shombre

Hi all - long time lurker (well, ever since I thought about getting a PFC anyway !) but first time poster. I'm from Australia - I own a mildly modified Toyota Soarer twin turbo (1JZGTE, straight six). The mods most germane to my queries are Sard 650cc/min injectors, HKS 264/264 cams, a Walbro GSS341 fuel pump and, of course, a PFC. I have *no* mods to my FPR.

Ever since I've had the 650s in (well before the cams were installed), I have had trouble with cold starting; by this I mean the engine, ambient temp and coolant temp are cool. It takes probably 4-5 full seconds of cranking, then fires up nicely. If it's shut down not long after an initial start, the problem does not occur; i.e. it starts straight away.

My fuel filter is clean, fuel pressures seem normal and spark plugs are new and amplified with an HKS DLI. The injectors are not terribly old, were purchased new, and were cleaned and flow tested prior to installation. Oil and oil filter are changed every 5000km. I have not a hint of fuel starvation through the rev range on any load. Injector latency and compensation (stock 1JZ injectors are 380cc/min) have been appropriately entered. Powering the car up and waiting for a few seconds before trying to crank (thereby trying to prime any of the line from the fuel pump) makes no difference.

After searching fairly extensively here, something that keeps coming up is the use of the water temp correction table to tune cold start. This is something I'm keen to explore. Most informative posts seem to suggest referring to pg 31 of the Commander manual, which I have consulted; however, I'm not sure what each table actually means. Searching online for general tips on cold start tuning of fuel injected engines has yielded nothing of value

Could I prevail upon somebody(s) to please explain what exactly the water temp correction tables are trying to achieve, and how the principles of cold start tuning might differ (if at all) between a rotary and non-rotary engine ? I'm a keen DIY'er but would like to avail of your considerable PFC resource base before messing around too much.

Thanks for any help you can provide.

cewrx7r1

iTrader: (2)

Water Temp Correction table:

A cold engine does not fully evaporate all the injected fuel, especially at idle. This unevaporated fuel sticks to the engine surfaces as a wet coating or as droplets in the air mixture. It doe not combust very well or smoothly. Extra fuel helps this problem. Left column is light load. Right column is heavier load. This table is more important after the engine has already started, then you adjust the appropriate cells.

Your problem is in starting, iI suggest you play around with the values in the page 32 Cranking Fuel Injection table. Which adds extra fuel only when starting.

shombre

Thank you, that's exactly the info I was looking for !

My car's in the bodyshop getting some minor stuff done, but I will post back here with my results; hopefully it might help somebody else.

Cubes

I had a similiar issue when dropping in larger injectors..

I bumped up the respective temperature cranking times until it came good, took a while to get right but eventually got there.

shombre

cewrx7r1 - just have three questions for my education, please.

Do the temperatures in the Cranking table denote temperature ranges rather than discrete values ? So for example, does "+80" refer to 80° +? And therefore "-10" refers to "-10° to +10°" ?

Are they referring to inlet air temp or water temp ?

Finally, this sounds axiomatic, but by adjusting the cranking value in ms, positive correction is applied to the injector opening times to prolong their opening only when starting. Is this correct ?

Thanks in advance.

Cubes

Yes, consider it a temperature curve.

and yes.

shombre

Cubes, cheers for that. Do you know whether the temp enrichment curve uses water or air temp for its x-axis ?

Cubes

The cranking curve only uses water temp. I've edited my post above as the word enrichment is incorrect for the cranking table/curve.

There's quite a few little inj enrichment tables used once the car is up and running.

Inj vs Airtemp
Inj vs Airtemp & Boost
Inj vs Watertemp & Boost
Inj vs TPS
Inj vs Accel TPS1
Inj vs Fuel Temp
and the usual Water temp correction enrichment table.

shombre

Excellent, many thanks.

One more question, if I may ?

In reference to cold starting - "Extra fuel helps this problem." Does this read at face value (i.e. adding extra fuel really makes a difference when there's a lot of uncombusted fuel around) ? The data on my PFC suggests that clearly it does; is this merely because on cold start, given that cold air is denser than warm, more fuel is needed to maintain an efficient AFR ? Or does it refer to more fuel being needed owing to impaired atomisation at low temperatures ?

Cubes

Not exactly sure.

Adding fuel in my case helped as obviously combustion is poor at cold engine temps hence the need for more fuel generally speaking.

The idea is to run it as lean as possible before drivability suffers. When I say lean it is still obviously richer than ideal due to poor combustion when the motor is cold.

shombre

Many thanks again, mate

shombre

Fixed with many thanks to Chuck W. and Cubes.

Reducing the cranking injection time by 2ms for all values at +10° and greater has led to instantaneous starting I worked out that the poor thing was running far too rich on startup - all sorted now.

Hope this is of some help to others.