A real test of the difference a fuel pump makes (dyno)

[Guest bastaad525]

Just got back from the dyno, and was... a little surprised and ... a little dissapointed by the results. Okay a lot dissapointed.

 

Last time I dynoed, like 2 mos ago, here is what I got at the wheels

 

199 rwhp @ 5200rpm (spiking... peak of 2nd run was about 194)

234 rwtq @ 4100rpm

A/F ratio was at 13:1 and leaning slowly by 5000rpm

 

After much discussion and seeing what people had to say here, I was convinced that my A/F ratio was going lean and my hp peaking shy of the expected 5500rpm (which is where stock peaks at, and this has been dyno-proven) was due to the lack of ability of my stock fuel pump to keep up with 10psi of boost on the top end. Most people here will say that the first three mods people HAVE to do to a turbo Z are exhaust, intercooler, and fuel pump. I fully expected that upgrading my pump would take care of the lean-ness after 5000rpm and I would get back a bit more hp on top as a result. Well... here's what I got at the dyno today:

 

200 rwhp @ 5200rpm (spiking, peak of second run was a more stable 197)

234 rwtq @ 4100rpm

A/F ratio? 13:1 by about 5200rpm and leaning slowly

 

The ONLY mods I have had done to the car between then and now were upgrading to an MSD fuel pump, doing the relay wiring trick for it (thanks for those Tim!) and switching over to a larger return line.... all three things that SHOULD be supplying more fuel more reliably.

 

 

 

I am not impressed.....

 

 

I can't speak for the guys who want to run 20psi on t3/04's and push 300+hp, I'm sure that a fuel pump upgrade IS a requirement for them, but it would seem that for me, running 10psi non intercooled, that the stock pump was perfectly cabable of handling the needs of my motor. Let this be an example for anyone that has similiarly low goals as me. Upgrading the fuel pump is NOT a necessity.. then again I'm probably the only one content to stay at 10psi

 

I have also installed a fuel pressure gauge so I could see what is going when she's on boost. At idle the fuel pressure is at about 35psi, goes up to about 40psi when throttle is opened wide, then jumps up as boost comes on, to about 50psi and stays there pretty steady all the way up to 5500rpm (the highest he took it during the testing) Judging by the fuel curves, the stock pump was probably doing just about the same. I'll get the new sheets scanned soon, but I must say, they are pretty much identical, including the fuel curves. Altogether some $200 spent and a fair chunk of a friend and fellow Z enthusiasts time with no return for the investment. Unless you count the the nice strong fuel smell in my car as a return Okay so there was like 3hp gained that could just be fluctuation in the testing equipment plus it was a colder day out today, started raining as we were testing.

 

 

Anyways... couple questions....

 

does anyone know why the stock ZXT EFI likes to run super rich from like 2500-4000rpm, at like 10:1, and then likes to lean out considerably and stay at about 12.5-13:1 for the rest of the rev range?

 

Is 13:1 A/F ratio safe at 5500rpm/10psi or am I just knocking on detonations door?

 

Ah well... at least I dont have to worry about that old pump going out on me any time soon anymore.

[Tony D]

i can't speak to the richness on the bottom end other than to say the pressure rises quicker than the engine can rev, and it gets rich.

 

As for the top end, it's due from what I have deduced (and others correct me if I'm off) as the injectors are just about maxed out anyway.

This is why the RRFPR seems to tweak the engines a bit on the top end keeping it richer up top thant stock. More fuel pressure, more fuel.

 

Oh, wait, you already know about that! LOL

[yo2001]

Did you happen to see what the timing is like in higher rpm?

 

I know the injectors are not maxed out. mine dynoed 240 or so with stock injectors. 253WHP with the regulator set at 44psi. with Z31 ECU.

[Tony D]

I should have clarified, stating that by "maxed out" I meant the pulsewidth hits a stopping point in the map, and stays level from that point onward.

Mazda does this on some systems. Rpm and pulsewidth maps go up, up, up then just stay at the last setting as rpm/boost rises off the maps. Very dangerous, but if you don't go below say 13 or 14:1 by the time the engine redlines, it's a cheap and simple way to cut costs.

