idle & intermitent hesitation

[kevinp]

Sometimes when starting boat does not want to idle and may have to re-started a couple of times before it will keep idling. After a idling for a while it sometimes as a slight hesitation when excellerating from idle.

[dogbert]

Re: idle & intermitent hesitation

Originally posted by kevinp
Sometimes when starting boat does not want to idle and may have to re-started a couple of times before it will keep idling. After a idling for a while it sometimes as a slight hesitation when excellerating from idle.

Two possibilities: poorly charged battery (it's bearly turning over) or bad gas. I recently had the same thing. Try increasing the octane in your gas. That and charging my battery helped my boat start better, especially after running it for a while on a hot day.

[chpthril]

Year, engine, carb or fuel injection?

[kevinp]

2003 tige 21i 350 mercruiser 315hp EFI. I just had a new PCM installed and since then it idles higher around 700 and stalls if it goes below 700, and somtimes hestitates when taking off after idling.

[chpthril]

First, I would check the basics like sparkplug gap and wear, fuel/water sep. filter, fuel pressure, ignition timing. Also check for loose or corroded connectors.

Next, I would look close @ the signal from the Throttle Position Sensor. Sounds like a 'dead spot' in that signal. A shop With a Graphing Meter should be able to test it.

P.S. was the pcm replaced for same or differant problem?

[kevinp]

PCM replaced because motor would beep twice & quit and when tested they found the PCM to be the problem. Fuel presure was good, new gapped plugs installed, new fuel/water seperator filter as well. I currently have the in-line filter removed as Merc rep suggested it would run better when it was real hot, I will putting this back on today.

[Domsz06]

kevin it sounds like you may have the same problem that I have. I just got off the phone with a dealer who is a member up here. He said that I may be vaporising my fuel. You have the same plant as I do. Have you checked to make sure that you dont' have anything clogging the water line from the hull up to the tranny cooler? Check that and also, try running your boat with a 2x4 lifting the motor box up to see if it gets cooler. Also feel your fuel pump. If it's hot, then that's a problem.

[chpthril]

He said that I may be vaporising my fuel

Do you think they meant 'Vapor Locking'. That is were the fuel boils in the fuel lines due to hi temps. This is usially not a problem we see on fuel injected engines. The pressurized fuel system raises the boiling point. Were is the fuelpump located on your boat?

[Tip]

I have a 2003 22v with the 350 MPI and mine has intermittently hesitated during acceleration ever since I bought it new, but my engine has never once completely died. I was told this was a problem with the programming in the electronic fuel control unit but I never believed that. The dead spot theory sounds interesting... can I check this myself?

[chpthril]

Tip,
below is the Graphing Meter that I use. It shows a 'live' signal. You can use DMM (digital multi meter), but they only 'sample' the voltage or ohm's signal and sometimes might miss a small glitch.

A typical TPS has three wires: one ground, one referance voltage in, and a voltage signal out that changes from low to hi as the throttle is opened.

[chpthril]

Here is what you might see if you had a bad TPS.

[Domsz06]

My fuel pump is right in my engine bay. After talking with Dom, a member on here. I have a few things to check. I'll keep you posted.

[chpthril]

Originally posted by domslude
My fuel pump is right in my engine bay. After talking with Dom, a member on here. I have a few things to check. I'll keep you posted.

It's possible that the fuel is vapor locking in the line coming into the pump!

[NICKYPOO]

Originally posted by chpthril
Here is what you might see if you had a bad TPS.

Oh man. Didn't you get that memo on the TPS reports? Yaaaaaa, ya see, we're putting new cover sheets on all our TPS reports, so if you could just make sure you do that from now on, that would be greeeeaaaat, mmmmm k.

[Domsz06]

Originally posted by chpthril
It's possible that the fuel is vapor locking in the line coming into the pump!

Yeah I have a few things to check, and you know I bought the evolution reprogrammer for my truck, so I got to try it out and pull my boat to the water