1995 3000GT VR-4: AEM Adjustable Fuel Pressure Regulator

• Why Do I Want To Do This?

  • Short Version: If you're running a larger-than-stock fuel pump, you've hot-wired your fuel pump, or both, your OEM fuel pressure regulator is not likely to be keeping your fuel pressure constant as you drive your car. A constant (differential) fuel pressure is an important factor in your ECU's ability to properly control your fuel injectors and deliver the correct amount of fuel to your engine. If the ECU delivers too much or too little fuel to your engine, it can cause drivability problems, poor gas mileage, and even engine damage. As much as possible, you want your fuel pressure to remain constant across the whole range of engine operating conditions.
  
  
  
  
  • Additional relevant information about my car's current setup is as follows:
    The powertrain is largely stock with the exception of an air filter, a downpipe, MSD ignition coils and wires, and a Supra fuel pump. The injectors are the factory injectors (80k miles) and have been cleaned and balanced by RC engineering (360cc +/- 1cc) within the last 500 miles. I have a Defi differential fuel pressure gauge, and all fuel pressure measurements are assumed to be differential with respect to manifold pressure. Knock information comes from the '94/'95 Hybrid Datalogger by Mirage Corp. For testing purposes, my boost controller was set to stock boost (~11psi) and my water/alcohol injection was turned off. Both oxygen sensors have less than 10k miles on them and are about a year old. The fuel filter has about 15k miles on it, and I always use Shell 92-octane gasoline.
  
  
  
  • More Problem Details:
    If the fuel pump is wired according to the RDR Fuel Pump Rewire Method, I see a slight (1-2psi) drop in fuel pressure as load increases toward the fuel pump voltage transition. I believe this is a result of the Supra pump's inability to flow enough fuel at this load with the reduced (8-9V) voltage. At the fuel pump voltage transition, fuel pressure spikes about 3-4psi over normal (total change 4-6psi). My suspicion, based on datalogs, is that this fluctuation in fuel pressure causes the ECU to be unable to set the fuel trim values to ensure proper fueling under light to moderate loads.
  • If the fuel pump is hotwired (~13V constant), then the OEM fuel pressure regulator is unable to lower the fuel pressure to normal (43-45psi) under low-load conditions. This results in a fuel pressure of around 51psi at idle, and this pressure decreases to 45psi as load increases. Once the fuel pressure decreases to 45psi, it stays there as long as fuel demand (IDC) remains constant or increases. Again, my suspicion, based on datalogs, is that this fluctuation in fuel pressure causes the ECU to be unable to set the fuel trim values to ensure proper fueling under light to moderate loads.
  • Some may argue that this fluctuation in fuel pressure (~6psi) is not significant enough to be a problem, but based on my datalogs and findings after installing this AEM FPR, I contend that it is a problem. I cannot say for sure whether this is unique to my particular car or typical of all 3000GTs and Stealths, as I have not tested other cars. However, based on what I've read of others' experiences, I believe a significant number of other owners have experienced these problems. The main symptoms I noticed after installing my Supra fuel pump were throttle-transition knock (knock when you abruptly open the throttle plate) and low-RPM/part-throttle/high-load knock (such as when you're at 40% throttle in 5th gear on the highway and you build reasonable boost). I tried having the Supra pump installed with the RDR Rewire method and with it simply hotwired to the battery. The hotwire setup actually made things *worse* in my car, so I encourage all owners with hotwired Supra pumps and the OEM regulator to datalog somlow-RPM/part-throttle/high-loade "regular" driving and look for knock at throttle transitions or low-RPM/part-throttle/high-load conditions. Note that during all of the aforementioned experimentation, I rarely saw significant knock at sustained WOT (wide-open-throttle), even up to 15psi of boost.
  
  
  
  • Supporting Data: Here are some graphs of some of the many data logs showing the types of knock I experienced with the Supra pump installed with the OEM fuel pressure regulator. The first two are typical of what I saw with the fuel pump wired with the RDR rewire method. The last 5 graphs are with the Supra pump hotwired. Note that the knock is both more lasting and more severe with the hotwire method.
    
