Stock fuel pressure on a 2g - why AFPR?

[Catbox_95]

What is the stock fuel pressure on a 2g? I think I remember hearing it is 42 psi at idle, then should increase about 1 psi per psi of boost. Is this correct?

I have a Walbro 255 plus loads of other mods (check out list). It seems that everyone has been telling me that I will overrun my stock FPR. I have an in-car fuel pressure gauge that reads 42 psi at idle, and at 11 psi of boost it was at about 56 psi fuel pressure.

So my question is, am I overrunning my stock FPR, because it doesn't seem so yet everyone is telling me that I am. If I installed a nice AFPR, it seems that I would adjust it to get the same fuel pressure performance I'm already getting.

Puzzled...

 

[daveyfx]

Stock pressure is 43 psi. With a Walbro 255 pump it could not hurt to install an adjustable AFPR.

dave

 

[Quasimondo]

Pulled from Chilton's, all pressure figures are with the vacum line removed:

1G n/t - 47-50 psi
1G turbo m/t -36 - 38 psi
1G turbo a/t - 41 - 46 psi
2G turbo - 42 - 45 psi
2G spyder - 47 - 50 psi

With vacum line attached:

1G n/t - 38 psi
1G turbo m/t 27 psi
1G turbo a/t 33 psi
2G turbo - 33 psi
2G spyder - 38 psi

Your fuel pressure is about 12 psi above normal. It won't kill anything, but you're probably running a lot richer at the low end of the rpm range since the engine can't lean itself out enough.

 

[Larry L]

Think those Chilton numbers are a mis-print. It is 42-45 and almost all have 42 stock.

 

[dsm-onster]

What? Where's the misprint? A turbo 2g has 42-45 psi. Just like you said and as was quoted.

Not all have 42 stock. 2g nt spiders have 47 psi, 1g 5 speed has 37 psi, 1g n/t 2.0L has 47 psi.

 

[steve]

I have an in-car fuel pressure gauge that reads 42 psi at idle, and at 11 psi of boost it was at about 56 psi fuel pressure.

Just in case you didn't understand what Quasimondo posted, you should be seeing about 33psi at idle and that should rise to to about 53 at 11 psi boost if you have a base pressure of 42 psi

The fuel pressure at any given point should = base pressure (psi) + manifold pressure (psi)

A normal DSM should idle at about 18 in hg manifold vacuum which is about -9 psi.

Steve

 

[DGajre777]

POSTED EDITED...

The in-car fuel pressure gauge you have is reading your fuel pressure WITH the vacuum line connected and you should be seeing 33 psi at idle (baseline 42psi - 9psi). Since the fuel pressure regulator (stock ones that aren't being over-run by big fuel pumps and good adjustable fuel pressure regulators) increase fuel pressure on a 1:1 ratio to boost, at 11 psi, you should be at 53 psi.

 

[dsm-onster]

You know guys, the OP posted his problem back in 2005 .

 

[DGajre777]

You know guys, the OP posted his problem back in 2005 .

Damn... I didn't even see that.

 

[steve]

I plead that I was trying to sucker the new wiseman in. Worked didn't it

Steve

 

[dsm-onster]

Man, I didn't even notice that DGajre777 is in "the red" now. I know he's help alot of us out here. Even if it's just through research.

 

[CanadianTSi]

your fuel pressure FPR should be at 33 psi+11 = 44 psi of fuel pressure, not 56 psi that you are seeing.

This is Incorrect, assuming a base FP of 42psi with the vacuum hose off (AKA 0psi) then Fuel Pressure at 11psi should be 53.

 

[jking29]

This is Incorrect, assuming a base FP of 42psi with the vacuum hose off (AKA 0psi) then Fuel Pressure at 11psi should be 53.

He's right. Pressure goes down with vacuum, and up with boost.

 

[DGajre777]

This is Incorrect, assuming a base FP of 42psi with the vacuum hose off (AKA 0psi) then Fuel Pressure at 11psi should be 53.

Damn, I was thinking positive boost pressure, not negative vacuum pressure. Sorry for the brain fart... post edited.

 

[dsmBear]

Glad i found this thread.. I just have a few questions that i need answers too. Im hoping for a friendly response.

I have 450cc injectors and stock fuel pump and FPR. I have a gm maf and a boost controller. Im currently running around 13 psi perfectly. I want to up it to 18 and call it quits until i build the engine. I know i will need a fuel pump and a new FPR. Can the stock injectors handle 18? And with the new fuel pump, what do i need the set the FPR at? I was researching all this and people were talking about things i havent learned yet so here i am!

 

[T is for TURBO]

What turbo? If it's a t-25, 18 psi will kill it real quick.

 

[dsmBear]

What turbo? If it's a t-25, 18 psi will kill it real quick.

I have the regular 14g turbo I'll get 16g if I need to but right now I'm just going to stick with the 14.

