350 mpi fuel pressure question

[alldodge]

In most cases no it won't fire

 

[Offthepath]

I forgot, but wanted to update the thread with the final solution.

Alldodge, thanks for the input. It was not turning over fast enough. I was only seeing 250-275 RPMs. I'm guessing cracking the throttle allowed it to spin a little faster and hit 300 to fire.


I only had 4g wiring going to the battery switch and probably the main issue, the crimp on lug for the main starter cable was loose. I replaced the lug, ran 1g cable from both batteries and it now starts right up when warm. Cranking rpm now is 400+

Thanks again for the help.

 

[Offthepath]

Well, I guess if it wasn't for bad luck.....

I thought I had this issue licked, but here I am again. On the tach, it's just shy of 300 rpm. I replaced the 4g battery to perko cables with 1g and found the lug on the 0g cable from the perko to starter was loose. After new battery cables and a new crimp on lug, the boat started perfect, no issues and no need to give any throttle.

We did 1 short trip, and 1 day into a multi day trip and it continued to start without issues. After that though it started having the same issue, slow cranking and needing throttle and both batteries to start.

I pulled the starter and took it to a repair shop. It bench tested fine, but when compared to a new starter, it sounded very rough and not spinning as fast. Figured I found the issue, replaced the starter. Did dozens of startes on the hose from cold to warm and it started right up with no issues.

Went to the lake today and still same issue, it is only turning about 275rpm.

Any ideas, I'm about to burn this thing.

Thanks

 

[alldodge]

Are the bat cables getting hot when cranking?

 

[Offthepath]

No, I've cannot fell anything getting hot. There is no major voltage drop when comparing cranking voltage between battery, perko, and starter either. Cranking voltage is around 11.5v.

I also cleaned the ground points on the block and ran new negative cables as well.

What cranking RPM is normal for a 350 mag mpi?

 

[dubs283]

What cranking RPM is normal for a 350 mag mpi?

the ecm needs to see at least 300 rpm in order to initiate start up sequence (fuel injectors/ignition)

it gets a rpm signal from the crank position sensor

 

[alldodge]

Its either the starter, the motor or drive

Starter doesn't have enough power when heated up
Motor is binding which needs more torque to rotate, or water/fuel in cylinders increasing compression
Drive is binding

The cables not getting hot and voltage staying up means power is being transferred. Listing 11.5V is low but when asked before this was just the gauge, and at starter it was higher

Voltage drop on Negative side should be no more then 0.3V (starter case to Neg bat post)

 

[Offthepath]

So the constant is the boat being in the water. What would change from the hose to actually being in the water that would make the engine or drive harder to turn?

I highly doubt it's water in the cylinders. The engine runs fine as soon as it starts and no signs of water in the oil. You can start it, turn it off and immediately re-start and have the same problems.

Then conversely, when doing mussel decon, it will run at the top of the ramp for a few mins on the hose, back it into the water while still on the trailer and the starting issue appears.....?????

 

[alldodge]

Don't know, but on the trailer at a ramp water can be higher in the exhaust

If it was mine I would still be looking at electrical

 

[Searay205]

Did you replace with a Quicksilver starter or is it aftermarket? When an engine is hot after a load its is harder to crank over, pistons expand etc. Good ole days people thought it was a tight engine if it turned over slow when hot. Engine never gets as hot on the garden hose as it does running across the lake pushing a 5Klb boat at 30 mph.

 

[Scott Danforth]

have the batteries load tested.