Checked Fuel Pressure Today

FORSFED · 11-22-2003

Well I rigged my gauge up to the windshield and here are the things I noticed.

- Base pressure was 42psi
- car has vac reading of 16 and raising it to 0 the pressure stayed at 42 and didn't raise 8 psi like I believe it should have. (probably due to the walbro 255 pump flowing more at idle....)
- At 10psi of boost, fuel pressure was 52psi
- Boost creeped due to 2.5" exhaust and fuel pressure increased with it.
- Car spools to 10psi by 3k, but misfire keeps occuring around 4800rpm, long after it's been at 10psi
- A/F ratio stays right around .9V and does not drop or increase
- minimal counts of knock ( 4-5 counts max)
- no timing retardation

only mods are 2.5" catback exhaust and walbro 255 pump

I'm thinking that this is too high of pressure and volume for the stock setup and that I'd need an adjustable regulator to lower the pressure down a ways...

**JET** · 11-22-2003

What car? 43 psi is right for a 2g, 38 psi for a 1g.

FORSFED · 11-23-2003

It's a 1g.

Pushit2.0 · 11-23-2003

plugs, wires, coil pack, bad grounds, bad gas, boost leak, clogged fuel filter, a problem with the turbo. It could be a few things. Fuel pressure sounds normal for a 255 and stock regulator.

~John

A//// Guy · 11-23-2003

I think you should post what you have done already, as many many of the things people will suggest were already mentioned in five other threads on this same topic.

Im assuming all the basics were done... (johns post)

FORSFED · 11-23-2003

Good Idea, I forgot not everyone knows what I've tried....

plugs
wires
coil pack
transistor
injectors
fpr
fuel filter
fuel pump
mas
fixed vacuum leaks
cbv
tps
cas
ecu

I think that's it, there might be something I've forgotten, but that about sums it up. Reason I think the pressure's too high is because when I disconnected the fpr vacuum hose it didn't misfire once....therefore lowering the pressure while making sure not to go too lean should fix my problem.

**Shane@DBPerformance** · 11-23-2003

What is the problem with the car? And how did unplugging the FPR line help exactly? I thought it ran the same pressure at 0 psi as at -16 vacuum. did you boost with the line unplugged or something?

Pushit2.0 · 11-24-2003

Then you need to buy a realy fuel pressure regulator, or turn the boost up. You could also use a wideband o2 sensor for tuning, it is my guess you are running WAY to rich if you only have exaust and a fuel pump. mo boost or a real FPR.

~John
ps. the B&M is a waist.

FORSFED · 11-24-2003

The problem with the car is that it severely misfires in every gear from ~4800 rpm's and up. The car does run the same fuel pressure regardless of whether there is 16-18psi of vacuum or there is 0, the fuel pressure always remains at 42psi, but it does rise to 52psi with 10lbs of boost so I know the fpr is doing its job. Then out of curiosity I unplugged the vac line on the fpr, and the fuel pressure naturally stayed at 42psi even when I stepped on it with 10lbs of boost. It ran fine up to redline like this, so I've been able to determine that there's too much fuel, and with that I planned on getting myself a regulator as john suggested and a boost controller is on the way too. Once I have these things it'll be a matter of fine tuning it so that the fuel curve is linear and the car doesn't run too righ or too lean anymore. Basically I was just looking for some input from you guys to see what your thoughts and suggestions were, that is why I keep posting what I've been doing and what has resulted.

**Shane@DBPerformance** · 11-24-2003

Maybe pull the lower honeycomb out of your MAS, that should make it run a little leaner across the board.

unreal808 · 11-24-2003

What plugs? NGK? and #

**JET** · 11-24-2003

If it idles fine, you don't need an AFPR. The regulator is going to get overflowed the most at idle, since the car is injecting the least amount of fuel then. That means more must go back in the tank, but it can't because the FPR is too small.

Sounds to me like a air to fuel ratio problem, or more like a spark problem. Check the gap on your plugs. You should be using NGK BPR6ES or BPR7ES gapped to .026" - .028". If that doesn't fix it, I would look at getting some new plug wires.

FORSFED · 11-24-2003

JET, the car idles perfectly fine and to answer your and unreals question, I am using new BPR6ES plugs gapped at .028 that the previous owner installed. When I got the car they were at .032 so I tried .030 and then .028 without much of a difference. The plug wires were also new and they are the yellow accel wires. Do you still think I should try a different set of wires then, could wires make that much of a difference?

**Shane@DBPerformance** · 11-24-2003

Pull out lower honeycomb or add an AFC?

redline · 11-24-2003

i had this car before you and tried both ngk and accel wires, to which made no diff.
also the car had a hacked mass on it, which i tried on another car and it worked fine. the mass it has now came off a good running car, which is unhacked.

redline · 11-24-2003

also the odd thing about the problem is that it remains completly consistent under diff. boost amounts. i even propped open the wastegate flapper and made only about 4psi of boost and the problem was exactly the same. thats why i thought it would be a problem with an electrical componet.

FORSFED · 11-24-2003

Hi Brandon, I was wondering if this might catch your attention! I was wondering if you had tried other wires or not, cuz I knew the accel's were new and I didn't feel like going and buying a new stock set. I've pretty much exhausted every electrical thing I can think of unless there's maybe a sensor I'm overlooking, so I don't think it's that. Then I got to looking into the fuel pressure more and it seems to be functioning properly except maybe being a tad too high compared to stock... what do I know though? Obviously not enough to fix this stupid pig!

**JET** · 11-25-2003

Well, it sounds like it is either ignition or A/F ratio. I would check out the coils. I have a set you can swap in if you want. If that doesn't do it I would get a SAFC and let Shane dynotune it for you.

redline · 11-25-2003

as he said before i tried another pair of working coils and it made zero diff. what kind of threw me off is if you rev it at idle, no load, it will go fine with no misfire, only under load. so by taking out the majority of the boost and having the problem persist would pretty much rule out compression related issues, so it must be something with the fuel system. although i thought in another post you said you had a afc hooked up and by lowering your upper-rpm fuel trims you were able to elminate the miss, but your o2's were very lean. like .76-.8 . i kinda wonder how accurate the stock o2 sensor is though. we just did some logs on mine with a big16 and stock injectors and even down to 11-12psi we were seeing o2's around .78-.80
but still had low knock and decent timing. i think i would try the afc route and go have it tuned on the wideband. i think you have tried just about everything else. :headache:

FORSFED · 11-25-2003

Jet, I did try the working coil from my other car without any difference.

Also worth mentioning is that Brandon had this car for a few days before I ended up with it and he basically tried everything that I did. I did not know this and that's why I proceeded to try fixing the easy stuff.

Yes as you guys remember I did try leaning out the afc that I installed in the car and the misfiring dissappeared. Not only were the o2's low, but I had hellatious counts of knock along with timing retardation as the o2's decreased doing a 1st, 2nd, and 3rd gear pull. That is why I zeroed the afc again as I don't want to ruin the car. The A/F stays pretty solid around 0.90 - 0.92 even when misfiring, so I don't know that it really is too rich or not. I know the best thing to be would have a wideband or dyno it, but this is my daily driver and I don't want to spend that money on it.

The only bit of luck I really had was when I replaced the 3" intake pipe with the stock accordian and hooked up the evap canister hose and valve cover vent hose. At the same time I also put in the cas from my other car. After doing these two things I took it for a drive and the misfiring was nearly completely gone. The only thing I heard were a few lean pops every now and then on the top end. This didn't last more than one run with the car because later that night I went out again and it was beginning to misfire again. That has me stumped...