Why do you need a AFPR with a 255?

mini zilo · 06-28-2007, 10:31 PM

Can someone please explain it the best they can?

A lot of people say you don't need it, a lot of people say you do.

I would just like to know WHY they are needed with a 255 fuel pump. What happens when you put a 255 on that the stock regulator can't handle? Thanks, just wondering.

GVR4592 · 06-28-2007, 10:33 PM

Too lazy to use the search? This has been covered hundreds of times before.

mini zilo · 06-28-2007, 10:46 PM

Then link me to the answer? I tried searching and couldn't find what I was looking for.

Before your reply:

1. No "Use the Search" replies - answer the question, link to the answer, or don't reply.

I have searched. I read everything they said. I still am not understanding this though. All anyone ever says is, you will overrun your stock FPR. I am just confused as to why some people who are extremely knowledgeable in DSMs say I will be just fine without one, and why other people (mostly on this site) say that You NEED to have one. Can someone just give me the technical explanation.

MrBoxx · 06-28-2007, 10:57 PM

My understanding is that the return orifice on the stock FPR is too small for the higher fuel flow that results from upgrading the fuel pump above the stock level. If there is too much pressure, the fuel injectors will inject more fuel, resulting in an overly rich condition. Upgrading to an adjustable fuel pressure regulator will allow you to drop the pressure back down to stock levels.

mini zilo · 06-28-2007, 10:59 PM

So what happens when it can't return back to the tank fast enough? Pressure just builds in the fuel rail?

MrBoxx · 06-28-2007, 11:02 PM

Pretty much, yes.

8urv8 · 06-28-2007, 11:03 PM

You will be running extremely rich at idle without an AFPR if you are running a larger fuel pump. Some cars are affected by it and some aren't. It's kinda like the whole venting your BOV to the atmosphere debate. It's just better to fork out a little dough for the AFPR and oil filled gauge just for the added assurance that everything is running correctly. Hope this helps. Oh, you should be at 43psi at idle and it should go up 1psi for every 1psi of boost. At 10psi of boost you should be at 53psi of fuel pressure.

mini zilo · 06-28-2007, 11:06 PM

Quote:

Originally Posted by 8urv8

You will be running extremely rich at idle without an AFPR if you are running a larger fuel pump. Some cars are affected by it and some aren't. It's kinda like the whole venting your BOV to the atmosphere debate. It's just better to fork out a little dough for the AFPR and oil filled gauge just for the added assurance that everything is running correctly. Hope this helps. Oh, you should be at 43psi at idle and it should go up 1psi for every 1psi of boost. At 10psi of boost you should be at 53psi of fuel pressure.

Thank you for information, you have been very helpful.

So because of the increased fuel rail pressure, is more fuel coming out when the injector opens because of the higher pressure? Which would cause the problem of running rich?

DGajre777 · 06-28-2007, 11:09 PM

Old man said it best...

Quote:

Originally Posted by oldman

I must say I'm rather disappointed, the amount of mis-information on this thread is just rediculous, some are coming from experience members.

1. 255 or 190 (to a lesser degree) will overrun stock fpr's, 1G or 2G. If you're running without an AFPR and you have a gauge to prove you have no overrun, something is wrong with your fuel system. I'll go ahead and say that most of you claiming no overrun doesn't own a fuel pressure gauge.

2. Much like you can't tune out venting a BOV with stock MAFs, you can't tune out FPR overrun. Why? Because the changes are NON-LINEAR and load based, anyone who claims they can tune it out, please provide detail information as to how, it would be the first.

3. No, higher fuel pressure will not make your injectors leak, there are people out there running 60 psi base pressure, the weak link when running higher pressure is the pump, not the injectors.

4. The smaller the injectors you have, the worse and the longer the duration of overrun.

5. An AFPR isn't just for dialing down base pressure and prevent overrun, it's a handy complimentry tuning tool when used properly.

6. The extra gas money you'll spend on overrun will pay for an AFPR in no time.

I'm not here to argue with you guys, these are facts, not opinions. The only reason this thread isn't closed, OP warned for asking a FAQ question and bunch of negative rep points handed out to some is because there are too many mis-information in here that needs to be addressed. Go ahead and ask follow up questions if you're unclear on my post, if you're going to dispute facts, make sure you bring facts of your own other than "I have been running one without any problems". The debate on this subject is long over, much like venting.

Walbro 255; stock FPR?
A couple questions about fuel pressure regulators

I hope this helps.