 

The N/A computers were analog, and from what I understand they will keep going up on the map linearly until redline, and this is why some people prefer the N/A computer for the turbo application when tweaking things.

 

I agree, the flow from the 270cc stock turbo injectors should support WAY more than 200HP, but only if you have the fuel flowing through the orifice through either pulsewidth increases, or fuel pressure increases.

 

I was kinda rushing when I typed it, hope this makes more clear what I was trying to convey. The Z31 ecu has a more-better mapping than the original ECCS that came on the 280ZXT's.

[yo2001]

I wasn't arguing with you Tony. I just don't understand why the injector cycles out on ZXT ECU and it doesn't on Z31. The way I figure it, the injectors are pretty much wide open pass 4000rpm on. I guess the duty cycle doesn't go as high on ZXT ECU or something

[SleeperZ]

That's really good data Bastaad, and it surprises me, as I was fairly sure it was your fuel pump causing the leanness. Of course I was running 10psi (at my altitude) before my intercooler was installed, witht he stock pump, and running fine. But I didn't dyno it or otherwise quantify what I had. I upgraded my ECCS, then my pump/intercooler, and found how far the stock injectors would carry me. Given that, I'd have to say it's a limitation of the stock ECU, either the internal fuel map or the AFM.

[Guest bastaad525]

That's really good data Bastaad, and it surprises me, as I was fairly sure it was your fuel pump causing the leanness. Of course I was running 10psi (at my altitude) before my intercooler was installed, witht he stock pump, and running fine. But I didn't dyno it or otherwise quantify what I had. I upgraded my ECCS, then my pump/intercooler, and found how far the stock injectors would carry me. Given that, I'd have to say it's a limitation of the stock ECU, either the internal fuel map or the AFM.

 

 

That's what I want to know... I know it's not the injectors, and now I also know that fuel pressure is good and constant and the fuel pump isn't falling short... it must be something with the ECU maps. I know mine isn't the only ZXT ECCS system to demonstrate this exact fuel curve. I've found two other peoples dyno's that show almost exactly the same thing. Anyways this is why I wanted to dyno right after and see exactly what differences every step is making and try to clarify w/o any doubt exactly what effect these upgrades are having. Anyways... no big loss on the pump, I know my stock one was old, beat up, and didn't always sound so healthy, I dont think it had a lot of life left in it. The only real downside is now that I have the extreme smell of fuel in the car and I can't tell why or from where.

 

These results do suggest that the theory of the AFM maxing out (the flap being as far open as it can go) after about 4000rpm at WOT, may indeed be correct. One of these days I'll pop the cover off of the AFM while I'm dynoing and see exactly what's happening there...

 

Knowing what I know now though I wish I had prioritized replacing my front bushings and waited on doing the pump... well at least I know the fuel will be there when I finally get my I/C installed and turn up the boost a bit... I wonder though will I have to add some other parts to make this safe? Am I back to needing an RRFPR? I kinda agree on the questionability of their effectiveness... but I'm still far and away from being able to afford programmable fuel management. I MAY be able to get a full Z31 setup soon though.

[Guest bastaad525]

some more questions I have are:

 

Without swapping out the stock '82 ECCS, is there a feasible way that I can simultaneously lean out the mid range and richen up the top end at the same time?

 

Is 13:1 A/F ratio dangerous with my setup?

 

Does timing affect the A/F ratio readout on the dyno? I believe my timing is either set to stock, 20* BTDC, or possibly set retarded a little to 18*, I forget where I last set it... should I retard it further?

[lifegrddude]

Bastaad, I dynoed my Z at 9 psi and it ran leaner towards the top, but nowhere near 13:1. It was more like 11:1 at the top. My car was running in the 10's for most of the run, I could see black puffs of smoke swirling out the exhaust during the run until about 5K or so. My timing is completely stock and the only mods I had on that run were a catback exhaust, K&N filter, MSD coil and a ProfecB boost controller. You could try a piggy back fuel controller to adjust the fuel map, but I don't know which companies have a product that's compatible with our old technology.

