PDA

View Full Version : Black soot on Spark Plugs - stumped?


Tom Jones
04-14-2010, 06:52 PM
I have a 2004 5.7 TBI GM Vortec (300 hrs) and the spark plugs all have a black soot on them.
When the ambient air temperature is hot (mid summer) it seems like the engine is runs too rich (it develops a miss and sometimes there is the smell of gas after it is warmed up), it is also a little hard starting and the idle is a bit irratic. It seems to run fine in the spring and fall when the air/water is cold outside.
I have had it checked on the computer and there are no codes, had the timing set according to spec., changed spark plugs, changed spark plug wires, changed distributor cap, checked the fuel pressure (right on at 31 PSI), checked the spray pattern on the injectors, checked for cracked hose on the MAP sensor, checked PCV valve and hose. changed to 91 Octane fuel.
I'm thinking my next step is to check the engine temperature sensor. There is not intake air temperature sensor on the TBI engines.
Any suggestions or thoughts on what to check next?

thatsmrmastercraft
04-14-2010, 11:42 PM
Coolant temp sensor sounds like a good place to start.

What temp does the engine run at? Could be a thermostat issue.

Tom Jones
04-15-2010, 07:46 AM
It originally had a 140 thermostat from the factory, I thought that wa the problem ,I changed it to a 160 and it runs at 160.
I'm thinking I may have to try a hotter set of spark plugs if the temp. sensor checks out OK.

Thrall
04-15-2010, 10:47 AM
If it's the same as the LT-1s, there's 2 temp sensors, one for the dash guage and one that teh ECM reads to adjust fuel mixture (like a choke). That one could be out of whack causing it to run read low/run rich.

Tom Jones
04-15-2010, 06:47 PM
I agree, I will make sure I test the correct sensor. I read in another thread that it is the one with the black and yellow wires.

JimN
04-15-2010, 07:14 PM
I agree, I will make sure I test the correct sensor. I read in another thread that it is the one with the black and yellow wires.

That's the one you want to check. If the resistance in above 1K Ohms when it's hot, it's bad. My TBI manual's chart shows a range of 177 Ohms at 100C/212F to 100700 Ohms at -40C/-40F so, if it's short sleeve weather and the ECT shows more than about 5KOhms, it's bad.

Verify base timing, too. That can cause it to run rich, but not as bad as a bad ECT. You need to put the ECM into diagnostic mode for this in order to disable spark stabilization.

Tom Jones
04-15-2010, 10:24 PM
Thanks for jumping in here Jim
I did have the base timing set at the marina ( they put it into service mode). The funny thing is that they set it once, I ran it for a week, then took it back and the timing had changed from 8 degrees to 17 degrees. I was present when they set it the second time and while we were getting ready to hook up the computer the engine sped up momentarily for no apparent reason when it was idling. The mechanic had a hard time getting the timing stabalized (10 degrees) even though it was in service mode. The RPM was solid at 1000 RPM but the timing was moving around. It finally did settle down and we set it at 10 degrees as per spec.

Sometimes when I am running the boat in the summer the idle speed changes after the engine is warmed up. it can range from 670 - 720.

I have a Clymer manual and it explains how to check the temperature sensor and it includes a table showing resistance at the various temperatures. Thanks for giving me the settings and explaining what to look for. I'll let you know if I find anything wrong with the temperature sensor.

Have you ever installed a hotter set of plugs in a TBI engine?

JimN
04-15-2010, 10:41 PM
Thanks for jumping in here Jim
I did have the base timing set at the marina ( they put it into service mode). The funny thing is that they set it once, I ran it for a week, then took it back and the timing had changed from 8 degrees to 17 degrees. I was present when they set it the second time and while we were getting ready to hook up the computer the engine sped up momentarily for no apparent reason when it was idling. The mechanic had a hard time getting the timing stabalized (10 degrees) even though it was in service mode. The RPM was solid at 1000 RPM but the timing was moving around. It finally did settle down and we set it at 10 degrees as per spec.

