This is probably a completely bonehead quesiton but:


I checked my fuel pressure last night (just hooking up a gauge to the fuel rail, I didn't disconnect any vacumn lines or anything) and it was 38psi at idle and surged a few (5?) psi when I hit the gas with the car in Park.

I have bought a TPIS adjustable fuel pressure regulator and I notice it comes with new gaskets for the plenum. No problem, I was planning on porting the plenum anyway so I'll do it all at the same time to save me having to buy another gasket.

But, if I understand correctly, I need to take the plenum off, fit the AFPR and in order to set the AFPR I need to start the engine? So I have to reassemble the plenum and so on obviously. No problem.

And to set the AFPR I leave the vacumn line to it disconnected and with the engine idling set it to 48-49psi?

If the AFPR is under the plenum how do I get to the screw on top to adjust it without having to keep taking the plenum off? (or to plug the vacumn line back in when I'm done for that matter!)

Surely I don't need to keep taking the plenum off or it'll cost me a mint in gaskets?!

 

Any AFPR is adjustable with the plenum still on. It's not the most convient adjustment, but it can be done. I don't like to adjust mine with the engine running because of how close you have to get to the ignition wires >>>> ZAP! Also, with a AFPR, you don't just want to pick a number, set it, and forget it. This is one more thing on your car that you can tune now. Experement with it and set it where your car likes it best, which could very well be at the stock 43.5 psi.

 

How would I know what pressure to set it to?

Would I have to take it to a chassis dyno and run it several times?

Or would using my gTech to tune it be enough (I would have thought that slight variences in driver technique would skew the results mind).

 

Ideally, you would go to a chassis dyno with a wide band O2 sensor and set the pressure so that you get about 12.8 to 13.0:1 AFR.

OR you can go to the dragstrip and whatever fuel pressure gives you your highest trap speed is yielding you the max power.

 

12.8 to 13.0 ratio? Isn't that a bit lean?

 

Install a underhood Fuel Pressure Gage. Problem solved. Parts needed: Fuel Pressure Gage. 3ft SS breaid line. mounting pod.
All available at Summit for about $100 total.

 

12.8-13.0 would be on the rich side, probably where you'd want it at in PE mode..

 

i put on a holley afpr and its great fully adjustable with 2 fingers. ,,, question on pressure setting

before i changed my fpr the stock one was at 40 psi. i thought that stock was suposed to be at 42-43. when im at 42-43 i loose 2 tenths in the 1/4. am setting it to high? or do i need to unhook anythign for a proper feul pressure reading? ? what is stock for a 91 5.7 tpi? im thinking of dropping to 40 or less but dont want to risk running lean..

any help???


-tony

 

ARGH!!! I ALWAYS DO THAT.

For some reason I always put fuel first, when I know better... must just be stupid.

 

Double posting n00b.

 

Well I set it to 48 (with vacumn disconnected) as per the TPI instructions. I have a pressure gauge but only to hook up to adjust, considering it has a habit of leaking I'm not gonna leave it hooked up...
I'll take it down to a chassis dyno that has a wideband in a few weeks.

Hard to say if it is the right setting as it happened to be a cold night when I tried it but the car seemed a lot faster in the 60-90mph range.

Could be a placebo effect of course and only the chassis dyno will tell.
I'm not consistent enough at the track yet to use that as a tuning tool as I've only made one visit there so far.

It is adjustable with the plenum on, but only just as the nut is too tight to turn with my fingers (teeny head on it as opposed to the Holley) and can just about get pliers in there.


Thanks for the help and advice guys!

 

FocusGhia,

are you heavly moded? the vaccume you are talking about is the one connected to the AFPR? because i left it on like a dummy when i was adjusting.

the holley is very nice. wouldnt use any other.


-tony

 

I unplugged the vacumn pipe that goes to the AFPR when I adjusted it to 48psi.


I have only just started modding the car.

The car was standard except for being decatted when I bought it in December.

