WHAT would shut off power to my fuel pump?

[mtnbkr738]

Hi All,

I have a 98 sunsetter w Monsoon and Fuel injection.

Something is telling the ECM to shut off my fuel pump... here are the details:

My 98 Sunsetter cuts out after 40 min of skiing. Actually the fuel pump is being turned off/on off/on off/on.... SOMETHING is telling the fuel pump to turn on and off when it gets hot. (ive put a test light on fuel pump terminals-- and can see that power to it is being turned on and off and on....pause.... off/ on /off/on .... pause.... repeat). also: i can put my hand on the Fuel Relay and feel it clicking on and off... just like the test light... so something is turning off the relay and therefore the fuel pump.

Engine always starts. i can always idle it and run it slow.....Problem goes away after engines cools off.... and i get another 40 minutes of running great. Again: this only happen when hot after 40 minutes of pulling skies etc... its almost exactly 40 minutes every time from a cold engine to intermittent shut off.

Ive replaced:

• rotor
• cap
• Ignition control module
• pickup coil
• fuel pump
• Fuel relay
• Kill switch
• Pulled EVERY connection on boat and inspected and greased and slightly bent connectors.

 

Im looking for ANY input as to WHAT may be telling the ECM to shut down fuel pump when motor is hot:

Oil pressure sensor?

Water temp sensor?

Trans Fluid temp sensor?

Trans Neutral switch?

ANY suggestions before i keep swapping parts???

thx!!

 

[formulaben]

As far as I know, the other sensors will only put the engine in limp mode...but oil pressure will shut it down.

 

INDMAR (CHEVY) ENGINE START UP SEQUENCE

Fuel Rail Pressurization:

When you first turn the key to the "on" position (aka “key up”), the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Schrader valve on the fuel rail near and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running. Test by attaching a fuel pressure gauge to the fuel rail at the shrader valve, on TPI and LT1 engines its located on the pass side fuel rail.

Initial Crank Action:

If you then rotate the key to the start position the engine will rotate.  Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run.  The crank position sensor will send a string of pulses to the ECM in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch.  The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees more than 0.54 volts, it will assume the engine is flooded.  Assuming the ignition module is good the engine will "catch".

Engine "Catches":

When the engine catches, the MAF sends a signal to the ECM advising that air is flowing and also just how much air is being pulled through to the intake manifold. The ECM takes note of the amount of air being consumed and adjusts the injector pulse width to around 2.2 ms nominally so as to attain a proper air/fuel mixture to insure combustion.  The engine should show an initial idle speed of around 900-1100 RPM and then slowly diminish to 600-700 RPM.  If this does not happen, the Idle Air Mixture valve may be mis-adjusted. Alternatively, there may be a leak in the intake manifold or another vacuum leak may be present. Listen for hissing sounds---there should be none.

ECM Mode:

The engine will now be in Open Loop mode meaning that the ECM is controlling the air/fuel mixture by referencing values stored in memory.  Once the Oxygen sensor <if you have Cats> reaches operating temperature of several hundred degrees, the Manifold Air Temperature (MAT) sensor shows an intake air temperature of more than 140 degrees and the Engine Coolant Temperature (ECT) has reached 160 degrees, the computer will switch to closed loop mode meaning the Oxygen sensor's output is examined along with the MAT and ECT outputs and the ECM adjusts the injector pulse widths (more "on time" or less "on time") to constantly strive for a 14.7:1 air/fuel mixture which is the best mixture to hold down pollution.

[mtnbkr738]

Hey @formulaben -

The oil switch is actually leaking oil (i never noticed that before!) and it does look like that and pressure sensor seem to be original. (looks like engine paint on them - maybe not)

Will get new ones today and swap out.

Ill test this weekend and let you all know.

thx!

dr

[formulaben]

FYI, don't use any teflon tape the threads as they are the ground for the sensor.

[mtnbkr738]

Hi All,

Ok I installed new Oil Pressure Sender and Oil Pressure Switch. (no teflon tape-- thx :))

NOTE: my oil pressure gauge on the dash ALWAYS seemed to float around alot. Every mechanic said "dont worry about it... thats normal". Hmmmm.

So when i just installed the New Sender and Switch, the gauge went right to 60psi and held firm on idle.. no floating anymore. (I assume 60 psi on the gauge is a good number to be at??)

Also: the switch and sender seemed to look like original parts (engine paint over spray) and they were leaking oil-- weird i never noticed that before... I guess i never looked and touched them.

Now i need to run it for about an hour to see if issue resurfaces.

Ill report back after the weekend!

thx!

 

 

[formulaben]

Good work!  Good to hear you replaced both.  The "floating" seems to be typical of these sensors when they get old.  Fingers crossed that it fixes your issue

[mtnbkr738]

bad news. 40 minutes of skiing this am and problem returned 

could transmission fluid temp sensor turn off fuel pump via ecm??

[shawndoggy]

I'm totally going from internet memory here, but aren't there TWO oil sensors on some indmar 5.7L motors, one for the gauge (an oil pressure sender), and another for the alarm/ecm (an "on/off" kinda switch)?

