5.4L Engine Runs Smooth, But No Acceleration?
01-10-2017, 12:47 PM
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5.4L Engine Runs Smooth, But No Acceleration?
I have searched the forum for months, and I have tried much of what has been posted. I have a 2005 F150 FX4 5.4L with 200K on the odometer. Previous owner stated the motor and transmission was replaced around 50-60K ago. I did not get any proof of the replacements, however the throttle body and exhaust would suggest it was only a block change. I digress, the truck runs and idles smooth, but there is no top end. With the foot down, the truck screams but isn't going anywhere. Seems like it runs well up to 30-40 mph and then there is no more power. It feels like there is only 200hp and not 300hp. I can drive 80mph (Wyoming Interstate) with no issue other than lack of power.
I have not changed all the spark plugs or coils. I had a miss and the dealership identified two cracked plugs (5 and 8 if I recall) and a bad coil on 8. The truck at that time had the same acceleration issue, but also had shudder under load going uphill. The two plugs and a coil solved the shutter issue but not the acceleration. I have not done anything with the injectors. I recently checked the back pressure and there is no restriction in the exhaust. Oil changed every 3k, new fuel filter and air filter every 3k (just to rule it out). Everything changed has been motorcraft.
The only other numbers I have to produce is from my live data that showed fuel pressure at 40 psi, MAF maxed is about 18 lbs/m and downstream bank 2 oxygen sensor does not level out (it continues to fluctuate voltage like the upstream).
I don't mind trying to solve the problem, but I want to start in the right direction. I'm a bit confused as to why it runs well but has no power. It feels like I'm towing a load, only will spin the tires on ice.
I have not changed all the spark plugs or coils. I had a miss and the dealership identified two cracked plugs (5 and 8 if I recall) and a bad coil on 8. The truck at that time had the same acceleration issue, but also had shudder under load going uphill. The two plugs and a coil solved the shutter issue but not the acceleration. I have not done anything with the injectors. I recently checked the back pressure and there is no restriction in the exhaust. Oil changed every 3k, new fuel filter and air filter every 3k (just to rule it out). Everything changed has been motorcraft.
The only other numbers I have to produce is from my live data that showed fuel pressure at 40 psi, MAF maxed is about 18 lbs/m and downstream bank 2 oxygen sensor does not level out (it continues to fluctuate voltage like the upstream).
I don't mind trying to solve the problem, but I want to start in the right direction. I'm a bit confused as to why it runs well but has no power. It feels like I'm towing a load, only will spin the tires on ice.
01-10-2017, 01:03 PM
#2
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How did you test the back pressure?
My first instinct is a plugged convertor. The only real test I have seen that is definitive is opening the exhaust at the manifold and driving it to see if power returns. I have seen more than one vehicle were a mechanic stated it was not a plugged cat only to find out later that it was.
It does not have to be completely plugged to cause an issue, simply restrictive enough to rob a bunch of power.
My first instinct is a plugged convertor. The only real test I have seen that is definitive is opening the exhaust at the manifold and driving it to see if power returns. I have seen more than one vehicle were a mechanic stated it was not a plugged cat only to find out later that it was.
It does not have to be completely plugged to cause an issue, simply restrictive enough to rob a bunch of power.
01-10-2017, 04:27 PM
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How did you test the back pressure?
My first instinct is a plugged convertor. The only real test I have seen that is definitive is opening the exhaust at the manifold and driving it to see if power returns. I have seen more than one vehicle were a mechanic stated it was not a plugged cat only to find out later that it was.
It does not have to be completely plugged to cause an issue, simply restrictive enough to rob a bunch of power.
My first instinct is a plugged convertor. The only real test I have seen that is definitive is opening the exhaust at the manifold and driving it to see if power returns. I have seen more than one vehicle were a mechanic stated it was not a plugged cat only to find out later that it was.
It does not have to be completely plugged to cause an issue, simply restrictive enough to rob a bunch of power.