Indmar 310 TBI running rich, rough and backfiring
Hi Guys, First post but been checking out this forum for a few months researching my next boat which I now have. A 2001 Mastercraft X5 with the 310hp TBI Indmar Preditor engine and 270 hours. It has stood for 2 years with very little run time. I live in Melbourne Australia and the local MC dealer is EXTREEMLY UNHELPFULL because I did not by my boat from them, so I do not have access to MC specific diagnostic equipment.
The engine is not very happy and last weekend used a full tank (30 Gallons) in about 2 1/2 hours. It also cuts out, runs rough and surges on half throttle. When you floor it, it pings a little on occasion but not always. After the work below it now seems to run better but with timing advanced it pings heavily on pull off and starts to back fire at about 4400rpm, then retarding the timing - no ping but backfiring at 4100. Then sometimes we will have no ping on pull off and no backfiring at 4500rpm. Max WOT seems to be 4500rpm on the origional prop. It also runs on a little after a full throttle run and shutting off after a short idle.
Initialy it was running so rich it looks like a diesel engine with the black smoke. The injectors were also sticking in full open position even with the wires removed so obviously new injectors were installed. Fuel pressure measures about 25 to 30. Plugs are new, fuel is fresh.
Next we tested and then replaced the MAF sensor with a little improvement. Temp sensor is also giving the right readings, as is the throttle position sensor. Today we noticed the idle adjusting motor was not opening / closing as it has a lumpy idle but it idles nevertheless.
Disconecting the temp sensor kills the motor, but removing the maf sensor, and the TPS does nothing and the boat runs ok with out them.
Finally after 3 weeks and 15 hour runtime (7 tanks of fuel) we have less smoke, the plugs are a tan color, and the idle is still lumpy untill we replace the above mensioned sensor / motor but it still is not what I expect.
Can any one shed any light please on what to do next to reduce the ping but stop the backfiring at high throttle openings.
have you checked the ignition control module?
the local auto zone should be able to test it
Thanks 1redTA. The Auto Zone here in Australia does not offer that service. Might order a new unit and keep the old unit as spare. Might also look at replacing the Distributer, the plug leads and the plugs at the same time. That will eliminate a spark issue at least.
always start with the cheapest part first when replacing things on a whim
Fnally managed to figure out the diagnostic codes thanks to this site!
Code 22 - TPS reading abnormaly low:
new one on order
Code 34- sensor is reporting less air is entering the engine than makes sense based on RPM and TPS :
expect faulty TPS causing this.
Code 44 - indicates that the O2 sensor is showing a persistently high exhaust oxygen content (lean):
This boat has no O2 sensor and is running so rich it looks like a diesel..... might be TPS again.
Will see this week end when we replace parts.
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
Good info that would be hard (for me) to find elsewhere, thanks for the post.
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