crank no start condition after incorrectly hooking up battery.

[Cdn20valve]

1996 doni lxc. 5.7EFI tbi MEFI-3

I reinstalled my engine after replacing my spun coupler. I must have been very tired, because I accidentally reversed the battery connection on one battery. Key was off, and battery selector switch was off as well. After a couple sparks on the neg post, I corrected the mistake.

Now the engine will crank and crank, but not start.

I followed the diag procedures in the mercruiser manual:
fuel pump works when jumping relay connection.
fuel pump relay ground was open. i added a new ground to the harness. ok now.
fuel pump ecu supply not supplying voltage to relay. harness is ok for continuity. swapping relays makes no difference. pin from ecu looks good.

engine will not run even on starter fluid.

i have a terrible feeling i fried the ecu. is there any other checks i can do?



btw all three fuses are intact.

 

[thumpar]

It should not have sparked if the battery switch was off. You need to fix that wiring. Have you checked for spark? Are the injectors firing?

 

[alldodge]

i have a terrible feeling i fried the ecu. is there any other checks i can do?

Dang I sure hope you didn't but I'm worried.

When you crank do you see any movement in the tach?

 

[Cdn20valve]

Injectors not firing. No spark.

 

[CaptainMak]

Just an idea, but do you have that big red reset breaker button on the top of the engine ? Did you try pressing that ?

I got a MEFI-3 system on my '99 and sometimes it's a PIA to diagnose. Those ECM's are an arm and a leg *IF* you can find one.

If you sprayed starting fluid and it still won't start, your problem is ignition-related. Possibly coil, ignition module (the 2 wire under the rotor). Also check the contacts on both the cap and rotor. You gotta find the spark !

 

[alldodge]

fuel pump relay ground was open. i added a new ground to the harness. ok now.

Had a spark, and had to add another ground.

fuel pump ecu supply not supplying voltage to relay. harness is ok for continuity. swapping relays makes no difference. pin from ecu looks good.

ECM doesn't supply voltage to the relay, it supplies a ground to the relay (Dk Grn/Wht). There should be 12V supplied from the fuel pump fuse to one side of the coil, and to one side of the relay contact.

The other two fuses are used to supply power to the DLC, ECM and ignition. They use Pink/Blk and Orange wires and go to several locations.

Since you lost a ground, it may also have lost another connection. Suggest tracing and verifying voltages the wires to see if they are still connected in all places.

Last thing, what is your engine serial number? Reason to ask is I don't see a MEFI-3 for the 1996 model, but could be 1 or 2. Do you have cool fuel or VST?

 

[thumpar]

A 1996 should be VST. Cool fuel wasn't until 1997. I have the same year and it is VST.

 

[Cdn20valve]

I tried the red button breaker. No dice.

I thought ecm supplied 12v to relay fo 2 seconds to prime pump? Hmm. I must have read the diagram wrong.

It's definitely cool fuel.

This engine has been replaced before I took possession of the boat. I have a feeling it's not the original engine. I can't find a serial number on it.

 

[Cdn20valve]

No Title

 

[thumpar]

That is different from my 1996. Mine has the VST up front by the lube monitor hanging oil filter and runs v belts. The pump should run to prime before start. It is probably going to be hard to diag. You may want to pay a shop to at least try to read the computer and go from there.

 

[CaptainMak]

If your mefi3 is the same as mine, you should have a Mercury distributor that had 2 wires coming out of it. Test the resistance between those 2 wires and make sure it's over 100 ohms. If not, the ignition module is fried.

 

[alldodge]

If it was a MEFI 1 or 2 then 12V would be supplied to the Dark Grn/Wht wire.

The MEFI 3 (which is also another manual) uses a ground Dark Grn/Wht wire to energize the pump

Now the one in your Pic is a MEFI 3, but the issue is they did not come out in your year boat, so it has probably been replaced, either the engine or harness. It does also show a TB5 type distributor and not a EST one, or at least from what I can see