Car stutters at low rpm... with some backfiring.

[Flowcus]

Ok I bought this car not that long ago... and it had a lot of problems. Basically the car would make 5-6psi of boost, and then lose it all immediately afterwards. We pulled the turbo and manifold... the exhaust housing on the turbo was cracked all the way through and down the side of it. So we replaced that, the wastegate, and crushed the BoV.

After that the car was running great, making full boost, and pulled like a mofo. Well we didnt regulate the boost, and I hit fuel cut off a couple times while test driving it. We put an MBC on it set the boost to 14-15psi and I took off for home.

Get the car home and let it sit for a while... go to start it up and run to the store quick and the car is studdering at around 800-1000rpm at idle. Basically it sounds like a big V8 with a big ass cam in it, and it slightly pops and backfires a little bit while doing this. So I start driving the car and until it hits boost the car still studders and shudders. Even while cruising in vacuum at 3000rpm the car does this. But when I mash it and hit boost the car pulls like there is no tomorrow. Also it seems only in 1st gear at WOT the car will bog around 5krpm then start pulling again, and this isn't all the time.... almost like its hitting fuel cut-off but not quite as bad.

I searched the boards, but there seems to be way to many reasons to why the car is doing this, and not all of the symptoms are the same. My only guess would be spark plugs maybe fouled out when I hit fuel cut-off a couple times. Anyone have any suggestions to help? There is no CEL on, I am running 92 octane pump gas in it.


Mods are as follows.

Buschur UPIC
Walboro 255 fuel pump
Turbo back 2.5" exhaust in some crappy nock-off can
K&N air filter on hacked air box
MBC set at 14psi
2g ported manifold
Ported and Polished intake manifold
Balance shaft eliminator kit

 

[15psi88]

That 255 is probably overrunning your fpr making it super rich, especially at idle. I'd start there.

 

[Flowcus]

That 255 is probably overrunning your fpr making it super rich, especially at idle. I'd start there.

Well actually before we replaced the exhaust housing and what not the car ran great. Minus the fact it was making no boost, and pulling slower then a honda... The ISC was bad and I replaced that right away... car would idle around 1k rpm with no problems. Would cruise with no boost with no problems as well.

Then after we replaced the housing, crushed the BoV, and replaced the wastegate it ran great as well. As soon as I took the car out did a couple pulls and hit the fuel-cutoff. The car started running like shit.... I noticed the oh so reliable (joke for people that cant recognize sarcasm) boost gauge shows it at idle barely in vacuum... so I am going to do a vacuum leak test.

The car is running a bit on the rich side, but thats because the BoV is venting to atmosphere. The only thing we did different after I hit the fuel-cutoff was add the MBC and turn the boost down to 15psi... thats why I don't understand whats up with it.

 

[jking29]

You can't run a 1g bov without recirculating it. It is not a normal blow off valve in that it is open under vacuum. I also suspect that you have a major boost leak somewhere.

 

[Empir3 X]

^ ^ +1 on the 1g bov venting. Bad idea there and definitely check your plugs (use NGK)
The fuel pump doesn't have anything to do with it. If anything it will just overload the fpr, but i have been running a 255 with no other fuel upgrade for awhile with no problem.

So.... Do plugs, a boost leak check (you should get an after market boost gauge) the stock one just is a vague reading from the ecu.... and also recirc. your bov. I betcha that will do ya great!!

 

[ekanddsm]

Your trying to drive the car off boost with the bov vented?

That bov is open the entire time off boost creating a big air leak past the mas.

Hook it back up and drive it, you may solve all your problems right there.

 

[Flowcus]

I hooked up the recirc on the BoV... nothing changed at all. In fact after hooking it up driving a 20mile round trip to work and back it seemed as though the car was in worse shape.

Under boost its still fine, but out of boost it studders, pops, and backfires a lot now. Whenever I shift the car will release a loud backfire, and when im cruising out of boost it backfires and pops a lot.

I found one little vacuum leak that I fixed, and added the recirc to the BoV. Neither worked... anyone else have any ideas? It seems to be getting worse every time I fire the car up.

 

[Zenja]

The V8 sound is from one cylinder not running at all. I've had the same thing happen when one of my injector plugs wasn't making contact. Check the usual like plugs, wires, and compression. You maybe have damaged the engine or plugs while running without regulated boost.

Other than that, it seems like it might be running way off tune in closed-loop. Datalog the car to see stuff like the fuel trims, and see if all the readings match up to what they should be while driving. Also, someone I know had similar symptoms and it turns out that it was his ECU. It seems kind of unlikely in this case though.