Sharif couldnt tune out the hesitation on mine around that same rpm either. But i dont get a AFR change really, just a jerk

 

The latency correction would only correct for a voltage drop at the injectors if the voltage dropped at the ecu as well. I assume the voltage will be the same at the ecu as it is at the injectors, but I am not ruling it out yet.

Going back to the datalog, I noticed something that might have a correlation. Look at the three lean spots. One is at 1200 rpm, one is at 1600 rpm, and one is at 2400 rpm. The gap between the first two is 400 rpm, and between the second two it is 800 rpm. The first lean spot has a lambda value of 1.07, the second is 1.14, and the third is 1.20, so the difference between the three lambda values is the same (.07). I can repeat this test and get the same results +/- 20 rpm and .05 lambda consistently every time. It hardly seems like a coincidence.

I am seriously starting to wonder if this has something to do with induction resonance. One of my two intakes is roughly twice as long as the other, and they have separate air filters. Does anyone else run a setup like that?

Random thought:

If x=4800, then
x/2 = 2400
x/3 = 1600
x/4 = 1200

Weird.

 

Maybe it is a ground loop causing a voltage drop in the injector circuit? I do have a bracket welded to my turbo intake that mounts to the the main grounding point on the front left of the engine. The grounding terminal in on top of the bracket, so it is basically grounded though the bracket to the engine (and through the bolt also). The bracket is bare aluminum though, so I don't see why that would cause a poor ground.

 

Let's think about this for a second:

Could this be related to a resonant frequency in the fuel system? When I installed the CJM return system it required me to remove the dampener at the rear of the drivers side fuel rail. Could the lack of dampening in the fuel system be causing these resonant frequencies in the fuel system? I suppose I would have seen a drop in the fuel pressure though.

 

The saga continues.

Tonight I used a needle to pierce one of the wires on the #1 fuel injector, and then hooked up the DMM to measure the voltage right at the fuel injector while I drove. I tried it with the negative battery terminal as ground and also using the chassis as ground. Both times I watched the voltage readout as I drove through the lean spot and both times it stayed rock steady at ~14.2 volts. So, it's not because of a voltage drop at the injectors.

I also took off the ~10" portion of the longer of the two intakes and test drove without the pipe or filter, just to see if it changed the rpm at which the lean spot occurs. After a quick test drive, it seemed to have no effect on the severity or the engine speed at which the lean spot occurred. IF it did change, it couldn't have been more than a 100 rpm difference (it's hard to tell, because the tach lags a little behind what the Haltech reads).

Oh and I did a little research - supposedly Aeromotive says that the fuel pressure regulator acts as a damper, so removing the stock damper and installing the aftermarket FPR in it's place should have little effect on the damping of the fuel system.

In summary:

The fuel pressure stays steady
The voltage at the fuel injectors remains constant
The voltage at the ECU stays constant
The injector duty cycle increases steadily
Both the MAF and the MAP agree that there is no significant increase in airflow

...And yet the lean spot is still there. I'm out of ideas. I'm ready to give up.

 

Try unplugging your cam solenoids and take her for a drive.

 

That is safe to do? They just wont advance beyond the base timing then correct?

 

Correct.

 

More testing last night:

I tried unplugging both cam solenoids, the lean spot is still there. Definitely didn’t help at all.

I also tried running another ground wire from the block to the chassis alongside the wire that is already there. Didn’t make a difference.

Finally I got fed up and just took the pipe in front of the MAF off, effectively turning the car back into N/A, and went down my street and back. The lean spot was still there, exactly the same as before. I think that pretty much eliminates induction tuning as a possible cause, and it also reinforces my findings that it is not an airflow issue. So it must be a fuel issue…

If it is a fuel issue, and my fuel pressure stays constant, and the voltage at the injectors stays constant, and the injector duty cycle doesn’t dip, what the hell could it be? I would have said a bad fuel injector for sure (they are used DW600’s) but when I switched the wideband to the other bank I saw the same readings. I might just buy a new set of injectors and try it. If they fix the problem then great. If not, I will just sell the old ones and be out a couple hundred bucks but either way I will have new fuel injectors.

 

why not just send them back to DW for inspection. that will make then basically 'brand new' again..

Pretty much guarantee its not the injectors though.

 

I ordered a new set of DW 600's this morning. If it doesn't fix it then at least I can be 100% sure that it's not the injectors.

 

Could your wideband sensor have a weird leak of some kind? Does the car actually buck at the lean spot with the Haltech in place or are you just getting a lean spot with no change in driveability?

Moving the wideband bank to bank and still having a problem makes an individual injector issue unlikely, as you've said.

 

hey, i had this when i switched injectors a few weeks ago. I had a dead spot (severe) at 1800 rpms only on accell in 1 block. Everywhere else was great and that block was perfect under cruise. I messed with everything. No matter how much fuel i put in there it would still go way lean but then under cruise it would be super rich in that cell from the added fuel.

i pulled my car apart for this new turbo kit. One of the plastic spacers for the plenum spacer had fallen down into my bank 4 and was blocking airflow.

as many times as i've had that plenum off i've never had that problem so idk what i did wrong that time.

i assume what was happening is a loss in airflow therefore causing the o2 correction for that bank to be out of wack (which it was on the logs) and it would pour fuel in to compensate and cause a nasty issue until i was past that frequency of air moving.

 

The car definitely bucks when it hits the lean spot(s). To the point where its a pain in the *** to drive. I don't even have to look at the gauge to know when it goes lean, I can feel it big time.

I have had my plenum off since the initial install. There was nothing out of the ordinary when I took it off, and I was extremely careful when I put it back in. In fact I glued those spacers to the gasket so they couldn't go anywhere (I have the Skunk2 spacer).

 

How would blocking airflow cause you to go lean?

My problem also occurs in both banks.

 

I wonder if it's some weird airflow resonance thing. Does this happen in boost as well, or only vacuum? Maybe get try taking off the spacer?

I'm running out of ideas man

 

because the airflow is more than likely blocked all the time EXCEPT at that specific frequency it could blow it up and out of the way thus causing a huge rush of air into that cylinder at that rpm and load. Therefore lean at that spot.

and yes, it sounds like a mechanical air flow issue.

 

I tried removing the spacer. There was nothing out of the ordinary, all of the little spacers were where they were supposed to be.

I swear that it felt smoother and bucked less as I went through the lean spot, but after datalogging it looks just the same as it did before. Lean spot at 1200, 1600, and 2400.

 

Maybe the cams are messed up and the valves are not operating properly. But both banks? I'm out of ideas. Maybe double check the decel cut off settings (that turn off fuel when you lift throttle)...

 

mx594,

I just wanted you to know that I came across your thread and directed it to one of our techs. We read the thread through, and it doesn't appear to be an injector related issue. Typically, when an injector fails, it will show itself at idle and throughout the rev range.

But, since you are planning to swap the injectors out, if it does solve your lean issue we'd like to check them out to see what is up.