Car pulls more at 10psi than 14psi

[carcrazy144]

Hey guys, got a funny question; i bought a mbc for my talon and was running 14psi on it. I currently backed it off because i got an odd sound when the turbo spools up, but the car runs about 10-12psi with the mbc backed off all the way. The car seems to pull much harder with the 10-12psi though which is odd to me, it should pull harder running 14psi obviously. Any ideas on why this may be?

 

[Bluefire16]

If you are running 14psi, you might be detonating and computer pulls ignition timing, resulting in less power. 15 psi is an absolute max you can run on pump gas with no FMIC or meth/water/alky.

What are you talking about guy? 15psi max? You must be kidding right? There are so many variables. I no guys running 22psi on a smic? No meth or anything...its called a tune and supporting mods. Please before you start running your mouth at least no what you are talking about.

Before my 16g and fmic, i ran a 14b and was running 17psi? So what are you telling me?

 

[tunethis]

Like i said my sensor was throwing a code that wouldn't let me get it inspected. Is it really that bad to drive a dsm without a knock sensor hooked up?

I don't know how the 2g ecu treats an unhooked knock sensor but, on a 1g, the ecu will show a constant default 9 counts of knock. The car will only perform worse as the boost level is increased. I highly recommend a logger (pda and logging software) to "see" what your car is really doing. You will also be able to see what is causing your Check engine light to illuminate.

Besides all that, you may also have huge boost leaks that bleed off your boost past 12psi.

 

[rEclipserGST]

Are they really? cause that may be what i got. would that really cause my car to pull more off of 10psi over 15? Doesn't seem like plugs would make that much of a difference to me. they're only plugs.

Have you EVER boost leak tested your car? The stock bov will definitely leak anything over stock psi. Which I believe is 12 lbs.
Get NGK copper. The stock spark plugs.

Could be knock, retarding timing. Buy a new knock sensor now that your inspection is over. Also do you have any fuel mods? Or at the least, a fuel pump rewire? If not, you should not but upping the boost that high yet. Even if it is a T25. Especially if you have a disconnected knock sensor.

 

[sketzshane]

What are you talking about guy? 15psi max? You must be kidding right? There are so many variables. I no guys running 22psi on a smic? No meth or anything...its called a tune and supporting mods. Please before you start running your mouth at least no what you are talking about.

Before my 16g and fmic, i ran a 14b and was running 17psi? So what are you telling me?

Same thing i posted above I was running 15psi on my T25 (98 GST) 90 Octane gas on BPR7ES everyday on a SMIC...no problems whatsoever. Eventually, I upgraded almost everything but that's a different story.

 

[Bluefire16]

^^ thats what i did as well, i was pushing 15/16 on the t25 ### i was upgrading the turbo so i didnt care about it, at 16 the efficiency is pretty much shot on the t25. If the guy is talking about efficiency then he has somewhat of a valid point, but by the sounds of it that was not what he was inferring. But u can run more than 15 psi without the other stuff, even without supporting mods like fuel pump, i ran 16psi on my 14b stock pump, stock injectors and smic.....

 

[carcrazy144]

Have you EVER boost leak tested your car? The stock bov will definitely leak anything over stock psi. Which I believe is 12 lbs.
Get NGK copper. The stock spark plugs.

Could be knock, retarding timing. Buy a new knock sensor now that your inspection is over. Also do you have any fuel mods? Or at the least, a fuel pump rewire? If not, you should not but upping the boost that high yet. Even if it is a T25. Especially if you have a disconnected knock sensor.

Ok, i already said i never boost leak tested the car and that i need to but just haven't gotten around to it. Wouldn't you know if the stock BOV was leaking because it would expel the excess air as though you were shifting when it hit its maximum ability, even while still accelerating? I have not upgraded my fuel system because there's no need to unless i upgrade my turbo or run more than 16psi. That's when you need to upgrade the fuel system. The stock fuel system can handle 16psi from what i have read. I have read a good bit on the site and know what i can and can't do with the mods i have. I have mistaken about the knock sensor; i did disconnect it at one time but i reconnected it, my CEL code was the front O2 sensor, i forgot that i had reconnected it the knock sensor. My bad.

