Z4 ecu overboost

[That Guy]

Question time.

 

So I am still having this fuel cut/boost issue. I have rerouted the vacuum lines to eliminate the b.c.s and run straight off wastegate pressure, this worked fine and gave me 7lbs, so that's sweet. I then plumbed in an m.b.c while still bypassing the factory boost controller, no matter what the m.b.c is set at I am still fuel cutting.

 

This lead me to have a look at the ECU. I have in place a Z4 which I am unsure if this is factory or a common upgrade. I am thinking that I must be maxing out injectors, coils and maybe fuel pump. The bit I can't get my head around is that with an m.b.c plumbed in, should I be able to lower boost levels below the 15lb that I'm seeing?

 

As far as mods go that would aid a boost rise, I have an f.m.i.c, open air intake, and a terrible slightly over 2-inch catless exhaust. I also have no provision for an o2 sensor post turbo, so I imagine that aint helping a heap either.

 

Any thoughts? I'm sure this would make perfect sense to some of you guys..

 

[BC5RA]

What is the car and what is the Turbo? 

[That Guy]

1996 V2 gc8 wrx running an ej20g and td05

[slystiguy]

you sure you plumbed it up right? Sounds like it's hitting the fuel/boost cut of 14.5 psi

 

Should be running 12 on that ecu I think so could possibly just chuck it back to stock setup. Not a lot of room to tweak those early ecus

[BC5RA]

Thats a suitable ECU if not the OEM one.

 

Cut on a Z4 is 15.6psi, you should be getting nearly 13 psi standard.

 

You can try another way to control boost: Return everything to stock and locate the hose going from the bottom of the boost control solenoid to the post AFM resonator that is often replaced with the "Coffee cup" mod.

 

This hose has a restriction inline, so remove the hose in total, and store for later use if needed. Now buy a length of hose to replace it and plumb your boost T somewhere in the middle, the idea is to make the restriction adjustable with the T, wind it fully back and you will get wastegate pressure (9 psi) then adjust in increments to the desired boost level.

 

[That Guy]

56 minutes ago, slystiguy said:

you sure you plumbed it up right? Sounds like it's hitting the fuel/boost cut of 14.5 psi

 

Should be running 12 on that ecu I think so could possibly just chuck it back to stock setup. Not a lot of room to tweak those early ecus

 

 

Yup yup, Definitely plumbed in correctly. Hence the head scratching!

47 minutes ago, BC5RA said:

Thats a suitable ECU if not the OEM one.

 

Cut on a Z4 is 15.6psi, you should be getting nearly 13 psi standard.

 

You can try another way to control boost: Return everything to stock and locate the hose going from the bottom of the boost control solenoid to the post AFM resonator that is often replaced with the "Coffee cup" mod.

 

This hose has a restriction inline, so remove the hose in total, and store for later use if needed. Now buy a length of hose to replace it and plumb your boost T somewhere in the middle, the idea is to make the restriction adjustable with the T, wind it fully back and you will get wastegate pressure (9 psi) then adjust in increments to the desired boost level.

 

 

2

 

Righto, this sounds to make sense. I will attempt when I next have a chance. Cheers!

[THUNDA]

4 hours ago, That Guy said:

 

This lead me to have a look at the ECU. I have in place a Z4 which I am unsure if this is factory or a common upgrade. I am thinking that I must be maxing out injectors, coils and maybe fuel pump.

 

 

 

Ive found the factory EBC has always been very reliable for me in the past, untill i got the BC5 that i own now and it was causing a similar issue

 

Boostgauge was reading 14psi with no MBC just the factory ebc

 

but with foot down it would suddenly fully cut as soon as turbo spooled up fully and gave me a pressure duty solenoid CEL

 

I was skeptical but i put a 2nd hand one in and it solve that problem which is the first time I can say the factory ebc has failed me, and ive F***ed with at least 10 others in the most amateur ways possible without having factory ebc failure in the past. 

