Car starts fine when cold. Drives normally from a few to many miles, shut off car and try to re-start. Engine cranks but does not start or show any signs of attempting to start. Wait until car cools down and starts immediately with no signs of fouling or sputtering. Runs normally until engine is shut off and symptoms re-appear.
got this from another forum, but this is waht this guy had to say....
start quote
"Typicaly", hot start problems (Hot, as in the fuel system has had time to heat soak after stopping, as opposed to trying to start immidiatly after stopping ) are becuase the fuel system won't hold is pressure when you shutdown when warm.
If fuel system pressure isn't kept up, fuel in the injector lines vaporizes easier when the hot engine is shut down, making the next start hard.
Fuel pressure dropping too quickly/fuel vapourization after shutdown can be becuase of any or all of the following:
1) Injectors leak
2) Accumulator is dead
3) Check valve at pump doesn't check
4) Injector cooling fan inoperative, or not pulling in cold air from down by the subframe
If that's too much to fix, I've heard of some that have wired a pushbutton switch to fire the cold start injector sensor. That lets you 'manually' force cold start injector to spray when hot. That will give some fuel for the motor to start on instead of vapours, and save your starter from getting trashed...
I have had the mis-pleasure of working on Bosch k-jetronic about 25 years ago. I bought an engine-less VW Rabbit from a bankruptcy case and an engine from a salvage yard. Installed the engine, put in some fuel and started it up. Everything was good for about 30 seconds. As it turned out, the gas tank was contaminated with moisture, rust, dirt, etc. After boiling out the tank, flushing the lines, replacing the filter, etc., the fuel system was never really fixed. I replaced the warm-up regulator, adjusted the sensor plate, tested the pressure regulator, checked the amount of fuel flow with each injector, tested the cold start injector as well as several other parameters.
As it turned out, one of the remaining problems was that the vibrating tips in the injectors were so worn that most of them would not hold any pressure after the car was shut off – they continued to drip fuel until all pressure was released. My solution – short of replacing the injectors, was to put a jumper in the fuel relay under the dash and run the fuel pump until the pressure was built back up – you could hear the pump when it reached the point of re-establishing pressure. Then I put the relay back in and the car started immediately.
The problem I have with the Audi is that I can shut off the warm engine and immediately try to restart – and it will not. It will only turn over with no sign of ignition. If this was a bad accumulator or leaky injectors, it seems that it would restart immediately upon shut down. As it is, I can fairly accurately predict when the car will restart based upon ambient air temperature and having the hood open. It is as if a switch is turned on – one minute it will crank with no sign of ignition and then literally the next minute fire right up with no signs of fouling, flooding or any other problem.
Thanks again for the advice, if I ever figure it out I will post the solution.
someone recently told me to try unplugging the cold start valve, because it could be going off everytime the cars started, so therefore the car would start great in the cold because its working properly, but making the car start poorly when warm, because its shooting off and almost flooding the engine and fouling up the start. I'm not too sure about this one, but at this point i'm willing to try anything, so you may want to give that test a try.
OK, here is the solution. The part in question had to completely fail before it was detected by a fault code. The code 2-1-1-2 finally appeared after the car would not start. Looking this up in the service manual indicated a bad REFERENCE SENSOR. $170 later and about 10 minutes to replace the car now starts cold or hot with no other symptoms.
Tripod. Audi owners need to know this is a very major problem with many 5000 Series Audi's.. I know a fellow who bought two new Audis with this problem.. He sold them both after being unable to solve this problem. Audi did modification by adding a fan afterrun system to run fan after hot engine was shut down. However, this seems not to have solved the problem.. My Audis do not have this problem, fortunately..
In my opinion this problem is likely caused by a malfunctioning temperature sensor.. I've had lots of problems with the "Electronic Thermoswitch" located on water jacket from head, lower one, near front of engine. The reason I mention this is because my Bentley Manual does not list a "Reference Sensor" and I'm wondering if this could be it... Or, where is that "Reference Sensor" Located? Or is it the Control Pressure Regulator on the Fuel Injection Distributor where the injector lines come from?
This is very important to know and I sincerely hope you have put your finger on the real problem which it appears you have. Thanks.
I resolved this problem about a year ago by replacing the "Ignition Timing Reference Sensor". This part is discussed in the "Ignition System" section of the Bentley manual (page 28.29). The part can be visually found on the drivers side of the motor. It is below and slightly in front of the mineral oil reservoir - at about the seam between the engine block and transmission - on the engine block side by about 1/2". It has one black wire coming out of it. The part has a round barrel-shaped cyllinder that fits down inside of the block to 'sense' the flywheel position so that the ignition timing is in synch.
Mine was 'failing' when the car would not warm start - as mentioned above - and did not present the 2-1-1-2 diagnostic code (Bentley p. 28.33) until the part completely failed - the car would not start at all - warm or cold. When I removed the sensor the cylinder had a broken seal and could easily be turned by hand. There were no other visual indications that the part had failed.
The car has been starting cold and warm ever since. I am now battling various leaks - otherwise all things are fine.
By the way, I have no idea how this was temperature related unless expansion by heat may have adversely affected the 'failing' reference sensor. The unusual aspect of this part failure was that the car started cold normally and ran normally under all conditions and temperatures. To me this implies that the reference sensor is only used by the ECU during start-up. Only conjecture by me at this time.
Car starts fine when cold. Drives normally from a few to many miles, shut off car and try to re-start. Engine cranks but does not start or show any signs of attempting to start. Wait until car cools down and starts immediately with no signs of fouling or sputtering. Runs normally until engine is shut off and symptoms re-appear.
Coil ? Relay(s) ? Fuel ?
Your problem is the crank position sensor (CKP) is getting heat soaked. Replace the ckp and your problem should go away. On the firewall near the ignition coil there is an electrical connection bracket which have three wire plugged into it.
Black is the CKP
Grey is the RPM sensor
Red or Brown is the Knock sensor.
Follow the black cable and it will lead you to the crank position sensor.
By the way, I have no idea how this was temperature related unless expansion by heat may have adversely affected the 'failing' reference sensor. The unusual aspect of this part failure was that the car started cold normally and ran normally under all conditions and temperatures. To me this implies that the reference sensor is only used by the ECU during start-up. Only conjecture by me at this time.
There is a pin pressed into the flywheel at 62 degree before TDC. As the pin passes over the sensor it distrubs the magnet field from the sensor. The ECU will see this signal and use this signal along with the cam and speed sensor and send a trigger signal to the coil to cause a spark.
The CKP or timing reference sensor is a magnetic sensor and as we all remember from high school physics a magnet looses it strength when heated.
The CKP is used by the ECU, but if it should fail it will default to a value at startup, the engine will remain running but will not restart until the signal is restored. On the other hand should the RPM (speed) sensor fail the engine will not start and if the engine was running it will die.
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86' 5000 CS Turbo Will not warm start...
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