AFM gone? Stalling/spluttering after releasing revs

[slystiguy]

After a bit of research I think my AFM may be poked. Car starts and runs fine but has a miss/backfire and when I give her some revs in neutral say above 3k it will rev fine but when dropping to idle it will drop down really low and sometimes stall.

Any other ideas or things I should look into?

Here is a video of what happens- Car is a 91 rs legacy which I\'ve just put a twisted setup on with front mount.

[Marky]

Leaky bov, or just not enough preload on it

To test just remove it and block the hole

[slystiguy]

Hmmm to be honest I\'ve only just set this stuff up and I don\'t think the BOV is even working. I get massive compressor surge CHU CHU CHU CHU sorta thing sounds kinda cool haha but I know it\'s not good long term. I\'m not driving it daily or anything haven\'t even done 20kms on the setup yet

I will try blocking it off see what happens

[slystiguy]

Bump video added. And this is with the BOV blocked off completely.

[Marky]

Youre on the right track, its either an air leak, a bad idle stepper thingymahoosit or a sad afm

The way it tries to catch the idle makes me look more at the air leak option?

[slystiguy]

So what would my method of elimination be for leaks? Soapy water on all the intercooler joins ? I think I\'ll start with a good clean of the iacv (its a very old car after all) and some upper engine cleaner. Then if no improvement I\'ll triple check leaks.

If no luck from there I look into a temp swap of AFM with someone on a running car

[Rosssub]

 Marky said:

a bad idle stepper thingymahoosit.

+1. Your IACV (Idle Air Control Valve), is sticking/gunked up or semi seized. Definitely start with giving that a good clean. Or replace it.

[Rosssub]

The AFM, doesn\'t effect Idle. An AFM fault would be more noticeable at Higher Revs/Higher Air Flow/Higher AFM Resistance/Altered Fuelling changing AFR/Loss of Power.

The TPS tells the ECU that the Throttle has closed, so the ECU opens the IACV to control Idle Revs/Idle Air Flow. Yours IACV isn\'t opening fast enough, or can\'t open enough.

A Vac Leak would more likely cause a Constant Low Idle or an Idle that Fluctuates/Hunts much lower than normal.

If you clean the IACV out, then get a Lower than normal, but stable Idle. You may also have a small vac leak somewhere.

With the new FMIC install, it would be worth doing a Boost Leak Test. By blocking your Intake, Post AFM (can or jar), then feeding 14psi in with an Air Compressor. Any Air Leaks will hiss and be obvious.

[slystiguy]

Darn I don\'t have an air compressor haha but I may be able to borrow one. I\'ll try get something sorted in the next couple of days and will post back the results.

Thanks for the information and help

Cheers

[Rosssub]

Sweet, the soapy water test does work just not as obvious. You can also spray Engine Start around possible leaks, if the Idle rises then it\'s sucking some in.

Re the Compressor Surge, you need to lower you EBC\'s Gain. With the Twisted/FMIC Boost is coming on too strong.

[slystiguy]

Hmmmmm I just had a thought... What if the reason my BOV isn\'t working and the potential vacuum leak are related. Is it a possibility the system is venting through the leak and the bov doesn\'t get enough pressure to actually work? I\'m interested in finding out now haha. I really need to do the compressor test I think it\'s the only way to be 100% sure of leaks. Spit balling and it\'s late haha.

In regards to the ebc I\'ve set it up on pretty much 0 gain 10 or so threshold and sensitivity right up but it just can\'t hold it at all. Instantly hits 15-16 psi and cuts. Tried playing around with it a few different ways but it\'s just getting to much boost and can\'t control it.

[Rosssub]

 slystiguy said:

Hmmmmm I just had a thought... What if the reason my BOV isn\'t working and the potential vacuum leak are related. Is it a possibility the system is venting through the leak and the bov doesn\'t get enough pressure to actually work? I\'m interested in finding out now haha. I really need to do the compressor test I think it\'s the only way to be 100% sure of leaks

The BOV is Vac operated, via the BOV Vac Hose straight from Mani. It gets boost pressure to hold it shut, when you lift off the gas the engine goes into Vac, so the BOV opens.

[slystiguy]

This is how mine is setup. Runs from manifold to bov and bov to intercooler. External is plumbed up the way the gfb booklet said to plumb.

[Rosssub]

 slystiguy said:

In regards to the ebc I\'ve set it up on pretty much 0 gain 10 or so threshold and sensitivity right up but it just can\'t hold it at all. Instantly hits 15-16 psi and cuts. Tried playing around with it a few different ways but it\'s just getting to much boost and can\'t control it.

Waste Gate too small? Waste Gate Spring?

Hoses look correct, the BOV Vac hose isn\'t kinked at the BOV end is it?

[slystiguy]

I think the spring is a 1bar or similar and these ecus cut at 1bar so it\'s a bit of a mismatch. This is the first external I\'ve owned so I don\'t really know the ins an outs yet. Could be something else I\'ve done wrong haha.

