Annoying surging problem

[Bolt]

I have a surging which comes and goes. My car surges between 1500 and 1700 rpm in 5th gear.

Here is my mods when it started surging:
Bellenger headers
Corsa exhaust
Steel cats
Paxton super charger

This surging is not consistent and is very slight. It is more of an annoyance.

Could it be?
Front oxygen sensors need replaced?
The vacuum control unit for the Paxton SC?
Spark Plugs?

Should I put on a different fuel control unit like a VECII and eliminate the vacuum fuel control unit which comes with the Paxton unit? Should I run both?

 

[Racer Robbie]

In my opinion you should not be running at such a low rpm with the mods you have. I would drop down a gear into Th. I run Th up to 75 mph and then 5th. I have never used 6th. The car surges in 6th at 80-85 mph.

 

[Jack B]

In my opinion you should not be running at such a low rpm with the mods you have. I would drop down a gear into Th. I run Th up to 75 mph and then 5th. I have never used 6th. The car surges in 6th at 80-85 mph.

It could very easily be the closed loop operation, where the PCM hunts for 14.7. All cars do it to a certain degree. It is just magnified at low rpm's and high gear ratio's.

 

[Landman]

What is surging??

 

[plumcrazy]

get a VEC2 or 3 unit on it

 

[Bolt]

My surging comes an goes . So far I found a pinched O2 wire. I changed out both front O2s. The major surging disapeared. 250 miles later I blew one of the new ones out. I'm going to try O2 simulators. I still get a minor surging at 1700 rpm. I think the computer is adjusting lean/rich Eventualy it get's it. Then I have no surging till I stop the car and shut off the engine. Now I'm being fussy at this point. the surging is monor now and most people would not feel this. Remember I'm supper charged. That may be part of it too. I kind of dout that at this point. That is a whole other post.

 

[Landman]

Sooo, what is surging??

 

[Bolt]

Sooo, what is surging??

When cruising at one speed and holding the gas peddle at one position the car acts link the gas peddle is being pushed a little then leave off this pulses quickly. I makes your ass slide front and back quickly. Very annoying. The surging varies depending on the intensity of the problem. I hope I was able to explain this good enough.

 

[Landman]

Thanks for the response. I was wondering because sometimes at lower speeds my car carries a higher rpm even when I'm completely off the gas. Coasting will stay around 1,500rpm's until I put the clutch in to stop. It only does it once in a while. I didn't know if that was surging, but it doesn't sound like it.

 

[dun4791]

What kind of wires do you have? My guess is you have 1 bad plug wire.

 

[PhoenixGTS]

When cruising at one speed and holding the gas peddle at one position the car acts link the gas peddle is being pushed a little then leave off this pulses quickly. I makes your ass slide front and back quickly. Very annoying. The surging varies depending on the intensity of the problem. I hope I was able to explain this good enough.

Sounds like bucking from non-syncronized throttle bodies, but that is usually a first gear problem. Never hear of a t-body buck in a higher gear.

 

[Bolt]

What kind of wires do you have? My guess is you have 1 bad plug wire.

New MSD wires. I was suspecting this. I should try another brand of wires.

 

[Bolt]

Thanks for the response. I was wondering because sometimes at lower speeds my car carries a higher rpm even when I'm completely off the gas. Coasting will stay around 1,500rpm's until I put the clutch in to stop. It only does it once in a while. I didn't know if that was surging, but it doesn't sound like it.

Your problem could be the idel position modulator.

 

[Racer Robbie]

You need to get a good scan tool and check for stored codes. Then check the sensors for proper values with the scan tool. Otherwise you are just changing parts and wasting money.

Robbie

 

[99 R/T 10]

New MSD wires. I was suspecting this. I should try another brand of wires.

Yes, try AB's wires, best quality wire out there!

