Author Topic: car nearly stalls after acceleration (Read 6690 times)

fez200 · « **on:** Sep 30, 2006, 08:40AM »

ive had this problem a while now. but i never done anything about it.

The problem is when i back off the accelerator quickly or under acceleration, the car revs drop quite low then almost instantly pick up again by aprox 500rpm. the car seems to idle ok on about 800rpm, but whenever you blip the throttle the revs pickup then drop as usual but drop too low then pickup to a normal idle. the car has stalled on occasions.

i was thinking it maybe leads or distributor cap.

i have recently replaced the plugs with platinum type, replaced alternator and battery. so it sorta rules out electrical.

Craazy · « **Reply #1 on:** Sep 30, 2006, 09:34AM »

what kind of BOV do you have?? this is the common sympton of having an atmospheric bov on a AFM equipped car.

if you have changed to say a turbosmart non plumback valve then change to your standard one to see if the problem stops

trxnut · « **Reply #2 on:** Sep 30, 2006, 11:18PM »

my u12 trx had the same problem as that and it was a faulty AFM (air flow metre)

Ka-Bluey · « **Reply #3 on:** Oct 1, 2006, 10:36AM »

Ive got the same prob on my NA U13. I am bought to believe that it might be a leak in my intake manifold gasket. But need to buy carby cleaner to test it, and that stuff aint cheap!!

Craazy · « **Reply #4 on:** Oct 1, 2006, 06:10PM »

it maybe a leak but with those symptoms it is unlikely coz with a leak the idle would be utter crap and wouldnt return to a constant idle.

carby cleaner IS cheap...... sounds like your a tight ass

it is partly to do with the afm but replacing it when its not broke aint gonna fix it, i could say with certainty that its the BOV

dave-trx · « **Reply #5 on:** Oct 2, 2006, 09:41AM »

I had a problem with my TRX similar to this, I know it uses a different engine but what it ended up being the ECM temperature sensor. The harness on the loom that plugs onto the the temp sensor. Nissan wanted a shit load for the loom which I didn't buy. I ended up getting a new plug for $15 bucks from my local auto electrician and fitting it my self.

To diagnose when the engine is running like shit wriggle the temp sensor plug and if the engine picks up and runs perfect your laughing.

fez200 · « **Reply #6 on:** Oct 3, 2006, 11:57AM »

on closer inspection i found a wire had been cut. it looks like its a sensor goin to the exhast.

its a white coloured wireand its at the front of the car in between the radiator fans and the bottom of the motor (sr20det)

i cant see anywhere for this wire to join to? does anyone know where this sensor leads to.

maybe this sensor could be giving me the trouble.

Budgie · « **Reply #7 on:** Oct 3, 2006, 12:03PM »

O2 sensor?

Is your O2 sensor connected? Should be screwed into the dump pipe with some wires coming out of the end of it.

phreeky · « **Reply #8 on:** Oct 3, 2006, 12:18PM »

definately o2 sensor, which is as budgie stated is screwed/bolted into the bung on the dump pipe. if the wire is dangling and shorting it may cause massive over/under fueling (i'm not sure which way around it works) i suppose.

it's not all that uncommon for that wire to become quite messed up. it often gets treated badly when the engine gets pulled out, and it sits right next to the exhaust.

Counterpunch · « **Reply #9 on:** Oct 4, 2006, 10:56AM »

From my personal experience I'm going to have to agree with Craazy. I had the exact symptoms including the stalling which can be quite dangerous. After changing the atmosphere BOV to a the stock plumback BOV the problem went away. Are you using an atmosphere or plumback BOV?

fez200 · « **Reply #10 on:** Oct 4, 2006, 11:33AM »

im using the apexi twin chamber BOV. not sure what type that is. i reckon its a heap of shit...

what would you recommend to be the best BOV to fit as i dont have my original one. i dont want anything too loud.

i cant find where the wire goes to from that sensor as there are no spare wires hanging around

Craazy · « **Reply #11 on:** Oct 4, 2006, 12:14PM »

i have used a gfb stealth fx and found that to be quite good and ou can adjust it to any amount of noise you want as it is plumback and atmo. from what i have seen of the U13's you should be able to get a skyline one to do a straight swap, thats what i have.
otherwise there is the turbosmart range that have a few good products, you would have to have a look at the plumback and atmo range they have to find the one that suits your needs, they have heaps to choose from

i havent heard to many good things bout the apexi bov's, i havent seen too many people using them though.

phreeky · « **Reply #12 on:** Oct 4, 2006, 05:55PM »

hmmm was under the assumption u were still running the stock bov. if you've got atmo, ditch or crank it so it needs bucket loads of pressure!

i had an apexi on for a few weeks, ditched it since, but unless i turned the pressure right up it would just run mega rich on changes and almost stall if i gave it any throttle at idle. just not a good thing on MAF setups.

