Rebuilt the engine, it fired up but....

[Quick Nick]

The first time the engine has started in a while and it fired up fine however instantly revved up and hit the limiter.

Cut the engine and tried again, and again zipped straight up to the redline and bouncing off the limiter.

Not sure what it is, gas pedal wasnt down and I'm thinking software issue but any help from you guys would be much appreciated..

 

[markkram]

You may need to include a little more info if you want a quick reply.
Type of engine / standard or modified induction / management etc.

 

[Gandi69]

Air leak from the inlet could be the issue too but more info needed

 

[Quick Nick]

Ahh apologies. Its a ph2 172 2.0 Sport. Completely standard on all levels, even got the standard air box and filter.

as soon as the engine started it fired up and gunned for the redline and stayed there. Not sure how it is possible, the butterfly valve in the inlet wasnt really opening (was flickering a little), yet the engine was still revving and staying up there.

I hope this helps, we jsut thought it was a software problem or something..

 

[Black Phoenix]

Disconnect the sensor from the accelerator pedal (I think that in the 172 it's an electronic one, not cable accelerator). Then start the car again.

 

[TheEvilGiraffe]

I'd suggest an (enourmous) air leak post throttle butterfly. Take the inlets off and make sure it's all OK under there !

 

[Quick Nick]

That is interesting I didnt spot anything when I was looking through the inlet, is this a common problem and is there an obvious area where this leak may be occuring from?

 

[Quick Nick]

Thanks black phoenix by the way I believe the throttle cable blug is a little one just by the black box on the throttle body, I unplugged it and still had the same problem..

 

[TheEvilGiraffe]

If it's letting in enough air to sit at 7k+, I would presume (probably wrongly haha) that there is going to be a rather noticable sucking noise.

It shouldnt take you 15 minutes to unbolt the TB, the inlet, and make sure everything is as should be.

Where are you based dude ?

 

[Silent_Scone]

could it not be something to do with the pedal assembly? I'm not familiar with this electric throttle shite

 

[Black Phoenix]

could it not be something to do with the pedal assembly? I'm not familiar with this electric throttle shite

I still say that it's the throttle sensor assembled in the throttle pedal.

 

[Quick Nick]

The throttle sensor in the throttle is working we read the ECU data and they are reading correctly in regards to the throttle positions.

The MAP sensor is reading 1,180 with the ignition on and the engine off, however it should read zero. When we unplug the MAP sensor it stops revving, and we can hold it at required revs manually using the throttle, tho obviously when we let off the throttle the engine stalls.

This would suggest the timing is either out (which I am sure we did correctly with all the neccessary locking/timing tools) or the MAP sensor is fcuked.

Giraffe, I am in North London/Radlett area.

 

[rampantreaper]

Timing done correctly. Magic words. Won't cause this problem tho I'm sure

 

[Quick Nick]

If the timing is wrong would it play with MAP sensor readings to the point where the map sensor would be reading an extra fuel requirement? If so then that would explain it however we were so careful with the timing I would hate to take it all off and do it again and then find it was right....

 

[Sean6545]

Map sensor wont cause the engine to rev up. Have you looked at the throttle valve when it revs up? Is it wide open?

 

[MicKPM]

If you suspect a TB issue remove the track and see what the throttle plate is doing... holding a 7k idle would most likely see it wide open. Personally, I think its nothing more than an inlet leak.

Check the sensors are correctly pushed in to the upper inlet plenum as the MAP and ATS can cause this kind of problem. So can the brake servo line if its not correctly fitted to the rubber sleeved section. Have you had the upper plenum off as these can sometimes get caught on the plug leads meaning it doens't seat correctly? If the above is 100% correct then its most likely going to be an inlet gasket and something like WD40 will help you trace it.

Mick

 

[Quick Nick]

Thanks for the advice guys, I will be back on it during the week and so will report on my findings, I alsmost came to the conclusion the timing was out so was going to re-check this, but will also look into the above and see what I can find out.

N

 

[sideways danny]

it will be the teardrop shaped rubber gasket under the inlet plenum missing or dislodged