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Rover SD1, Unconventional Solutions

When you own an old, modified car, you start to get used to finding unusual ways to fix things.

There has been a question in my mind around what the Over-Run valve is doing with my current setup, and if it’s the cause of the huge lean out on overrun/decel.

Long story short, the Over-Run valve is a mechanical valve that resides on the rear of the plenum. It has a spring-loaded piston inside it, which opens when there is a period of high vacuum in the plenum. The valve lets air straight from the air rail under the plenum, into the plenum.

In the standard Lucas setup this is designed to lean out, or correct, the overly rich mixture in the intake with the throttle closed, so that it doesn’t end up in the exhaust and causing undesirable backfires on deceleration.

Of course with a tunable ECU having a mechanical device like this is undesirable in itself, as the ECU has no way to control it, and is left trying to work around it. With my ECU I can switch the injectors off completely on deceleration, and control the fuel mixtures at high vacuum, which completely negates the need for the Over-Run Valve.

The Over-Run valve is visible on the RH end of the plenum

And this is what’s inside it

Now, like everything else I have done, I didn’t want to permanently remove the valve, as everything has to be able to be returned to standard. The simple option was to just block off the inlet for the valve, and the end of the air pipe. This would allow the valve to still open and close, but it wouldn’t pull any extra air into the plenum.

So what does one plug a 16mm pipe with? A trip to Mitre10 came up with a cheap and easy solution.

High durability, non-slip and low noise. Just what I needed.

A minute or two with a screwdriver, and this is what I had

The results? The engine doesn’t run as lean on deceleration anymore (it was going crazy lean, regularly over 20:1 AFR), and seems to have gained a little more response. No crackly bang bangs on overrun through sadly.

Oh, and the horrible droning noise I had on deceleration? GONE. Obviously that was the sound of the Over-Run Valve opening and pulling air through the air rail. Massive win.

So with that fitted, I figured I would need to hit the road and do some more tuning to clear up some of the odd spots the valve would have created. So with my lovely assistant in the passenger’s seat, watching the vitals and VEAL map, we set off.

We made an effort to hit as many cells as we could, as many times as we could. I would be driving along, whilst being told at which RPM and throttle position I needed to hit, and we would aim to get the car into those conditions. This was a great help, knowing what needed to be done, and how I needed to drive, as I cant do this whilst driving alone.

The results were good. The car is driving really well, it’s idling smoother and accelerates like a beast. This is the VEAL map after that run

Lots of coverage, lots of changes. Theres still some spots that need touching, and a few cells didn’t need changing at all, which is cool. I also need to rescale the top end of the RPM on the map as my rev limit is now 5500RPM, so it doesnt need that extra 1000RPM on the end.

Another quick job I did was to upgrade the battery from the smaller one that came with the car, to a big beast. The one in the car, although quite new, just wasn’t in great shape. The previous owner let it run dead flat and left it flat for a week, and it’s taken its toll. It’s still good as a backup, but I can’t trust it.

The new one I got is a huge commercial battery, with a 600CCA rating. It’s the biggest battery I can physically fit in the space provided, with the standard mounting. It’s a tight squeeze. No tight,  that I even had to remove the washers from the mounting bolts, or there wasn’t enough thread to get the nuts on.

Old battery. 520CCA. MF55R

And this what I fitted, NS70MF

This provides ample cranking for the engine, without slowing down or worrying that it will die if the engine doesn’t start first try.

Unfortunately, upon our return from the tuning trip, during my post drive inspection, I noticed some coolant on the crank pulley and PS belt.

The waterpump has given up, and it’s leaking from the weep hole in the snout. Lame. This means there is an internal seal failure.

There has always been a question in my mind on what state the waterpump is in. It looks old, it’s been painted black in the past, and for some reason it has numbers hand engraved in the snout. It’s also corroded on the radiator lower hose connection and doesn’t make a good seal there, and it’s weeping from the gasket too.

It’ll be good to get a new one in, so I then know what state it’s in

To keep my spirits up though, on the drive we did notice that the heater is working, and its HOT. Win.

So now its a waiting game. I need to spend some hefty money with Rimmers in the UK to get a replacement water pump, and then I need to dump the coolant AGAIN and replace it. Fingers crossed most, if not all, of the bolts come out in one piece (i’m not holding my breath, they are well known for breaking off. Replacements will be ordered anyway).

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