Ok, I just got my car running again on Saturday after dealing with the '99 Immoblizer that self-destructed and shut down the engine while at the strip.

I was just running the car on the trailer and revving up against the rev limiter and listening to the engine cut out and restart itself (just because I could) and I wondered just what is being cut off and how ??

I didn't see anything in the '99 FSM, and ORG search didn't turn up any details, so I thought I'd ask here. Does the ECU cut off ignition pulses, cut off injector pulses, shut down fuel, or what??? I really want to know what EXACTLY is cut off.

If it's ignition, I need to be REAL careful when testing my MSD version of the Shift_Fast automatic shifter - if its the injectors, I'll still have spark at rev limiter cut and fuel/nitrous from the NX nozzles. If it's both, then I still need to be real careful....

I'm going back to KCIR this Wednesday and spray a bit - I need to finish testing the manual and MSD versions of the Shift_Fast controller. My last baseline run was a 13.41ET with the stock automatic shift points - then my Immoblizer self-destructed and the car went back on the trailer.

 

I have always been told and learned that its a fuel cut off. Thats why its VERY bad if you hit the rev limiter while spraying nitrous, because theres berly any fuel going to be present at limiter and cause instant detonation and blown motor.

 

yeah, fuel cut

 

But does what you heard mean that the fuel is cut at the pump, or that the injectors are cut off, with full fuel pressure still there?

Wet shots use nitrous and fuel from the pump. I've sprayed a 50-shot through the rev limiter going from 1-2 and 2-3 and the engine belched but didn't blow.

Did I lose the fuel pump pressure, or not? I don't know. I need to find out EXACTLY what happens when you hit the rev limiter. I expect some folk here will know the details - we'll see.

 

But is that fuel cut because the injectors are not being triggered from the ECU, or is the fuel pump shut off?? Or something else ??

 

i believe it means the injectors are not pulsed by the ecu.

 

Grey, with all the datalogging I've done via Consult and with EU I can tell you what happens.

First off, the others are correct, the cut is fuel only. But nothing else takes place. The fuel pump operates normally, and the ignition is not cut at all, in fact the stock timing map continues up to at least 8000 rpm from what I can tell (haven't revved my car past that though... )

The fuel cut is not a complete cut though, nor is there any missing pulses or anything. The only thing that happens is that the injector PW's get greatly reduced. For example, on DEK injectors (290cc) at stock 4th gen fuel pressure I was seeing pulses around ~1ms (at 6500 rpms this corresponds to an injector duty cycle of about 5%).

Hope that helps.

 

Just because your nitrous fuel jet is supplying fuel doesn't mean you are safe. Your fuel injectors supply BY FAR the majority of the fuel going into your engine when you are at WOT, just a little extra being supplied by the nitrous fuel jet. If for instance your car is making 250whp with a 50 wet shot on it, your fuel injectors are supplying 200hp worth of fuel, and your nitrous fuel jet is only supplying the extra 50hp worth of fuel. When you hit the fuel cut, your 250hp worth of fuel becomes 50hp worth of fuel, because 200hp worth of fuel that was coming from the injectors has just disappeared. 250whp worth of oxygen and only 50hp worth of fuel = bad. Using some very crude math, if you were at 11:1 AFR right before the rev limiter, and then you hit it, your airfuel would jump to approximately 55:1 because your fuel injectors just shut off (actually they don't shut off completely but they come damn close).

 

Dandy, many thanks for the verified information. Bet you can guess where i'm going with this - if you had normal-width injector pulses all the way up to 8000RPM, would the engine then operate normally? In open-loop, are the injector pulses a constant width, or do they vary somewhat with upper-range RPMS? Maybe the FSM would have clues - that's for later.

If there is an injector pulse of any width, simple electronics (a one-shot) can extend that pulse width to a fixed pulse width. If varying pulse widths are required, that would be a little more complicated, but not much.

This might be the key to eliminating the rev-limiter in the 1998 and 1999 ECUs. If the only thing that happens at "fuel cut" is shortening the injector pulse, then the pulse can be re-stretched.

Do you have any hard data on the injector pulse duration and the DEK injectors? Or any other thoughts on the subject ???

 

Nealoc187,

I understand the point your'e making here - but- I'm not caring about remaining safe while spraying beyond the stock rev limiter. I want to find a way to keep the injectors spraying beyond the factory fuel cutoff point.

If that can be made to happen, will the engine continue to pull past the old cutoff point?

 

Oh ok I see what you are saying. yes it will continue past the old fuel cutoff, dandymax is already doing this with emanage ultimate on his 1998.

 

Thanks - and I just spotted Dandy's post about injectors pulse width from yesterday. Duh.

Now if I can keep the injectors at normal duration after 6650 RPM up to maybe 7500, can I blow up yet another engine while spraying ??

