2000 4.6 warm start long crank and raw gas smell
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Junior Member
Joined: Mar 2012
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2000 4.6 warm start long crank and raw gas smell
Hi all, new guy here. (sorry for the long first post)
I've been a diesel guy my whole life so bear with me please. I recently picked up an 00' F150 4.6 4x4 with 67k miles. The truck sat for long periods of time and was only driven locally when it was. It had a rough idle problem that i found to be a switched vacuum line but i also replaced the DPFE, EGR, fuel pressure regulator, cylinder head temp sensor, cleaned and checked the IAC.
The previous owner pulled the motor and did the headgaskets when he noticed the pass side leaking. While it was out he did the rear main, had the heads decked and checked the valve lash.
My problem now is when the engine is up to temp it cranks for 4-5seconds and gives off a raw gas smell from the exhaust. It is also getting really bad mileage. It's not throwing any codes and the truck runs like a top at all speeds (no hesitation or sputtering). It starts just fine when the engine is stone cold though.
I've checked the fuel pressure a few times and it seems to be ok. I know 30 is at the lower end of spec but it shouldnt be affecting the warm start and mileage should it?
With the key on 30psi
Start up 30psi steady
Key off drops to about 28-29psi
After 20 mins only drops to 26psi
Im lost and so are the mechanics at my brother in law's shop (they havent spent a full day on the truck, just me stopping by after work) Any ideas or info is appreciated.
I've been a diesel guy my whole life so bear with me please. I recently picked up an 00' F150 4.6 4x4 with 67k miles. The truck sat for long periods of time and was only driven locally when it was. It had a rough idle problem that i found to be a switched vacuum line but i also replaced the DPFE, EGR, fuel pressure regulator, cylinder head temp sensor, cleaned and checked the IAC.
The previous owner pulled the motor and did the headgaskets when he noticed the pass side leaking. While it was out he did the rear main, had the heads decked and checked the valve lash.
My problem now is when the engine is up to temp it cranks for 4-5seconds and gives off a raw gas smell from the exhaust. It is also getting really bad mileage. It's not throwing any codes and the truck runs like a top at all speeds (no hesitation or sputtering). It starts just fine when the engine is stone cold though.
I've checked the fuel pressure a few times and it seems to be ok. I know 30 is at the lower end of spec but it shouldnt be affecting the warm start and mileage should it?
With the key on 30psi
Start up 30psi steady
Key off drops to about 28-29psi
After 20 mins only drops to 26psi
Im lost and so are the mechanics at my brother in law's shop (they havent spent a full day on the truck, just me stopping by after work) Any ideas or info is appreciated.
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Check for gas leaking into the vacuum line from the regulator and being pulled into the intake. A test is to remove the vac line and plug it. The fuel pressure should go a bit higher but not enough to cause a seperate problem from doing so.
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The CHT sensor out of calibration can richen the fuel.
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Thermostat to low in temp or missing. Use SCANNER to look at the live operating temp.
.
From the fuel presure action you gave, I would not believe it's leaking fuel injectors because the pressure would drop off fast after shutdown. Also the pressure is a bit on the low side but nothing to worry about at this time.
.
Open OX sensor circuits.
One test to try is open the throttle wide open before cranking a hot motor.
If this shortens the crank time, it's proof of a flooded condition because it shuts fuel injection off untill the cylinders clear enough to fire.
.
Next is to have a look at live data with a good Scanner the shop should have and someone who knows what their looking at with it.
.
Be very carefull about running with so much fuel in the exhaust.
The cats will burn it with the results that their temperatures will go too high and melt the internal structure, then your in for more expense to replace both sides.
It seems there should be codes indicating the OX sensors are detecting too much fuel and have the fuel tables shifted to their lean limits trying to correct the over rich condition unless it clears after the motor runs.
.
Info for hot start:
When the ign switch goes to 'run' before cranking, the PCM looks at the CHT value and the intake air temp sensor IAT to know it's a hot restart.
These values set fuel injection amount , ignition timing and IAC opening point.
One or more of these signals are either missing or wrong at that time, to cause to much fuel from a PCM control point of opertion.
Anything else is a hardware fault allowing to much 'uncontrolled' fuel into the engine.
Trouble shoot from these points and the cause has to be found.
Good luck.
.
The CHT sensor out of calibration can richen the fuel.
.
Thermostat to low in temp or missing. Use SCANNER to look at the live operating temp.
.
From the fuel presure action you gave, I would not believe it's leaking fuel injectors because the pressure would drop off fast after shutdown. Also the pressure is a bit on the low side but nothing to worry about at this time.
.
Open OX sensor circuits.
One test to try is open the throttle wide open before cranking a hot motor.
If this shortens the crank time, it's proof of a flooded condition because it shuts fuel injection off untill the cylinders clear enough to fire.
.
Next is to have a look at live data with a good Scanner the shop should have and someone who knows what their looking at with it.
.
Be very carefull about running with so much fuel in the exhaust.
The cats will burn it with the results that their temperatures will go too high and melt the internal structure, then your in for more expense to replace both sides.
It seems there should be codes indicating the OX sensors are detecting too much fuel and have the fuel tables shifted to their lean limits trying to correct the over rich condition unless it clears after the motor runs.
.
Info for hot start:
When the ign switch goes to 'run' before cranking, the PCM looks at the CHT value and the intake air temp sensor IAT to know it's a hot restart.
These values set fuel injection amount , ignition timing and IAC opening point.
One or more of these signals are either missing or wrong at that time, to cause to much fuel from a PCM control point of opertion.
Anything else is a hardware fault allowing to much 'uncontrolled' fuel into the engine.
Trouble shoot from these points and the cause has to be found.
Good luck.
Last edited by Bluegrass; Mar 12, 2012 at 01:14 PM.
