Noticed pretty recently while logging with hptuners that my MAP drops when Im doing a quick WOT pull in 2nd gear, around 4000-5000rpms it starts to drop off from the 90ish KPA range. It slowly climbs up to the 90s with RPMs and then as soon as it hits the 90s range it immediately starts to drop back down and basically continues to drop as the rpms go up until I let off. I have older logs Ive checked where it jumps up to the 90s KPA really quick when I go WOT and holds it there the whole time until I let off. I can't think of any mods/anything Ive done that could have caused this, but maybe I just don't realize something I could have done caused this. Could this be the MAP sensor going bad? The car runs great otherwise and still pulls hard at WOT.

Just rewatched again and noticed my MAF reading goes down as well with the MAP reading, wasn't doing that before either. What is going on? Bad MAF too? vacuum leak?


EDIT:
This is fixed for anyone who has a similar issue, turns out it was a corrupt tune file, more details in last post.

 

Its extremely unlikely that both the MAP and MAF sensors are going bad. And vacuum leaks have no effect at WOT, because there isn't any vacuum.
The output from those sensors is clearly stating that something is reducing your air volume through the engine. Do you have CATs that are getting clogged?

 

What is the MAP reading with engine not running and what elevation are you at?

 

What does your AFR do when MAF drops?
If it's going lean then this is a serious problem.
If it stays on target then it's merely strange.

​​​​​​It's hard to believe that actual air flow would drop as RPM increases.

What happens to the load values as this happens? It's normal for load to go down a bit as RPM increases, since VE goes down, but it shouldn't go down by a lot.
​​​​​

 

I have high flow cats from stanlessworks with their LT headers, I doubt the cats are clogged (and Id be surprised if the could really clog since they are not thick honeycomb style, I would assume if they start to break up they would just shoot through the exhaust since its not like a standard cat that have the thick honeycomb you can barley see light through). But there is also nothing else that I think would indicate they are clogged, would there be other signs of them being clogged?


98kpa. Elevation is around 600ft.


I do not have a wide band 02 sensor and Im not WOT tuning, but according to the hptuners scanner commanded AFR is not leaning out when the MAF and MAP drop. Look at various logs when this happens the AFR will be anywhere from 12.19-10.86 depending on RPM, higher the RPM the higher the AFR. Front 02s read in the 900s MVs.
Right, thats why Im thinking the MAF and MAP might just be starting to fail or something. Im using the new style GM MAF replacement from autozone, its a black plastic one and not silver/black like the stock one, but have been using it for years with no problems. MAP sensor has never been replaced to my knowledge.

load stays at 100%.


Another thing that is weird is the histogram graph with the cells that log the timing you are at(cylinder airmass vs RPM) dont actually record the timing in the cells that Im in when this happens, I can still see the commanded timing/actual timing its at but its just not on the graph.. The cells highlight as it goes through them but doesn't actually log the timing, it remains blank. In previous logs when I wasn't having this MAF/MAP problem the histogram worked like it was supposed to. Its almost like it goes through the cells so quickly that it doesn't bother to record it.

I just checked the air filter, airbox and MAF and everything looks fine. MAF still has screen but it did before too and had no problems like this.

 

90 kPa is a huge pressure drop. Something is restricting air flow. Considering the combined results of your data readings, I'm going to guess something is collapsing in the intake.

 

i have a stock LS6 intake manifold and an SLP lid, stock style dry air filter, stock throttle body, and a smooth bellow. What would be collapsing you think?

Would any other mod/tuning details help?

you think i should try a run with no air filter or something?

 

I wanted to bump this as I think Ive solved it. I had a 1 way check valve that would vent out from the valve cover in case crank case pressure built up too high. Apparently I guess it was venting out under WOT load and causing this issue. I read a post on here about a guy who had a similar issue with his catch can that had a pressure release valve that made me think of my setup. I took it off and did a log with a couple WOT runs and it looks like things are back to normal.

edit: Maybe not totally normal. When going WOT the MAP reading climbs with RPMs rather than jumping to the high 90s and holding there as soon as I go WOT. Time for more digging I guess...

 

I wouldn't think that would have any effect at all on the intake. From what I understand you basically cant have to much case venting unless its so unrestricted it pukes oils and stuff out with it. Ideally you want no restriction in the venting but just a way to let oil vapor condense in the catch can or drip back into the valve cover.

Now if the case venting became restricted, that could cause some issues with gases not going the direction they should. But I think it would cause the MAP to go up not down because it would be putting case pressure back into the cylinders and the intake as it would be venting it's normal 10% of combustion gasses back up the cylinder instead of down past the rings and out the vents.

If you turn the key to the on position and crank the engine over one or two turns but don't start it. This activates the MAP reading in the scan and it should say something like 87kpa or close to depending on your elevation. Doing that will tell you if the MAP is reading right.

I literally just had to sniff this same issue out 3-4 weeks ago, I had a bad MAP sensor that blew out my last track run of last year and I could not figure it out. The car ran like it had a severe vacuum leak. Super lean at idle, had to give it pedal to keep it running... I had to ride the brake while driving it home to load the engine and get the AFR's lower....turns out the MAP blew something but it didn't just stop working. No, that would be to easy. It just started reading the wrong pressures and lying to me. Couple that with an injector change when I was trying to diagnose it and it was one big pain in the ***.

