mx5cartalk.com

I'm still having stumbling problems on the track on hot days.
I'm wondering if there is any point in installing a more beefy Walbro high output fuel pump on a stock naturally aspirated car? Will it make it run "rich"?
Alternatively I would like to give it to a mechanic to solve the problem any recomendations?
I just want to track the car all day and shift only when I hit the rev limiter its not a big ask.

What octane fuel are you using? The knock sensor could be pulling the car back...

What temp plugs are you using?

Have you ever run any injector cleaner or the like through the fuel system?

....It could be many things other than the fuel pump. I don't hear anyone else here having to buy higher flowing fuel pumps due to stumbling issues.

fuel filter?

Wun,
I tried to have a look at your garage to check your specifications but couldn't see very much on there. Apart from checking the usual stuff as posted above, please provide the following information:
Have you run diagnostics to see if there is anything wrong with factory sensors (etc etc)?
Have you dyno-ed your car to see if you can replicate the "stumble"? This will provide some useful insight especially in regards to air to fuel ratios.
Do you have a stock fuel system (i.e. injectors, fuel pump, regulator, etc)?
What (if any) modifications have you made (other than that in your garage) to your MX5?

what year model is the car? what exactly is it doing? mine is a 99 and used to cut power on and off at the track turned out to be a loose cam angle sensor plug.. then another time it was some what less violent and more like the car was loosing timing on and off and it turned out to be a sheared/dying altenator/lower cam gear key on the crank shaft.. not a pretty problem.. check and see if you alternator pulley wobbles alot

Depends what exactly you mean by stumbling, i did have problems with strange flat spots/missing under hard acceleration (in a non MX5), that turned out to just be utterly rooted spark plugs & Leads .

Might be totally different to what you are getting, but its an idea

irwin83r wrote:what year model is the car? what exactly is it doing? mine is a 99 and used to cut power on and off at the track turned out to be a loose cam angle sensor plug..

Having been in the car at the time, that sounds pretty accurate.

It would stumble then lose all power, only at high temp though. A few minutes of barely idling and it came good again.

Wun, I wouldn't go throwing aftermarket bits at it until you verify what is wrong. Factory setup should run fine, as most people's cars did that day.

I have NB8B:
Fuel filter has been replaced, pump has been replced OEM.
Leads are new 8.5 magnacore.
Both coil over plugs have been replaced.
Sparks are Iridium NGK BKR5EIX-11
Fuel is premium unleaded (shell)
All above parts have been replaced with less that 10,000 km

I doubt is cooling with the engin:
new thermostat
new rad cap
new 50mm PWR rad
AC removed
on distilled water
Temp guage in car never more than half on the track.

Sorry for the nube question is this part a cam angle sensor??
http://www.mx5parts.co.uk/product_info. ... ts_id/1173

And what and where does this part go?
http://www.mx5parts.co.uk/product_info. ... ts_id/1379


Thanks for all the help, still trying to touble shoot it my self before I hand it to someone to fix...

At idle the fuel pressure for 94-96 models should be 216-264kPa mine was 175 , time to upgrade! I brought a Walbro low pressure 255 l/hr fuel pump went in and works fine.
Ted

Sorry for the nube question is this part a cam angle sensor??
http://www.mx5parts.co.uk/product_info. ... ts_id/1173

Yeap, goes on the rear of the valve cover

And what and where does this part go?
http://www.mx5parts.co.uk/product_info. ... ts_id/1379

That's the crank angle sensor. It fits on the front of the engine near the bottom pully on the exhaust side of the engine. Right near where your A/C compressor used to be.

My problem is solved thanks for all the help.

I got a new cam angle sensor.

Went to Wunton thrashed the car, no problems.

wun911 wrote:
... on distilled water

...

And coolant (the green stuff) or similar, I hope?

Alloy components do not like plain water.

wun911 wrote:Fuel is premium unleaded (shell)

My car still coughs whenever I even drive past a Shell station.

Yeah I used premium mobil 1 that track day, seems to be good stuff.

I like the distilled water for the track but I'll put some AF in it later.

wun911 wrote:Fuel is premium unleaded (shell)

i'd rather use biodiesel from a fish n chip shop than shell fuel