John 82ZXT

[Guest bastaad525]

yeah I remember you posted a link to your dyno sheet before. Again... it seems very typical for the '81-83 ECCS to do this... You'rs was the ONLY one that wasn't into the 13:1 range by around 5000rpm though, out of like three others that I've seen. I still wonder if it's because you're running less boost but I dont see it as making that much difference... 1psi goes from 11:1 to 13:1? I've been considering doing a piggy back ECU for a while... there are some like the HKS which can be had for $200 or less, and there are one or two guys on here who say they can be rigged to work with a first gen turbo ECCS. I still want to get as much info as possible on swapping in the Z31 ECU as the couple guys who've done this say it runs great and dynos a good, level 12.5ish to 1 AFR, and is something I wont have to mess with hopefully?

[Z-Gad]

Hmmm I wonder if auto/ 5-speed ecu's have different maps programmed in?

 

Just a fleeting thought...

[Len]

only way I can think of to lean out your midrange is tighten your sprocket in your AFM a few more cogs. At WOT the AFM flap will be fully open anyway. So tighten it a bit so at midrange you will have enough resistence not be as open to tell your ECU to not flow the injectors as much........

[Guest bastaad525]

only way I can think of to lean out your midrange is tighten your sprocket in your AFM a few more cogs. At WOT the AFM flap will be fully open anyway. So tighten it a bit so at midrange you will have enough resistence not be as open to tell your ECU to not flow the injectors as much........

 

 

Great idea... was thinking this exact thing before, and posted a week ago or so if I should or should not do this (http://hybridz.org/phpBB2/viewtopic.php?t=30754) but didn't really get any direct answer to that specific question. Well... it does make sense though and I guess the only way to find out is to try it... too bad my pay check is already dried up or I'd give it a shot on the dyno... coulda done this yesterday but was freezing my butt off there and just wanted to get home before it really started pouring, so I did only 2 pulls instead of three and they charged me $15 less.

 

Z-gad - I've asked this question also but no one seems to know... I know that there are other differences in how an auto setup is, for instance, it seems that only motors originally mated to autos have the vacuum hose that goes from the intake manifold to the bottom of the throttle body. This hose makes it so that when you let off the throttle it stays open for a second or two and keeps the revs at whatever point they were when you let off... makes shift a real pain in the butt as you either have to wait a sec for the revs to come down, or let it slam into gear. Makes sense for an auto though not to let the revs come down. I bet you're probably right though and that the ECU for autos does have a different curve... and 9 out of 10 turbo ECU's out there are probably for auto...

 

Does anyone know if they have any different designation to differentiate between auto and manual ECU's?

[Tony D]

similar curve...

 

the AFM goes wide open, and after that, the ECU is on the assumption that thethrottle is WOT, so it's basically calibrated to the HP Peak way "safe rich" and that is good enough to hold the engine waaay past redline at the stock boost.

 

At 10psi, it starts getting ragged towards the big end. At stock boost, take a look at your AFR at 6500 under full boost (stock boost remember!)

 

Yeah, this is somethign to do with the capabilities fo the chip in the ECU---probably saving memory for other calibrations due to emissions. This is the tradeoff made for most GM vehicles---way lots of code for emissions stuff, very little in actual code for the actual fuel map.

 

So having a map that only goes to the hp peak at the point the "emergency relief valve" lifts is fine, as even though the engine revs above that point, at 11:1, the leaning outthat will occur between 5500 and 6500 will not blow the enigne.

 

Follow?

 

This, BTW is the same thing JG Engine Dynamics knew 10 years ago. His comment to everyone with a J pipe was "don't go over 10psi, you won't get any more HP" It was his conclusion then that the map was stopped at 10psi/5500rpm and anything beyond that was iffy... We all seem to be confirming that now, all these years later...

[Guest bastaad525]

Okay... so how about this: get an adj. FPR, and turn the fuel pressure up, enough to bring the top end down to about 12:1. Then tighten the AFM spring to lean out the mid range, everything from boost onset to 4000rpm. Would this work reasonably well and not kill driveability during just normal driving around town?

[Tony D]

That's how you should approach it.

