260 EFI bogging

**ShadowFlier** · 08-02-2020, 06:23 PM

I've been having a problem for the last month and a half that I have yet to figure out. My top crank bearing went and put a hole in the front half. Ever since I had it welded it has had this persistant bog. In neutral it will run perfect and the first holeshot is great but everything after that it bogs right down to the point of where it is going to die. At this point I have replaced all of the electronics other than the main engine harness and temp sensor. New sealing rings in the crank, new top bearing, new bleed lines, map sensor fitting cleaned and hose replaced, and swapped ECU with a known good one. I also checked and verified that my front half was still straight after being welded (which it was) but put a different one on to eliminate that. Fuel pressure is correct and staying a consistant 56lbs. Four button box confirms that temp sensor is reading properly. This motor ran perfect before the top bearing went. I have a hard time thinking it could be something electrical but obviously it's possible. There was a groove on the block and front half from one of the screw heads but that has been filled in with JB weld. Any help would be appreciated.

**G-Train** · 08-03-2020, 07:26 AM

Someone Please help here...He's been fighting this for almost 2 months...Changed almost every electrical component to date.
There are some very intelligent Merc experts on this board...maybe someone has a new idea for him to try.

Thanks
Greg

**thomas t** · 08-03-2020, 08:24 AM

Check map sensor

**Dave Strong** · 08-03-2020, 11:46 AM

Have you run it on the lake with a fuel pressure gauge hooked up?

Dave

**ShadowFlier** · 08-03-2020, 01:24 PM

Yes fuel pressure is good, gauge reads correctly also.

**Euroski** · 08-03-2020, 01:45 PM

is Fuel pressure is correct and staying a consistent 56lbs correct. thought there only around 40psi? I'm sure someone knows, but away from OB's longtime?

**Dave Strong** · 08-03-2020, 02:02 PM

Originally Posted by Euroski

is Fuel pressure is correct and staying a consistent 56lbs correct. thought there only around 40psi? I'm sure someone knows, but away from OB's longtime?

Depends on the ECU.

Dave

**ShadowFlier** · 08-03-2020, 02:20 PM

Originally Posted by Dave Strong

Depends on the ECU.

Dave

I have the A63 with the 56lb regulator

**Dave Strong** · 08-03-2020, 02:47 PM

Originally Posted by ShadowFlier

I have the A63 with the 56lb regulator

Thats correct for 56lb horn motor.

Dave

**Merc 2.5** · 08-03-2020, 06:09 PM

Has the tps sensor been checked? Didnt see it mentioned above

**Markus** · 08-04-2020, 01:46 AM

Originally Posted by ShadowFlier

I have the A63 with the 56lb regulator

Well, that is a place to start.

That is not the setup for a 2.5 260. That is the setup for a 2.5 Drag which requires a different fuel curve. Your engine may be running way rich.

If it turns out not to be your only problem, you need to get back to basics instead of swapping parts:

1. Is it fuel related or spark related?
2. What cylinders are affected?

The best way to see that is to buy plenty of spark plugs, put in a fresh set out on the lake when you know the engine will run like crap, make a plug chop and see what the plugs tell you.

__PRESENT

**ShadowFlier** · 08-04-2020, 06:19 AM

Originally Posted by Markus

Well, that is a place to start.

That is not the setup for a 2.5 260. That is the setup for a 2.5 Drag which requires a different fuel curve. Your engine may be running way rich.

If it turns out not to be your only problem, you need to get back to basics instead of swapping parts:

1. Is it fuel related or spark related?
2. What cylinders are affected?

The best way to see that is to buy plenty of spark plugs, put in a fresh set out on the lake when you know the engine will run like crap, make a plug chop and see what the plugs tell you.

__PRESENT

new plugs were put in multiple times, it is getting plenty of fuel, plugs are wet. ECU is set to 101. Compression was checked when warm and it is 120 across. Coils were checked and are functioning properly, to eliminate it I swapped with a good known set anyways and no change. If I’m lucky enough to get it on plane while it’s bogging if I let off the throttle it will catch and run perfect for a split second then go back to bogging bad.