stumble at high boost

[jo_91gs]

I'll keep it as short as possible so here's the problem. Car runs fine with 0 boost. Also runs fine boosting through the low gears. Its when i boost in like 3rd to 5th (over around 4000 rpm) that the car starts stumbling pretty bad. I can boost on 3rd, but it has to be a slow steady increase in boost (for example if i floor it and boost reaches 14lbs, it will start stumbling). It goes the same for 4th and 5th. The car is 91 talon TSI FWD 5 spd and is stock. Anyone that has had this similar problem and got to the bottom please hit me with some advice. I know for sure that the gas tank is not as pretty as i want since the car as parked for like 2 years before i took it off a mechanics hands. I've removed the tank to clean and removed alot of junk (??rust and old gas??) but not all of it. Do you think junk is getting to the pump and interfering with the acceleration.

 

[razrman8]

First things first, boost leak test.

 

[ALBurgundy]

what happens when you turn the boost down?

 

[4g63jojo]

i have a 91 tsi awd and i had the exact same problem you have , my car sat for a long time before i got it and did the rebuild, after we got it running i experienced the same EXACT thing your saying, so we dropped the tank out and drained it and cleaned it, put it back and it helped a little, so we figured we were on the right track, then we simply changed the fuel filter and held boost all the way to redline.

 

[jo_91gs]

I will definately do the leak test to eliminate the possibility, and i dont have a boost controller. Will get back with the results tomorow. Until then, hit me up with more advice..thanks.

 

[1TireFireTSi]

i have a 91 tsi awd and i had the exact same problem you have , my car sat for a long time before i got it and did the rebuild, after we got it running i experienced the same EXACT thing your saying, so we dropped the tank out and drained it and cleaned it, put it back and it helped a little, so we figured we were on the right track, then we simply changed the fuel filter and held boost all the way to redline.

My car was acting similarly on the dyno, until we through a new fuel filter and plugs in it. Preventive maintenance goes a long way and it never hurts to throw some cheap, easy parts at it.

 

[jo_91gs]

This is for 4g63jojo, how did you clean your tank and how well did you clean it. I have been wondering how hard it would be to find a replacement tank and fuel pump assembly to be on the safe side. I would be alot more comfortable just replacing the whole thing because it was pretty bad when i actually cleaned it. Or is cleaning it out enough. Thanks..

 

[jo_91gs]

im back and before i could even think about doing a boost leak or begin looking for a tank and fuel pump assembly, something worse happens.....TIMING JUMPS. Yeah, so i go over to a friends house like half an hour from home, its about time to leave, crank the car....turns on.....metal hitting metal sound.....TIMING JUMPED FOR SURE....!!
I get the car home and will be taking apart timing components etc...see how it goes wish me luck.

OK, i got in there and re-set the tiiming, and turned it on. YYEESSSS, from what it sounded and felt like the head was in good shape. Just goes to show the strength of the mighty 4g63. So i take the car for a spin and notice that the (supposedly) boost leak is way worse. Now the car will not boost at all without what feels like a boost leak. So the car is running nice and smooth (besides the "boost leak") until just a little while ago. Yep, i go to turn on the car when suddenly....very rough idle, and sounds bad...timing jumped again. My opinion, gotta go get that component kit. Ive already been looking at some and making sure i get the right parts according to quality and reputation.

 

[jo_91gs]

i went to rockauto.com and ordered the GATES timing belt kit with water pump, and a DELCO auto tensioner. i then removed my cylinder head and replaced two intake valves that were just slightly bent enough to see a little bit of light through the cylinder (bottom) part of the head. i got zero compression on that cylinder when i did the test. anyways, i picked up a head and intake gasket, and some antifreeze at the autozone., then torqued everything down.., installed the timing belt.., thats it. oil and water level were good so i cranked it up and everythings good. i also found the bolts loose on the intercooler hose (turbo side), so that was the "boost leak". the car has been running fine for about 5 days now and am confident it will keep running strong for a long time.