260hp Help

[hangn]

I am having trouble finding the fault with my 260hp merc. It has a very short miss in the engine at about 7000 rpm. The engine cuts out for a split second then cuts straight back it.
I have changed 2 x switch box's. I have fitted a loan stator i have also tested the trigger and coils as per the manual which all shows in spec. I have had the injectors cleaned and tested. I have also checked the fuel pressure with a gauge whilst running it and all okay.
It only happens around this rpm, other then that it runs fine.
I have a digital ecu with a A36 chip (it also had this problem with my original chip in it)

[Michael J Giesler]

I have seen some 260's go lean at the 7000 grand mark but with an a 36 chip that's probably not the case some one will help you out for sure Jay Smith will be able to help you:thumbsup:

[flabum1017]

check the tps through it's range, look for dead spots

[M. HARDEE]

without knowing your fuel tank and disrubution set up ----check for a fuel restriction --- anti siphion valve not removed, kinked feed hose , piece of foil from oil bottle in pick-up or fuel inlet hose or sump --- weak fuel pump , loose fuel pump wire,or batt cable , bad relay, found one of these to cause that problem on more than one accation cheersMitch

[bringit2]

also suspect the voltage reg on top they would cause a slite miss,no joke!

[Jay Smith]

Several things come to mind.If the issue is happening just at 7000 and you have a rev limited chip ( both ) it may be getting on the limiter on both boxes. Does the motor ever pull higher than the 7000 that its seems to be hitting? Is it at exactly at 7000 RPM's ? I would start simple :

1. Check and replace ALL fuel filters
2. Make sure tank is vented
3. Clean all air signal barbs from the plemium to ECU and regulator.
4. If its possible to get a DVA meter hook to each coil feed with a long jumper have someone monitor the voltage at time of failure and see if you can see if its a single cylinder failing or the compete system.
5. If you can possibly narrow to a single coil remove that suspect coil and put in the spot of a known good coil and see if the issue follows that coil.
6. If you have converted to a digital box make sure the air barb is the correct part ( you need the one with the ultra small hole part number 22-822715 )
7. With digital box conversion you will need to go to a resistor spark plug I suggest NGK BR9HS gapped @ .035"
8. Spark plug wires can also break down after age.
9. Check and clean all grounds
10. Battery MUST be HOT ( Over 12.5 volts before the motor starts )
11.Disconnect the 8 pin key switch harness and with an ecto knife spread the male terminals to make better contact clean with brake clean and re install
12. Hopefully you have used Brucato for injector cleaning.
13. There is an ongoing failure of fuel supply lines with the ethnol fuel causing the inner fuel line to collapse this can starve the motor.
14. If you can safely kill the motor at the time of failure do so and tow the boat so you can remove the cowling. Remove the #5 plug ( starboard right rear at bottom) roll the piston to bottom dead center and with a light see if the motor failing is lean ( piston dry ) or rich ( piston wet ) and then you can procede with the troubleshooting path..
15. If your key switch choke is still hooked up at the time of failure hit the key switch choke , if it picks up the motor is becoming lean if it dies down its too rich.BUT lean and rich can also be associated with voltage to the ignition or the lack there of.
16. Also a shot in the dark if you tack is acting goofy look at the rectifier.
17. Remove the red wire from rear voltage regulator at the rectifier and make a test run.
18. Another long shot but I had a racer I was helping and the motor was shutting off and cutting back on ( Dangerous for an Allison )I found a plate in the battery to have been broken loose and was making contact with the other plates shorting the battery out ..

Sorry but these suggestions are not in any correct order just as I thought of issues I've seen ...

Hopefully it will be something simple and not expensive to fix and I have given you some ideas.

Good luck,
Jay

[hangn]

Thanks Jay, that leaves me with a few things to think about and some things to check.
When you talk about the rev limited chip (both) what do you refer to. As far as i know i only have a chip in the ecu which i have changed. I got it from John Mahles.
the revs will go past the 7000rpm. i think i have had it at about 7400.
The engine only cuts out for maybe not even a second then cuts back in you would not have enough time to hit the choke key before it cut back in. it only does it once on each pass but it is enough to feel it.
I picked up some of those spark plugs. the ones they had were NGK BR9HS-10, i assume these are the ones.
Without knowing much about a DDT machine - would this pick anything up??

[hangn]

I have attached a few pics. I don't seem to have a voltage regulator on top of the block were it shows it in the manual. Why not or is it somewhere different???

[patchesII]

I've had my motor act like that before. With mine it was a loose connection at the ecu plug. I could take zip ties and pull it up tighter and it would stop

[jas638]

i had sort of the same problem my motor would cut off and die completely. jays tip on using the ecto knife on the pins of the ecu and the harness ends worked for me.

[Jay Smith]

First observations is you have no voltage regulator ( Thats OK ) and as Patches said you have you ECU attached with tape instead of the plastic attachment coupling ring ( Mercury part number 19049-1 ) this "could" create the issue. I keep these in stock and replace on most all 260 and drags I build as most ECU coupling rings are long broke and held together on by tape or ty raps.

Jay

[hangn]

Thanks everyone for the help. It looks like my problem has been solved.
I purchased a new plastic clip for the ecu plug and cleaned up the pins (one had a small amount of green collosion on it) and put a new ecu air barbed fitting on and it seemed to go well on the weekend so the miss seems to be fixed.
Again Thanks Very Much

[Jay Smith]

Great....

Happy boating Mate !

Jay

[hydrostreamvking4m]

These are just the posts that make this web site what it is today.

And Jay your the man..