Help.. Boat will not start

[ericinmich]

With the scan tool you could command the fuel pump LSD to turn on. A lot cheaper way to prove if it's your ECM than to buy one.

How do you know that the ECM was getting the correct inputs to command the fuel pump to turn on?

[IDBoating]

Pardon the slight interruption, but I have a hint to share.

A friend's boat started having difficulting accelerating. It would start and idle but couldn't accelerate hard. Long story short, we determined that the fuel rail pressure dropped under hard acceleration. I presumed this was because the injector duty cycle was so high that the high pressure fuel pump (HPFP) couldn't keep up. The question was WHY - it obviously worked under normal circumstances, so why was it failing now?

What I determined was that the low side driver coming out of the ECM to the HPFP had started to deteriorate. The ECM specs said it should pull that side of the HPFP motor down to no more than ~1.2V (a value determined by whatever semiconductor device they were using to drive it). That means the HPFP motor should be seeing at least (13.8 - 1.2 =) 12.6V. Measuring without the HPFP showed it going down to around 0.7V, a standard voltage drop across a bipolar transistor, but when the pump was there (i.e. increased current flowing) it was only going down to around 2.1V. Thus the pump was thus seeing only about 11.7V. Low voltage meant the pump could not keep up... it could manage the pressure when fuel demand was low (idle), but not when demand was high (acceleration).

The manufacturer's recommendation when the voltage exceeded 1.2V was "replace the ECM". $$$ $$$

As noted earlier in this thread, new ECM's are incredibly expensive. And they're often potted, which means they cannot be easily repaired at the component level. So my solution was a sealed marine relay with a 12VDC coil. The HPFP drew something like 6 amps, whereas the relay coil drew something like 50mA (0.050 amps). I let the ECM drive the relay (which, importantly, meant the ECM was still in charge of when the HPFP was running), and let the relay pull the HPFP motor to ground. Remember, relays don't have an inherent voltage drop like transistors; they have hard contacts which have relatively low resistance, usually in the tens of milliohms. In other words, the pump motor now saw the entire battery voltage - 13.8V, better than OEM - and everything ran perfectly again. From the ECM's point of view, nothing changed. (Yes, I did confirm that the HPFP motor was rated for the full battery voltage.)

It's been running fine for several seasons now. That ECM transistor may be continuing to deteriorate, but the pull-in voltage on that relay coil is something like 7.5V so this fix will keep working for a long time. And now that we aren't flowing anywhere near the current through the transistor, it's quite possible that it's deterioration has been stopped.

A few dollars for a relay, versus a kilobuck+ for a new ECM. Something to keep in mind!

[UNSTUCK]

What I determined was that the low side driver coming out of the ECM to the HPFP had started to deteriorate.

If I'm reading that right, I'd say your friends situation is quite a bit different than this one. There is no circuit between the fuel pump and this ECU, whereas your friends ECU did have a circuit between the pump and ECU.

[IDBoating]

In every EFI engine I've encountered, the ECM controls the fuel pump(s). Reading back in this thread, there are several exchanges regarding the ECM's control of the fuel pump relay. That's what reminded me of my friend's boat. Sounds like some designs have the ECM control a relay, while others have the ECM directly control the pump (either pull-down current sink or pull-up current source). But however it's done, the ECM controls the pump. Since this thread has been discussing the ECM controlling the pump, I thought the story might be useful to anyone else encountering similar problems who does a search and finds this thread. YMMV.

[dustinsnipes]

In every EFI engine I've encountered, the ECM controls the fuel pump(s). Reading back in this thread, there are several exchanges regarding the ECM's control of the fuel pump relay. That's what reminded me of my friend's boat. Sounds like some designs have the ECM control a relay, while others have the ECM directly control the pump (either pull-down current sink or pull-up current source). But however it's done, the ECM controls the pump. Since this thread has been discussing the ECM controlling the pump, I thought the story might be useful to anyone else encountering similar problems who does a search and finds this thread. YMMV.

Well this thing has been really kicking my butt. Got the fuel pump running by grounding the relay and bypassing the ecm. Now I have no fire at the ignition coil. Havent checked anything yet other than spark. Tomorrow going to jump the kill switch to be 100% sure that it isn't the problem. Then will check voltage at the coil. Previously was getting spark.

