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GT40 electrical/fuel pump issue

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    Posted: October-07-2017 at 6:22pm
Hi guys,
hope you can help me out here! Boat is '97 SS.
Just recently had a fuel pump issue. Turned out to be the relay of the computer. Boat ran perfect, even better then before, which was already good. Happy me!
Only a week or so, and a couple hours of use later: same issue it seemed (no priming of the fuel pump. Engine turns over but doesn't start). Not so happy me.
Figured maybe the relay for the pump went out this time. Changed that out, but no.
A friend told me to bypass the relay and connect fuel pump directly with battery to see if fuel pump worked. Tried that, but killed the whole engine. Somehow, I must have caused a short circuit. (Yes I'm an idiot, and I know it, that's why I usually don't try stuff like this myself). Engine didn't turn over anymore; nada.
I checked the fuse between the battery and the engine, it's fine. Changed relays again; nothing. Really unhappy me.

Had a mechanic look at it today. 3 Fuses (? 60, 15, 12.5) on front of engine were checked and are OK) He found out that the signal from the ignition doesn't reach the pump. He put a wire straight from battery to relay (computer's relay, if I'm correct) to the green/pink wire, so the pump engages as soon as you put ignition on. It now starts giving extra gas, but runs really rough. Doesn't idle.
Mechanic says it's the spark plugs, but since it ran phenomenal only a week ago I don't think so. They might not be perfect (had fuel on them) but that's mainly of the rough running today, I think. Or they must have gone bad overnight.
My guess is that wiring the pump straight to battery 'confuses' the computer, and that that's why it's not running well. Maybe not, or even probably not since I'm an idiot... but either way I don't think the main issue are the plugs.

Any ideas and suggestions?! What might have gone bad when I tried hooking up the pump to the battery? What else to check or try?

Thanks all!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gun-driver Quote  Post ReplyReply Direct Link To This Post Posted: October-07-2017 at 8:32pm

Here's the proper way to jump the pumps
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-08-2017 at 10:54am
Great, thanks!
Maybe it's obvious when I'm on the boat, but where exactly does it plug into?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: October-08-2017 at 12:25pm
That is the test connector where the code reader plugs into. It is plugged / housed into that cover,marked ECC TEST,that is just to the left of the red colored alligator clip. What you are doing is providing the ground to the pumps,which is what the computer normally does when you go to start.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-08-2017 at 1:10pm
Awesome, thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-08-2017 at 2:44pm
No improvement whatsoever yet. Jumped the pump as in the photo. Same thing: no idling, running rough, lots of smoke from the exhaust. Changed spark plugs, just to be sure, but still the same.
Any other suggestions?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-08-2017 at 4:14pm
Hmmm, removed jump wire and it started again. But ran same as the time it all went bad: surging at idle. As soon as you put it in gear it stalls. Managed to start a few times like this . Sometimes didn't start, then had to use wires to jump it again, with some extra throttle. Starts and runs super bad/rich, then as soon as I remove wires runs great, then stalls when I put it into gear.
Edit: pump still doesn't prime, but starts anyway, sometimes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-09-2017 at 12:13pm
Buddy says IAC valve or MAP sensor maybe. How do I check those?
Would this reader help me here?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: October-09-2017 at 12:22pm
No the reader won't test those. Keep in mind the testing of components will not differ from that of automotive ones. Google how to test them, some Mustang sites are really good.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MI-nick Quote  Post ReplyReply Direct Link To This Post Posted: October-09-2017 at 12:56pm
did you verify that the LP pump was indeed pumping fuel when you used the test jumper to ground? it's possible the LP pump is shot or the screen (internal filter) inside it is all gunked up. I had a very similar problem and the old LP pump worked intermittently. new pump fixed it. autopsy on the old pump showed the screen was all skuzzed up.
As far as I can tell, I'm not quite sure...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MI-nick Quote  Post ReplyReply Direct Link To This Post Posted: October-09-2017 at 1:00pm
As far as I can tell, I'm not quite sure...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-09-2017 at 1:08pm
LP pump is brand new (changed it when I only needed to change the relay , and yes you can hear it pumping as soon as ignition is on.