So far I have done the following mods:


TPIS Air Filters
Cut bottom of air box off and removed obstructions in top lid
Removed obstructions in plenum behind throttle body bores.
TPIS Adjustable Fuel Pressure Regulator set to 48psi
TPIS Throttle Body Airfoil
Descreened MAF sensor
275/50R15 BFG Drag radials on 15x10 Weld Draglites

And after I have got the base timing corrected (currently 18deg BTDC apparently) I will be adding:

Throttle Body Coolant Bypass
TPIS HT Leads
New spark plugs
Performance Resource PROM


And before hitting the track I will have fitted a B&M transmission cooler too.

Then I will switch the rear end gears from the 2.72 to 3.43

With all these mods and the tyres I'm hoping for mid 14s and will then sort out some rear suspension bits and chassis bits to try and get to low 14s.

So not heavily modded just starting out really.
I don't plan on doing much more to this engine anyway as I would prefer to drop in a 383 or blown 350 or something as a cheaper way of getting the 600BHP or so that I want.
But money is an issue (as always) and I have enough to get on with for now before I can start saving for that sort of thing...

 

I have pretty similar mods, along with hooker 2055's ceramic coated headers, no cats, flowmasters, and im able to run 13.6-13.5 range. im trying to run low 12's hopefully by next summer.. im saving now for the bbsdesigns turbo kit. good luck

 

Headers and exhaust will go on after that lot.

I'm trying not to get my hopes up too much with regards to track numbers.
If I could sneak into the 13s with my 305 and all the bits we've mentioned I'd be absolutely over the moon...

 

hey guys i am trying to figure out what is wrong with my 87 gta 350tpi. i have a stock fpr and i am running very rich. i checked the pressure with the vac lines on at idle and the lines off at idle i get 36 pis and 43 respectivly now i want to go to an adjustable one an i see that you guys set your afrp to 48 with vac lines off would that make my car run richer. i mean to ask if the higher the psi number the richer the mixure?? or no. i know my injectors dont leak and the rails hold pressure when the car is off but i turn the key on and let the fuel pump go on it read 43 then drops about 3 psi and stays.

 

I haven't checked mine since adusting it.

Presumably you mean you run rich at full throttle as the car should adjust your mixture by monitoring your o2 sensor in your exhaust.

I read one place that raising the pressure causes more fuel to go through the injector for the time it is open, thus causing you to run richer.
But I read somewhere else that the fuel burns better thus meaning you go a bit more lean.

So I won't know until I get mine checked ona chassis dyno with a wideband sensor up the exhaust...

 

no may car runs to rich at idle and fine at wot it passes the sniffer tests at 2500 rpm but not at idle. i have to many hyrdrocarbons almost double!!! at idle but i a well below at 2500 rpm and my co output is well below at both rpm speeds. i am trying o figur eout what the heck is going on. i have a heated o2 sensor, a new egr, no leaky injectors or fuel rail. stock chip for 730 ecm i changed it from maf to sd. my ecm throws no codes... what the hell. pressure holds fine at 36 psi at idle and at wot it is 43 psi. sounds like normal settings from what i hear. so if i get an afpr and adjust it lower think it wil solve my problem or is something else wrong?? i know lowering the pressure will lean it out but is that what is causing this or is something else wrong?

 

i forgot to mention i have flowtec headers with smog tubes. a 160degree t-stat and a throttle body bypass kit an air foil and a k and n throttle body air filter.

 

you have cats? if you have the low temp thermastat and the fans on at lower temps it can be play a problem with the full combutstion. GM built the cars to run hot to help with emissions. might help you pass. Also you might want to do a tune up . new plugs/wires/bap/rotor. any corosion on the cap might give you a week spark at idlol..

lowering you pressure may work but i wouldnt run the car very long. as you might hurt the motor. Id only runt the lower pressure for the sniffer and raise it when done. Id look to other ways to pass, it may be something simple your overlooking.


-Tony

 

i did the plugs wires cap and rotor still same problem. it seems very weak at all points though not just idle and runs very rich at all points but it passes the sniffer at 2500 rpm not at idle. i want tit to run like it used to before i swicthed over from maf to sd. the car had ***** of steel. i think i just have to tune the chip but i cant get my max232 circuit working. i am going to turn the pressure down just to pass then turn it back up and do my tuning. thanx for the advice

Nate