2006 Mercury 60hp bigfoot 4-stroke running rough

jparkerri · #1 October 10th, 2008, 03:00 PM

I have a 2006 Mercury 60HP Bigfoot 4-stroke that's been running great until this summer. At high speed it's fine but at slow speed it runs rough and at idle, it runs al little while then finally stalls out. It starts right up again without choking it or pumping the fuel line bulb. I've used new gas, bought a new gas tank because I thought there was an air leak. I checked the plugs but they all seem to be firing. I watched the fuel filter bowl but don't see any lack of gas. The fuel line bulb seems ok, not too soft. Pumping it doesn't help at all, it still stalls. I suspected the fuel pump for a while because it seemed to be ticking and it stopped when I pumped the fuel line bulb. When I bought the new gas tank that seemed to stop. At one point the engine seemed to pop with pre-ignition like the timing was off but not recently.

Any suggestions.

Dunaruna · #2 October 10th, 2008, 07:16 PM

I'll watch this one with interest, I didn't know that merc were still offering carb models in 2006.

jparkerri · #3 October 10th, 2008, 10:05 PM

This it's not carburated but rather fuel injected.

Dunaruna · #4 October 10th, 2008, 10:29 PM

Yeah, that's what i thought. Your 'choke' comment got me thinking that you may have the year wrong.

First port of call should be a regular tune/service to eliminate any faulty consumable parts (plugs, filters etc).
There are 2 fuel pumps on that motor, a high pressure and a low pressure. The low pressure pump delivers the fuel from the tank to the high pressure pump. Even though merc supply one, there should be no need (ever) to prime the bulb, the low pressure pump does that for you. The fact that it is running would indicate the high pressure pump is working but I would suggest a fuel pressure test to confirm. Me thinks you have a low pressure pump problem.

These motors are complicated and can be difficult to diagnose faults, I would highly recommend a genuine service manual.

jparkerri · #5 October 25th, 2008, 05:42 PM

Well, I got a service manual and checked out the low-pressure fuel pump. I took it apart and found a tiny crack in the check value (small plastic disk) in the input chamber. Just to see if it mattered, I switched it with the good check valve in the output chamber. It didn't change the behavior of the motor at all. Everything else is was fine. The cooling water was working, etc. No restrictions from the fiuel filter. I checked all the spark plugs, etc. I started checking anything else I could find and pulled the hose off the cowling for the intake manifold that goes to the Idle Air Control (IAC). I used my finger to control the air getting sucked into the cowling. By letting a little in I got a nice idle for as long as I wanted. So I checked the IAC. It may have been stuck because when I first put 12 volts to it, nothing happened but after several times I heard the solenoid click and then got air through the valve. I plugged it back and still it didn't always allow air in. I got 12v on the wires going to the IAC some times but not always. It thought it may be the connector but when I got 12v, the valve opened.

My question now is what controls when the IAC is opened to allow extra air to the engine at idle? If this is always opened at idle, I think my problems would go away. I realize that the ECM controls this. Any ideas? I'd follow the wires back but don't have a wiring diagram.

Anyone ever use the CDS to diagnose their motor?

Thanks.

jparkerri · #6 November 7th, 2008, 07:18 PM

I replaced the IAC and nothing changed. It still ran rough and stopped at idle. I put in a tee in the hose from the IAC to the intake cowling and put a small hole (about 1/8") in the tube to always allow some air. It definitely idles better, doesn't die and doesn't seem to have any effect at high speeds. I'm sure there is still something wrong with whatever controls the IAC. Any information on what controls the IAC? How would I go about checking it?

hamit59 · #7 November 8th, 2008, 05:59 PM

take a look at your tps. If it's not reading spec it would not tell the ecm to pull in the iac valve. when you are at idle. ddt is the only thing merc says that will talk to the ecm .

Dunaruna · #8 November 9th, 2008, 02:40 AM

Throwing parts at an EFI is is hit and miss, and can become VERY expensive.

The ECU directly & soley controls the IAC, the signal that it sends the IAC is dependant on input from 6 other sensors (CPS, TPS, ECT, MAT, MAP and oil pressure). Any or all of these will cause the ECU to adjust the IAC. The only way to see if the ECU is giving the correct instructions is to get her connected to a scanner.

Does the IAC test within specifications when isolated?