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Old 03-21-2013, 11:39 AM
mig mig is offline
TT Enthusiast
Join Date: Jun 2006
Boat: 02 19Skier
Location: Montana
Posts: 304
Good info that would be hard (for me) to find elsewhere, thanks for the post.

Originally Posted by JimN View Post
The black smoke- does it smell like rubber, or unburned gas? Running lean doesn't produce black smoke. Also, a bad MAP shouldn't cause a TPS code- either the TPS is good, it's bad or the harness is faulty. To check the TPS or MAP sensors, you can/should check for 5VDC on the blue wire to each and measure the sensor's resistance across the other two pins. Also, measure the resistance from the black wire on each plug to the ground at the rear of the engine- if it's more than about .5 Ohms, find out why.

Your post indicates that you have a 2001 boat- I thought they added the O2 sensor after 2001 and I don't remember seeing one on the TBI when I went to training in Oct of 2000.

Before you replace a lot of parts and might not see results, make sure the grounds at the rear of the engine are clean and tight- the TPS and MAP sensors share their ground wire.

Also, make sure the two-wire engine coolant temperature sender (ECT) is operating properly.

If you want to "cheat" the ECM into thinking the engine is hot, go to Radio Shack and buy a pack of 100 Ohm resistors (buy a 5-pack- they're cheap). Remove the harness from the ECT (the two-wire ECT has one yellow wire and one black wire) and insert the ends of the resistor in the plug. You can do this while the engine is running and you should see a difference in how it runs- if you see no difference between running with the plug attached and unplugged but is clears up when you insert the resistor, it indicates that you need to check the sender. Substituting the resistor should ECM put the engine in RPM Reduction and if you try to increase RPM to >2000, it should run rough and it won't want to go much higher than 2000. You would then wire two or three resistors in series and insert the ends in the ECT plug- it it runs normally, the ECM and the rest of the sensors are OK, but the ECT is bad.

To test the ECT, it's best to remove it and measure the resistance, place it in hot water and measure the temperature with an IR thermometer or a confectioner's thermometer and refer to the temperature/resistance chart that's available online (or in a manual). If the resistance is high when the temperature is high/resistance is low when the temperature is low, the ECT is bad. If the black smoke doesn't stop when the engine warms up, I would suspect a bad ECT.

Here's the resistance range for a GM ECT-

In the Helm manuals there is a table:

degC degF Ohms
150 302 47
140 284 60
130 266 77
120 248 100
110 230 132
100 212 177
90 194 241
80 176 332
70 158 467
60 140 667
50 122 973
45 113 1188
40 104 1459
35 95 1802
30 86 2238
25 77 2796
20 68 3520
15 59 4450
10 50 5670
5 41 7280
0 32 9420
-5 23 12300
-10 14 16180
-15 5 21450
-20 -4 28680
-30 -22 52700
-40 -40 100700
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