I did see quite a bit on o2 placement for underhood mounted turbos. To get more specific I have a 1996 3.4L toyota 4runner with a rear mount turbo, with a URD 6 injector kit, comes with a fuel and timing piggyback box that can be tuned and a "partial boost enrichment" function. Initially I fabbed up everything got it going and it ran well at 7 psi. After some time I got some light crackling noise, stop driving it and upgraded fuel injectors, pump, plugs, and a piggyback system. Found a few partially plugged injectors so I assumed that was the issue but was already there so I figured to keep going with the upgrade. Ran good once again for a few months and now back to the crackling sound, and getting lean under any boost pressure with partial throttle, gets to 12.5 afr under WOT at any boost though. Checked plugs today and they looked fine, no sign of det or anything. I did notice I may have have a small leak at the plenum gasket, potentially the crackling noise? Now my o2 question, I have the factory o2 pre turbo, the signal is intercepted by a split second fuel and timing calibrator to adjust as needed. Along with the innovate o2 sensor afr gauge. What I'm wondering is, is the fact that my o2 sensor is pre turbo could that be skewing the actual readings and making it difficult for the piggyback and ecu to work together as needed? I did try adding some fuel in the tuning map and it seemed to help a very small bit but not as much as expected and I was still hearing that crackling sound, so I'm worried I'm getting some pre ignition or something of that nature. Or do I need to work on timing? All the tuning is very new to me and very intimidating. And unfortunately here in boise all the shops I have contacted have "never used the software" and won't take the money I'll give them to learn it and tune my vehicle...
Thanks for reading!

 

In a rear mount turbo system the 02 sensor goes 6-12" from the collector. What are you doing for fuel system filtration? What are your fuel pressures doing under boost, what are you using for a fuel pressure regulator? What are your AFR's at cruise, low load, and under boost? How much timing are you pulling at 7 psi?

 

Not sure on pressures, it will go pig rich at WOT and high rpm boost, same system proven to work on boosted applications for my vehicle. 190 lph pump and in tank filter. 14.7ish for cruising afr 13.5-14.5 afr for low load, gets upwards of 15- 16 afr under any boost not being WOT. Not sure how much timing is being pulled will need to look into that this evening. I glanced the other day at timing at 7 psi and the piggyback showed a positive voltage on the timing. Which makes me believe is was adding timing? Not to familiar with any piggyback or standalone system. It's new to me.

 

A wideband should always be post turbo. They don't like to read correctly under pressure. I can't speak for narrow band sensors since they work differently.

This doesn't get discussed often. I had no idea until I had strange readings on my rear mount setup and started researching.

 

Extensive research lol. Thanks for the input, I plan on moving both sensors but will check into the narrowband first to be sure. As the individual above posted it should be after the collector, which would be preturbo. This thing has me beating my head against the wall. I don't have enough knowledge at this point to pinpoint my issue and as soon as you go digging for info it's just an overload and takes a few nights to learn one topic .

 

Do you have a rising rate fuel pressure regulator? If not that is your problem.

 

I don't have one, technically, but the piggyback system has something of that sort programmed into it. It is supposed to have a "boost enrichment" module that reads the boost on the fly and adds extra fuel when it picks up boost reading accordingly. URD doesn't do a great job in, well much, for someone who is doing anything outside of what they sell. If it's not their SC and kit they don't have much for help and they're tech specs for their equipment is non existent.

 

Boost enrichment is not the same as fuel pressure. Boost enrichment just tells the pcm to shoot for a richer AFR. You NEED a boost referenced FPR, there is no way around it. That is your problem, right now your effective fuel pressure is dropping 1 psi for every psi of boost.

 

NB miatas (99-05) do not have a manifold referenced regulator and are very commonly turbocharged on the stock system. You do lose 1 psi of fuel pressure for every 1 psi of boost, but if you can increase injector pulse width accordingly it's a non issue until you reach very high boost.

Is a manifold referenced regulator a good idea? Definitely. Is it absolutely necessary? Not at 7 psi.

 

You presented a problem, it was diagnosed and a solution provided. It is not your wideband. Why you would try to skirt a rising rate regulator, or half ass any part of the fuel system is beyond me.

 

It's not half ass? It's the setup that works perfectly fine for boosted applications with the 5vzfe. Proven by the thousands who are running either stock ecu with SC, or urd aftermarket and SC. But the guy you are trying to insult is not the guy who asked this topic. Not to say I'm not going to look into it now but c'mon man. No need to be condensending towards people sharing and learning information.

 

It is half assed, it doesn't matter how many people have done it, just means lots of people are lazy hacks. If you want to take it personally that's fine, I couldn't care less. This board is about turbo tech and doing things right, it is unacceptable to try to justify bad practice.

The fact that you don't know what is going on with your fuel pressure is a real concern, the wideband readings prove it, fix the problem, don't, whatever... But arguing that it is good practice because "thousands" do it with some unique engine combo when what you are experiencing a problem that is easily traced to fuel pressure proves otherwise says you need to take a step back, reanalyze your build, before something breaks.

