Car cutting out and hesitating

[dsfelton]

Well I went out of town for two weeks. Every since I got back my car has been running horrible. It is cutting out and hesitating really bad at times and is also dying from time to time. It is only seeming to do it once the car is up to operating temperature.

It kicked on the check engine light so I pulled up the code on my tuner and it was p0102 which is Mass Air Flow circuit Low Input. I pulled off the maf and checked all of the connections and cleaned the maf sensor. I check the battery. Running it was 13.8v and with the car off was 12.5v. The battery and alternator are only four months old.

I also data logged the car. The only thing out of the ordinary was the maf voltage. When it was cutting out the maf voltage froze at .7v no matter where it was in the RPM range and when the car started running normal again the maf voltage would jump back up and be normal again.

I also have a mafia and was thinking that it could possibly be malfunctioning. Has anyone seen the mafia go bad? I thought it could possibly be a vacuum leak as well so I checked all of the vacuum lines and all seems normal there. I also just changed the fuel filter less than a month ago.

From what I read in other threads the frps could also be the culprit but the fuel pressure stayed constant and never dipped or spiked while the car was cutting out and the a/f seemed normal as well. I pulled the line off of the frps and it didn't smell like fuel but I know that they can go bad and not rupture the diaphragm.

I am thinking that the maf sensor or the frps is bad but I'm not sure. Any advice is greatly appreciated. I really don't want to just start ordering parts and not fix the problem...I thought someone might have some insight as to what problem might be.:shrug:

Thanks!

 

[03cobra#694]

Do you know what the MAF counts were when you logged it?

 

[exdeath]

Divide and conquer. Looks like you already know where the problem is. Disconnect the MAFia and putt around a little and see what it does. (go back to a stock tune if you have to, just to use the stock MAF curve temporarily to test the MAF sensor without the MAFia) Borrow a MAF from another car if you can. Etc. Obviously don't go balls out with it or give it any boost until you've got it straightened out and flashed back to your current tune with all those mods.

If the MAF reporting low, you're running lean (more air than the computer can see due to low input), so it's running better when it's cold from the extra enrichment which compensates to some extent.

If you logged fuel pressure from the rail PID, not just a custom gauge, then that is the FRPS and it sounds fine.

 

[dsfelton]

Do you know what the MAF counts were when you logged it?

No I'm not sure what the maf counts were when I logged it. I'll check and see.

 

[dsfelton]

Divide and conquer. Looks like you already know where the problem is. Disconnect the MAFia and putt around a little and see what it does. (go back to a stock tune if you have to, just to use the stock MAF curve temporarily to test the MAF sensor without the MAFia) Borrow a MAF from another car if you can. Etc. Obviously don't go balls out with it or give it any boost until you've got it straightened out and flashed back to your current tune with all those mods.

If the MAF reporting low, you're running lean (more air than the computer can see due to low input), so it's running better when it's cold from the extra enrichment which compensates to some extent.

If you logged fuel pressure from the rail PID, not just a custom gauge, then that is the FRPS and it sounds fine.

Won't disconnecting the mafia throw off the maf tables and make it run even worse? I check and see if I can find someone locally and borrow thier maf.

I did log the fuel pressure from the tuner not from a standalone guage. So that does measure right off of the frps?

I thought I would be running lean as well with the maf reporting low but I have a wb in the car and the a/f stayed pretty constant while it was cutting out, but I have only just been putting around. It kicked up another fualt today. I think it was p1100 Mass Air Flow Sensor Intermittent. So signs are pointing to the maf or the mafia.

Anyone one else have any clues?

 

[707svt]

When mine did this it was the FRPS, mine cut out a few times and died 3 times finally it wouldnt start no more. Then I unpluged the FRPS and it stared up, $100 at for replaced it in 5min.

 

[exdeath]

Won't disconnecting the mafia throw off the maf tables and make it run even worse?

Hence using the stock tune and babying it (eg: keep it in vacuum) while troubleshooting with just the stock unmodified MAF and original table just to eliminate the MAFia as a cause. If it still acts up just putting around on the stock tune, flash back to the current tune, reconnect the MAFia, and swap the MAF out.

Just saw you have 60# injectors too so nevermind about the stock tune. Might be easier to just swap a MAF first and assume it's the MAFia if you still have problems. I've never used a MAFia and have no idea how it interacts with the MAF signal. Is it a dyno tune or just a canned tune? If it's a canned tune that wasn't specially dialed in with the MAFia you may be able to get away with just disconnecting the MAFia.

And yeah, measuring FP off the tuner = straight off the FRPS output.

 

[dsfelton]

Is it a dyno tune or just a canned tune? If it's a canned tune that wasn't specially dialed in with the MAFia you may be able to get away with just disconnecting the MAFia.

It is dyno tuned. I had it tuned at ST Motorsports. The tune is a little on the conservative side but is spot on.

And yeah, measuring FP off the tuner = straight off the FRPS output.

Awesome thanks.

 

[dsfelton]

When mine did this it was the FRPS, mine cut out a few times and died 3 times finally it wouldnt start no more. Then I unpluged the FRPS and it stared up, $100 at for replaced it in 5min.

I haven't had any problems starting the car. Every time it started acting up the maf v and the flow through the maf freezes and when it stops the maf v is totally normal and fluctuates just as it should. I am thinking it is the maf sensor or the mafia.

 

[dsfelton]

Well I replaced my MAF sensor and that wasn't the problem, but the MAFv and MAF counts are good to go. The car is just randomly stalling from time to time. No matter how much gas if give the car when it is stalling the RPM's just continue to drop. When I was data logging it I noticed my Short Term Fuel Trim Banks 1 and 2 are all over the place and I noticed that when it was cutting out that the 02 sensor v was stuck at 0 or .1v. I replaced the 02 sensors and that seemed to make the car run worse. After I replaced the 02 sensors I then noticed that my fuel pressure is at 68psi when it is normally at 38-40psi. I kicked on the check engine light and when I check for fault codes there wasn't any. I haven't had a chance to actually drive the car since I changed the o2 sensors because it don't want to f#$% anything up. AGHHHH!!! I am getting so frustrated I thought I knew what it was and now I don't have a clue.

Anybody have any insight? Blown FRPS maybe.

 

[dsfelton]

Well I disconnected the battery for about an hour. I data logging it the fuel pressure is back to normal and everything seems good so we'll see. I'll take it for a test drive here in a bit and let you guys know.