A while back I posted my car was bucking and idling rough and going in to limp mode. I have driven the car since and when cranked, it idled fine, ran fine boosted normal about 5 miles and then all of a sudden I was back in limp mode with no tiptronic kickdown or downshift in auto and very little boost. I decided to try what MARKSI advised some others and unhooked the MAF at the intake tube and went for a drive tonight. Car ran great, boosted down shifted and actuall felt like it had more power than I have felt in a while. With the abs and psm disabled the car was loosing traction in first even when rolling and rarely does that when all is hooked up and normal. I think the car goes into some sort of default map when unhooked and has to figure out some things but ran very well. Do you guys think that because of this test my MAF was the culprit for causing limp modes? Sometimes it would throw a code and other times not but be in limp mode. In other words should I go ahead and buy a new MAF? One possible thought is one time a few weeks ago it went into limp with very erratic behavior and I found the F hose was blown off at the larger end. I re hooked it and all seemed fine. I am wondering if car was trying to boost and boosted higher than it should have before limping to keep up with request and the higher voltage the MAF experienced with this extra airflow toasted the MAF? Any thoughts?

 

I believe its the maf...
if you have a durametric you can log the values for the maf in Kg/hour... there are some write ups as well how to check...

 

Does kevin offer a mafless tune? Might be something to consider if it is just a MAF issue which could pop up again since you're well past the reading capability of the stock MAF.

 

I need to ask him. He has never mentioned one but he is an incredible tuner. I ran this tune for years with no trouble track days etc. but this has popped up recently. I have ordered a new bosch MAF and will try that. if that does not solve it it is off to the dealer but that is and hour away with a ride home and back to deal with. A pain in the ***. Thanks to everyone for the replies.

 

Silver,
Like Markski recommends, you should get a durametric and look at the codes. My car was doing some similar things as you describe. Decided that the missing was due to the Coils never being replaced (65K miles). Replaced those and the spark plugs and it pulled linear, but not as great as it should. (Missing was gone) I took it to the track and ran the worst times ever... On the way home I spoke with Sambot - who I got the tune from. He also recommended I disconnect my MAF and doing a run. Just like what you described, the car felt more powerful then it ever did. I was at 130mph quick. We also believed that the MAF was bad so I replaced it. Turns out the MAF was ok, but when I data logged the car it showed I was maxing out my MAF at 4500 rpm at 1.3bar and 4700rpm at 1bar. (reading 5v) with both my old MAF and my new one.
This told me that I have boost leaks and I was bleeding air out of the system. I have since found my DV's were leaking. (Fixed that and at 1 bar my MAF hit 5v at around 6K rpm). I have since found leaks at my #16 check valve, and #9 Venturi Tube. I am putting everything back in the car to run a pressure test and see what she will hold.
When is the last time you did a pressure test?

 

I have more of a build with my 18gs and run 1.4 bars with my Protomotive tune in which my car makes great power and runs smoothly with the original MAF still in,,as many others do still run MAF and make 600HP.
I have had no problems and I have over 40,000 miles on it,,But I know some do blow maps but for what real reason?

 

Yes you certainly can run stock MAF at those power levels as many do. But the MAF is simply beyond it's reading capability after a certain point ( some say ~500whp, easy to tell with a log of the MAF voltage or flow measurement). I think most the tuners leave MAF's in place just to make idle and daily driving a bit easier to tune for. But it seems on most cars, proto has the mafless figured out for dd stuff. It's been fine for me and I'm at relatively low power levels. I know markski will tell ya a lot of the 800+ guys run it fine as well.

I can't say for sure why some constantly kill mafs and why others don't. But if it was designed to constantly taking a measurement up to 5v and measure the voltage very accurately, I'm sure it can't enjoy being pegged at 5v from 5k-7k every time the car is run hard as many high hp guys do. Heck even just a flashed car is hitting 4.95V at 6k from what I've seen. A sensitive electronic piece can't enjoy that constant excessive flow as it's trying to figure out what's going on. Any issue in grounding or harness could also add to the issue as it's trying to do something with the voltage beyond it's reading capability.

 

i agree...high boost levels with a boost leak is dangerous for the maf

 

Well I'm not referring to a boost leak, I'm just saying that with no boost leak, the MAF still pegs out way early on most modified cars. On a car with no leaks at all, it can't read all the air coming in for a car making 550whp. I.e. the maf is pegged at 5v (it's max reading) for extended periods of time.

With a boost leak this problem is exacerbated though because the turbos are sucking in more air, but the air is leaking out before the motor. So then it just tries to suck in even more air to hold load/boost levels.

 

When Todd at Protomotive did my tune on his dyno ,,my car was data logged and taking other data and monitoring ,,my MAF was responding within the perimeters at my 625 rear wheel HP on his dyno Packs..
Also I have been hitting the 7,400 rev limiter now and then in the last few years..LOL..
So I guess I am one lucky guy with my MAF,,,,so far..

 

of course with a boost leak the maf is over his limit because the airvolume over the maf is a lot more , the airvolume with a boost leak is very high and the ecu try to heat up the maf...5V says nothing about the ampere at 5V that needed from the ecu to hold the temperature at the maf sensor ...too much air and the ecu is at his limit with the voltage but not with the ampere ....P=U*I ...5Volt is only one part

i can run 1,45 bar and do it with extended periods without any problems....

 

Thanks for all the replies. I have not done a boost leak check but plan on doing so. I have ordered the MAF so I will try that when it comes in also. I did blow the F hose off once and wonder if that event contributed to harming the maf. I also need an durametric to read codes but have not bought one yet. Thanks again guys for all your help. I will keep you posted.

 

Curious if you discovered and solved the issue?

 

this..
..and we're still "figuring it out" some 14 years later