You need to either make the correct fueling calculations and get tune straight, or get the appropriate regulator, and set it up to rise with boost so your PCM can do what it needs to. At a minimum you need to get a fuel pressure gauge, without that you have no idea if your fuel system is keeping up, you could have a bad pump and not know it, or a line obstruction. These are things that kill boosted engines. Read plugs, tune, read plugs, tune. The plugs are going to give you real feedback and either verify your wideband, or tell you it is wrong.

 

first of all the guy you decided to insult wasn't even me, the person who posted this topic. And maybe, just maybe you don't know everything, such as the SC was released from TRD (toyota) as a factory upgrade on a completely stock ecu.. no regulator. So toyota put boost to a motor with no rising rate regulator at you think it was bad practice or half ass? You really think they would allow that type of liability? Always pleasant to have the guy to bash people on a forum, who knows everything of course, instead of just leaving it be. I'm for sure checking into a new regulator for the sake of simplicity, but God forbid us younger guys try to learn and can't afford to everything perfect and just use what we got. We'll just call it bad practice instead of learning, cool.

Alright, plugs look good after every read. Bump in fueling on tune did almost nothing for the amout I increased, I see a hard spike on the timing input when it's fully boost, it's showing a positive increase in power on timing voltage, so I assume it's increasing it? Back to my original question, I know you said at the collector for narrowband o2 but I've been reading alot saying the increase in pressure and temp pre turbo could be skewing actual numbers? What my concern is, is that a proven system which normally works is not functioning properly. To me, that says there is a lack off communication somewhere, the piggyback system was soldered in correct so my first step is to insure the ecu is getting correct input, that's the first line of communication after the controlled explosion. Start at the beginning of the process and work my way through the system. If I get the correct regulator, I could in theory go back to stock injectors and no piggyback, from what I've read the stock ecu will handle timing changes under 8-9psi, and delete a potential problem? Assuming it is not the factory narrowband o2

 

https://www.aemintakes.com/instructions/AEM-30-4100_inst.pdf

Page 8.

AEM says "On turbocharged engines the UEGO sensor must be installed after the turbo charger, if not, the pressure differential will greatly effect the accuracy of the unit"


https://www.innovatemotorsports.com/support/manual/LC-2_Manual.pdf

Page 4

"Weld the bung at least 24 inches downstream of the exhaust port outlet (after the collector), or 24 inches after the turbocharger if so equipped. The bung should be welded before the X or H pipe if so equipped."


https://cdn.shopify.com/s/files/1/0...l_863b29af-76fa-4c51-9a6a-8f20e621840f.pdf?60

14point7 Spartan widebend installation manual.

"For Turbocharged engines the sensor should be installed after the turbocharger."



I'm not trying to be difficult I just don't think OP should discount the possibility of a wideband issue considering his sensor placement.


I thought more about the fuel regulator argument and B E N may be right in this application. In the miata example I gave, guys are typically running standalone ecu's that allow total control over the fueling using a speed density strategy. Running reasonably low boost levels with speed density will allow you to easily adjust for the lack of a manifold referenced fuel pressure regulator. Since you're on the stock ecu which is almost certainly running a MAF strategy things are likely different.


I did some digging on your specific engine and it seems there is a stock regulator on the rail that has a reference line run to the air intake pre-throttle body. This makes it atmospheric referenced in it's stock form. What you can likely do is move the reference line from the stock location to any location post throttle body and have a manifold referenced system that will increase fuel pressure with boost.

If you do this you should definitely hook up a gauge and verify you're getting the results you think you are.

 

One hundred percent the wideband is poor placement. I read up on that and found that little important bit of info too, thanks for the check though. I knew the stock system worked somehow but in all honesty I hadn't dug enough to understand how it worked. Knowing now that I can potentially get a pressure reference off is extremely helpful, assuming I didn't already do that and just not realized I had, possibly following another build and not asking questions about specific items.

 

Definitely put the WB02 after the turbo. I would put it as close as possible to the turbine.

 

The schools of thought on wideband in remote turbo placement are split. You put it after the turbo and you end up with more transfer delay, and you have to have perfectly sealed exhaust. If you put it before the turbo you can get false readings due to pressurization.

Because this vehicle was made in 1996 it has cats, you cannot place a wideband after a cat and get an accurate reading, so it needs to be in the collector, before the cat. The reading will begin to skew at higher pressures, but in a 7 psi remote system the pressure shouldn't be very high. And there is always some pressure in a exhaust system.

Calm down, reread the posts. You are upset over nothing and taking things personally that are generalizations. If I was insulting you, it would not be a generalization or in a round about way, I am not that guy.