    

    	3rd Gear, Partial Throttle, Building Boost
    	This data is with the Supra fuel pump wired with the RDR rewire method (switched voltage) and the OEM fuel pressure regulator. From 141sec to 145sec, I slowly increased the throttle from closed to a little over 30%. As load increased above 40% (raw load of 64), some mild knock (2) appeared. As soon as the load dropped, the knock disappeared. During this time the ECU was in closed-loop mode with an A/F target of 14.7:1 (shown by the oscillating O2 voltage). Ignition timing was in the mid- to low-30s and RPM was between 2000 and 3000.
    	4th Gear, Partial Throttle, Building Boost
    	This data is with the Supra fuel pump wired with the RDR rewire method (switched voltage) and the OEM fuel pressure regulator. From 206sec to 212sec, I slowly increased the throttle from closed to a little over 40%. As load increased above 60% (raw load of 96), some mild knock (2) appeared. The knock stayed around until the load dropped below 45%. During most of this time the ECU was in closed-loop mode with an A/F target of 14.7:1 (shown by the oscillating O2 voltage). For a brief time (abut 212sec to 213sec), it appears that the ECU went into open loop mode, but the O2 voltage was only 0.85 or so, which is relatively lean for open-loop. Ignition timing was in the mid- to low-30s and RPM was between 2500 and 3200.
    	6th Gear, Partial Throttle, Building Boost
    	This data is with the Supra fuel pump hotwired (~13V constant) and the OEM fuel pressure regulator. From 36sec to 42sec, I slowly increased the throttle from 20% to a little under 40%. As load increased to the high 40% range (raw load in the 70s), some mild knock (2) appeared. The knock got worse as load increased, and it did not go away until the throttle was reduced back to 25% and load dropped back to the 35% range. This knock lasted for 3 whole seconds and peaked at 6. It did not show any signs of going away until I backed off of the throttle. During most (perhaps all) of this time the ECU was in closed-loop mode with an A/F target of 14.7:1 (shown by the oscillating O2 voltage). Ignition timing was in the low-30s and dipped into the high 20s as load increased. RPM was between 2000 and 2100 RPM the whole time.
    	6th Gear, Partial Throttle, Building Boost
    	This data is with the Supra fuel pump hotwired (~13V constant) and the OEM fuel pressure regulator. This one is pretty much the same as the above data, except that the knock peaked at 4, which is a little less severe.
    	5th Gear, Partial Throttle, Building Boost
    	This data is with the Supra fuel pump hotwired (~13V constant) and the OEM fuel pressure regulator. Same type of thing in 5th gear. Knock at will if I allow boost to build with partial throttle. The ECU is still in closed-loop mode and timing is in the low 30s.
    	5th Gear, Higher-Partial Throttle, Building Boost
    	This data is with the Supra fuel pump hotwired (~13V constant) and the OEM fuel pressure regulator. Here's what happens if I give it a little more throttle (55% or so) and allow the ECU to go into closed-loop mode. The O2 voltage makes it up to 0.90V, and we still get knock.
    	4th Gear, Quick Throttle Transition, Building Boost
    	Here's what happens when you go from under 30% throttle to floored (100%) in a fraction of a second and hold the throttle floored. The knock count is at 5 even before the throttle is fully open, and knock is up to 14 once the throttle is fully open. The throttle is wide open for over a tenth of a second before the O2 voltage gets to 0.9V. The ECU pulls the timing all the way back to 12 degrees to combat the knock. The knock tapers off and finally goes back to 0 exactly when the throttle begins its decent. This situation did not occur often, but I don't want it occurring at all!

  • Other Benefits of the AEM FPR:
    There are other options for those wishing to install an aftermarket fuel pressure regulator, but this is the only one I know of that does not require remote-mounting the FPR. If it weren't for the big AEM logo and the red color of the FPR, one might assume FPR and adapter plate came on the car from the factory. It really looks like it belongs there. Also, for those wishing to keep everything looking as close to stock as possible, AEM does offer the FPR in a silver color.
    
    The most significant benefit of this particular FPR (to me) is that it does not require you to run fuel lines all over your engine bay to remote-mount the FPR. I see this as a huge safety and convenience benefit, in addition to its cheaper cost (vs another regulator and the associated fittings and lines required to connect it).
  
  
  




• How Long Will It Take Me To Do This?

  Note: This does not include time to perform any pre- or post-tasks.
  
  
  • First Timers: 180 minutes
  • Seasoned Enthusiast: 90 minutes




• Anything I Should Do Prior To Attempting This Procedure?

