|Well, just got off the phone with my mechanic. They have no idea why my boat starts, runs for 30 seconds, then shuts off. They hooked a scantool up to it and everything checks out. For some reason the ECM shuts off the fuel pump after approx 30 seconds. I asked if they would swap out the ECM, but Mercury won't let them until they figure out for sure that is the problem. |
End result is I'm stuck without a boat :-(
They're now waiting for Mercury to call back to tell them what to do next.....(sigh)
Anyone have any ideas?
P.S it's a 2002 Merc 315hp Mag tow sports with fuel boost pump
(Message edited by trash on August 29, 2003)
|Call Mercury customer service and raise hell dont wait for your mechanic to figure it out make them ship the ecm |
|Sounds like the resistor between the PCM power relay and fuel pump relay might have gone bad. Long explanation but I think your mechanic might know what I'm talking about. This would explain why nothing shows up on the diagnostics.|
|This would especially make sense if you have a fuel boost pump which could act like a two-speed fuel pump depending on how it's set up. The PCM activates the relay upon startup and once the engine is running and idling it tries to route through the resistor assembly to activate the other "speed" relay.|
|Is your mechanic at a delaership that carries mercruiser? If so ask him to swap the ECM with one from a different boat. Simple to do and the easy way to see if it is the ECM. The dealership should have no issues with doing this for you. |
Another remote possibility: It sort of sounds like the ECM is not getting the engine start signal and is shutting the fuel pump off like it does when you just turn the key to "on" and not start the motor. 30 seconds is a really long time if that were it so this is pretty unlikely.
If you have it narrowed down to the fuel pump being shut off by the ECM, sounds like the problem should be easily fixed.
|Ref. 001 Tommy Boy; Get yourself a new map! |
|Yes, it's a Mercury dealer. They do not have another engine in stock that has the ECM555 engine control module (I already asked him about that). |
The time that it stays running varies. When it first happened it went from 5 seconds to about 20 seconds on before the fuel pump shut off. Before bringing it in I checked the fuel pump relay (I actually swapped it with the other power relay on the engine) and it's fine. When I talked to the mechanic, he said it will run for him for about 30 seconds before it shuts off. The scantool shows that when it's running, everything is normal (i.e oil pressure, engine temp, etc). It just seems to shut off on it's own......
It's not as easy as that. These new engines are all closed-loop style feedback. Basically this means that any number of things could be telling the ECM to shut down the fuel pump. I would just think that the ECM would log this as a fault.
Ridin'High might have the right idea in that it is something mechanical that the computer isn't tracking. The fuel pump relay does click off though, and AFAIK that section is pretty simple: ECM wire drives the relay coil.
I have to wait until Tuesday before I can call Mercury on this. Damn Canadian holiday weekends.... :-/
|Try to look for an external resistor between the PCM and the fuel pump relay (there may/should be two relays if my theory is correct). The resistor is used to lower the voltage once the engine is running and idling thus reducing pump speed. If the resistor is broken when the PCM switches power to it after the start up period the fuel pump will shut off.|
I understand what you are saying now. That makes sense to me, but is that actually how it is done? I thought they would just turn the pump on and off to keep line pressure up. I'll have the mechanics look and see if Mercruiser does something like this. What engine did you find this type of regulation on?
Where on the engine would this resistor be? I would imagine it must be big enough to dissipate heat (same size as what's on the PP servo?) but I've never seen it..
Thanks for the tip!
(Message edited by trash on August 29, 2003)
|Yessum, that's how it's done on "two-speed" fuel pump systems. I think GM first started doing this in the mid to late 90's. As far as the resistor location in a boat I would guess that it wouldn't be too far from the second relay. Just start tracing the wires back from the fuel pump and see if you can find something. If you can't find a resistor somewhere I am full of horse doody and try someone with a few more brain cells... ;) Good luck! |
|Well, I looked on the mercruiser parts store exploded diagrams of the electrical, fuel pump, and boost pump diagrams and I don't see that resistor anywhere. It's possible that it is integrated into either the ECM or relay housing or ??? |
I'll talk to the mechanic and see what he thinks about this.
|Seems like it's documented for car engines anyways |
|I don't have anything to offer technically, but it seems to me that the Mercruiser 350 MPI is a bad choice of engines for anyone looking to get a new boat. I have a 2003 with this engine and I have had nothing but problems: Low oil pressure, serpentine belt problem, transmission went out. And the problem that Trash is having I have heard others having a similar problem. If I had to do it all over again, I wouldn't buy a boat that has a Mercruiser engine. |
|Kill switch? Seen it before........The wires on the back of switch came loose. (Thanks for the info Chris) Somtimes the OPS controls the ECM functions also. The dealer should be able to hook up test equipment and get a more accurate picture.|
|the fuel pump wont work if the engine isn't running. many engines sense this via feeback from the output of the alternator. loose connection?|
|Thanks for all the tips guys! Mercury has decided () to send an ECM and see if that will fix the problem. If that doesn't fix it.....I'm hoping for a new engine, but who knows?!? |
Peter, I checked the kill switch and I think it's ok. After it conks out you can restart it right away (the fuel pump comes back on like it should when you start). I'll have them check the wiring again just in case.
Charlie, the engine will run fine if the fuel pump is hardwired to the +12 volts, so I don't think the ECM is thinking the engine isn't running.
|Have you checked your anti-siphon valve at the gas tank? Could be clogging up shutting your engine down. Just a thought.|
|By Bob (bob) on Wednesday, September 03, 2003 - 12:00 am:
|I have had pretty good luck with my merc but its not the 350 its the 305. Did have one sensor go bad on the throttle body, T.S. it for the dealer and he checked it and replaced it. I have heard of some problems with mercs but not anymore then indmars?? Actually i think there is way more mercs on the market so the R&D gets passed on to the next line and untimately the customers.|
|Well, the Merc dealer called me back today. They got a new ECM from merc and installed it. Didn't solve the problem. In desperation, they swapped out the fuel pump from another MPI engine they didn't know they had on the lot (what dealer doesn't know his stock on the lot?!?!?!?) and voila! It works. Turns out they tested the fuel pump by powering it directly to the battery and it worked. When the pump speed was varied by the ecm (by PWM or what I don't know) the pump would die. I think I need to see the schematics and make sure it's not a 2 stage pump. |
So to sum up: Engine dies on the water. I put it on the trailer and diagnose what I can trying to get it to run on land. My prognosis was the fuel pump was gone. Take it to dealer, who says it's not the fuel pump, but something else (but they don't know what). 2 weeks later, they say it's the fuel pump. (sigh)
I think I'm going to get a shop manual for this engine real soon......
(Message edited by trash on September 04, 2003)
|Glad they finally got it figured out.... you are probably ready to get back out on the water. |
This reminds me of a problem I once had on one of my motorcycles when it was new. It would occasionally stop running on two cylinders (out of four). Amazingly it would continue running, with enough revs. I suspected a coil (typically 2 on a 4 cylinder bike). Each time I took the bike in to be checked, the engine was running fine and all checked out. Finally, one day I got it in there to the shop while it was running bad and they tracked it down; was an intermintently bad coil.... They promptly replaced it under warranty.