Gary Knox

I recently had two experiences I'd like to share concerning StaBil as a fuel system and injector cleaner. Both of my 928's have fuel pressure gauges on the passenger side fuel rail, allowing me to get some "real time" data.
1. The auto 94 GTS pressure is about 55-60 psi (pulsating) while the engine is running. Within a few hours after shut down, the pressure nearly always dropped to 10-20 psi, then within a few days could be lower than that. It appeared to me as if I had leakage in one or more injectors - or the relief valve. I added 12 oz of StaBil to a full tank of gas (based on a suggestion from someone on this list, whose name I've forgotten, and couldn't fine a reference in my short "search" mode. IF you are the one who posted it, please take credit!). Over the next 2-3 weeks I only used the car for short trips. When the "Achtung" indications came on for low fuel, I filled up. From the time of that fill up, this car now holds pressure of at least 45-50 psi for 4-5 days. I always drive the car within that time frame, so don't know how long it will actually hold pressure.
2. My '89 S4 manual is only driven to and from the various Road Tracks in the eastern US. Recently while at a 3 day DE at Virginia Int'l Raceway, I noticed the fuel pressure was dropping to 5-10 psi almost immediately after I shut the engine off when returning to the Paddock (same 50-60 psi when the engine is running). That evening, I bought a 10 oz bottle of StaBil and added it to the tank that was ~3/4 full. I drove the next day (obviously, mostly full throttle and very little idling etc.). The car is only shut off for ~90 minutes, then back to "fun and games" again. By the end of the day, the fuel pressure was holding at ~50 psi for the full 90+ minutes between runs. Same thing the following day. Since then, I've driven the car ~650 miles home and the fuel pressure is still holding at 45-50 psi for 7 days.

Needless to say, I am SOLD on the use of StaBil to clean the fuel system, including the injectors. I don't know whether it cleaned the back of the intake valves or not. I've never had such prompt results from Techron when I've added it to a fuel system. And, StaBil is about 1/2 the price of Techron.
As Ed Ruiz used to say "Your Mileage (experience) May Vary", but I thought my experience might be of interest.
Cheers,

Gary Knox
West Chester, PA

IcemanG17

Gary
Very interesting.....hmmm....I have an occasional semi-warm engine startup problem.....Maybe leaky injectors dropping fuel pressure would cause it? I'm gonna try this!

BTW where did you get the pressure gauge?

Peter F

That is very impressive I must say Gary,
my car holds the pressure per WSM but drops to 0 in an hour or two after shut down.
My injectors have been serviced and tested for leakage with no issues.
I wonder what makes the significant difference?

/Peter

danglerb

Is there some kind of check valve to prevent flow back to the tank?

AO

Inersting observations Gary. My only concern is that your conclusion is that you've cleaned the injectors through this prcess, but there is no direct evidence - just indirect (i.e you didn't watch/measure the flow before & after).

Obviously you've affected the ability for the fuel system to sustain fuel pressure for a few days - which I think is a good thing, but are there any other culprits that could have allowed the flow of fuel and thus a decline in pressure?

All in all, it's a pretty compelling set of observations to try it. I've got a bottle in the garage that I think I'll give a try! Thanks! :thimbup:

the flyin' scotsman

Brian...........I got my FP guage 928 Motorsports, good fit and works well.

Gary...........thats interesting results; my car looses all fuel pressure within 1/2 hour off engine shutdown. I believe the WSM has specs for what pressure it should be after 20 mins..............have to re-check.

Jim bailey - 928 International

There is a check valve at the fuel pump the supply side and the pressure regulator at the back of the fuel rail is a "check valve" on the return. The 80-84 use two , 85-95 just one at the rear of the passenger right side fuel rail.

the flyin' scotsman

I just check the WSM; 24-211:

with the FP relay jumpered 3.8 bar +/- 0.2 bar

min. pressure after 20min 3.0 bar

So now the question: if the system is not holding pressure where does one start investigating?

Leslie 928 S2

Carl sells Nordskog gauges, nice equipment. If you want really nice equipment, or have the need, you can also call Phil Beutz at Nordskog and ask him to sell you the high pressure digital fuel gauge that they custom made for my husband, Kevin.

It will read in .5 pound increments up to 100 pounds, and yet will also withstand pressures of higher than 100 pounds with no ill effects to the gauge. This is an issue, according to Phil, with the regular gauges they sell that go up to 100 pounds (in only 1 pound increments, by the by)...going over 100 pounds of FP can hurt those gauges. It comes in multiple choices of LED colors and it also has hi/lo memory callback. Pretty nice stuff.

If you do call, tell Phil that Kevin and Leslie in NJ sent you and that we say hello!
Best,
Leslie

worf928

I've been a StaBil proponent for many years. I never let my cars sit for more than a week or three without StaBil in the tanks. StaBil will help prevent varnish buildup. Look's like it may also get rid of it.

docmirror

Hmmm, I've been using it, and recommending it for years as well. From my marine background. Not saying I'm the one that gave the initial recomendation, but it does what it says on the bottle. After cleaning the Quadrajet carb on my boat one year, I started using Stabil. That was a job I never want to repeat.

Doc

Gary Knox

Andrew,
You are exactly correct. This is - as the medical industry would say - essentially anecdotal evidence. But - it certainly did do something to whatever it was that was causing the pressure leakdown. I didn't mention it, but before the StaBil treatment, the GTS would start slowly if it had been turned off for ~30 min to 2-3 hours. Always started better if I gave it about 10% throttle. Now, it starts up without any movement of the accelerator pedal, in the same period of time regardless of whether it's been turned off for 15 minutes, several days, or any time in between. That made me "believe" that it was a fuel injector leakage problem that the StaBil treatment has now eliminated.

Again - YMMV!!!!

Gary Knox

ceedee

i use lucas oil... the injector cleaner i quite like it but i don't have any numbers that would suggest it really is all that good. maybe one of you has some ideas

danglerb

Since gasoline doesn't compress, pressure drop time has two factors, how compliant the fuel lines etc. are, and how much leaks. The more the fuel system "flexes" the longer it would hold pressure, a system with all hard lines would lose pressure almost immediately with even a tiny leak.

Bill Ball

Fascinating. The WSM spec for pressure doesn't require it to hold that long. I think it is less than 0.5 bar drop in 30 minutes. My car seems fine, starts OK, etc., but it will drop pressure slowly over several hours. What the hey, I have a can of this stuff I haven't used. How long is Stabil stable in the can?