Hi I've built a haynes roaster with a 1.6 mx5 engine (1995 90hp one) car goes great but it sometimes struggles to go past 500rpm after 10 minutes of driving. I've read this could be the coil packs or one of them so I thought I'd hook up a gauge to measure the fuel pressure.







Went out to test it and low and behold the power stutter returned after 10 minutes of driving. Fuel pressure remain solidly at 40psi (3bar), after a little thinking as I was driving I thought this must be coil pack related then but then thought what happens if i turn the lights off during a stutter ( I have been driving around with the lights on for safety/visability). Well the car took off like a rocket when I turned off the lights and when I turned them back on the car started struggling again. Now is this coils, the alternator, or could the tiny battery be the issue. I'm pretty sure the battery does nothing really when driving other than charge, car always starts first time so does that rule out the alternator. SO coils then?!?!:confused:

I have always noticed that if I turn on the lights at idle the revs drop momentarily. Don't really want to spend any money on this engine as I'm getting a 1997 JDM 1.8 mx5 engine ready to drop in sometime this summer.

Help!

esit: oh and I have swapped out the ht leads as well, alt has a new belt on it and might need a little tightening up as it squeals a little on a hot start.

[Edited on 18/5/15 by ctwv50]

have you got a volt meter ?.
could be volt drop in the wiring to the coils,alternator down on output,dodgy earth,coils are a weak point but i would check the other things first.

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Originally posted by theconrodkid
have you got a volt meter ?.
could be volt drop in the wiring to the coils,alternator down on output,dodgy earth,coils are a weak point but i would check the other things first.

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put it across the battery and run the engine,lights on etc and see what happens,shouldnt matter if you are moving or not.

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Originally posted by theconrodkid
put it across the battery and run the engine,lights on etc and see what happens,shouldnt matter if you are moving or not.

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Possibly a bit 'out of the box', I'm almost thinking bad earth to be honest, you switching the lights on is sending 12 volts where it shouldn't be going and one of the sensors is being affected?

If its electrical.. check the earths... first time everytime.

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Originally posted by loggyboy
If its electrical.. check the earths... first time everytime.

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So this morning I had a look at the coil packs and they seemed fine no bad connections or anything, removed the fuel pressure gauge and then fired it up, then I turn it off and put the spark leads in the correct order! Measured the voltage at the battery 14.4v turned on the lights 13.5v, rear fog and main beam and I was dipping into 12v territory. Thanks for the tips everyone my finger was hovering over the "buy it now" button for some coil packs last night, I did check the earths, but I was paranoid about good earths when wiring up the engine and the earths were solid.

Going to take the 1.8 alternator off the 1.8, change the pulley on the alt or the 1.6 engine pullies and see how I get on. No money spent and a easyish solution.

[Edited on 19/5/15 by ctwv50]

[Edited on 19/5/15 by ctwv50]

All fixed, managed to get the crank pulley off this morning and fit the 1.8 pulleys, this evening I got the 1.8 alternator in and everything back in the engine bay including fixing that coolant leak from the rotted 6mm pipe I disturbed, it was going to go eventually anyway.



I now have a steady 14.4v with the lights on or off which is much better than before. 1.8 alt is bigger and needs a larger ring connector which fortunately I had. Ribbed belt is a better design too so it solves the v-belt 1.6 issue aswell.

Nose on in the morning and then fit the 300lb springs and take it for a drive I guess!

[Edited on 22/5/15 by ctwv50]

Tested it last night, all good! Thanks for the suggestions really helped me out.