Long crank / weak start when warm
Thread Starter
3rd Gear
Joined: Sep 2023
Posts: 3
Likes: 2
Long crank / weak start when warm
Hi. I'm having an issue with starting the car sometimes (especially with warm engine). Might crank up to 5 seconds hesitates even then. Other times it starts up like a brand new car (usually when cold). At least it does start every time, it's just embarrassing.
General opinion seems to be that this is caused by weak fuel pump prime. And I tend to agree, since if I prime it few times (ignition on/off x 3), it does start much better.
But can someone explain me the logic behind this phenomenon? How can the fuel pump work completely fine while driving, even with full throttle, but at the same time is also weak enough to just prime the fuel rail pressure for start? And why does it start much better when cold? Does it not sometimes prime at all when it's warm?
And the fix would be to replace fuel pump?
General opinion seems to be that this is caused by weak fuel pump prime. And I tend to agree, since if I prime it few times (ignition on/off x 3), it does start much better.
But can someone explain me the logic behind this phenomenon? How can the fuel pump work completely fine while driving, even with full throttle, but at the same time is also weak enough to just prime the fuel rail pressure for start? And why does it start much better when cold? Does it not sometimes prime at all when it's warm?
And the fix would be to replace fuel pump?
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,620
Likes: 4,066
From: Cape Coral, Florida
If you have to prime the fuel pump prior to starting may be a faulty fuel line check valve (fuel draining back to the tank) or maybe a cam or crank sensor issue…hard to diagnose without testing.
Thread Starter
3rd Gear
Joined: Sep 2023
Posts: 3
Likes: 2
"check valve (fuel draining back to the tank)"
Shouldn't the fuel pump prime every time once I turn the ignition on (despite the engine being warmed up from last drive)? Surely it will not drain back in half a second before cranking. And why doesn't it drain back when the engine is cold?
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,620
Likes: 4,066
From: Cape Coral, Florida
If you cycle the key a few times before every time before starting and now it starts normally every time the fuel feed line is losing prime…a quick way to tell if a bad CRANK sensor is watch the Tach during starting…if it doesn’t move it may be a faulty sensor…unless you can get yourself a fuel pressure gauge and a labscope to test the cam and crank sensor you will only be guessing.
Thread Starter
3rd Gear
Joined: Sep 2023
Posts: 3
Likes: 2
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,620
Likes: 4,066
From: Cape Coral, Florida
Le Mans Master
Joined: Jan 2001
Posts: 5,015
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From: Hilton NY
That's interesting because my '98 also has the sometimes difficult to start problem. There is no tach movement during cranking but the sensors have been changed. The next step will be to check the wiring to the crankshaft position sensor and for a possible bad new sensor. One thing I never did was crankshaft position learn procedure.
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Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,620
Likes: 4,066
From: Cape Coral, Florida
If you used an aftermarket sensor like a Dorman for instance that can be your problem…you ALWAYS check the wiring before replacing…it’s a 3 wire Hall Effect sensor…12 volt power, a ground, and a signal to the PCM…with a labscope you will see a 0-12 volt square wave..with a voltmeter you will see around 3-4 volts if I can remember.