26 replies to this topic

[Kyle Burkhardt]

So I replaced the timing wheel on my 99 with the slotted one from MSM and found that the PO had already slotted the OE one. Now I'm wondering if the PO had his OE fuel psi regulator modified. I just installed my davew AFPR, but havent tested yet cause I need to replace an OE fule line.

Anyway, two questions:

1. If davew present my AFPR to 53ish (with the assumption that my OE reg was unmodified) but my OE reg is modified, probably to 54ish, what would my guage read at the AFPR. I'm guessing still 53 unless for some reason the OE was set lower?

2. Anyway to tell if the OE reg has been modified by looking at it?

Goofy questions, I know. I guess ultimately once I put it all together and I get 53-54 at the AFPR, I don't have to worry about it, but I wanted to make sure I was prepared to see something crazy if the OE was modified.

I need to stop working on this car and just drive it! 3 more weeks!!!

[Mike Collins]

Dave's gauge comes wide open. Test it before you adjust it, if it is at 53 ish then the pump in the tank has been adjusted. If the wheel was slotted then I bet they already adjusted it in the tank.

[Kyle Burkhardt]

The car was a SSB car before I bought it. I think SSB allows open timing which explains why the wheel was modified, but doe the rules allow open FP? If not, it should be stock, right?

[Mike Collins]

SSB as far as I know does not allow for open timing beyond the FSM. I bet the FP was adjusted. Those SS? guys cheat more than we do!

[Kyle Burkhardt]

Cheat? It ran runoffs every year since 99. I'm sure if it was a cheater car it would have been caught!

[Mike Collins]

Cheat? It ran runoffs every year since 99. I'm sure if it was a cheater car it would have been caught!

Oh, that's right, only angels go to the runoffs, and if something were wrong i am certain they would have caught it in the tech shed.

[Kyle Burkhardt]

So I suppose you can't tell if its been modified by looking at it cause that wouldn't be good cheating, right? Or can you?

[Johnny D]

Stock you get 60PSI (I think) If you get less it's modified.

Long story short, test it and see what you have with the reg wide open.
If you were going to set it and forget it and you like the # leave it.
You may not need the AFPR then.

If you were going to dyno and dial it in maybe think about changing it.

Sound like you had it the way the rule change is now before you did anything.
J~

[Mike Collins]

So I suppose you can't tell if its been modified by looking at it cause that wouldn't be good cheating, right? Or can you?

Yes, I could tell. Take the fp out of the car, create a closed loop in a bucket with a gauge and test it.

[Johnny D]

You're the expert Mike, but can't you just hook up a gauge to the Fuel Test Port on the reg. and see what it says without taking everything apart?
J~

[Kyle Burkhardt]

Dave's gauge comes wide open. Test it before you adjust it, if it is at 53 ish then the pump in the tank has been adjusted. If the wheel was slotted then I bet they already adjusted it in the tank.

Dave told me it would be preset (but to confirm after installed). Any idea what the range of adjustment is on it? 0-stock?

[davew]

Here is the long story.

Fuel pressure has been adjusted for years on many different types of cars. Mostly by squeezing them in a vise. Some people where not very carefull and it is very obvious. Others took their time and it is almost undetectable to an unexperienced eye. Some makes of cars want more pressure, some want less. Miatas want less.

99 Miatas have the regulator in the tank. So inspection was a little more complicated and was never teched to my knowledge.

99+ Miatas use an in-tank regulator, right next to the fuel pump. When the pressure gets higher than the factory setting the regulator bypasses the extra fuel and dumps it right back into the tank. The line from the tank to the injectors always has the same pressure in it. No vacuum adjustment as on the early cars. Also no return line. Whatever fuel leaves the tank will get burned in the engine. What looks like a regulator under the hood is just a pulsation damper, so that on quick wide open throttle applications the volume of fuel in the line does not drop faster than the pump can supply.

90-97 cars have their reg on the exit side of the fuel rail. The pump pushes full pressure up to the fuel rail. The regulator then allows a pre set amount of fuel to return to the tank via a return line. Any atom of fuel may make several trips from the tank, to the engine and back again. This requires a totally different regulator design. The oem reg uses a vac line to lower fuel pressure at idle. For our purposes, we don't need that feature.

Back to the 99:

Since the reg is in the tank, if it was modified, the pressure will read lower on a guage installed near the engine. Stock is 61 psi +/-. Any adjustable regulator can only lower the pressure from what the input pressure is. If the in-tank reg is modified to 54psi, then the max on the adjustable reg would be 54. You can only go lower. If the max pressure out of my regulator is below the normal stock spec of 61, your in-tank reg has been modified. You can leave it alone and use the adjustment to go lower, or you can replace the in-tank reg with a facttory umodified unit and have full adjustability.On a 99 Miata the car won't run at all below about 35 psi, and will missfire at about 48.

Most 99+ cars like the 51-54 range. I test all my regulators and preset them to 54-55 to be on the safe side. Don't blame me if your engine melts down.

On my version of the 90-97 reg, the factory reg is removed and replaced with a machined fitting. The adjustable reg is then mounted on the shock tower, with a return line going to the factory steel line.

I hope this takes some of the mystery out of these regulators
dave

[Kyle Burkhardt]

Nice write up Dave. Waiting for my new pulsation damper (Thanks to Dave, now I know what my $70 is doing) and then I can hook everything up and see what we have.

The instructions for your reg says turn screw in to increase pressure. Does that mean CW?

[Mike Collins]

You're the expert Mike, but can't you just hook up a gauge to the Fuel Test Port on the reg. and see what it says without taking everything apart?
J~

What Dave said.... Except... With my method you know if they "altered" the FP at the regulator in the tank. There are other places that is can be done. I once saw a fuel filter that had been modified to conceal a FP regulator.

Dave when I was Line Chief for SM at the Runoffs we visually inspected the FP regulators. We had them pulled from the top three cars.

[davew]

[quote name=
Dave when I was Line Chief for SM at the Runoffs we visually inspected the FP regulators. We had them pulled from the top three cars.
[/quote]

I stand corrected

[Johnny D]

You're the expert Mike, but can't you just hook up a gauge to the Fuel Test Port on the reg. and see what it says without taking everything apart?
J~

What Dave said.... Except... With my method you know if they "altered" the FP at the regulator in the tank. There are other places that is can be done. I once saw a fuel filter that had been modified to conceal a FP regulator.

Thanks Mike, your 100% correct.

I was just going for "IF" it was "altered" somewhere along the line you would see a lower #.
Defining if there's problem before taking everything apart.

I would think Kyle does from the looks of it but he doesn't know yet.
J~

[Keith Andrews]

Looks like I called Dave around the time he was writing about these regulators. I was at the track with the newly installed regulator. A big thank you for the support. I was unsure how to adjust the regulator and had forgotten the directons at home. Turned out to be a good test and tune, VIR this weekend .

[FTodaro]

After reading about all the cheating that was going on modifying regulators in the tank and fuel filters, What is next?

I guess to some people its more important to win than the compete on an even playing field. If that is what they want why don't they go to an unlimited class?

[Kyle Burkhardt]

UPDATE (cause I know you guys couldn't sleep til you heard):

Got it all back together. Got 56psi on the guage before touching dave's "preset". Havent tested how high it will go cause I have a question first.

Can you make adjustments while the motor is running, or do I need to measure, turn off, adjust alittle, remeasure, repeat until I get what I want?

Thanks,

[Johnny D]

I adjusted the AFPR while running.
J~