fez200 · « **Reply #13 on:** Oct 5, 2006, 04:18PM »

yeah the old apexi BOV never goes pssssht (not that it bothers me), even if you are in neutral and rev it up you only get a slightly muffled ffffccchhh kinda sound.

ive also noticed that i get a flutter noise in the airbox when you back off on slight throttle is this ok?
i always thought that the BOV was making this noise, until i was doing some tuning and was manually revving the car through the throttle cable, i noticed the flutter coming from the airbox.

i think i need to ditch the BOV and get something decent.

phreeky · « **Reply #14 on:** Oct 5, 2006, 04:52PM »

yeah, a recirculating one

i run on bov, but only the stock turbo so i'm not all that concerned about it. been like that for about a year, i replaced the gasket that is used to bolt the bov on with a piece of sheet rubber cut to size, so you can't tell that it's blocked by looking.

Craazy · « **Reply #15 on:** Oct 5, 2006, 07:14PM »

the flutter is NOT good, it means that your BOV is not flowing enough and you are getting back pressure on your turbo and it is pushing air back out your AFM...... this is why your car will be stalling

get a large valve diametre bov. and have it adjusted properly, you will knwo when it is coz you wont get the flutter

bungs · « **Reply #16 on:** Oct 5, 2006, 07:23PM »

Quote from: Craazy on Oct 5, 2006, 07:14PM

the flutter is NOT good, it means that your BOV is not flowing enough and you are getting back pressure on your turbo and it is pushing air back out your AFM...... this is why your car will be stalling

Not really.. I don't have a bov, it flutters like mad and I have perfect idle and no stalling between gearshifts.

My guess is there's a leak somewhere after the maf, the bov being the first place i'd look.

Craazy · « **Reply #17 on:** Oct 5, 2006, 07:28PM »

yes but you have a apexi safc helping to stop the stalling, its part of the safc programming

and yes the fact you dont have a bov will help the situo slightly as you are not losing metred air and also causing the flooding of the engine.
so your fluttering is definately not good, the amount of compressor surge would be terrible

bungs · « **Reply #18 on:** Oct 5, 2006, 07:47PM »

Debatable, there is nothing to suggest that running a bov will make a turbo last longer.

edit: I don't have an safc anymore, I'm running purely on a custom chip i made myself

phreeky · « **Reply #19 on:** Oct 5, 2006, 10:36PM »

i'd like to know how an safc could compensate for over-metering of air on compressor surge

the air rushing back through the afm does make it meter it again, so it will overfuel a little, but nothing like an atmo bov. i've had no bov for ages, no dramas at all, never stalls (or even seems like it's going to). just make sure you haven't got a leak in the return line or anything, or that small line on the intake pipe that connects to the stock boost solenoid.

Counterpunch · « **Reply #20 on:** Oct 6, 2006, 04:24PM »

Quote from: Craazy on Oct 5, 2006, 07:14PM

the flutter is NOT good, it means that your BOV is not flowing enough and you are getting back pressure on your turbo and it is pushing air back out your AFM...... this is why your car will be stalling

get a large valve diametre bov. and have it adjusted properly, you will knwo when it is coz you wont get the flutter

If fluttering is not good, then how come a lot of stock cars imported from Japan come standard with that noise? I mean my car has always fluttered since I owned it with standard and aftermarket turbo. My understanding was that the fluttering was cuased by gradually releasing the air back into the system as opposed to one massive release of air, which is what creates the PSSSTT sound.

As for pushing air back into the AFM, is that possible as the air has to get past the turbo first? For it to due that the turbo needs to be running in the opposite direction.

phreeky · « **Reply #21 on:** Oct 6, 2006, 05:11PM »

yeah it does but only ever so slightly, that "flutter" noise is the reversion of air passing back through the blades getting chopped up nicely i suppose

that's what people claim does damage to the turbo when not running a bov, it very suddenly has a hell of a lot of force trying to make it spin the opposite way, or at least stop spinning altogether.

omad · « **Reply #22 on:** Oct 6, 2006, 06:22PM »

If it was a leak after the AFM, it'd idle shit as well and it would dip weather you were giving it stick or not.

All worth checking though... but BOV would likely be the first place to start. Other than that, check your air filter and intake for blockage. I doubt it'd be leads or plugs if it's not missing or giving you trouble up top.

Compresser surge is a controversial topic, one which was debated on the VR4 forums just recently. Some run BOV's, some don't. Some claim it does damage and others say it's fine. It does slow you down between gears, though. Unless you're blipping through them REALLY fast. As the surge makes the turbo spin down quickly, it needs more time to spool up again. It does sound damn hot though.

