Negative LTFT at Idle, KR at WOT
- Thread starter Duey1083
- Start date
Duey1083
Greenie N00B Member
Awafrican
Moderator
Yes removing that plastic Shield is key tm take it off. I personally applied some electrical tape in its place once I had repositioned everything.
Edit: other replies didn't load before I responded I think it's safe to say we've established that you can remove it lol
Solarsurge
Greenie N00B Member
Fully admitting I skimmed the thread, so I may have missed whether or not the original issue was solved, but vacuum should be over -11 at idle. The LTFT and low vacuum combined, the first place I’d look is the PCV hose on the back of the intake manifold.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Duey1083
Greenie N00B Member
By vacuum being over -11, are you referring to my boost pressures, which are currently sitting around -8 to -9?
I checked the PCV and OCC lines and they are perfectly fitted and all clamps are tight.
I would like to unbolt the throttle body and intake manifold so that I can retorque them, but I'm not confident my gaskets can be reused. I bought the Felpro kit off of Rockauto...IM gasket is OEM style and TB is paper gasket.
EDIT: wouldn't a vacuum leak there also result in an in-rush of unmetered air, which would result in the ECU adding fuel (+ trims), rather than removing fuel (- trims)? Just want to make sure I understand the issue.
Awafrican
Moderator
Boost = +psi, vacuum = -psi
No a vacuum leak does not equal positive trims: explained here
No a vacuum leak does not equal positive trims: explained here
Duey1083
Greenie N00B Member
Haha, I know that boost = + psi and vacuum = - psi.
I should have been more clear in my clarification to him...when he says vacuum should be more than -11, is he saying more negative (< -11) or more positive (> -11)...I'm assuming I'm higher than I should be as per Enki's original comments.
Assuming I have a leak between turbo and intake valves:
At idle, during vacuum, atmospheric air would enter at the leak site unmetered (too much air), so wouldn't the computer add fuel to compensate (+ trims)?
As a counterpoint, when in boost, I'd be losing metered air, and have a rich condition and the computer should pull fuel (- trims)?
Clarification:
I'm not stating the above as fact, but it's how I currently understand things.
@Solarsurge / @VashEXE, I read in another post from you guys that the lower right bolt for the intake manifold can prevent the intake manifold from mating flush on the gasket surfaces.
I believe you recommended removing or loosening this bolt to see if the issue resolves? If I did this and the issue resolves, do you just leave it as is?
Most people I've talked with do not use that bolt. That was causing the IM not to mate up properly and I had a huge vac leak from there when I initially did my build. Just remove it and be done with it. Some people do washers and stuff, but if 8 bolts around the runners isn't enough I don't know what is.
Solarsurge
Greenie N00B Member
Think of a Boost/Vacuum gauge as two separate gauges. If the number is negative you are measuring vacuum. If the number is positive you are measuring boost. Higher number = “more” of either one. You should be in the ballpark of -11 PSI “or more” at idle, depending on elevation. Enki’s comments were referring to fuel trims, not PSI. As for the lower bolt, there is a gasket that goes in there that looks like a plastic washer. I’m of the firm belief that if it wasn’t necessary to be there for a proper seal, Mazda would not have had it to begin with. In other words, if you don’t have the gasket, get it, and torque the bolt to proper spec.
Sent from my iPhone using Tapatalk
Duey1083
Greenie N00B Member
Appreciate all the help guys...I really do.
Enki had me do a KOEO check to make sure my MAP sensor was correctly reporting the vacuum pressures at idle, as mine seem a high (-8 or -9). This checks out okay, though I'm going to confirm with my tuner that he scaled me to a 3 bar MAP sensor and not a 3.5 bar.
I never noticed a plastic shim under that lower tab for the IM...never knew it existed to be honest.