  • Release the pressure from your fuel system. This is done the same way as when you change your fuel filter.
  • Make sure you have a well-ventillated work area that has no sources of open flame or sparks. You will be working with gasoline, and the fumes are both highly flamable and hazardous to your health. Work outside if possible, or at least open your garage door all the way and get some fans blowing air through it.




• What Mitsubishi Parts Will I Need?

  • None.




• What Other Parts Will I Need?

  • Mitsubishi-Honda Fuel Rail Adapter Kit
  • AEM Adjustable Fuel Pressure Regulator




• Where Can I Get the Stuff To Do This?

  	Part	Company/Contact	Part Number
  	AEM Adjustable Fuel Pressure Regulator	Altered Atmosphere Motorsports	AEM 25-303
  	3000GT/Stealth Fuel Rail Adapter	Rob Beck (e-mail) or Rob's 3Si Thread with Details	N/A





• What Tools May/Will I Need?

  • 5mm Allen Wrench
  • 9/64" Allen Wrench
  • 9/32" Allen Wrench
  • 5/16" Wrench
  • 1/4" Drive Socket Wrench
  • 10mm 1/4" Drive Deep Socket
  • 3/8" Drive Torque Wrench
  • 19mm 3/8" Drive Socket
  • Small Curved or Straight Pick
  • Masking Tape
  • Latex Gloves
  • Paper Towels or Shop Towels
  • Clean Engine Oil
  • Pliers
  • File, Dremel, or Small Grinding Tool
  • #2 Phillips Screwdriver
  • Bench Vise or something similar
  • Fire Extinguisher (better safe than sorry)




• Erik's Review

  • Woohoo! This thing rocks. The adapter plate fits like a charm and is easy to install. The regulator works beautifully and keeps my fuel pressure constant under almost all conditions. I occasionally see it rise by 1psi under high vacuum (engine braking) or drop by 1-2psi at high RPM. The rise under engine braking is a) very small and b) only when the injectors are off, so I don't think that's significant. The drop at high RPM is somehting I haven't been able to explain yet. I don't think it's that the fuel pump is not able to flow enough fuel because I see the same drop in fuel pressure whether the target fuel pressure is 43psi or 48psi. If you've got an explanation, please let me know. It doesn't seem to cause problems at this point, so I'm leaving it alone.
  • After resetting the ECU putting a few hundred miles on the car, my throttle-transition knock and my low-RPM/part-throttle/high-load knock are drastically reduced. I still see a little knock every once in a while under low-RPM/part-throttle/high-load conditions, but it's generally in the 1-2 range and it's very infrequent. I still occasionally see some throttle transition knock, but again, it's significantly less frequent, and it generally doesn't occur unless I'm running higher-than-stock boost. This is a huge change from the previous setup (hotwired Supra pump with OEM regulator) where I could get knock counts of 3-7 virtually on demand under low-RPM/part-throttle/high-load or when punching the throttle in 5th or 6th on the freeway.
  • Additionally, I've found that with the fuel pressure set between 43 and 48psi, the smallest (black, pre-installed) discharge port for the AEM FPR works just fine.
  • As I have more time, I'll probably play around with my fuel pressure a little more. As long as the pump can keep up, I'll probably bump it up 5-10psi to get some extra flow out of the stock injectors. I've run it at 48psi for a couple days now, and it seems to work fine. My fuel trims have come down from their previous settings, and the car seems to run great.

