Random delayed start
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Junior User
Joined: Apr 2011
Posts: 74
Likes: 2
From: Tennessee
Random delayed start
Not all the time, but I've noticed it after the truck has been driven - shut off - then started again within a few min period. When truck is cold or has been sitting for an extended it starts no problem. By "delayed" I mean once I try to start the truck it takes a sec or two longer than normal before it cranks. Then when it does start it will idle very low for a sec or two then pick up and act normal.
So far I've done this to remedy it:
- new fuel filter
- new air filter
- cleaned MAF sensor
- cleaned throttle body
- seafoam thru vac hose
Only thing else I suspect is weak fuel pump but looks like it was act up all the time not just when the truck is started back to back. Truck has good power when running, I did a couple short blasts up to 80mph and everything was fine.
So far I've done this to remedy it:
- new fuel filter
- new air filter
- cleaned MAF sensor
- cleaned throttle body
- seafoam thru vac hose
Only thing else I suspect is weak fuel pump but looks like it was act up all the time not just when the truck is started back to back. Truck has good power when running, I did a couple short blasts up to 80mph and everything was fine.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Sounds like a Hot start issue only.
Areas to check out.
1. Crank sensor Plug for seating or poor contact.
2. Fuel pressure for being to low.
Attach a gauge to the test port and cycle the key on and off with no cranking to see how much pressure is built on the gauge.
.
If you don't find an isue with the above, you need to get a bit deeper into other area that cause poor hot start.
The only difference between cold and hot start is the engine and engine bay temperature the sensors report it to the computer.
Good luck.
Areas to check out.
1. Crank sensor Plug for seating or poor contact.
2. Fuel pressure for being to low.
Attach a gauge to the test port and cycle the key on and off with no cranking to see how much pressure is built on the gauge.
.
If you don't find an isue with the above, you need to get a bit deeper into other area that cause poor hot start.
The only difference between cold and hot start is the engine and engine bay temperature the sensors report it to the computer.
Good luck.
Senior User
Joined: Jul 2007
Posts: 123
Likes: 0
From: Jackson
Same but worse here
My 1999 5.4 with 300,000 miles does the same thing except it will take 30 seconds or so of cranking to start, then it runs rough at 350 rpms or so then revs to 1000, back down to 750 and all is fine. I used to let the starter rest with the key in run, but it's like it has to crank awhile continuously to start. I started turning the key to off and sometimes it will start fine. Cold, it's fine. Hot it's fine if it's shut off and immediately restarted. It seems to happen when it sits for 30 minutes to an hour.
I figured it was the IAC and recently it wouldn't idle, so today I replaced it and being cold, it started up and idled great. I drove about five miles to a friend's hourselves, visited for about 45 min, and the darn thing was hard to start! Drove a couple miles to a restaurant, 30 minutes later I left, hard start again! Drove about six miles home, turned it off, restarted fine. Messed around about 20 minutes, tried it again, started fine. Just tried it again after 30 minutes, starts fine!
It's an aggravating gremlin.
I figured it was the IAC and recently it wouldn't idle, so today I replaced it and being cold, it started up and idled great. I drove about five miles to a friend's hourselves, visited for about 45 min, and the darn thing was hard to start! Drove a couple miles to a restaurant, 30 minutes later I left, hard start again! Drove about six miles home, turned it off, restarted fine. Messed around about 20 minutes, tried it again, started fine. Just tried it again after 30 minutes, starts fine!
It's an aggravating gremlin.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Long crank time is no or low fuel pressure or lack of IAC opening for air.
A. Fuel pump.
B. Fuel filter.
C. Crank sensor plug seating.
D. Fuel regulator.
Letting key in run doers no good because it does not run the fuel pump.
It does cause the OX sensor heaters to heat the sensors.
Low rpm start, than goes to high rpm indicates the motor was not getting air or enough fuel.
You have to investigate all these area.
There is actually no difference between cold start and hot start except engine temperature.
The difference between cold and hot starting is what the CHT and IAT send to the computer as the only way the computer knows what to do with the IAC, ignition timing and amount of fuel plus the idle speed.
I would think you want to get this fixed for cold weather coming because it causes excess wear on the starter and battery capacity.
Good luck.
A. Fuel pump.
B. Fuel filter.
C. Crank sensor plug seating.
D. Fuel regulator.
Letting key in run doers no good because it does not run the fuel pump.
It does cause the OX sensor heaters to heat the sensors.