Getting back to my issue...it's really not behaving like a vacuum leak if I'm being honest. And if I may make a suggestion to @JohnnyTightlips suggestion for fuel trim targets, as there are two operating scenarios that can present (please correct me if I'm wrong):
Idle Condition:
Pre-turbo = + trims, air added or sucked in
turbo to TP = + trims, air added or sucked in
post TP = + trims, air added or sucked in
Boost Condition
Pre-turbo = + trims, air added or sucked in
turbo to TP = - trims, air lost or pushed out
post TP = + trims, air added or sucked in (vacuum leak) OR - trims, air lost or pushed out (boost leak)
+5 or -5 is ideal
+7 or - 7 not crazy might want to look into it
+10 or -10 look into it , you got a leak
+20 or -20 shits broke yo
Since my issues are negative trim at idle, I think my issue probably lies elsewhere...and it's going to be very hard for me to diagnose myself without throwing gobs of money at new parts:
1) MAF sensor gone bad ($$)
2) MAF Calibration ($ - check with tuner) and check MAP calibration (3 bar MAP sensor installed)
3) Fueling issues:
- Leaking injectors ($$$$$) - just recently serviced, cleaned and bench tested...unlikely? Had a hard time removing them, and may have damaged two, but nothing detected by shop that serviced them and no misfires.
- Faulty PRV ($$) or spill valve (cleaning)? Can these cause negative LTFT?
4) Exhaust issues?
- EGR problems?
- Turbo issues?
- Exhaust leaks?
5) Is there anything else you guys can think of that would cause my car to pull fuel at idle and start knocking at high load during WOT, dumping gobs of fuel to prevent detonation?
Enki had me do a KOEO check to make sure my MAP sensor was correctly reporting the vacuum pressures at idle, as mine seem a high (-8 or -9). This checks out okay, though I'm going to confirm with my tuner that he scaled me to a 3 bar MAP sensor and not a 3.5 bar.
I never noticed a plastic shim under that lower tab for the IM...never knew it existed to be honest.
Getting back to my issue...it's really not behaving like a vacuum leak if I'm being honest. And if I may make a suggestion to @JohnnyTightlips suggestion for fuel trim targets, as there are two operating scenarios that can present (please correct me if I'm wrong):
Idle Condition:
Pre-turbo = + trims, air added or sucked in
turbo to TP = + trims, air added or sucked in
post TP = + trims, air added or sucked in
Boost Condition
Pre-turbo = + trims, air added or sucked in
turbo to TP = - trims, air lost or pushed out
post TP = + trims, air added or sucked in (vacuum leak) OR - trims, air lost or pushed out (boost leak)
+5 or -5 is ideal
+7 or - 7 not crazy might want to look into it
+10 or -10 look into it , you got a leak
+20 or -20 shits broke yo
Since my issues are negative trim at idle, I think my issue probably lies elsewhere...and it's going to be very hard for me to diagnose myself without throwing gobs of money at new parts:
1) MAF sensor gone bad ($$)
2) MAF Calibration ($ - check with tuner) and check MAP calibration (3 bar MAP sensor installed)
3) Fueling issues:
- Leaking injectors ($$$$$) - just recently serviced, cleaned and bench tested...unlikely? Had a hard time removing them, and may have damaged two, but nothing detected by shop that serviced them and no misfires.
- Faulty PRV ($$) or spill valve (cleaning)? Can these cause negative LTFT?
4) Exhaust issues?
- EGR problems?
- Turbo issues?
- Exhaust leaks?
5) Is there anything else you guys can think of that would cause my car to pull fuel at idle and start knocking at high load during WOT, dumping gobs of fuel to prevent detonation?
Solarsurge
Greenie N00B Member
I can think of 500 things that might cause symptoms like yours. But when I think of your symptoms, and other people think of your symptoms, and we all arrive at the same advice, it’s probably because 95% or more of the time we see these symptoms they are the same issue and we nearly always have 500 message long threads in which it’s impossible to have a vacuum leak. Look at all the solved issues. Those usually ended with “You were right, it was a vacuum leak.” The rest of those threads end with “I sold the car because I got tired of throwing money at all the things I thought it SHOULD be.”
