Anyone know anything about Malibu boats? No fuel pump signal from ECU

[Chad-1stGen]

I have a 1997 Malibu VLX. It has the monsoon motor which is built by Indmar based on a Chevy 350.

It has MPFI and after not starting last weekend and lots of fun with my multimeter I'm pretty sure I'm getting no fuel pump power signal from the ECU.

I've found the signal wire from the ECU and when you first turn the key I get a split second spike to 0.5 volts. When cranking I get 0.01 volts.

Neither is likely strong enough to activate the really and I'm thinking both readings are more noise than a signal from the ECU. So I'm thinking I'm just not getting a signal.

I'm not sure what else I can test or look for? I'm concerned I might have to replace the ECU at this point.

[Chad-1stGen]

If it helps the ECU used my Indmar that year is the GM MEFI 2 which they also use/used in their EFI crate motors like Ramjet 502, Ramjet 350, LT1, LS1, LS2, LS6, LS7, Ecotec

[LSXfan]

does the system use an oil pressure safety switch ?

[Chad-1stGen]

I've read that Malibu's do have that feature. I'm not sure if my 97 does or not.

Assuming it does wouldn't the initial 2 second prime when you turn the key on still activate?

I know it's making oil pressure when cranking.

[LSXfan]

it would depding on what the switch is set at, of course all the oil pressure in the world wouldnt matter if the safety switch itself was bad...

[CarlC]

Just thinking here Chad...

Is the signal from the ECM + or - ? Most of the switching functions in later ECM's switch negative.

If you hot-wire the relay does it start?

[Chad-1stGen]

Carl I think you are spot on. Lucky for me the google book search shows some of the relevant trouble shooting pages from the Indmar manual.

Reads:


13. Turn the key switch to OFF or STOP. connect the cord of the test lamp to the positive battery terminal. touch the test probe to the No. 85 terminal in the relay mounting bracket or harness plug. The lamp must not illuminate. If the lamp illuminates, the dark green/white wire connecting the No. 85 relay terminal to the ECU is shorted to ground, or the ECU is faulty. Either condition will cause the fuel pump relay to remain in the energized position, and the pumps will operate anytime the system relay is energized. Check wiring and terminals for shorts. Replace the ECI only if all other components and the wiring on the circuit are good. Failure of the ECU is extremely rare.

14. Touch the test lamp probe to the No. 85 terminal on the relay mounting bracket or harness plug. Observe the test lamp while an assistant turns the key switch to ON or RUN. The lamp must illuminate for 2 seconds and then extinguish. /snip

Now 14. doesn't say where to touch the probe cord so I think it's still positive carried over from step 13. Plus the bolded area indicates if the wire connected to No.85 grounds the pump will remain energized. Time to go back and do some more testing lol. Maybe I'll get lucky and it will be the relay after all!!

[Chad-1stGen]

Well I was so excited at the thought it still might be the relay I went over and test it tonight. Just got back. No deal.

Testing under the presumption the signal wire from the ECU grounds to energize the fuel pump it still didn't work. Also, since I now knew what the other identical relay did I swapped the fuel pump relay into that harness and it worked.

So the fuse is good, the relay is good, my ohm meter testing says the wiring is good I back to thinking it's the ECU. Will go play around some more when it's daylight and I have time. Will try to jumper the signal wire to get the fuel pump to energize manually just to be sure.

[CarlC]

Chad,

Disconnect the wire from the ECM to the relay at the relay. Run a jumper wire to the relay to verify both polarity and function. The engine may start if the ECM still produces the other engine management functions. If the ECM has failed the engine may not start even if the fuel relay trigger was bypassed.

[Chad-1stGen]

Good tip Carl. I actually tried jumpering the ECU signal wire to ground last night with the relavant plug to the ECU disconnected and it still didn't work. Wasn't sure if the ECU plug disconnected had anything to do with it. Was planning on removing the signal wire from the ECU plug to test and still will probably try.

However, it turns out that the missing pages (98 & 99) from google's book preview were key to my testing. They contain the pages relavant to my MEFI 2 system and the one I was reading is the newer MEFI 3 and 4 system. According to a helpful poster on the Malibu website the MEFI 2 system does supply positive power to the relay.

Good thing the first thing I did the morning was order the manual of Amazon for myself lol.

I will still try jumpering it to be sure.