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Old 07-01-2013, 03:10 PM   #1
akatagyourit
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2001 zx3 slight hesitation/surge under light accel

I'm back everyone. Been looking into the car trying to figure stuff out. I have recently started having a slight surging feeling while driving down the road under light acceleration, usually 10-50% throttle while driving. We have replaced the spark plugs with autolite 104's gapped at .050. Plug wires replaced. My buddy hooked his diagnostic reader up to the car and the fuel trims look perfect, spark advance, fuel pressure, everything looks spot on. Makes us think its a mechanical failure coming and going under the right conditions. The car has 166k miles. The stock airbox was removed and a cone filter put onto the maf sensor, not sure if the pcv hose from the airbox to valve cover being open makes a diff or not. Also cleaned the maf sensor and iac while I was working on it. Any other ideas that might fix this?



Last edited by akatagyourit; 07-01-2013 at 03:11 PM. Reason: Updating title
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Old 07-01-2013, 03:26 PM   #2
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......maybe the fuel pump
A known focus problem
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Old 07-01-2013, 04:15 PM   #3
akatagyourit
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Fuel pump is brand new and I swapped out the assembly with the newer style that is supposed to fix that issue. Issue happens regardless of fuel levels.
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Old 07-01-2013, 06:19 PM   #4
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Changed coil yet? Common to do that on these, the symptoms could be that easily. Pull it and look close for very small cracks if so, dead or dying. Look close at coil connector wires too, they are often cracking right at the connection.
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Old 07-01-2013, 10:09 PM   #5
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I was going to suggest a coil also. Mine ran smooth if I granny drove it, but if I got on it mid to heavy throttle I'd get a studder or shudder and no codes. That and it was intermittent. Then one day I just lost #3. Replaced it and magic. It always ran good 4000 rmp to redline, but smooth everywhere now.
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Old 07-02-2013, 11:04 AM   #6
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Car has 166k miles on it. I've barely looked at the coil, but my buddy and I were figuring it was spark or fuel. Since fuel pump, assembly, and filter have been replaced it only leaves injectors and regulator, but i figured i'd have more problems than I am if it was those. Plugs and wires were replaced, just not the coil. So next question, is there a specific coil pack that anyone recommends on rock auto to order? This car is just a daily driver, just trying to get it running better and get the mpgs up.
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Old 07-03-2013, 12:08 AM   #7
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The pcv hose to the valve cover is unmetered air and will cause surging, as will the cone filter on the mass air flow sensor.
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Old 07-03-2013, 06:41 AM   #8
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Quote:
Originally Posted by jdmzx5 View Post
The pcv hose to the valve cover is unmetered air and will cause surging, as will the cone filter on the mass air flow sensor.
This was something I was hoping someone would answer. By design th pcv system is always introducing unmetered air into the intake. One side is on the airbox before the maf. By design this car is supposed to take in unmetered air. Can anyone confirm?
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Old 07-03-2013, 08:16 AM   #9
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Yes, it is by design,to take in metered air, that is why the pcv fresh air hose is just behind the maf. It is metered. If you disconnect it and plug the hole it is then allowing unmetered atmospheric air in, and your fuel trims will show this.
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Old 07-03-2013, 08:36 AM   #10
akatagyourit
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Quote:
Originally Posted by jdmzx5 View Post
Yes, it is by design,to take in metered air, that is why the pcv fresh air hose is just behind the maf. It is metered. If you disconnect it and plug the hole it is then allowing unmetered atmospheric air in, and your fuel trims will show this.
Incorrect on my focus. Although I can't say if this setup is entirely stock on the my zx3, but the the air box has a port on the bottom or side where the hose from the valve cover goes to the airbox. All of this connects in before the MAF sensor. This is introducing unmetered air, not metered air.

The hose for the pcv system is the one illustrated in red in the photo below.


This hose is connected in before the MAF sensor to the valve cover. Which when used in with the pcv system the vacuum from the intake should pull air through the motor from the valve cover. So it is still pulling unmetered air into the system through this setup from Ford. Unless i'm mistaking this for something else and i'll glad be proven wrong.

Last edited by akatagyourit; 07-03-2013 at 08:37 AM. Reason: forgot some lines
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