98 250HP - Can't keep an idle

[Spartan811]

Hey guy's, Hope you can help.. I'm stuck!

This whole thing started when my fuel pump died...
Replaced pump with after market brand and currently works now. (30-40psi)
Then my Float pin was slightly bent which was jamming my needle and not
allowing my VST tank to fill up. Replaced the Needle, Float and problem pin.

I was hoping I fixed the problem, went out, running great and then I noticed that when I would trim the motor while moving, the motor was losing power as I would press the tilt button. A little while later the motor started Sneezing/puffing and wouldn't hold an idle and completely died with no start.
(Had to get towed in)

When I got it home, I checked the pressure w/ a gauge and noticed that the pressure would drop every time I pressed the tilt, like it was sucking voltage from the pump. The motor starts and idles at 4k RPM for about 10-20 seconds and dies.

All cylinders have spark... Compression is good.
ECM is communicating with sensors..

Sorry for the long post... Just trying to give full description.
Thank you in advance for any help!

[boscoe99]

Text book case of poor electrical connectivity.

Battery power is required to use the trim/tilt unit. Battery power is not available. Voltage drops to the point that the motor does not have enough juice to run itself.

[Spartan811]

During all this... Battery voltage was at 12.2 without motor running.
13.8V with motor running...

I thought about this as well and recharged batteries while performing
tests.. same problem exists..

[rodbolt17]

what is the battery voltage at the PUMP when you hit the trim and it dies??
that is what is important.

[Spartan811]

Thanks for trying to help guy's.

So.. My battery voltage is 12.34 (not running)
At the top of the fuel pump its... 11.28V
Discounted the wiring harness to pump and the volts there 12.15V.
However, when I turn pump on and press the tilt, voltage drops to
10.20V. At the pump and harness.

Harness Has continues voltage with key on at 12 .20V and drops to
10.84v. If key is left on.

Tried simulating the same problem by turning on wash down pump and got
No voltage drop from that.

I'll change my connection to the pump but I'm still confused about the voltage drop ... From the tilt.

Any ideas???

[Dashunde]

Couple of thoughts...
You need a amp meter to test each part, not just checking for voltage drops.
A voltage drop is a symptom of excess amps being drawn elsewhere.

I dont know the specs of your 1998 alternator, but the new motors are around 44 amps.
Compare your alternator rating then add up the actual operating amps drawn by your trim pump, fuel pump, ignition, ecm and whatever else is running.
If that combination exceeds your alternator's abilities then its reliant on the battery to make up the difference and voltage will drop.
The battery is already acting as a system balast and provides the real muscle when called upon, meanwhile the alternator is topping it off and keeps the voltage up.

If I read you correctly, you've indicated a significant voltage drop if the key is left on... for how long?
Could indicate the battery is having issues, few things will create widespread strange problems with any fuel injected vehicle moreso than a failing battery.
Even if it takes and holds a 12-13v+ charge it may not be providing the amps its supposed to under load. (Load test it, even if its new)

I'd wonder if the aftermarket fuel pump is making the correct pressure while drawing the correct amps?

Is your trim motor well-worn or is your 250 a low-time engine overall?
A tired electrical motor can start to draw more amps than it should, particularly if it has a bearing failing, same for the pump attached to it.

Specific question - does the motor start and run normally on a fully charged battery that is still connected to a battery charger providing 10+ amps and you DO NOT touch the trim at all?

Lastly, what killed your fuel pump to start with? Age? Dirt? No idea?
Are you positive it was really the faulty part?

Not trying to insult... just wondering if a underlying electrical problem was missed from the start?

[Spartan811]

Thanks Dashunde!

That's a lot of good information you sent my way!

I think my problem may be with the pump...after all...

After I posted, I checked for continuity on the Neg and Pos
of the fuel pump and rest assured Continuity existed.

Should I be having Continuity? sounds like a short is happening.

I'm getting a replacement Pump, Batteries and going to check my
Stator, my motor doesn't have a Alternator but I get the idea...

as soon as I know I will repost the results.
Thanks again for all your help guy's

[Dashunde]

Sure, it should have continuity, it should also have a specific resistance value (Ohms), and that value should be similar to the oem part.

If it has near zero resistance across its poles then it would be shorted.
A short literally takes the path of least resistance, bypassing the motor windings that would give you a proper resistance reading on the meter.

If its shorted, even partially, it would probably get hot as hell along with the wires powering it.

Stator, right. Doesnt it also have a rectifier / voltage regulator of some sort? Check that too per the book for your motor.

[rodbolt17]

on an Ohm meter guess what a DC motor looks like??????
a short.
cause it is.
why not simply go find and fix your bad connection?
most likely a poor ground.
but that is why your voltage is dropping and your engine stalls.

[Dashunde]

The windings in a dc motor will show a resistance, and that value should change slightly if the motor is rotated and the separate fields are checked.

[zenoahphobic]

And if a motor is rotated it can produce some DC output (acts like a generator from tiny residual magnetism), and depending on your Ohm meter and it's orientation will give you false/ inconclusive readings.

[boscoe99]

What if the DC motor is brushless?

[zenoahphobic]

A brushless motor has very strong permanent magnets and when a coil is turned in the magnetic field a voltage is produced.

Maybe not as same as series or parallel wound past conventional DC motors.

[zenoahphobic]

I had a green light. Maybe I needed to add that a brushless motor has no commutator and actual one permanent magnet as the rotor. The voltage produced between any pair of the three phase stator on the outside. I tried it before posting.
And this arrangement "opposite" to convension.
There are examples of combustion engines where the crankshaft is fixed and the rest of the engine rotating around it. Relativity.

[Dashunde]

What if the DC motor is brushless?

Brushless motors are checked the same way for resistance, two wires at a time, and its an excellent way to measure their efficiency.
Brushless motors have static windings, they never rotate, the magnets rotate instead.

Brushless motors do not have a simple two wire connector, instead its three or more wires depending on the type of speed con*****er being used... sensored or sensorless.
Resistance can be measured between any two pairs of wires, and what that reading means depends on how the stator windings are terminated - Delta or Wye (google it)
The most important factor, aside from using quality wire in the first place, is that the resistance values are the same for all three phases.

A three-phase DC brushless motor has 3 separate strands of wire wound around any number of stator poles in a specific direction, the result is 6 wires hanging out; Delta termination has 3 sets of paired wires, Wye is 3 wires twisted together, leaving the other 3 ends to connect to the con*****er.

A brushless speed con*****er (ESC) does not simply apply current to the wires making the motor go round.
It applies switching current in a way that pulls some magnets closer while pushing others way, effectively creating waves of magnetism that travel around in a circle dragging the magnets with it.
Modern ESC's are marvels of electronics and you have one in every cd player you own.
They can precisely control rpms, and they can even make a motor "beep" out a song by making the motor try to run both directions at the same time, creating loud resonance inside of the "can" or "bell"

Below is one of the many motors I hand-wound a few years ago, it is a small 12 pole / 14 magnet "outrunner" wound with #24 wire terminated in Wye.
It weighs about 1 ounce and produces 19 ounces of static thrust on 8 amps at 11 volts turning an 8 inch propeller at 11,000 rpm.

There are very simple brushless motors that use a basic integrated circuit for switching polarity using a internal sensor to detect rotational position. Your computers cooling fans are a good example.
The two wires leading to this type are not directly connected to the motor windings, instead they go to the little IC chip, then from there on to the motor.