Or do we need to get bigger injectors? A buddies car ran @ 99% duty cycle before putting on an FMu and volt blaster. We thought adding those two (and not tweaking the program at all) would lower the duty cycle. It's higher now (115%) and I'm wondering if we change the offset will it lower things back down. Which way would we change the offset (a little higher than the rating on the injector or lower)? The car runs pretty rich (950+) and has enough injector to supposedly run without an FMU. Is it even possible to lower the duty cycle? Any info is appreciated, thanks and take care.

 

The problem is the PCM doesn't have any way to know the FMU is there. The FMU raises the actual fuel pressure, increasing the flow rating of the injectors under boost, but the PCM doesn't have any way to know this.

And you probably don't want the PCM to know this. You are using the PCM to supply the fuel based on (I am assuming) the 1 bar MAP sensor. Then you are relying on the FMU to increase fuel pressure in proportion to boost, to address the fact that the actual manifold pressure is now above 1 bar - while the stock MAP sensor/PCM is only set up for 1 bar. The PCM is supplying the fuel for an NA setup, the FMU is supplying the fuel for the boost.

If you have established that you have the correct A/F ratio with that setup - and using the stock narrow-band O2 sensor mV's is a serious mistake in that respect - then the duty cycle calculated by your data logging software is somewhat meaningless. Duty cycle is calculated from what is visible to the PCM, but the PCM doesn't know about the extra fuel pressure.

Hard to explain, but you have two different fuel controls that need to work in concert.

 

Fred,
I understand the need for a wide band O2 set up (in the works) as well as the fact that to data logging records PCM function and FMU is seperate from that. I will hold off on the tuning till I wrap a few things up (like the wide band) and go from there. I would ask this though, can 36# injectors feed 6-8psi withOUT an FMU on the right tune using pump gas? Was I there in the past with maybe my injector offset being a little low? I added the FMU and volt blaster fearing another blown head gasket. May have been overkill instead of tweaking an already useful tune. Any info would be great. Thanks and HAPPY NEW YEAR...

 

As usual, Fred provided excellent info. But in case anyone reading this is still confused, I'll attempt to clarify one aspect. There is no point in trying to do any tuning of the fuel delivery until you know if it is rich or lean. The best way to do this (by far) is with a wide band O2 sensor. In lieu of that, the old fashioned method of reading the plugs may be of some use. You want it pretty rich (some black soot on the plugs) if using this method for tuning a blower car.

BTW: if you saw the duty cycle increase from 99% to 115%, you must have made some other change. There's no way the PCM would do this just based on adding an FMU and the Voltblaster. One other thing: why did you anticipate that VB would increase fuel delivery? It might, if the pump couldn't maintain FP at stock voltage, but otherwise would have no effect.

Rich Krause

 

Rich,
The bad news is, I never saw the 99% duty cycle logged run. My friend (who did the tune) was the LT-1_Edit master and he told me everything looked good except that the duty cycle on the new injectors were a bit high, as high as 99% at the peak RPM. Shortly after that I popped a headgasket being dumb. It was hot out (nearly 100 degrees) and I stayed in the throttle much too long. So anyways I decided it needed more fuel. My friend had moved and I was just getting hooked up with LT-1_Edit. Never datalogged the car myself before and I totally agree, NEED WIDEBAND. It's on the way but I decided to at least datalog and see if there was any knock (ran CAM2 and all the safety devices in effect). Ran SLOW, pumped a pretty healthy amount of black smoke in the video and looked rich in the log (I know, not detailed enough to know for sure). I saw on the log that as the VB kicked it, the duty cycle went from 70% to 105% instantly (could be coincidence) so I disconnected it and tried again. The duty cycle stayed a little lower but was still too much for my liking. I have not been WOT since. I notice that the duty cycle stays fine till the upper RPMs (4500+), then it gets well over 80%. I saw my program had the injector offset at about 35 and change and got a link through the LT-1_Edit mail list to different offsets which recommended 38 and change (If memory serves me correctly). I have not tried that yet (I'm out of the country for a few months with work) but would like to dive in when I get home. By the above statement of safety devices, I mean SFMU, VB, and water/alcohol injection. I run with the Knock window in view on the laptop and back out if I see any knock (nothing more that 6-8 degrees of retard on one run). I wanted the car rich and to tune down from there so I don't lose another head gasket (or worse). What do you all think? It has only been tuned by my friend and he got it from a 13.2 @ 107 to a 11.5 @ 120 so I think he made headway. That was no FMU, no VB and no water/alcohol injection. It's on the stock pump with T-Rex and I'm leaning towards a racetronix pump upgrade to do away with the T-Rex. I haven't seen the pump fall off but I was dumb (again) and put the gauge in a bad place for monitoring. To be honest I'm not even sure of the boost. It's supposed to be 8psi but I've heard on the board that you can't get a pulley set for 8 psi. I had the stock 6psi set up and bought a pulley and 42.5 in belt. I can't remember the size of the pulley but the seller claimed it'd make 8 psi. Sad huh? I have months away from the car due to my job and the details get lost in my mind sometimes. I have it all on paper or data on the laptop at home though. Anyways, I'd love to get this dialed in and any knowledge you can pass on would be great. I have a TT Supra I need to stay a head of. Thanks and take care.

