V8 wouldn't start hot, started hour later!

Ofeelya · 07-23-2003, 05:24 PM

Here we go again. Took a hour long trip (with A/C on). No problems. Turned car off. Went into a store. Came out 15 minutes later and car wouldn't start. Came back an hour later and no problems. I've replaced plugs, fuel filter, air filter, checked wires with multimeter (all have same resistance). Also, cleaned and dried the TPS connector which seemed to have water in it and two oxidized pins. Could it be the temp sensor? Maybe the cat? This seems to happen after it rains and when it is very humid. Tomorrow I will check the TPS again for water. Any thoughts are much appreciated.

Ofeelya · 07-23-2003, 05:28 PM

tragopan86 · 07-23-2003, 05:50 PM

Does the starter turn slowly when you turn the key? Or does it turn fast like usual but just no ignition?

Ofeelya · 07-23-2003, 06:05 PM

No, it isn't the starter or battery . . . or the alternator. This problem is specific to hot starts. Fires right up and idles smoothly when cold.

audiqv8 · 07-23-2003, 06:08 PM

Heat soaked crank position sensor. If you can't remember when the last time the crank position and the speed sensor were replaced then replace then now. They are both mounted on the same bracket (cost about $140.00 to $160.00 each). Hard starting when hot is a known problem with these sensors. Being only a couple of inches away from the exhaust manifold the heat tends to fry these sensors.

Ofeelya · 07-23-2003, 06:14 PM

audiqv8 · 07-23-2003, 06:25 PM

When the engine doesn't start pull the DTC (Diagnostic Trouble Codes). They will blink out the code for a Crank position sensor problem (2112) flywheel pin missing .

The crank position sensor sends a signal to the ECU (engine control unit) to let it knows when the number one cylinder is approaching TDC, which cause the fuel injectors to fire in sequence. Your injector aren't firing because the signal is missing. This is a magnetic sensor which reads a pin on the flywheel. The magnetic property of the sensor decrease as the temperature increase. As the pin from the flywheel passes over the sensor it distrub the magnetic field which is used by the ECU.

DTC Quattro V8

Scott Miller · 07-23-2003, 06:37 PM

Sensors are the same as on my '90 200, same symptoms when mine failed. My manual has a test, testing resistance I believe. Find the sensors, mine are on the left side front of the flywheel about 10 or 11 o'clock (looking forward). Two wires come from a row of connectors on the right, upper firewall to the two sensors. Next time it happens, get a cup of cool water and pour it on them, it should start right up. Good luck!

zsolt1 · 07-23-2003, 06:54 PM

not sure about the V8 setup, but in the 5k it would be a probable cause.
Zsolt

Ofeelya · 07-23-2003, 07:08 PM

07-23-2003, 05:28 PM	#2
Ofeelya New Member Garage is empty, add now Join Date: May 2003 Posts: 98	Also, found and replaced cracked breather hose.

07-23-2003, 05:50 PM	#3
tragopan86 New Member Garage is empty, add now Join Date: Mar 2003 Posts: 138	Re: sounds like my truck. Could be starter... Does the starter turn slowly when you turn the key? Or does it turn fast like usual but just no ignition?

07-23-2003, 06:05 PM	#4
Ofeelya New Member Garage is empty, add now Join Date: May 2003 Posts: 98	Not the starter . . . No, it isn't the starter or battery . . . or the alternator. This problem is specific to hot starts. Fires right up and idles smoothly when cold.

07-23-2003, 06:08 PM	#5
audiqv8 AudiWorld Super User Garage is empty, add now Join Date: Apr 2002 Posts: 3,041	Re: Also, found and replaced cracked breather hose. Heat soaked crank position sensor. If you can't remember when the last time the crank position and the speed sensor were replaced then replace then now. They are both mounted on the same bracket (cost about $140.00 to $160.00 each). Hard starting when hot is a known problem with these sensors. Being only a couple of inches away from the exhaust manifold the heat tends to fry these sensors.

07-23-2003, 06:14 PM	#6
Ofeelya New Member Garage is empty, add now Join Date: May 2003 Posts: 98	Is there anyway to test these sensors?

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07-23-2003, 06:25 PM	#7
audiqv8 AudiWorld Super User Garage is empty, add now Join Date: Apr 2002 Posts: 3,041	Re: Is there anyway to test these sensors? When the engine doesn't start pull the DTC (Diagnostic Trouble Codes). They will blink out the code for a Crank position sensor problem (2112) flywheel pin missing . The crank position sensor sends a signal to the ECU (engine control unit) to let it knows when the number one cylinder is approaching TDC, which cause the fuel injectors to fire in sequence. Your injector aren't firing because the signal is missing. This is a magnetic sensor which reads a pin on the flywheel. The magnetic property of the sensor decrease as the temperature increase. As the pin from the flywheel passes over the sensor it distrub the magnetic field which is used by the ECU. DTC Quattro V8

07-23-2003, 06:37 PM	#8
Scott Miller New Member Garage is empty, add now Join Date: Nov 2001 Posts: 200	Re: Is there anyway to test these sensors? Sensors are the same as on my '90 200, same symptoms when mine failed. My manual has a test, testing resistance I believe. Find the sensors, mine are on the left side front of the flywheel about 10 or 11 o'clock (looking forward). Two wires come from a row of connectors on the right, upper firewall to the two sensors. Next time it happens, get a cup of cool water and pour it on them, it should start right up. Good luck! __________________ '90 200qa - sold '96 A4q 2.8l auto '96 BMW 740iL '97 FZJ80 Landcruiser '06 Specialized Epic Comp Disk - daily driver Holland, MI

07-23-2003, 06:54 PM	#9
zsolt1 AudiWorld Member Garage is empty, add now Join Date: Mar 2003 Posts: 468	Could it be a check valve? not sure about the V8 setup, but in the 5k it would be a probable cause. Zsolt

07-23-2003, 07:08 PM	#10
Ofeelya New Member Garage is empty, add now Join Date: May 2003 Posts: 98	Where might I be able to get one (other than "stealership")?

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07-23-2003, 07:08 PM
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