eriksseven

iTrader: (6)

First off, I have a MAJOR vacuum leak on my '88 TII.

It's so bad, that with +50% fuel enrichment via S-AFC, pumping a Walbro 255 and Greddy 720's, the car pulls 10mm/hg at a crappy 1100 RPM idle. Or, it'll drop down to about, ohh, 3mm/hg at an 800 RPM idle--barely staying alive. It's so lean EVEN with the crazy amounts of fuel, that it doesn't even register on my (narrow-band) A/F gauge!

Question 1: Does a vac. leak ALWAYS mean a boost leak? Like when you transition from vac. pressure to boost pressure, is the leak ALWAYS present? If no, can someone explain why, or how this works?

Also, I've "heard" that a vac. leak would actually suck in more air, causing your car to run leaner and therefore make more power? I don't believe this, because as soon as I'm boosting I'm no longer "sucking" air... Right?

My power-band has suffered drastically. Whether at 20% throttle or 100%, there's sporadic hesitations, especially as soon as I go WOT. Is this more likely to be too MUCH fuel, or too much air? It could actually vary and be either or... Since I'm really un-tuned (on the S-AFC) and I've got such a terrible vac. leak.

Also, would the amount of power I'm making suffer from the leak? I can hit 12+ psi no problem, but I don't reach max. boost until 5500 RPM's (!?!?!) Would my boost response / total power be increased with the vac. leak being fixed? Explain, please.

Important question: I wired my S-AFC to the boost sensor (instead of the AFM, I believe?) Can someone explain exactly what this does? Correct me if I'm wrong; the S-AFC increases fuel as the boost rises. I've been taking turns (new suspension) and let's say if I let off part way through, at like 6k RPM's in 2nd gear, the car will buck and hesitate until I resume WOT or shift. Is my car leaning out because there's no boost (no added fuel) in conjunction with the terrible vac. leak?

Random question: Does "brake boosting" hurt anything?

Any imput would be appreciated.

Thank you!

BTW, I ordered a set of sweet block-off plates from Banzaitoyota from E-bay. I'm hoping that by getting rid of everything, I won't ever have to deal with a vac. leak hunt again...

I've pretty much given up after removing the UIM 3x to 'fix' my problem, replacing all the lines with new silicone and doing a bunch of other crap. I even payed a local forum member to find and fix my vac. leak, to no avail!

If I spray carb-cleaner around, it seems like it's coming from behind the UIM but mostly BEHIND THE ALTERNATOR?!?!?!

Either way, I'm going to show my TII who's boss as soon as those block-off plates get here.

It's stupid, because everything is on hold until this is fixed... Meaning I'm not going to install a FMIC, TID or tune my car until this nonsense is over.

Overall, my car is getting slower (lol)

Honestly (don't tell anyone) I was dead even with a 350z and an E430 Mercedes on the freeway *gasp*. I had no problem pulling on a 'new' style 3000GT VR4 running my stock turbo at 11psi!

I know there's hope, but my ONLY power-band is from 5k-7k RPM's in 3rd and 4th gear, period. 1st and 2nd gear are so sporadic and hesitant that it's not even worth it to go WOT.

Ottoman

yes ur sucking in more air,

but it's unmetered air...

so the ecu is compensating incorrectly for the air flow..

so in theory if u were rich, then it would lean u out a little and make more power..
or if ur already in "normal" territory, then the leaks can tip u into the lean territory...


i'm not exactly sure if it's the same on an S5 TII... (i have an S4 TII) but did u check the 2 nipples under the UIM... there's one down near the prim. fuel rail and OMP system... sticking straight up. easy to miss... it runs up and to the back side of the UIM,

the second one is the angled nipple pointing towards the firewall on the LIM, that connects to the secondary fuel rail...

hope that is some help...

eriksseven

iTrader: (6)

Yeah, I've got a s4 TII as well. I'm pretty sure I've got those two nipples covered.

Isn't 'boost' the opposite type of air pressure than vacuum? If so, during vacuum, the car would be sucking in extra air from the leak. But wouldn't the opposite be true for boost? That instead of extra air being sucked in, it would be PUSHING out extra air from the leak?

RETed

Are you doing this under boost or are you revving it with the car sitting in one place???


-Ted

eriksseven

iTrader: (6)

I don't quite understand what you're asking...
+50% fuel enrichment is set at 'low throttle' for 1000RPM's. Any less than 40% fuel enrichment at 1000RPM's causes the car to die.