Low rpm start, than goes to high rpm indicates the motor was not getting air or enough fuel.
You have to investigate all these area.
There is actually no difference between cold start and hot start except engine temperature.
The difference between cold and hot starting is what the CHT and IAT send to the computer as the only way the computer knows what to do with the IAC, ignition timing and amount of fuel plus the idle speed.
I would think you want to get this fixed for cold weather coming because it causes excess wear on the starter and battery capacity.
Good luck.
Fleet Mechanic
Joined: Sep 2003
Posts: 1,716
Likes: 15
After shutdown of a hot engine, under hood temps rise, and the fuel in all the fuel lines gets well heated up. Fuel Injection system design keeps the supply line and everything upstream of the pressure regulator pressurized, to avoid the formation of gas (gaseous) bubbles in the fuel lines. The pressure slowly bleeds down over hours.
If it bleeds down quickly, due to things like one or more leaking injectors, pressure regulator that leaks to the down side, or leaking check valve in the fuel pump assembly, then gas bubbles will form. Similar to the vapor lock of old.
Decades ago, I had a VW with the CIS fuel injection system that I bought new. Ran great. Until they started adding alcohol to the gas. Then it had terrible vapor bubble problems after hot shut down. If I gassed up at a station that was still 100% gas, all ok. If not, then there was a dead zone between ~15 minutes of being shut off, to about 2 hours, during which it was a devil of a time trying to get it started and running on all cylinders.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
If the fuel leaks into the intake or the cylinders after shutdown, the motor is flooded.
A good reason it will not start.
Cranking at this point adds even more gas from the injectors causing more flooding.
A possible way to tell if this is happening is to get the motor into a condition you know will not start normally.
Hold the throttle wide open, then crank the motor and see if it starts much sooner.
If yes you have the problem of flooding.
Find out why.
Holding the throttle wide open at cranking ...shuts... the fuel injection OFF and allows only air through the cylinders evaporating the gas that is there much sooner.
Good luck..
A good reason it will not start.
Cranking at this point adds even more gas from the injectors causing more flooding.
A possible way to tell if this is happening is to get the motor into a condition you know will not start normally.
Hold the throttle wide open, then crank the motor and see if it starts much sooner.
If yes you have the problem of flooding.
Find out why.
Holding the throttle wide open at cranking ...shuts... the fuel injection OFF and allows only air through the cylinders evaporating the gas that is there much sooner.
Good luck..
Junior User
Joined: May 2017
Posts: 96
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From: Pacific Northwest
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Posting Guru
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From: Fort Smith, Arkansas
If your truck has a distributor, you have posted in the wrong section.
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Junior User
Joined: May 2017
Posts: 96
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From: Pacific Northwest
Lol I was on my phone responding to multiple posts at once, got mixed up on what thread I was in.
Senior User
Joined: Oct 2011
Posts: 485
Likes: 1
Delayed start when hot
Helping a friend with an 03 F150 4.6. When hot, after sitting for about and hour, it is a long start. I've only observed it once. I tried to start and it was long start so i stopped after a few seconds (would have normally fired up). I then pressed the accelerator to the floor. It took less time to start, but was a bit longer than normal. After it starts it will start right up each time if parked for less than hour. It does have some idle fluctuation after each start up so there may be some IAC. i'm going to recommend a fuel pressure test. I'm assuming that the fuel rail should hold pressure??? If it's leaky injectors, how do i know which ones or should all of them be rebuilt?
any other suggestions appreciated.
any other suggestions appreciated.
If the fuel leaks into the intake or the cylinders after shutdown, the motor is flooded.
A good reason it will not start.
Cranking at this point adds even more gas from the injectors causing more flooding.
A possible way to tell if this is happening is to get the motor into a condition you know will not start normally.
Hold the throttle wide open, then crank the motor and see if it starts much sooner.
If yes you have the problem of flooding.
Find out why.
Holding the throttle wide open at cranking ...shuts... the fuel injection OFF and allows only air through the cylinders evaporating the gas that is there much sooner.
Good luck..
A good reason it will not start.
Cranking at this point adds even more gas from the injectors causing more flooding.
A possible way to tell if this is happening is to get the motor into a condition you know will not start normally.
Hold the throttle wide open, then crank the motor and see if it starts much sooner.
If yes you have the problem of flooding.
Find out why.
Holding the throttle wide open at cranking ...shuts... the fuel injection OFF and allows only air through the cylinders evaporating the gas that is there much sooner.
Good luck..
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