Hi all I have a MGB roadster with s13 sr20det swap. Went out Driving this afternoon And everything was great . It started getting dark so I turned driving lights on and then issue started . Motor would splutter from idle to about 2,500-3000 rpm then come good at higher revs . AFR gauge showed it was leaning out too. I tried multiple times with lights off (all good) and with lights on ( spluttering ) ??
I got home and plugged laptop in to check voltages
Idle
13.3v no lights
12.6V with lights
Reving to about 2,500 rpm
14.2v No lights
13.8V with lights
Are these voltages ok or not ?
Any help would be appreciated
Some more info
S13 SR20det
Tomei cams
Gr2871r
1000cc injectors
Nistune
E85
sr20det voltage issue ?
Moderator: Matt
Re: sr20det voltage issue ?
The voltages are okay at the ECU, but the lights affecting injection seems to indicate a wiring issue with this particular transplant
Most likely there is a grounding issue. Main ones to check are ECU to plenum bolt, then battery to chassis, and battery to engine. Ground goes from battery to EFI system via the engine and plenum bolt. The engine is the main grounding point (star configuation)
Your lights might not be grounding properly either and pulling their ground through another system (higher current)
Most likely there is a grounding issue. Main ones to check are ECU to plenum bolt, then battery to chassis, and battery to engine. Ground goes from battery to EFI system via the engine and plenum bolt. The engine is the main grounding point (star configuation)
Your lights might not be grounding properly either and pulling their ground through another system (higher current)
Re: sr20det voltage issue ?
Sounds like the alternator is charging but you usually see higher voltages than that. More like 14.5V when revving. Lights on/off shouldn't change things much.
On top of what Matt said, make sure your voltage sense wire from the alternator is going to battery. NOT just to 12V on starter etc. The alternator needs to know what the voltage at the battery is.
Also there should be a fat earth wire from alternator case to chassis. Make sure your earths to chassis (from battery, engine inlet manifold, and alternator) go to the same GND point on chassis.
ECU power should also come direct from battery. Lots of guys just hook into the 12V on the starter etc. Not right.
PL
On top of what Matt said, make sure your voltage sense wire from the alternator is going to battery. NOT just to 12V on starter etc. The alternator needs to know what the voltage at the battery is.
Also there should be a fat earth wire from alternator case to chassis. Make sure your earths to chassis (from battery, engine inlet manifold, and alternator) go to the same GND point on chassis.
ECU power should also come direct from battery. Lots of guys just hook into the 12V on the starter etc. Not right.
PL
Re: sr20det voltage issue ?
Thanks I replaced the alternator and it’s all good now 
Hey PL a little oddf topic bud to you still sell the conversion box that can convert my speed sensor output to my ecu speed sensor input ? Thanks
Hey PL a little oddf topic bud to you still sell the conversion box that can convert my speed sensor output to my ecu speed sensor input ? Thanks
Re: sr20det voltage issue ?
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