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2001 Nissan Sentra Question: Lack of power under 2k, ocassional stalling on a cold engine. No codes.

 

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Rostasteve, 1.8L 4 Cylinder, New Providence, NJ, July 26, 2011, 20:39
 Rookie

I need help diagnosing an issue with an 01 Nissan Sentra 1.8L GXE. Many thanks in advance!

On a cold engine, the engine sputters and stalls once I put into gear.
On a warm engine, lack of power and hesitation under ~2k RPM. Gets worse the more I push the throttle.

No idle issues in P or N ever. No idle issues when warm in any gear. No unusual noises. No impact on MPG.

Has been like this for at least 1k miles.

No codes.
MAF and ECM replaced 7 months ago. MAF just cleaned.
New filter (Purolator)
New spark plugs (NGK Iridium)
OBD II readings seem reasonable for throttle position, Coolant temp, and air temp.

Vacuum test shows: rapid fluctuation 18-21 at idle, rapid fluctuation bet. 19-23 at 2k RPM, crazy fluctuation 13-22 at 3k, and a steady 21 at 4k. Video: http://www.youtube.com/watch?v=msCholgxizA

At first I thought was a vacuum leak or a faulty EGR diaphram, but the vacuum test makes me think I have a broken/sticky valve... Please advise.

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  • Answer #1

    patrick mannion from Greg Solow's Engine Room, July 26, 2011, 22:17
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     Master

    You are the first person in 10,000 questions I've answered that put a Youtube link to show results of their tests. Its hard to say what is going on. Look for vacuum leaks, sometimes misfire code criteria is pretty high before a fault code is actually set, my suspicion if it were an Infinity Q45, some VW and Audi, or Lexus RX300 ,and Camry or V8 Jaguar would be to say a coil is breaking down even thought the misfire code is not set. I wonder could you have a dirty injector that once the engine warms up the fuel atomizes better and makes the engine perform better. Nissan Maxima and Pathfinder had problems with Mass Air Flow meters and many after market replacements were junk. Do you have a workshop manual. Alldata is best. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
    Your intake manifold vacuum is good!If you drove the car with a vacuum gauge taped to the windscreen with the engine under constant load (not wide open throttle ) the vacuum readings would be smoother.

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    Rostasteve, July 27, 2011, 09:10
     Rookie

    Thanks for replying Patrick. I've had coil issues on my BMW and this doesn't feel like it (there's no jerkiness typical of a misfire). I checked coils for corrosion when changing plugs and they looked good. My MAF is aftermarket (made by Altrom) and has worked fine for the last 6 months FWIW. I have the Nissan workshop manual and it's nearly useless.

    And I forgot to mention, I run seafoam in the gas tank every 3-4 months. Just did the seafoam crankcase and intake treatment too. It idles smoother, but the hesitation persists.

    My initial suspicion was a leaky or stuck open EGR as the symptoms are similar (power loss at low rpms and at WOT). Unfortunately I can't hook the vacuum up to it to test b/c it's hardlined into the intake manifold. Is this possible? probable?

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