Recently I’ve noticed my 8 has been starting kinda rougher when it starts cold. Some days it starts right up with no issue in the idle at all, but some days it’s rough and causes a p0302. I did a block test to make sure no coolant was leaking in and that checked out. I have also noticed that my LTFT has been at 13.8-14.8(today at idle was 18-19). I’m not sure if this is normal at all. I did just put in the BHR Midpipe but even before I installed, I was having the same issues and thought maybe I was a bit clogged.

Is it possible i have leaky injectors or is it a tuning issue?

 

Are those trims +14-ish or -14-ish?

Positive means you could have a vacuum leak, bad front O2 sensor, bad MAF, clogged fuel injectors, bad fuel pump, or any of a few other things. But probably a vacuum leak.
Negative means you could have leaky injectors, bad front O2 sensor, bad MAF, or any of a few other things.

 

theyre positive. I probably have a bad MAF. I in my infinite wisdom cleaned it with brake cleaner XD I’ll try replacing that and see if the LTFT changes at all

 

Before you throw parts at the problem, you should probably test for a vacuum leak.

 

dumb question: how do you test for a vacuum leak?

 

What is the airflow g/sec you see in the OBD data on a warm 800ish rpm idle? Should be a it over 5. If it's not, that's further evidence of a vacuum leak.

Testing: just examine everything after the MAF for gaps, holes, disconnected hoses, cracked hoses, etc. Your intake after the MAF all the way to the block, and all vacuum connections have to be airtight. The MAF's mounting point as well. Beyond that you or a mechanic can fill the intake with a smoke machine and see if smoke comes out anywhere.

 

Driving/Running at temp

Driving slower at temp
as far as I could tell, no obvious leaks after the MAF. I do have it zip tied to the tube but it isn’t moving all that much. I am working to get some screws to get it tied down correctly. I did notice that my air box has a little opening to it. Would that opening affect things?

I also got some screenshots while I had it at idle and driving.

Idle at startup

 

This same data but on a warm idle please. Not driving

Where exactly is the opening in the air box?

Zipties aren't exactly air tight, usually. That could contribute for sure.

 

got the data below


At idle

Pic#2

Opening

“Fancy Ziptie work”

 

It's likely leaking at the MAF. It is unlikely that is sealed properly

The airbox leak will not cause proble.s as it is before the MAF.

 

could it be a bad MAF as well? I know about 3 months ago I had a ton of oil coming back into the intake. I installed a catch can to fix the issue. could it be a fouled plug? I did go out and get MAF cleaner and sprayed it down.

 

The ECU compares what air the MAF says is going in.....adds fuel it expects and compares it with what the O2 sensor gets as a result.

If the ECU needs to add fuel ( + fuel trim) to get the Lamba it expects it means there is more air than the MAF says is coming in...or the O2 sensor is wrong.
The additional air is either a MAF that isn't working as expected or a Vac leak or injectors that aren't outputting the amount of fuel expected.

If the MAF says the airflow is more than actual...or the injectors are adding more fuel than expected or the O2 is wrong you will get a -ve fuel trim. The ECU is trying to get rid on some of the excess fuel that would otherwise be added

The ECU stores fuel trims in different areas of the maps.... so if your LTFT are normal everywhere but at idle the most likely reason is a vac leak...and it doesnt take much. If the VFAD nipple is uncovered it will usually trigger a CEL for having a LTFT over spec...+ or - 25.

I would almost bet that your MAF is leaking the way you have it attached with the zip ties. Make sure the o-ring is still on there as well.....

 

that makes sense to me! I will check it again once I get the screws in. I went to advance Auto parts to get the right screw and they didn't have the M4 screw in stock. I'll post what I have once I get them put into the Intake.

 

Yeah I don't think those zip ties will hold the MAF tight enough.

If your holes are stripped(which happens easily), you can either just get some bigger screws, or you can get some JB Weld Kwik epoxy, fill the holes with it(get a chopstick to help you do this), wait for about an hour, and put the screws back in.

 

So I got some proper MAF screws and these are the numbers from DashCommand. Are these normal/within the acceptable range?

 

Drive it for a bit to let the fuel trim relearn. +10 long term is better than +20! See if it goes closer to 0 on a warm idle.

 

Still think you have a small vac leak

Although +10% isn't that big of a deal for a LTFT at idle. Did you try using some carb cleaner to find the leak? If you spray it on a leaking area it will cause the RPM's to change for a bit as it gets sucked into the intake.

Did you check that your VFAD nipple is plugged if it is disconnected? Or check to see if the lines are connected properly?

Another common vac leak is the vac distribution block under the fuel rail... if it's ever had the upper intake off and the primary injectors out it is easy to break that.

