Always lean at specific RPM

[Skud]

Hi All,

I wanted to see if anyone else has seen something like this. Basically, my car will go lean as it goes through ~2500 to ~3000 RPM. This happens regardless of load, gear, etc. It also doesn't seem to be related to the MAF or MTF because it does it with a different MAF and CAI.

If I'm accelerating onto the highway it starts to go lean around 2500RPM, peaks at 15.5 - 16AFR and then drops back to normal by around 3,000RPM. It does this through each gear. I can also make it happen when driving normally in fourth gear. If I bring the car up to 0" of vacuum or low boost (2 - 3 psi) at 2500RPM it will start going lean, peak and then go back to normal by 3,000RPM. This is at steady throttle, too. Outside this RPM range it seems to be OK. It doesn't appear to be a sensor issue because if I accelerate I can feel the car slightly pull back as it goes through 2500-3000 and then take off again.

I was thinking it might be a transient fuel issue, but it happens after the transient. So, I can make the tip-in rich, but it will still happen after that. I've had a well-known tuner work with me and he's as stumped as I am. MAF counts, throttle position, etc are all steady through the range, but the AFR drifts lean, peaks and goes back to normal.

Logs are below and you can see it happen beginning at 144 seconds and end at 174 seconds. This is accelerating onto the highway going through 2 - 4 gears. It does it at the same point in each gear.

Log File

Thanks!!
Riley

 

[fbody83]

I have a similar problem but it was much worse on a previous setup. On my old setup it was so bad that once I hit around 0" of vacuum in that same rpm range, it would buck and pop out the exhaust for a split second and then pick right up again. The previous setup had 60 lb injectors, a MAFia and a tune that was scaled. I'm now running ID1000's, a BA2600 and updated my tune to use the "BP modifier" method. This helped tremendously. I still get a tad lean in that area but no more hesitation or popping.

What injectors are you running and did you mess with the values or did you load them from a file? Is anything in your tune scaled?

 

[ugotbit03]

Fbody-

Not to hijack but when you made the BP modifier tune was your load low?

 

[fbody83]

Fbody-

Not to hijack but when you made the BP modifier tune was your load low?

It did lower my load but it was too high when I had the tune scaled. The higher loads made my car feel like a dog at lower throttle positions because it the spark was way too low. Once I modified the BP value, my load actually looks correct and my car woke right up at part throttle. It feels so much better now. I still see a load of 1.96 - 1.99 at WOT as I approach redline.

 

[ugotbit03]

Hmm. I must have screwed something up then because my load is low, only seeing .98 on the hit and working up to 1.3

I tried scaling displacement to get load up and it worked, but it seemed to create the exact drivability problems the BP Modifer method is supposed to remedy.

 

[Skud]

I have a similar problem but it was much worse on a previous setup. On my old setup it was so bad that once I hit around 0" of vacuum in that same rpm range, it would buck and pop out the exhaust for a split second and then pick right up again. The previous setup had 60 lb injectors, a MAFia and a tune that was scaled. I'm now running ID1000's, a BA2600 and updated my tune to use the "BP modifier" method. This helped tremendously. I still get a tad lean in that area but no more hesitation or popping.

What injectors are you running and did you mess with the values or did you load them from a file? Is anything in your tune scaled?

I'm running ID1000s, so it shouldn't be an injector issue.

I've tried using the BP Modifier method, but it makes my load real low - it will never go above 1.0. SCT has looked into it a few times, but they couldn't find an issue. Regardless, it still does it even with the BP Modifier..

I'm stumped..

Riley

 

[watman02]

mechanical prob? u sure your wb is reading correclty? what does the o2's say is going on at that same instant do they confirm the issue?

 

[Skud]

mechanical prob? u sure your wb is reading correclty? what does the o2's say is going on at that same instant do they confirm the issue?

It is possible that it's a mechanical issue - I'm not sure what it could be, though. I've replaced everything I can think of and there are no vacuum leaks (the whole system has been pressure tested). It is happening because when the car is in closed loop the fuel trims line up with my wideband.

Riley

 

[watman02]

is your manifold volume updated to show the change from NA to F/I? this can have an effect on transient fueling.

 

[itzl0l]

I have a similar issue with my 03 whippled Cobra .....lean at 1500-1800 rpm ...any speed...any gear and most any load. Im starting to think its actually a slight misfire at that rpm and have been thinking about changing cops. I've tried multiple sets of plugs with no effect.

 

[Skud]

Well - upon the advice of James (Tuning By James) I swapped out the ID1000s with my old SD 60s and pretty much all the issues I've been having are gone. I swapped the injectors and loaded the 60lb injector values into my tune (scaled 0.47). When I fired the car it was a bit rich. I took out 15% from the MTF and the trims are within 5% of 1.0. Nothing else was changed.

The problems I've had that are now fixed:

- Lean spot between 2500 - 3000RPM
- AFR changing with load/RPM. Rich low load, high RPM, etc. There were very distinct transition points where the AFR would jump up or down 10%.
- AFR changing with fuel pressure. I'd see a 10% difference in fuelling between 39 and 45psi
- AFR changing with how heat soaked the car is. I'd see a 1 - 1.5 point movement whether or not the car was soaked.

I'm going to get in touch with ID to see what's up. With all the success people have with the ID1000s it's possible I just got a bad set.

Riley

 

[cj428mach]

Well - upon the advice of James (Tuning By James) I swapped out the ID1000s with my old SD 60s and pretty much all the issues I've been having are gone. I swapped the injectors and loaded the 60lb injector values into my tune (scaled 0.47). When I fired the car it was a bit rich. I took out 15% from the MTF and the trims are within 5% of 1.0. Nothing else was changed.

