Warm start problem refuses to be solved
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Joined: Oct 2005
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From: TX
Warm start problem refuses to be solved
91 LS. Had the best shop I know of in Houston, C&C Northside Automotive, try to diagnose my car further and Kurt said it was DEFINETELY fuel related and probably the fuel pump. I changed the pump, no difference. It is either the fuel pressure regulator, which I'm having a VERY difficult time finding discounted, or one of the sensors that allows the fuel pump to activate. Anyone have a resource I would use to check which sensors it is and what Ohm reading each should be in? Anyone know of a better place to get a fuel pressure regulator for a 91 LS400 for less than 166.xx$?
Lexus Test Driver
Joined: Oct 2005
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From: The BIG Apple
You're experiencing "vapor lock" which could be caused from a bad coolant sensor.
http://aa1car.com/library/2002/us30232.htm
"At the last International Automotive Technicians Network (iATN) convention in Dearborn, MI, a roomful of top technicians from all over the country was challenged to correctly diagnose several real-world driveability problems. They were given a description of some vehicles and their symptoms, then allowed to view actual test data that was taken from the vehicles using a variety of different diagnostic tests and equipment.
The challenge was to figure out which diagnostic tests and equipment would provide the most useful information, and to then analyze this information to come up with a diagnosis. It proved to be a difficult task because opinions differed as to what data should be looked at first, and what the data actually meant. Some people resorted to making wild guesses in an attempt to solve the problems.
One example that stumped a lot of technicians was a car that would start and run fine when cold, but had a hot-start problem. It would crank but not start. It had fuel, spark and compression. Fuel pressure and vacuum readings were normal. Coil resistance, spark plugs and wires were all within specifications.
The hot-start problem turned out to be a bad coolant sensor. The sensor was preventing the fuel system from going into closed loop, which created a rich mixture that flooded the engine when a hot start was attempted.
The diagnostic approach for solving a no-start condition that evolved from this was to:
1. Check for spark to rule out ignition problems.
2. Check for fuel to rule out an empty tank, dead fuel pump or plugged fuel line.
3. Check compression to rule out a broken cam, timing chain or OHC timing belt.
If all of the above are OK, remove and examine a spark plug. If the plugs are wet, it would tell you the engine is flooded due to too much fuel. The underlying cause would be a defective coolant sensor or leaky injector(s).
Another approach when confronted with a no-start condition is to check cranking vacuum. It should usually be at least 3". If lower than this, there is a compression problem. Also, look at the amount of HC in the exhaust. If you see at least 7,500 ppm of HC, there should be enough fuel to start. If the HC reading is below 7,500 ppm, there is not enough fuel.
On many vehicles, a no-start can occur if the oil pressure switch is bad. The oil pressure switch is wired into the fuel pump relay circuit to cut voltage if oil pressure is lost. This is to prevent fuel from spraying out of a ruptured fuel line in the event of an accident. Some vehicles also have an inertia crash switch hidden somewhere in the bodywork (look in the trunk, under the back seat or inside the rear seat side panels) to cut off fuel in case of an accident. An inertia switch can be reset by pressing its reset button.
Hard starting on some older fuel injected systems can be caused by a faulty cold start injector. A timed relay energizes the injector when the engine is cranked to provide extra fuel. Most problems here can be traced to electrical faults in the control relay or wiring. Use a test light to check the cold-start injector when the engine is cranked. No voltage means the relay (or its fuse) is bad."
http://aa1car.com/library/2002/us30232.htm
"At the last International Automotive Technicians Network (iATN) convention in Dearborn, MI, a roomful of top technicians from all over the country was challenged to correctly diagnose several real-world driveability problems. They were given a description of some vehicles and their symptoms, then allowed to view actual test data that was taken from the vehicles using a variety of different diagnostic tests and equipment.
The challenge was to figure out which diagnostic tests and equipment would provide the most useful information, and to then analyze this information to come up with a diagnosis. It proved to be a difficult task because opinions differed as to what data should be looked at first, and what the data actually meant. Some people resorted to making wild guesses in an attempt to solve the problems.
