What you are looking at is a picture of the MAP sensor on my LSJ rotated and held down by my TVS...



I believe I am having a vacuum leak from this area because I am getting really inconsistent fuel trims and I am having a hard time getting my tune dialed in. I am also throwing a P0300 code about once every day or two. I have read a couple times that the random cylinder misfires could simply be a lean or rich condition caused by a vacuum leak, and I believe this is my problem.

I have tried 2 different sets of spark plugs with different gaps. Also switched around the coil packs.

I sprayed brake parts cleaner on different parts of the engine and listened for differences in idle. If I douse the area irectly to the left of the MAP sensor, the engine will stumble and rev up and down. This leads me to believe that there is a vacuum leak there.

Anyone have any pointers on how to fix it? The MAP sensor is not being held down by the bolt anymore, but it is rotated and held down by the weight and bolts of the TVS. It is a very tight fit, and I do not see how it could be possibly leaking. The rotated MAP is supposed to be the alternative to grinding the MAF in half and bolting it down.

Any suggestions? Possible injector seat leak? The injectors and o-rings are very new, so I doubt it's the injectors themselves. Please help me diagnose and solve this problem!

Help please!

 

I don't see how you could of just rotated it and still have **** fit and seal. I tried that and had to grind mine down to fit correctly.

I actually just had issues myself today that I thought were from vac leaks, but I tested everything with starter fluid and everything seemed fine.

If you are spraying stuff at MAP and it ***** with the idle, then you have a leak there. Grind the sensor down and make it fit better, imo.

 

Thanks for the advice. I'll tear the TVS off and grind the sensor to fit better. I was pretty certain that rotating the MAP would work though. It appeared to sit flat there. Ohh well, I'll dremel it and bolt it back down.

Any further advice or info on the vacuum leaks? What all to test? Better ways to diagnose this issue? Do you think something like that would cause the P0300 codes and the sweeping fuel trims?

 

Which way are the fuel trims going ? Rich or lean?

 

Mine is not held down by a bolt and I threw the same code today.....maybe I need to check this too lol

 

I cut the MAP sensor and bolted it down (couldn't use the original hole, used a notch in the bracket to bolt it down). I was only able to idle the car for a minute, and I didn't get a chance to check the trims, but brake cleaner on the sensor didn't cause a stumble. This might have fixed it... I can only hope lol.

I sprayed cleaner on all the injectors, around where the blower meets the manifold, and around the TB. I didn't hear anything unusual so I am really hoping the problem is gone...

Well I have LTFT's disabled in my tune right now to try and dial it in... STFT's sway back and forth +- 10-20. If I turn on LTFT's they go -20 pretty fast which would be the car running rich and pulling fuel.

Worth a shot... Spray some brake parts cleaner or starting fluid around the sensor to check.

 

I popped a code about one of my o2 sensors too? if that helps

 

What were ur short/term readings? Small fluct is normal 3or5or less but the long term is the concern. If its removing that much fuel something is makingit rich. Either ur MAP failed or there is a vacuum leak which apparently there is via the aerosol spray enrichment. Ur MAP sees more air coming in because of the pressure change and the injector pulse increases. Either scan the map operation or isolate ur vacuum leak(get creative),, or both

 

Well this morning I threw the P0300 code again right while the car was idling to warm up.

I need to try and dial in my tune and see how off the trims are now.

Thanks for the suggestions guys. Anything else?

 

MAF dialed in for closed loop? Calibrate MAF using trims.

 

I hope to try and do some logging over my lunch break soon, and get the MAF dialed in better. Hopefully that will bring my trims back into spec. My AFR error calculations off my wideband only shows a couple percent off, but the STFT's are pegged at -21 in some spots. I also threw my 2.8" TVS pulley back on last night, so my MAF is definitely off. I guess I'll have to wait until I get the MAF settled before I draw conclusions.

The P0300 code did come back too when I first started the car this morning. I am hoping this is because it was running so rich with the mis-calibrated MAF.

 

Changing pullies shouldn't affect MAF. Reason you calibrate MAF is so you can change pullies as much as you want and car will adjust and you dont need to touch the tune.

Use trims instead of wideband to get MAF dialed for closed loop.

 

Can you please elaborate on the trim method? Setup histogram of STFT's versus MAF frequency? My LTFT's are turned off right now. Should I also put in a filter so that it only picks up trims where the pulse width is over .8ms for instance to filter out clutch in lean and other spikes? eg, "[PID.6200]>.8"

Would a bad front O2 seriously effect the trims and hence the MAF scaling? My O2 sometimes doesn't seem to do the full voltage switch and the graph plot is super jagged, other times it is a nice curve (like a SIN curve).

I was under the assumption that all AFR tuning should be done with a wideband if you had one. Are you suggesting doing all closed loop tuning with trims and only doing open loop with the wideband? I'm MAF only BTW.

Thanks for the input!!! More is certainly helpful!

 

Could be similar to my problem. I had a slight vacuum leak on my MAF sensor too. The one screw somehow shimmied loose. Put new screws in and it seems better. Would always get a cylinder 1 miss and timing over advanced when I went on the highway..

And good suggestion on the 02. I had a bad 02 after doing a header/dp combo. Was throwing stuff all off. Replaced both of those, and am also on new plugs.

 

Changed my plugs and no more misfire! And my maf sensor isn't bolted down

 

Plugs can certainly cause the P0300.

I'm not 100% sure my vacuum leak is solved, but some quick MAF tuning with STFT's got my STFT's down to about plus or minus 4-8 which is a great improvment over pegged lol. Car seems to run a bit better midrange, but I am still having a little bit of issue getting it dialed in on the low end.