[shawndoggy]

 

[tvano]

all of my observations are based on my '04 wiring diagram.  some of the stuff may have changed over time.

ign and fuel pump relays and fuses could be involved in this hunt as they supply power to the fuel relay.  all three (ign, fuel and starter) fuses and relays are alike so swap them around to see if your issue changes complexion.

then i'd be moving that test light from the fuel pump to the fuel pump relay looking to see which of the lines (ecm(green), ign(pink/black) or power from the fuel fuse(pink)) are cycling similar to what you observed at the pump (none should).  

if you don't find a smoking gun then meter that gray wire which feeds the fuel pump through a connector.  if it's solid at the relay and cycling at the pump you have an intermittent likely at the connector.

if the signal from the ecm to the fuel pump relay is cycling then the ecm or one of the ecm inputs is suspect.  the ecm is directly connected to: tps, map, crank position, oil pressure, coolant temp, trans temp, trans neutral and iac.  maybe knock sensor too?  

re trans over-temp switch; it's normally open and supplies a ground during fault.  while it would not test the wiring involved i would remove that connector at the switch TEMPORARILY while your fuel pump is cycling (at fault).  a no-change in behavior might rule out the switch as a potential source of the problem.

iirc crank position sensor may become fussy with temperature but i'd surely eliminate some of the above potential problem areas before spending the long dollar.

again a reminder i'm looking at docs for a newer rig so i hope i'm not sending you a false flag.  good luck w it.

[electricjohn]

What you have to find out is if you are losing +12 volts or -12 volts to the relay.  Loss of +12 volts is a wiring issue, and loss of -12 volts is an ECM issue. Your engine does not have a crank position sensor, and limp mode has no effect on the fuel pump control circuit, only distributor reference.  My guess to your problem is a wiring issue that is effected by heat.

[mtnbkr738]

46 minutes ago, electricjohn said:

What you have to find out is if you are losing +12 volts or -12 volts to the relay.  Loss of +12 volts is a wiring issue, and loss of -12 volts is an ECM issue. Your engine does not have a crank position sensor, and limp mode has no effect on the fuel pump control circuit, only distributor reference.  My guess to your problem is a wiring issue that is effected by heat.

i just put the light meter on the fuel pump.... i  didnt check to see "which" was lost + or -.

could you step me through the procedure to verify which im losing? and should i check at the relay instead of the fuel pump? 

thx!

dr

[electricjohn]

Since you stated you hear and feel the relay clicking, that is where you want to test.  The procedure would be hard to explain if you don't understand how a relay works with terminal identification, socket connections, or wiring diagrams. 

[mtnbkr738]

OK  I  HAVE THE SOLUTION!

So, i bought this MEFI SCAN TOOL:

https://www.obd2allinone.com/mefiscan.asp

- I ran the boat- had my laptop plugged into the boat via the MEFISCAN. Recorded a running log during the entire boat trip-- which included the failing sequence after the 30 minutes.

- Went home- replayed the log on the laptop- while watching all the different engine performance tools in the MEFI SCAN program (which BTW-- I'm amazed at how MUCH info is available on this program) (see image from their website below)

- turned out there is a VOLTAGE spike- then intermediately after the spike, the ECM trys to shut down the engine, then the spike disappears, and the engine comes back to life -- and this keeps repeating itself randomly

- so the guys at OBD suggested the Alternator/voltage regulator would cause a spike. 

- Bought new alternator, ($225) and the boat ran perfect for the 10 hours on the lake this weekend!! Problem solved!

QUESTION: so i spent $2100 with 2 marinas (one of them a Malibu dealer ) in the area trying to solve this issue-- and NEITHER OF THEM put a scan tool on the engine- nor detected a voltage spike????!!!!????? REALLY????!!!

bottom line: MEFISCAN was best $200 i ever spent on the boat.

Thx all for the input and help!

 

 

[robbennett]

Wow really good info! Just another reason to work on everything yourself! 

[Rednucleus]

Send the dealers a bill for your time and the cost of the scanner and see if they want to hire you as an expert tech! Good job trouble shooting this one. I had no idea an alternator could shut you down like that.

[Bowen]

wow- I have exactly the same problem!  I had a rough summer last year- put the boat in- ran around the lake- got some ski buddies and headed back out.  No start- no spark!  took me a couple weeks to find defective pick-up coil.  oh- I had the injectors cleaned and flowed over the winter- so chased the fuel system thinking I had connected injectors wrong- but of course it wouldn't have run so good right off the trailer.   I also had the Ig module checked when replacing the pickup coil - it was good.   So a month later- quits- dead in the water- after warm up and getting out to the course.  tow in.  could not find a problem.  following weekend- same deal.  I replaced the ig module , cap & rotor.  next weekend- had to get towed back in.  Fuel pressures were all good.  started and ran fine - right up to WOT.  as soon as I go to pull a skier- dead. no start. tow in.    I had to give up as it is now October.  I will look at the alternator first thing this spring!  ( never has been replaced anyway- 1999)