HP 500EFI Loss of Power
 

Would like to know if anyone has experienced any of my following symptoms, at a loss right now.

First off I think I have two unrelated things going on, but maybe not.

First, when starboard engine is cold it fires right up with barely even cranking over, when it gets warm it will crank for a few seconds and seems to need throttle input to start. Once its running it seems to idle fine without stumbling or anything else.......I'm assuming this may be the IAC?

Second, same motor, starboard, seems to lag and not turn the same RPM's with the same throttle input. This year the plugs, wires, cap, rotor, fuel/water filter and in-line fuel filter were replaced. I pulled the air cleaners and checked the position of the butterfly against the port motor with the same input and and they appear to be equal, especially at WOT. The faster you want to go the more the shifters are out of sync and that motor drinks more fuel as well. I'm going to try a different set of props tonight to see if I'm having prop issues but I don't think that's going to be my problem. I even switched which fuel tanks the motors draw from and no better results.

Could I have a bad injector, should I send these out to be cleaned? I'm at a loss, any suggestions or help would be greatly appreciated.

I would rule the props out first. Is this a new to you boat? If so has the throttle position you are talking about always been different? When I bought my boat the props were way out and mine was diffeerent by about 600 rpms with the throttle lined up.

It seemed to get a little worse when I change the props last year but i believe it was off a little even with the old props. Hopefully the new props tonight will solve the problem.

I would check fuel pressure, should be 40 psi or so. And I would see how fast it drops when the engine is shut off. If it drops quickly (less than 15 minutes) you could have a leaky injector that would cause your hot start issues.

Tried the new/different props last night and nothing changed, i still lack anywhere from 200-500 rpms, the more throttle input the larger the variance. I also noticed that problem engine seemed to emit some smoke out the exhaust on start up and seems to be running richer at idle.

What about the IAC, when is this working and what exactly does it do........if its faulty can it cause problems throughout the whole rpm range?

it sounds like you have a leaking injector,like ted said,i recomend sending all 8 from that motor to be checked.

It does sound like a IAC, you should be checking this with a scan tool so you can see for any codes, or be checking the counts on the IAC. I would be keeping it very simple, have you checked your ignition timing? Yes, you could have a bad injector, but you should follow simple troubleshooting first.

Would a bad IAC cause a lack of power/rpms in the mid range to full throttle?

The timing was set at the start of the season so I have to assume that its still ok, but could have it checked as well.

How do you check the counts on the IAC, can this only be done with a scan tool?

WTF....My 500 just took a crap too.....Blown head gasket and unkown cause....that means $$$$$$$$$

The IAC will not affect anything except idle and will not cause a lack of power.

Marty, I saw your post, that is a great run, 535 hours, WOW. I had my heads done prior to the season at 282 hours and none of my valve springs would meet spec (all were weak) and my head gaskets were just about burnt through. My engine guy told me that if I would have run the boat this season I would have had major issues.

This lack of power or inability to get the rpms out of one of my engines is griving me nuts, I'm going to run a fuel pressure check this weekend and probably send out the injectors next week regardless. We want to do another NYC run this year but I'm not 100% comfortable bringing the boat anywhere until I figure out what's wrong with it.

I am having the same issue as you are experiencing Vette, but I have no issues with hot start up.
I changed the fuel filter and one of my 525's responded to the change, now spinning 5200 rpm. (there was no debris in the fuel)
One engine is still down about 300 rpm, I scanned the engine and it has no codes and 100% available power.
Since 1 of the 2 engines responded to a fuel filter change I will do the high pressure fuel filters.
If this fails and I am still down on rpm, I was thinking dirty injectors, pending fuel pressure is fine.

I change both fuel filters on the the down engine and it didn't make a difference. Hopefully the fuel pressure test will tell me something this weekend. Let me know if you find anything as well.

Will do...but I won't be running the boat this weekend...other commitments.

Did you or anyone else ever find out the issue on this? Can you please post? Mine is doing the exact same thing.

I don't mean to hi jack a thread but what did you think would happen at 535 hours without doing preventative mainentance. Blue motors are known for springs and head gaskets.