The problems I've had that are now fixed:

- Lean spot between 2500 - 3000RPM
- AFR changing with load/RPM. Rich low load, high RPM, etc. There were very distinct transition points where the AFR would jump up or down 10%.
- AFR changing with fuel pressure. I'd see a 10% difference in fuelling between 39 and 45psi
- AFR changing with how heat soaked the car is. I'd see a 1 - 1.5 point movement whether or not the car was soaked.

I'm going to get in touch with ID to see what's up. With all the success people have with the ID1000s it's possible I just got a bad set.

Riley

Its possible but aren't every single set of ID's tested, thats part of what you're paying for. I thought I had some paperwork that came with mine saying something like that. I'll have to dig around and see.

 

[Skud]

Bringing this back up for an update:

I sent the injectors off to ID a few months ago and they looked at them. All were within 3% of each other and all were in spec. They cleaned them and this brought the variance down to just under 3%. According to ID there are no issues with the injectors. They sent them back and I'll put them back in when spring rolls around.

Since I sent the ID1000s back to ID I've been running my previous set of SD 60s and the car runs superbly. So, I'm not too sure what's going on here, but now that I *know* everything else is working as it should I can focus on the injectors and try to figure out what's going on. It's behaving like something it wrong with one of the slopes or breakpoint, but I tend to believe their data is good.

Riley

 

[cj428mach]

Are you using the value file? or the data off their site?

 

[Skud]

Are you using the value file? or the data off their site?

I've tried both with the same results.

 

[itzl0l]

I had a similar issue, but with 60# inj. Just out of curiousity, what MAF are you running and more importantly how much did you have to adjust the MAF curve to get the car to lambda?

In my case (BA3000 and JLT highboost) I had to add roughly 20% to the curve for afr to match commanded....

...how I fixed my issue: Instead of increasing the MAF xfer ....I reduced the high/low slopes and breakpoint by 20%. Then, instead of massive change to the MAF xfer I just had to tweak it here and there. I know the experts say dont change the injector data (its known good data!) BUT...it worked...resolved both my issues. All I had to do was tweak the timing tables a bit and I was good to go.

 

[Skud]

I had a similar issue, but with 60# inj. Just out of curiousity, what MAF are you running and more importantly how much did you have to adjust the MAF curve to get the car to lambda?

In my case (BA3000 and JLT highboost) I had to add roughly 20% to the curve for afr to match commanded....

...how I fixed my issue: Instead of increasing the MAF xfer ....I reduced the high/low slopes and breakpoint by 20%. Then, instead of massive change to the MAF xfer I just had to tweak it here and there. I know the experts say dont change the injector data (its known good data!) BUT...it worked...resolved both my issues. All I had to do was tweak the timing tables a bit and I was good to go.

I've tried it with two different MAF/CAI combos. The first and current is a JLT Hight Boost (Gen1) and BA2400. The second is a VMP3500 slot MAF and JLT High Boost (Gen2).

Both would give the same result, but the Gen2 was a lot harder to tune. At idle the car would be in the ~80 counts range and there was a lot of turbulence in the flow. So, counts would fluctuate +/- 20-30. I ended up putting in a screen, but it didn't help a whole lot. Now, the Gen1 and BA2400 with a MAF screen is really good - I think it's fluctuates only +/- 5 counts.

Literally, the ONLY thing I changed was the injectors - other than the necessary values in the tune of course.

Riley

 

[MethCobra]

Well - upon the advice of James (Tuning By James) I swapped out the ID1000s with my old SD 60s and pretty much all the issues I've been having are gone. I swapped the injectors and loaded the 60lb injector values into my tune (scaled 0.47). When I fired the car it was a bit rich. I took out 15% from the MTF and the trims are within 5% of 1.0. Nothing else was changed.

The problems I've had that are now fixed:

- Lean spot between 2500 - 3000RPM
- AFR changing with load/RPM. Rich low load, high RPM, etc. There were very distinct transition points where the AFR would jump up or down 10%.
- AFR changing with fuel pressure. I'd see a 10% difference in fuelling between 39 and 45psi
- AFR changing with how heat soaked the car is. I'd see a 1 - 1.5 point movement whether or not the car was soaked.

I'm going to get in touch with ID to see what's up. With all the success people have with the ID1000s it's possible I just got a bad set.

Riley

Bringing this back.....im having the exact same issues!! I got the ID1050X injectors. I hired Malcolm Strydom to tune for me and he figures its mechanical. I have almost the exact same symtoms you are expaining. We sent each other datalogs and tunes about 40 times. Ive replaced parts to rule out mechanical issues, this is interesting and i want it fixed. JLT high Boost gen 2 ba3000 MAF also. Did you ever get this issie fixed? Or does anyone know what to do to fix this. Malcolm has got my tune pretty darn close but the symptoms are the same. Im hoping Malcolm will pitch in here on his experience.

Sent from my [device_name] using the svtperformance.com mobile app

 

[Goza]

I have a 03 that is doing the same thing! Mine is doing it from 5200-5400 rpms and then coming back. the tuner is saying that it must be mechanical but I don't know what the issue is. Are ya'll saying the injectors were the issue? Any help would be appreciated!

VMP 2300 SC
2.8 pulley
60lb injectors Sieman Deka/Motron
VMP GT500 throttle body
SCT BA3000 MAF
JLT high boost CAI
fuel pump voltage booster
aeromotive fuel pump 340 LPH (dual)

 

[Skud]

I'm thinking it's a slope/breakpoint issue. My issue was different in that it was more of a low speed/low load thing. If I was on the low or high slope I was fine. It was that transition that caused issues. I honestly haven't put the ID1000s back in since I haven't had the time or motivation.

Riley