One example that stumped a lot of technicians was a car that would start and run fine when cold, but had a hot-start problem. It would crank but not start. It had fuel, spark and compression. Fuel pressure and vacuum readings were normal. Coil resistance, spark plugs and wires were all within specifications.
The hot-start problem turned out to be a bad coolant sensor. The sensor was preventing the fuel system from going into closed loop, which created a rich mixture that flooded the engine when a hot start was attempted.
The diagnostic approach for solving a no-start condition that evolved from this was to:
1. Check for spark to rule out ignition problems.
2. Check for fuel to rule out an empty tank, dead fuel pump or plugged fuel line.
3. Check compression to rule out a broken cam, timing chain or OHC timing belt.
If all of the above are OK, remove and examine a spark plug. If the plugs are wet, it would tell you the engine is flooded due to too much fuel. The underlying cause would be a defective coolant sensor or leaky injector(s).
Another approach when confronted with a no-start condition is to check cranking vacuum. It should usually be at least 3". If lower than this, there is a compression problem. Also, look at the amount of HC in the exhaust. If you see at least 7,500 ppm of HC, there should be enough fuel to start. If the HC reading is below 7,500 ppm, there is not enough fuel.
On many vehicles, a no-start can occur if the oil pressure switch is bad. The oil pressure switch is wired into the fuel pump relay circuit to cut voltage if oil pressure is lost. This is to prevent fuel from spraying out of a ruptured fuel line in the event of an accident. Some vehicles also have an inertia crash switch hidden somewhere in the bodywork (look in the trunk, under the back seat or inside the rear seat side panels) to cut off fuel in case of an accident. An inertia switch can be reset by pressing its reset button.
Hard starting on some older fuel injected systems can be caused by a faulty cold start injector. A timed relay energizes the injector when the engine is cranked to provide extra fuel. Most problems here can be traced to electrical faults in the control relay or wiring. Use a test light to check the cold-start injector when the engine is cranked. No voltage means the relay (or its fuse) is bad."
Thread Starter
Rookie
Joined: Oct 2005
Posts: 60
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From: TX
Thanks with the help
Unfortunately, that is A LOT to check. I work 60hrs/wk and do not have the free time, even if I used all of it, to test all of that. I'm going to attempt to bypass the fuel pump ECU to see if that helps any. I've finally given up on this battery and am going to replace it as well. With my luck it's not the battery's fault it keeps needing to be recharged.
I've replaced the timing belt, waterpump, cam seals, crank seals, plugs, entire coolant system, and so on with nothing more than bare bone write-ups and 100 bucks in tools, but I'd need step-by-step directions for testing things like cranking pressure. The cold start injector was replaced a couple thousand miles ago, though for some reason that doesn't mean a whole lot to me considering other maint. supposedly done on the car by the PO.
All the fuel pump ECU stuff I find is quite old, and all the pictures are now red 'x's. The ECU is located just behind the driver's side back seat's door correct? It's NOT under the door panel correct? I just replaced my fuel pump and put the back seats in YESTERDAY. Awesome luck. The bottom portion of the seats were a COMPLETE PITA btw, not looking foward to removing those.
I've replaced the timing belt, waterpump, cam seals, crank seals, plugs, entire coolant system, and so on with nothing more than bare bone write-ups and 100 bucks in tools, but I'd need step-by-step directions for testing things like cranking pressure. The cold start injector was replaced a couple thousand miles ago, though for some reason that doesn't mean a whole lot to me considering other maint. supposedly done on the car by the PO.
All the fuel pump ECU stuff I find is quite old, and all the pictures are now red 'x's. The ECU is located just behind the driver's side back seat's door correct? It's NOT under the door panel correct? I just replaced my fuel pump and put the back seats in YESTERDAY. Awesome luck. The bottom portion of the seats were a COMPLETE PITA btw, not looking foward to removing those.
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