The Procedure

	AEM Regulator Kit
	Oops, technically, the lock washers on the right side of the picture belong in the picture below with Rob's kit. Everything else is correct, though.
	Rob's Fuel Rail Adapter
	Also included in the kit, but left out of the picture, is an o-ring for the fuel rail adapter.
	Unbolt Wiring Harnesses
	On the passenger's side of the intake plenum are 3 wiring harness connectors. The OEM setup uses two 10mm bolts to secure the harness bracket. As you can see, I have the ek2mfg cover plate installed, so I had to remove two 5mm allen bolts.
	Disconnect Wiring Harnesses
	Disconnect the three wiring harnesses so you can move them out of the way.
	Disconnect TPS Harness
	There's a little clip that secures the harness. Using a pick or small screwdriver, remove the clip - be careful that it doesn't fly off somewhere! After the clip is removed, the harness will just slide off.
	Pull Wiring Harnesses Out of the Way
	Since you have all four harnesses disconnected now, you can pull them toward the front of the car so they're out of the way.
	Remove Rear Valve Cover Breather Hose
	The hose just slides off of the nipple on the rear valve cover.
	Remove Fuel Pressure Regulator Vacuum Hose
	Clear Out Area Around Fuel Pressure Regulator
	Move out of the way, and disconnect if necessary, any PCV hoses, spark plug wires, or other miscellaneous stuff that might be necessary to get some working room. You'll also want to stuff some paper towels or shop rags or something absorbent under the FPR to catch the fuel that will come out when you remove the FPR from the rail. Plan on catching 4oz (0.5 cups) if you de-pressurized your fuel lines like you're supposed to. You DID de-pressurize the lines, right?
	Unbolt Stock Fuel Pressure Regulator
	There are two 10mm bolts that secure the FPR to the rail.
	Remove Fuel Pressure Regulator from Fuel Rail
	Just pull it out - you may find that rotating it as you pull may make it come out easier. You might want to don your latex gloves at this point, lest you get fuel all over your hands and have your wife complain that you reek of gasoline and... well, nevermind.
	Loosen Return Line Clamp
	The rubber hose attached to the bottom of the fuel pressure regulator is the fuel return hose that returns unused fuel to the fuel tank. You'll need to remove the clamp to get it off of the FPR. Squeeze the tabs together and slide it down the hose.
	Remove Fuel Pressure Regulator From Return Hose
	At this point, you just need to get the hose off of the FPR. Warning: this part may cause you to bleed. If the hose has been on there a while, then it's probably pretty stuck onto the nipple on the FPR. I used a combination of twisting the FPR back and forth, gently prying between the end of the hose and the FPR, and good ol' fashioned "yank the crap out of it" to get it off. Just be careful not to damage anything if you get frustrated. It WILL come off. Eventually.
	Transfer O-Ring From FPR to Fuel Rail Adapter
	If your existing o-ring on the FPR is still in good condition (mine was), then you can reuse it if you like. I found that using a curved pick made the removal of the o-ring easier. Install the o-ring (or a new one if you like) on fuel rail adapter.
	Seal Off All Openings Near FPR
	Since you're going to have to do some filing, sanding, grinding, or cutting of metal in the general area, you'll need to seal off any openings where metallic dust could enter the engine. This includes the fuel rail, the rear valve cover breather port, the rear valve cover breather hose, the fuel pressure regulator vacuum line pipe on the throttle body, and the fuel return hose. I used painter's masking tape (the blue stuff) as it doesn't leave a residue and is easy to work with. If you like to keep your engine bay clean, you may also want to place some paper towels or shop towels in the area below the FPR to catch the metallic dust that falls down there.
	Remove Material from Rear Head Protrusion
	You'll need to trim this rectangular protrusion on the rear head so you can get a wrench on the rear bolt for the new fuel pressure regulator. I used a Dremel tool to chop off the top of it, and a file to finish off the edges. I also filed down the bottom corner a little just to be absolutely sure that there was no interference between the rear head and the new FPR. Shown are before and after pictures.
	Install Fuel Rail Adapter
	Put a little (tiny!) bit of clean engine oil on the o-ring, and it should slide right into the fuel rail. If you get a lot of resistance, back off, and try again. You don't want to tear the o-ring. Once the adapter is fully seated in the rail, use the provided screws to secure it to the rail. The torque spec for the stock bolts is 9 lbf-ft, so that should be fine for these.
	Clearance the Edge of the FPR's Banjo Bolt
	Assemble the AEM fuel pressure regulator and place it onto the fuel rail adapter as it is to be installed. Note which side of the banjo bolt will be closest to the coolant neck. This was a really tight spot on my car, and I wanted to be absolutely sure there was no interference. This step may or may not be necessary. That said, I slightly filed down the edges of two of the sides of the 6-sided bolt, as shown in the picture. If you're using a vise to hold the bolt while you file it, make sure you wrap the bolt in something soft (wood pieces or the like) so as not to damage the threads.
	Install Banjo Bolt Onto Fuel Pressure Regulator
	Using a vise with soft jaws (or soft wooden blocks between the regulator and the metal vise jaws), secure the regulator body so that you can properly torque the banjo bolt. Even if you could find a way to get a wrench in there with the FPR on the car, I wouldn't advise torquing this bolt on the car, as it might damage the fuel rail. That said, place one of the supplied crush washers on either side of the banjo fitting, thread the bolt through them, and then thread the assembly into the regulator body. The instructions (instructions?!? that came WITH an aftermarket part?!?!? How did that happen?) supplied with the regulator state that the bolt should be torqued to 20lbf-ft. Use your torque wrench and snug it up. In the picture, you can also see a good view of how much of the bolt I filed down. Since the bolt is only torqued to 20lbf-ft, removing this material should in no way affect the strength or durability of the bolt.
