Kenne Bell A/F Questions

[Copperhead]

Hey Guys,

I've got the KB 2.2 running 15psi, Denscharger, Bassani Off Road X and Catback, BAP, and Diablo MafIA (set to 2). My question is fuell pressure. Rick@Amazon is tuning for me, but as I am in TN, not on the Dyno. The problem I am having is that I am datalogging on a Predator, but not seeing consistant Fuel Rail Pressures above 40lbs at WOT.

I checked the voltage coming from the BAP tonight, and at the top setting, it read 17 volts. I bypassed the boost activation switch so I was sure it was running, yet when I drive down the road, I don't get any increased fuel pressure. I am on stock injectors.

What is the problem? I dynoed today and and only made 527rwhp and 460tq. It was lean as hell down low (14.5:1), and then pig rich (10:1) around 4.5k to 5.5 k, then lean again above that (12:1).

Thoughts on fuel pressure? Does the tune control it, or should it be at 60psi regardless? Will it be more than 40psi at cruising and non-boost throttle? I'm getting worried here.

Any help would be appreciated.

Thanks!

 

[Zinc03Cobra]

According to KBs instructions, your fuel pressure should be at 85psi, if I'm not mistaken. I would also not trust the fuel pressure that the predator displays. it's best to get a fuel pressure gauge. That's what I use, and it's very accurate.

It would be best to contact Rick on the matter. Everyone here knows he's very knowledgeable when it comes to these cars. Best of luck! FP at idle should be around 38psi if I'm not mistaken.

It may also be time to upgrade those injectors.. 55/60/72s, good luck doing that, you'll have to remove the blower again.

 

[Copperhead]

Yeah, Injector upgrade is next. Rick is a little baffeld at the low FRP too, but I have a lot of faith in him.

Frankly, you may have addressed my concern. Does the predator read FRPs accurately, Or has my FRP sensor crapped out? I've hit the rev limiter a few times, which is hard on them.

 

[AMB]

Copperhead

The normal idle fuel pressure is 30psi.(STOCK). The fuel pressure should increase with the amount of boost you have. If the "DELTA" is 39psi. (STOCK) than the fuel pressure will be 54psi. at 15psi. boost. The fuel pressure you have depends on what the tunner has the "DELTA" fuel pressure set at for your tune.

AMB

 

[injectedracing]

If your reading FRP, then thats delta pressure which should remain around 39psi. Your maxing out the injectors. Datalog the PW if you can. 39lb'ers can only handle about 520 at the crank. Get some 60's and a new tune

 

[Copperhead]

What is the PW? Are you saying with stock injectors I shouldn't see more than 39 or so at the FRP reading on the predator even with the BAP?

 

[Shadowgray03]

What is the PW? Are you saying with stock injectors I shouldn't see more than 39 or so at the FRP reading on the predator even with the BAP?

PW is injector pulse width, or simply put how long the injector stays open to deliver the amount of fuel needed. Simply put to maintain a safe A/F ration you need so much fuel at a given RPM. The stock injectors only have a certain size apeture so there are 2 main factors that play a roll in how much fuel is delivered. One is the pulse width, or how long the injector stays open. The other is the fuel pressure. Increasing the pressure of the fuel means that more fuel will come out of the injector when it opens for any give pulse width.

Once caveat to blown engines is that our intake pressure does not remain constant which means that at times the fuel pressure needs to be increased to overcome the pressures inside the intake. The increase is fuel pressure needed to overcome boost is generally proportional to the boost level. So, as AMB said if a normal deltaP (fuel pressure) is ~39 and you are at 15psi boost the fuel pressure will go up 15psi to overcome the pressure in the intake (ie 39psi deltap + 15psi boost = new deltap of 54psi).

Now, the stock injectors ARE NOT capable of flowing enough fuel at 54psi deltaP to feed a KB topped engine so one if not both of the following have to be done. Fuel pressure needs to be increased to more fuel flows through the injector when it opens and also the injectro may need to be kept open longer.

If your pulse width is at 100% then they are staying open as long as they can and are maxed. At this point all you can do is raise fuel pressure to increase amount but this has limitations as well. As fuel pressure increases flow decreases.

 

[injectedracing]

This is how KB makes an example. http://www.corral.net/forums/showthread.php?threadid=418287.
Read that. Get some new injectors and a new tune and you are all good.

 

[FoMoCoDave]

Yeah, Injector upgrade is next. Rick is a little baffeld at the low FRP too, but I have a lot of faith in him.

Frankly, you may have addressed my concern. Does the predator read FRPs accurately, Or has my FRP sensor crapped out? I've hit the rev limiter a few times, which is hard on them.

Bring some beer :beer:

 

[Copperhead]

Will do Dave. I changed fuel filters today, and that did nothing. From what everyone is saying though, it sounds like I shouldn't expect to see 60psi at the rails.

 

[Sho Off]

Will do Dave. I changed fuel filters today, and that did nothing. From what everyone is saying though, it sounds like I shouldn't expect to see 60psi at the rails.

You need new injectors, the stock ones will not be enough.

 

[AMB]

Copperhead

Where do you have the BAP installed? Before or after the FPDM? Do you have the wiring upgrade (from the battery to the FPDM)? Do you have MJCHIPs modified FPDM?

AMB

 

[Copperhead]

After the module. I do not know if I have the upgrade or not. The BAP is definitely putting 17volts into the Pump though. That really makes me wonder if I am reading the predator wrong. If I turn the key on, but do not start the car, the FRP shows over 54lbs. But once started, It shows 39lbs, and doesn't deviate from that much.

The question is, while the throttle is wide open with a stock feul system and BAP, what should the FRP read on the Predator? Should it be 39ish because the FI's are wide open and pumping out as fast as fuel is coming in?