All this started when we were trying to test the brakes, long term readers may remember that we had got the brakes all sorted but when we went to test the car wouldn't start. It was quite embarrassing really, we had an audience, it had started no problem first thing in the morning but didn't want to know when we got it to the test track. We loaded it back up took it home, had a look at the plugs - they were very very black and sooty, so much so that they simply wouldn't spark. With a new set in it fired straight up but was running very rich indeed, something was clearly wrong.
The integrale was built in 1990, cars didn't have OBD ports back then but the Marelli ecu does have a 3 pin port so we set about trying to find something to talk to it to give us a clue as to why it was over fuelling so heavily. We tried for days to get a diag box talking to it but for various technical reasons we had to give up on that and find other ways. The system is simple by today's standards, you only have a map sensor, an air temp and coolant temp sensors, the workshop manual and sensor manufacturer's data tells you the resistance curves and the pins on the ecu that the devices connect to. By using a DVM we could see that the sensor values were all credible and that the wires were intact and not shorting.
This led us to the only other thing - a faulty fuel pressure regulator - if that was not regulating correctly too much fuel would be injected in to the cylinders for any given injector duration. Sadly there was no way of verifying the rail pressure, no gauge or any schrader valve where we could connect a gauge and no way of interrogating the ECU to see what it thought the rail pressure was.
I ordered a new variable regulator with gauge so we can set and monitor the fuel pressure and see where that takes us. i thought it might be good to discuss the regulator in a bit of detail as it may not be clear quite how it works and why it needs a vacuum pipe from the manifold - it's not obvious at first glance.
The system spec on the Integrale is 2.5 to 3.2 bar, an adjuster on top of the new regulator allows that to be set quite accurately. The problem comes on turbo cars when they start to produce boost - what then happens is that the fuel rail now sees however much boost is being provided by the turbo, which reduces the differential pressure being supplied by the fuel regulator. For example we start off with say 3.5 bar, the turbo produces say 1 bar, the pressure differential is now only 2.5 bar and so the fuel delivery is reduced and the engine will go lean or the spray pattern will go from fine spray to globby drippy nastiness. To counteract that a vac take off goes from the manifold to the regulator to allow it to increase pressure as the turbo kicks in and the rail pressure increases - it's all very clever yet quite simple.
The kit we had bought seemed alarmingly cheap, it was only about 40 quid yet it had the regulator, a viscously damped gauge, 3 lengths of stainless braided pipe, numerous fittings and no instructions, which is really annoying, I like to have written instructions that I can ignore. It's a bloke thing. anyway, it was all pretty straight forward, by turning on the electric pump I could see the pressure on the gauge and set it roughly so we could start the car and then set it more accurately. I set it so it was 2.9 bar at tickover. it worked perfectly and even at cold we could see the black smoke had diminished significantly, we let it warm up to it's approx 80 degree normal running temp and the exhaust was completely clean. After a short period of cooling we removed a spark plug and it was a lovely sort of slightly dark grey elephant skin sort of colour. We now have an air / fuel ratio meter to make sure it is perfect across the range but that won't get deployed until we get a chance to road test it, I can't see that happening before the spring now.
Sadly my phone was knackered at this point so I have no photos, I will update once I get a chance to take some. However, here is a piccy of the kit that we installed.
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