	Attach the Return Line to the AEM FPR
	Warning: This part may suck. Apparently, Hondas have a 7mm return hose, and our cars have something smaller (like 5mm or 6mm). Thus, you have to shove a really big nipple into a relatively small hose. The alternative is to buy a small section of 7mm ID hose, and a 7mm-to-5mm barbed adapter and properly attach the hose. Since I had no such hose or adapter and it was both a Saturday and New Year's Day (everything's closed), I opted for the more economical approach: stuff that 7mm nipple into the 5mm hose. My secret method was to warm up the hose slightly (exactly how, I'll leave to you, but remember you're working around fuel vapors, so NO FLAMES OR SPARKS), lube the nipple with a small amount of clean engine oil, and stuff that puppy in there. It put up a valiant fight, but in the end, I won. Before you reattach the clamp, make sure you rotate the FPR as necessary so that there will be minimal stress on the hose when the FPR is bolted to the fuel rail. Also, after fighting with the stock clamp (it's a little small for the 7mm nipple), I opted to use a screw-type clamp I had lying around.
	Attach FPR to Fuel Rail Adapter
	Oops, forgot to take a picture. There are plenty of other ones to follow, so you'll get the idea. Place the AEM-supplied o-ring into the circular depression in the FPR. You may find that wiping the o-ring with a little engine oil before placing it in the depression will hold it in place as you maneuver the FPR into position for mounting. Don't lose this o-ring, and be extra sure that it doesn't fall out before the FPR is bolted down, as it's required to get a proper seal between the FPR and the adapter plate. Now, using the AEM-supplied bolts (or the bolts and lock washers provided in Rob Beck's Fuel Rail Adapter Kit), bolt the AEM FPR to the fuel rail adapter. AEM recommends 9 lbf-ft for this connection.
	[Optional, but Recommended] Clock FPR Head 180 Degrees
	I guess you don't technically HAVE to do this, but it sure does make the installation cleaner. Remove the six 9/64" allen bolts from the upper regulator housing. Be careful as you remove the last bolt, as there is a spring under this upper housing, and it may make the bolt fly off somewhere as you remove it. Having an 8/32" screw in your parts bin would be a good thing if you're prone to having things fly off into the nether regions of your engine bay. As you can see from the second picture, I, of course, have no need for such a screw. But I digress. ... rotate the upper housing such that the vacuum hose nipple faces toward the back of the car, like the stock FPR's nipple. Then reinstall the bolts and torque them to 24lbf-in (that's INCH, not FOOT).
	Check For Leaks
	At this point, even though you haven't buttoned everything back up yet, your fuel system should be a closed system. Thus you can safely run the fuel pump and pressurize the system to check for leaks. To make it easier to find small leaks, and to catch any leaked fuel if it does leak, place some paper towels or shop towels under the FPR before running the fuel pump. I used the fuel pump test feature of my datalogger to briefly run the fuel pump to pressurize the system. You could also use the blue test connector located between the battery and the firewall to power the fuel pump. This is safer than starting the engine, and it also allows you to listen for leaks without engine noise. If you find a leak, fix it. If you don't have any leaks, continue.
	Button Everything Back Up
	Replace your FPR vacuum line, your rear valve cover breather line, and reconnect the wiring harnesses (TPS, knock sensor, rear fuel injectors) you disconnected.
	Crank Engine, Check for Leaks
	Fire up the engine and check for leaks again. When working with fuel, it's better to be overly paranoid about leaks and fumes rather than risk an engine fire that could destroy your baby or kill you.
	[optional] Adjust Fuel Pressure
	You can adjust your fuel pressure by loosening the 5/16" (the AEM instructions say 3/8", but mine is 5/16") jam nut on the top of the regulator and then turning the shaft with a 3/32" allen wrench. Turning the shaft clockwise raises the fuel pressure, and turning it counter-clockwise lowers the fuel pressure. It comes pre-set at 40psi, and Mitsubishi recommends 43-45psi of fuel pressure with the vacuum nipple disconnected. Thus, I tightened the shaft a on my regulator a little to get it up to 45psi. Then secure the jam nut back down so that the shaft doesn't move.
	Close-ups of Clearances
	Additional Note
	So, when I first got everything put back together and pressurized the fuel system, I had a fuel leak. It was coming from the banjo fitting on the return line of the regulator, specifically between the regulator body and the banjo fitting. I couldn't see if it was leaking between the bolt and the fitting as there was too much fuel leaking out of the upper connection. I tried reseating the AEM-provided aluminum crush washers, as I noticed the strange wear on one of them, as shown in the picture (note the shiny and dull parts of the left crush washer). That didn't work. I also tried some copper crush washers I got at an auto parts store. No dice. Finally, as a last-ditch measure to get my car on the road, I tried some M14 Nylon washers, officially billed as oil drain plug gaskets. This sealed the fitting. Since I'm not comfortable with nylon in the engine bay over a long time (heat + Nylon = deterioration), I called Altered Atmosphere Motorsports (where I bought the FPR) and explained the situation. Dave, the sales manager, was very courteous and referred me to AEM's customer support, saying that they've always taken care of him in the past. I called AEM's tech support and explained the problem. They are sending me a new banjo fitting, a new bolt, and new crush washers at no cost to me. I'll update this page once I get the new fitting and metal crush washers installed.