MrBoxx · 06-28-2007, 11:12 PM

Quote:

Originally Posted by mini zilo

Thank you for information, you have been very helpful.

So because of the increased fuel rail pressure, is more fuel coming out when the injector opens because of the higher pressure? Which would cause the problem of running rich?

Exactly. As 8urv8 mentioned, it's wise to invest just a hundred dollars or so for an AFPR kit to keep your car running happily. If you don't want to, that's fine, but the "venting BOV" analogy is pretty good: some cars won't seem to run any differently and you may think you have no problem, but do you REALLY know what's going on? DSMTuners members tend to take the safe side of modifications, so this may be why you find that most of the members here will recommend an AFPR when running a 255lph pump (and sometimes even a 190lph pump) while some other people don't recommend it. It's the same with the BOV venting thing. Tons of people do it, say their car doesn't suffer from it, and encourage it. Here at DSMtuners, we all know that it's not the wisest thing to do (without a MAFt/speed density/MAP setup), so we don't encourage it.

kenamond · 06-28-2007, 11:22 PM

Quote:

Originally Posted by mini zilo

Thank you for information, you have been very helpful.

So because of the increased fuel rail pressure, is more fuel coming out when the injector opens because of the higher pressure? Which would cause the problem of running rich?

Exactly. The injectors are rated based on the upwind fuel pressure. If you open an injector for X milliseconds at 43.5psi it will flow less fuel than if you open it for the same period of time at 45psi.

There are two ways out of the fuel rail: FPR and injectors. When the FPR is overrun, the fuel pressure is too high. As you increase RPM and/or load on the engine, more fuel is getting through the injectors. Eventually, you can reach a point where the injectors are letting enough fuel out that the fuel pressure is back to normal, but that depends on how bad the overrun is.

mini zilo · 06-28-2007, 11:28 PM

Ok, so the only harm that is happening is running rich (and wasting fuel)?

GVR4592 · 06-28-2007, 11:29 PM

Quote:

Originally Posted by mini zilo

Then link me to the answer? I tried searching and couldn't find what I was looking for.

Before your reply:

1. No "Use the Search" replies - answer the question, link to the answer, or don't reply.

I have searched. I read everything they said. I still am not understanding this though. All anyone ever says is, you will overrun your stock FPR. I am just confused as to why some people who are extremely knowledgeable in DSMs say I will be just fine without one, and why other people (mostly on this site) say that You NEED to have one. Can someone just give me the technical explanation.

Don't quote the rules to me, you obviously didn't read them yourself before you posted.

http://www.dsmtuners.com/welcome.php

Now for the links you requested.

Fuel pressure clarification/$70 fpr

B&M commandflo AFPR any good??

Injector suggestions t3/t4 16psi

Fuel Pressure Regulator question

When do you absolutely need a non-stock fuel pressure regulator

Fuel Questions

S-AFC with Stock Injectors

255 fuel pump- overkill?

Do I *need* a fuel pressure regulator?

Is that enough or do you want more?

mini zilo · 06-28-2007, 11:37 PM

Thanks for the links, I appreciate the help.

However I got the responses I was looking for in my thread. I just wanted to know the technical explanation.

You know yourself that it sucks to have to go through tons of threads that are named one thing, but turn into another, and waste you time while you are looking for something.

We obviously both didn't follow the rules so let's not point fingers. I appreciate the links. You see what I mean though? Simply searching AFPR and 255 comes up with people talking about how to set the pressure, I was just looking for a good explanation as to WHY you need one. I have had extremely reliable sources tell me that you don't need one, and others say you do. I just wanted to set the record straight.

GVR4592 · 06-29-2007, 06:40 PM

The problem is you limited your search to those two keywords, try using different words next time. I used "regulator" and "overrun", I found a post that mentioned the orifice was too small, then I changed my search to "regulator" and "orifice" It took me less than 5 minutes to find those links, I can do the same for any subject, so everybody else should be able to do it as well.

2mchtoy · 07-01-2007, 11:35 AM

Quote:

Originally Posted by 8urv8

You will be running extremely rich at idle without an AFPR if you are running a larger fuel pump. Some cars are affected by it and some aren't. It's kinda like the whole venting your BOV to the atmosphere debate. It's just better to fork out a little dough for the AFPR and oil filled gauge just for the added assurance that everything is running correctly. Hope this helps. Oh, you should be at 43psi at idle and it should go up 1psi for every 1psi of boost. At 10psi of boost you should be at 53psi of fuel pressure.

You can not explain it any better than that!