Jump to content
SAU Community

Recommended Posts

R33, stock except for 3 inch turbo back mandrel exhaust, pod filter.

I found that i had a compliance 2.5" cat, so i figured it's restricting the system, and changed it to an xforce 3" highflow.

A quick rundown on my boost gauges. they're both splitfire. Gauge A runs off the factory nipple on the plenum and is mounted on my steering column. Gauge B runs off the hose going to the bov(was there when i got it), and sits in my glovebox for double checking stuff like this.

Before the new cat, Gauge B showed about 0.5psi above Gauge A. So boost was showing as 8.5psi on A, and 9psi on B.

After the new cat they show 9psi on A, and 8psi on B.

If they both went up or both went down, it'd make sense. but they've gone in opposite directions. wtf?

Firstly, someone re-assure me that there is no way the new cat is causing more restriction than the compliance cat (which was not gutted or damaged). ie. it was a sound move, and of benefit to the system, even though i couldve gone with a more expensive option like a 5inch big body catco, but i didnt.

Secondly...what is with the boost readings?

I've confused myself, and you, no doubt. If you've read thru this, congratulations, you're more patient than i am.

Link to comment
https://www.sau.com.au/forums/topic/144130-lets-see-you-answer-this-onegenius/
Share on other sites

ambient temps both the same?

you werent taking one reading from a cold night

and the other form a hot day or something similar?

either way, if both gauges have taken two different readings contrary to each other... makes me wonder about how accurate they are

boost guages are not acurate at all, also length of vacuum hoses may make some difference aswell, and guages are only a guide not a real representation of what the hell is going on, if you wanted results dyno it then see how acurate the guages are, compared to dyno result of boost, plus dont forget the error that may be seen from reading at an angle, same as if passenger looks at your speedo from an angle it will look different to what it really is, same as if you go by your speedo guage then your stupid as 99.9% of them are in accurate.

My opinion on this

Not only saying that, how do you know there isnt the slightest leak in one of the vacuum to guage hoses??? :S

Edited by Devils_Advocate21

i understand that gauges arent accurate etc. and leaks can cuase bad readings.

but...the gauges were reading about 0.5psi apart, and now they're reading 1 psi apart in the opposite direction.

u see?

also, is it even possible that a highflow cat can cause more restriction than the standard cat?

even if it is the cheap xforce option i went with?

the readings were at the same time, so same temp.

had a passenger reading the one in the glove box.

So... took inital reading... fitted cat, went for a drive immediately after fitment and took another?

Thats weird.

The gauges should be accurate, that is if your not running 11ty billion meters of hose...

was your old cat stuffed? collapsed inside?

So... took inital reading... fitted cat, went for a drive immediately after fitment and took another?

Thats weird.

The gauges should be accurate, that is if your not running 11ty billion meters of hose...

was your old cat stuffed? collapsed inside?

no, i didnt explain that properly, or you misundertood :D

the readings before and after the cat were not taken on the same day.

what i meant was, the readings showing the difference between the gauges is taken at the same time. ie, i'm not going out, reading one gauge, then coming back in, swapping etc, then out for another reading.

but i'm still baffled as to how one gauge showed higher by 0.5psi, and now it's showing lower by 1psi.

if the gauge on my steering column is correct, then changing the cat netted me extra flow which resulted in ~0.5psi gain (i'm happy with that).

If the other gauge is correct, then changing the cat actually cost me flow, losing about 1psi (not so happy).

the standard cat looked to be fine inside. all mesh intact, no loose rattling, etc.

Gauge A runs off the factory nipple on the plenum

Gauge B runs off the hose going to the bov

Where does the hose going to the BOV come from?

If it comes from the plenum, they usually do, then my guess is the BOV is leaking 1.5 psi.

:D cheers :)

Gauge A runs off the factory nipple on the plenum

Gauge B runs off the hose going to the bov

Where does the hose going to the BOV come from?

If it comes from the plenum, they usually do, then my guess is the BOV is leaking 1.5 psi.

:D cheers :)

hmmmmm, interesting. yes it's coming from the plenum.

why now though? why not before the cat? is it maybe an extra 1psi that did it?

it's a gfb hybrid bov (full plumback), and the spring is set to quite soft. would tightening the spring fix a leak?

if not, how do u fix a bov leak?

