Hesitation At Top End

[Charlie 0 1 Cars]

Gents,

 

Another problem has reared it's head - after fixing the various running issues you have helped me with, I've been driving the car more regularly.

 

If I take it to the top end of the rev range in 2nd or 3rd, there's a strange hesitation/characteristic. Basically it feels as if the car suddenly get a surge of power, then drops back to normal. This repeats until I change gear, and then starts again once I hit the top of the rev range again.

 

It's definitely not the rev limiter as no where near that point in the rev range.

 

Could it be a symptom of the vacuum advance playing up? I fixed the hose to this, and think it hasn't been connected properly for about 4/5 years.

 

As always, your advice is much appreciated.

 

Regards,

Charlie

[Tom Fenton 1,524]

When at full throttle there is no vacuum in the inlet and so the vac advance isn't doing anything. The vac advance pulls the timing up at light loads/cruise, this gives better mpg as you can effectively use less throttle to maintain the same speed.

Its worth checking that the diaphragm inside the vac advance isn't split, this is a common fault, by sucking on the pipe to it. There should be resistance- if there isn't and you can suck air through then its split. However this isn't your issue.

I have a similar problem with my 1.6 GTI, I'm planning to check the fuel pressure as I suspect it may be the pump is tired and cannot maintain pressure under engine full load.

[Thijs_Rallye 86 4 Cars]

Check if there is oil in the distributor. You'll have to take the plate out below the rotor to have a good look.

 

Is it also temperature related? (I.e. that it doesn't occur when the engine is cold.)

[Charlie 0 1 Cars]

Thanks for the replies guys -

 

Tom, I'll keep an eye out for the results of your fuel pressure check!

 

Thijs - I will check distributor this weekend. I'm not particularly keen on taking the car up to close to the redline when it's cold... I guess I could try it the once.

 

Regards,

Charlie

[Thijs_Rallye 86 4 Cars]

Yes I can understand. Those aluminium heads and blocks don't like being put through their revs as they are cold. The engine does not have to be ice-cold, but try to test it in after the first 15 minutes of driving or so.

 

Another thing you can do with a warm/hot engine though is to keep a close eye at what rev's your issue occurs. Keep a close eye if you detect that the revs @ the issue start to drop. I.e. first at 5500, then maybe at 5300 etc etc.

 

We had a sort of similar issue at our trackday car which took us two "days" to figure out since the problems got worse troughout the sessions in the day. It appeared to be the oil leak as stated before. It felt like a soft-cut rev limiter. You notice the engine wants to go but is held back.