Indmar 310 TBI running rich, rough and backfiring

[JimN]

Originally Posted by Mark rsa2au

Now I am stumped!!!

Motor still running very rich, black smoke from exhausts and black sooty plugs from an hour on the water. Also backfiring over 4000rpm!! Dream boat not so much fun anymore

This is what we have done so far:
IAC broken unit replaced with new one - working perfectly.
Injectors reconditioned, all good. Also tested with New injectors - no change. New injectors had same flow rate as old injectors ( I wonder if old injectors were swaped for bigger flow units at some time)
Fuel pressure tested with dodgy fitting onto guage. Read 25psi before leaking so I think 30psi would be a safe bet.
ECT tested as above post, all good. Reading a little high but at least telling ECM it is HOT.
TPS tested as above post, all good. Replacement part no change.
Map sensor tested as above, all good. Replacement part makes no difference.
Plugs changed & gaped at 1.3 (from factory) will adjust down to 1.1 tomorrow but should not change issue above.
Distributer cleaned.
Timing checked as per manual and 10degree BTDC @1000rpm. ( floats a little on the timing light - not rock steady but easily visible).

What the hell else is these to check - service - replace to stop it running so rich and stop the backfiring?

Have you checked the compression?

ECT- you mean the temperature gauge on the dash? That has nothing to do with what the ECM sees. The ECT you need to check has two wires and you need to check its resistance. If the resistance is high when the engine has been warmed up, it's bad.

The timing mark should be rock steady if the engine has been put in diagnostic mode. If it moves, it's either not in diagnostic mode or the shaft bushing may be worn.

How old are the cap, rotor and plug wires?

[Mark rsa2au]

Originally Posted by JimN

Have you checked the compression?

ECT- you mean the temperature gauge on the dash? That has nothing to do with what the ECM sees. The ECT you need to check has two wires and you need to check its resistance. If the resistance is high when the engine has been warmed up, it's bad.

The timing mark should be rock steady if the engine has been put in diagnostic mode. If it moves, it's either not in diagnostic mode or the shaft bushing may be worn.

How old are the cap, rotor and plug wires?

I pulled the correct temp sensor out (with the 2 wires) and tested resistance at 10deg C intervals up to 90degC and it was fine. A few ohms out from spec or the thermometer I was using was a little out, but either way it was registering HOT.

Engine was in Diagnostic mode at 1000rpm. How do I check the shaft bush, which shaft? the distributer shaft I assume?

Cap rotor and plug wires are origional - 270 hrs on a 2001 boat

[thatsmrmastercraft]

Originally Posted by Mark rsa2au

I pulled the correct temp sensor out (with the 2 wires) and tested resistance at 10deg C intervals up to 90degC and it was fine. A few ohms out from spec or the thermometer I was using was a little out, but either way it was registering HOT.

Engine was in Diagnostic mode at 1000rpm. How do I check the shaft bush, which shaft? the distributer shaft I assume?

Cap rotor and plug wires are origional - 270 hrs on a 2001 boat

Cap and rotor definitely need to be replaced. I would replace the wires as well. You may be dealing with a simple cross-fire issue.

[JimN]

Originally Posted by Mark rsa2au

I pulled the correct temp sensor out (with the 2 wires) and tested resistance at 10deg C intervals up to 90degC and it was fine. A few ohms out from spec or the thermometer I was using was a little out, but either way it was registering HOT.

Engine was in Diagnostic mode at 1000rpm. How do I check the shaft bush, which shaft? the distributer shaft I assume?

Cap rotor and plug wires are origional - 270 hrs on a 2001 boat

Can you run it at night or in total darkness? Your plug wires are old. The fact that they "only" have 270 hours is immaterial, they age, even though they're silicone. One thing that happens is, if the engine has been run hard at all, the conductor eventually loses conductivity at high frequencies, which means it may measure good with a multi-meter, but run like crap. A meter checks for DC resistance, but spark isn't DC voltage.

If you do run it in darkness, you may see arcing between the wires and this is likely to be part of the problem. Could be ALL of the problem. Caps can also develop carbon traces and if this happens, it may not be visible, but it has a bad effect on how the engine runs. It will be inside, not outside of the cap.

[Mark rsa2au]

Contacts on the inside of the Distributer cap are corroded. I have sanded then back a little to remove this but there is still some surface pitting. Looks like the best option is to get a new one and new leads as well. I agree this might solve the misfire.

Do you think will solve the running rich? I have been researching injectors and cannot find out what mine are. No colour coding and the numbers on top do not come up with any search. What if the fuel pressure regulator was messed with previously? Should I unscrew the adjuster to lower some pressure in the injectors? Or would a pressure gauge show this up at the shrader valve?

[JimN]

Originally Posted by Mark rsa2au

Contacts on the inside of the Distributer cap are corroded. I have sanded then back a little to remove this but there is still some surface pitting. Looks like the best option is to get a new one and new leads as well. I agree this might solve the misfire.

Do you think will solve the running rich? I have been researching injectors and cannot find out what mine are. No colour coding and the numbers on top do not come up with any search. What if the fuel pressure regulator was messed with previously? Should I unscrew the adjuster to lower some pressure in the injectors? Or would a pressure gauge show this up at the shrader valve?

Never mess with a factory-adjusted part. That's set under controlled conditions, which we don't have. If the pressure is too low, the fuel won't atomize as well as it should and that means some cylinders will get more than enough, some the right amount and some won't get enough. Running hard and having some cylinders too lean will burn the valves and probably the piston, possibly scoring the cylinder(s). There's no way to "un-mess with" the regulator. If you think/know it was messed with, replace it. Also, leave the idle stop alone. This isn't like a carb- there's really nothing to adjust in the field. If you have correct compression, spark timing/intensity and fuel/air delivery, a sensor problem is the next most likely problem. Since you have replaced most of them, it's unlikely that you replaced a bad sensor with another bad one.