 

[russ96gst]

I have the regular 14g turbo I'll get 16g if I need to but right now I'm just going to stick with the 14.

He asked becasue 2g's (95-99) have a t-25 stock, so unless you or someone else changed it, thats whats in there and I will assume you mean a "14b" not 14g as that is what came in the 1g's.

 

[dsmBear]

He asked becasue 2g's (95-99) have a t-25 stock, so unless you or someone else changed it, thats whats in there and I will assume you mean a "14b" not 14g as that is what came in the 1g's.

oops! Sorry. Im not all that educated yet . I also want to know when i change my fuel pump, what do i set my FPR to? or do you even set them? And with bigger injectors do you have to change the fuel pressure?

 

[T is for TURBO]

Is it actually a 14b? because the difference between a 14b and a t-25 are pretty significant.

Why do you want to run specifically 18psi?

Personally I like to have a robust fuel system. I don't want to be pushing my injectors to their MAX duty cycle. Nor do I want to be pushing my fuel pump to it's max.

A stock 2g fuel pump with a 14b at 18 psi would be to close to the limit for my comfort. I would defiantly rewire the stock pump to be on the safe side.

Same goes for fuel injectors. You'll probably be pushing north of 80% duty cycle, and a general rule is to keep the injector duty cycle at or below 80%

Your regulator, as long as it's not leaking, should be just fine.

If you're running a t-25. forget it, you'll kill the turbo in less than 1000 miles. I have a garage littered with blown up t-25s that were just fine... up until the boost was turned up past 15-16 psi.

As for fuel pressure, always leave it at stock value. I have 950s and I run 43.5 psi base fuel pressure.

 

[dsmBear]

Is it actually a 14b? because the difference between a 14b and a t-25 are pretty significant.

Why do you want to run specifically 18psi?

Personally I like to have a robust fuel system. I don't want to be pushing my injectors to their MAX duty cycle. Nor do I want to be pushing my fuel pump to it's max.

A stock 2g fuel pump with a 14b at 18 psi would be to close to the limit for my comfort. I would defiantly rewire the stock pump to be on the safe side.

Same goes for fuel injectors. You'll probably be pushing north of 80% duty cycle, and a general rule is to keep the injector duty cycle at or below 80%

Your regulator, as long as it's not leaking, should be just fine.

If you're running a t-25. forget it, you'll kill the turbo in less than 1000 miles. I have a garage littered with blown up t-25s that were just fine... up until the boost was turned up past 15-16 psi.

As for fuel pressure, always leave it at stock value. I have 950s and I run 43.5 psi base fuel pressure.

Beautiful. Thank you for clearing things up. But i actually plan on getting a 16g turbo. Idk what i have. Its a stock 97 gst turbo so whatever that is. And i want to get a bigger fuel pump. Ive never heard of rewiring one before. But also if i want to do 18 psi, i can have these things and do it safely? -- 16g turbo, 550cc injectors, 255 fuel pump, and air fuel controller? Will i also need an aftermarket FPR or will the stock one handle it? and what duty cycle do the 550s run? Ill get bigger if i need.

 

[T is for TURBO]

If you have the stock turbo, it's a T-25, which is not a good turbo for making power on these cars.

If you go with a 16g, 550s should be fine at lower boost levels, but I would go bigger. Going to a bigger injector doesn't cost a whole lot more, so if you ever want to make more power later on, you won't have to buy new injectors. As far as a fuel pump goes, if you stick with a 16g, a walbro 190 should be enough.

and what duty cycle do the 550s run? Ill get bigger if i need.

Duty cycle is completely dependent on how far you push your injectors. The more air your turbo is pushing into the engine, the harder the injectors work. That is something you have to watch when tuning/logging. Any logging software will show you your injector duty cycle.

Rewiring the fuel pump; the stock fuel pump circuit is kind of a bottle neck, losing over one Volt from battery to pump. While it doesn't sound like much, it is in fact very significant. Also, it's easy and cheap to do, so there's no reason not to do it. Link

If you stay with a walbro 190, the stock regulator will be fine. Some people report that their car runs fine with a 255 and a stock regulator. I personally wouldn't do that though.

But the biggest question is, what are you going to tune with? In my personal opinion, ECMLink is the BEST option you have. It's more than you'll need, it's reasonably priced, and it is EASY to learn.

I would stay far away from MAF Translators and AFCs. They just don't provide the best solution to tuning, and aren't that much cheaper than ECMLink

Can I ask why you are stuck on setting it at 18psi? Manifold pressure is just a measurement and doesn't mean as much as some people think. More important than manifold pressure is mass air flow (measured in lb/min), timing, and Air/Fuel ratio.

You would make less power at 18psi and no timing, than at 17psi with a bunch of timing. My point is, you ultimately want to tune for zero knock, good timing, and a solid A/F ratio. 18psi might be enough for you, but you might find 20 PSI is better.

