175 Merc EFI intermittent issues

[sparky31]

Guys, I need your help please. I don't know where to start. Here goes........The motor starts like it always has before......when I am idling around It sounds like it is missing......when I give it more throttle it doesn't pick up rpm......I even had it WOT and it wouldn't get up on plane.....if I play around with the throttle for awhile it comes out of it and runs fine. I get to where I am fishing and drop the trolling motor for an hour or two it will run fine then also. This has happened the last 2 times I have been out. Any and all info. will be helpful and appreciated. Thanks.

 

[Faztbullet]

Re: 175 Merc EFI intermittent issues

When it does this you need to check the spark on all cylinders as you may have a stator or switchbox problem. Is it smoking bad also??

 

[sparky31]

Re: 175 Merc EFI intermittent issues

It's not smoking anymore than usual. I bought this boat last July. I fish several tournaments and lots of fun fishing also. It just started doing this the last couple of times out on the water. What I don't get is that it does come out of it and runs great. I am going to do some looking at it today. I will post anything that I find. I am not real mechanically inclined, which is why I am asking for your help. Just want to get some ideas that a normal guy like myself could look at. I will def. check battery connections. Thanks alot guys.

 

[Coloradolakeboy]

Re: 175 Merc EFI intermittent issues

I have a 1980 Merc 175 that has the same problem. Mine is not an EFI. I am replacing the old fuel lines. The line from the tank to the bayonet plug had cracks in it. What is changing after the warmup?

Some ideas are...
Fuel line stops allowing air in line.
Float in carb unsticks and stops engine from flooding and reduces smoke.
Bulb check valve starts holding gas.
I don't suspect battery connections because after warm up my motor runs fine.Check out this article.
http://forums.iboats.com/showthread.php?t=283363

 

[sparky31]

Re: 175 Merc EFI intermittent issues

Here's what I done today. I checked my battery connections. I checked all my ground connections. I did find one that was a little loose. The ground I found loose was on the back where the sparkplugs are. I took the fuel filter off and looked inside it. It was probably 3/4 full of fuel. The fuel looked real clean and I could see the bottom of the filter. I don't know if that really means alot. I put it back on. I took it to the lake and went for a spin. It started on the 3rd crank like always. When I put it in gear it was doing the low power, sputtering thing. I put it in neutral and reved the motor up around 2000rpm. I watched the tach and it would rev up to around 4000 and drop back down to 2000. It did that a couple of times and then it stayed around 4000. I put it in gear and it ran fine after that. Got up on plane and went 60mph with no hesitation or sputtering. I shut the motor off a couple of times and never had a problem again. This is the same that it has been acting the last few times I've had it out.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

For giggles I took the boat out again tonight. I had no problems with it at all. This is leading me to believe there is a leak in the fuel line or bulb. My theory is that it didn't sit long enough to lose pressure. I will have to let it sit a few days and take it out again. If the problem is still there, I will be checking my fuel line connections and replace the bulb.

 

[CharlieB]

Re: 175 Merc EFI intermittent issues

You haven't mentioned the spark plugs. How old are they? What do they look like?

Sputtering, poor running, clearing by reving the motor is often a sign of a failing ignition caused by carboned spark plugs, test spark while cranking to be sure the system is making the voltage necessary for a hot blue arc at 7/16 inch gap then change to a new set of plugs and retest on the water.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

The motor had a tune up this spring before I started fishing. This included new plugs. My son and I went fishing this morning. It ran fine all day. We were on a no wake lake.

 

[CharlieB]

Re: 175 Merc EFI intermittent issues

ALWAYS carry a spare set of plugs and a wrench.

At the first sign of any trouble, remove the plugs and look at them, if they are excessively sooted and fouled the motor will be difficult to accelerate.

Excessive idle time can foul a plug and reduce power until the plug burns clean again. Once fouled and cleared there are residues that will NOT totally burn off and eventually the plug(s) will need replacement. Having a spare set and wrench aboard can save your trip/weekend.

