| Author | Message | ||
| Bob Vandawalker (Rav221)
Rating: N/A |
Since we've had our 6V92TA (1986) it has been a bit hard starting when cold (especially after a cool night. It will crank a bit, fire then stall a a number times before it starts. While cranking it puffs pure white smoke which lingers and appears/smells like fuel. After the engine starts and runs for about a minute the smoke disappears. The engine runs nice and smooth. Normally runs about 180-190 degrees. By the way, if the engine heater is plugged in, it starts right up, no smoke. But the hard starting is occurring even now in the middle of the summer.. Today, the head mechanic at a local bus company ran drove the bus. He said that he suspects the hard starting is due to a loss of compression just due to age. He said it is nothing out of the norm for these 2 cyl's when they age. I questioned whether it could be due to worn injectors or seal. He didn't think so, because the bus ran too smooth. When I got back, I took my infared therometer and checked the individual cyl temps. All are running within 5 degrees of one another. My questions: If I was loosing compression, wouldn't I see some crankcase pressure or oil blowby which I don't? Does the loss of compression in a diesel translate to smoking, which this engine doesn't? Funny I respect opinions here more than I do a diesel mechanic.... Thanks Bob | ||
| TWODOGS (Twodogs)
Rating: N/A |
a 2-cycle is built different.....remember those little air plane engines when you were a kid...the piston comes down & gets a bite of air ...same here,except DD has a pressurized box that shoves air in that slot... when you worn engine doesn't want to go when cold ,it's the parts swell slightly when it's warm..things fit better | ||
| Don/TX
Rating: N/A |
Something else to think of is batteries. A diesel has to crank fairly fast, or it will not combustion/ingnite as it should, and acts like yours is doing. Sometimes this comes on slowly as the batteries go bad or connections get dirty and you don't really notice it is really cranking more slowly.. | ||
| L jensen Rating: N/A |
Make sure the starter and battiers are in great shape . The speed the engine turns over makes a big difference in the way a DD starts | ||
| Geoff (Geoff)
Rating: N/A |
Your problem is either low compression or air getting into the fuel system when the engine is shut off. A real simple cause of air in the lines is a bad check valve in the inlet fuel line. If you want to eliminate the low compression just have the engine tested, it should have a minimum of 450 psi in any clyinder since it is a turbo (500 psi for a non-turbo engine). Once you know it is not compression, then it is a matter of replacing fuel lines and making sure all the fuel line connections are tight. | ||
| John MC9 Rating: N/A |
TD- "the parts swell slightly when it's warm..things fit better" After reading that about fifteen times, I want to thank you for providing an enjoyable evening. | ||
| TWODOGS (Twodogs)
Rating: N/A |
Imagine...standing in the cold all night....the piston doesn't fit  | ||
| John MC9 Rating: N/A |
"The shrinkage factor" | ||
| Brian Brown (Blue_velvet)
Rating: N/A |
It certainly sounds like low compression. The compression rings are likely worn, or some broken, and not the oil rings that lead to smoking. Cause(s): if someone got too energetic with the ether a few too many times, or used the wrong oil (multigrade), or there's just a lot of miles on the mill. But lower compression doesn't necessarily mean a rebuild. You'll just have to baby it more. Keep it warm to start it, and keep your batts in tip-top shape, like suggested. If you always give it some block heater time, maybe 30 min. in the summer and a couple hours in the winter prior to starting, you'll be OK for many more miles. Also, have your oil lab tested for possibly more insight. Even a high-compression DD likes some quality time with the block heater when things get below 50deg F. or so. 40wt turns into syrup when it's cold. So they just start easier and it's better on the rings, valves, etc. bb | ||
| John MC9 Rating: N/A |
hmmmm... "It will crank a bit, fire then stall a a number times before it starts. While cranking it puffs pure white smoke which lingers and appears/smells like fuel. " Have you checked for a pinhole leak or loose fuel connection yet? If it's drawing air into the line. it will show white smoke, right? Be tough starting, too? After it's hot, the connection may have been tighter, no smoke.... until now.... That sound about right? | ||
| John MC9 Rating: N/A |
Ooops. Sorry. Geoff said that already!! | ||
| David Hartley (Drdave)
Rating: N/A |
Low fuel pressure may be the problem. If the fuel pump is worn it will cause the type of problem that you describe. Stalling at low idle or starving for fuel may cause the white smoke because there is not enough fuel mixture density in the cylinder to ignite. (Detroits don't fire on leaned out fuel ratios very well.) Also although not normally probable is an air leak in the primary fuel filter line such as the o-ring seal on the filter itself. A partially clogged secondary filter could exhibit similar problems. You may want to add a manual fuel pressure gauge on the secondary filter anyway just to be sure about the health of the fuel pump. I have experienced the same thing on my RTS and when I ran out of fuel on the way home with my MCI. I also see it with my kubota genny engine when I get air bubbles in the fuel line after changing filters. | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Hi, Bob. Prior posts have hit all around what you are dealing with, but I'll try to add a little more detail. Four sroke engines often reach the point of needing a rebuild because they become difficult to start or use too much oil. While they lose enough compression that starting is difficult, the efficiency of the engine when warm usually does not fall off far enough to be the cause of a rebuild. Two strokes have a different set of problems. The major loss of compression comes from compression ring wear and liner wear near the intake ports. Often, compression rings break, adding to the loss of compression. Before the engine gets to the point that the oil rings are really bad, quite a bit of blow-by can be happening at the compression rings. This pulls down the efficiency of the engine and reduces the heat of compression, making it harder to start. Since you are dealing with a turbocharged engine, you are already dealing with lower compression and harder starting because of it. Any heating of the engine with a heater will make up for lost heat of compression, however. With a port fed engine, blow-by never reaches the crankcase unless it is really bad. We had one with 6,000 hours that was getting really hard to start with the low compression, but it had no crankcase pressure that we could detect. That's because the blow-by reaches the airbox by way of the ports and becomes part of the intake air. If there is any unburned oil or fuel in that mix, it will be in the next intake stroke, whether or not it burns on the following stroke. This tends to make Detroits really smoky when cold. The lower efficiency will increase the fuel consumption and produce more heat in the exhaust and cooling system. If the engine has any tendency to overheat when new, this will be worsened with wear. We have a 350 hp. Detroit powered dump truck that uses twice as much fuel in the same work as a 335 hp. Cummins powered dump truck, so the efficiency loss is drastic. It takes a real big shot of ether to get that Detroit running, too. I hope this answers some of your questions. Tom Caffrey PD4106-2576 Suncatcher |