Black Scorpion Service

My 99 sanger has about 290 hours on it. I just finished the 300 hour tune up. One thing I have a question on is modifying the throttle body. From experience with LS1 (chevy camaro and corvette) when installing big cams you can drill a hole in the throttle body with a 9/32 bit to help get rid of the hissing and help with the idle when comming back down from RPMS.

What im getting at is on my black scorpion if you blip the throttle you can kill the motor, you can hear it gasp for air. Ive cleaned the spark arrestor, and checked the IAC. My thoughts are to drill a hole in the t/b to help smooth out the idle. Any ideas whould be appreciated Ive looked around for any mercruiser forums and comming up empty handed.

thanks

I would hesitate drilling a hole in TB unless you are sure that is a fix. Based on your description I would be leaning more toward the throttle position switch and/or its adjustment.

Nate,

You might want to give the Arizona Speed and Marine guys a call. I talked to them about recalibrating my ECM, it was too expensive but they gave me some insight to my MEFI controlled GM powerplant.

Rich, the T/B is controlled by the IAC and the TPS. Both are non adjustable, I have pulled tHe IAC and cleaned it but it did not help the only other thing is to replace it.

Mike thanks for the tip im going to give them a call.

Just a thought sorry no help. Do let us know the outcome though and good luck.

I have a similar situation on a Merc 315 MPI. When I get it out of storage in the spring, I plan to do some measurements on the TPS. This is nothing more that a potentiometer. I'm thinking it has a dead spot.

Nate, An idea from auto repair world-make sure the throttle plate edges are clean (not carboned or gummed up) this can cause the air starving/stalling you describe. Easy to shine a light in on them and check, just as easy to clean using carb cleaner and light rag or old toothbrush. Some do have a coating on them but are normally marked with a warning about the coating. A slow IAC motor can also cause it also. I also agree about not drilling a hole as than can cause an unmetered air situation and throw off the ECM. Hope this helps

Fred, thanks for the suggestion it was the first thing I did after I noticed the problem was to clean the T/B and lubricated everything. I found a place online that sells the IAC for 80 bucks. I might pick it up and a High flow K@N filter to see if it helps...


Paul-- Did you find a ohm resistance information about the TBI and what it should be set at? thanks nate

Nate - What you want to look for is a smooth increase/decrease in resistance between the wiper terminal and either one of the other two terminals while SLOWLY rotating the pot. A dead spot will read as an open (infinite resistance). I'd guess that the total resistance across the pot (as measured across the two non-wiper terminals) is somewhere in 2k-10k range. But again, you're looking for a dead spot, not a specific resistance value.

This test procedure assumes the TPS is disconnected from the wiring harness. Another option is to leave it connected and with the ignition on and measure voltage at the wiper with respect to the pot terminal that's connected to ground. With a good TPS, the voltage will smoothly ramp up as the TPS is rotated in one direction and ramp down in the other direction. I'd expect the total range to be somewhere between 0-5 volts dc.