 

[Achelea]

I just checked your profile and there is some SERIOUS details that need to be filled in.

The 3" Downpipe. How much of your exhaust is still stock? If you have a huge downpipe to stock exhaust, it might be choking at higher boost because the exhaust isn't escaping as fast as it could be.

The Fuel pump rewire is so the fuel pump can provide more fuel at top end, even on stock cars. More so when you crank up the boost. More air means you need more fuel. It's also a good mod to do because when you actually get a bigger pump, the wire would already be there for you to use. Some of the fuel system upgrades help the factory set up do the job better. Mind you, throwing huge pump on factory injectors or huge injectors on factory pump is counter productive. I'd suggest doing the pump and injectors and other needed mods around the same time.

Do you have a 2g or 1g BOV? the 2gs are notorious for leaking at anything above stock. The plastic can't hold as much as the metal in a 1g does.

It's been debated over and over and over again. There is a reason the NGK plugs are suggested. THOUSANDS of these cars run best on the factory plugs because it's one of the few things from the Evo that they kept identical. It Works.

O2 sensor would cause it to run bad because the motor has no clue how it's burning fuel so it throws more in to make sure it's not running lean. So when you get into the higher boost, the car is running richer and richer. Haven't you noticed your fuel milage take a dump since increasing the boost?

On that subject, do you have a Boost Gauge? The factory Guage doesn't read boost. It looks at the air passing by the MAF and calculates approximate boost. ((Which is the reason why you can have a boost leak, and your factory gauge is happily reading 14lbs of boost despite only having 5 get to the motor.))

On a MBC, I wouldn't advise just cranking it up as high as it will go. You turn it up a bit at a time to find where your current set up is happy. Nothing on a car is completely independent from everything else. You change something it's going to effect something else. Why do you think people wait until they are finished with their build before they Tune it fully. Or they retune after changing a part?

Everyone is insisting on the boost leak because it is notorious for being the root of a lot of boost issues. You could have a boost leak at an injector, and your the factory and aftermarket boost gauge shows you're still some where near your desired boost. Though the after market one would waver more as the pressure bleeds off than the factory one.

You would think after 19 years of trial and error, the established route would be, well, established.

 

[carcrazy144]

ok, first off the three inch downpipe was bought and put on because the stock one had a hole in the flex pipe and it had to be fixed in order to get the car inspected. My O2 sensors are good, i recently replaced the front one and i did the aluminum foil jimmy for the rear. The stock exhaust is actually ok to use; until you get up around 350-400 hp it's not necessary to run full 3" exhaust, besides i can't exactly afford a $400 cat-back system as of right now. I have the stock BOV and want to get an aftermarket one but again i can't afford one. I do have aftermarket gauges including boost, and i didn't just turn up my MBC all the way when i bought it. i did it a little at a time like your supposed to. The rewire for the fuel pump doesn't seem necessary since i didn't even hit my fuel cut while upping my boost. If i was running too much boost i would have hit my fuel cut and would have had to reset the computer. I know i have to do the boost leak test and that the stock BOV could be leaking as well as many other spots in the intake system.

 

[Achelea]

ok, first off the three inch downpipe was bought and put on because the stock one had a hole in the flex pipe and it had to be fixed in order to get the car inspected. My O2 sensors are good, i recently replaced the front one and i did the aluminum foil jimmy for the rear. The stock exhaust is actually ok to use; until you get up around 350-400 hp it's not necessary to run full 3" exhaust, besides i can't exactly afford a $400 cat-back system as of right now. I have the stock BOV and want to get an aftermarket one but again i can't afford one. I do have aftermarket gauges including boost, and i didn't just turn up my MBC all the way when i bought it. i did it a little at a time like your supposed to. The rewire for the fuel pump doesn't seem necessary since i didn't even hit my fuel cut while upping my boost. If i was running too much boost i would have hit my fuel cut and would have had to reset the computer. I know i have to do the boost leak test and that the stock BOV could be leaking as well as many other spots in the intake system.

