I recently purchased a set of Siemans 83lb top feed primary injectors. I am using them with 10ohm 10watt resistors. The conversion factor to go from lbs/hr to cc/min is 10.5. The injectors have a resistance value of 2.8ohms. Under settings 5 I change the front and rear primary value to 63 (550cc/871cc *100). The lag time is set to .04 and the Q primary is 871.

After making these changes the car would not start. I tried adding and subtracting fuel from the base map 5% at a time up to 30% change with no luck. I then reloaded the 550 settings and the car started right up. With the car running I reduced the primary value from 100 to 95 and the afr leaned out so I added about 10% more fuel to the base map. Slowly I worked my way down from 100 to 63. By the time I got down to 63 I had increased the amount of fuel in the base map by about 70%. Even with this increase I couldn’t get the car to start without tripling the cranking ms value and the afr shoot past 15:1 if I slowly rev it past 1400 in neutral.

Now here is the really odd thing. With the stock 550s the car idled at 950rpms with an afr of 14:1 at 5.3% duty. With the 871s at 950rpms with a 14:1 afr the duty value is 5.3-5.5%. If the injectors are in fact larger than the 550s I would expect to see a lower duty value for the same afr. Initially I thought the injectors were the wrong size, but I verified the part number with RC engineering. Next I thought the injectors may be defective, so I replaced them with a different set and still have the same problem.

Any thoughts/suggestions will be appreciated.

 

I would suggest try running them without the resistors and see if that helps.

 

First, I want thank you for replying. Last week I spoke to one of the Japanese engineers that developed the PFC (through a translator). According to him the PFC injector drivers are safe up to 2amps and no higher. The translator noted that they frequently get units back with broken injector drivers.

With the stock injectors the total amps=12 volts/13.8=.87amps
With the 83lb injectors and resistors=12/12.8=.93amps
With the 83lb injectors without resistors =12/2.8=4.29amps ---well beyond 2amps.

I may try to use a resistor with a lower value, such as a 6ohm unit, to see if that makes a difference. However, other people have used Siemans style primaries with 10ohm resistors and haven't had this problem so I do not think that is the cause of my problem. Shawn Keeney is using 720cc Siemans injectors with 10ohm 10 watt resistors. Apparently all he had to change was the settings 5 tab values.

 

VICTORY!

I swapped out the 10watt 10ohm resistors for 5watt 5 ohm units and it started right up. I had to add 5-15% more fuel to the map in places, but that's a far cry from the 70% I had to add with the 10ohm resistors.

I still don't like the fact that I had to use 5ohm resistors and Shawn Keeney did not. I hope the lower impedence resistors aren't covering up a more fundamental problem.