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In 1998 I bought a Triumph Herald 13/60, here you can read about it's restoration and share in a few photo's from it's travels. Please feel free to leave comments to any of the posts, of even email me if you want to.

Sunday, February 26, 2017

Converting a Triumph Herald to EFI (Part 5 - Starting, Tuning & Cold Idle)

I was more worried about the next stage of the conversion than any other part. All the research, head scratching, fabricating & wiring that I'd done and I could have been left with a non-runner. So with some trepidation I sat in the drivers seat and cranked over the engine, 3 or 4 attempts and nothing much more than the odd cough. I waited a minute or 2 and tried again, this time she seemed keener to get going, one more try and she burst into life.

Thankfully the base settings that came with the ECU seemed good enough to at least get the car running, so first target was to see if I could get a reasonable idle. I kept the revs up until she was at operating temperature and tweaked the idle control screw on the throttle body. The gods must have been smiling on me as it wasn't long before she settled down to a steady idle.


Once the idle was acceptable, the next step was to improve the starting, particularly when cold, this you can only really try once a day when the engine has been left overnight. Within the tuning software (Tunerstudio) you can adjust the duty cycle of the priming & cranking pulses of the injectors, these are calculated on increased percentages of what fuel is required when running and by water temperature.

So over the next few days, the attempts to get her started were fairly lengthy affairs, each day I gradually increased the duty cycles of the two settings until such things were better, but they were still not acceptable. Then I realised that I hadn't set some of the engine constants, particularly the flow rate of the injectors I was using and engine displacement, so these were changed and instantly the cold starting improved. A few more days of minor adjustment and she then began to start consistently right through the temperature range.

If you get the paid version of Tunerstudio, it comes with a great function called Tune Analyze Live. You basically plug your laptop in, turn on the Tune Analyze Live and drive, it will make adjustments to your fueling table through all the various driving conditions. It does need a few runs, so I just used it on every journey over a couple of weeks. This is why I fitted a wideband 02 sensor, if I'd have fitted narrowband it would have meant manual adjustment or getting the car on a rolling road to get set-up. Tune Analyze Live also works on the warm up enrichment, so a couple of runs from cold and that was working well also.

So now I had a car that started well, drove well and idled nicely when warmed up, but I still had nothing to control the idle from cold. Each cold start involved trying to keep the revs up with my right boot, whilst trying to brake and change gear without the car stalling, I needed 3 feet....

This is where the Idle Air Control valve comes in, this is a relatively simple valve which opens and closes based on temperature, allowing more air through to increase revs. Sounds pretty straightforward, but so far this has proved to be a real thorn in my side.

Bosch Idle Control Valve
Again it's something that can only really be tested when the engine is stone cold, so you get one chance per day to make adjustments. After a couple of weeks, 3 different used Bosch valves and and a brand new aftermarket version and no success. I decided that I would have to try a different approach, even if it was an interim fix.

The old choke cable was now redundant, so this was removed and a longer universal one was purchased. The Rover Throttle Body has 2 cable connections, so I fitted the new cable, made an additional mounting for it and connected it up. Simple but effective!

Throttle & Fast Idle Cables
So the choke knob doesn't look so great on the dash, but if this proves to be a longer term fix, then I will find a way of grafting the original knob onto the new cable to make it look a little more authentic.

Universal Choke Cable on Dash
I have now covered several hundred miles since the conversion and I'm very happy with the results, even on a engine that has never been right since it was rebuilt (that's another story). I have another engine almost ready to go in, so I'm looking forward to see how it performs with that.

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