Have you tried swapping the vacuum lines to see if you get the same readings?

yeah i was going to replace the line to the gauge that reads low, and see if it was just that.

but i'd also like to know how to check/fix a bov leak.

will tightening the spring on the bov do anything for a leak?

so how do you check for, and fix a bov leak ? (gfb hybrid bov)

if there was a leak somewhere else, it would affect both gauges equally, correct ?

Check is easy, disconnect the vacuum hose from the BOV and block it off. Then compare the gauges. If the guages now read the same, then you know you have a leak. So check the hoses and the clamps between the BOV and the plenum, a 1.5 psi leak is easy to have and hard to find. If you can't find any leaks then it's the BOV, try tightening it.

:nyaanyaa: cheers :happy:

did you have the same person reading gauge b both times. and were they looking at it at the same angle. or maybe the person just rounded up, or the needle had flickered.

go for a drive and look at gauge a and have someone look at gauge b. then compare readings. then swap places and repeat. then you will be able to tell if it is how the other person is reading the gauge.

yeah, i thought of that. and i will get someone to video cam the gauge so i can check it myself afterwards. lol.

but all this heat in syd right now. not the best time to be pushing the skyline. might wait for a cooler day.

i might just change the hose from the plenum to the bov, and then see what the reading says.

what diameter is that hose anyway?

  • 2 weeks later...

i put a new silicon hose on from the plenum to the bov, with a new T-piece just before the bov, running to gauge B. all very secure, i cant imagine there's any leaks in the line.

gauge B is still reading 1 psi lower. tonight is a cold night, so i got 10psi on A, and 9psi on B.

the bov itself is bolted up well.

what bothers me is that there might be a pressure leak somewhere, hence the readings.

will adjusting the spring on the bov, to a harder setting, make a difference?

any others ideas of what to try, or where to look?

no, i havent swapped the gauges over.

i guess i should try that. the reason i havent is that the drivers side gauge is a bitch to remove, and the hoses in the engine bay arent long enough to swap over. i might extend the hoses and try that next.

yeah damn it, wouldnt you know it, it was the gauge playing up.

swapped gauges around and the bov line showed 9psi, while my factory nipple showed 8psi (with gauge B).

so gauge B was giving a false reading.

i shouldve tried this first, but i didnt imagine the gauge would all of a sudden give a false reading, after reading consistently for so long.

anyways, let that be a lesson to me.