Craazy · « **Reply #23 on:** Oct 6, 2006, 07:53PM »

an safc doesnt compensate for the compressor surge or more to it "cavitation", it compensates for the sudden loss of metred air that is meant to be in the system but isnt as its been released from the atmo bov. i am not 100% how it does it but most aftermarket ecu or air fuel computer can do it as it just leans out the mixtures on throttle closing or something like that.

the cavitation in resultant of the throttle snapping shut then the pressurized has nowhere to go. so goes back the way it came. and since the engine is slowing down it physically cant be forcing the air through the turbo when it is pushing back on the turbine, so something has to give and so the turbo effectively stops and starts as both ends of the shaft is trying to go in opposite directions.

it may sound "hot" but it is definately "not". put it this way, if you had to car wheels on a single long shaft both spinning in the same direction then suddenly one was clamped up to try and stop it while the other is still being forced to spin. at some point the shaft is going to give. this is the same thing that is happening with your turbos as your getting the "flutter". so how long do you think the shaft would last in the situation.

no matter how much you think it is ok, the evidence is there that it is bad for your turbo. and it is simple physics.....

fez: have you gone about to adjust your bov?? or not bothered as your not a fan of it..... either way i would say fit you a turbosmart model that is plumback, or a gfb one, it will cure the problem. having been around alot of car that do this i also have to say that it will need to be adjusted correctly otherwise it wont open fully and close in the right amount of time. its a pain to get right but worth it.

have fun with it

phreeky · « **Reply #24 on:** Oct 6, 2006, 09:42PM »

i agree it probably isn't great for the turbo, but hell when a stock replacement is $150-$200 imo it's worth the risk. at present i cbf getting a new plumback, and i gain 1psi or so from blocking the stock bov, so to be it's a worth while risk. been like that for around a year, maybe more now. btw the turbo doesn't instantly stock spinning or anything, it's a gradual thing still, the clamping of a wheel analogy is a bit extreme.

as for the ecu/safc stuff, your stock ecu cuts fuel on deceleration as it is. aren't the safcs just voltage benders for the afm signal anyway? i'm pretty sure the original ones were.

fez200 · « **Reply #25 on:** Oct 7, 2006, 12:56PM »

i have no idea how to adjust this apexi one. i really dont think it works properly.

i am getting the manual trans conversion done on wednesday. so i will get a new BOV put in then.
my mechanic told me to get rid of the bov anyway. he reckons they arent all there cracked up to be.

Budgie · « **Reply #26 on:** Oct 7, 2006, 09:14PM »

Hugh, if all that is true why does the CA18DET not run a stock BOV and many CA engine/turbo combos run well into the 150,000km + range without issues?

I understand the idea behind what occurs, I guess a small turbo like a T25 thats only pushing say... 9psi only has 9psi of air thats coming back at it when the throttle is snapped shut.

Craazy · « **Reply #27 on:** Oct 8, 2006, 11:15AM »

what you will actually find budgie is that cars without a stock bov have a small valve on the plenum that is also plumbed through the idle control valve, this releases some of the pressure

omad · « **Reply #28 on:** Oct 9, 2006, 02:11AM »

I think you might find if you asked around or dug a little deeper, that there are a lot of people running their turbo cars without a BOV and a large amound of hi-po drags cars that don't as well.

I personally wouldn't do it, but that's just me. Still doesn't change the fact that there are guys that have been running without a BOV for 3+ years on the same turbo. Or others that have street driven cars on 18+ PSI with no BOV for about a year with no problems (they still have the car and same turbo).

Craazy · « **Reply #29 on:** Oct 9, 2006, 07:48PM »

i am more than aware that guys do it, i really dont care if they do. its everyones choice if they want to run a car with a bov or without one.

what would be better for your car at the end of the day, i dont have to say which one i would choose

fez200 · « **Reply #30 on:** Oct 10, 2006, 09:33AM »

well ive changed the BOV to a turbosmart type 3.

its working better than the apexi, i actually now get the old psssh sound...haha

however im still getting the flutter in the airbox at low throttle back off...
is there anything i can do apart from going back to a plumb back type BOV.

Craazy · « **Reply #31 on:** Oct 10, 2006, 06:39PM »

loosen off the spring on the valve as it is not staying open long enough

omad · « **Reply #32 on:** Oct 10, 2006, 07:09PM »

Quote from: fez200 on Oct 10, 2006, 09:33AM

well ive changed the BOV to a turbosmart type 3.

its working better than the apexi, i actually now get the old psssh sound...haha

however im still getting the flutter in the airbox at low throttle back off...
is there anything i can do apart from going back to a plumb back type BOV.

It should be fine. It's doing that because the BOV is designed to hold more boost than you're putting into it. If you loosen it off too much it will leak at idle etc and give you the same trouble you had to begin with. You can try adjusting it down to a happy medium, but if it's doing it's thing at high rpm it'll be just fine.

phreeky · « **Reply #33 on:** Oct 10, 2006, 07:15PM »

agreed, you'll get some slight "flutter" noise (not the loud "angry pigeon" noise, haha excuse the explainations) even with the stock recirc bov, i always did. just on very low boost levels.

fez200 · « **Reply #34 on:** Oct 10, 2006, 08:06PM »

ive noticed that the car isnt stalling anymore and i think ive adjusted it just right.

still get the flutter but at high RPM you get the BOV working like it should... thanks guys..