Alright. The Downpipe makes sense. The O2 didn't cause you mentioned the CEL saying for the front O2, I assumed it was still bad. I would say try to get a hold of a 1g BOV. It's metal, it can hold boost better. As for the fuel pump rewire, it's not that you are hitting Fuel Cut. It's that with the factory wiring, the pump can't push enough at WOT at the higher Rpms. I know I mentioned Rich condition, but that was under the assumption the O2 sensor was bad.

Here's Road Race Engineering's Take on it.
Eclipse Fuel Pump Tech Tips

As you look these specs over you can see how it is worthless to compare fuel pump flow with out specifying both voltage and pressure. Lph = liters per hour. All Denso 50mm (1G) and 38mm (2G and GVR4) Dia. in-tank fuel pumps start out with the part number 195130-xxxx


T/E/L turbo stock pump, GVR4 and 323GTX too:


$20 used good

(1G and 2G both even though they are different sizes)

part #s: -0510, -0153, -0670, -0440, -2020, -0022, -2760 :

100 lph @43psi @12v 70 lph @58psi @12v

140 lph @43psi @14v 110 lph @58psi @14v

When dealing with boost, it's always better to do supporting mods before the boost itself.

 

[carcrazy144]

What if i'm already running rich? I was riding down the road with a buddy following me and he said when i get on it i get black smoke coming out of the exhaust, one puff. typical sign of a rich mix. why would that happen if i can't get enough fuel at 15psi?

 

[tim4g63fast]

Alright. The Downpipe makes sense. The O2 didn't cause you mentioned the CEL saying for the front O2, I assumed it was still bad. I would say try to get a hold of a 1g BOV. It's metal, it can hold boost better. As for the fuel pump rewire, it's not that you are hitting Fuel Cut. It's that with the factory wiring, the pump can't push enough at WOT at the higher Rpms. I know I mentioned Rich condition, but that was under the assumption the O2 sensor was bad.

Here's Road Race Engineering's Take on it.
Eclipse Fuel Pump Tech Tips


When dealing with boost, it's always better to do supporting mods before the boost itself.

Bernoulli's principle really does work

 

[Achelea]

What if i'm already running rich? I was riding down the road with a buddy following me and he said when i get on it i get black smoke coming out of the exhaust, one puff. typical sign of a rich mix. why would that happen if i can't get enough fuel at 15psi?

That's normal. When you floor it, the injectors shoot more into the cylinders, which is a bit rich so it lets out a puff of black smoke before the RPMs climb to burn the extra fuel. IIRC a lot of the higher tuned cars do that anyways. But thats on the low end, not the high end.

Bah, at this point it sounds like I'm contradicting myself and making no sense. I think A wiseman needs to explain.

Also,

Bernoulli's principle really does work

How so?

 

[tim4g63fast]

Also, How so?

Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

so you increase pressure and oppose flow


if you run the same voltage but up your pressure you oppose flow

100 lph @43psi @12v
70 lph @58psi @12v

140 lph @43psi @14v
110 lph @58psi @14v

 

[Achelea]

Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

so you increase pressure and oppose flow.

Right. Sides. Doing the rewire won't hurt anything. ^.^

 

[carcrazy144]

So to get back on my original question; i have better acceleration at 10psi than 15psi because i have a boost leak and at 10psi the turbo can compensate for it but when i up the boost the air escapes quicker than the turbo can compensate thus making acceleration slower, correct? And i need to change my plugs and rewire my fuel pump as well. Will fixing the leaks, changing the plugs and rewiring the fuel pump fix my problem or just eliminate things that could cause it?

