1998 Tige pre2200i running rich/high idle

[Seanj]

I have a 5.7 mag in a 98 pre2200i that I believe is running rich. Toward the end of last season gas consumption was up and you can see dark exhaust, smell fuel, and see what looks like soot in the water exiting the exhaust when I run it in the the driveway on the hose. I got it started today for the first time this season with no issues, but it still seems to run rich. I do not have a scan tool and did some research which leads me to possibly think the engine temp sender may be bad. I disassembled the thermostat housing and the thermostat was rusty, but seemed to work. I have ordered a new thermostat and engine temp sender. The only other thing I located was maybe a vacuum line coming from the bottom of the throttle body and going down to the fuel pump. This line was barely connected and loose fitting. If it is in fact a vacuum line I'm guessing it was leaking. While in the driveway it is idling at approximately 1200 rpm and did not reach operating temp in the short time I had it running. Also if I attempted to go from idle to full throttle it would bog down. I came back to idle and the engine recovered and did not stall. Is there anything else I am missing that could be fairly easily checked?

[freeheel4life]

Are you throttle body injected, multi port, or carbed??

[Seanj]

It is MPI.

[freeheel4life]

That vacuum line is likey for the fuel pressure regulator. If you have a fuel pressure gauge that would help to confirm but I'd make sure that vacuum line is in place and in good shape.

[Seanj]

Ok I will make sure it is not clogged and may use a small zip tie to ensure it stays in place and sealed

[freeheel4life]

Seanj make sure there are no cracks or holes in the line as well.

[boatwakes]

Post your serial number please. There was a short run of MPI mercruisers with manifold air temp senders (MAT) located near the PCV. The MAT would get covered in oil vapor if the crankcase was overfilled, basically shorting the sensor and cause the computer to think the engine was still cold thus continue to over fuel it. If you suspect the thermostat, replace it as well (160* for MPI), it's old.

[Seanj]

The engine serial # is 0L008114. I have a thermostat and the gaskets on the way along with the temp sender. I think it has the MAP sensor that is on the manifold near the throttle body. I ordered one of the Rinda technology code reader ( the 80.00 one) and it showed up today. Gave a code for the temp sender and the throttle position sensor. I’m will replace those senders and report back. Does that sound right?

[boatwakes]

Okay yours doesn't have it so you're on the right track, change the CTS (coolant temp sensor) SENSOR (#805218T) and thermostat kit 807252T5 (only use 160* thermostats on these engines. If you install the 140* ((for carbureted engines)) it will always over fuel the engine. The ECM cuts the pulse width of the injectors in half at 142* but doubles it prior to that temp to help the engine warm up.). Only use OEM, this cheap Chinese crap has been known to be faulty from the beginning and who needs more headaches this season? Keep us posted.

[boatwakes]

Actually after fully reading your post, the TPS may be the entire culprit. Change it first and check because it may be sending incorrect throttle position causing the ECM to adjust fuel delivery. However, if the temp is still suspect proceed as above. The TPS is spring loaded so be aware when you replace it you'll have to index it to the throttle plate shaft FIRST and then twist it until the screw holes line up on the throttle body. Be sure to cover the intake after the flame arrestor is removed. Had one of my techs get an unlucky ricochet with a TPS hold down screw and it went into the intake. Magnet saved the day but took some time to find it with the borescope (resting on the unopened intake valve for #4.).

[Seanj]

Awesome I appreciate the help. Yea I bought factory parts. If I didn’t have bad luck I wouldn’t have any so I don’t even chance it with the cheaper stuff. Good tip on covering the intake. Hopefully all the parts will be in early next week and I can get it all installed.

[Seanj]

So I got all the parts installed and believe it corrected the problem. Haven't had it on the lake yet yet but running in the driveway it seems to run smoother and makes a lot less smoke. Just need to throw a new set of plugs in. Thanks for all the help. I will report back once its on the water just need the weather to cooperate here in the midwest.