Help! I have an intermittent stumble at 4000 RPM. The car will jerk as if it has hit a brick wall for a split second and then continue on as normal. The strange thing is it only happens randomly and I do not have any check engine light. Does anyone have any idea? The dealer "can't find anything wrong" and they have replaced the O2 sensors, plugs, wires and re-flashed the ECU. Could this be a bad BOV? Thanks!
Killer Stumble at 4000 RPM
- Thread starter adzamzoom
- Start date
Sounds like you've experience hesitation my friend... Does it do it only when you're hard on the accelerator and then off it fast when you're shifting? 
Get your ECU flashed or an Air/Fuel controller. There's a specific thread about this on the forums.
Get your ECU flashed or an Air/Fuel controller. There's a specific thread about this on the forums.protege3690
Member
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- 2003.5 MSP #290
Sounds like hesitation and/or fuel cut....... ssafc, unichip, or full standalone and a FMIC
It hapens, as you have stated as well as lifting lightly off the gas to avoid hitting slower trafic and if you stay on the gas above 5000 RPM I only get a mild hesatation at 3500, 4000, and 4500 RPM. I have a stock ECU and it was flashed 2 days ago at the Mazda dealer along with an o2 sensor
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- 1989 RX-7 GXL Blaze Red
fuel cut. use the search and you shall be rewarded
You rock! Wish I read this before droping $720 at the dealer :O(
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- 1989 RX-7 GXL Blaze Red
even after spending that you'll most likely have the fuel cut still.
hornsfan10609
Certified Mazda Tech
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- 2003.5 Mazdaspeed Protege x2
What did the dealer do to the car?
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- 1989 RX-7 GXL Blaze Red
The brick wall at 4k rpms is your car going into open loop and maxing out the injectors. When your duty cycle hits 100% from the PCM it cuts spark. Not fuel. Everyone calls this fuel cut, but it is actually ignition cut. Anyone who disagrees with me can put a scope on pins 74, 75, 100, 101 and pull their WGA line and watch what happens when they overboost.
As soon as ignition is cut the MAF isn't reading nearly as much air and the car can continue on its merry way. There is actually a little spike in boost just before the wastegate opens and can cause the car to reach spark cut. The first couple hundred rpm of open loop are also programmed to be excessively rich to safeguard against negative short term fuel trims. I've seen my car go into the 9s completely stock.
If your car is completely stock the most likely reason you would hit cut is because your WGA is bad. Take the vacuum line from your WGA and follow it back and pull it from the T and blow in it. If you can blow through your WGA, it needs to be replaced. The diaphragm is rubber and over time will lose its seal with the housing.
I had this happen around 50k miles and replaced it with the ATP one from PG and it's been solid for the past 26k miles.
As soon as ignition is cut the MAF isn't reading nearly as much air and the car can continue on its merry way. There is actually a little spike in boost just before the wastegate opens and can cause the car to reach spark cut. The first couple hundred rpm of open loop are also programmed to be excessively rich to safeguard against negative short term fuel trims. I've seen my car go into the 9s completely stock.
If your car is completely stock the most likely reason you would hit cut is because your WGA is bad. Take the vacuum line from your WGA and follow it back and pull it from the T and blow in it. If you can blow through your WGA, it needs to be replaced. The diaphragm is rubber and over time will lose its seal with the housing.
I had this happen around 50k miles and replaced it with the ATP one from PG and it's been solid for the past 26k miles.
hornsfan10609
Certified Mazda Tech
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- 2003.5 Mazdaspeed Protege x2
My car would hit 9 AFRs all day on the stock tune.
Jason94Cobra
Member
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- 03.5 MSP and 94 Cobra
My exhaust manifold has a couple of nice cracks in it and the WGA could also be contributing... well not currently because now there is a giant hole in the back of the block... but before it did the same thing....
hornsfan10609
Certified Mazda Tech
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- 2003.5 Mazdaspeed Protege x2
I installed an FMIC and SSAFC in my car and it runs like it should so that's what I recommend and was recomended to me. Also properly gapped correct plugs, good coil packs and Milennia S PCV.
7urdF3rguson
Member
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- 2003 mazdaspeed protg
I'm having the same problem. The kicker tho is I have a ssafc, brand new ATP wga, and fmic with relocated maf...
7urdF3rguson
Member
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- 2003 mazdaspeed protg
So I talked to Mark from split second. He recommended that I check the vacuum line running to the unit. He said 90% of complaints are due to that line. However my issue is that other 10%...