One more thing. There are sever different 16g turbos. Small 16g, Big 16g, and EVOIII 16g. All slightly different animals.

 

[dsmBear]

If you have the stock turbo, it's a T-25, which is not a good turbo for making power on these cars.

If you go with a 16g, 550s should be fine at lower boost levels, but I would go bigger. Going to a bigger injector doesn't cost a whole lot more, so if you ever want to make more power later on, you won't have to buy new injectors. As far as a fuel pump goes, if you stick with a 16g, a walbro 190 should be enough.

Duty cycle is completely dependent on how far you push your injectors. The more air your turbo is pushing into the engine, the harder the injectors work. That is something you have to watch when tuning/logging. Any logging software will show you your injector duty cycle.

Rewiring the fuel pump; the stock fuel pump circuit is kind of a bottle neck, losing over one Volt from battery to pump. While it doesn't sound like much, it is in fact very significant. Also, it's easy and cheap to do, so there's no reason not to do it. Link

If you stay with a walbro 190, the stock regulator will be fine. Some people report that their car runs fine with a 255 and a stock regulator. I personally wouldn't do that though.

But the biggest question is, what are you going to tune with? In my personal opinion, ECMLink is the BEST option you have. It's more than you'll need, it's reasonably priced, and it is EASY to learn.

I would stay far away from MAF Translators and AFCs. They just don't provide the best solution to tuning, and aren't that much cheaper than ECMLink

Can I ask why you are stuck on setting it at 18psi? Manifold pressure is just a measurement and doesn't mean as much as some people think. More important than manifold pressure is mass air flow (measured in lb/min), timing, and Air/Fuel ratio.

You would make less power at 18psi and no timing, than at 17psi with a bunch of timing. My point is, you ultimately want to tune for zero knock, good timing, and a solid A/F ratio. 18psi might be enough for you, but you might find 20 PSI is better.

One more thing. There are sever different 16g turbos. Small 16g, Big 16g, and EVOIII 16g. All slightly different animals.

Wow thanks for educating me without getting mad at how little I know. I had no idea how important the timing was. I just wanted 18 psi because I thought the more pressure the faster. I've been looking at link and all but its pricy. And my 97 gst ecu is obviously not eprom . Its my daily driver so I can't send it to ecm and not be able to drive to work. I've been looking at aem ems though. Like a used one. But I can handle the price of link, only thing that gets me is how much more do I need to spend on getting my ecu all set up for it.

 

[T is for TURBO]

Wow thanks for educating me without getting mad at how little I know. I had no idea how important the timing was. I just wanted 18 psi because I thought the more pressure the faster. I've been looking at link and all but its pricy. And my 97 gst ecu is obviously not eprom . Its my daily driver so I can't send it to ecm and not be able to drive to work. I've been looking at aem ems though. Like a used one. But I can handle the price of link, only thing that gets me is how much more do I need to spend on getting my ecu all set up for it.

No problem man. I was in your shoes once. But I do suggest reading, and reading, and reading. Read as much as you can before you start to modify. Also maintenance is alway a prerequisite to modifications.

I would suggest you check the DSMTuner classifieds, e-bay, craigslist... People are always selling used ECMLink setups/EPROM ECUs. AEM EMS is not for the faint of heart. The learning curve is STEEP. I wouldn't know where to start. You pretty much tune the car from scratch. Even for a pro tuner it takes a good amount of time and cash. Not a direction I would suggest you take. Plus it's waaaay overkill for a 16g setup.

But take it from me, and I'm sure there are plenty others who will attest to this: ECMLink is, hands down, the best modification (for the price) I've done to my car. And I have somewhere around $25k stuck into my car. I too had to source a 95ECU, and I bought the full version plus the socketing service.

 

[dsmBear]

No problem man. I was in your shoes once. But I do suggest reading, and reading, and reading. Read as much as you can before you start to modify. Also maintenance is alway a prerequisite to modifications.

I would suggest you check the DSMTuner classifieds, e-bay, craigslist... People are always selling used ECMLink setups/EPROM ECUs. AEM EMS is not for the faint of heart. The learning curve is STEEP. I wouldn't know where to start. You pretty much tune the car from scratch. Even for a pro tuner it takes a good amount of time and cash. Not a direction I would suggest you take. Plus it's waaaay overkill for a 16g setup.

But take it from me, and I'm sure there are plenty others who will attest to this: ECMLink is, hands down, the best modification (for the price) I've done to my car. And I have somewhere around $25k stuck into my car. I too had to source a 95ECU, and I bought the full version plus the socketing service.

Thank you. So your saying I can just buy an eprom ecu all set up and swap it with my 97 and the car will still run fine? Because I will get link if that's the case. I have a few tasteful mods where I sit right now, but tuning an ecu just sounds like a fun project!