No kinks in line it\'s got about 30cm extra which I need to trim. I had actually taken if off completely in that video and plugged with a std bov put in the wrong way around if that makes sense

[Rosssub]

A 44mm, Tial Spring Chart:

http://www.tialmedia.com/documents/w3_tial_44_sp.pdf

Found here:

http://www.iwsti.com/forums/2-5-liter-litre-factory-motor/220134-external-wastegate-spring-2.html

[Rosssub]

 slystiguy said:

I think the spring is a 1bar or similar and these ecus cut at 1bar so it\'s a bit of a mismatch. This is the first external I\'ve owned so I don\'t really know the ins an outs yet. Could be something else I\'ve done wrong haha.

No kinks in line it\'s got about 30cm extra which I need to trim. I had actually taken if off completely in that video and plugged with a std bov put in the wrong way around if that makes sense

If you do have a 1bar (14.5ish psi) Spring in your WG, the EBC wont be doing anything. (EBC can\'t adjust below WGSP)

So your running WG Spring Pressure, hence the Compressor Surge and un-effective EBC Adjustment.

If your planning to run Boost at 14-15psi, I "think" you want a 7lb-9lb Spring? Then your EBC takes control over the Waste Gate Spring. (Bleeding until Target Boost is reached, then Pulsing to stabilise Constant Boost)

[Marky]

 Rosssub said:

The AFM, doesn\'t effect Idle. An AFM fault would be more noticeable at Higher Revs/Higher Air Flow/Higher AFM Resistance/Altered Fuelling changing AFR/Loss of Power.

Yes it does

Dud afm can often show up as a terrible idle but seem fine to drive with

[slystiguy]

I\'m starting to understand how it works more and more. Still fuzzy. I get the concept but just not the troubleshooting. I know the spring is probably running higher psi spring as the wastegate is a larger one. I personally haven\'t had a bad AFM to date but I hear the stories and hence I never fully rule it out. I have a friend with a green afm he\'s going to let me borrow for a test if the cleaning IACV doesn\'t work.

I will post results tomorrow!

So in my own crude words this is my understanding of what a waste gate does

Basically it\'s a fail safe to stop the car running stupid amounts of boost. The turbo/exhaust setup may be capable of running say 30psi but the engine can only handle a portion of that so rather than having all that pressure build up it vents it using a wastegate which is controlled by a spring (with different spring ratings) to allow the excess exhaust pressure out the exhaust pipe(or screamer if you a boy racer) and thus saving the engine? What I don\'t really understand is how a boost controller works in relation to the wastegate opening...

I also don\'t really understand how the pill in the compressor lines works

Can someone put me on the right track

[Guest]

Google garrett 101 and read the first one.

[Marky]

http://www.clubsub.org.nz/forum/index.php/topic,35842.0.html

Youre on the right track at least

The pills are like... bottlenecks, they reduce air flow to manageable levels for solenoids to bleed off, or slow down how fast pressure gets to a point

[Rosssub]

 Marky']

[quote name='Rosssub said:

The AFM, doesn\'t effect Idle. An AFM fault would be more noticeable at Higher Revs/Higher Air Flow/Higher AFM Resistance/Altered Fuelling changing AFR/Loss of Power.

/quote]

Yes it does

Dud afm can often show up as a terrible idle but seem fine to drive with

Cheers Marky. I\'ve been assuming a (non afm effected) base fuelling rate for Idle. Going to go and hide in the corner now. ;D

[slystiguy]

Took the iacv apart looked almost new and didn\'t have anything to point out it wasn\'t working. It moved freely ect

But I\'m now getting CEL - code 45

45 - Pressure sensor and pressure exchange solenoid valve

Which is boost solenoid? Possibly not working because I\'m running the EBC. I just blocked off a hose that was going to it will reconnect and test.

Actually another thought. Do I need to plug up the unused boost solenoid hoses after installing the EBC? Could that be source of vacuum leak?

[Marky]

Only if they still go to manifold or intake pipe

[slystiguy]

Had already blocked them off apparently haha. Put it back to how it was and code 45 gone. Ummmmm still got the problem took it for a 20km drive and it doesn\'t stall anymore which is good and it does seem to be getting better. Might try the engine cleaner and some injector cleaner see if that helps. It has been sitting a few months with near empty fuel so I chucked in half a tank today and took for a blast over the motorway which was fun. I really wish it wasn\'t hitting boost cut haha it\'s so disappointing to not be able to boost through the gears. I should really get it tuned.

Another thought is I currently don\'t run an o2 sensor in the extractors. Hijacker pointed this out and it could be potentially giving me issues so I will probably put that in when the cars cooled down. I don\'t think it\'s related to my fault as I never ran one on my old car and never had issues like this but I don\'t really know much about them. Hijacker had a good look over the car and thought it might be a water lock? I have just replaced the radiator and fixing water leaks.