 

Alright Ive attached 4 images from scan logs, the first three have the weird MAP/MAF readings and the 4th image has a normal MAP/MAF reading I was getting last year.

Ok what if something is mechanically wrong with the engine and that is causing this? The engine otherwise runs great, but what would be some things that could cause this? Bent pushrod? cracked/broken valve spring? Piston ring(s) bad? bad lifter?
What about a maxxed out fuel pump or maxxed out injectors? What about bad fuel?

Clogged cat was mentioned, and I have an endoscope that I used to fish into the 02 sensor hole to look at both cats and both look fine to me, checked the back and front using both 02 sensor holes, could still clearly see the mesh, no blockage that I could see. I used the endoscope in the intake manifold to see if something was in there and everything looked good as well. I double checked the throttle body, SLP lid, air filter and MAF (and used a different spare MAF I had that was also de-screened that didn't seem to change anything) - Im currently using the new style Delphi MAF that is a full plastic housing and not the silver/black old style stock one. I pulled my passenger side valve cover to look at the valve springs and everything still looked new, going to pull the drivers side this week to check when I have time. One thing I noticed that might be a fluke is with a temp gun aimed at the headers it seems like cylinder #2 has slightly lower readings than the rest, but this header pipe also has the AIR fitting with a block off plate, not sure if that would make a difference. The plug for that cylinder looks good and looks the same as the other plugs that I have pulled (haven't pulled all of them).

You can see the second image that as soon as I went WOT the MAP jumped up to where it should be and then the reading slowly dropped from there, while the other two images the MAP climbed up slowly with RPM and then as soon as it hit its peak it dropped back down again. Also notice that like I said in a previous post that the histogram on the top right is not logging and timing when this happens.

Last picture is the way it was before.

 

Interesting. I may just replace the MAP for the hell of it, just a pain in the *** to get to. The thing is the car drives fine otherwise and I wouldn't have even known if I wasn't paying attention to the scanner and seeing the weird behavior.
With the key in the ignition in the "on" position the MAP reads in the high 90s, I have not tried to crank it and not let it start to check.

 

you still need to post the actual scan here so the rest of us can download it and look through it proper. Screen shots are just not enough to make a call from. The first thing I notice from them is that it appears you MAF is going down as the RPM went up?

That's strange and also maybe related to the MAP? Is your airfilter collapsing or something?

 

log and tune

log and tune

......

 

Yup sorry, Ill post logs and Ill upload the tune file as well, thanks for the help guys really appreciate it.

I would love for it to be something as simple as the air filter collapsing but I doubt it, its just the stock style paper filter in an SLP lid. When I get the chance Ill try to find an area I can do a quick run with no air filter and pull over to put it back in. I even switched out the aftermarket smooth bellow for the stock bellow just in cause that was collapsing and it didn't change anything. Using stock throttle body, stock LS6 intake, new style Delphi screened MAF (also tried the oem stock MAF that was descreened). I have stainlessworks LT headers into their catted Y-pipe into a corsa catback that has a cutout on the I-pipe. I opened the cutout for a few runs just to see if it made a difference and it did not at all. And again I checked the cats with an endoscope for them being clogged and they looked like new, plus the car doesn't run like they are clogged and is still loud as hell when WOT.
What is strange is I can't think of anything I changed between now and about 6months to a year ago when I had my last WOT run that I had logged and it didn't show this weird issue. What about adjusting injector timing? That is something I have done more recently but Ive read it has little to no effect at WOT.

One more thing, I have a current code for the L-Termianal, no SES but just the code, and from ive researched its just an alternator wire or the alternator itself, I have a new alternator sitting in my garage that Im going to install when I get a chance. Just threw that idea out there in case someone though this would make the MAF or MAP have strange readings due to electrical issues.

I have uploaded 3 log files with examples of what Im experiencing. I can upload older log files that didn't show this problem if you would like too.
Also uploaded the current tune im using.

Thank you again to everyone helping.

 

Nothing guys?

 

The MAP sensor on my Jeep is the GM style, I get about 2 to 3 years on one and they die, and I've had 2 DOA sensors out of 3..
Standard Delphi parts..

 

That MAP is all over the place. Either the sensor is bad or perhaps the wiring is ran next to something giving off some serious interference. Try a new sensor.

 

Update:
Replaced MAP sensor with an autozone one, was able to get to it without taking the intake manifold off.
First test pull I did seemed it helped some, but still didn't fix the issue. Went WOT around 3000rpms, the MAP shot up to the mid 90s and held there until around 4500rpms when it slowly started to drop. Normally before as soon as the MAP would hit its peak number it would immediately drop down and not hold at all. MAF sensor did the same as before and dropped at that peak number too.
Second pull and third I did and now things are back to just the way they were before, it climbs to peak number slowly and then immediately drops back down...

WTF is the deal...

Also tried a new still-in-box MAF I had bought years back from autozone. Plugged it in and apparently its totally dead somehow and the scanned wasn't picking up any numbers from it at all and then it threw the MAF code... Thats weird.

edit: notice on the third log the knock learn factor is reading weird, normally its 1 at operating temperature but this log its reading .30-.40 ish...

 

Have you checked ,as suggested earlier, that you dont have an intake pipe collapsing?

 

Has anyone asked what your mods are?

My H/C/I/E car with a LS6 intake, stock TB and stock MAF pulls 93kpa at WOT.