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A few months back I installed RP's secondary rail with a set of 2200cc injectors. After getting it tuned, my tuner commented that the primary -> secondary transition was rough and that he though it was because of the size differential between the stock 550cc primaries and the 2200cc secondaries. Indeed, driving the car, anything over ~5K the motor seems boggy/hesitant to change RPMs.
In the weeks after installing the new injectors and before the tune I had used the PFC commander to set the PIM voltage to +10% across the board. I told my tuner this, but after getting the car back the PIM was still at +10% (I guess he forgot...). Since I hadn't read about any similar hesitation issues here, I have been assuming that the cause of the hesitation was ultimately related to the PIM adjustment. Bummer -- but I've been planning some additional work and thus a re-tune in the near future anyway -- should fix the issue, right?
Well yesterday I was watching a YouTube video from "Kenny McKee" where he mentioned that a large differential from primary to secondary injectors can cause hesitation issues:
There's recently been some discussion about this in the PowerFC tuning group (formerly via Yahoo groups and recently switched to Google groups). I joined the group years ago by contacting arghx or possibly cewrx7r1 from this forum. I don't have a PowerFC so I may have skimmed over some of the details, but it sounds like very specific values may be needed in some maps to avoid running the big 2000cc injectors at low pulsewidths when you first stage them in.
I'm not certain how the PowerFC stages the injectors, but the OEM throttle won't allow airflow to the secondary intake ports when it's below 30% open. I've accidentally operated the secondary injectors when there's not much air going through the secondary intake runners, the engine didn't run very well.
2200's are really big, and don't modulate well (or they do but 1% difference is a lot), with the non PFC ecu's we can turn them on a little later, which helps, or change the staging strategy.
it can be done i'm sure, but its going to be tricky
What 2000s are you using? We have no issues running the stock 550/ upgraded 2000 combo. We've use Injector Dynamics, FIC, and others. Sounds like you have a tuning issue. Pim voltage shouldn't matter if it was tuned that way but if you change it now it will throw the tune off. Try changing where the secondaries stage.
Last edited by IRPerformance; 06-08-20 at 09:50 AM.
These are the settings I got from Chris at RP for setting up that injector/fuel rail combo from them -
Front and rear injector lag times 0.24 each Q Sec Injector size 2160cc Pri/sec transition % 65 Sec transition (ms) 0.90
Inj Sec lag (ms) vs Bat V 16V 0.629 14V 0.767 12V 1.011 10V 1.38 8V 2.134
6V 2.95
I would make sure they are set up properly.
There is a lot of new discussion about the transition with some injector setups causing dangerous lean conditions. It's REALLY early in the process and at this time not much is known about what setups are safe, what aren't, and where the problem lies.
But, this is a problem that most likely you would't feel driving around, if you are feeling that stumble/hesitation on the crossover something probably isn't set up or tuned right.
Agree with scotty. I would get on the google PFC tuning group with your questions.
Can't comment on the hesitation. I've never fiddled with my PIM voltage or had a hesitation issue. Why did you do that? As a safety precaution prior to tune?
I have the stock 550's and 2200's in the RP rail. Apparently you can safely run the 2200's with the correct settings, but you need to be sure the transition % is correct or you can drive the injectors below their minimum pulsewidth msec. It only happens in certain areas of the map. Not talking about base msec. It's the real injector pulsewidth that is the issue.
Personally, I used FC Tweak to change RP's recommended settings for better safety.
These are the settings I got from Chris at RP for setting up that injector/fuel rail combo from them -
Front and rear injector lag times 0.24 each Q Sec Injector size 2160cc Pri/sec transition % 65 Sec transition (ms) 0.90
Inj Sec lag (ms) vs Bat V 16V 0.629 14V 0.767 12V 1.011 10V 1.38 8V 2.134
6V 2.95
Here is a scan of the sheet that came with my injectors near the end of 2019:
They are properly added to the PFC on the "Settings 5" page. I even called RP in January and asked a few questions to make sure I was inputting them properly.
Suspicious that these number do not match yours. I assume yours are for the same injectors... When did you get those numbers?
Originally Posted by DaleClark
But, this is a problem that most likely you would't feel driving around, if you are feeling that stumble/hesitation on the crossover something probably isn't set up or tuned right.
I can definitely feel it cruising above 5K.
Originally Posted by scotty305
There's recently been some discussion about this in the PowerFC tuning group (formerly via Yahoo groups and recently switched to Google groups).
I'll ask arghx about getting into that group, thanks.
Originally Posted by scotty305
the OEM throttle won't allow airflow to the secondary intake ports when it's below 30% open
When the throttle is below 30% open or when secondary injectors are below 30% duty? I wonder if there is a setting for this in FC Edit... I'll look around.
Originally Posted by alexdimen
I've never fiddled with my PIM voltage or had a hesitation issue. Why did you do that? As a safety precaution prior to tune?
Yeah. Before the tune I set the boost to 10psi, set the PIM up to like 140%, and drove around with the wideband for a bit watching the A/F and slowly lowering the PIM.