This doesn't leave many things to look at, but I did recommend measuring resistance from the sensors to the battery negatives and the ground at the back of the engine. If your ground is bad, it can run exactly as you described. It's too bad nobody in Australia has taken it upon themselves to buy the necessary diagnostic equipment for these, although I don't know how many ski and wakeboard boats are over there.

[Mark rsa2au]

Ok Still stumped.... Engine has a huge misfire / backfire at anything above 4100rpm, and on occasion limits revs to 2500 - shut down restart and rev limit gone.
Today had Code 22 (TPS reading low) and 44 (O2 sensor reading lean but this boat has no O2 sensor).

So far have replaced the Idle motor, the TPS, the MAP sensor, the Spark plugs, the spark leads, distributer & rotor. Tested Temp sensor ok, fresh fuel, New injectors. Also timing 10deg BTDC @1000rpm in diagnostic mode. Fuel pressure arround 29 - 31psi.

Checked earth from sensors to ECM and all good, but earth wire at sensors to rear earth connection shows 0.7 - 1.1 ohms difference. Is this ok and if not what would cause it?

Checked water pump, trans cooler, and calibrated temp sensor for the engine warning light. The check light comes on and goes off when I dissconnect this temp sensor. Calibrated to 95degrees C (203F) and it comes on after a hard run but the dash temp shows 160F and this sender is in the same water channel is it not?

JimN there are many Mastercrafts (also Malibu- made locally, Nautique, Supra, Mobius,etc) over here, its just the dealer will not support boats not imported by them - even though this boat was imported before 2004 when MC officialy started in OZ.

Not sure where to go next.... any suggestions other then a match?

[SkiDaddy]

You might want to check out automotive internet forums for vehicles that use the same engine as yours and then search those sites for similar problems. Maybe something like www.chevroletforums.com and there are a bunch of others.

Aside from you checking the fuel pressure with the dodgy gauge, have you done anything else with the fuel system? To me it seems like you've kind of ignored the fuel system so far. I think that some of the 5.7L Vortec engines needed around 50-60 psi for fuel pressure.....are you 100% sure that 30 psi is what this engine needs? I don't know the answer, just throwing out some ideas.

Cheers & good luck!

[JimN]

Originally Posted by Mark rsa2au

Ok Still stumped.... Engine has a huge misfire / backfire at anything above 4100rpm, and on occasion limits revs to 2500 - shut down restart and rev limit gone.
Today had Code 22 (TPS reading low) and 44 (O2 sensor reading lean but this boat has no O2 sensor).

So far have replaced the Idle motor, the TPS, the MAP sensor, the Spark plugs, the spark leads, distributer & rotor. Tested Temp sensor ok, fresh fuel, New injectors. Also timing 10deg BTDC @1000rpm in diagnostic mode. Fuel pressure arround 29 - 31psi.

Checked earth from sensors to ECM and all good, but earth wire at sensors to rear earth connection shows 0.7 - 1.1 ohms difference. Is this ok and if not what would cause it?

Checked water pump, trans cooler, and calibrated temp sensor for the engine warning light. The check light comes on and goes off when I dissconnect this temp sensor. Calibrated to 95degrees C (203F) and it comes on after a hard run but the dash temp shows 160F and this sender is in the same water channel is it not?

JimN there are many Mastercrafts (also Malibu- made locally, Nautique, Supra, Mobius,etc) over here, its just the dealer will not support boats not imported by them - even though this boat was imported before 2004 when MC officialy started in OZ.

Not sure where to go next.... any suggestions other then a match?

The 1.1 Ohms is high. Get the resistors and substitute them for the ECT, as I posted. If the check engine light goes off when you disconnect it, it has a problem (or, the plug/wires on its harness). The sensor going to the gauge has nothing to do with what's going to the ECM.

44 may be IC module- contact Mastercraft or Indmar and ask them about it- my manual isn't here at the moment, so I can't check this.

Disconnect the battery, let it sit for a few minutes and remove the plugs from the ECM. Open the plastic shell and look for the black wires and measure from the ECM plug to the battery posts, not the terminals. The resistance between the terminal and post can be enough to cause problems.

Here's a manual for MEFI 4, but it's not exactly for your engine. The pin out,, diagrams and diagnostics are basically the same. You'll notice that the MAP sensor is different (the one in the link is like the one on the LTR. MCX and some of the others that aren't TBI).

http://www.pirate4x4.com/tech/billav...510005P%29.pdf

[Mark rsa2au]

Originally Posted by SkiDaddy

You might want to check out automotive internet forums for vehicles that use the same engine as yours and then search those sites for similar problems. Maybe something like www.chevroletforums.com and there are a bunch of others.

Aside from you checking the fuel pressure with the dodgy gauge, have you done anything else with the fuel system? To me it seems like you've kind of ignored the fuel system so far. I think that some of the 5.7L Vortec engines needed around 50-60 psi for fuel pressure.....are you 100% sure that 30 psi is what this engine needs? I don't know the answer, just throwing out some ideas.

Cheers & good luck!

Thanks Mate, I have been looking at the other forums for similar issues, some have been helpfull, most not because it seems the issue might be specific to the Indmar electrics.

The workshop manual states 30 PSI for fuel which is what we are measuring. We have also used both the origional and the new injectors with no change. Dismantled and checked fuel pressure regulator - seems fine. Fuel lines not kinked and pressure ok with neither set of injectors changing the issue means we crossed this one off the list.