 

After a bit of research into my own ECU (which is a W6 out of a 93 wrx RA) I noticed the Z4 was used alot when running a TD05 and seemed like a very oftenly mentioned suitable ecu for your engine combined with your td05

 

After doing the Fuel pump wiring mod in my car I cant say it made any difference, have never had issues with factory fuel pumps in these cars and the same goes with the fuel pump wiring, although many people have had troubles when upping the boost etc, if your fuel pump is maxing out on a resonably standard boost with reasonable standard parts I would be surprised

 

Failing coil symptoms arnt boost cut - if youve got 4 seperate coils and one fails a symptom is misfiring under load then goes to complete misfire

these are easy to check when you do get a misfire - just unplug each one untill the one you unplug doesnt change running engine condition then thats the bad one

 

Dont think maxed out injectors boost cut either, with just over or under fuel. if youve got grey tops and a td05 and a z4 then thats what its ment to have to run right 

[THUNDA]

If your car is boost cutting (sudden complete cut out for 1 second on boost)

 

Then id say you are likely to be over boosting and your gauge  will be inaccurate or your gauge will be reading vac of a bad vac line? 

 

Best to go straight off manifold, I usually unbolt a square shaped bolt on the left/centre had side of the manifold, then drill a 3.2mm hole in the bolt and put the 3.5mm boost line into it (hose is plastic and bigger so goes in tight as F***)

MAPs are accurate as F*** imo and it will definately know whats up if boost goes too high it will signal the ecu instantly

[slystiguy]

I thought the 3rd port is just a bleed valve? I don't think you can adjust the rate it bleeds at to control boost lol... . The boost control always goes between the turbo nipple and wastegate nipple. ? You're adjusting the rate at which the wastegate opens and closes, that is what controls the boost and allows it to build higher. Adding a restriction to the bleed nipple on boost control solenoid will do nothing? Me and a bunch of others don't even plumb this back in... (you must block the nipple post air intake if you are doing this) . Tbh it's been yonks since I used a factory solenoid 

[BC5RA]

33 minutes ago, slystiguy said:

I thought the 3rd port is just a bleed valve? I don't think you can adjust the rate it bleeds at to control boost lol... . The boost control always goes between the turbo nipple and wastegate nipple. ? You're adjusting the rate at which the wastegate opens and closes, that is what controls the boost and allows it to build higher. Adding a restriction to the bleed nipple on boost control solenoid will do nothing? Me and a bunch of others don't even plumb this back in... (you must block the nipple post air intake if you are doing this) . Tbh it's been yonks since I used a factory solenoid 

 

Adding an adjustable restriction and doing away with the inline restriction does control your psi, but not anything more than that.

 

[That Guy]

Alright BC5RA, your knowledge has been of valuable use!

I plumbed the m.b.c in between the bottom port of the stock solenoid and the post airflow meter vacuum port hole thingy. This has helped a great deal and I now have a constant 9lb. Adjustment to the m.b.c while plumbed in here does not change boost pressure at all, I have tried adjusting from all to nothing and have seen a constant 9lb. On closer inspection, I have discovered that there was, in fact, no restrictor pill present in the vacuum line. I found this a bit buzzy as I was under the impression that no restrictor pill would drop boost levels, not increase them. Anyway, that seems to be the issue so I will pop down to the local Subaru parts place tomorrow and order in a new vacuum hose (with said pill) and hopefully, that will bring things right.

I'm not really willing to go on the record and claim that this 9lb is actually an accurate 9lb, I feel that my $20 no named boost gauge is full of S***, but at least it gives me an indication and it does appear to be consistent with where it peaks now.

Again, I'm also not too sure if this rip-off turbo smart boost T is doing what it really should, as when plumbing it between the wastegate and turbo nipple there was no change whatsoever, regardless of adjustment level. Then again this could be linked to the restrictor pill issue, I'm not really too sure. I'm still pretty new to this kind of thing so its all a bit of trial and error!

 

[slystiguy]

wastegate actually working? 

[That Guy]

5 hours ago, slystiguy said:

wastegate actually working? 

 

It appears to be. Hooked up a bike pump to it and tested it a few times, seams to be all good

[SpeedySub]

Are you sure the gauge reads over 9 lbs? could be faulty and giving you wrong readings. Also are you hooking the mbc into the factory boost controller? from what I've read and been told you hook it up without the factory controller but leave it plugged in.

[BC5RA]

When I get my ride back, I'll pop over for a look.

 

Whas your location? Pick a part maybe better than ordering a new item which will probably be from Japan.