Re: "How to adjust IAC & TPS" On Merc EFI
 

Hi Dave:

We did replace the IAC motor and checked for activity with the scan tool. It is working. We can get into gear and not stall if we blip the throttle. The IAC is following the throttle. I see what you are saying about these adjustments not making any difference, because they didn't help us.

I don't know how fast the IAC can react, but wouldn't the idle spark control be the ECUs first and fastest way to compensate for the extra load of going into gear? Since the other engine works fine are we looking for some failure on the spark side that would prevent the idle spark control from doing it's job?

Re: "How to adjust IAC & TPS" On Merc EFI
 

Dave, care to comment on my results I noted when I checked my motors? Keep in mind these are cold readings. Thanks

http://www.offshoreonly.com/forums/s...&highlight=iac

Re: "How to adjust IAC & TPS" On Merc EFI
 

The IAC is very fast and should be able to react in plenty of time to open when load is increased (shifting into gear). What is the IAC count at idle? What does the IAC do when shifted into gear? Does it react? Does the desired IAC position stay the same as the actual IAC Position? What is it IAC count at idle on the other motor? Does your scan tool have the ability to connect to both engines at once (to do a "side by side" comparison)?

A problem with the EST should set a code 42.

Dave

Re: "How to adjust IAC & TPS" On Merc EFI
 

Looks normal to me. The IAC counts will always be higher when engine(s) are cold.

Dave

Re: "How to adjust IAC & TPS" On Merc EFI
 

Thanks Dave. We have not seen an error code. Next time the boat is in the water we will see how the IAC reacts to shifting on both engines. It stalls right away so I don't know if we will see anything.

Re: "How to adjust IAC & TPS" On Merc EFI
 

Do you need a special scan tool or will the snap on scanner work on the 502 Mags ?

Re: "How to adjust IAC & TPS" On Merc EFI
 

American,
A Snap-on scanner will not work on marine systems. As far as I know, Vetronix is the only tool maker that offers an automotive / marine scan tool (requires proper cartidge).

tomcat,
I know I said that throttle plate adjustment is not the problem, but considering it has been messed with, It could be the problem.

It the throttle plate is adjusted too closed, and the IAC position is high to compensate, it may not have enough counts left to increase the airflow enough when the boat is shifted into gear. Again, it should be about 40 counts at idle (normal operating temp engine).

Dave

Re: "How to adjust IAC & TPS" On Merc EFI
 

Where can I pick up a scan tool... How much loot ?

Re: "How to adjust IAC & TPS" On Merc EFI
 

Check out Rinda.com. I think handheld tools run about $400.00, scan software (Called "Diacom") is about $580.00. I find the software to be far better than trying to use a handheld. Below is a screen shot of the Diacom software. I have highlighted the IAC data. The ability to display graphs of any (and multiple) data parameters makes it easy to analyze data (in this case IAC function). This screen shot does not show any IAC activity, just one I had handy.

Dave

Re: "How to adjust IAC & TPS" On Merc EFI
 

Thanks again Dave:

We have gone through the throttle plate adjustments and low IAC counts procedure. It is set correctly. When shifted into gear the scan tool does show the IAC counts going up quickly but the engine doesn't seem to fight the stall at all, it just dies. We could increase the rate at which the IAC opens by reprogramming the ECU, but again, the other engine is fine.

We have replaced the IAC and also exchanged it with the one from the good engine, no improvement. By process of elimination we are thinking that idle spark control may be the problem. We have no error codes but have you ever had a distributor go bad? Apparently there is a switch that changes spark control between the ignition module and the ECU.

I assume that the scan tool and the Diacom software both tell you what the computer is asking for, not necessarily what the controlled device is actually doing.