High fuel trims at 2,500 RPM only
 

Searched, found several fuel trim issues, but none that were this RPM based.

Idle is about 6.6 g/sec, no vacuum leak indication

No load, 2,000 RPM, LTFT around +6
2,500 RPM, LTFT around +14
3,000 RPM, LTFT around +9

Steady driving
2,000 RPM, 40 MPH, LTFT around +6
2,500 RPM, 50 MPH, LTFT around +16
2,850 RPM, 55 MPH, LTFT around +8

all the numbers above are after STFT stabilized around 0.

No Air Pump
Evap connected or disconnected
recent rebuild, but did not do it out of the box

The high trim goes away as soon as you accelerate, hitting cruise control button is enough. It is a step between about 48 and 52 MPH with cruise control on. Car is getting 27 MPG while all this is going on according to ultra gauge.

What turns on at 2,500 RPM?
When do secondary fuel injectors start to come on?

Um, help?

anything that can make the engine lean or think it's lean

fuel injector issue
O2 sensor issue
low fuel pressure
MAF issue
etc.

how old are the primary injectors?

Primaries are original. We're cleaned and tested at Pettit during rebuild. O2 is less than a year old.

Just cleaned MAF. Dumped in injector cleaner.

What really has me confused is the narrow band of dumb. I cannot generate a fuel pump failure mode that heals at 2,650 rpm, unless that is when the resistor cuts out. But, I think that is when the secondaries kick in, and that is a lot higher, right? 3,700+..

I cannot find anything that changes at 2,500.

The secondaries open up based on load and rpm

If you could post a log file with this occurring it might help diagnose the problem.
Make sure you have the Injector Duty cycle logging

You can use that to help you see when the secondaries kick in...

Sec injectors don't start until the SSV opens, which is not occurring under the noted conditions

you didn't answer my question about the primary injectors. They don't operate well forever regardless of how they may have tested.



.

What's your load and MAF at those different trims?

@ Team. The primaries are the original ones, they have 145,000 miles on them. I believe they were tested and cleaned about 6 weeks ago.

@ wcs, I will dig out the AP and see what I can come up with.

@ logal, issue is only at very low load. The instant I add power, STFT drops and LTFT starts to follow.

I did cap off the evap system on the manifold. That seemed to remove some of the volatility based on one drive to work I am watching the EVAP %, there is no real pattern, to what it is trying to do. It tries to open at various RPM and at various percentages, though most are above 95%.

More background. Engine is a fresh rebuild, Pettit in West Palm. One of the improvements is a porting job. I wonder if the street port happens to have a flow bump around 2,500 that is confusing the system. But, I would think if the trims are real, fuel would be running out the tail pipe, and MPG would take a hit.

Every piece of data I have save one says fuel pump. If it were the pump, it would get worse as RPM (demand) goes up. I do not know why things get better after 2,500 RPM.

Thanks all.

Fuel Trims are based on specific MAF break points. That's why I asked. There is only really 3 that seam to affect us. 0-9G/sec 10-21 G/sec and 21-60 G/sec. Then you end up in open loop. I'm thinking it's the 10-21G/sec range you're seeing the high trim. Why I don't have a clue, but all your fuel trims are a bit high, and your MAF at idle is also.

Are you tuned? Do you have a non stock intake?

You have a vacuum leak.

Thanks,

Tune is MM base tune, I pulled the custom tune to troubleshoot this. Cam indicated it would be fine with the new motor, but I am trying to remove variables. Intake is stock.

I was thinking vacuum leak, but the 6.6 gps at idle is pretty much right on the money. Even a little leak would impact that. Last time I had an issue, it was in how the valve for the evap system attached to the intake manifold. I have evap locked out and capped at the manifold. I will check the lines before the throttle body. A leak there will cause a steady high trim, that gets worse as rpm rise (higher flow, slightly lower pressure in tube) but it would need to be considerable to cause this much trim. And, the cure after 2,500 RPM just makes no sense for a vacuum leak scenario.

If the growth was gradual, I would blame the fuel pump and replace it. I may do that anyway. BHR pulled the one they sell, so I need to find a decent source. I have a backup housing. I think I have 60,000 miles on this one.

The LTFT ranges are something I did not know about. I will watch gps big time on the drive home and play with different gears for loading around 2,500. I am also curious as to if fuel trims are managed differently by the ECU when the ranges change.

Thanks again.

High fuel trims at 2,500 RPM only
 

I'm with you on this, but how does a vac leak get 6.6g/sec at idle.

High fuel trims at 2,500 RPM only
 

Trims are managed differently based on g/ sec. What is you idle maf volts. The 6.6g/ sec at idle may be manufactured. Volts will show if it is or not.

As load increases vacuum drops. So a vac leak will correct itself as load increases. If your maf is not stock scale that would explain the lower trim at idle.

Or go to a stock tune and check idle g/ sec

sorry in a meeting so i didn't read the rest of the thread.

once had this issue when a intake screen fell out of alignment.

OH, you are on a MM tune created for your last engine. Yes, got to a stock tune and drive around for a day or two and then report back. If it is the same then you have a vacuum leak.

Good stuff.

On the stock tune, AP still installed,

@ pamion, will be checking screens. thanks for the tip.

@ loga., will see if I can pull MAF volts from the ultragauge, I may need to splice in.

High fuel trims at 2,500 RPM only
 

Ap will get the volts

The whole issue is you talk about data yet don't really provide any in the real sense. IMO 6.6 g/s @ idle is high, but without IAT, MAF volts, idle speed, etc. it's impossible to provide an accurate assessment. With summer IAT temps I usually expect OE idle speed to be in the mid-high 4.x g/s range.

If you want help then you need to supply logs with the appropriate data.

I would never bother to even test 145k mile injectors, let alone use them on a newly rebuilt engine. That's just me though.

Did you check all the LIM and UIM bolts for sufficient tightness?

Short term news.

With the base tune and a few drive cycles, most volatility is gone. Evap is still locked out. Idle gps is in the 5.5 range. LTFT across the zones is 7, 10.5 and 13. <<-- looks like fuel pump. Will be going over everything today for a vacuum leak and putting a wrench on the manifold bolts. Maybe hook evap back up then test.

Then I will break out my AP manuals and look at logging and tuning. I have not used the thing to do other than load maps for years. Cool, a new hobby. Reread all posts by Kane, Team and a few others on tuning.

Thanks all.

High fuel trims at 2,500 RPM only
 

5.5 is about right at idle. Dont worry about the volts. Im sure it was off due to the mm tune. I would suspect a vac leak either with that:

Careful with the manifold bolts, they often get seized and when they break it is a PIA. I would verify fuel pressure but I doubt it is that. Just get a 30 second idle log with the engine fully warmed up on the Cobb and post it here.

email sent

Log File
Had to work to remember.

Thanks

About the log file

LTFT of +6 isn't bad.

If I was tuning I might add +3 to the Maf in the idle range and see what happens

edited
- removed wrong info about calc load -

AC was off. Went back and checked it. Is still 26 or so resting, warmed up, in garage. I think load is a function of airflow and RPM, but I do not want to start a tuning discussion. I am dealing with a street ported motor. My plan when I get back in town is to start scaling the MAF and see what happens (I have the first suggestion above). If I start this now, it will not end well.

FYI, evap is back in, catch can is still vented to atmos, and I think, as of a few minutes ago, the car was running well, rich, but well. Interestingly enough, the Calc Load goes down to about 18 at 2,200 RPM.

Thanks all, be back in a few weeks.

There's nothing wrong with your idle log/cal load, you'd be well advised to carefully consider the source of certain posts/information