trouble starting when engine is hot (Full Version)

Audi >> Audi Models >> All Other Audi Models

trouble starting when engine is hot

  

1992audi4life100 -> trouble starting when engine is hot (9/12/2005 6:22:00 PM)

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

  
kakarot -> RE: trouble starting when engine is hot (9/12/2005 8:12:56 PM)

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.

0fframp -> RE: trouble starting when engine is hot (9/12/2005 8:47:48 PM)

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.

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 8:50:18 PM)

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?

0fframp -> RE: trouble starting when engine is hot (9/12/2005 9:00:06 PM)

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.

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 9:05:47 PM)

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?

0fframp -> RE: trouble starting when engine is hot (9/12/2005 9:48:04 PM)

quote:

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.

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 9:55:01 PM)

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?

0fframp -> RE: trouble starting when engine is hot (9/12/2005 10:17:56 PM)

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.

kakarot -> RE: trouble starting when engine is hot (9/12/2005 10:30:37 PM)


quote:

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?

0fframp -> RE: trouble starting when engine is hot (9/12/2005 10:40:10 PM)

Blue - you're burning oil
Black - you're running too rich
White - you're blowing steam (coolant vaporizing in the combustion chamber)

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 10:41:59 PM)

the smoke is black, but as i said this occurs when i have to literally floor it to start it. It doesnt blow smoke any other time. Does this help at all?

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 10:57:07 PM)

Offramp, you're on to something with this statement:

"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."

Because if I park and go into a store for 10 or 20 mins it doesn't cause a problem. But when the car sits for more like an hour it has alot of trouble starting. And if it sits for a few hours, and cools way down, it starts up great. Also it will go through cycles while im driving. After the car is completely warmed up it will run kind of crappy for a few miles, then it will return to normal. This only happens when the engine is completely hot, like when I've been driving for 20 + mins.

Please let me know if this makes any sense to you.
Thanks alot,
-Matt

0fframp -> RE: trouble starting when engine is hot (9/12/2005 11:31:17 PM)

If it takes an hour for the problem to rear it’s ugly head then it might not be vapor lock. It might still be a good idea to check the residual and system pressure but the problem might lie elsewhere. If the check valve is bad it shouldn’t affect the driving cycle because the pump is running.

Generally speaking what I often notice on older vehicles is electrical problems due to oxidation. Especially the ground points. If you live in an area where lots of salt is used during winter check all the electrical connections.

1992audi4life100 -> RE: trouble starting when engine is hot (9/12/2005 11:41:51 PM)

Unfortunatly yes, Upstate NY! Lots of salt here. But, does it make sense that this would only cause a problem when hot? If there was corrosion it seems as though it would be a problem all the time... Let me know what you think, Thanks alot.

Also how hard is it to change the check valve, where is it? I might just change it and see what happens. Is it in the back near the pump or near the engine?

-Matt

1992audi4life100 -> RE: trouble starting when engine is hot (9/13/2005 10:52:51 AM)

I have checked alot of other Audi forums and many other people have had the same problem. They lose fuel pressure too early when the car is off. If the car sits long enough it cools down and the CSI (cold start injector) sprays extra fuel into the intake tract. But it doesn't spray when the car is hot because ideally there would still be fuel in the rails/injectors ready to be dumped into the intake tract when starting.

So, since my car looses pressure before the engine has a chance to cool down, when I go to start the car there is no fuel readily available for the engine, and the CSI doesn't spray because the engine is still hot...

Other people have rigged the CSI to a button in the car. So they can activate it even when starting the car, when hot. Has anyone done this or would anyone be able to give me some info on doing this, my repair manual won't be delivered for a couple of weeks and I have no clue where I could tap into the wires for the CSI. Anyone with a book on a 1992 100 would be a huge help to me!
Thanks alot,
-Matt

kakarot -> RE: trouble starting when engine is hot (9/13/2005 7:28:25 PM)

You can buy a one way valve and instal it at the entrance of the fuel rail. If you feel that fuel is going away. But remember that you have electric fuel pump and each time you turn the key on it pumps fuel in.
You should look into engine electric schematics, particulary stuff for starting up. Or run a diagnostic using Vag com

0fframp -> RE: trouble starting when engine is hot (9/13/2005 10:39:06 PM)

I am not sure where the check valve is located on a 1992 100. Usually there are few, the filter has one and some fuel pumps had them as well.

I don't recommend bypassing the CSI as you want to cure the disease and not just treat the symptom.

Oxidation on sensors and connectors can provide the wrong signal voltage to the ECU. This results in the ECU going into all sorts of funky modes. I think on your 92 you should be able to flash some codes without using the expensive VAG tool.