Under boost is when the sporadic nature of the power-band is noticable. When I'm revving the car, I think everything is pretty much normal...?

I still don't *quite* get your question.

Ottoman

Ted is trying to say that u get little to no boost i.e. positive pressure in the manifold when u rev it in Neutral


we'll worry about ur SAFC boost sensor hack, later... after u get the car running properly

are these vacuume leaks WITH the emissions stuff on? or off with no plates?



ur logic holds true.. a vacuume leak can become a boost leak when the manifold is pressurized

S4 TII? oh good, are u using a FMIC or the TMIC? did u check to make sure all the hoses are clamped properly and seated well? including the 2 "nipples" that come off the TMIC... they need to be plugged/re-routed after doin all the emmissions/pump/ret nest cancel... (3 nipples on the front of the manifold as well)

eriksseven

iTrader: (6)

I've yet to receive my block-off plates. Until I can get this vac. situation under control I'm going to hold off on everything else.

Boost sensor hack... lol

The only part of the emissions that's been removed is the EGR, which was blocked off using a home-made plate and sealant. I had originally thought this was the source of the leak, but I'm not even kidding, I swear it moves around, lol.

I really don't think I'll be able to find the heinous vac. leak until I remove all the emissions etc. Hopefully, by the time I get the car put back together after installing the block-off plates, the leak will have disappeared.

I've still got the stock TMIC on as of right now. All of the nipples/lines you mentioned in that last paragraph have been accounted for/installed correctly.

Ottoman

hows ur UIM/LIM gasket?

sometimes it's hard to find cuz of the echoing of the sound....

hopefully u'll get ur block off plates soon... I personally had my own made.. local machine shop some aluminum plate, real easy...

when u simplify all the emissions bullshit, seal up those plates, and get urself all new silicone hoses to replace to hold cracking brittle ones...


that would be a good start...

PS.. ur logic on the Boost sensor hack is wrong... the AFC is a step design... u got Low and High... u use the RPM steps to adjust the fuel in the high map... the AFC wont compensate for more and more boost...

it uses the TPS% in order to decide at which point to crossover into the High fuel map..
once it's in the map. that's it...

the reason ppl put it on the boost sensor.. is cuz if u have a big laggy turbo, and u suddenly go WOT... AFC see's 100% TPS, dumps more fuel... and u bog... cuz u have no boost...

where as if it's on the boost sensor... u mash the pedal.... the TPS % raises slowly with the boost... and then x-over at the point u hit X psi which will equal X TPS%... (upto 1bar)

especially us S4 ppl with narrow band TPS sensors.. we really suffer the most

ddub

All his gaskets are fine, and have even had RTV sealant added to them for better sealing.

I was working on this car, Erik's, recently and wow it's interesting :|

He was right that the EGR was one of the original problems, the diaphragm in it was torn and if you squirted it with carb cleaner the idle raised for a few seconds. I made the stupid little blockoff plate for it hoping this was the only leak, but I was wrong. The car had a couple vac line issues, those were fixed, the EGR was blocked off, it was stripped down almost completely and everything was gone over, reassembled, all lines checked, all unused nipples capped, sealant added to gakets, etc etc etc. Start it back up and initially it seemed slightly better, but that didn't last. I started squirting other stuff with carb cleaner and well, the EGR wasn't the only issue. His BAC got screwed a while ago from other issues, so that wasn't even working anymore really. You could turn the idle screw for days and it wouldn't do a damn thing. Then when you squirt the BAC with carb cleaner, idle raises again. Squirt the ACV and again idle raises. Yet... all the vac lines for this stuff and the vac rack were either connected or capped

I also spec'd his water thermo sensor, found it to be within spec but not the best, grabbed one of my spares that was better and put that in. Tested a few other sensors and they were fine, restabbed the CAS, checked TPS, bla bla bla. Everything is fine now except the damn leaks. I basically told him that it was a mess whatever it was, and since he told me before he was "thinking" about going bare block and removing emissions, now was a good time. There are too many of the pieces having issues to make it worth while fixing each one, at least in my mind.

I think if all the emissions are removed, the vac rack removed too (with rerouted fuel lines obviously), and only using the remaining vac lines needed with anything else capped, it should be a lot better. At that point I really hope there is no more vac leak...