Engine surging/losing power

[tbowman]

I have a 2002 20V/350 Mercruiser MPI with about 350 hours. At cruising speed the engine will surge (RPM's drop) and lose power, this will happen 3-4 times then stall completely. It starts right back up every time but then stalls again after cruising a short distance. The throttle position does not move at all during the surges. It happens with Perfect Pass on and off. Last Spring I replaced the fuel filter and water separator. It was idling rough, changed the Idle Air Control Valve, that fixed the idle. Tried a new Throttle Position Sensor but did not help.

Has this happened to anyone else? Any ideas?

Thanks,

[chpthril]

Fuel pump.

By what means did you check/adjust the new TPS? Also inspect the vacuum hose going to the MAP sensor.

[tbowman]

I did not check/adjust the TPS, just installed a new one. Do you think it could be the fuel pump? Would the fuel pump draw a code?

Thanks,

[chpthril]

I did not check/adjust the TPS, just installed a new one. Do you think it could be the fuel pump? Would the fuel pump draw a code?

Thanks,

Although most TPS's are adjustable, some do not have slotted bolt holes, but the actual tab that the throttle pushes on can be adjusted. This requires a DVOM (digital volt/ohm meter) and this will also tell you if the TPS circuit is good.

Also make sure the battery is good and the grounds are good and clean. Poor voltage can be the root of many problems on ECM controlled systems. I doubt the ECM will have a code triggered by the fuel pump. If the engine had O2 sensors, that's a different story. Fuel pressure gauge and volt meter are the best tools to test a fuel pump. The fact that it starts right back up after stalling leads me a way from the ignition module. They tend to need to cool down before working again when the begin to fail.

[tbowman]

My TPS is not adjustable. I just bought one from the local auto part store. Should I get a Mercruiser part or is the standard GM TPS OK? Battery is brand new last Spring, terminals are clean.

Thank you so much for the advice.

[chpthril]

My TPS is not adjustable. I just bought one from the local auto part store. Should I get a Mercruiser part or is the standard GM TPS OK? Battery is brand new last Spring, terminals are clean.

Thank you so much for the advice.

It would be worth it to take a volt meter and just see what the idle TPS volt ready is. At the same time, you are testing the ECM and wires running to the TPS.

Is the ground on the block clean and tight?

[tbowman]

I will check the TPS and ground. Would you do that before replacing the fuel pump?

Thanks,

[jsz]

I'm thinking fuel pump also. I have a 2002 350 merc and last trip we started having issues. The shop thought fuel pump or maybe anti-siphon valve. I'm taking it in tomorrow so we'll see.

[tbowman]

Thank you for the reply, hopefully that fixes your problem. Please let me know if it does.

Thanks

[jsz]

I'm thinking fuel pump also. I have a 2002 350 merc and last trip we started having issues. The shop thought fuel pump or maybe anti-siphon valve. I'm taking it in tomorrow so we'll see.

I just got mine fixed and it was not the fuel pump!

1st repair - My anti siphon valve was sticking and needed replacement.

2nd repair - one of the sensors on the motor (I think it was the oil sensor) was partially clogged by deposits. The computer read this as low oil pressure and started shutting down the motor.

To back track a little, the boat would run fine for me every morning but after being shut off for a while, it would start for a few seconds and then stall. At first I thought it was a dirty IAC, then vapor lock, bad fuel, fuel pump, ???. Every day I tried something new with the same results. After the boat was hooked up to a code reader, the problems were found.

[tbowman]

Glad you got your boat fixed. Will check those things too.

Thanks

[jsz]

I like fixing and figuring things out for myself with the help of you guys here on tigeowners. I also hate paying $100/hour for someone to make a silly repair I could have done myself. But in this case the money was well spent. With so many electrical / computerized parts and sensors everywhere, hooking it up to a shop computer was the only way to go.

I talked to a lot of smart boating guys and got a lot of "oh, it has to be..."

Looking back I should have taken it in once my fist couple attemps to fix didn't work.

Good luck to you.

[TeamAllen]

Could you post up the part that was replaced? It might come in handy in the future.
Thanks and glad you got it fixed!

[jsz]

I'll try and get some pics up.