Other leak sites are the intake gaskets and seals, the injector seals, and one of the solenoid vac lines. I have even seen the one way valve on the brake booster cracked and leaking

 

will definitely keep an eye on it and update you guys!

I need to get some Carb Cleaner and try that out!

My VFAD nipple actually broke off while I frustratingly cleaned the SSV. :'( I did however get some black sealant (butyl tape) and put it over it. I've checked it multiple times to see if its sealed and it has not moved. It also does not make the sound it makes when it is uncovered.

I haven't replaced any injectors yet, so I would hope its not the issue. How would you check the solenoid vacuum lines for that issue? I know I have been getting a p2070. Is it the line that comes off the manifold?

 

The MAF Screws have worked pretty well but I’m still having some issues. The LTFT has gone up to 18 once then back down to 10.9, then sometimes to 8.6, 9.4, or settling back to 10.2. Is it normal for it to jump around like that or do you guys think it may be some bad sensors. I have screwed down every bolt on the UIM down real snug and then made sure the connection between the throttle body and the UIM was clean and snug.

 

A common place for a vacuum leak is the VFAD nipple on the underside of the UIM aft of the throttle body. It's not visible you have to feel for it.

But yes normal LTFT is 0. +/- 5-8 is ok-ish. - 10 or +10 is indicative of a problem, but a problem the computer is able to compensate for it. 18 and more is getting close to the limit of what the computer can accommodate. STFT will jump around, that's more normal.

At this stage only warm idle LTFT matters. Don't worry about what it does while you drive.

 

Keep in mind that the ECU keeps three LTFT values and switches between them based on MAF rate. IIRC, the values are 0-8 g/s (idle), 8-20 g/s (cruise), and 20+ g/s.

The LTFT takes a while to update and does so incrementally. It would be odd to see a genuine swing in one of these values greater than a few % over the course of 30 minutes.

I'd bet what you are seeing is the ECU switching between the LTFTs based on MAF. The idle and cruise trims will update fastest because you spend the most time in those regions.

 

If you end up finding your vacuum leak, I'd be interested in knowing where it was. I'll be doing my own vacuum leak inspection here soon as my LTFT's are consistently at 22. Sometimes they jump down to around 15 when driving. I'll do my best to report my findings as well.

 

If you are having LTFT problems at idle look for a vac leak... if you are having LTFT problems at cruise or at higher MAF flow rates I would look elsewhere.

A vac leak big enough to alter airflow 15% at idle is small. A Vac leak that alters flow 15% at 100g/s is huge. If the trim problems are there you likely have a problem with either how much fuel is injected or how the MAF is measuring air.... or with the O2 sensor system that is measuring the AFR

Also remember that fuel trims are only valid in closed loop operation and are not doing anything in open loop. Sometimes that will show up in a log as 0 LTFT in those areas... but sometimes it seems to carry forward whatever value was in play just before the crossover into open loop.

Misfires can cause strange AFR readings....even if it is super rich it will look to the O2 sensor like there is a lean condition as extra oxygen ends up making it through combustion into the tailpipe where the sensor is located.

Best thing to do is to do logs and see what your AFR does at differing loads and see if there is a pattern. With the staged onjectors coming on at different times you may see a correlation between that and LTFT and be able to figure it may be an injector.

You can also have an exhaust leak that gives you AFR problems. Basically the sensor can't tell where the O2 in the exhaust is coming from so it assumes you need more fuel to burn it and It will try and trim that away.

Dont be discouraged... there is always a way to figure it out if you are meticulous in your data collection and thinking about all of your options

Dont start throwing parts at it in the hope that will fix it.... MAFs and O2 sensors and injectors are all pricey.... and if they aren't a problem changing them won't do anything

If you can.. try and throw up a log on here so we can have a look at it... If your scan tool won't do logs.... try and borrow one from someone that does... it really makes things a lot easier. It is almost impossible to catch things watching a display. Especially if you are driving

 

My issues are at both idle and cruise. I'll log a run and see if it's the same throughout the RPMs. Just driving to work and back over the past couple weeks, I've kept the live values of LTFT and AFRs, and the AFRs seem fine, nothing stands out. It does run slightly rich at start up, but I figured that was due to the engine warming up. Once its up to temp, I'm getting right around 14.7 at idle.

I am a bit suspicious of my O2 sensor. I've got a catless midpipe that used to cause the CEL to turn on, but for what ever reason it doesn't anymore. I wonder if that's related to my fuel trims.

 

The sensor that causes the CEL for the midpipe isn't the wideband that does the AFR. The early cars often dont throw a code....or do it intermittently.