This might be a way to beat the RPM cut - I gotta try this - build some IC one-shots that trigger on any pulse and hold the injector open for the same duration that exists at 6650 maybe ......

 

wat if you dont trigger it on time? lol. n completly screw everything up? cant u just get an EU and take care of the rev limiter with it?

 

EMU and EMB should both be able to keep the pulsewidth up all the way to 8000. After that the ignition stops.
I would not try reving that high spraying until you have it working well NA.

 

I can trigger the "RPM extender" with a MSD switch, for testing - that way, the RPM extension can be automatic.

It's knowing what is really happening with the rev limiter that gave me the idea. The electronics should be simple to build and test. If I can just push the engine to 7000 under full power, I've got it.

But for now, I've got a date with a live engine and a dry track at KCIR on Wednesday.......

 

Truth - but i want to try it - but i'm gonna sneak up on this one. It will take some reading and measuring to find out how much current has to be switched to ground to pick each injector solenoid, then must locate an IC one-shot that will trigger on the negative slope, that can be either slaved to the incoming pulse or switched to the extended pulse. I know, I know -

How many people can benefit from removing the RPM limiter from their stock ECUs ??? Let's hear it from the Maxima racers out there!

 

SR20DEN and I discussed the possibility of increasing the rev limiter with EMB at length and came to the conclusion that it wouldn't work because EMB doesn't control pulsewidth directly but rather increases or decreases it by a percentage. We thought that at the rev limiter, IPW was 0. so any % increase of 0 would still be 0. but if it's not 0 but rather some small number, then that means you could increase it with EMB. However, EMB only allows you increase IPW up to a certain percentage - I wonder if the allowable percentage increase will be sufficient to get the injectors pulsing long enough to maintain the required fuel flow? What is a typical IPW at 6500 rpm? like 10-12ms is what is sticking in my head for some reason.

I realllllllly wish I would have tried this on my old motor before I yanked it. Motor still ran fine (hell I trapped 119mph on it) but it just had a blown HG, so it would have been a prime test candidate. dang.

 

I wouldn't just jump to that conclusion... also, how do you know the ignition stops after 8k?


He and I also talked about it several times a few months ago. I just posted about this very thing over in the boosted forum thread... But yes, the Blue seems to be limited in that it uses DC%'s only, not durations on the Additional Injection map. Meaning if you only have 5% DC past the fuel cut, and can only add up to 100% DC, you can still only get to 10% DC when you need around 60-70% or so. 10-12ms is in the ballpark yes but a bit low for stock 4th gen injectors. I see around 10ms now with DEK injectors at 46 psi fuel pressure. We had also discussed using the sub injectors but there are only 2 channels so you'd run each bank off one channel, it's batch fire etc... not sure how it would work, and the EB doesn't have a crank/cam sync either IIRC.

Grey, IMHO your best bet for a good all round tuning solution really is the EU. But it's up to you of course. Keep in mind too that the IPW's won't usually stay constant over a certain rpm range. It depends on the mass of air the engine is inhaling (ie the VE). If you still want more detailed info I can get you some PW data from logs I've done.

 

Dandy - I hear you - but I'm not willing/able to take on the EU project at the moment. My spare time is kinda limited - and the season here effectively ends in October. First I want to push the automatic tranny shiftpoints a little higher and document any gains, then see if I can push beyond the factory rev limiter by continuing IPs with some add-on circuitry. Maybe the combination will put me into the 12s. Maybe. By then, snow will be flying.

I would very much like to see your logs and anything else you think might educate me. You can Email them to hwb123@aol.com if you want. I appreciate the comments from the serious racers here on the *.org. I try to give something back when I can, but that's not too often. Mostly I just share the pain.

LATER EDIT: Dandy - Ok, I read some of the Emanage Ultimate specs, and I gotta agree with you - this looks like the best solution for my /rev limiter project. How about a quick opinion? - I can connect the EmanageU to just a few points (tach, injectors) and control the fuel flow to the injectors up to ignition cut (or 8000 RPM) using an internal map? Or what is required to do the job???

 

I haven't looked at EMBlue as much. I didn't think about EMB not being able to control the injectors via duration. Shows the advantage of someone who has actually done something vs. an internet mechanic like myself.

I posted this before you corrected me in the other thread. I saw you and SR20 talking in the other thread and I must have gotten ahead of myself when you confirmed that you don't need the RLC map.

Once again I haven't tested it myself, but Travis (TurboS13Hatch) said that most Nissan ECUs can't go past 8000, unless they rev pretty high stock, and that was one reason he was putting a stand alone in one of his projects. I don't know for sure whether this applies to the A32 ECU or not. I have also not heard of anyone going over 8000 with a JWT ECU, although this could be a limitation of the actual ECU, JWT limiting their own liability or something, or it could just be that no one has ever needed to or been able to rev that high before.

