Sleepy in upper RPM's
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New User
Joined: Dec 2004
Posts: 10
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From: Missouri
Sleepy in upper RPM's
What type of RPM's do u guys pull from your 4.6's. At wide open mine seems to pull very smooth til around 3,000 or 3,500 rpms, then it just doesnt wanna climb past that...4,000 tops. It doesnt miss violently or anything it just lingers at 3,500 to 4,000 until I get out of it and let it shift. Here is what we got: 2002 4.6L about 68,000 miles. I just changed the plugs, good air filter, cleaned mass air, ran seafoam through gas tank. All stock except at the moment from the cat-back there is no exhaust. What idea do you guys have for me to check out?? There is no check engine light on. I dont expect 7,000 rpm's but I know there should be more than this. Thanks for any advice1
Senior User
Joined: Jan 2005
Posts: 105
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From: Nor*Cal (Bay area)
yeah, could be... mine only has 50k on it, and when i took off the fuel filter and blew through it, pressure built up and actually blew gas back in my mouth lol pretty nasty 
only a little bit though, but enough to tell me it was plugged up... the new one blew through with no problems make sure you have a fuel line disconnect tool, dont fall for the one that they say is an "A/C Fuel line disconnect tool for Ford vehicles" that one doesnt have a ring small enough for the fuel lines on it, you must use the actual "Fuel line disconnect tool" with only 2 sizes on it... and the smallest one works
only a little bit though, but enough to tell me it was plugged up... the new one blew through with no problems make sure you have a fuel line disconnect tool, dont fall for the one that they say is an "A/C Fuel line disconnect tool for Ford vehicles" that one doesnt have a ring small enough for the fuel lines on it, you must use the actual "Fuel line disconnect tool" with only 2 sizes on it... and the smallest one works
Junior User
Joined: Aug 2002
Posts: 96
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MidnightXLT - if you are still having a problem, there might be a problem with a valve in the plastic part of your lower intake. That valve opens in the approximate RPM range where you are having problems.
The below picture shows our intakes upside down, you can see where the electrical connector socket on the front of the black plastic piece in the below picture.
The below picture shows our intakes upside down, you can see where the electrical connector socket on the front of the black plastic piece in the below picture.
Senior User
Joined: Mar 2004
Posts: 224
Likes: 1
From: Central Ohio
I'd bet on a fuel delivery problem. Best, almost only, way to check is to borrow a scan tool (at least a code reader that will also read sensor values). Connect it up, select either bank1sensor1 or bank2sensor2 O2 sensor. It should be switching between low (0-300mv) and high (600-900mv). Low is lean and high is rich. The computer switches back and forth to feed the cat. When you go to wide open throttle, the computer switches fuel calculation mode, stops using the O2 sensors and starts using the MAF, and richens the mixture to protect from heat and knock. Under wide open throttle, the O2 sensor on the scan tool should go high and stay there. If it goes low instead, you probably have a fuel delivery problem, that is the pump or filter.
The keys to this test is at wide open throttle the fuel demand is the highest so it will expose weak fuel delivery you can't find in the shop and also at wide open throttle the mixture goes rich so you can spot a fuel delivery problem by watching for low O2 sensor values while at wide open throttle.
The keys to this test is at wide open throttle the fuel demand is the highest so it will expose weak fuel delivery you can't find in the shop and also at wide open throttle the mixture goes rich so you can spot a fuel delivery problem by watching for low O2 sensor values while at wide open throttle.