Originally Posted by alexdimen
Apparently you can safely run the 2200's with the correct settings, but you need to be sure the transition % is correct or you can drive the injectors below their minimum pulsewidth msec.
My tuner did say he messed with the Transition % a bit and found that the one on the spec sheet (65%) seemed best.
Originally Posted by alexdimen
Personally, I used FC Tweak to change RP's recommended settings for better safety.
Here is a scan of the sheet that came with my injectors near the end of 2019:
They are properly added to the PFC on the "Settings 5" page. I even called RP in January and asked a few questions to make sure I was inputting them properly.
Suspicious that these number do not match yours. I assume yours are for the same injectors... When did you get those numbers?
I can definitely feel it cruising above 5K.
I'll ask arghx about getting into that group, thanks.
When the throttle is below 30% open or when secondary injectors are below 30% duty? I wonder if there is a setting for this in FC Edit... I'll look around.
Yeah. Before the tune I set the boost to 10psi, set the PIM up to like 140%, and drove around with the wideband for a bit watching the A/F and slowly lowering the PIM.
sec transition time
My tuner did say he messed with the Transition % a bit and found that the one on the spec sheet (65%) seemed best.
What do you mean? What did you change?
Those are the same injector settings RP supplied me as well. I am using the lag vs voltage table values at the bottom. And also the .90 transition.
FC Tweak is a software program meant to accompany FC Edit that (among many other things) can determine if your real injector pulsewidths are too low. If they are too low they are in a non-linear region where you have no idea how much they are injecting. FC Tweak will adjust your transition % to minimize this. Mine is at 60%, but that may not be the case for every tune. There's a very small window where switching between 550 primary and 550+2200's avoids under driving the big injectors. The software makes determining that point much easier and makes the change for you if you allow it to.
FC Tweak also adjusts the F/R lag times to compensate for the irregular stock LIM.
I can't comment on the PIM correction because I left my PIM voltage correct and tuned by logging afr's and correcting the basemap.
Here is a scan of the sheet that came with my injectors near the end of 2019:
They are properly added to the PFC on the "Settings 5" page. I even called RP in January and asked a few questions to make sure I was inputting them properly.
Suspicious that these number do not match yours. I assume yours are for the same injectors... When did you get those numbers?
Just looked at my emails, that was in an email from Chris Ott at RP on September 2017.
I got these for a friend's FD that we put all back together at that point. He's been driving it but it's basically un-tuned and running very little boost. We just haven't been able to get together to start working on getting things tuned for power.
I know very little about tuning, but for what it's worth, I installed the Rotary Performance rail with the Bosch 2200s and after updating the injector settings to match above ^ on the PowerFC base tune it ran OK but had hesitation. I mostly noticed it at lower speeds and RPMs, light throttle stuff. After getting a professional tune the problem vanished and the car is perfectly drive-able.
Dale I have the same injector sheet as OP that came in my kit. That's what I entered for my page 5 settings and FC Tweak added additional injector lag and lowered the transition as well (I believe it put it at 60 instead of 65).
So I did join the Google PFC Tuning group and am slowly going over the documents there. Looks like a great group!
I messed around with FC Tweak a bit over the weekend. My "real pulsewidth" was fine through transition, but there was a collection of unstable cells on primaries in the very low pressure region (P0/P1 with default scaling). I adjusted those and it actually seemed to improve things. I still get some hesitation in 1st and 2nd gears above 5K though (not that I cruise a lot at 5K in 1st )
FC Tweak is also recommending some changes to the injector settings from RP:
Secondary Front Injector Lag .24ms -> .26ms
Secondary Rear Injector Lag .24ms -> .36ms
I'm reluctant to make any changes here yet as I don't really understand what they do.
Another thing that stood out to me is that leading timing seems quite far advanced in the low pressure/high RPMs region (as high as 51 degrees at P01/N20). After doing some logging I don't seem to be getting much knock there, but maybe I should bring that down a bit and try just to make sure that's not a contributing factor.
So I did join the Google PFC Tuning group and am slowly going over the documents there. Looks like a great group!
I messed around with FC Tweak a bit over the weekend. My "real pulsewidth" was fine through transition, but there was a collection of unstable cells on primaries in the very low pressure region (P0/P1 with default scaling). I adjusted those and it actually seemed to improve things. I still get some hesitation in 1st and 2nd gears above 5K though (not that I cruise a lot at 5K in 1st )
FC Tweak is also recommending some changes to the injector settings from RP:
Secondary Front Injector Lag .24ms -> .26ms
Secondary Rear Injector Lag .24ms -> .36ms
I'm reluctant to make any changes here yet as I don't really understand what they do.
Another thing that stood out to me is that leading timing seems quite far advanced in the low pressure/high RPMs region (as high as 51 degrees at P01/N20). After doing some logging I don't seem to be getting much knock there, but maybe I should bring that down a bit and try just to make sure that's not a contributing factor.
The pri/sec injector lag is (according to FC tweak manual) correcting for the LIM irregularity. The transition change is supposed to optimize pulsewidths to avoid low msec values. Honestly you are better off asking these questions in the tuning group. They can explain the how and why of it better than I can. And there you can get it straight from the source re FC Tweak.
