Can an adj. fuel pressure regulator help a lean L98? I have been advised that I should add the AFPR to the list of things I should do to help the engine with the exhaust mods I've added. Is a AFPR a hard install project? Please chime in.

Joe B.

 

Can't say on an L98 but the istall on my LT1 was a breeze. Maybe 15 minutes.

 

They are rather difficult to install in the L98 motors. If I remember correctly, the AFPR in that is under the upper manifold plenum in between the runners. It is a one day project that isn't difficult, but it is time consuming. It is most likely a 12pk project... meaning you will need to keep a 12pk of your favorite lager on ice for all the times you get frustrated with the crap... but I could be wrong. It has been 4 years since I have done one.

 

Eh, it's not as easy as the AFPR for the LTx engines, but it isnt all that difficult. It will probably take 2 hours or less. It's been a while since I replaced mine, but Im pretty sure you only need to remove the plenum to gain access to it. It will be tight, but you can get to everything you need from there. I replaced mine when I replaced the injectors so I had the entire fuel rail off.

Do this in a well ventilated area!!! Wont hurt to have a shop fan circulating some fresh air.

Bleed off as much of the FP that is built up in the system as you can. Open the gas cap. Allow as much of the fuel in the system to drain from the fuel rail as possible. You will still have some fuel spilling from the old FPR location when you remove it so be sure to have rags ready to absorb it all. Make sure to let all the spilt fuel evaporate before you start up the engine so you dont burn down your car along with where you have it parked.

You will need some security torx bits to remove the mounting screws.

***Note the hole in the tip of the bit***

http://www.cvfsupplycompany.com/tor7pctordri.html

I believe it is the T-10 size.

Hope that helps.

 

If you are running lean at WOT it will likely help; if lean in closed loop there could be another problem. In any case an AFPR is a great tuning device as you make air flow mods.

Installing an AFPR on a L98 is a piece of cake:
-put a fuel pressure gaute on the Schraeder valve
-disconnect the vacuum tube from the FPR and plug the tube
-start the engine and record fuel pressure at idle
-shut down the engine

-remove the linkage & brackets from the side of the plenum
-remove the TB bolts and move it slightly forward
-remove the vacuum lines from the plenum
-remove the upper runner bolts and rap on the top of the plenum to loosen it

-lift the plenum and remove the IAT connector from the bottom
-lay the plenum aside
-carefully depress the core of the Schreader valve on the fuel rail to discharge the fuel pressure
-use the security Torx (supplied with the AFPR) but to remove the FPR bolts
-install the AFPR and carefully tighten the Torx bolts
-install the plenum, TB and all accessorie hoses, lines and cables
NOTE: When installing the plenum finger start all Torx bolts to avoid stripping any; install bolts loosley in one side and then muscle the plenum to get the other side bolts all aligned and started

-start the engine and set fuel pressure to the stock value
-bump fuel pressure by 2-4psi increments till power gains drop off
-then back off fuel pressure by 1/2 tic

Nothing to it; if you are careful on removing the plenum you will be able to reuse the upper runner gaskets and the TB gasket.

 

Yeah.... What said!


Gonna go edit my post now and remove the evidence of my ineptness .....

 

Sorry VetteNoob I'm a slow typist.

 

Well I'm gonna offer my $.02 here, it's the same $.02 that I always offer on this topic.

If you can prove that your A/F ratio is rich or lean across the board, then yes an adjustable fuel pressure regulator may be a cheap and easy way to tune. If your A/F ratio is not linear than it is a miserable attempt at a way to tune a car. By bumping the fuel pressure you may richen it up where it needs to at one point so it makes more power at that particular RPM, but it will likely make it too rich at another point, costing you power. Ultimately you might gain a few HP, but if you really need tuning you can gain more by leaving the fuel pressure alone and adjusting the fuel in the computer.

The AFPR only addresses the WOT situation as well. Under part throttle conditions your car will only see that it is running richer for any given pulse width. As such the computer will start scaling back that pulse width. It has no idea why it has to scale it back, it just knows that it does. The computer knows what your fuel injectors are rated at, so it thinks they are flowing X amount of fuel. In reality you are flowing more than that. As such the computer will THINK you're getting better gas mileage than you really are and all of those fancy readouts on your dash will be completely useless.

If you want it done right you need to get some data logging software and all the stuff required to burn custom computer chips. After you've got all the part throttle BLM's where they need to be, then you get somewhere with a wide band O2 sensor, the dyno is usually the best way here, and you spend some time getting the wide open throttle air / fuel ratio worked out.

Does it take more time? Of Course
Does it cost more money? Hell yes
So why bother? Because it's a real tune, not a cheap band-aid

 

Thanks for response guys. Thanks Jim for the instructions. As usual Nathan, your analysis is food for thought. I have to process the information. Thanks again for your help. I'm going to go drive the car and see if any codes come up, as I said in other threads, the engine light came on, but after I took out the Hypertech chip it has not resurfaced. Lets see what happens, I'm going over 100 miles or so.
I plan on hitting the wot a few times on the Southern State Hwy in NY.

Joe B.

 

The 94-96 PCM will automaticly compensates for changes in FP. Within a few miles of part throttle driving the PCM will change the tables that set the WOT injector pulse width. If you have a 94-96, save your $$.

 

My car is a 91 Coupe. Well I drove the car 135 miles, and at the 125 mile mark the car threw another code #32. Car is running great other wise without the Hypertech chip.

It was a nice ride, opened her up and she responded awesomely. Some guy in a V8 Thunderbird wanted to play, so hammered down and dissapeared in about 9 seconds. Will porbably install the AFPR, and a custom chip to eliminate the code 32, and lastly, the 354 differential. Would like to put those gears in ASAP, but Christmas is blocking the way. Hey, thanks for the help guys.

Joe B.

 

Since you got the code 32 while driving and not at startup, the ECM was calling for EGR and did not detect proper feedback so threw the code. Since I've heard that '90 & '91 L98s do not have the EGR Temp Sw, I'm not sure how the ECM gets feedback when it calls for EGR.

Do you still have the EGR system on the engine?

An easy way to get around that EGR code is to run a 160deg T-stat, as the ECM will not call for EGR till over ~175deg F.

BTW, I run a 160deg T-stat & fan switch all year here in Rockland Co, NY and will be driving to NE OH for the Holiday. Heat is ample and it easily passes OH emissions in the middle of Feb, though I do get oil changed on frequent & regular intervals.