trouble starting when engine is hot

  #1  
Old 09-12-2005, 09:21 PM
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Default trouble starting when engine is hot

Can anyone give me a clue as to why when my engine is hot it gives me alot of trouble starting? It cranks over fine but, it won't "catch." After a minute of cranking it will usually start and generally run real crappy and blow out black smoke. Today I tried to start the car when it was already hot and it wouldn't start. Finally with the gas pedal all the way down it started, and blew out alot of smoke. Then I had alot of trouble keeping it running on the way home. The car starts and runs great when cold though. This is a 92' Audi 100 with the 2.8 V6. Any input is greatly appreciated! Thanks alot,
-Matt
 
  #2  
Old 09-12-2005, 11:12 PM
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Default RE: trouble starting when engine is hot

its look like its too reach, I would check the fuel pressure, and if it doesn't help I would disconnect one by one the injector.
example disconnect the first cyl injector and try to start, then conect it back and try the second then therd etc...
and therir is definatly more that I said.
 
  #3  
Old 09-12-2005, 11:47 PM
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Default RE: trouble starting when engine is hot

If the car starts and runs OK while hot but refuses to start after a short break. The problem could be inability to hold pressure due to a defective check valve. When the engine is hot and there is no or low pressure in the fuel line, the fuel boils and you get a vapor lock. Perform a residual pressure test.
 
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Old 09-12-2005, 11:50 PM
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Default RE: trouble starting when engine is hot

Offramp, I'm guessing you mean to check the fuel pressure when the engine is hot?

P.S. Sometimes the car will start up and run perfectly when hot. This is not a consistent issue. Does it still sound like a check valve to you?
 
  #5  
Old 09-13-2005, 12:00 AM
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Default RE: trouble starting when engine is hot

That's the idea. There should be a procedure in the manual on how and where to hook up the pressure gauge. Then you follow a chart, I think it should be fuel pressure vs. time. Warm up the engine, shut it off, then watch the gauge, I think you should have at least %50 of pressure after 30 minutes.
 
  #6  
Old 09-13-2005, 12:05 AM
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Default RE: trouble starting when engine is hot

Haha that's just my luck, I've looked all over for a manual on my car and finally had to order one... It'll be in, in about 2 weeks! Anything I can do before that? Does anyone know if this is a return or return-less style fuel system? Could I try turning the key on and off priming the fuel pump over and over again and filling the line with fuel?
 
  #7  
Old 09-13-2005, 12:48 AM
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Default RE: trouble starting when engine is hot

P.S. Sometimes the car will start up and run perfectly when hot. This is not a consistent issue. Does it still sound like a check valve to you?
One correction besides the check valve, it could also be a fuel leak which may be obvious or not. If the injectors are leaking then it is not going to be so obvious. If the problem is poor residual pressure then symptoms are not going to be consistent. There are too many factors: like how hot is the engine, how long was the engine shut off, 5 minutes might not be enough but 15 to 30 might be long enough. Outside air temperature is also a factor.

All modern fuel injection systems have a return line. I don't think that turning the key on and off will help. This is due to the fact that injectors don’t have a return line.

It is also very likely that you might have an electrical problem. When the car fails to start try pulling a trouble code of the ECU.
 
  #8  
Old 09-13-2005, 12:55 AM
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Default RE: trouble starting when engine is hot

I just want to understand this alittle better. One possibility is that my fuel line is losing pressure, and making it difficult to start. Why does it start right up in the mourning when there's no fuel in the line? Does the car have a different procedure for starting when the engine is cold?
 
  #9  
Old 09-13-2005, 01:17 AM
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Default RE: trouble starting when engine is hot

In theory the fuel boils, vaporizes and the gases expend. Once the vapor cools it condenses and contracts sucking the fuel back into the lines.
 
  #10  
Old 09-13-2005, 01:30 AM
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Default RE: trouble starting when engine is hot


ORIGINAL: 1992audi4life100

Finally with the gas pedal all the way down it started, and blew out alot of smoke.
What smoke, Blue, Black or White?
 

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