[LSJ] MAP reading not what I expect, and I can't find any vacuum leak; Help?

[tycoonbob]

Hi all,
Fairly new to this tuning thing, but have had some great guidance so far. I've got a 2006 Cobalt SS/SC, LSJ engine, TVS 1320 blower with 2.9" pulley, Siemens 80# injectors, K&N CAI, ZZP Shorty Headers, 2.5" catless downpipe, some resonator, back to a Megan Muffler, running E85. I've been slowly playing/learning by doing some MAF tuning on idle and cruise, but I'm noticing my MAP reading (which is at 96 kPa with the car off), doesn't really drop down below 60 or so. It's my understanding it should be like 26-30 at idle? Naturally I suspected a vacuum leak, but I can't find one. Using carb cleaner, I've sprayed my vacuum lines, where those lines connect, as well as around the map sensor and get no change. I'm just not sure where else to go at this point.

Side note, probably related, using the stock TB I have to set my ETC Scaler up to like 7000 to get it to idle, and my spark is around -3* or so, which I take it my overspeed table is pulling timing to get idle down to around idle command. I assume this is a consequence of improper MAP reading? Is there a chance my MAP sensor is bad, even though I get a correct reading with the car off (96kPa), and it does change with the car running? Could it be something in my tune? Any advice at all? I'm stuck, and not sure what to do.

Attached is a latest log (warm idle) and the tune I'm running.

Thanks in advance!

EDIT: Also, ignore the AFR reading in my log. I think something is wrong with my 30-4110, or how I have it setup or something. That should be unrelated, though.

[TCSS07]

I'm mobile atm so if no1 responds I'll take a peak when I get home in a few hours. What map are you running? Factory lsj? And yes your can be bad. You should not have to mess with the scaler unless your cammed or running ls4 tb. I'm cammed wirh ls4 and my scaler is 5650

[tycoonbob]

Hey, thanks for the reply!

Stock bottom end and head (cams, valvetrain...all stock), though I did get a valve job and had the head resurfaced within the last 2 months. Thought I had a couple bent valves from the timing jumped a few teeth (I assume), but turns out nothing more than a couple burnt valve seats which were taken care of, or so I was told.

I do have a LS4 TB, but have decided to pull it back off for the time being. With this current tune, on the stock TB, if I leave the ETC scaler at 2950, it idles about 500rpm too high, and it's pulling tons of timing out to try and correct, but it just cant get my idle down to command. Playing with ETC scaler, I was able to bring rpm down, but I know I shouldn't have to do this.

I'm hoping it's just something simple as a bad MAP sensor, but I wasn't sure a failure like this would be possible. Figured it was either that it worked, or it didn't work.

FWIW, I've only had this car for about 3 months now, and it wasn't running when I got it. The previous owner is the one who told me he thought it had bent valves from timing issues, and he could never get it started after he put new timing and balance components in it. I managed to get it to start and run some back then, but was dealing with low compression in cyl 1, which is what prompted the head work. I also replaced the piston rings and cleaned up the pistons. I've checked compression twice since the rebuild, and both times it was showing all 4 cylinders within 5psi of each other, somewhere around 160-170. FWIW, I think my cheap Chinesium compression tester reads a little low, but the fact remains i have compression, and all 4 are definitely within 10% of each other.

Anyway, I do really appreciate the help, and am open to any advice at this point!

[TCSS07]

the tune isnt set up right at all for e85. stoich is still set up for pump fuel(not saying you cant do it this way but its just not correct - i use 10 for stoich on e85), idle rpm is screwy you shouldnt need to idle that high. im zzp stage 3 cammed with ls4 and i idle around 950 and it starts at 1200 and tappers down to 950 - commanding 1300rpm at 90F is high imo, set the scaler to 4950 for the ls4, open loop eq for in gear and p/n are all set to 1's. dont know why. change the sc boost control to the 07 settings prop gain .005 and integ to .001 - they work better. and spark to me isnt really set up well, id return the idle and coastdown back to 07 settings along with the under/over speeds. if you would like futher help pm me and i would change that map sensor because it doesnt appear to be reading right i idle at 70kpa your above 80

[tycoonbob]

Hi, thanks for the input!

So my base tune was done by a fella who seems confident, but is new-ish himself I believe. He's been a great help in teaching me about this, but I obviously have no reasoning for what he did for a base tune. I do know it's all MAF based and that he said he leaves stoich at 14.7 and only modification needed for E85 was increasing MAF values. Sounded logical to me so I rolled with it.

So I did order a new MAP sensor, same Bosch model, which I'll have on Tues. Do you think it's really likely that I have a faulty MAP sensor and that's the reason for the high reading? Or is it possible that bad boost control settings are causing the bypass to stay open and not build vacuum or something? Would that even make sense?

