I just installed new secondary fuel rail, 1600's, and fpr, and now my car has a slight hesitation whenever i step on the throttle. anybody know what could be causing this problem? I am running a power fc, and i moved up the secondary size to 1500cc in settings, this is all the commandar allows. anybody in phila. area with a data logit who would be willing to up my injector size to 1600 in the power fc there would be a case of beer in it for whoever helps me out of this one.

thanks,

brad

 

As I understand it, that is the nature of running 550/1600

 

you are probably running very rich because it thinks you have a 1500cc injector so you will be running aroud 6.67% more fuel everytime, maybe the richness is causing the bogging

 

did that on my FC. 550/1600 extreme hesitation

running rich as hell

 

It is hard to get the "stumble" out completely w/ that set-up. When cruising around. I get a slight "stumble" when the 1600 begin to open. We have worked the microtech cruise maps on the street to make a bit better, but not perfect. My wideband indicates it as a rich condition (9.0) which is normal for the size difference. I never have problems at WOT though. G

 

I had the same injectors on my car and ran the map on the bleeding edge of lean under light load without any bucking or hesitation. Here is my advice:

1. You should be using resistors that are in the 3-6ohm/watt range. The lower you go the better the injectors respond, but the more strain it puts on the pfc injector driver. I spoke to one of the hardware engineers that developed the pfc in 04 (through a translator) while he was at Apexi's CA office. I had to set the call up 4 weeks in advance, but it was very informative. He said 2 Amps is the max the injector driver should see.
Since Amps=volts/resistance 12v/2.8ohms (bosch 160lb injectors) =4.29 amps without resistors

With 6ohm resistors 12v/2.8+6ohm resistor =1.36 amps
With 4ohm resistors 12v/2.8+4ohm resistor =1.76 amps
With 3ohm resistors 12v/2.8+3ohm resistor =2.07 amps

I used 4ohm resistors on my car. I purchased them from Mouser Electronics on the web. The physical quality of them is much better than those flimsy things people get from Radio Shack and trust their motor to.

2. Adjust the size, lagtime,and transition settings using a datalogit. The value I used are as follows:

lag = .14
size =1680cc
pr/sec transition =40%,
transition (ms) 1.500 sec.

BOSCH TOP FEED INJECTORS ARE NOT 1600CC. They are 160lb injectors. The conversion ratio is 10.50. So 60lb/hr x 10.50 =1680cc/min. The fact that 90% of the people on the forum call them 1600cc injectors should give you a sense of the level of understanding here .

3. Make sure your fuel pressure is set correctly.
4. Make sure your AFRs are where you want them to be during steady load. Changing the injector size in the PFC will get you in the ballpark, but it is not exact. The Bosch injectors are fundamentally different than the stock 850s, so you will need to do some fine tuning.
5. AFTER 4 and only after 4, adjust the throttle tip in. You can do this with the commander. "and now my car has a slight hesitation whenever i step on the throttle." That sounds more like an accel enrichment problem than an injector transition problem. You can fix this by adding more fuel to the accel enrichment for whatever rpm range you are have the problem in. When this is setup correctly you should be able to drop your foot to the floor at any rpm with virtually no shudder.

Best,

Chris C.

 

wow very informative guys, thanks for the help, chris, thanks for taking the time to explain some of this to me, my fuel pressure should be about 40psi at idle correct?

thanks,
brad

 

No problem. You should have a pressure gradient of 40psi. So at ZERO manifold pressure it should be 40psi. At idle the car is operating in vacuum, so it should be less than 40psi. At 15psi it should be 55psi =40+15.

The easiest way to set it is to start the car, unplug the vacuum/boost line from the regulator, and then set the fuel pressure. You can also do it with the engine off by jumping the fuel pump relay as long as the battery is in decent shape.

FYI, 'normal' fuel pressure in the car world is 43.5psi I believe. However, if you use this graident value you will have to make more changes to the fuel map.

 

Another + to the microtech user.. You dont have to fool w/ any resistors!

 

Just FYI guys, I ordered these resistors, which should be the proper ones (3 ohm 5 watt):

http://www.mouser.com/search/Product...lkey71-RH5-3.0

 

I have the RX7 store Bosch 1600, which some say are really 1680.
My previous setup was 550/1200 with the 1200s being 850s enlarged to 1200 by RC and I had their tested flow rates as 1200. When the 1200s were replaced with the 1600s, they were setup as 1680s. AFR testing showed that this cause lean AFRs. When my setup was changed to 1600, the AFRs were almost dead on.
Thus I question the statement about understanding! Also a friend who has Bosch 1680, told me his injector color is different than mine which have a light gray top.

The values given for pr/sec transition =40% and transition (ms) 1.500 sec are totally wrong. I am the only one on the PFC forum to log and show results with what happens here with these values. Best values are: pr/sec transition =30%, transition (ms) .100 . My testing results with DL charts are part of my PFC/DL tuning package.

TOTAL proper tuning is the key to a great running car which many modifeid RX7s are not. ILDE, CRUISE, BOOST TRANISTION, and FULL BOOST: all must be properly tuned for a truely smooth running car.