Reading up on how to check if IAC and MAP are doing their jobs correctly.

Thanks for the input gentlemen!

Edit: reading that other thread; what is the "STO"?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MI-nick Quote  Post ReplyReply Direct Link To This Post Posted: October-10-2017 at 6:10am
STO is Self Test Output...the test connector you can use the jump the pumps to ground..
As far as I can tell, I'm not quite sure...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-12-2017 at 3:33pm
I'm stuck. Anyone know of a REALLY good GT40 mechanic in or close to Miami? Perhaps Orlando, if I can find a cheap ticket. See if they want to come out here for a day or 2 and fix this problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sport1999 Quote  Post ReplyReply Direct Link To This Post Posted: October-13-2017 at 11:55am
Just my $.02, but I think the guys here could walk you through some troubleshooting if you provided a little more information and feedback on your tests. It's still not clear whether your fuel pumps are running with turning the key or using the STO and verifying what the fuel pressure is at the rail and whether its holding pressure (to start or running (rough)). I would spend a little more time trouble shooting before I flew someone down and spent that kind of money.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: October-13-2017 at 8:35pm
One thing to remember with all this testing. Electric Fuel Pumps are lubricated by the fuel flowing through them. If you dry start an electric fuel pump you can do damage in as little as 10 seconds run time.   Saying you have a new pump in there might mean nothing if it was dry started due to some supply issue.   Sorry to pass this on but those are the facts with an electric fuel pump.   What do you see for pressure in the system as you try and start? If it is not at full pressure they don't start or if they do they run poorly.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-14-2017 at 2:07pm
Well I wish had brought in a mechanic from the US 2 weeks ago, would have saved me lots of $$. A wakeboard school without boat...
But I did find some good info that gives me some hope again.
Now to find a good mechanic that understands English so I can show it to them.

And fingers crossed it's not the ecm...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: October-14-2017 at 5:56pm
Even if it is the ECM it's not the death of it. I had mine running on a 4cylinder Ford ECM with a Moats chip. I think some have had success having their ECM's repaired too, PlanetNautique has the guy's who are up on that. Might not be a bad idea to have a spare
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: October-15-2017 at 8:25am
Never been to Costa Rica :)
If you're going through hell, keep going

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-16-2017 at 1:07pm
Originally posted by lewy2001 lewy2001 wrote:

Never been to Costa Rica :)


Any $250-tickets from Aus to CR out there?!

Heading to boat tomorrow to check things from that screenshot. Well you're involved in fixing it anyway lewy2001!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lewy2001 Quote  Post ReplyReply Direct Link To This Post Posted: October-16-2017 at 5:57pm
Originally posted by TRIP TRIP wrote:

Any $250-tickets from Aus to CR out there?!
Heading to boat tomorrow to check things from that screenshot. Well you're involved in fixing it anyway lewy2001!

If there was I would already be there

Lots of good info in that old GT40 Fuel Supply Thread Trip

If you read the whole thread and follow the trouble shooting logic it should pin point your problem. What has me a little worried is that you may have fried your ECM by applying 12volts to the wrong input on the ECM in your initial trouble shooting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRIP Quote  Post ReplyReply Direct Link To This Post Posted: October-18-2017 at 4:23pm
The culprit


So relieved it's fixed! Cleaning the contacts with contact cleaner was all that was needed it seems. Thanks for your help all. Lewy, your info in all those threads is amazing.
Hadn't had a chance to run it much yet after we got it going, but hoping to ride some sets behind it tomorrow to see how it holds up. Confident it's good now though
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: October-18-2017 at 4:29pm
I knew Mark's (Lewy) info would come through for you.


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