I just put a gauge on my HO, fired it up. It won't really idle anymore with the stick all the way back. I have to push to stick about 3/4" forward to maintain 700-800 idle. Smells real rich, and I have been having a nasty soot problem.
So, I fired it up and the gauge reads 36psi at idle. Romp on it, and it goes up a few pounds, so it looks like the regulator is adjusting somewhat.
The question is, what should the idle FP be? The book says 6psi running?
Book says 43PSI, key on, engine off, pump running. 36 is low, but that should not cause a rich condition, unless it was due to a leaking injector. Rich condition could also be due to a bad sensor.
Since you did not mention it, I guess you are not getting any engine alarms? Do you have a smartcraft display or scan tool?
Dave
I don't have the SmartCraft display.
I have scanned it twice, when I took it to the mechanic. 1st time I had an unplugged exh sensor that was giving the beeps. No codes or beeps as of right now.
Fire it off and it just starts surging. FP is stable at 36. Constant surge. No beeps. Push the stick forward about 3/4" off of the idle stop and it smooths out to 7-800.
So, we ask what is the engine wanting? Giving it some throttle blade opening, I am thinking it is wanting more air. My next idea is finding out what the Idle Air Control readings are / are supposed to be.
For surging, the Mercruiser ECM book (#50, I think) says to change spark plugs. I have never had plugs cause surging, but hey....it's worth a shot.
Engine runs great at cruise as well as WOT.
Back on the trailer after a day at the lake, the transom is covered in soot.
Those are my symptoms.
Anyone else? Opinions? Ideas?
Where did you tap in for the new guage? Was it in the main fuel line, anywhere after the filter, but before the fuel rails? Is there a possibility that you got some teflon tape, or some other kind of debris in the fuel line causing stuck injector(s)??? Just a thought...it wouldn't take much.
Where did you tap in for the new guage? Was it in the main fuel line, anywhere after the filter, but before the fuel rails? Is there a possibility that you got some teflon tape, or some other kind of debris in the fuel line causing stuck injector(s)??? Just a thought...it wouldn't take much.
I am beginning to think that.
I put the gauge on the schrader on the fuel rail for the injectors.
A leaking / stuck injector or two would cause rich condition. It is, however, holding fuel pressure. Shut it off, and it stays at last setting. The gauge does not have a check valve, so it is reading real-time residual pressure.
I suppose pulling the plugs would tell alot. Are some dirtier than others type of thing.
I do know that on the 502 EFI if the idle air motor setting or counts are off it will cause this. I am not up to speed on the 496 and how to set though sorry. Check out the link it has more info. Problems are with a procharged 500 EFI but you could pick up something.
http://www.offshoreonly.com/forums/s...ht=setting+IAC
Anyone else? Opinions? Ideas?
Beer-30,Did you disconnect the vaccum line to the fuel pressure regulator while checking the fuel pressure?Make sure you disconnect the vaccum line to the fuel pressure regulator,this is a must to get proper fuel pressure reading.
It does not sound like an IAC issue. A bad IAC valve will usually cause an alarm. Sounds more like a sensor or leaking injector. But your probably going to need a scan tool to figure it out.
In any event, from what I have seen, the following graph is typical of how an IAC (on a 496HO) will function at startup (note that engine RPM is divided by 10). It will go to 99.98% right away and then drop after a couple of minutes of running and become very active around 20% to 30%. Keep in mind that other problems will affect how the IAC operates.
Dave
http://www.hometown.aol.com/newprtdave/496iac
Beer-30,Did you disconnect the vaccum line to the fuel pressure regulator while checking the fuel pressure?Make sure you disconnect the vaccum line to the fuel pressure regulator,this is a must to get proper fuel pressure reading.
No, I didn't. I mainly wanted to see if it was fluctuating or not. I have heard of plugged fuel systems causing the FP to "search" and have erratic readings all over the scale. It was rock steady. It jumped up each time I romped on it, showing the regulator was responding to vacuum readings.
I will try that next. I disconnected the fuel gauge, as I was going to take it to the lake tomorrow. Looks like my plans may change, due to some illnesses in the family members that were supposed to go. Anyway, next plan is to change plugs, read the old ones, and put the FP gauge on again. After all that, I will disconnect the vac line and go from there.
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