 

Maybe Bosch's rating is off, but my understanding is that they are listed as 160lb/hr injectors by Bosch and that translates into 1680cc not 1600cc. If you search the web you will find values ranging from 1785cc-1300cc. Without flow testing them I felt 160lbs/hr was a good starting point. What are you using for resistors and lag time values?

So you've cut the transition point to when the primaries are at 30% from 40% and basically eliminated the transition time compared to the factory setting of 1.5. Hey if it works it works, but that sounds kind of odd.

Couldn't agree with you more. It's easy to dial a car in at WOT. The trick is getting it to consistently perform smoothly and efficiently under different conditions (temps ect). I can't tell you how many dyno 'tuned' maps I have seen where values in the low load rows cross .

 

all i can say is wow. very informative thread. im going to read it about 10 times more, lol

 

Q1: What are you using for resistors and lag time values?
3 ohm as supplied by the RX7 Store. Ended up with .30 lag to get the 1600s to totally even out with the previous 1200s. Still had to do a little fine AFR tuning to the base fuel map to get it cell perfect. I tune to +- .1 from my standard. Thus one P row will have a total deviation of only .2AFR from 4000 - 8000rpm. I am a fanatic tuner, ask people who have been in my car.

Q2: So you've cut the transition point to when the primaries are at 30% from 40% and basically eliminated the transition time compared to the factory setting of 1.5. Hey if it works it works, but that sounds kind of odd.
A2: When I logged my duty cycle where the injectors switch from pri to pri & sec, even though it was set at 40%, it did not actually happen until 48%. The 30% gives it vary close to 40% now. Normally when running 550 pri and changing the secondaries, you determine the trans (ms) by (850/1600) * 1.500 ms = .797.
Logging shows that this still causes the secondaries to come on too strong and also causes the primaries to drop too much, uneven tranistion. After lowering the trans (ms) so much, nothing more happens as the PFC software has limitations.
I settled on the even .100 ms. Logging tranistion and viewing in a chart format, you can see how the injectors and duty cycle work together. With my fine tuning and inj setup, I now run an injector overlap of 2-3-4 instead of the common 4-7-7. I can slowly rev to 7000rpm under vacuum in 2nd or 3rd without fuel induced stutturing.

Q3: tuning
A3: I have my idle and cruise so well tuned, not only does it run great but the exhaust runs medium/light gray without a cat instead of black.

 

bump for a thread with some good info!

 

I am about to switch to 6 ohm resistors in my FC versus the standard 10 ohm that everyone wires in. I have had a lean spot at the injector transition that I just can't get rid of.

 

Definitely keep us updated if that clears up your problem.

 

I suppose it should be no surprise we have these problems when using the resistor 'band-aid' for low-imp (2.5ohm) injectors. If your ecu is running off 12V, then
Injector current (high-imp) = 12/12.5 = 0.96A
Injector current (low-imp) = 12/2.5 = 4.8A
The low-imp injectors are expecting 12V@4.8A

With 10 ohm resistors in-line, the low-imp injector only sees 2.4V@.96A, thus causing turn-on delay
With a 6 ohm resistor in-line, the it sees 3.5v@1.4A

hopefully that is enough to cure the turn-on delay

 

/\ assuming the injectors see 12v, that i am not sure of, but you get the idea of the voltage difference

 

I have a ?. Last year I had a new fuel rail installed with 1600cc secondaries and a PFC. I have noticed that my idle may drop to <750 RPM and when that happens I tend to be very careful when I have to move from a full stop. It does not happen all the time, but just wondering if it is a setting on the PFC. I am very ignorant of the settings. Dynoed four months ago and ran ~10.3 AFR at 4600 RPM and above. I do have an upgraded fuel pump, stainless lines, and fuel pressure regulator. Anyone have any ideas.

TIA
chagar

 

6 watt, 10 ohm resistors fixed my hesitation on my 88 Turbo II with low impedence upgraded secondarys. http://www.mouser.com/search/Product...key71-RH10-6.0

Most 88's use high impedence injectors stock.



This is the stock resistor pack on an 87 Turbo II, which actually comes with factory low impedence injectors. As you can see, it uses 6 ohm resistors.
I think we should lay to rest the old idea of 10 watt, 10 ohm resistors that has been floating around at least on the FC forums for a while.

Honestly though, I may eventually switch to 4 or 5 ohm resistors. There is still a slight lean spot at the secondary injector transition.

 

Do you have any specs for running top feed 850cc injectors?

Also CMonakar, do you have any idea how to test the pfc secondary injector driver?

 

I use:

0.26 lag
30% pri/sec trans
0.900 sec transition

my car runs very very smoothly from 1000-8000 at all throttle positions.

I think that each car needs to be custom tweaked as resistors used and fuel pressure play into it.

 

^ What would you recommend if I were not using resistors? Being that I will have the FJO Injector Driver Modual Box installed. Would it just completely take away both the primary and secondary lag?

 

Good thread. In for future reference