Get a good pressure gauge, as trimming the rising rate can be a bit tedious.

 

But on standalone, you say "bin at 2000 to 3000 rpm 5% less fuel", "bin 5000 to 6000 10% more fuel" one of the GREAT advantages over carburetion and older EFI systems.

[Guest bastaad525]

wasn't gonna get a rising rate, just a regular adjustable FPR that raises or lowers the fuel pressure as a whole. I dont want more fuel pressure only on boost... would richen up that mid range even more. Just a regular adj. FPR, and raise the fuel pressure a few PSI, across the board. Then use the spring tension of the AFM to lean out the low and mid range. I do run too rich even off boost, the dyno guy commented on the smell of unburned fuel from my exhaust as the other guy was backing my car up on the ramps, and it is always kinda stinky, so I think I might do well to tighten up the AFM even in normal driveability. I'll mess with this tommorow.

 

I know this would be a tough one to answer, but just as a starting point can someone make a rough guess... if I'm running that rich, around in the 10 or 11:1 A/F ratio range up to 4000 rpm, how much adjustment of the AFM should I do to start with? How much should I turn that toothed gear? 1/4 turn? 1/2 turn? less/more? I know some of you guys were tuning bigger injectors with the AFM... how much did you adjust your afm's to compensate for that? Can't search for those old posts

[Len]

Adjusting the sprocket on your AFM is not a exact process. As we all know dealing with 1981/83 electronics. I've noticed every AFM is slightly different what works for one won't be same for another. If you have just a $25 A/F gauge tied into a 4 wire O2 sensor you can dial it in a bit before dyno testing (yea I know won't work really until wot but to me a 4 wire seems to do a bit of readings before wot ).

A thought.......... "intermission "....A sidebar: Now do you think if right now you invest in a $340 wideband A/F guage. Where you can then basicly tune pretty close since alot of dyno places use a wideband. All the money you save over longterm would pay for the purchase of a wideband? (that's what I'm planning)

Now back to the AFM sprocket; be sure to mark position of sprocket before your changes, then move 2 or 3 teeth at a time? Without a measuring device really can't say...Good luck

[SleeperZ]

Okay... so how about this: get an adj. FPR, and turn the fuel pressure up, enough to bring the top end down to about 12:1. Then tighten the AFM spring to lean out the mid range, everything from boost onset to 4000rpm. Would this work reasonably well and not kill driveability during just normal driving around town?

 

That sounds like a reasonable approach from the data you are taking and from TonyD's voice of experience. I think a RRFPR would be more work, and probably not necessary; a regular adjustable FPR could be made to function reasonably well.

[Guest bastaad525]

Len - heheh getting a W/B is on my list of things I want to do, definately.... I've already talked the guys at the dyno place down... they're really cool guys... anyways I got them down to $60 a session, which is three pulls. Admittedly I'd be saving some money with the W/B but so far I dont consider the dyno as money wasted because I haven't been tuning there at all, rather, the first time was just a baseline, the second time was to settle my own question, once and for all, of how much difference a better fuel pump would make (which it didn't). But for tuning you're right a W/B is definately the better investment, as two or three hours of tuning at the dyno would have already paid for it. Glad you brought that up though and reminded me that I should be thinking of that first before spending more money at the dyno chasing down this fuel curve. I think I can do the W/B for even less, Yo2001 gave me a link a while back for a cheap wideband sensor and I think I can get a gauge for it for reasonably cheap... maybe $200 total invested?

 

Sleeper - I'm gonna take a shot at adjusting the AFM today... this is what I shoulda been doing on the dyno well... at least I do have something to judge 'improvement' by. Basically I'm going to try to lean it out enough as to get rid of the light misfire I have at idle and low throttle cruise. I can only assume this is still due to running too rich... I know it definately became much worse when the fuel pressure was way high from the too-small-return, and if I clamp down on the fuel feed to lower the pressure even more, the idle raises and smooths out even more, even though the fuel pressure is now exactly where it is supposed to be. I'll order the MSD, boost referenced adj. regulator hopefully next week... amazes me that it's so cheap at around $50, whereas the next cheapest one I can find is $120+.