 

[vprtech]

I believe the surging you are describing is the result of the pcm moving the mixture back and fourth. This can happen on stock vehicles, but is usually most noticeable on vehicles that have headers, and / or larger than stock camshafts. As most people who have put a decent wideband on there vehicle can confirm, the stock pcm moves the mixture slightly above and slightly below 14.7 afr. The main reason for this is to optimize catalytic converter efficiency. Catalytic converters need a slightly rich mixture (less oxygen) to reduce NOx, and a slightly lean mixture to consume CO and HC’s. It’s this back and forth mixture swing that makes the catalytic converter work most effectively.

Normally, this back and forth shift is not enough to really feel much to most drivers. When you modify the exhaust or camshaft several things can happen. First moving the O2 sensor can change the time it takes the pcm to measure a commanded mixture change at the O2 sensor, thereby affecting the response time, the end result is the pcm makes larger corrections in the pulse width and the fuel mixture changes more dramatically and you feel it when you are driving as a surge. This is because when the mixture goes too lean, you lose a significant amount of engine torque.

The second thing that can happen, is that with some exhaust headers and with more aggressive camshafts with high overlap, you can get mixture dilution. The end result is that the stock O2 sensor cannot accurately determine the mixture strength, and the ecu will over correct the pulse width before seeing an expected voltage at the sensor, causing a surging condition.

If anyone has any questions about this problem, and what can be done to correct it, please don't hesitate to call me.

- Chris 310-841-6996

www.dcperformanceinc.com

 

[Bolt]

I believe the surging you are describing is the result of the pcm moving the mixture back and fourth. This can happen on stock vehicles, but is usually most noticeable on vehicles that have headers, and / or larger than stock camshafts. As most people who have put a decent wideband on there vehicle can confirm, the stock pcm moves the mixture slightly above and slightly below 14.7 afr. The main reason for this is to optimize catalytic converter efficiency. Catalytic converters need a slightly rich mixture (less oxygen) to reduce NOx, and a slightly lean mixture to consume CO and HC’s. It’s this back and forth mixture swing that makes the catalytic converter work most effectively.

Normally, this back and forth shift is not enough to really feel much to most drivers. When you modify the exhaust or camshaft several things can happen. First moving the O2 sensor can change the time it takes the pcm to measure a commanded mixture change at the O2 sensor, thereby affecting the response time, the end result is the pcm makes larger corrections in the pulse width and the fuel mixture changes more dramatically and you feel it when you are driving as a surge. This is because when the mixture goes too lean, you lose a significant amount of engine torque.

The second thing that can happen, is that with some exhaust headers and with more aggressive camshafts with high overlap, you can get mixture dilution. The end result is that the stock O2 sensor cannot accurately determine the mixture strength, and the ecu will over correct the pulse width before seeing an expected voltage at the sensor, causing a surging condition.

If anyone has any questions about this problem, and what can be done to correct it, please don't hesitate to call me.

- Chris 310-841-6996

www.dcperformanceinc.comhttp://www.dcperformanceinc.comhttp://www.dcperformanceinc.com

Great reply! I'll be calling you.

 

[Bolt]

Yo People And Chris. I Fixed My Surging Problem. Reading What Chris posted Made Me Move My O2 Sensors Closer To My Head And On The Belanger Header There Is Two Places To Put The O2 Sensor. One Near The Collector And The Other Near The Head In One Of The Down Tubes. I Moved Mine T0 The Single Down Tube And Now The Car Is Running Perfectly. It Runs 10 Degrees Hotter But That Is A Small Sacrifice.

 

[RedSrt007]

So your sending a/f readings to the pcm based off the one header tube?

-Red

 

[Bolt]

So your sending a/f readings to the pcm based off the one header tube?

-Red

Yea, It's kind of working. Not exactly what I would think would work.

 

[ViperJohn]

Chris (vprtech)

Based on your post, I took a look at where the front 02 sensors are located on my B&B headers. They didn't seem that far away, although each sensor is only reading 1 cylinder per side. What has been your experience with the position of the 02 sensors on these headers? Where would you recommend relocating them to improve the surging issue?

On a different note, can the rich to lean curve be adjusted in the PCM to better suit the new 02 sensor location?

Thanks, John