good news, there's no leak :D

thanks for the help :D

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • So, that is it! It is a pretty expensive process with the ATF costing 50-100 per 5 litres, and a mechanic will probably charge plenty because they don't want to do it. Still, considering how dirty my fluid was at 120,000klm I think it would be worth doing more like every 80,000 to keep the trans happy, they are very expensive to replace. The job is not that hard if you have the specialist tools so you can save a bit of money and do it yourself!
    • OK, onto filling. So I don't really have any pics, but will describe the process as best I can. The USDM workshop manual also covers it from TM-285 onwards. First, make sure the drain plug (17mm) is snug. Not too tight yet because it is coming off again. Note it does have a copper washer that you could replace or anneal (heat up with a blow torch) to seal nicely. Remove the fill plug, which has an inhex (I think it was 6mm but didn't check). Then, screw in the fill fitting, making sure it has a suitable o-ring (mine came without but I think it is meant to be supplied). It is important that you only screw it in hand tight. I didn't get a good pic of it, but the fill plug leads to a tube about 70mm long inside the transmission. This sets the factory level for fluid in the trans (above the join line for the pan!) and will take about 3l to fill. You then need to connect your fluid pump to the fitting via a hose, and pump in whatever amount of fluid you removed (maybe 3 litres, in my case 7 litres). If you put in more than 3l, it will spill out when you remove the fitting, so do quickly and with a drain pan underneath. Once you have pumped in the required amount of clean ATF, you start the engine and run it for 3 minutes to let the fluid circulate. Don't run it longer and if possible check the fluid temp is under 40oC (Ecutek shows Auto Trans Fluid temp now, or you could use an infrared temp gun on the bottom of the pan). The manual stresses the bit about fluid temperature because it expands when hot an might result in an underfil. So from here, the factory manual says to do the "spill and fill" again, and I did. That is, put an oil pan under the drain plug and undo it with a 17mm spanner, then watch your expensive fluid fall back out again, you should get about 3 litres.  Then, put the drain plug back in, pump 3 litres back in through the fill plug with the fitting and pump, disconnect the fill fitting and replace the fill plug, start the car and run for another 3 minutes (making sure the temp is still under 40oC). The manual then asks for a 3rd "spill and fill" just like above. I also did that and so had put 13l in by now.  This time they want you to keep the engine running and run the transmission through R and D (I hope the wheels are still off the ground!) for a while, and allow the trans temp to get to 40oC, then engine off. Finally, back under the car and undo the fill plug to let the overfill drain out; it will stop running when fluid is at the top of the levelling tube. According to the factory, that is job done! Post that, I reconnected the fill fitting and pumped in an extra 0.5l. AMS says 1.5l overfill is safe, but I started with less to see how it goes, I will add another 1.0 litres later if I'm still not happy with the hot shifts.
    • OK, so regardless of whether you did Step 1 - Spill Step 2 - Trans pan removal Step 3 - TCM removal we are on to the clean and refill. First, have a good look at the oil pan. While you might see dirty oil and some carbony build up (I did), what you don't want to see is any metal particles on the magnets, or sparkles in the oil (thankfully not). Give it all a good clean, particularly the magnets, and put the new gasket on if you have one (or, just cross your fingers) Replacement of the Valve body (if you removed it) is the "reverse of assembly". Thread the electrical socket back up through the trans case, hold the valve body up and put in the bolts you removed, with the correct lengths in the correct locations Torque for the bolts in 8Nm only so I hope you have that torque wrench handy (it feels really loose). Plug the output speed sensor back in and clip the wiring into the 2 clips, replace the spring clip on the TCM socket and plug it back into the car loom. For the pan, the workshop manual states the following order: Again, the torque is 8Nm only.
    • One other thing to mention from my car before we reassemble and refill. Per that earlier diagram,   There should be 2x B length (40mm) and 6x C length (54mm). So I had incorrectly removed one extra bolt, which I assume was 40mm, but even so I have 4x B and 5x C.  Either, the factory made an assembly error (very unlikely), or someone had been in there before me. I vote for the latter because the TCM part number doesn't match my build date, I suspect the TCM was changed under warranty. This indeed led to much unbolting, rebolting, checking, measuring and swearing under the car.... In the end I left out 1x B bolt and put in a 54mm M6 bolt I already had to make sure it was all correct
    • A couple of notes about the TCM. Firstly, it is integrated into the valve body. If you need to replace the TCM for any reason you are following the procedure above The seppos say these fail all the time. I haven't seen or heard of one on here or locally, but that doesn't mean it can't happen. Finally, Ecutek are now offering tuning for the 7 speed TCM. It is basically like ECU tuning in that you have to buy a license for the computer, and then known parameters can be reset. This is all very new and at the moment they are focussing on more aggressive gear holding in sports or sports+ mode, 2 gear launches for drag racing etc. It doesn't seem to affect shift speed like you can on some transmissions. Importantly for me, by having controllable shift points you can now raise the shift point as well as the ECU rev limit, together allowing it to rev a little higher when that is useful. In manual mode, my car shifts up automatically regardless of what I do which is good (because I don't have to worry about it) but bad (because I can't choose to rev a little higher when convenient).  TCMs can only be tuned from late 2016 onwards, and mine is apparently not one of those although the car build date was August 2016 (presumably a batch of ADM cars were done together, so this will probably be the situation for most ADM cars). No idea about JDM cars, and I'm looking into importing a later model valve body I can swap in. This is the top of my TCM A couple of numbers but no part number. Amayama can't find my specific car but it does say the following for Asia-RHD (interestingly, all out of stock....): So it looks like programable TCM are probably post September 2018 for "Asia RHD". When I read my part number out from Ecutek it was 31705-75X6D which did not match Amayama for my build date (Aug-2016)
×
×
  • Create New...