I'm still concerned that the code will have shortcomings. I remember how poorly the Edelbrock PFI conversions ran using TBI strategy. But the first step is determining how the memcal will cause the driver to fire.
I'm still concerned that the code will have shortcomings. I remember how poorly the Edelbrock PFI conversions ran using TBI strategy. But the first step is determining how the memcal will cause the driver to fire.
personally.... my opinion/route would be to grab a MEMCAL or mod one to use single-injector peak/hold TBI mode and use a mask that is intended for single-injector TBI on a 7727/similar. then just skew a few values in the calibration and you have a more or less fully functional unit. BPW at idle could be pretty low even with factory sized injectors.
or internally mod the 7727 to use the second driver. requires some delicate solder work. then you just need to use a mask that supports the second driver natively(or mod the code to use it). would allow twin injector TBI scheme.
or on the really oddball end of things... run a pair or more of low impendance injectors wired in series... kind of defeats the purpose of low-z injectors, but it would work, just need some serious tweaking of the BPW offset tables.
factory applications, the 7727 was used on the 90-91 corvette L98 with high-impedance injectors, so 8 amps per driver is safe enough for GM to release on the road in their highest echelon of car.
1995 Chevrolet Monte Carlo LS 3100 + 4T60E
No progress made today on the bench testing, maybe I'll get time in the next few days. I have a few Old School EFi business appointments that I need to complete in the next few days. My plan is to verify I have a fully functioning TPI / MPFI configured '7727, then use the o'scope to get a "baseline" DRP / alternating injector firing. This is not my first "from scratch" EFI harness I've built, but I need to verify everything is functioning first, then experiment with a '427 Memcal. This entire system is already sold, so I need to be cautious with my experiments.
dave w
Some progress this morning before going to work (day job). I connected the O'Scope to the injector, O'Scope ground to Battery Negative and O'Scope positive to the Ignition On connection to the injector. I have the injector harness unplugged from the injectors and a noid light on one of the injector connectors, thinking some sort of load is needed? The electric drill motor I'm using is at max speed about 2600 RPM shown in the .adx dash screen shot. I'm going to keep the speed at about 2600, hoping the dual trace measurements will be consistent.
dave
Last edited by dave w; 04-26-2012 at 04:43 PM.
The drivers will supply a current path without a load but since they're on the ground side you'd have to measure between B+ and the injector- to see what's happening. The P+H drivers will stay in P mode without any current.
and IIRC, you'll need to give it at least 4 amps of load to get it to switch into hold mode, yes?
1995 Chevrolet Monte Carlo LS 3100 + 4T60E
I plan to test / O'Scope with the injectors connected to the ECM wiring. I'm wanting to make sure I still have a good system to deliver to the customer, so I'm going at a slow pace.
dave w
Just to let you know I ran a set of TBI injectors dry on the test bench probably 10 minutes each time at least 100 times and they were serviced at Mr Injector as fine and have been running in kids truck tuned fine for over a month now. So I don't beleive short periods of dry testing hurts them...
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
I have a few very quick video's of the stock TPI, showing dual trace. The upper line is the injector, the lower line is DRP. I'm having trouble getting a good sync. BTW, after blowing two main battery fuses, I figured out one of the probes I was using was bad.
dave w
I have attached a zip folder with the data capture, O'Scope Video's and a couple .xdl files. The only change I made between the O'Scope video's and .xdl files was the TBI memal. The O'Scope settings were not changed. The same PROM chip was reused. I've varied the distributor speed (ENGINE RPM) for the O'Scope videos hoping to get a good sync. I can't tell for sure, but I'm not seeing a change in the DRP's vs Injector Trigger? Maybe what I'm seeing is the TBI video is showing 2 DRP's and 2 Injector Triggers compared to the TPI video showing one 1 DRP and 1 Injector Trigger in the same time interval? The video's are Quick Time, so hopefully a frame by frame review of the video will capture the data? I'm on a very strict timeline, the Harness / ECM has to be delivered Monday!
If anyone has a suggestions on how I can better capture the data, "NOW" is the time to speak up! I'm not likely to have another opportunity to reproduce this test setup in the near future! I will make a very focused effort to accomplish a logical suggestion!
Feel free to link this post to other forums, hopefully to cast a larger "net" of ideas.
dave w
Last edited by dave w; 04-28-2012 at 08:15 PM.
More Pics of the O'Scope settings.
Channel 1 is the injector pulse.
Channel 2 is the DRP.
dave w
Dave, I'm swamped with work and have not been able to keep up here and probably won't this week. If you are referring to needing some help from me give me a call and I'll get the scope out with shots of whatever your looking for so you can verify your findings.
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
Mark, I'm looking for alternative ideas for data collecting while I have the test bench set up. The video's / .xdl's should serve as a library to reference at a later date. If you happen to have time in the future to review the data, that would be welcomed and greatly appreciated!Originally Posted by EagleMark
dave w
Dave,
Capture both injector outputs with TBI memcal installed. Forget DRP as we know synchronous pulses are tied to it. Do same with 7727/7730 memcal.
Excellent idea, that is exactly the kind of suggestion I'm looking for!
dave w
Posting Permissions
Reply With Quote
Bookmarks