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Hard to start

Understanding AFR

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I have recently tuned hill climb car with an engine based on a gen 2 suzuki hayabusa engine. While warm starting is perfect it is very cold blooded and most times requires some "start ya bastard" to get started when cold. Would this be and IAP problem , all the std sensors for this IAT IAP APS are std and in modified airbox. Has anyone had this issue and if yes how did you fix it .

Thanks for your time

Hello Graeme what ecu are you running and would you able to post the tune and a log file

Regards Ross

The right amount of fuel and sufficient spark at the right time should start an engine. So when an engine is hard to start, you can start by checking the following:

- What are the conditions you are trying to start?

- What is the engine speed (RPM) while cranking?

- What is the the battery voltage while cranking? (BTW, I have customers with Hayabusa powered sports racers that start much easier at a faster RPM achieved by putting an additional 12V battery in series for the starter only -- 24V will spin the starter faster)

- What is the Engine / Air temp when trying to start?

As long as those conditions are good enough to expect the engine to start, then next you need to figure out what the engine needs for Fuel Quantity and Spark Intensity, and Spark Timing. The spark is relatively easy to check and modify (changing coil dwell, fresh plugs, and modifying the cranking timing (try 5-10 degrees, my GSXR-1000 starts easily at 7deg). To make sure you have spark initially, leave the plugs in, and remove one coil and connect it to a fresh spark plug that you ground to the head so you can see the spark. Note how long you have to crank before there is a spark.

Fuel is trickier, and I would suggest after you have cranked the engine and seen a spark, remove one of the plugs that had a coil attached. Is the plug wet with fuel - if so, injector spray pattern might be an issue, or your tune is just injecting too much fuel - try reducing it by 25%, remove and dry all plugs and try again. Or if the plug is dry and you haven't heard any combustion attempts at all -- I would increase the cranking fuel by 25%, and repeat the test. Now the fuel might just be needed for cranking? Or it could be an indicator that your temperature compensations aren't correct.

Depending on the ECU, there might be other things that could improve the start -- some offer a first-injection pulse (often 2-3x amount of fuel required for idle), or you might find that adjusting the injection timing helps minimize any fuel atomisation issues.

Of course, you could just have some other problem like connecting the upper / lower injectors incorrectly (cranking fuel should all come from the lower injectors). Or the Idle Air Control isn't functioning (I would expect it to open more when cold) and be less sensitive when warm.

My vote will be lower battery voltage while cranking when cold. If the voltage at the ECU drops below 11.5v the Stock Suzuki ECU doesn't want to start -- we find that is an issue the first couple of times per year when the battery has gotten discharged while stored.

Do you use a jump battery? Try running the starter with a separate battery, so the ECU has a fully charged battery to run the fuel pump, ignition and injectors.

Hope that helps -- good luck!

Thanks for the replies , for you Ross The ECU is a std suzuki one , which can only be programmed while off line. The program I use is the Woolich software (australian). I can log the data from the engine with an onboard cable which allows me to have engine diagnostics live while running.

for you David , the start is assisted by a secondary battery plugged in while we go through start , they in parallel so 12 volts.

conditions are varied but engine is un-started cold. Engine rpm would be around 500 rpm

I am having some cold start testing in the coming week I will try some of the suggestions then and see if I can get you more info.