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[IDBoating]

Could the ECM suppress spark like it suppresses the fuel pump(s) when it believes circumstances aren't "perfect"? You've overridden its control of the pump... which doesn't mean the ECM is "happy" and wants to start the engine.

[dustinsnipes]

Could the ECM suppress spark like it suppresses the fuel pump(s) when it believes circumstances aren't "perfect"? You've overridden its control of the pump... which doesn't mean the ECM is "happy" and wants to start the engine.

It cranked before when I jumped the fuel pump relay with a wire and ran fine. I just have to do some more digging. If I'm not getting voltage to the coil guess the ICM is faulty and causing all the problems. When I turn the ignition switch on I do here a loud click which sounds like it's coming from the ICM I don't know why it does that.

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[chpthril]

In theory, you could likely wire a relay thats triggered by ignition feedback. Relay supplies the input to the fuel pump relay in substitution of the ECM's output to the fuel pump relay. The tricky part is making it safe. Dont want a run-on fuel pump, which is why the ECM controls the relay based on an RPM singal

[dustinsnipes]

In theory, you could likely wire a relay thats triggered by ignition feedback. Relay supplies the input to the fuel pump relay in substitution of the ECM's output to the fuel pump relay. The tricky part is making it safe. Dont want a run-on fuel pump, which is why the ECM controls the relay based on an RPM singal

Yeah the way I have it is not the right way but I was only doing it for a temporary fix. But now I'm having ignition issues. Something weird is definitely going on with this boat.

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[chpthril]

But now I'm having ignition issues

Ignition as in secondary or as in key switch? Ignition secondary would explain why the ECM doesnt trigger the pump relay.

[dustinsnipes]

Ignition as in secondary or as in key switch? Ignition secondary would explain why the ECM doesnt trigger the pump relay.

As in no spark at the coil but couple days ago I had spark so it's an intermittent problem.

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[ericinmich]

It was mentioned earlier to check crank sensor. If I was a betting man I would look at that.

A scan tool would tell you if the ECM is seeing the crank signal, RPM would show up. Buy one or borrow one. Heck, buy one and sell it for half price, you will be way ahead of the game IMO.

[dustinsnipes]

It was mentioned earlier to check crank sensor. If I was a betting man I would look at that.

A scan tool would tell you if the ECM is seeing the crank signal, RPM would show up. Buy one or borrow one. Heck, buy one and sell it for half price, you will be way ahead of the game IMO.

I checked it and it's still there and plugged up haha but yeah looks like I'm going to have to buy one .... The only ones I can find are $700 and up

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[UNSTUCK]

In every EFI engine I've encountered, the ECM controls the fuel pump(s). Reading back in this thread, there are several exchanges regarding the ECM's control of the fuel pump relay. That's what reminded me of my friend's boat. Sounds like some designs have the ECM control a relay, while others have the ECM directly control the pump (either pull-down current sink or pull-up current source). But however it's done, the ECM controls the pump. Since this thread has been discussing the ECM controlling the pump, I thought the story might be useful to anyone else encountering similar problems who does a search and finds this thread. YMMV.

Not to beat a dead horse or anything, but I think it's important (for our posterity) to clarify what you're saying. It is true to say that the ECM controls the fuel pump, but in this case, the ECM is really only controlling a relay. That is all it knows. It could turn on the horn, radio, ect. This is important, because if our posterity ever run into a low voltage problem at the pump, like your friend's boat did, our posterity needs to know not to look at the ECM. As long as the relay is closing the switch between terminal 30 and 87, the relay and the ECM are doing their job. Corrosion at the ECM could cause a low voltage issue, causing the relay not to close, but then you would have a seemingly bad relay causing the pump not to run. Bottom line, if the relay clicks, the ECM is not the problem if a poor running fuel pump. If your fuel pump does not use a relay (I haven't seen this), the ECM could be suspect.

[Stingreye]

I checked it and it's still there and plugged up haha but yeah looks like I'm going to have to buy one .... The only ones I can find are $700 and up

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https://www.obd2allinone.com/mefiscan.asp

I have this one. It reads the data points in tuner pro. I have no idea if it will tell you what you want though. Call the company and I am sure they can tell you if it will work.


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