Won't Rev Freely Above 5500rpm

[Dan57 0]

I have a problem that has been bugging me for a while now. My 1.9 Gti 8v reaches 5500rpm then coughs and splutters, as though the rev counter is cutting in. I have new leads and plugs, ignition amp. I did an engine tune yesterday so the ignition timing is spot on, cam timing is good and I set the CO at 0.8%. If I free rev the engine it will rev right through to 7k (given inaccuracy of rev counter), it only seems to be under load but even easing of the throttle doesn't make the spluttering any better until the engine revs fall below 5500rpm. I have checked all the usual stuff, tps, throttle valve, breathers etc. My only concern is the AFM which reads 100 ohms closed, reaches about 600 ohms almost half throttle but then doesn't increase above that. (My figures show it should read 1K ohm.) I don't think this is the cause as surely this would make the injection think it is just on half throttle and just lack a little power. No??

 

This problem is starting to get to me as it cuts in right in the power band and I am gagging to unleash it's potential. Other than this fault I cannot fault anything else, the engine pull surprising well up to this point.

 

I have searched but cannot find any conclusion only to check what I already have.

 

Any ideas? I'm stuck.

[inferno 1]

spark plugs? mine started doing the opposite this morning... revs crap to 5k then nicely to 7.5! service time me thinks, its intermitant though in this case.

[Mikey G 3]

Do you know of another good AFM you can try?

 

As said also check sparks, maybe a weak spark on the top end could be a problem as well as a lack of fuel.

[Guest rich1977]

my Mi16 did this few months ago when the dizzy was buggered swapped the dizzy and never had a problem in this area since.

[taylorspug 7]

The AFM doesnt sound right so id try a decent one to eliminate that first. If not the ignition amp would be a good thing to check.

[chris1986 1]

when i had one do this, take the plug off the throttle position sensor try it then. if it works with out the connected try a new sensor

[Dan57 0]

Thanks for the advice Guys. I took the dizzy out yesterday to cure an oil leak from the seal, I noticed small amounts of corrosion on the cap ends. (The bits the HT leads plug onto.) I cleaned these up and it will now rev to 6k before doing it. I think I am now on the right road so will clean up coil terminals and replace the cap so fingers crossed.

[Dan57 0]

UPDATE:

Well!! It's been a while but eventually managed to get to bottom of the problem today. Well ish anyway. After replacing all of the ignition system and the fault still aparent I resorted to reluctantly disconnecting the rev limiter and this has now cured the fault completely. I can only assume there must be a fault somewhere with the signal to the ecu?? Maybe time to consider an aftermarket rev limiter and shift light...

[Henry Yorke 269 3 Cars]

Glad you have sorted it and thanks for posting an update. It helps people searching in the future