If this starts to become a more common issue then you may need to check your EFI system for possible slight over fueling at idle/low RPM which could be caused by a restricted vacuum sensor/plugged hose, or a Throttle Position Sensor (TPS) slightly out of adjustment.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

I know it's been awhile since I have posted anything here. Sorry for that. The motor is still doing the same thing. The mechanic I have been talking to said he probably won't be able to diagnose the problem, unless it does it while he has it. It happens so sporatically, I can't see taking the chance of spending $150 for diagnosing and not finding the problem. It doesn't happen enough for it to be a major problem. Just very annoying. I have some new info. that might help narrow it down. I had a tourney on the Mississippi a couple of weeks ago. I made a 12 mile run and it died on me 3 times. WOT and died, just like somebody hit the kill switch. I put it in neutral and turned the key over. It fired up right away and would run fine. That was on Fri. On Sat. it died 2 times on my first run. It was probably like 7 miles. On Sunday it ran perfect all day.

 

[coolguy147]

Re: 175 Merc EFI intermittent issues

does it like bog down it just shut off like you turning the key off?

sounds electrical to me.....

 

[sparky31]

Re: 175 Merc EFI intermittent issues

All that it usually does is act like it's running on half the cylinders. WOT going pretty much no wake. It doesn't have enough power to get it onto the trailer when it's doing this. It doesn't happen all the time. It comes out of it and runs great, usually the whole rest of the day. The only time I had experienced the dying part was when I was on the river going 60mph. It acted like I reached down and turned the key off. Here's the kicker......I could trim down a little and throw it in neutral and hit the key and be back up on plane before my wake would catch me. It would start right away.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

Bump

 

[CharlieB]

Re: 175 Merc EFI intermittent issues

When it dies like this, would it restart if you DIDN'T trim down?

The reason I'm asking is if there is a wiring fault (intermittantly) killing the motor, changing the trim may shift the wire, possibly disconnecting a short that could be happening in the kill circuit.

A low power condition CAN also occur with a 'slight' grounding of the kill circuit.

Disconnect the black wire with the thin yellow trace from the ignition modules to the motor harness. Connect an Ohm's meter to this wire at the motor harness side. Observe the Ohm's reading, with the key off you should see lots of continuity, turn the key ON there should be NONE. Now trim the motor to the position that it is in when you run into these problems, start jiggling the wire harness and watch the Ohm's meter for ANY change. ANY continuity indicates a problem, finding it and correcting intermittent electrical problems takes massive time and diligence.

 

[maxamy]

Re: 175 Merc EFI intermittent issues

I've been having very similar problems....I have a 1997 Mercury EFI 150 and it has died on me the last two weekends I've used it (coincidentally during tournaments also) I run real hard at the beginning of the tournament and I am sure you do also. Someone has pointed out to me that it could be junk in the VST floating around and clogging up the needle and seat, which could explain why it is intermittent. I will let you know how it has worked out for me...I took mine apart (warning 40+ dollar o-ring) and cleaned it, drained all the fuel and replaced fuel lines and bulb...I hope this works for me because it wasn't real expensive maybe it could work for you also....your problem could very well be fuel and not electrical....

 

[sparky31]

Re: 175 Merc EFI intermittent issues

I will check that Charlie. You think that it would also make it be underpowered like I also have described? Let me know what you find out Maxamy. I have been advised to change the fuel line all the way from the tank to the motor. I was told by one guy that he says it sounds like my fuel line is collapsing.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

Sorry about the thumbs down icon. Don't know why it is on the last post.

 

[sparky31]

Re: 175 Merc EFI intermittent issues

bump

 

[Faztbullet]

Re: 175 Merc EFI intermittent issues

Whats the fuel pressure?

 

[maxamy]

Re: 175 Merc EFI intermittent issues

So far my problem seems to be a combination of fuel and electrical.....Mine died again and this time I found the problem...there was no power going to the elec fuel pump.....still trying to determine if it was a loose wire, bad connection or hopefully not a bad ECU......but either way I am starting to get a handle on whats wrong....I changes the fuel lines, bulb and replaced all my fuel which doesn't hurt to do that every few years anyway.... it was less that 50 dollars to do that and worth the piece of mind....now to the problem at hand....when yours dies see if there is power going to your fuel pump (simple test light check)....if not, create two jumper wires off the battery and run to your fuel pump....if she runs you got the same problem I got....Hope this helps you ......