Yeah, that timing sounds unnecessarily advanced. Did FC Tweak flag it?
The pri/sec injector lag is (according to FC tweak manual) correcting for the LIM irregularity. The transition change is supposed to optimize pulsewidths to avoid low msec values. Honestly you are better off asking these questions in the tuning group. They can explain the how and why of it better than I can. And there you can get it straight from the source re FC Tweak.
Yeah, that timing sounds unnecessarily advanced. Did FC Tweak flag it?
Yeah TC Tweak did flag the timing.
I will post on the Google group after I finish reading through some more of the documents there and experimenting. Thanks for the help.
Just wanted to jump on here and report for future searchers -- after using FC Tweak to change the injector transition, lag times, etc (as well as a number of other settings) my motor is running WAY smoother. It's much smoother through transition, and no longer hesitant/buck-y under light throttle >5K. It even idles better and doesn't bob around with the AC on anymore. FC Tweak is as close to magic as you can get. If you have a PFC, buy FC Tweak (and no, I was not asked to say this, it's just a no-brainer investment).
Also, although I haven't yet bugged anybody on the PFC Tuning Google group for help yet, that place is a treasure trove of information.
That FC Tweak sounds like a great program. I wonder if he has figured out how to eliminate the off idle hesitation problem. I stopped using my PFC and went back to the OEM ECM because of that annoyance. Also boost transition from primary to secondary turbo is so much smoother with the Mazda ECM, virtually no dip at all versus a 2-3 psi drop with PFC. if the FC Tweak program could help improve those problems I would give it a try, and my PFC a try again. I see he also now has a more robust Pro version with an auto tune system using LAF signal, that would make it even better.
I wanted to update this thread again with more information about my transition/high RPM hesitation saga and the things that have further improved it in my case.
Basically, although FC Tweak helped A LOT (see post #17 above), it didn't completely alleviate the problem. It seemed to solve it at first, but after more driving time it was clear something still wasn't right as there was still some hesitation when on very light throttle in high RPMs. I called RP again to ask them about this, and also to ask if they'd ever heard of people fitting ID1300s into their secondary rail (because they apparently have very good low pulsewidth behavior). Chris basically said anybody making a fuss over low pulsewidths didn't know what they were talking about, and that older injector tech had terrible linearity down low but that they were always able to make them run smoothly. He also reiterated four points he had mentioned in the past:
1. Rewire the ignition switch power to the FP relay (see here: https://www.rx7club.com/3rd-generati...ewire-1124167/) He said this was the single most important thing to do. He also commented that he thought eliminating the low-speed circuit was stupid because it was loud, caused the pump to wear fast, and heated up your gas. (His words, not mine -- don't shoot the messenger!)
2. Replace the low-speed resistor. He said that the OE low-speed resister would cause a voltage drop right before the high-speed relay kicked in. Apparently they install a different resister on customer cars but they don't sell it on the site. He sold me one on the phone which I installed -- it appears to connect in parallel with the OE resistor. Here is a photo (1.5 ohm):
2. Improve the wiring at the fuel pump cover. He shared a few photos of what he often does for customers (below). Looks like he's using ~10awg positive wire through the bulkhead with the negative grounded directly to the hanger body. I chose to do it a little differently and more similar to what @alexdimen did in this post: https://www.rx7club.com/3rd-generati.../#post12260935 I've actually done this twice now. The first time I used 14awg Teflon coated wire, and this time 12awg PTFE coated wire.
Chris's:
Mine:
3. Upgrade the FP ground. The factory FP ground wire I believe connects to the ground block just under the trim behind the spare tire. It seems to be pretty beefy 14-12awg wire. However, when I removed the bolt holding the ground block into the body, the threads in the body were covered pretty good with paint. I can't imagine that creates a very good ground contact. So I threaded the bolt in and out a number of times until it looked like the paint was cleaned off the threads, and used a Dremel wire brush to remove some paint from the face of the hole. I suspect that this may be good enough by itself, but just to be sure I ran a new 10awg ground wire on a ring terminal through the fuel access door and soldered it into the OEM harness ground wire just under the access panel.
So at the time I had run FC Tweak, I had done #1, and #3 with 14awg wire. Now I have also done #2 and #4, and revised #3 with 12awg wire. This has again made a BIG different in the hesitation issues and general smoothness of the rev range (and I haven't even done any logging or re-tuning yet). Not as big a difference as running FC Tweak in the first place, but very noticeable regardless. I'd put my money on the resister being the main contributor to that.
Thanks for sharing, Rotary Performance has been building fast RX7's for a long time and it's nice to hear their opinion. Adding that second resistor in parallel with the original will send a bit more power to the fuel pump at low speed (including idle), I wonder if it would be possible to simply configure the PowerFC to activate the bypass relay earlier.
Seems weird they don't mention any of that when you buy the fuel rail/injectors from them, at least I don't recall anything in the instructions that mentioned any of this.
Seems weird they don't mention any of that when you buy the fuel rail/injectors from them, at least I don't recall anything in the instructions that mentioned any of this.
06-07-20, 11:29 PM
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