Car doesn't want accelerate when in boost!

[vernvision]

My car starts bucking and backfiring sending brown smoke out of my external dump pipe. When I hit about 4500rpm at half to WOT and under full boost that is when it starts running like crap, sputering and bucking. It started with a worn out stock engine and since then I have replaced everything. The engine (full blown race engine), turbo, all the sensors, hacked my MAS, SX fpr with a gauge set at 40psi, intercooler and all new pipes, MBR, EGT gauge boost gauge, ECU, A'PEX S-AFC, you name it I have replaced or added it! I have put almost $16,000 into this DSM piece of shit and it doesn't run any better than it did when I replaced the worn out old stock engine. One thing that did happen in the original engine is my O2 sensor wires right at the base of the sensor got fried some how and wrapped all around each other shorting out. I am thinking now it might be the MFI control unit or wire harness. I don't know it really pisses me off since this car should be pulling 11 seconds! I have had the car since it was brand new. Anyone that can help would me most appreciated.

 

[echo]

maybe the ECU got fried?

 

[91TSi FWD]

It could very well be the MFI control unit. Have you used a data logger on it? Never realy heard of this problem before.

 

[vernvision]

I got a new ECU and replaced it, didn't help at all unfortuneately. I haven't had a chance to check it with a Datalonger because its in the mail. I let you know what I come up with.

 

[vernvision]

I ment to say the MFI control relay.

 

[ericismyname]

i would still take the ecu out and smell it, for that nasty sea food smell jut to be safe...couldnt hurt nething to check it.

 

[vernvision]

Thanks but I think i have got the problem sort of figured out. It's not the ECU per-say but it is fuel cut from running to much boost than what the stock ecu can handle so I am going to install a HKS fuel cut defencer. I had to install NGK 5's from 7's and turn the boost down a bit. I'll let you know what I come up with. If anyone has had simular problems with this let me know.

 

[vernvision]

No, I am not going to install that HKS FCD. I was told it sucks. I am going to probably upgrade to a 2g MAS.

 

[9DTSiAWD]

Man i think i am having the same problem. I hooked up a boost gauge and found out that im running 15psi factory and when at idle -15. When i floor it or go half WOT you will hear my turbo spool up then a very loud sounding turbo spooling noise sound seems to come from the driver side, then a sound that is similer to an 18wheelers horn, then its feels like i just hit a 2x4 in the road. my email is [email protected] please email me if you figure it out, im going to re-wire my fuel pump soon so that might help me out. My mods are hacked air car and a boost gauge.

 

[vernvision]

Souds like fuel cut. Why are you running so much boost with a stock set up? Could be fuel pressure but also check for a code 12 air flow sensor. When you hacked your can it's possible that you are leaning it out a bit and then there is a lot of air flow going through there and then if you aren't getting enough fuel pressure, add all those up and you will have fuel cut. Hope this helps.

 

[Happy]

When u guys are talkin fuel cut, i was just wondering if that is what my car is doin too?? And it is possible to have fuel cut on a stockm otor isnt it?? And if u have fuel cut is hard as hell on fuel, and does it give out a lot of black smoke??? Thanks!

 

[vernvision]

Sounds like you are running too rich which will cause gas smell in oil and will break down engine oil rapidly. Check your O2 sensor as it is probably bad. If that not it then check fuel pressure maybe there is to much and on a stock set up FPR solenoid. Fuel cut is from leaning out or too much air on a stock MAS from high boost or race engines with big valves and porting, Big turbo and even huge exhaust can all mess with it. I am going through it now but on my old stock engine I had all kinds of problems from running lean to running rich and most of it is limited to the O2 and the MAS. The car will run lean when the O2 working and rich if its not the only way to get it to run perfect is with some sort of AFC.

 

[Happy]

so ill take out the o2 sensor tonight clean it and then if that makes a difference what should i do after that?? Find out why its carboned up??
And how do i go about finding the fuel problem again check the pressure,and to see if its at the right psi?? What else should i do?? Iam getting a super afc this weekend so that might help me a bit??

 

[vernvision]

No, you need to check the output voltage to see if it is working, its not a spark plug you can't just clean it. It likely that it stopped working a long time ago which has led to your rich condition. Like I said when they are working it is usually on the lean side which generates a lot of heat which makes them wear out. In my old engine I went through one every 10 months because of the fuel additive MTBE. Usually they last around 3 years and then they need to be replaced. They are only about $70 dollars and can make a big difference in gas mileage if they are not working. If you have a datalogger you can read the voltage and match it with the factory specs. The AFC works off the ECU and ECU measures the output voltage from the O2 so you see you need to have the O2 checked and replaced if bad. Only once out of the dozen times did the Check Engine light come on when the O2 went out. Had to be checked manually, so keep that in mind. To check FPR you need to hook it up to a gauge and check it at idle. I don't know what the stock specs are. Try and get yourself a service manual it will tell you step by step howw to check everything out. I run a completely race engine with an adjustable FPR and larger injectors and I am at 4500' above sea level which totally is different at sea level.

 

[Happy]

I see but the only thing to me is that i just put a new o2 sensor in a week ago from the dealer and they aint no 70 bucks try like 180 bucks!! So it can be cleaned cant it? i aint buying one every second week.For the rest i can figure out the pressure and stuff.

 

[Newlogics]

Originally posted by Happy
I see but the only thing to me is that i just put a new o2 sensor in a week ago from the dealer and they aint no 70 bucks try like 180 bucks!! So it can be cleaned cant it? i aint buying one every second week.For the rest i can figure out the pressure and stuff.

They're $50 actually.
Don't believe me ?
Look at www.oxygensensors.com

 

[Happy]

Thats great and dandy if u live in the states.... But idont so its no 50 ,70 whatever its 180 trust me i just put one in from the dealer the other day!! But thanks for ur input!!

 

[vernvision]

Well your getting raped!!! Drive across the border and buy one and mail it yourself. I don't know what else to tell you and when I said 70 bucks it was a ball park. I know you can shop around and find them for less.

 

[jtalon]

my car had that problem once. i had put a new battery in it, and the post were reverse from the old battery. tried to start the car and it would only make a weird humming noise, and every single light in my dash came on though they were not turned on. switched around battery cables and every thing was then fine. 2 days later the car would buck and nearly stall when the boost kicked in. apparently trying to start the car with the switched battery cables had blown the 80amp fuse for the alternator. 2 dollars later the car boosts just fine, other than all the other normal POS problems i seem to have

 

[HiRevRacing]

I may have your answer, i had the same problem, I would hit about 4500 and my car would jut buck and bog out and some more weird shit like that. I was thinking fuel cut. but then just out of couristy I checked my UICP (the flexible part that goes the the TB) and noticed a small crack in it. Then I started to think that I had the same problem when they pipe came loose before. So I decided to wrap some duct tape around it and try to seal the hole, when I went for a cruise I was set. My car runs great now. So I would suggest checking that tubing. Good Luck!!