Revs dropping

[dan182]

Hi there recently fitted piper cam lighten fly wheel when driving and its a warm day the revs keep dropping and picking back up again if you floor it perfect but if your driving alone ,at 2000rpm it stutters and gets worse the more you drive is there anyway to check fault codes?

[kwijibo_coupe]

Does the rev counter play up too?
Sounds to me like it could be the coil starting to fail.

[dan182]

No rev counter seems fine its almost a juder

[GR40]

Did you remap the ecu or are you running on stock map?

[dan182]

It had a chip in the ecu but that was for the r1 charger but thats it

[GR40]

What are the specs of the cam? If you have gone too aggressive with the duration of the cam then this is to be expected, especially with a lighter flywheel! You may need to remap the ecu to match your cam.

[dan182]

Its a schrick 275 but at idle engine perfect and it dosent do it every journey

[GR40]

I am starting to suspect the blue temperature valve that connects to the ecu. When was the last time you changed that? They are known to go bad over time. If its faulty your mixture at idle will change drastically. Its worth replacing, they are dirt cheap. Also, did you time the car after you replaced the cam? Did you time it with the blue temperature valve disconnected? If not timed that way it may be throwing the ignition too far out.

[dan182]

Didnt time it at all but surly it would run like a pig all the time?

[GR40]

Actually no it wouldn't. Since the cam is designed to work with this engine it would need some adjustment but would work even if it's a bit off. In General when you are changing a cam you have to adjust timing and fuel for the simple fact you have changed the duration that the valves stay open and as a result the amount of mixture that goes in and out the cylinders. So what I am thinking is that the car is fine as long as the engine is cold but when it reaches operating temperature the ecu changes its timing and fueling according to the new chip and that is when you start bogging and rev haunting. That being said it could be 100 other things that the car bogs down I am just throwing some information out there that might help.

[dan182]

Where do you plug a g40 see if there any faukt codes?

[GR40]

I think there are 2 cables under the dash at the driver side. There are supposed to blink the code if you connect a light to them but I have never done it so I am not sure of it! You may find the correct info in here somewhere if you are willing to spend some time searching!

[hayesey]

check the FAQ sections, there's info on this in there and a free tool that'll read the codes off a g40 from a laptop if you have a vagcom type lead.  however, the diagnostic system on a g40 is not like a modern car, it's very basic and pretty limited in it's usefulness, more than likely there will be no codes.

[dan182]

Just checked fault codes only one is 00521 co potentiometer g74 no signal any ideas ?

[GR40]

that is the cubic sensor right before the throttle body
looks like this
http://www.bar-tek-tuning.com/cosmoshop/pix/a/n/1290785646-24110.jpg