MX5Ireland

Wondering can anyone shed any light on this. the engine is running well and will rev all the way to limit in neutral and in 1st gear, however, the car will only rev to 5000rpm in 2nd, 3rd etc. When it reaches 5k it makes a popping, pressure release type sound and loses power. has this happened to anyone else or does anybody know what could be causing it?

It's a mk1 1.6 btw

NA engine? Any mods?

Na engine no mods except stainless steel exhaust with cat. Could this be a timing issue? I have only just bought the car but didn't cop this on test drive

Could the cat be blocked?? Should rev out to 7000rpm

Yeah I did think of that but the engine behaves normally until 5k and the revs stop at exactly the same spot every time. Kind of like a limiter.... If the cat was blocked surely it would be down on power

Maybe the clutch switch or the neutral switch in the gearbox would trigger a lower limiter?
Nico

Pull out the spark plug wires and see if there is oil/water in the plug wells.
May as well check the spark plug gaps while you are in there. Theres a chance they are possibly gapped to wide and spark is being blown out at higher revs.

If you havent changed them already they are def worth changing : the fuel filter, spark plugs, spark plug wires
Might be worth checking the timing too.

Are you sure your ECU is the original? Its located under a metal plate beneath the carpet on the passenger side footwell.

I am not sure about the ecu but I will have a look. The plugs and leads are new so there shouldn't be an issue there.

Could this be a problem with the coolant temp sensor? Also someone on another forum seemed to suggest a faulty idle speed control valve.... The car is idling fine and raises when ac turned on etc. Surely that doesn't affect higher rpm?? I have ordered an led to do diagnostic anyway maybe that will make it clearer. Other than that I thought maybe a dodgy coil pack?

Thank you for suggestions so far btw

Ok so I got the led today and did a check. I got back 3(cam angle sensor) and 25(prc solenoid valve). There is a walbro fuel pump in the car which I forgot to mention before. Would a cas from a breakers be advisable?

Maybe first check if ignition advance is set properly at idle with a stroboscopic lamp, then check CAS wiring, and possibly try with a known good CAS if you can borrow one? Robert should have a few of them in stock anyway
Nico

Most likely Fuel related. Check throttle is opening fully and check fuel pressure also.