Merc 5.7 TBI Stalling Shifting Into Gear

[sarnone]

Hi, I have twin 350 5.7 TBIs with B3s, which stall when shifted into gear. More often when warm and port more than stbd. I also have noticed a drop in rpms when applying throttle just off idle before take off. I have new cap, rotors, wires, iac and tps are newer. Engines have been well-maintained. Haven't looked at plugs yet or checked for any codes.
Thanks for the help.

1998 formula 280ss

 

[alldodge]

What rpm do the motors idle at?

Where the IAC and TPS changed for this problem and who replaced them?

 

[sarnone]

Alldodge, the port wants to stay at about 850, this is the side which stalls far more, and the stbd is at about 650. The iac and tps were changed before I purchased the boat. I have the service records. I was checking throttle response in neutral earlier today, and clearly the port side has a small lag when you quickly apply some throttle. If I rev it a little at operating temp the rpms will come down, but return to 850.

 

[alldodge]

Need to find out if the IAC is functioning correctly. Need a test light


If IAC and connections check out, suggest pulling plugs for a look and then check fuel pressure (30 psi)

 

[sarnone]

Thank you Alldodge. I will get back with you this afternoon.

Sarnone

 

[sarnone]

Alldodge, is there a procedure for testing the ECT using a test light as well?

Kind Regards
Sarnone

 

[alldodge]

There is a 5V check with ignition ON to ground, voltage should be above 4V

Resistance readings are
Degrees Ohms
210 - 185
160 - 450
100 - 1800
70 -3400
40 -7500
20 - 13500

 

[sarnone]

Alldodge, while completing the test of the IAC, I discovered that the connector was being stressed and the pin contacts were starting to spread. Straightening the harness caused the rpms to correct. The IAC contacts are also very corroded, compared to all the others, which are still shiny. I assume the corrosion developed from the loose connection, I hope. I plan to replace the pin contacts, I think I have some that will fit the connector.
Besides that, the rpms are about where they should be, no more stalling and I gained back about 200 rpms at the top end and both engines are running identical at full throttle. Thanks!