Follow-Up (January 12th, 2005)

	Don't Use Nylon Washers on the FPR!!!
	Upon removal of the FPR to replace the defective banjo fitting, I found that the bolt for the banjo fitting was only just barely more than finger tight. I'm assuming that the Nylon washers didn't respond well to the 140F+ heat of my engine bay and the 30F ambient temps right now. In any case, that could have been really bad if that return line had gotten loose. I'm almost embarrassed enough to remove the mention of the Nylon washers from this page entirely and pretend that I didn't do that, but hopefully somebody else will learn from my mistake. Again, DON'T use Nylon washers as a band-aid to work around a defective banjo fitting on your FPR!!!
	New Banjo Fitting
	A week after my initial installation, I had a new banjo fitting, a new banjo bolt, and 4 new crush washers in my hands, courtesy of AEM. I decided to try just replacing the banjo fitting first, rather than using both the new bolt and new fitting. That way, I'd know for sure which one was the culprit. I didn't notice until after installation, but the exterior of the "head" of the new banjo fitting was smaller than the old fitting. The interior dimension was the same, so it still bolted up to the FPR just fine. I also noticed that the interior diameter of the return nipple was smaller on the new fitting than the old fitting, even though the exterior dimensions of the barb for the hose were the same. I don't think this will be a problem, though, since the original nipple was much larger than the ID of the OEM return hose. In any case, I installed the new banjo fitting with the new aluminum crush washers and torqued it to the recommended 20 lbf-ft, the same way as the original one. I noted that the bolt was in a different position (WRT rotation) than before, mainly due to the smaller thickness of the new banjo fitting. This led me to wonder if I'd have to file down some of the other edges of the bolt to clear the coolant neck.
	Reinstalled Fuel Pressure Regulator
	Everything went back together perfectly. As a consequence of the thinner banjo fitting, there is plenty of clearance between the bolt and the coolant neck - no filing required! After pressurizing the fuel system, there were no leaks, and everything seems great. Thus, my conclusion is that the original banjo fitting supplied with the FPR was defective.
	Test Old Banjo Fitting
	Since I knew that my new banjo fitting worked, I decided to test out the old fitting to see if it was true (flat) or not. I rubbed it lightly against the flat side of my grinding wheel to see if the black coating came off evenly or not. If the whole side showed silver equally, that would mean that the fitting was true (flat). If part of the fitting showed silver (bare metal) while other parts showed black (not touched), then that would mean that the fitting was not true. As you can see from the above pictures (left is one side, right is the other side of the fitting), the fitting was not true on either side. I probably could have filed down the edges of the banjo fitting and used it successfully (and not had to get a replacement from AEM), but I'm of the opinion that if I buy a brand new product, it should work. That includes that the fittings should be true and seal properly without modification. In case there was actually a batch of bad fittings in AEM regulators (as some have reported to me), the manufacturing date stamped on the box of my FPR was April 19th, 2003.