 

Man, if you've got a Supra to beat we've gotta get this nailed

Like I was saying in the previous post, you need more data. A:F ratio, FP, MAP at a minimum. Leaving that aside, if the PCM is really trying to command a duty cycle of 115%, that's bad. The injectors will overheat if you try to run them at >90% duty cycle and may begin to operate erratically, so this is to be avoided. If you verify that it is really rich, you need to back off on the injector pulse widths (usually done via PE tables) untill you see duty cycles in the <90% range, while monitoring AF ratio.

If you can get a decent AF ratio (~12.5:1) with a duty cycle <90% you are golden and can save your money as far as the fuel pump goes. If this doesn't occur, there are too many things to look at than it's worth trying to list at this point. But a couple of other things. I have nothing against the Racetronix system, in fact I like it and may need it myself this year. But most people who get it don't need it. My current setup is >700rwhp with a single 255lph intank Bosh pump, stock lines and regulator, and a Kenne Bell "Boost-a-Pump". The BaP is a great little device which increases voltage to the fuel pump when the car hits boost. I used to use a Voltblaster, but it made me really nervous putting high voltage through the whole electrical system. I am convinved it shortens Opti life span. Anyway, the BaP is a much more specific solution to getting higher voltage to the fuel pump(s).

Rich Krause

 

The T-Rex in-line pump will do very little to improve your available fuel volume offered by the factory pump. For the most part it will extend fuel delivery somewhat at high pressures usually for the FMU’s function. The T-Rex pump does not flow as much as a HP Walbro plus the factory pump acts as a restriction that it must draw through. We had a C4 customer on the dyno this past summer with a Vortec supercharger + in-line booster pump (aka T-Rex), factory in-tank pump, and a FMU. When he punched the gas the fuel pressure would spike really high (75PSI) and then drop 10-15 PSI as the boost went up with RPM. The pump system could simply not keep up. We removed the old system and installed a single in-tank HP system. The FP then hit 75PSI+ under WOT (max boost) and stayed there. This was way to much pressure as the car had been tuned to compensate for the old fuel pressure drop. We installed a 1:1 regulator, dialed the base fuel pressure in at 44PSI and recalibrated the PCM. Problem solved.

The B-A-P / pump booster is a good item but it costs as much as or more than a HP pump upgrade but offers much less gain in performance. Installing a B-A-P before an HP pump is like putting the cart before the horse IME. The B-A-P can be added as a plug & play option to the Racetronix Series II upgrade harness if the capacity of the single in-tank pump needs to be extended without the need to cut into that factory wiring. To install a B-A-P as-is would require splicing into the factory wiring.

The injector duty cycle can abruptly skyrocket on an LT1 if large calibration values are input into the ECM/PCM or if the MAF is maxed out at higher RPM’s. (typically 4700RPM+ and or 425gm/s). This has to do with the mathematical limitations within the factory computer and / or the transition between mass air and speed density fueling.

Using a volt-blaster is a good idea provided the voltage is not set too high. A good range to shoot for is 14.5 +/- 0.5V under WOT. Any more than that will cause the alternator load to shoot way up and may cause certain watch-dog functions of the ECM / PCM to alter the engine’s operational parameters. The slightly higher voltage will improve fuel pump performance, injector opening time and ignition voltage.

The Opti-Ppark will not be affected by this voltage increase as the optical sensors inside the unit are powered via isolated voltage regulators within the PCM/ECM. The Opti-Spark produces low level CAM and CRANK signals for the ECM/PCM only. The spark distribution function of the Opti-Spark system will not be damaged by the increased ignition voltage as the addition of a MSD or similar type device will amplify ignition voltages way beyond the factory system with no detrimental effects. Rammchargers distributes a volt-blaster with adjustable voltage and TPS trip points.

HAPPY NEW YEAR!!!

Jack
Racetronix

 

Jack, Rich and Fred,
Thanks for the great info. I've wondered about the MAF possibly maxing out and will have to check my logged runs. It does seem to go from "OK" to "OH $HIT" in a hurry on the logs. Decent injector duty cycle one second and overboard the next so maybe it's something like the MAF tripping out a bit or the fuel pump falling off. My biggest desire is to keep the set up simple and safe. Add-ons like the water injection and VB were not part of the original plans but neither was a blown head gasket. I wish there was a decent guide to tuning via LT-1_Edit and some common mistakes that people make. I want to keep 99% of the tune as is because the car seems to run around fine for the times it runs. No overheating, no stalling, no SES lights, tranny issues, etc, etc, etc. So I just want to fine tune the fuel and timing, and keep the rest as is. Thanks a bunch for the advice and I'm pretty sure I've got the Supra covered (at least .7 sec and a few MPH so far).

