This is one long 2014 thread, with the final answer posted in 2016. The cars were supercharged NAs (M62 or similar) on an aftermarket ECU with OBD Tuner software, and they differed in several ways. The three cars did not necessarily have the same fault. For a standard car that won't start, see P1512 and a car that won't start, and for a different case study on the same software, Supercharged car: relay K18 earth fault.
The symptom
From cold, the engine cranked for 3 to 10 seconds before it caught. Sometimes the first catch was lumpy and needed gas to stop it stalling. Once running it was fine, and hot starts were mostly fine. One car started without trouble on a different (mapped) ECU and only had the problem on the aftermarket software, which made it look like a software setting. Another car had started fine before its conversion, including for a short time on the same software in NA form.
What owners checked
- Crankshaft sensor learning. The tuner who wrote the software saw one car do 35 crankshaft position learn cycles in two weeks, where normally it is done once, and asked whether the battery had been disconnected overnight. The owner replaced the crank sensor and the problem stayed.
- Throttle body idle position. The tuner thought it was related to the throttle body: most of 100 cars with the software idled with the butterfly about 10% open, while one problem car sat at about 17%, and two others were more closed than normal (one logged about 6%). A second-hand throttle body brought the first car down to under 14%, with little change in starting. A more closed butterfly than normal can mean an air leak.
- The conversion loom. The man who built the conversion looms said the throttle body plug pins are moved within the plug, not cut, and that only the injector, MAP and tank vent valve wires are lengthened. Owners suspected a loom or throttle body difference, because only about 3 cars in over 100 on the software had the problem.
- Sensors and codes. One owner had P0141 (the post-cat lambda heater circuit) on the new ECU, which had been blocked in the other map. Another had had P1512 (throttle minimum position not learned) at one point, and the tuner said that could affect starting. One owner who had P1512 straight after fitting the supercharger had it clear itself, and his cold start was fine.
- MAP or TMAP. A MAP-only sensor set up as a TMAP was one worry. The owner who had swapped from MAP to TMAP months earlier still had the problem.
The fuel system
One owner noticed that when he pressed the test valve on the fuel rail after priming, only air came out, and fuel appeared only with the engine running and was gone seconds after switching off. Two simple findings from that:
- Press the starter during the prime. Turn the ignition on and press the starter button while the pump is still priming, with only about a second between the two. One owner said that, and an owner who tried it found it made no difference. Another said to ask the tuner to lengthen the prime cycle in the software.
- The relay contacts. One owner pulled the fuel pump relay and found white corrosion on the blades. He rubbed them with paper and swapped it for a clean one from the front, and the car started within two or three seconds, with no spluttering, over the next several mornings. Another owner tried the same relay cleaning and swap and saw no difference.
- After a pump change. A different pump may not behave like the original. One owner said the aftermarket pump appeared to let the pressure drop when it was switched off, so you should check pressure with the engine running. Another said his aftermarket pump held pressure like the original. A third owner said his original pump had lost pressure quickly and primed poorly before it failed.
- Pressure test. One owner connected a home-made gauge and found the pump primed but didn't hold the pressure. His video later showed the difference between the split hose and the fixed one.
Air leaks and the supercharger
- The bypass joint. One owner could see a lot of the green gasket between the supercharger bypass and the manifold. Other owners said that on a correct fit you shouldn't see it, or barely. He took the supercharger off three times.
- A lost injector seal. While the fuel rail was off he found an injector O-ring missing. It had fallen into the inlet port, where it was found sitting on the valve with a small LED on a wire, and retrieved. Owners said to put Vaseline on the injector seals when refitting. Another owner saw injector 1 with the rubber burnt away on two sets of injectors.
- Coolant in the cylinder. In the same job he pulled a coolant pipe off and coolant ran down the injector hole. Other owners said to turn the engine so the piston is at the top, draw out what you can with a pipette, and change the oil if it is more than a splash.
- Blocked breather. He asked about a blocked breather hole in his manifold gasket. Another owner said it is normally blocked unless you have a Saab engine or head, and he cut it open. A third said to seal round a modified hole with a light coat of silicone.
- Oil on the bulkhead. He saw a line of oil spread across the bulkhead, from the supercharger pulley.
How it ended
In 2016 the owner said there had been three separate faults, which is why diagnosis had been hard:
- A split internal fuel hose where it attaches to the pump in the tank. It was found by a fuel pressure test at start-up.
- The supercharger and bypass flange was warped (no idea how), which gave a slight boost leak with very few symptoms.
- The pulley shaft was damaged and leaking supercharger oil.
He said the car ran fine for the couple of years afterwards. The other two cars in the thread didn't post a final result, so we don't know what fixed them. For the pump itself see Fuel pump replacement.