Alright so here's the deal. I am trying to tune my fuel delivery on my turbo G. I have a CJM stage 0 RFS, Walbro 255, Deatschwerks 600cc injectors, and a blow-thru MAF arrangement mounted in a 3" (2.875" ID) pipe in about the same location as it was stock. I am currently only getting 3psi of boost, due to lack of a boost controller. My fuel pressure is set at 50 psi with the vacuum line connected, which translates to about ~60 psi at 0 psi of boost and ~63 psi at 3 psi of boost. Yes I know this is a little high but it shouldn't really matter since I can scale back my IPW's to account for the extra pressure.

So here is my problem: under boost the car runs strong and smooth. I was able to tune the fuel pretty well for a relatively consistent 13:4 A/F at 3 psi of boost. The problem is that the car runs like crap in the 0% column, especially right before transitioning into boost. I have it set to crossover into open loop at 0 psi, and my map is scaled from 0-10 psi. I can get the A/F at cruise to be close to 14:7 throughout the rpm range, but when I give it some throttle and get to the 0~5 in-hg vacuum range, the A/F goes to 10:1 and the car stumbles. If I stay on it and it finally gets into positive pressure, the car jumps back to life and the A/F goes to 14:1 at ~1 psi.

At first I tried to scale my 0% with a -15 throughout like everyone always says, but this resulted in a VERY lean idle…off the gauge in fact (AEM UEGO). It seems to idle well with a 0 in the 0%, 500 rpm cell. However it seems like everywhere else, it needs -10 or less. The problem is that I get a relatively lean cruise but as soon as I give it ~50% throttle or more the A/F takes a dive and pegs the gauge at 10:1 until it crosses over into open loop.

I thought that this might be due to the rising rate regulator, which causes the fuel pressure to vary by ~10 psi between high vacuum and 0 psi - a variable that cannot be accounted for with a single MAF voltage offset in the 0% column. It made sense to me that this could cause the stock computer to dump too much fuel with more throttle (less vacuum) and yet be fine with a -10 in the 0% at cruise. What does the stock fuel pressure do? Does it stay at 51 psi in the fuel rail at all times or is it higher at WOT than it is at idle?

I also get surging when cruising at a constant speed….the A/F will swing back and forth between 13:1 and ~17:1 and I can feel the power surge, back and forth back and forth all day long.

Is the UTEC just a POS when it comes to larger injectors or what?

 

I had a similar situation to you this last spring.

I have a CJM Stage 2 FRS, Walbro 255, and Deatschwerks 650cc injectors with a UTEC.

I've been running this setup for 3 seasons and for the most part it ran fine until I played with the temp correction for fuel after a trip to the track when it was pretty cool out and my car was running a little leaner @ WOT than I normally like.

I have my map scaled from 0-20psi (since I run around 14psi most of the time). My issue was that the car would transition to the 10% load site before I reached 0psi. Somewhere between 5 and 3 in. of vacuum. It would go super rich and make my car stumble BAD. My UTEC is set to transition @ 0psi just like yours.

I don't know if the temp correction change caused my issue, but I was able to fix it by cleaning my MAF with carb cleaner. (I think I had a good bit of oil built up on it). I think my MAF might have been sending the wrong voltage signals @ that throttle position.

Anyway, my car runs great (albeit has crappy, lean cold starting and sometimes crappy hot starting) with the UTEC and big injectors.

Good luck.

 

Thanks for the insight. My temp correction was set to all zeros and now I have adjusted it to compensate for the temperature at which I did my tuning. Neither way seemed to make a difference with regard to the stumbling.

What about the MAF housing? Are you still running the stock housing? I Made a flange and put my MAF in a 3" pipe. I am starting to think maybe that is why I am having problems. I'm not sure the UTEC can handle a larger MAF housing when you only have one column worth of adjustment (if you were running in MAF mode, you would have 10 columns so it would probably work). I have all the parts to put the stock MAF housing back in so I might try that tonight.

What are you running for idle fuel pressure, with and without the vacuum line connected?

 

I just went to a doctors appointment and tried setting the 0% column to start at 0 and gradually go up to -17 at redline. This equates to about -10 at cruise ~3000 rpm. Cruising under light throttle the car would stumble and jerk and go lean, especially when throttling out of decelration. However the stumble upon transition to boost smoothed out greatly. It still gets down into the 11's just before it goes open loop, but it doesn't peg the gauge anymore.

So it looks like I can either have good A/F at light throttle/cruise and super rich just before boost, or I can have stumbling lean cruise with a good transition to boost. WTF.

 

I have an APS Twin kit so my MAF is installed in the APS charge pipe about 14 inches from the TB. I think the APS charge pipe is similar in diameter to the stock MAF housing.

Idle fuel pressure is 45psi and I think just over 50psi without vacuum. I'd have to check though.

 

Well I reworked my setup to include the stock MAF housing, and it didn't seem to make much of a difference

I'm no really sure what to try now. Maybe I will get Osiris and throw the UTEC in the garbage.

Anyone ever tried to use the UTEC to control fuel in boost and in vacuum? Like a standalone?

 

I wouldn't blame you if you just trashed the UTEC. I'm probably going to a Haltech this winter, since it's got a lot more features, a better tuning interface and O2 targeting so I don't spend forever trying to fine tune my AFRs.

 

It's strange…the car is running the best yet, but my 0% doesn't look like I would expect. I have a -3 in the 500 rpm cell, then in gradually goes to a -10 in the 1750 rpm cell, then stays at a -9 until 2500 rpm, then all the way up to a -15 around 4000 rpm and keeps going down to a -18 toward redline. Almost everything I have read on here indicates that the MAF offset should be relatively consistent throughout the RPM range (most people say anywhere between -10 and -17 to get the car to idle) and yet I need only a -3 to make the car idle well…if I go to a -5 or a -7 it idles lean. Why would my car be so different?

