Audi S4 fuel pressure

[aliencurv]

Hey cats. What's the fuel pressure on idle and wot that i should be seeing? only Mark G knows what my fuel pressure regulator psi is. i'm having terrible misfires over the past few months and haven't had time to look at it, until this week. swapped in new coil packs. swapped new ignition modules. swapped your mothers. new plugs. and even swapped injectors... but nutta.

Anything above 5 psi just fits the shed. Even at idle it'll misfire like a mofo. And you know how mofo's misfire!

So i thought maybe the fuel pump is letting go. Usually they just fail, but who knows - this is an audi.

i hooked up my fuel pressure gauge and it bounces between 55-57 psi at idle and hits 70 psi at WOT. although, even at WOT I never see an AFR less than 14 - which is why i thought "hey this might be fuel related, yo".

Those numbers sound fine to me, do they sound fine to you?

I'm unsure what else to check! Suggestions?

[Triple G]

Re: Audi S4 fuel pressure

Blown turbos

[Mantis]

Re: Audi S4 fuel pressure

Thanks smartass

base pressure is 4 bar above atm , so 58.4psi, during full boost add 20psi ish on to that, and about 3.5 (50psi) bar while idling

[Mantis]

Re: Audi S4 fuel pressure

I just reread the entire post, pressure does not necessarily indicate fuel volume if your pump is aerating your fuel. Check your fuel filter

[R-Audi]

Re: Audi S4 fuel pressure

only Mark G knows what my fuel pressure regulator psi is.

Say what?

IIRC I changes the fuel filter the year before you bought it.... so it could be due?

[aliencurv]

Re: Audi S4 fuel pressure

Fuel filter has been replaced already also.

I think i'll be checking the evap system next.

Following that, I dunno. I guess I can scope the cam position sensor - but i figure that'd throw a code

[R-Audi]

Re: Audi S4 fuel pressure

Id post on Quattroworld and see if anyone there has answers...

[Natty54]

Re: Audi S4 fuel pressure

At idle, pressure should be between 3.8-4.2 bar (55.1-60.9) psi

The vacuum hose should also be pulled off the regulator and blocked off - If there is fuel there your regulator is shot

Have you checked the residual pressure?

[aliencurv]

Re: Audi S4 fuel pressure

Thanks Natty

I don't think it's fuel related. I do have a small leak in my evap i think... But that's not causing it because i blocked off the evap vacum lines and still misfire.

I wonder if i'm over looking something important: O2 sensors. I don't throw any codes for O2, and my adaption values for both banks fluctuate between -2% and +2% ... And my air fuel gauge, which has its own O2 sensor shows stoich at idle, so the adaption and O2's "should" be fine.. Unless they are reacting like crap "sometimes"

So the question is... Could bad O2's cause a misfire at idle? And a misfire on multiple cylinders at idle?

But i do not get any misfires if i have cruise set on highway. I drove from 60 KM this morning on the highway and did see a single misfire with cruise on... I only receive misfires at idle, or slight acceleration.

[Natty54]

Re: Audi S4 fuel pressure

Hows the harness?

Any codes stored?

What is the MAF reading?

Have you tested for Vacuum leaks? - I would be leaning towards this

[aliencurv]

Re: Audi S4 fuel pressure

Hey Natt, It looks like all the harness and plugs are connected. I checked the terminals on teh plugs and there is no corrosion. I sprayed some cleaner in there about 82 million times over the past few weeks.

I have no codes

I would think vacuum leak too but my adapted fuels hover around 0% (plus minus 2%) .. My vacuum is normal. I've went through every hose and looked for a leak, i can't find any. My requested boost and actual boost look great, up until 7-8 psi - then timing is pulled and limp mode.

This happens at idle .. It happens more in warm weather .. Today the engine idled like a tractor. Misfire counts on cylinder 3 were counting 1 every second. I've changed everything - ignition modules - coil packs - plugs.

I burn absolutely zero oil. I drive the car often and my oil level is still perfect from the last oil change 2 months ago.

I even thought it was the timing because my timing correction was pretty high (i forget the number). So i put a new belt and tensioner on... My timing correction is zero now - the timing is perfect because Sam gave me a good deal on a cam timing bar . Thanx sam!

I'm starting to wonder if it is power related... Today in the warm temperature, my battery light came on during acceleration. The voltage holds at +14 but the battery light was flickering - not on steady. And when the light flickered, the timing would cut and out and the engine would hesitate.

I wonder if its a main power relay. Or if there's a lose connection somewhere - could have happened from road vibrations.

I used a snap-on coil-on-plug spark tester. You lay the receiver on the coil and it will flash when it sparks. You can clearly see the misfire. It's not firing. So the next step i think is to connect my oscilliscope up to it and trace the misfire back to the PCM through the ignition modules and harnesses.

So much technology in these cars, but not enough to actually tell you what's wrong!

[Mantis]

Re: Audi S4 fuel pressure

Graeme had a flickering battery light when he relocated his battery to the trunk, and he had a bad ground

[Natty54]

Re: Audi S4 fuel pressure

any pending codes at all?

have you tried testing for vacuum leaks with a combustible fluid? ie like brake clean or throttle body cleaner?

is the car missing hot and cold? or just after it warms up?

[aliencurv]

Re: Audi S4 fuel pressure

So the Audi got a lot of love today. Not the kind of love i'd like to give it *nudge nudge wink ugh nevermind*

I installed new coils, new icm, new plugs. Then I replaced every relay and checked every fuse. Then I went through every harness and disconnected and cleaned every connection. I used my automotive dentist tools to squish the connector inserts to ensure they're all night and tight. Theeeeeeeen while looking for vacuum leaks I decided to change all of my samco hoses to new ones, since i had a brand new box lying around.

Because of the battery issue, i wondered if it was indeed the alternator? So I checked it - 14.54 volts. I even disconnected the battery while the car was running and drove around with all of my accessories on - no problems. The battery light must have been related to something other than the alternator... I'm suspecting it had something to do with a lose ground or plug and it has been resolved by my super duper awesomeness.

Since I have a PCV delete, i also went through all my vacuum lines to make sure none of the connections are loose. I replaced some older stock lines with newer hose and new clamps.

This thing is absolutely brand new under the hood now ... In the past short while i've replaced sooooooo much - no more excuses for misfire.

Well, after spending a few hours ripping the car apart and putting her back together. I started her up and plugged my dink into her vag port for a little scanny scan. The result? We're looking good boys. Under load I receive ZERO misfires *pantless dance party time*!!!

However, at idle I do receive misfires - not a lot - just a few. Mark G says "it's okay, shut up". So I'm trusting his balls - but I honestly don't think I had any misfires at idle before. The good news is I can actually drive the car! The great news is it's fast again!

Here's my misfire count at idle. Sometimes it's fine - othertimes there are a few misfires:

[Ur0Drivr]

Re: Audi S4 fuel pressure

I know when I was having similar issues Jordan told me that anywhere below 8 was considered normal...at least that's what I remember