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rspiecha
08-05-2005, 01:22 PM
Does anyone know how many sensors are on the standard TBI 275HP engine in 1994???? I'm tracking down a rich run condition.

TPS - on throttle body
MAP - hose to back of engine location of sensor
Knock sensor - driver side of block
Coolant sensor - driver side of thermostat
IAC - on throtte body (not really sensor)

Is there a intake temperature sensor to check intake air temp?? others???

thanks

Rob

Engine Nut
08-05-2005, 05:49 PM
Does anyone know how many sensors are on the standard TBI 275HP engine in 1994???? I'm tracking down a rich run condition.

TPS - on throttle body
MAP - hose to back of engine location of sensor
Knock sensor - driver side of block
Coolant sensor - driver side of thermostat
IAC - on throtte body (not really sensor)

Is there a intake temperature sensor to check intake air temp?? others???

thanks

Rob

There is no inlet air temp sensor on your engine.
You have all of the sensors identified. Is the engine coming up to temperature? That engine has a 143 degree thermostat so it should be running close to that temp. You have to be a little careful because the temp sender that sends the signal to the gauge is not the same as the coolant temperature sensor that sends a signal to the ECM. If the engine is running cold or if the ECM thinks it is riunnung cold because of a faulty coolant sensor, it will enrichen the fuel by keeping the injectors open longer. You can check the accuracy of the CTS by removing it from the engine and placing it in a container of water. If the water temp is 77 degrees F the resistance between the two terminals of the CTS should be close to 2796 ohms, at 95 degrees 1802 ohms, at 113 degrees 1188 ohms, at 140 degrees 667 ohms at 176 degrees 332 ohms and at 212 degrees 177 ohms. WE see engines with thermostats stuck open or faulty CTS to be the biggest reasons for rich running.

Rngine Nut

rspiecha
08-06-2005, 02:44 AM
Thanks for responding. A couple of years ago, www.skidim.com talked me into installing 160 degree thermostat. I have a MAP and CTS on the way to see if this will fix it. The temperature guage gets its reading from a small pencil size sensor on top of the thermostat housing, the CTS is to the driver side of it. With a screw holding the wire. The gauge sensor is a push on connector correct????

Do you think I should go back down to the 143 degree thermostat????

Thanks

Rob

JimN
08-06-2005, 09:04 AM
The temperature sensor that sends info to the ECM has a 2 wire plug with yellow and black wires. The gauge sensor has a tan wire, possibly with a black stripe. The MAP sensor is a vacuum sensor. Before replacing all of the sensors(possibly unnecessarily), why not start with the basics and check the flame arrestor, plugs/wires/cap/rotor, verify the timing, check compression, fuel pressure/quality/filter/regulator and see if the injectors are leaking? The IAC won't cause a rich condition. If it's open too far, the idle speed is too high and if it's not open far enough it will either stumble or won't idle at all unless you crack the throttle.

Exactly what is it doing (black smoke, gassy smell, bogging, fouling plugs, leaving fuel deposits in the water behind the boat) and what have you done to diagnose this problem?

If you lost the fins on your impeller and the problem started immediately after, you may have parts of the impeller stuck in the thermostat.

Also, since you have one of the early TBI motors, the ECM is mounted at the side of the motor with the MAP sensor tube going downhill from the throttle body plate to the sensor. This sometimes causes gas to collect in the tube and cause erroneous map sensor data. Try removing the tube from the MAP sensor and see if any gas comes out, and if the tube is cracked, broken or brittle, replace it.

rspiecha
08-07-2005, 02:50 AM
This two wire coolant temp sensor is located where?? I have found a single wire sensor on top of the thermostat housing that when I disconnect (a round push on type plug) will cause the temp gauge on dash to drop. To the driver side of this temp sensor is another sensor with a single wire going to it with a nut holding it down on the sensor. I do remember another sensor on the drive side of the engine going into the head, with two wires. Is this the sensor you are talking about???

Thanks for the help so far.

thanks

Rob

chico
08-07-2005, 07:48 AM
the temp sensor for the ecm is on the side of the block above the ecm.it has two wires
,a black&yel.the one beside the t-stat housing is the overheat light on the dash.

chico
08-07-2005, 07:54 AM
if you had accsess to a scan tool life would be much easier.you can get a dtc tool from skidim for around $100.

Engine Nut
08-07-2005, 09:03 AM
This two wire coolant temp sensor is located where?? I have found a single wire sensor on top of the thermostat housing that when I disconnect (a round push on type plug) will cause the temp gauge on dash to drop. To the driver side of this temp sensor is another sensor with a single wire going to it with a nut holding it down on the sensor. I do remember another sensor on the drive side of the engine going into the head, with two wires. Is this the sensor you are talking about???

