MoTeC Global Forum

Hi all fellow Motec users, installers and experts.

I am a Motec dealer in Moscow, Russia and seeking and advise
on tuned Evo engine cold start problems I'm having.

The problem is fouled plugs on tuned engines with cold plugs.

The worst case I have at the moment is as follows

Evo 9
Cosworth head with Tomei 260-10.7 cams
HKS Kansai intake manifold w. Nissan 75mm throttle
Tomei pistons and rods
C/R dropped to 8.3
Greddy TD06 20G turbo kit
RC 1000cc injectors
Denso racing plugs #31
Motec M800 OEM Evo 89 ECU

My cranking and post start enrichment tables are time based against
water temp. The injection time is about 6 msec on cold engine (20C).

I have tried different combinations of start, post start and
water temp compensation tables values however unable
to get consistent cold starts. Engine does couple of power
strokes on 2 cylinders and then just cranks with fouled plugs.
Reducing compensations takes longer to fire it initially
with same result, fouled plugs. Increasing the compensations
floods the engine immediately. Even when engine is warm (50C)
its starts with difficulty if at all.

I used my calibration file from similar Evo 9 setup that
I tested and managed to start up to -25C last winter.
That car had stock engine and 1000cc injectos too.

I would highly appreciate any suggestions on start up parameters.
If it is of interest, I can send my calibration files for examination.

I have done many Subarus and Nissans and did not
have such cold start problems. I think its may be related to the Evo
ref/sync setup with only 2 teeth on ref/sync trigger wheels.

I also tried increasing dwell at 7-11V battery range.
Nothing changed.

The stock ECU or some aftermarket ECUs I tried (Power FC, Link)
do not experience such cold start problems. Link was tried
on the same car and engine and it started in a split of a second.

Changing plugs to hotter range (7-8) normal (projected electrode) type
solves the problem, however I have to retard ignition timing,
which affects performance.

Our drag Evo 6 starts perfectly on Motec CDI paired to Mercury
coils and Magnecore leads, however I am reluctant to change
ignition system on street car just to get stable cold starts.

Thanks in advance for your help


Alex Briginevich

What was engine speed and battery voltage during cranking?
Was the injector calibration given by Motec Research centre?
Was there a resister pack in the injector circuit?
What is injector resistance?

Engine speed 150-200 rpm
Battery voltage 10V +/- 1V
No, injector delay is set based on similar injector with known data.
Yes, stock Mitsubishi injector resistance pack.
2.6 Oms from my memory, but will check tomorrow.

Actually we are using RC injectors (750, 1000, 1200, 1600cc) quite often, so
it will be helpful to have the verified data based on voltage and fuel pressure.

Is it possible to send the injectors for testing?

Regards
Alex

I would highly recommend http://www.yawpower.com/injectordynamics.html for your injector flowtesting needs. Paul did mine and does many for Motec USA. His service is excellent and worth every penny!

Later,
Mike

Big injectors, racing plugs and cold starting can cause problems because of poor atomization. You could try changing your injection timing at cranking speeds so that injection is taking place with the inlet valve closed. This will give the fuel a chance to atomize rather than just "hose" the spark out.

The other problem could be your dead time at low (cranking) voltages. It would be worthwhile testing the injector to make sure that you have the correct dead time setup.

Thank you all for the input.

I agree that mine dead times may be off, further worsened by injector spray pattern.
RCs spray worse compared to stock injectors e.g. STI's. They basically spray
3 spurts compared to fine mist of OEM injector from what I've seen on
injector flow bench. The presence of ballast resistor on Evo makes matter
even more complex, I think, reducing voltage on the injector.

I've found a source of saturated injectors with published dead times, flow rates
and good atomization and ordered sample sets for testing on Evo and STI.
In particular they offer 1000cc saturated injectors that definitely
will interest performance Subaru owners and shops.
Here is the link http://www.t1raceparts.com/

Also researching dwell time significantly affects starting performance.
I found a dwell map (RPM/Voltage based) in Subaru OEM ECU calibration
file and made similar table in Motec calibration. The engine would start
much better at lower temps.

On the final note I would like to suggest to make a section on the Motec
site with published data on popular engines (EJ20-25, 4G63, SR20, RB26, VQ35 and prehaps others)
coils dwell as well as tested aftermarket injectors data, so tuners
would have easier time figuring these out and make better calibrations.

Regards
Alex

To ROSSB: Could you suggest any timing number to start with, given stock engine?

I assume that you mean injection timing. For this yuo need to avoid changes of more than 100 degrees between sites but I would suggest that you try adding about 200 degrees to your normal injection timing at cranking speed. In other words if you have 280 degrees at idle set it to about 500 at cranking speed.

Thank you Ross,

I'll give it a try.

One thing that I can't explain tough is why the outer cylinders (1 & 4)
always get flooded while 2 & 3 stay dry. On 3 engines that we had cold
start problems it was the same thing.

Obviously its impossible to start the engine on 2 cylinders.

Any ideas?

Cheers
Alex