 

[fran_drivertsi]

Disconnecting knock sensor: It is like f...ing a hooker with no condom: It feels great, but when you get an STD - don't complain.

All other comments regarding running 15 or more psi on pump gas: my opinion was aimed primarily to the creator of the original post. I am quite sure that he has a stock SMIC, and if you are telling me that you can run more that 15psi through that thing on stock turbo efficiently with pump gas - you are out of your freaking mind.

 

[carcrazy144]

Disconnecting knock sensor: It is like f...ing a hooker with no condom: It feels great, but when you get an STD - don't complain.

All other comments regarding running 15 or more psi on pump gas: my opinion was aimed primarily to the creator of the original post. I am quite sure that he has a stock SMIC, and if you are telling me that you can run more that 15psi through that thing on stock turbo efficiently with pump gas - you are out of your freaking mind.

Ok again i disconnected my knock sensor at one time to eliminate the CEL code but reconnected it after it wasn't the problem.

Secondly, i am not running more than 15psi, i have never said i planned on running more than 15psi, the stock smic can handle 15psi fine, but its advised to get a bigger smic or an fmic, but not necessary. You can also run pump gas on 15psi no problem. people run 20psi on pump gas, though they might have an fmic, you can safely do it. I'm not an idiot, i've done my research and can safely run 15psi with my car on pump gas and the mods i have. though it is a good idea to get a couple other supporting mods, hard ic piping, 1g BOV, i don't need an fmic or racing fuel as your suggesting to run 15psi.

 

[fstfcs]

Good luck.

I tried running a measly 13.5lbs through a stock BOV and SMIC, granted i had a 20g. But either way i learned real fast that the factory intercooler shiz.....SUCKS!

 

[sketzshane]

Good luck.

I tried running a measly 13.5lbs through a stock BOV and SMIC, granted i had a 20g. But either way i learned real fast that the factory intercooler shiz.....SUCKS!

13.5lbs on a 20g is a totally different than 13.5lbs on a T25.


Re:carcrazy144 I would say just go and do all the things suggested 1 by 1. I would go the cheapest route first(Boost leak test etc...) and see exactly what going on. I don't know your budget but I believe it shouldn't be hard to get a reputable mechanic in your area to make a run through it or if you want to do it yourself then borrow the equipment.

Below is a boost leak tester sold on ebay(btw, they are a easy DIY)

boost leak tester, great deals on eBay Motors on eBay!

 

[dsm-onster]

Did you ever put a logger on there to see what is going on with your car as to why you have less power at 14psi than 10psi? I've run the 13g at 14psi (same size as t25 w/ about the same shape efficiency map). It felt grate. In fact, all turbos feel good up to choke. Some better than others depending on the size of the turbine.

The t25 can handle 15psi it may fall a little in boost up top but that doesn't mean it's losing flow. It just means that the motor is matching the velocit of the incoming mass from the turbo. . .

 

[carcrazy144]

Did you ever put a logger on there to see what is going on with your car as to why you have less power at 14psi than 10psi? I've run the 13g at 14psi (same size as t25 w/ about the same shape efficiency map). It felt grate. In fact, all turbos feel good up to choke. Some better than others depending on the size of the turbine.

The t25 can handle 15psi it may fall a little in boost up top but that doesn't mean it's losing flow. It just means that the motor is matching the velocit of the incoming mass from the turbo. . .

No, i never put a logger on, i'd like to get one so i could tune the engine with what i have on it, but i just can't afford something like DSMLink, is there any kind of logger that still works well and allows me to tune without breaking the bank?

 

[dsm-onster]

EvoScan. And you have a 1998+. So you can use that same EvoScan cable and reflash your ecu for almost any injector size out there, any timing map you want, any fuel map you want. Plus many other features.

EvoScan spits out a real knock count and injector duty cycle too. Something only dsmlink or a 1g logger can do. No trying to track knock with a drop in timing numbers. No guessing. It's VERY nice. I loved using it back when I had the 97 talon.