Thanks for the help so far.

thanks

Rob

The CTS on older units may have been insyalled in the side of one of the cylinder heads. Later models had extra ports in the intake manifold for tyhe CTS, temp sender, heater etc.

Engine Nut

rspiecha
08-07-2005, 12:22 PM
thanks guys, several things to look at. The sensors are cheap and easy to replace. I don't see any harm replacing them given they are 11 years old.

One last question, does the 1996 Prostar 205 have any additional sensors over the 1994?? The reason I ask, I'm running the MEFI-2 computer on the 1994 that originally came with the MEFI-1 computer. The dealer did this, no more MEFI-1 are available. $1000 bucks, it really sucked, but the boat is flawless.

Thanks

rob

JimN
08-07-2005, 01:03 PM
There aren't any additional sensors, but they were about at the end of the line for the MEFI 1 controller, anyway. The MEFI 3 won't work on yours without modifying the harness because they went to (-) output on the relay drives and internalized the knock sensor module electronics.

Engine Nut
08-08-2005, 07:44 AM
As JIMN indicated, there are no additional sensors. It is extremely unlikely that your ECM is bad. Your rich running issue is most likely due to a mechanical issue (stuck thermostat) or a sensor issue. Have you had your dealer hook up a scan tool and check for codes or sensors out of range?

Engine Nut

chico
08-08-2005, 10:02 PM
Engine Nut. any mods to do in switching to a mefi2 ecm in a 94 tbi?

JimN
08-08-2005, 10:08 PM
No mods, just make sure to get the right calibration ID and checksum for your motor. By now, there have probably been quite a few updates if you haven't had any and these will generally help in economy and smoother transition of power through the throttle range.

rspiecha
08-09-2005, 11:06 AM
The computer was replaced last fall. I assume they have the correct and most recent flash on it. The TPS was also replaced with the ECM, it was showing 1 degree of rotation at closed position. The knock sensor, CTS, MAP are all cheap components. I thought I would replace them before having to haul the boat back to the dealer 3 hours away. The thermostat was replace about 2 years ago. The temp gauge is right on with the temperature of the thermostat.

Thanks guys for all the info.

Rob

JimN
08-09-2005, 08:15 PM
The temperature gauge has nothing to do with what the ECM sees. If you want to buy the sensors, go ahead but I wouldn't change them until you find out they're actually bad. If the rich condition is at idle and all other speeds, it's most likely the two wire temp sensor. A TPS with a constant fault causes the ECM to default at 12% throttle position with no variation read. If this causes richness, it won't be a lot.

Have you done the basic testing I listed in an earlier post? I don't remember seeing any compression specs. Remember, low compression will keep the gas from burning completely. This test needs to be done dry, after the motor has been warmed to normal operating temperature. To do the dry test, you can either remove the injector harness from the injectors or remove the fuel pump relay(or fuse). Having gas getting into the cylinders during the test skews the results higher than they should be.

rspiecha
08-09-2005, 11:30 PM
I'll be doing the compression test this weekend. The temp gauge comment was dealing with I don't think the thermostat is stuck open causing the eninge to run cool. I replaced thermostat about 2 years ago and gauge seems to parallel the thermostat operating temp. But it's always a possibility.

Thanks again for the help.

Rob

rspiecha
08-09-2005, 11:38 PM
I never did say what my symptoms are. When engine is cool, everything seems to be fine. No rich smell coming from the exhaust. But once the boat is good and warm, ran around the lake for 30+ minutes. The idle becomes rough, the exhaust smells rich, and pulling a salom skier up, the engine want to bog, then go.

Boat has 300 hours, oil religeously changed every fall before winterization. Taylor 8mm spiro-wound plug wires (3 years old), MSD Blaster 2 Coil, MSD cap and rotor (3 years old), spark plugs replaced (3 years ago from ski dim, not sure of brand) water/fuel separator removed (advise of the dealer) and a clear plastic filter installed right out of the fuel tank in the back going to the pump then to the stock high pressure metal can filter before the TBI. Metal fuel filter replaced (by dealer) last fall with new ECM and TPS.

Thanks again guys.

Rob

rspiecha
08-14-2005, 11:44 PM
I replaced both the CTS and MAP and the boat is not bogging during hard pulls. Overall, running better in all situations except at idle. Still smells a litle rich at idle and runs rough. I didn't get a chance to do the compression test.

Thanks guys.

Rob