spark plugs
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New User
Joined: Jan 2013
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spark plugs
99-f150 5.4 V8
I was wondering what normal starting rpms should be the truck has 141K miles on it.
When I start it it goes striaght up to about 900rpms for a second than dips down to about 700 rpms and stays steady is this normal? for the truck to rev up right after starting then dip down a second later, also it takes my truck an abnormally long time to start, the battery is fine and the fuel filter and air filter are fine. The starter cranks it just takes about 4 seconds to start i run sea foam through the gas, and in the booster line regularly. What could cause this?
I was wondering what normal starting rpms should be the truck has 141K miles on it.
When I start it it goes striaght up to about 900rpms for a second than dips down to about 700 rpms and stays steady is this normal? for the truck to rev up right after starting then dip down a second later, also it takes my truck an abnormally long time to start, the battery is fine and the fuel filter and air filter are fine. The starter cranks it just takes about 4 seconds to start i run sea foam through the gas, and in the booster line regularly. What could cause this?
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
It is normal for the starting RPM to go high then return to normal.
How high it goes depends on the ambient outside temperature sensed by the coolant and intake air sensors.
At starting the intake air controllwer is opened that causes the higher RPM.
The computer uses the crank sensor to find the 'target' rpm by controlling the IAC air until that target is found.
It amounts to a feedback loop control action..
.
The long crank time usually is low fuel pressure to the injectors.
A possible way to determine this is to cycle the ignition key to run several times then crank.
If it shortens the time, likely it's the fuel pump or regulator.
It will be time to tst fuel pressure for how fast is come up with key cycling.
.
As to using Sea Foam that often, I would not do it.
I have 187,000 and have never used a cleaner in the motor.
If quality 5w20 oil is used and changed often along with the filter, no cleaner is needed. The oil has enough cleaners in it for the change intervals.
Good luck.
How high it goes depends on the ambient outside temperature sensed by the coolant and intake air sensors.
At starting the intake air controllwer is opened that causes the higher RPM.
The computer uses the crank sensor to find the 'target' rpm by controlling the IAC air until that target is found.
It amounts to a feedback loop control action..
.
The long crank time usually is low fuel pressure to the injectors.
A possible way to determine this is to cycle the ignition key to run several times then crank.
If it shortens the time, likely it's the fuel pump or regulator.
It will be time to tst fuel pressure for how fast is come up with key cycling.
.
As to using Sea Foam that often, I would not do it.
I have 187,000 and have never used a cleaner in the motor.
If quality 5w20 oil is used and changed often along with the filter, no cleaner is needed. The oil has enough cleaners in it for the change intervals.
Good luck.
Postmaster
Joined: Oct 2009
Posts: 3,432
Likes: 7
Bluegrass, he wasn't talking about putting Seafoam in the oil. Running it through the intake is usually a good idea, cleans all the carbon and junk out of the cylinders.
As far as what your idle is doing, sounds normal. On the delayed starting, fuel pump could cause it, a could any loss of fuel pressure after the engine is turned off. Have to check that with a fuel pressure gauge. Basically you hook up the gauge prime the pump a few times, see what the pressure builds to, then see how long it holds it. If the pressure is drifting down over time, it means that it is leaking past the check valve in the pump, and injector is leaking, or the regulator is bleeding it off.
As far as what your idle is doing, sounds normal. On the delayed starting, fuel pump could cause it, a could any loss of fuel pressure after the engine is turned off. Have to check that with a fuel pressure gauge. Basically you hook up the gauge prime the pump a few times, see what the pressure builds to, then see how long it holds it. If the pressure is drifting down over time, it means that it is leaking past the check valve in the pump, and injector is leaking, or the regulator is bleeding it off.
Senior User
Joined: Mar 2013
Posts: 114
Likes: 0
Have to check that with a fuel pressure gauge. Basically you hook up the gauge prime the pump a few times, see what the pressure builds to, then see how long it holds it. If the pressure is drifting down over time, it means that it is leaking past the check valve in the pump, and injector is leaking, or the regulator is bleeding it off.
pressure while idling should be between 28-45 psi
?'s
do you have a check engine light on?
does it run smooth or rough?
is it a daily driver or does have old gas in it?
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