1992audi4life100 -> RE: trouble starting when engine is hot (9/14/2005 7:04:00 AM)

How would I "flash codes?"
Thanks for all the help,
-Matt

0fframp -> RE: trouble starting when engine is hot (9/14/2005 8:36:54 AM)

It is easily done on the 91 and earlier models but the 92 and later use a different fuel injection system and I am not sure if the same procedure would work. You might want to check this link to get some idea as to how it is done. It may or may not be the same procedure.

1992audi4life100 -> RE: trouble starting when engine is hot (9/14/2005 5:11:01 PM)

Here's an up date... I was looking around at my engine today and noticed that the spark plug closest to my driver's side headlight had liquid around it where it screws into the head. Just above the spark plug is the fuel injector. My question is, if I have a "leaky injector" which is a popular theory among those who I have asked, would the fuel be leaking into the engine or could it be leaking out side? I don't know why else there would be liquid collecting here and I dont know what other liquid it could be. Let me know what you think! Thanks alot,
-Matt

0fframp -> RE: trouble starting when engine is hot (9/14/2005 5:30:58 PM)

On warm or hot engine, fuel will evaporate very quickly. Also a puddle off fuel that big will be noticeable, you will smell it. Normally liquid shouldn't be there it could be just plain water. Water is also no good as it can rust and seize the spark plug, definitely have it checked out.

1992audi4life100 -> RE: trouble starting when engine is hot (9/18/2005 7:35:45 PM)

OK, I looked at the engine more closely today. The liquid around the spark plug is from a coolant line that passes just above the spark plug. It's cracked in one spot and dripping down, I've already replaced the line. Many people are telling me that the reason my car doesn't want to start when its warm is because I have a leak in the fuel system. Probably an injector leaking... Someone told me to pull all the spark plugs about half an hour after running the engine to see if any of them were wet, like if one of the injectors was leaking onto it. I did this today and none of them were wet. But, the injector isn't directly above the spark plug on all of the cylendars so I don't see how this is effective. Can anyone give me any idea's on how to find the leak in my fuel system? As usual I appreciate it!
-Matt




http://www.cardomain.com/ride/2117331/1

gmatov -> RE: trouble starting when engine is hot (9/19/2005 11:59:31 PM)

The "clouds of black smoke" is the tipoff, here.

You are not lacking fuel, you are lacking spark to light it when hot.

Pushing the pedal to the floor to start might even be an indication that the airplate is sticking, wide open throttle, full fuel, no air, flooding the cylinders, airplate moves, get air, fire, burn all that excess fuel, mucho black smoke. Only thing is, with the air plate stuck, you only get idle or start fuel, but do get cold start fuel, WHEN ENGINE COOLANT IS COLD.

When the airplate doesn't move, the ports don't give that much fuel flow.

Still, the overrich start smoke indicates TOO MUCH starting fuel, not too little.

As to the fuel pump check valve, it is on the top of the fuel pump, inside the tank, under a lid under the rear seat. 8 buck item, so my parts house tells me.

First thing I would check, though, is airplate binding. I think about a .010 feeler should go all around it.

It is NOT boiling and vapor lock, else you would not have the excess fuel black smoke when it does fire . You have fuel, it's just not firing, so when it does, it has to burn that excess fuel, hence, black smoke.

Cheers,

George

I don't know if leaky injectors CAN wet the plugs. They spritz their fuel slowly if they leak, drops or a weak stream, don't think they can wet the plugs. And, they leak into the manifold, not into the cylinder itself. Smaller, shorter lines, they would pressurize more quickly than charging the main delivery line from the pump to the distributor.

1992audi4life100 -> RE: trouble starting when engine is hot (9/21/2005 2:06:10 PM)

George, first I wanted to thank you for all the time and thought you put into the post. If it weren't for people like you who go out of their way to help strangers with their cars, I would be very broke right now by letting dealerships do my diagnostic work!!

As I said I just picked this car up a couple of weeks ago and my repair manual hasn't come in yet. Im not sure where the "airplate" is located. Unless you're referring to what I call the throttle plate, inside the throttle body? If so why would this only be an issue with warm starts?

Also here's an interesting twist... Now when I start the car with the engine already warm, I push the gas to the floor and start it. The car starts up perfectly. As soon as it starts I let off the gas and it runs great thereafter. (I should note that when the car would give me trouble starting when hot, it would run poorly once I did get it going.)

The hot start issue somehow is diverted when I give it wide open throttle at start up.

What does this tell you? Does this help you to understand what the problem is. Either way, atleast I am able to start the car now. Before I'd have to wait an hour or so for it to cool down!

Just to recap:

1) Could you specify on the airplate?
2) Why does applying the throttle at start up avoid the hot start problem?


I don't just what the problem to be fixed I am interested in understanding it!

GREATLY appreciated!

-Matt

  

Page: [1] 2   next >   >>

Return to Audi Forums home page or view the Full Version of this page.