PorKen

For a quick cold start, turn the key to run, then turn off, before quickly turning all the way to start. Fires right up! Yay!

Confirmed after a five hour wait at 41F/5C. On, off, start, whirr, whirr, vroom!

Another overnight cold start. On, off, start, 3 x whirr, vroom. I'm sold. Some cold mornings I was crossing my fingers as it seemed like it was cranking forever and the often battery drains quickly when left sitting for a few days.

PorKen

If you want to precisely control the injection time, use the code below (replacing a useless loop) instead of the 33 patch, which might be too rich.

0080 75
0081 83
0082 EC
0083 74
0084 33
0085 F0
0086 74
0087 (pulse length)
0088 F0
0089 00

Repeat at 4080-4089 for SharkTuner

I found a pulse length of 10~30 to work best, in hexidecimal, as follows. Over 38h slowed starting.
...1F,20,21,22,23,24,25,26,27,28,29,2A,2B,2C,2E,2F,30...

I am currently using 18h for instant hot starts and not worrying about cold starting.


You want to have the minimum amount of injection time, so a (pulse length) of 10h might be a good place to start, then work upwards. If you have larger than stock injectors, you will probably need a smaller value.

Michael Benno

@PorKen offered to modify the LH BIN file on my GTS to see how it would impact fast starting. I took some videos of before and after. I'll let the videos speak for themselves. Sorry for all the magenta. :-)


Cold Start - no mods


Cold Start with Ken's mods


Warm Start with Ken's mods.

FredR

Impressive!

Petza914

Is one of the changes to allow the fuel pump to prime with key in the full accessory position? If so, the 2nd video should not go from key off immediately to start but rather key off to full accessory, wait a few seconds, then go to start.

But, I thought it had been determined that Porsche didn't do this so the car could build a little oil pressure while cranking before it actually fired, but maybe not...

Alan

That was suggested. I don't put much credence in it frankly - no evidence to suggest that was the case IMO. Porsche certainly simplified the structure to not need a tachymetric relay with the '85 CE panel update, probably because these relays had(/have) reliability problems. By doing this they integrated the safety fuel cutoff differently, the quick start by priming could have been added into the code as Ken has done - but that was probably Bosch developed, and maybe the right people just weren’t talking together… The LH/EZF had already previously been deployed with a Tachymetric relay, so it was certainly easier to make no more changes.

Alan

Petza914

Thanks Alan.

My 79 CIS car primes on the key with that odd FPR but my 84 Euro S doesn't, so has the longer crank on cold start. When warm and being restarted, it fires immediately,.like surprisingly so - even faster than video #3 in this series.

Alan

That suggests the priming pulse feature of your Tachymetric FP relay on your '84 no longer works - that's the most common "fail' mode on these* - but apart from longer cranking - you'd never really know. When warm you may still have some fuel pressure and it spins faster when everything is warm too.

*makes me wonder if these just have a simple RC time constant for the delay and perhaps a timing caps break down over time - something commonly happens here that still leaves the tachymetric part perfectly functional.

Alan

Petza914

My 84 Euro S doesn't prime on the key like the 79 does. If it's supposed to, then you're correct. I just assumed it was like the later cars that don't run the pump unless cranking. Fires up just like video #1 in the series when it's cold after sitting overnight.

Alan

It should have it - all cars through 84 had the same style of tachymetric (priming) relay. In 85 along with the new CE panel there were many changes - including the non-priming standard Bosch SPST style ('53) FP relays

Alan

Petza914

I'm sure I have a new spare (or 3) for my 79. I'll pop one in and see what happens.

PorKen

Fuel pump prime happens at the "run" key position. The pump needs at least one second to build pressure so the pump prime is more of a help with cold starting.

The injector pulse happens essentially at the same time as the pump prime start so is mainly for hot starts, with previously pressurized fuel rails.

Ideally, the pulse would be mapped by coolant temp, but at the start of the RESET code, the coolant temperature has not been read yet.

Petza914

Thanks for the info. Yea, that was my point to allow for a little pause at run before moving on to start and not going directly from off to start.

Nice work!