With that said. Yours might actually be in the 5% of the actual mechanical or electrical issues. But before you throw money at it or try to do too much mental gymnastics, it’s FREE to do a proper leak test. Do that first.
Also, check ALL your hoses. Not just the intake path. Check your vacuum hoses from the valve cover, EBCS, BPV, PCV, etc. Something is leaking, and it will probably require more than just your eyes to see it, otherwise your LTFT would be +/-20
Sent from my iPhone using Tapatalk
Last edited:
Duey1083
Greenie N00B Member
Don't get me wrong, I know I haven't officially ruled out a boost/vacuum leak at this point. I have a replacement BPV recirc on route as well...found it was cracked (so also a possibility).
I have an appointment on the 18th with a local tuning shop that has done work for me in the past and will have them perform a boost leak test as I'm not equipped to do that.
I'll also work with my tuner (Stratified) to see what they recommend as well.
I just did the PRV test and after driving with the engine hot, I checked to see what the rail pressure did KOEO...it very very slowly built up to 540 psi and then started to taper down. So, the PRV may be shot...not sure if that explains some of my issues or not though. EDIT: I have noticed odd hesitations while lightly accelerating, so the car does seems to stumble and bog a bit.
EDIT 2: I will follow JohnnyTightlips build for a boost leak tester.
Last edited:
JohnnyTightlips
Motorhead
It could be your purge valve. Have you looked at that?
Duey1083
Greenie N00B Member
I disconnected the vacuum line and plugged the end...ran the same as with it plugged in.
The chat in the Shoutbox this morning thinks my PRV is failing...not a full out failure like some, but it doesn't hold pressure very well.
JohnnyTightlips
Motorhead
Pressure Relief Valve is a pretty common issue on higher mile cars.
Duey1083
Greenie N00B Member
I realize I never updated my thread.
I had a shop complete a boost and exhaust leak test and they found a couple small leaks on the flange between the intercooler to the BPV/throttle body hose and on the EGR valve itself. The leaks were fixed and the EGR was deleted.
This improved, but did not fully resolve my issues. I still occasionally see up to -10% to -12% total fuel trim at idle and nearly normal range while cruising.
I also recently replaced my PRV, which didn't do much to resolve my issues.
My next steps will be to send in a MAF Cal datalog to my tuner and see if we just need to revise the tune...I'm thinking this is most likely.
I mentioned to @Awafrican, that when I put two gallons of e85 into my tank, my trims go back to normal...as in perfect, couldn't be better. Since Stratified did an e30 and a 91 octane fuel map for me, I'm wondering if they made a mistake and sent me an e30 tune that was mislabeled as the 91 octane tune. I've checked several times and I'm running the correct map.
I had a shop complete a boost and exhaust leak test and they found a couple small leaks on the flange between the intercooler to the BPV/throttle body hose and on the EGR valve itself. The leaks were fixed and the EGR was deleted.
This improved, but did not fully resolve my issues. I still occasionally see up to -10% to -12% total fuel trim at idle and nearly normal range while cruising.
I also recently replaced my PRV, which didn't do much to resolve my issues.
My next steps will be to send in a MAF Cal datalog to my tuner and see if we just need to revise the tune...I'm thinking this is most likely.
I mentioned to @Awafrican, that when I put two gallons of e85 into my tank, my trims go back to normal...as in perfect, couldn't be better. Since Stratified did an e30 and a 91 octane fuel map for me, I'm wondering if they made a mistake and sent me an e30 tune that was mislabeled as the 91 octane tune. I've checked several times and I'm running the correct map.
JohnnyTightlips
Motorhead
The mafcal should not really change with an e30 as you change the fuel specific gravity field to compensate for the ethanol. That being said I generally do a touch up mafcal when I switched to e30. I am guessing you just need the mafcal cleaned up.
Duey1083
Greenie N00B Member
I think you are right...they adjusted my tune for a 3 bar MAP and we didn't adjust the MAF Cal afterwards.
I have a datalog that I'll send in to them this week.