IanM

I've got an aftermarket boost gauge and an Autometer fuel pressure gauge in my center console. Otherwise I'd have never seen this problem occurring...

A few days ago, I noticed that under boost, my fuel pressure initially rises at 1psi for every psi of boost, as it should. So, with my 3bar setting on the afpr, 16psi of boost translates to about 60psi of fuel pressure. Problem was that at full throttle above around 5500rpm, my fuel pressure would start dropping, even though my boost gauge still read 16psi!! I swapped out DME relays, problem seemed to go away. Then I put the old relay back in, problem was still gone!! I figured it wasn't the relay, but I threw the new one back in just for the heck of it. My theory was that my 14year old fuel pump was getting tired, and that when I pulled over to swap relays, the pump had cooled down and regained some strength, so that when I got back on the road the problem initially seemed to have gone away.

So, I went ahead and installed a high-flow fuel pump yesterday, same one that David Floyd got from Lindsey Racing. Well, last night I did some 3rd gear pulls, and unfortunately the problem is still occuring. Anyways, now I'm starting to wonder whether it's my afpr, which I bought from Huntley and is only 1 year old.

What do you guys think? The fpr is working properly initially, but is it possible that it's just not able to hold pressure at the upper rpm range? Anything else I should be looking at before changing fpr's?

IanM

I just heard from Danno...sounds like it's not an uncommon thing for the Huntley afpr's to go bad. I'll swap it out for a fixed 3-bar fpr, and see what happens. Warning to others...the only reason I knew this was happening was because I've got an Autometer electronic fuel pressure gauge inside the car (as opposed to at the end of my fuel rail). It's definitely not a good thing to be going lean under boost at high rpm!!! I'd definitely recommend an on-board fuel pressure gauge to everyone!!

OZ951

Ian, its great to be well informed about your engines operting condition- keeps your engine safe when thigs start to fail.

Were you running an AF gauge as well ? did it start to show your mixture going lean ?

Let us know if the new FPR solves the problem.

SamGrant951

ian, how do you have the sender mounted? does it screw right in to the end of the rail, or do u need a piece like the 9xauto sells that makes it lower so as not to hit the hood. just curious.

IanM

Yes, I'm running the Huntley MAF/ARC2/ARM1 setup - uses a Split Second ARM1 a/f gauge, which is plumbed into my stock O2 sensor signal. Not the most accurate thing on the planet. I didn't have my eye on the a/f ratios, but it should have been showing a leaning out at high rpm as well. The Autometer kit uses a sender which mounts in exactly the same place on the end of the fuel rail as the mini VDO gauges. Same thread size as well (1/8" NPT). Just screws right in, doesn't hit the hood. There's a little control box the comes with it as well, I've got mine mounted under the dash. I've posted pics of the sender and the gauge panel previously, maybe you can find it if you do a search. I'd repost them, but I can't anymore (not a Rennlist member).

SamGrant951

sweet, thanks Ian. good luck sorting it all out.

DangerIsland

Ian: where did you buy the Autometer kit? Huntley? What did you pay for it?

IanM

I bought it from a muscle-car shop in Vancouver, called Mopac. I'm pretty sure they have a website. It was actually a bit pricey, something like $350CDN

tecart

hey ian is the afpr from huntley you got the older style one or the newer style one, the new style they were selling recently has like a 2 piece design with about 6 small allen screws holding both pieces together, the older one is more of a 1 piece design, you must know about both types/styles right? let us know which style you are using ok... Also make sure the lock nut it tight on the AFPR and the vaccume line is on tight and its other "T" lines are on tight aswell, let us know asap

Alan C.

One thing not to overlook is voltage drop. What is the voltage doing at higher pump pressure/flow.
Most pumps will flow enough in short spurts. It's when you get to the track and use the high flows for extended periods of time that the problems surface.

Bigger may not always be better but it is safer in fuel pumps.

IanM

My afpr is a 2-piece design. Lock nut is tight, vacuum line is sealed, and it used to work perfectly well. I'm interested in this voltage drop issue. Are you talking about a problem with the pump, or a problem with the wiring and/or alternator?

tecart

ian, we now must get you to do the full throttle run again, look for the fuel pressure drop thing to happen again... then make sure the boost is set at 16 psi max and not higher, then look at the arm1 and see if the car is going full lean when the fuel pressure drops... You need to get 2 people in the car, 1 to watch the fuel pressure gage and yell out "im loosing fuel pressure what is the arm1 doing?" the 2nd guy will let you know when the arm1 goes full lean or if it stays rich like it should at only 16 psi with 3 bar regulator, then let us know what happened as soon as possible, i suspect the fuel gauge your using is not accurate and the arm1 will stay rich/ in the o.k. region, but this is my theory, let us know what happens on this test ok

IanM

tecart,
Actually, I'd say that my Autometer fuel pressure gauge is very accurate. It uses an electronic pressure transducer tapped directly into the end of my fuel rail, and is the same transducer used by such names as Motec. I would say though that my ARM1 is questionable, as it's using the signal from the stock O2 sensor (even though my sensor is quite new). I have compared the led ARM1 display to air:fuel readings from a wideband sensor while driving the car (with wideband O2 sensor tapped right into my exhaust, upstream of cat, rather than up the tailpipe). The ARM1 doesn't respond to changing a/f ratios very accurately at all.

I will however do some more tests. I'm sure you'd be interested to know whether the ARM1 or other air:fuel monitor picks up problems with fuel pressure dropping at high rpm. Otherwise, you'd never know if you have this problem, unless you get a fuel pressure gauge like mine inside the car.

I'll let you know. This weekend I'll be installing a fixed 3-bar fpr, hopefully that cures this dropping fuel pressure problem. Even though it wasn't the fuel pump, it does make me feel better to know I've got a WAY oversized brand new pump back there. I was getting a bit worried about my 14 year old stock one anyways...

tecart

still ian, we need to see if the arm1 goes full lean when the fuel pressure drops, do not change fuel pressure regulators out yet until you see if the arm1 goes lean or not, either way let us know/mark that down then change to the 3 bar and do a full throttle run and then watch both devices and again report the results to us, i do believe your arm1 is highly accurate enough to tell us if your either rich or lean, yes 1 or 2 dots may be off as its not the most accurate thing but it will not be off by 4 dots, get me, so we should be able to see if your going full lean as your pressure drops, yes we all need this information and the gage may be still faulty but maybe its the FPR but dont rule out anything yet

951carter

What fuel pump are you using?