2007 Mercury Optimax 150hp Rough Idle Especially When Hot Outside

[DHott]

Hey guys I’ve searched this forum and can’t find what I’m looking for. I think I have a pretty unique problem. I had a 2005 optimax 135 that blew a cylinder about a year ago. I got a fully dressed 2007 150 powerhead put on and it hasn’t ever idled right. I’m still using my old 135 ecu. It runs fine at anything other than idle but missed/runs rough at idle and sometimes dies. Sounds like it’s bogging down. I’ve noticed this problem is much less noticeable when it’s cold outside and much worse when it’s hot. I’ve been battling this for a year now. Things I’ve replaced/done:

tracker diaphragm
fuel regulator diaphragm
reeds and stuffers
primer bulb
all injector o-rings
spark plugs
one coil
spark plug wires
cleaned vst
cleaned air regulator
Cleaned fuel filter

its not throwing any codes and the dealer can’t figure it out. He tested compression, all fuel pumps, all coils, all injectors. Pressures right on at 80/90. He said my plugs were really black and he replaced them again. The best thing he could tell me is that it wasn’t quite getting up to temp so he thought it was running rich and fouling plugs and told me to change thermostats. I did that and it didn’t help (I didn’t think it would). I’ve also noticed the voltage gauge is lower than the old powerhead although voltage at the battery and at the motor is where it should be. Also rpm gauge bounces around every now and then which it didn’t used to do. I’ve checked all grounds and seem fine. About the only thing I havnt done is sent the injectors to be cleaned/flowed. Before I spend $300 on that I just wanted to see if there’s anything else I should check? Or is this most like likely the cause of dirty injectors? I just dont see why outside air temperature would effect it. Thanks a lot guys.

[EuropeanAM]

If you would, please take a moment to review the Announcements, and be sure to provide the Required Info (serial number) when posting. Thanks!

There's more to this than $300 of injector cleaning.

Let's get the serial number for the 135, and the serial info for the 150 powerhead. WHICH engine's grommet have you used between the throttle body and attenuator/flywheel cover?

A few pictures from various angles of the powerhead may also prove helpful (especially if you don't know the serial number for the 150 donor).

[DHott]

Thanks for the response. The serial number for the 135 was 1B070297. The serial number for the 150 is 1B508381. I believe the correct grommet is being used. I will take some pictures of the motor when I get home

[DHott]

It’s not letting me upload photos. I’ll keep trying. I’ve heard that it’s important to lap the cages when installing new reeds. I didn’t do that. Could that be my problem?

[EuropeanAM]

Yes, because the reed blocks are not true/flat. Inspect that block very carefully for marks, chips or cracks in the RUBBER coating on the reed block (which can grab the reed tip causing it to break).

[DHott]

Ok I’m going to inspect and lap them either today or tomorrow. Is there anything else I should check? Do you recommend changing the springs in the fuel and tracker diaphragms when replacing the diaphragms?

[EuropeanAM]

Just take your time and do a good job on the blocks, and make sure everything is fitted well when done.

I do NOT recommend replacing any rail components unless they have failed (or are bad). This would include diaphrams.

[DHott]

So update, I lapped the reed cages and sent fuel and air injectors out to be cleaned and flow tested. All of this with still no change to my poor idle. What should my next step be? Possibly leaking air somewhere? Could I hook up an air compressor to the Schrader valves and pressure the rails and listen for leaks?

[DHott]

Also I noticed that my fuel pressure drops pretty fast when you turn the engine off. It drops down to about 50 psi in 5 seconds and in 12 seconds it’s at 10 psi where it stays. Is that too fast? I know the fuel pressure follows the air pressure so could I have an air leak? Or a bad air regulator?

[JOE54]

So update, I lapped the reed cages and sent fuel and air injectors out to be cleaned and flow tested. All of this with still no change to my poor idle. What should my next step be? Possibly leaking air somewhere? Could I hook up an air compressor to the Schrader valves and pressure the rails and listen for leaks?

yes regulated air

[JOE54]

Also I noticed that my fuel pressure drops pretty fast when you turn the engine off. It drops down to about 50 psi in 5 seconds and in 12 seconds it’s at 10 psi where it stays. Is that too fast? I know the fuel pressure follows the air pressure so could I have an air leak? Or a bad air regulator?

to fast internal leak somewhrere

[EuropeanAM]

What is happening with the AIR PRESSURE during this time?

[DHott]

Im not 100% sure. I got the fuel pressure measurements from a video I took but I forgot to take a video of the air pressure after shutoff. When I pressurize the air rail with an air compressor the air loses pressure very slowly. That seems normal. I’m thinking now about the diaphragm pump (pulse pump). Is it possible that its leaking fuel back into the engine causing it to run rich at idle? My plugs are very black and look rich after not many hours.

[DHott]

Also while troubleshooting today with the motor running I unplugged the low pressure pump and left it unplugged for about a minute. Plugged it back in with a hand on it and I couldn’t feel or hear it start running. Also no change in how my engine was running. Is this normal? Is it supposed to run all the time or only when the fuel in the VST is low? Sorry if these are stupid questions

[JOE54]

all time , unplug hp pump turn key on listen for other / boost pump to run

[DHott]

I verified the pumps are working. I noticed when I pump the primer bulb fuel was coming out of the fitting on the diaphragm pump that leads to the crankcase to get pressure. So I rebuilt the diaphragm pump. Same symptoms are there and the primer bulb is soft when running. Not flat, but I can pump it several times and it never really gets hard. Anything else I should check? You think the fuel leaking into the crankcase caused it to run so rich that my plugs are already fouled?

[JOE54]

very possible

[EuropeanAM]

Also, did you use an OEM (Mercury) pulse fuel pump kit? There's ZERO room for error on those pumps- they're either 100% right or they're "wrong" (and don't work properly). Something as simple as one gasket in the wrong place (or oriented the wrong direction) will cause problems.

[DHott]

I used the sierra rebuild kit. I think as my next step I’ll replace all of the hose from the tank to diaphragm pump and primer bulb with oem. 3/8 to the bulb and then 5/16 to the pump?

[DHott]

Also after researching more about primer bulbs, I’ve learned how important they are and really the purpose they serve. When I replaced mine I replaced it with some cheapy one from Walmart. Stupid I know. I have the oem one now but havnt gotten to test it yet. Im learning a lot through this whole process and I’ll be pretty proud of myself if I can figure out what two mercury dealers havnt been able to. Thanks to everyone for the help thus far