Soopra Posted July 28, 2020 Share Posted July 28, 2020 Prior to lockdown Soopra (93 JSpec N/A) was running fine, in daily use. Went in to lockdown with 3/4 tank fuel (normal unleaded, been using this for 9 years, no problems). I was starting him every weekend and leaving him running for about 30 minutes About 6 weeks in to lockdown he developed a misfire at idle when he was up to temperature. I replaced the ignition coil and this made no difference. Once I got down to about 1/4 tank fuel I added some octane booster and this fixed the misfire. Refuelled the car with Normal unleaded. Misfire back Refuelled the car with Super and the misfire has gone again... Any idea what the problem is please? Link to comment Share on other sites More sharing options...
Chris Bailey Posted July 28, 2020 Share Posted July 28, 2020 Don’t fill the car with 95 octane fuel? Link to comment Share on other sites More sharing options...
rider Posted July 28, 2020 Share Posted July 28, 2020 It reads like either a weak spark or weak fuel delivery. Seeing you've changed the coil then the spark should be good so If you have the means, I'd suggest check the fuel pump pressure. From memory, which is a constantly fading facet so its well worth checking, the fuel pressure should be around 40psi. Link to comment Share on other sites More sharing options...
Soopra Posted July 28, 2020 Author Share Posted July 28, 2020 It reads like either a weak spark or weak fuel delivery. Seeing you've changed the coil then the spark should be good so If you have the means, I'd suggest check the fuel pump pressure. From memory, which is a constantly fading facet so its well worth checking, the fuel pressure should be around 40psi. Where is the fuel pump and how do I test it please? Link to comment Share on other sites More sharing options...
rider Posted July 28, 2020 Share Posted July 28, 2020 Where is the fuel pump and how do I test it please? The pump is in the tank. If you head off down to any half decent garage if you don't have pressure gauges to hand they should be able to read the actual pressure as you wait and tell how well the pump maintains the correct optimal running pressure with the engine running. Link to comment Share on other sites More sharing options...
Soopra Posted July 28, 2020 Author Share Posted July 28, 2020 The pump is in the tank. If you head off down to any half decent garage if you don't have pressure gauges to hand they should be able to read the actual pressure as you wait and tell how well the pump maintains the correct optimal running pressure with the engine running. Thank you Link to comment Share on other sites More sharing options...
SupraLEDrears Posted July 28, 2020 Share Posted July 28, 2020 First things first, test the ecu. If it runs fine on the cold map, then the ecu has a problem on the hot map side. Believe me, I've spent over a 1000 quid on new parts just to find out it was the ecu. It's the simplest thing to start with and mine was intermittent too. Link to comment Share on other sites More sharing options...
supra_aero Posted July 28, 2020 Share Posted July 28, 2020 (edited) My bet is it's the ecu. Mine did similar and was to do with how long it ran for would determine the misfire. Longer it ran more likely it would disappear. You can get them repaired or replace them relatively inexpensively if you can find a good one Edited July 28, 2020 by supra_aero (see edit history) Link to comment Share on other sites More sharing options...
tintinmt Posted July 28, 2020 Share Posted July 28, 2020 If N/A auto and not had ECU repaired it would definitely be worth checking. Link to comment Share on other sites More sharing options...
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