spark was good at idle and could tell a difference in engine sound with plug wire pulled & reconnected... Anyhow this time I took the ECU from the 150 EFI with me also just to rule out it also... Swapped the ECU and fired it up and seemed to run better at idle...? Hit the gas and just bogged and died...? Did this a couple of times and would not rev up in gear but in neutral it rev`s real quick...? Checked all my connections and everything was ok...? Without the cowl it all of the sudden took off running perfect (almost lost my darn cowl too)... I put the cowl back on and it just bogged again and again till all of the sudden it took off like crazy... I ran for about 2-3 miles and went to slow down to turn around and about half way through the turn it died...? I mean it just cut off...? Cranked right back up but bogged again a few times then took off like a rocket again... Got back in close to the dock and went to idle through the no wake zone and it wont rev over 1200rpm or it just boggs and dies... But still revs up like a rocket when not in gear...?

Parts that have been changed... STATOR, switch boxes, complete fuel injection unit, plugs, 1 coil & wire...

I`m starting to think maybe the wiring harness for the motor has a problem...? Possibly the connector for the ECU (why else would it start firing on all cylinders)...?

I`ve been fighting this damn 175 EFI for over 2 weeks and now really regret changing from the 150 EFI which was running perfect and is where all the parts have come from...



PLEASE HELP...!!! thoughts and or idea`s

[northeastcat]

Sounds like a connection problem somewhere, running good then bad then good, I would unplug and plug back in all connectors and see if it helps. Ck all wire eyelets on studs for corrosion. Have you checked fuel pressure?

[Bartman39]

Yes on the fuel pressure its a good steady 41-42 psi... I went over all the grounds and other terminals and all seem to be tight and free from crud...

With the swap of the ECU`s and it went back to running real strong it does make me really want to look at the ECU connector possibly even a complete new engine harness...? I`ll check the connector in the AM tomorrow... What can be done to make better contact if this is the problem...?

[northeastcat]

Use 2-4-C mercury grease on all connectors. I've had small issues due to poor contact at connectors and have had good luck with using the 2-4-C.

[trashy]

Yes on the fuel pressure its a good steady 41-42 psi... I went over all the grounds and other terminals and all seem to be tight and free from crud...

With the swap of the ECU`s and it went back to running real strong it does make me really want to look at the ECU connector possibly even a complete new engine harness...? I`ll check the connector in the AM tomorrow... What can be done to make better contact if this is the problem...?
One thing you can do. FIRST, disconnect the battery. Then on the engine harness at the ECU connector, take an exacto knife and kind of spread the male pins in the connector.

[kingsbiship]

Make sure the foam inside the cowl isn't loose and blocking the air intake.
Just a guess!

[dzalj1]

hi, just my 2 cents, this happened to me not long ago, with the cowling off it ran and started beautiful, once u start putting the cowling on while it is running, it would start to drop in rpm's and then die, couldnt even put it in gear, soo the guys here on s&f helped me out, and they found out that i had a exhaust leak, and that was the problem. just make sure that your base gasket on your exhaust plate in your mid is in one piece, or if it is sealed with some sort of gasket glue.
hope this helps, oh that was just my 02c

[Bartman39]

Thanks to all that have replied... :)

It does run like a rocket with the cowl on too so dont think the foam is the issue its getting plenty of air in and no exhaust leaks (had not thought of that...?) But just about to go mess with it again and try the pin spread trick... (makes sense after swapping the ECU`s and it changed how it ran)

Do have a question about swapping the ECU`s though...? Will it hurt anything to use the 150 ECU on the 175 EFI motor...? I would figure the fuel curve would be different...? If I do find the 175 ECU is bad or has a problem would it be in my best interest to save up and get a Brucato unit rather that find the correct Merc stock box...?

[Bartman39]

Well did everything I thought I should which is... Checked every connection and ground, spread the pins on the main engine harness plug but could not figure out what to use on the ECU plug...? But did notice before that all the plugs and connectors including the plug wires had die electric grease on them...? I had read this was a no-no...? I did not do it but did clean everything of this stuff... It seemed to run better on the hose...

Put it in the water and right off the bat it took off just fine and this is with the 175 ECU too... I ran it for about 15 or so miles at various throttle settings and it never missed a beat... On the way back to the dock I had to idle for a short distance (no wake zone) and when I took off it was missing again so ran it that way for a short time to be sure of which plug it was and again it was #4...? But...! This is the hole that I had just put a plug hole saver in (one of those metal threaded sleeve types) and had used 2 part epoxy to put it in... Could this be the problem, not making good contact with the metal in the head...? I swapped plugs and it ran ok for a short time then went to missing again... Changed it once more and seems to be ok for now... But could the helicoil be the whole issue or causing it...? New head time...?

Man thought I had it with the connections all cleaned...?