I did also order a new boost bypass solenoid because it was pretty cheap on Amazon. Figured it'd be worth trying.

FYI, I may very well PM you this evening or tomorrow. Thanks again!

[TCSS07]

it will work that way sure but like i said its just not correct and then depending on where you end up on the maf hz scale you might out run the ecms max airflow which is 68 lb/min (not saying you will) because your now adding a ridiculous amount of fuel now to which may require you to pe rape because you cant add anymore fuel on the maf chart which shouldn't be done to get wot fueling in line but that can only be checked with a wideband and if you dont have one you need to get one. tuning in lambda is the best way to tune e85 because stoich is always 1.0 no matter what value you use for the base afr and always shoot for a .78-.80 when boosted. but as i said people have their own ways going about it.

its possible the map is bad. your numbers for using the lsj 2.5bar map are correct so either the ecm is reading the map wrong because its bad or possibly something with the ecm which i doubt. any dtc's? it is possible to have a vac line or something along those lines messing up the map. you could disconnected the lines going from the bypass and cap it off and see if your values come back to normal. but map is a easy replacement kinda the tvs sits on top of it lol. i have the lnf 3 bar map in mine just because i had one lying around and wanted to change it.

[tycoonbob]

Yeah, sensor replacement is pretty easy, and the OE I ordered was like $34, so definitely worth trying. Hopefully I'll get lucky and that will be all it was, or the bypass solenoid which I will also be replacing since it's like $30. I hate throwing parts at a car, but it's a lot easier when it's cheaper parts.

I've triple checked that all the vacuum lines are connected correctly, and have sprayed them down with carb cleaner looking for holes, as well as spraying the MAP sensor and around it, and on the bypass...just can't find anything. I know the SC is mounted down good, I know the gasket is between it and the intake, I know the intake mani gasket is in place, and I know the green gasket for the bypass on the endplate is in place. I know the little plate with 2 screws on the side of the TVS is mounted firmly, as is the MAP/IAT sensor on top of the blower. I know the gasket on the TVS inlet is there as well, and I know the TB is good and tight. Between the TB and the CAI, the rubber hose is clamped down firmly. I really have no idea where else it could be leaking at this point.
Looking back at old logs, it seems that I've always had this high MAP reading ever since I got the engine running, back still with the M62. Same thing with the LS4, so I know it's not my TB (which I'm back on the stock right now).
Are there vacuum lines anywhere else on the car I should be aware of? One for the brake booster? Anything to the trans?

[TCSS07]

Not on the trans no. The brake booster would probably cause a lean code before it would skew the map sensor. You can also maybe un plug the maf and see if the car reads better. You should be around the 30-40kpa

[tycoonbob]

To follow up on this, believe I got my issue fixed. Pulled the TVS and MAP sensor out yesterday evening, and found a decent size crack/gap in the bottom side of the MAP sensor. Almost looks like it cracked, and somehow twisted, but there was a decent hole that was definitely leaking.

Replaced with a new MAP sensor, used some RTV to hold it down better, and definitely getting better vacuum now, but haven't checked actual MAP reading in HPT yet. Definitely need to adjust my tune, though.

@TCSS07 I appreciate the info about tuning incorrectly on E with stoich set at 14.7. I'm going to set that to 10.1 and retune my MAF. I do have a wideband, but not working correctly, but not sure if that was because of my vacuum issue or not. But, I plan to use it in lambda once I get it installed and working, so thanks for letting me know to target .78-.80 at WOT. I've barely gotten into idle and cruise MAF tuning, so I'm still a bit away from WOT tuning.

[TCSS07]

Yeah that will do it. Double check later but at warm/hot idle you'll be between 30-40kpa. The car will run better to.

You can do it the way it is and it will work fine. I was just saying it's not the correct way to go about it. But yeah tuning in lambda is just easier all around. For pump gas you can use afr if you want but e85 lambda is much easier to deal with. Report back if you run into any issues

[cobaltssoverbooster]

E percentage wanders too much per area so unless you guys are in the same area then your stoichs will be slightly different.
best way is to read the manual on your wideband gauge and set it to report lambda. set the ecu up to open loop control no trims and change the scanner wideband to transform the channel to report lambda values correctly.
from here tune idle until lambda actual reports close to 1.0. switch the gauge and wideband channel back to afr and record the actual reading at idle in afr.
this is now your new ecu stoich value.
tune your ecu based on this stoich value for that ethanol pump in your area.

[TCSS07]

forgot to mention that. checking the alcohol % to suit your area/vs me. thanks cobalt. i seem to always forget one or two things lol so its good to have you drop by

[cobaltssoverbooster]

its just something that i always do. over the years i just learned how important it is to have the correct base data and targeting values.