Sometimes when I am running the boat in the summer the idle speed changes after the engine is warmed up. it can range from 670 - 720.

I have a Clymer manual and it explains how to check the temperature sensor and it includes a table showing resistance at the various temperatures. Thanks for giving me the settings and explaining what to look for. I'll let you know if I find anything wrong with the temperature sensor.

Have you ever installed a hotter set of plugs in a TBI engine?

The idle speed is supposed to be 650-700 RPM and base timing for EFI motors of any kind is 10BTDC although they may have changed it after 2001, when I stopped working on these.

In service mode when using the Tech 1, it automatically goes to 1000PRM and that's the correct engine speed when the base timing is supposed to be set. Once it's set, it won't change unless the hold-down is loose. My truck has a 5.7L TBI and it hasn't changed in the 9 years I have owned it. It was dead on when I got it, too.

onejdgreen
04-16-2010, 08:29 PM
The other thing you may want to is run is a fuel condition in the tank, especially if you are running an ethanol blended fuel. Ethanol does not burn as clean as regular gas and you get water in the system. Notice that on the exhaust of you car that uses ethanol there is water that runs out of the tail pipe. Fuel conditioners help the engine run cleaner and more efficient.

JimN
04-16-2010, 10:13 PM
The other thing you may want to is run is a fuel condition in the tank, especially if you are running an ethanol blended fuel. Ethanol does not burn as clean as regular gas and you get water in the system. Notice that on the exhaust of you car that uses ethanol there is water that runs out of the tail pipe. Fuel conditioners help the engine run cleaner and more efficient.

Water is a natural byproduct of combustion- there's no way for water in the tank to make it out the tailpipe in liquid form- the in-cylinder temperatures when the motor is running properly can be over 1000F. Any liquid water that comes out is due to condensation after hitting cold air or exhaust system components. However, alcohol doesn't store as much energy as gas and it doesn't necessarily burn as hot or as fast because of its higher octane rating. This is one of the biggest problems when it comes to finding a good replacement- what should we use that will provide the same BTU/pound?

The best thing to do when trying to diagnose a problem with combustion is test it with gas that is known to be good and fresh. Putting in additives when the problem isn't known only confuses the issue- we need as few variables as possible in order to be able to come to a fast solution.

Tom Jones
04-17-2010, 10:27 AM
Thank you for your suggestions, any thoughts are much appreciated.
I have tried fuel conditioner as recommended by the MC dealer and I have poored bottles of Fuel Injector cleaner in the tank.

JimN
04-17-2010, 10:32 AM
Thank you for your suggestions, any thoughts are much appreciated.
I have tried fuel conditioner as recommended by the MC dealer and I have poored bottles of Fuel Injector cleaner in the tank.

How much of that stuff is in the tank at one time? If it's several bottles, I would recommend using up the gas, make sure the tank doesn't have a bunch of water and crap in it, then put some fresh gas in it before taking it out. If you have a pair of those mechanic's gloves, run it around the lake for a while and get it to normal operating temperature, shut it down and pull some of the plugs, one at a time. That's when you want to check them, not after it has been idled to the ramp and onto the trailer or lift. They should be light brown- boats tend to be a bit richer than cars, so a car's plugs should be light tan.

Tom Jones
04-19-2010, 07:53 AM
Hey Jim,
Is it possible that the temperature sensor (to the ECM)and temperature sender (to the gauage) are all in one? I can only find one sensor right near the thermostat on my engine. When I unplugged it and turned the key on the temperature gauge didn't work.
Anyway, I checked the sensor and at around 140 - 150 degrees F it read 665 Ohms. This would seem to be within parameters (book says 467 ohms at 158 F). I'll check it again when it is cold.
Any thoughts?