 

Sorry Harry didn't mean to ignore you this ^^ somehow escaped my attention and I just realized now..

Yes you can connect the EU up to just the basics, -power, ground, tach, injectors and MAF etc- and control fuel with 16x16 programmable maps via a laptop. If you add the coils in you can also control timing advance and retard.

 

Dandy, I'm used to being ignored - I'm married.....

That sounds good - the EU would be easier to slide into, with just a few functions at first - don't know if you noticed, but I got the Shift_Fast to shift at any programmed RPM, so if I can use the EU to bypass factory rev limiter, then I can control shift points to match - although shifting an automatic at 7500 would take some getting used to....

That auto does take a lickin' and keeps on tickin' , though. I was screeching slicks at the 1-2 and 2-3 shift last night - just banging the gears...

I think you were going to Email me some details of injector timing maps as well. I was curious about what settings you use to extend the fuel-cut.
"I would very much like to see your logs and anything else you think might educate me. You can Email them to hwb123@aol.com if you want. "

Thanks.... Sorry about your engine - that's an impressive car (I'm on my third engine)

 

Dandy, nealoc,

I have heard that possibly while spraying nitrous, if you hit the rev limiter, it won't stop you all the time. Say i spray while in neutral, would it just keep going but my only additional fuel like nealoc was saying would only be my fuel from my fuel jet and hardly anything from my injectors, or is this just a whopper... I don't wanna try it but I was wondering if it could be true.

grey, I gotta finish installing my 00vi still, argh, its been one thing after another with my car I have 2 full bottles waiting for me, bad news is the track is now officially closed. BTW, I am still on my first motor, 165,XXX and still strong, with a 125 shot. I sense a nearing to the end of it soon though.

 

You married yet? That can excuse a lot of delays, you know...

Sheesh - 165K and still spraying a LOAD? That's impressive. Don't break it, replace and keep as an honored spare engine.

With recent developments, I'm looking forward to 175-shot and shifting my automatic at 7500 rpms. There's a 12sec run out there with my name on it.
-- or another junkyard engine....

 

uhhh, *cough* junkyard motor *cough* is what I see, lol no really i think i could spray 175 with 100 octane, maybe i will see before my 3.5 goes in.

I did get married, the 15th, got back from the honeymoon a couple days ago, alls good

 

Hah! Let's race and see who sprays 175-shot first! Junkyard motors are OK - I swear the Maxima 3.0 is much stronger than any US product - after 100K miles, anyway. My present motor is a '99 Infiniti w/88K, pulled from a yard in Wichita KS and dropped in my car. It's now running 13.4s consistently, and all I've changed is oil and plugs... Shaved ground plugs and Sunoco 104 FTW. If I blow it, I've got enough engine parts to make another one! But, a 3.5 is next.

Congrats on the marriage - she's obviously a brave woman...

Don't spray through the rev limiter - You'll go so lean so quick........ The fuel cut at 6550 doesn't stop iginition - just the injectors, and that won't save you. If you're worried, use a MSD 8969 RPM switch and set it to 6500, use it to open the spray solenoids at that point. That way, the fuel cut will also be your nitrous cut. Just my opinion..

 

I did have that MSD switch but I sold it, I do have a spare RPM swith I could use, I really should use it especially when I get my 3.5 in. I am just having a hard time deciding who I want to go with in regaurds to building it. Too many people have been having problems with Tilley so I am lookign around right now.

I should have my 00vi done TODAY and if so, I will be spraying tomorrow, keeping my fingers crossed..

 

Let us know what happens - I can help you locate a good junkyard engine...

 

Sorry Harry just haven't had time to dig through a bunch of old log files and find something applicable to send you. Maybe in a couple weeks time after I've moved into my new place. I'm trying to finish up an EU write up too, having a hard time even working on that with the move goin on...

 

Dandy, I'm mostly interested in the actual width of the injector pulse just before cut .......... I know it can vary a bit from the ECU, but I still have some circuit mods I might try to defeat fuel cut...

I can trade you some info on how to raise the 12 volts to your ignition coils for about $50 US... a power supply actually switchable from 15 volts to 24 volts to the common plus-bus of the ignition coils. I'm running one now, and it did open the OEM 10-amp fuse, but a 15-amp fuse is golden. The local weather has been too cr*pp* to go out and spray a few on-ramps for that top-end pull, but maybe this weekend.

I don't like the .030 spark gap I have to use - I'm shooting for .045 or greater.

I like lots of spark - my old '68 850cc street/strip Triumph fueler bike could be kickstarted instead of using a roller, using Mallory epoxy coils, which made me a believer in plenty of spark, but I'm just getting to this Maxima's spark issues.