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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14305
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Jason: I installed a new IAC in my engine this morning, as

Customer Question

Jason: I installed a new IAC in my engine this morning, as shown below....Harley
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hi Harley. Is the issue better with the new IAC? Or the same?
Customer: replied 1 year ago.
Jason: Per my earlier question, better by about 100 RPM
Customer: replied 1 year ago.
Perhaps I can tinker with lengthening the stroke on the throttle cable by a turn of the barrel or two???
Expert:  Jason replied 1 year ago.
Is the throttle all the way closed? Remove the throttle cable from the engine all together and start it up. Is it any better?
Customer: replied 1 year ago.
I'll do that and get back here in 20 minutes....Harley.....Done, starts readily, stabilizes at 750RPM for 30", surges to 1000RPM, then quits....Harley
Expert:  Jason replied 1 year ago.
What is the fuel pressure reading? Can you measure that.
Customer: replied 1 year ago.
I have no fuel pressure guage in the boat, but I am sure I can rig one up if I knew which port to try to tap into....... even where the pump is in my Limestone 22' boat woud be a help. This boat is new to me. I would prefer to continue typing because your website says "live chat" is available only in continental USA
Expert:  Jason replied 1 year ago.
Let me ask you another question. When we spoke the other day you said it only stalled when you shifted it. Now you are saying that it starts, rev's up, and then stalls. Are we getting a different behavior from the engine after the IAC was installed?
Customer: replied 1 year ago.
Yes, Jason; with the throttle cable disconnected, it starts well, stabilizes at about 750RPM for 30", momentarily surges to 1100RPM. then quits. So, this is quite a change since installing the new IAC. If the engine stalled only when I shifted, I guess we would both be looking at the switch that prevents shifts at higher than the recommended idle RPM of around 600RPM,,,,,,no??
Expert:  Jason replied 1 year ago.
I think the engine has more than one issue going on with it. There is also a possibility the new IAC is bad. When you changed the IAC, did the passageway look clean or dirty
Customer: replied 1 year ago.
Jason:It looked pretty clean....I had already cleaned the soot off the flame arrester as well. It's beginning to look like I should bite the bullet and import (75 miles) a marine tech with an OBD to track down the problem.....much as I hate to go that route. Harley
Expert:  Jason replied 1 year ago.
Being a fuel injected engine at some point the engine might have to get hooked back up to a scan tool. Do you still have the old IAC, and if yes, have you thrown that back in to see if it went back to at least not stalling on you?
Customer: replied 1 year ago.
Jason:
Good idea. I will clean up the old IAC after lunch and try it out.....Harley
Expert:  Jason replied 1 year ago.
See what happens. If it's actually better, then you might have gotten a bum part.
Customer: replied 1 year ago.
Hi, Jason:'cleaned up the old IAC and found that it performs pretty much as the old one did.....'surges to about 1100 revs, drops down to about 700 then quits. I find with either IAC installed but unplugged, I can "catch" it with the throttle and hold it at 1100 RPM but, as I drop the revs toward idle, the engine does a little surge at around 700 revs then quits. I believe this behaviour is what we can expect with a plugged or water contaminated fuel filter????
Expert:  Jason replied 1 year ago.
Bad fuel or water in the fuel would definitely cause a similar symptom. I know we are trying to delay the inevitable here which is hooking the engine up to a scan tool. But take the fuel filter off and dump it into an old glass jar, let it settle for a few hours, and then see if it smells like gas or not. And then see if there is a separation line in the fuel.
Customer: replied 1 year ago.
Jason:Fuel filter is fine and the fuel has no water in it whatsoever. However, the engine now goes into surge mode any time I allow the RPM to drop below 1000 RPM. I will see if I can't lure someone with a marine OBD to come out here and do a diagnostic scan....money should do the trick...... along with some very expensive parts. Any more tips, Jason???
Regards,...............Harley
Expert:  Jason replied 1 year ago.
Hi Harley. Were you ever able to measure fuel pressure?
Customer: replied 1 year ago.
No.I had too many other chores going on. I will test the fuel pressure sometime late in the AM and get back to you...Thanks for what you've done for me so far....Harley
Expert:  Jason replied 1 year ago.
You are very welcome.
Customer: replied 1 year ago.
Hi, Jason:I tricked a marine tech into coming out ...perhaps tomorrow, who has 25 years as a marine guy who's forte is in fact the Mercruiser 7.4L. He has the latest scanner with the latest updates and an internet connection......Wish me luck!! I'll let you know what the results are.Regards,...........Harley
Customer: replied 1 year ago.
........as well as the fuel pressure......H
Expert:  Jason replied 1 year ago.
Good luck!

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