JimN
04-19-2010, 08:38 AM
Hey Jim,
Is it possible that the temperature sensor (to the ECM)and temperature sender (to the gauage) are all in one? I can only find one sensor right near the thermostat on my engine. When I unplugged it and turned the key on the temperature gauge didn't work.
Anyway, I checked the sensor and at around 140 - 150 degrees F it read 665 Ohms. This would seem to be within parameters (book says 467 ohms at 158 F). I'll check it again when it is cold.
Any thoughts?

If the sensor has two wires (yellow and black), that's the one you want.

Which plugs are you using? Are they OEM or the same part number?

Tom Jones
04-19-2010, 12:04 PM
Yup that's the one I tested.
Spark Plugs were GM OEM originally and I'm now using NGK equivalent.
I'm thinking of trying a hotter plug.

JimN
04-19-2010, 02:49 PM
Yup that's the one I tested.
Spark Plugs were GM OEM originally and I'm now using NGK equivalent.
I'm thinking of trying a hotter plug.

You shouldn't need a hotter plug if everything is working correctly. If you can, have it connected to a diagnostic computer and look for:

Correct operating temperature
Correct MAP and TPS readings
Correct base timing and total advance- I remember seeing that it had changed but not that it was re-set at 10BTDC.
Knock sensor hearing knock/working at all
Correct battery voltage- this isn't the same as checking at the battery, it's what the ECM sees.
Proper compression (did you post a range of 155-165#?)

How much gas was left over at the end of last season? If it was a lot, I would recommend removing it and trying fresh gas. "Dry gas" is just gas with ethanol and if what you already had has experienced phase separation, it won't help that. You'll end up with a mix of bad gas that has more ethanol than it normally would.

Tom Jones
04-19-2010, 07:59 PM
Hey Jim,
thanks for the additional thoughts.
I had the engine hooked up to the diagnostic computer twice last summer.
There were no fault codes, temperature was good, we set the timing at 10 degrees in service mode. How do I check battery voltage at the ECM?
Mechanic said the MAP and TPS were working but where do I find the operating parameters for the MAP sensor and TPS? I can't find them in my Clymers manual.
When I first bought the boat (used) in 2008 it had 127 hrs on it. It ran like a dog and I finally figured out it was bad gas, I think it had been sitting around for a long time. I have 300 hours on it now so I would think I would have run all the bad gas out of it by now.
I ran the boat the last two weekends (its still cold here) and the boat ran well, but it does seem to use more fuel than I think it should. It starts well, idles well at 650 - 670 RPM.
Maybe I have a sensor or something that only acts up when the weather gets warmer?

Thanks

Tom

JimN
04-19-2010, 08:16 PM
Hey Jim,
thanks for the additional thoughts.
I had the engine hooked up to the diagnostic computer twice last summer.
There were no fault codes, temperature was good, we set the timing at 10 degrees in service mode. How do I check battery voltage at the ECM?
Mechanic said the MAP and TPS were working but where do I find the operating parameters for the MAP sensor and TPS? I can't find them in my Clymers manual.
When I first bought the boat (used) in 2008 it had 127 hrs on it. It ran like a dog and I finally figured out it was bad gas, I think it had been sitting around for a long time. I have 300 hours on it now so I would think I would have run all the bad gas out of it by now.
I ran the boat the last two weekends (its still cold here) and the boat ran well, but it does seem to use more fuel than I think it should. It starts well, idles well at 650 - 670 RPM.
Maybe I have a sensor or something that only acts up when the weather gets warmer?

Thanks

Tom

Did they look at the ECT last year? It could still be bad- I would remove it, put it in a pan with water and heat it up, watching the resistance so you can compare it with the chart.

The voltage is shown in one of the screens of the diagnostic computer. Also, if it's ever connected to that, the data should ALWAYS be printed out or written down. ALWAYS. There's no excuse for not documenting any data acquisition. Without it, there's no way to compare one test with another and there's no baseline.