I am still fighting between too lean at light throttle and way too rich just before boost. If I am idling and I stab the throttle to rev up the engine it will peg briefly at 10:1 A/F. It seems like a basic MAF voltage offset just isn't enough to account for larger injectors. I noticed that if I roll into the throttle very gradually, it will transition to boost very well and maintain a pretty consistnet 14:1 as it transitions. Its when I give it more throttle more quickly that the A/F dives briefly before boost hits.

The other thing that is weird is that sometimes while I am sitting there just idling, the A/F will be dancing around in the 14's and 15's for a long time, and then all of a sudden the engine will bog, the rpm's will dip a little, and the A/F will peg the gauge at full lean (18:1) for a second and then gradually level itself back out in the 14's. I have no idea why the hell it does this. There is absolutely no reason for it.

 

Are you using a MAP sensor?
You have it set for speed density tuning right?


Your need such extra fuel at idle is very odd. The rest of the transitioning problems are all tune related on your map.

post your fuel and timing map and your params so we can take a look

 

Yes I have a MAP sensor, and yes I am in speed density mode.

Here are my parameters and map. I think this parameter file may have the map threshold set to 1 psi becuause I was trying some different things, but it didn't seem to make a difference if it was set to 1 or 0.

 

u should start -14 -15 -15 -15 -15 -14
-13 -12 -11 -9 -9 -9

 

Try reseting your ECU (do a battery disconnect just to be sure) and set your lower rpm to around -15. This will lean a bit but the ecu should correct it after a while. -4 to -8 with 600cc injector is not enough. Heck I have -4 with my 440cc DW (I have the older core so it is really just 400cc).

 

It doesn't really make sense - the first time I started the car with the bigger injectors I had a -17 in the entire 0% column and it ran so lean that it barely kept from stalling and I got a CEL. This is after the battery had been disconnected for over a month. After that I did the pedal procedure to reset the ECU, the CEL went away but I had to keep it around -5 to get the A/F where I needed. I have it at -8 right now and it idles fairly well, but every now and then it will bog and go full lean for a second all by itself, just sitting there idling.

Is it really that hard for the ECU to un-learn what it has learned? I can go anywhere from 0 to -8 in the 750 rpm 0% cell and the idle A/F hardly seems to change.

 

I had this issue in the winter when my car will all of a sudden go lean to about 17:1 - 19:1 for a second and then it will go back to normal. No problem when driving what so ever. Only happen when idling. I did the same thing and added tons of fuel and that didnt fix the problem. You cant really do much in the 0 column because the ECU is self correcting via 02 feedback. It turn out I have a vacuum leak in my catch can. I went crazy looking for that leak for 3 months until the leak got worst that I can hear it. I fixed the leak and pull back all the fuel I added and no more problem and trouble free for 7 months now.

 

If it were a vacuum leak causing my random idle stumbles, could it be the PCV?

 

Where did you hear that the original DW 440s were only 400cc? I pioneered DWs on my car 3 years ago, and I have the flow sheet sitting in my garage that clearly states 3bar test pressure and between 430-440cc flow across all 6 injectors. All DW injectors have been rated @ 3bar.

 

My car also idles pretty lean (16s to 17s). Cruise is a little better (high 14s to high 15s), but it wasn't always like this. The first season I had the UTEC in my car idled perfectly.

 

Are you using the Denso core? The old DW used the Bosch core and it was rated at 3.5bar. I have the flow sheet and DW verified it.

 

What about the fact that I have a rising rate fuel pressure regulator? Essentially I have 50 psi fuel pressure at idle and roughly 60 psi fuel pressure at 0 psi of boost. The stock ecu normally only has to deal with a constant 50 psi in the rail, and fires the injectors accordingly. Now, if you apply a single MAF offset to lets say 3000 rpm then wouldn’t you expect it to be leaner 3000 rpm cruising (high vacuum, maybe 52 psi fuel pressure) and richer at 3000 rpm ~50% throttle (just before boost, 60 psi fuel pressure). Basically I have introduced two variables - bigger injectors and varying fuel pressure, and I don’t think the UTEC is sufficient to trick the stock ecu into behaving nicely with both of these additions with MAF based tuning.

I wish the UTEC would let you use multiple columns for MAF based tuning and also let you run open loop speed density. That way you could have 3 or 4 columns for MAF based tuning in vacuum and then switch to open loop in boost for the remaining 7 or 8 columns.

Has anyone ever tried using the UTEC to control fuel in a standalone fashion 100% of the time with speed density? My Miata only has a MAP sensor (no MAF of AFM) and it runs far better than the G35 (so far). The ecu in the Miata has 3 columns for vacuum and 3 columns for boost - that's it. You could do something similar with the UTEC, and set your mapping values from say -15 to 15 psi so you would have 5 columns of vacuum and 5 columns of boost. Then you could just set your timing to "ECU" for all of the columns in vacuum. The only question I have is what would happen with cold and hot starting, since the UTEC has no provisions for such things...

 

I had the first set of 440cc injectors that DW made from stock cores, I also have the flow sheet for them and for my APS 440cc injectors. Both flowed 440 @ 3bar test pressure.

I now have newer 650s that are denso cores and the flow sheet shows the same testing pressure.

EDIT: I just called my buddy Mike @ Deatschwerks to verify. My injectors were the first set they made and rated @ 3 bar. When they decided to enter the 350Z market after working with me on the test set, they decided to rate their injectors @ the stock VQ35 fuel pressure. This only served to confuse people, so very shortly afterward they changed back to the 3 bar rating. Mike said that there are not many sets out there that were rated @ 3.5bar.