 

I appreciate having someone who knows a lot about fuel systems (like Jack!) posting. I agreee about the BaP, of course it would only make sense after installing a high outpput pump first. Once you have done this, get rid of the T-Rex. If it's still inadequate, the BaP is a nice intermediate step that make make more costly solutions unnecessary. And it installs very easily.

Electrical stuff is my weak point wrt automotive knowledge. So I may be way off base and would like to know if I am. But the VB will further increase voltage on the high voltage (distributor) side of the Opti, right? Yes, the necessary aftermarket ignition does this already. But the VB will make it worse, no? I went through two Opti's in one season with the VB and a Crane box. The VB was cranked up (it didn't do any good without being cranked to the max), admittedly. Took the VB out, installed the BaP, and the Opti has lasted two years since then.

I don't think maxing the MAF will make a "sudden" spike in the PW unless it is maxed "suddenly". I am not doubting what anyone else has observed, but I have never seen this and have seen a lot of LT1's on the dyno with maxed out MAFs. What is "sudden"? It would be helpful to see the datalogs and know the operational conditions when this occurred to really figure out what's happening. Otherwise we are just speculating. For example, my datalogging software has a 0.2sec sampling interval. If I am logging during a road test and am in a low gear, I can see pw go from ~3msec to ~12msec bewteen two data points when I crack the throttle. This is in the range of 50-75% of duty cycle. Once the throttle is wide open, the delta is less, but the pws still go up pretty quickly.

Rich Krause

 

It seems like he noticed a simultaneous deterioration of the duty cycle and the VB kicking in. But the rough measurements of the stock O2 sensors aren't showing a simultaneous deterioration in fuel flow. That would lead me to believe there may be a glitsch in the PCM fuel calculation tables. Almost like the PCM is calculating the pulse width with new data based on the voltage change, and getting calculated pulse widths that exceed 100% of the time available.

What does the stock PCM use to correct for system voltage? I would assume it's offset vs. volts. Is it possible you have this table screwed up? Almost like you put a larger value for offset at higher volts instead of a lower value, resulting in longer calculated pulse widths.

Just thinking out loud at this point.

 

I wish I had the logged runs to email to you. I am half way around the world right now and my laptop is sitting at home (of course). I had the sampling set quite short as well and I know giving you the play by play won't help much without raw data to see for yourself. Still the tune could be off, we only tweaked it once since the basic tune (went from 11.9 @ 116 to 11.5 @ 120 with a drop in outside air temps helping). The car still has some left in it, I'm fairly sure of that. I know that injector duty cycle really went sky high when the RPM's climbed through 4500+. It could still be in need of upper RPM fine tuning or maybe just the fuel pumps aren't quite keeping up at those RPM's, maybe the VE's are off as the boost really starts to build. Hypothetically though, 36# injectors should be able to feed a motor at about 8psi (non intercooled) without an FMU right? General consensus seems to be against using any FMU if I remember correctly. It's the Vortech SuperFMU but I think it's overkill and adds complexity. Either way, I wish I had the laptop to review and pass on for you to look at. Thanks for the help so far though and maybe we can nail this down when I get back stateside (hopefully in March). Take care and have a great new year.

 

Why do you feel the VB will not do any good without being cranked to the max??? Are you looking for some illusive visual indicator(s)? Even a small increase in the range of 1-2 volts will do much to improve my previously mentioned areas of vehicle operation. The VB has nothing to do with Opti-Spark failure. Opti-Spark units in general are unreliable. We have seen new out-of-the-box units fail. Perhaps you had a bad ignition system component that was causing excessive arcing within the Opti-Spark unit? A CD ignition box, low-resistance ignition wires, plug-gap and cylinder pressure will have a much greater effect on what goes on inside an Opti-Spark's distributor section than the effect of 1-2 battery volts. To put it quite simply your situation was related to something else but NOT the VB.

This fueling change is very abrupt to the point of one numerical value. As soon as the MAF tables jump out of range SD mode takes over. If the VE tables and WOT fueling tables are not calibrated well the transition can be very rough. Datalogging will not always show this as the frame rate is not high enough. If the MAF readings are within 25gm/s you are too close to the edge and should be tuning the VE and other RPM related WOT tables to compensate.

Jack
Racetronix

 

I can certainly understand that. You speak plain english Jack and that helps a dolt like me. I'll have to check the MAF readings and see if they are near the point where things get "out of sorts". I still like the idea of a pump upgrade but I'm going to wait and see if I see my FP falling off. Anyone know if the 36# injectors will feed the motor safely without an FMU (pretty much stock, just beefed up internals with a supporting cast of bolt ons)? And I was wondering, when I get the wide band, any advice on tuning for approx 12.5:1? Is it all done in the VE tables? I only touched the LT-1_Edit myself for 2-3 days. Maybe there is a guide out there somewhere I can scan while I'm away and needing some decent reading material. I've read a lot of the scanmaster stuff on Freds (Injuneer) site. Well night all, I hope the first day of the new year went well for everyone.