In cold weather, no motor will be as efficient. Cold air needs more gas to maintain the proper fuel/air ratio and a cold engine doesn't burn the fuel completely. If your transom has a black smudge from unburned gas, I would go back to the OEM plugs (AC MR43LTS) and make sure the ECT is working properly.

How clean is the flame arrestor? If that's clogged, it will definitely run worse.

Tom Jones
04-19-2010, 11:28 PM
they didn't look at the ECT last year but they did change the thermostat from the 140 F the original from the factory that was in it to a 160 F. We thought that was the problem but it wasn't.
I don't see any black smudges at the back of the boat.
I'll remove the ECT and check it against the values in my manual.
The original plugs were Delco BPR6EFS, I am currently using NGK TR5 which is supposed to be a cross match to MR43LTS according to SkiDim.

JimN
04-20-2010, 01:15 AM
they didn't look at the ECT last year but they did change the thermostat from the 140 F the original from the factory that was in it to a 160 F. We thought that was the problem but it wasn't.
I don't see any black smudges at the back of the boat.
I'll remove the ECT and check it against the values in my manual.
The original plugs were Delco BPR6EFS, I am currently using NGK TR5 which is supposed to be a cross match to MR43LTS according to SkiDim.

BPR6EFS is an NGK number and it crosses directly to the R43LTS, with is a car plug. The MR43LTS is similar but has a stainless body. The TR5 is a direct cross to the MR43LTS. You can use the TR5 but IMO, the MR43LTS is a good plug- anyone who says they can't get it just doesn't want to.

What is the normal temperature range of your water? If it never gets above 70F, you could go with a higher temperature thermostat without problems, as long as you don't have a weed problem. Remember- hotter plugs don't burn hotter, they retain more heat.

Tom Jones
04-20-2010, 07:27 AM
The water here does get above 70 in the mid summer and we do have a lot of weeds in the lake. I clean the transmission cooler screen once a week. I think I will try a set of MR43LTS as that is what I used in my LT1 and they worked great.
By the way, I did check the Ohms on the ECT when it was at 60' F and it read 3970 Ohms, my manual says 3520 ohms at 68' F. (665 Ohms @ 140-150' F and the book says 467 ohms at 158' F)I would think both readings I have taken are within range. I cleaned my spark arrester last year so there is no restriction there.

You know how the MPI engines have an air intake sensor. How does a TBI handle differences in air intake temperature? Since my problem seems to occur in the mid summer when the air temperature is hot could the lack of an air temp. sensor just be the nature of this TBI engine?

JimN
04-20-2010, 11:37 AM
The water here does get above 70 in the mid summer and we do have a lot of weeds in the lake. I clean the transmission cooler screen once a week. I think I will try a set of MR43LTS as that is what I used in my LT1 and they worked great.
By the way, I did check the Ohms on the ECT when it was at 60' F and it read 3970 Ohms, my manual says 3520 ohms at 68' F. (665 Ohms @ 140-150' F and the book says 467 ohms at 158' F)I would think both readings I have taken are within range. I cleaned my spark arrester last year so there is no restriction there.

You know how the MPI engines have an air intake sensor. How does a TBI handle differences in air intake temperature? Since my problem seems to occur in the mid summer when the air temperature is hot could the lack of an air temp. sensor just be the nature of this TBI engine?

It doesn't do anything about the intake air temperature- its control isn't that precise but it will run richer if the coolant temperature is low.

The fact that the plugs have black deposits isn't necessarily a problem, especially if you need to idle for any length of time before shutting it off. If you had the black smudge on the transom and you smelled unburned gas in the exhaust all the time, I would worry a bit.

Tom Jones
04-20-2010, 07:06 PM
Jim,
I ordered a set of MR43LTS plugs today. I'll try them and let you know if they make a difference.
I used to use Esso 89 octane in my 94 205. I think I'll try that gas instead of the cheaper brand I've been using also.