 

It seemed you were worked up haha. I was getting a chuckle over it, but no harm no foul. So when I fabbed it up I assumed the cats were just another obstacle on the way to the turbo and got rid of it and wrapped the pre turbo exhaust to conserve some of the heat. Once home I plan on moving the wideband back and checking my fuel regulator. Just from this topic here and some reading, why not just put it post turbo to rule out any chance of false readings. I have a hunch I don't have the regulator line that reads atmosphere in the correct spot showing manifold pressure. It wouldn't make sense for me not to but it's the only reasonable explanation I can come up with. Or I potentially have a plugged line somewhere, which just doesn't sound reasonable... or it just dawned on me, if that potential blow out in my intake manifold gasket could be dropping the pressure in the manifold and not allowing the regulator to see the appropriate pressure? It's shows correct psi on gauge to the manifold, but could it somehow not be getting correct pressure to the regulator?

 

Plugged line doesn't seem real likely, kinked line or plugged fuel filter maybe. If the intake has a bad gasket that is going to create all sorts of tuning trouble so it should be taken care of first thing.

If you aren't running cat's placing the o2 after the turbo will work great, the transfer delay is easy enough to recognize and if your tuning software allows it you can compensate, make sure you have ~12" or more of exhaust after it.

I am not sure I understand the fuel regulator being vented to atmosphere, there were some cars that ran a barometric air pressure sensor that was routed to atmospheric air during that time, but that is an engine control reference. If you have a pressure regulator I would assume that it is hooked to a vacuum source. Think of how the injector sees pressures, when your engine is idling and you have 18" of vacuum that is 18" of vacuum on the tip of that injector. If your stock fuel pressure is 43.5 psi and 18inhg is an additional 8.8 psi you are now seeing 52.3 psi of effective fuel pressure at idle, but only seeing 43.5 at wide open, that is the opposite of what you want. Boost compounds this further, if you are running 7 psi at wide open your manifold is now pressurized above atmospheric and the injector is now only acting like it has 36.5 psi of fuel pressure.

Look at this chart of how an injector responds to fuel pressure:
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This is just some random injector I could find data for, yours will be different. But they all behave similarly. Notice how as effective PSI becomes less the flow rate goes down. This makes tuning a pain, it can be done but without a dyno and some time it really sucks. Turbo's make this type of tuning even more difficult, because they aren't a linear boost curve and getting into boost depends on load, so there isn't a flat RPM programming strategy that will compensate for the changes in fuel pressure. The other thing that changes dramatically is spray pattern, your injectors may go from a beautiful cone of fuel to a sputter, this messes up transient delay, screws up burn efficiency, and lessens cylinder cooling.

Also notice that as your boost rises your injector size effectively shrinks, and having your fuel flow diminishing with boost is not desirable. There are PCMs that run a PID program that can probably get around the changing fuel pressure using wideband data, but I am totally alien to Toyota PCM and cannot provide any insight to how your stock PCM will handle it.

Fueling is key to making a boosted engine survive. There are people out there who run a boosted engine and have no idea what there fuel system is doing, but the vast majority have a way to read fuel pressure, be it part of and engine management unit using something like HP tuners, a standalone control system, or a separate gauge. And trying to hit moving target fuel pressures is not something you need to worry about when you are first learning to tune, there is so much other stuff going on, and this is an easy thing to set in stone, and having a fixed injector behavior will mean one less piece to the puzzle.

I know from the experience of having the GT500 pumps in my mustang start to flake out and not realizing my fuel pressures were crap how much of a pain inconsistent fueling can be. It also happened in my CJ, one of the two 255's in it started to die off and the thing just ran like total crap no matter what I did in the tune, it was great for a minute then falling on its face and had no rhyme or reason. Don't be me.

 

O man, today got the intake plenum gasket done, quick and took care of the crackling noise. Went for a spin, lean, boost was inconsistent, and now a almost labored groaning noise, I think the noise is my cheap BOV i got just to get it out of the garage and to move. Still now sure what quality bov I want to go with, open to suggestions. Also had a wonderful bug next a grip of larva in my atmospheric port ok my wastegate, so that was fun trying to find out why my wastegate was fluttering and acting strange. Added fuel on my tuning map, the afr's improved quite a bit but presented a whole new issue... under moderate throttle and 1-5 psi afr is around 12.3-14.0, any heavy throttle input and it goes rich 10.1 ballpark. It seems that no matter the tune it always has a ton more fuel wot, not a smooth transition, all or none type of thing, before it would go from real lean to pig rich as soon as you went wot, same scenario now. Still haven't moved 02 wideband post turbo yet, thought the lead from gauge to sensor was long enough and I came up about 1 foot to short. Going to get a gauge to check fuel pressure, o2 extension and have been looking at rising rate pressure regulators. Intake temps were very high today too, I may have sucked the air filter in on itself again, another part that just got the vehicle moved to the new house and i have parts to build a correct intake filter, seems it may be to counterproductive to not build it at this point. So that could be contributing to noises and fluctuating boost pressure. List of shit to fix before I can even get to serious about the tune at this point... didn't realize how much shit I did just to get it 60 miles down the road in a hurry then let it sit for 6 months. Regretting it now... I do appreciate the insight and any other thoughts you have are appreciated. I mulled over that last response with the hood open and checked anything thing I could find in relation.