Smoke and Fuel in Exhaust

[kevbo5566]

All,

I've got a 2003 Supra Launch SS (EDIT: Indmar Assault 320 HP TBI) and in neutral / at idle speed, there is sometimes white smoke / fuel droplets / a smell of gasoline coming from the exhaust. Spark plugs and distributor cap were replaced 15 engine hours ago, but I'm not sure what else might cause unburned fuel to pass out the exhaust. Any thoughts on what might need to be checked to identify the cause?

Another symptom worth mentioning is that when first started, the engine occasionally starts and runs (albeit not well) at about 300-400 RPMs rather than the 600-700 RPMs which is typical. Addtionally, on two occasions this past weekend the engine did not seem to respond when the throttle was increased, i.e. lack of power.

Any help is much appreciated, thanks.

[gnarlydude]

This is serious...
Get some thoughts from guys on here and see a mechanic stat.


Sent from my iPhone using Tapatalk

[CJD]

This is serious...
Get some thoughts from guys on here and see a mechanic stat.


Sent from my iPhone using Tapatalk

LOL!

Kev, what Knarl is trying to say is your boat is behaving absolutely normal for a carb'ed engine. The no power can very well be from punching the throttle to fast. With a carb you have smoothly accelerate...if you punch it too fast it'll bog and give you nothing.

[kevbo5566]

I misspoke. I've got an Indmar Assault 320 hp TBI, not carb'd engine.

[gnarlydude]

O2 sensor? Fuel filter?


Sent from my iPhone using Tapatalk

[CJD]

In that case...

White smoke is steam or oil. Steam is normal with a hot engine. Oil burning means the valve guides or rings are worn...normally described as "blue" smoke, but it looks white to me. Rings or guides are not a simple fix.

If you are really smelling unburned gas, you will get black smoke. Black smoke on a fuel injected engine will set a malfunction code. You will need a reader to find out "why" it is running rich. Could be a sensor, bad injector, any number of reasons.

I have no idea why your engine would stall on acceleration. Again, reading malfunction codes may shed light on what is going on.

[2500HD]

Check your tps sensor.

[jzelt]

Agree with checking TPS, here was my symptoms.
https://forum.supraboats.com/showthread.php?11376-2004-Indmar-Assault-5-7L-Throttle-Bog-Issue

[kevbo5566]

I finally got down to the lake and continued to have issues starting it cold and also getting more power when increasing throttle (the problem diminished once the engine was warm), so I went out and bought a new Throttle Position Sensor.

After installing the new sensor, I started it up and the engine immediately idled at 1300 RPM, instead of the recommended 650 rpm. Thinking that perhaps I needed to adjust my throttle cable, I went ahead and did that in accordance with the shop manual ensuring that at idle, the throttle lever is in contact with the idle stop screw, but this had no effect.

So, does anyone have any idea why the new TPS might cause an idle at twice the RPM's of the old one? I made sure to unplug the battery and allow the computer time to reset and also adjusted the throttle cable to ensure the butterfly valve in the throttle body was returning to idle. Additionally, I checked to ensure the idle stop screw had not been tampered with, as the cap is still on the screw head.

Could there be a vacuum leak that's only manifesting itself when the new TPS is installed? I replaced the Idle Air Control Valve about two years ago, when I was having issues with the engine stalling after returning to neutral so I doubt that sensor has gone bad...

Could the TPS that I bought (technically a Mercury part) be sending a different voltage signal to the ECU? From looking online though, the TPS that is on the 5.7L TBI Indmar engine is a universal part.

[jzelt]

When you installed the TPS, you need to rotate it to get it on the end of the rod. (I don't recall the direction). The first one I installed I did just put it on so the screws lined up and tightened down. After repeated issues, the next one I bought, I put the rod end in first, then rotated it back to get the screws to line up and tighten down. Resolving the issue. If you didn't run it too much yet to strip out the plastic insert, try un mounting and re mounting it.

[kevbo5566]

The TPS was functioning properly after install (disengaged transmission and increased throttle), so I'm pretty sure it was installed correctly, it just was idling way too high with the new sensor. When I put the old sensor back on, the idle speed returned to normal.


Sent from my iPhone using Tapatalk

[kevbo5566]

Resolved. Turns out, all TPS's are not created equal and while the TPS I bought fit, it was sending the wrong signal to the TBI. One call to skidim and I had the correct sensor shipped, which solved the problem. Thanks.


Sent from my iPhone using Tapatalk