HELP with V8 shut down gremlin

cert349 · 08-04-2002, 09:37 AM

My 1990 V8 Q. has developed a frustrating shut down habit when driven 25-35 miles on a hot day. The engine just shuts off and will not restart untill the car cools to ambient temps. My mechanic, who is good is stumped. We have replaced the fan control, distributor, fuel pump, engine Computer relay, fan relay...to no avail. Anyone have any other ideas?

quattro920 · 08-04-2002, 10:49 AM

Will not restart? Does the starter crank at all? Or does it crank but the engine won't start?

cert349 · 08-05-2002, 04:41 AM

It cranks but will not start. It will fire if you shoot starting fluid into the air intake but doesn't continue to run.

quattro920 · 08-05-2002, 11:14 AM

Sounds like a fuel problem. Do a search on hot start problems on the forum, and my guess is the fuel pump check valve on your car is bad, and doesn't allow residual fuel pressure to stay high enough after your car shuts off.

Wilson.

cert349 · 08-05-2002, 12:19 PM

Would this explain the engine Shutting down after a normal start? This is occuring at highway speeds.

quattro920 · 08-06-2002, 10:08 PM

It's definitely a fuel problem. How did your mechanic come to the conclusion of changing the fuel pump? Did he get a chance to flow and pressure test the new fuel pump? Heat is definitely an issue here, as it somehow keeps fuel from getting to the engine and stalling it. Wouldn't hurt to try a new fuel-pump relay either...but definitely keep us posted.

Hope that helps,

Wilson.

cert349 · 08-07-2002, 08:32 AM

I believe he relied on past experience with fuel pumps doing intermittant shut offs. He did not do a flow/pressure test to my knowledge. He did replace the fuel pump relay, before he replaced the fuel pump. Would the fuel pressure regulator be effected by heat so as to cause it to shut fuel supply off?

audiqv8 · 08-08-2002, 01:03 PM

There are two sensors, crankshaft reference sensors and speed sensors located on the left side (driver side) near the bellhousing. The cranshaft reference sensor is used by the ECU to start the sequence of firing the injectors. Hard starting when hot is usually caused by this sensors. If the speed sensors should die then the engine will fail to run. The speed sensor is a magnetic sensor which reads the teeths on the fly wheel producing an AC current, which the ECU use to determine the engine rpm. Both of these are magnetic sensors which will fail eventually because of heat from the exhaust manifold. Replace both sensors at the same time cost anywhere between $135-$190 each. Blink out the DTC codes. Go to the following site to get help in blinking out the DTC codes.

http://www.sjmautotechnik.com/ecufv8.html

http://www.sjmautotechnik.com/ecufv8.html

cert349 · 08-26-2002, 02:33 PM

Thanks to all who posted suggestions. My fingers are still crossed...but we have replaced the RPM and Crank Position sensors and so far that seemed to be the end. I hope. This made me (at the wife's suggestion) start looking for a new car. Well may be I'll get to hold on to it a little longer. Bill Cline

08-04-2002, 10:49 AM	#2
quattro920 AudiWorld Member Garage is empty, add now Join Date: Mar 2002 Posts: 231	Re: HELP with V8 shut down gremlin Will not restart? Does the starter crank at all? Or does it crank but the engine won't start?

08-05-2002, 04:41 AM	#3
cert349 Audiworld Junior Member Garage is empty, add now Join Date: Aug 2002 Posts: 96	Re: HELP with V8 shut down gremlin It cranks but will not start. It will fire if you shoot starting fluid into the air intake but doesn't continue to run.

08-05-2002, 11:14 AM	#4
quattro920 AudiWorld Member Garage is empty, add now Join Date: Mar 2002 Posts: 231	Re: HELP with V8 shut down gremlin Sounds like a fuel problem. Do a search on hot start problems on the forum, and my guess is the fuel pump check valve on your car is bad, and doesn't allow residual fuel pressure to stay high enough after your car shuts off. Wilson.

08-05-2002, 12:19 PM	#5
cert349 Audiworld Junior Member Garage is empty, add now Join Date: Aug 2002 Posts: 96	Re: HELP with V8 shut down gremlin Would this explain the engine Shutting down after a normal start? This is occuring at highway speeds.

08-06-2002, 10:08 PM	#6
quattro920 AudiWorld Member Garage is empty, add now Join Date: Mar 2002 Posts: 231	Re: HELP with V8 shut down gremlin It's definitely a fuel problem. How did your mechanic come to the conclusion of changing the fuel pump? Did he get a chance to flow and pressure test the new fuel pump? Heat is definitely an issue here, as it somehow keeps fuel from getting to the engine and stalling it. Wouldn't hurt to try a new fuel-pump relay either...but definitely keep us posted. Hope that helps, Wilson.

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08-07-2002, 08:32 AM	#7
cert349 Audiworld Junior Member Garage is empty, add now Join Date: Aug 2002 Posts: 96	Re: HELP with V8 shut down gremlin I believe he relied on past experience with fuel pumps doing intermittant shut offs. He did not do a flow/pressure test to my knowledge. He did replace the fuel pump relay, before he replaced the fuel pump. Would the fuel pressure regulator be effected by heat so as to cause it to shut fuel supply off?

08-08-2002, 01:03 PM	#8
audiqv8 AudiWorld Super User Garage is empty, add now Join Date: Apr 2002 Posts: 3,041	Re: HELP with V8 shut down gremlin There are two sensors, crankshaft reference sensors and speed sensors located on the left side (driver side) near the bellhousing. The cranshaft reference sensor is used by the ECU to start the sequence of firing the injectors. Hard starting when hot is usually caused by this sensors. If the speed sensors should die then the engine will fail to run. The speed sensor is a magnetic sensor which reads the teeths on the fly wheel producing an AC current, which the ECU use to determine the engine rpm. Both of these are magnetic sensors which will fail eventually because of heat from the exhaust manifold. Replace both sensors at the same time cost anywhere between $135-$190 each. Blink out the DTC codes. Go to the following site to get help in blinking out the DTC codes. http://www.sjmautotechnik.com/ecufv8.html http://www.sjmautotechnik.com/ecufv8.html

08-26-2002, 02:33 PM	#9
cert349 Audiworld Junior Member Garage is empty, add now Join Date: Aug 2002 Posts: 96	Re: HELP with V8 shut down gremlin Thanks to all who posted suggestions. My fingers are still crossed...but we have replaced the RPM and Crank Position sensors and so far that seemed to be the end. I hope. This made me (at the wife's suggestion) start looking for a new car. Well may be I'll get to hold on to it a little longer. Bill Cline

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08-26-2002, 02:33 PM
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