tazz

ok,maybe someone could help me with this,i have a 1988 chevy step-side,with the lo5 engine,i rebuild it my self ,got a eagle steel crank shaft,lunati forged steel rod,speed-pro flat top light weigth pistons, the block is a one piece rear main seal bored 0.30 ,the heads are stock swirl type, but massively ported,the intake is the stock one but massively ported ,comp cams276extreme energy roller camshaft with 224-230 duration 503-510 lift with 400pds valve spring and double roller1.5rocker,and double roller timing set ,the tbi is bored and shaved i got the injector spacer and the 454ss injector in it,i modified the stock fpr to adjustable mode ,work well but way to much fuel at idle,buy the vaccum one from goodwrench, install it ,9 psi at idle good,crack the throttle 15 psi good,hold the throttle steady to any rpm and fuel pressure drop back to 9psi, why??? is my vafpr loss vaccum or there' s less vaccum into this beast at steady throttle,my fuel pump is the in line outside the tank15psi one from holley for the tbi. by the way this truck is a little beast it turn on fire 33inch swamper on a dead stop simply by cracking off throttle with 3.42 gear we estimate the hp to be between 375 and 400 and 400 and 435 ftpds of torque at the crank,stang owner cry like baby's wen i look at them getting smaller in my rearview mirror lol.. ok thanks need a little help here!!!

BMmonteSS

The engine is loosing vacume when you crack open the throttle, but when you hold the throttle steady, it builds back that vacume. Thats why your fp drops back down. My engine actually makes more vacume with the throttle held open steadily than at idle.

Your not going to have much luck tuning a highly modified vehicle with just an VAFPR. Once you start changing cams, intakes and TB's you need look into learning to tune your ecm. I'm sure there are some on here that say that mail order chips are fine, and they might be for a mostly stock vehicle, but a vehicle like yours really needs some computer attention.

Fast355

iTrader: (2)

BM is right but I am going to add something, the vacuum level without an engine load will decrease on throttle tip in and come back to normal or higher as the engines speed increases. Put a load on the engine (road load) the vacuum will drop and your fuel pressure will come back up.

The VAFPR is just a band aid for lack of tuning. I use it so that I can lengthen the pulse width at idle so that I can control the injector better.

You really need to look to tuning and prom burning. Winaldl is a freeware scanner that you build a $7.00 cable and get your info from.

The "747" that is in trucks is easy to work with. That is what is in my van.

tazz

ok guy's i already got the hypertech superchip program for my set-up ,i call them and send my spec via e-mail and receve a 450.00$$canadian money order bill,the chip is good they did what they can for the basic computer and the hard set-up that i have but still the engine run to rich at idle,man you should listen to that hot rod when it gets that choppy idle,its like a custom chopper,but because its to rich the computer jump off idle to 1200 rpm to burn the extra fuel ,it idle only 2 to 3 minutes,thats why i really need to stabilise it with the vafpr,man fuel is cosly here in canada1.10$ per liter, premium grade is a must still running 11/1 cr,and forgot to tell i keep the orange spring that came with the vafpr, the 18 psi that this spring give is perfect at hight 6500rpm,spark plug are tan and rubber lay down on asphalt lol, but maybe i could install a vaccum and a remote fuel pressure gage inside the cab this will make tunning lot easier.anyway thanks guy's for answering me,i just have and idea, should i connect 2 vaccum source from different place on the intake into the vafpr,one from the intake port and one from the base of the tbi maybe???ill try it tomorow???

Ronny

iTrader: (1)

tjhis issue has come up often. i ran a vafpr for a while. it would be interesting to log the FP values along with the WB02 values as we do tps - rpm- map with the vafpr installed. run the car on a road course with a lot of WOT then slam on brakes around the corner then WOT for a mile and on and on. the 'puter reads the tps-map-02 and other sensors but not the FP. it may have a meltdown.

ps there is a trird spring between the stock(green?) and the orange vafpr maximum spring. top down solutions.

Fast355

iTrader: (2)

You are lucky you are able to get a speed density setup to idle at all with a mail order chip and that cam. Learn to burn your own chips and you will be much happier. No amount of tuning on the VAFPR is going to make you idle or happy. Not to mention that cam is going to chop some no matter what due to the overlap and duration.

As far as fuel economy you have a high rpm race cam in a heavy truck with 33" tires, a 3.42 gear and I am guessing a 700r4. You are trying to cruise way out of this cams powerband which will make you eat gas. If you are serious about keeping the cam I would want to see your rear gear in the 4.10-4.56 range. That will put you to the 2,600-3,000 rpm cruise range that this cam will want to cruise in. Right now you have a peak torque of probably 3,500 rpm and are trying to cruise at less than 2,000. That will make you guzzle gas. Trust me I found out the hard way too. I had a Comp XE-274H in a 305,(headers, Edelbrock Performer RPM intake, Quadrajet, recurved HEI) in a van with 3.08 grears, 700r4. The thing would flat haul butt, at part throttle in OD just cruising it was a dog. With the cruise set at 70 mph, the transmission would downshift for the slightest grade or head wind. I actually got better MPG (about 16-17 compared to 13-14) in 3rd with my cruise rpm around 2,600 rpm.

tazz

hey ,my 2 vaccum line set-up solve the problem,one at low vac on the intake and one at hight vac at the tbi with 2 delay vac valve,by the way my truck have the getrag 5 speed manual,it is a standard cab with fiberglass complete front end,and stepside fiberglass rear fender,the box is stainless steel custom made by me,the bumper are replace by ss custom one that i made with 3inch ss tubing ,all tig welded,the rear diff is a 14bolt corporate with 6lug (hard to find),front suspension a-arm are all aluminium custom made by me and rear torque arm to,the thing weigth only 1400kilo's about the same as a stock camaro,that's why it is so fast... at 650rpm it sound way cool and at 6500 its scream like a nascar... enought said