andydoody

Appreciate the help on the FPRs. Far as leaks are concerned I'm never a 100% on that, however, I had a whole new set of original Audi intake hoses which were installed after the problem started. I was kid of hoping for an air leak but found nothing so far. I will try again.

Even with the CEL 00537 code the car idles almost as smooth as it should be. I hope that's an indication that a solution is close at hand.

UrS4boy

I didn't get much (any) response on my shoutout for FPRs with "adjustable" return orifices. Just the comment that the "A" FPRs were fine. Duh. Except you can't buy new ones.

As for the 00537, just to be clear:

2341 (Blink Fault Code), 00537 VAG1551/2 Fault Code Number
Oxygen Sensor Control Limit exceeded,
fuel pressure too low or too high, intake or exhaust leak, defective ignition system component, intake air leak after air mass sensor, O2 sensor is faulty.

Lots of things besides too high fuel pressure could also cause the 00537 light.

andydoody

Yup there is more to the 00537. Here's my process of elimination:

1. Fuel pressure too high or too low - Per the pressure gauge, fuel pressure is too high even with an original Audi fuel pump, it still indicated 69PSI @ idle. Other symptom was rich exhaust.

2. Intake or exhaust leak / intake air leak after air mass sensor - Did the smoke and then soapy suds test and found nothing. Replaced all the large intake hoses with Audi originals. Had professional mechanic check exhaust for leaks or blockage. He too didn't find anything.

3. 02 Sensor defective - The one on the car is about a year old. I swapped it out with two new spares and still the same result. Checked the voltage and it is ok.

4. Defective Ignition system component - Been using the 034 HO ignition for about 18 months and the only problem its ever had was a bad ignition cable. I swapped out the set with Magnecors and its been good since - I think. All the plugs were equally sooty when checked, so either the system is working or all the coils or cables are bad. A higher revs the CEL is not present. There was a great improvement in idle stability and smoothness (almost normal) when the fuel pressure was brought down from 94 to 69 PSI. Finally, there is no bucking at WOT, though admittedly my boost is down to 12 PSI from what is usually 21 PSI.

In the next couple of days I will try increasing the orifice bore on one of my C series FPRs. At least I will try to get it increased from 0.84" to 0.125". The Mance thread said 0.125 is big enough at least for the stock pump. I'd still like to have an adjustable FPR system and so far leaning toward AEM brand universal FPR because of its replaceable orifice feature.

As always I'm open to suggestions. Thanks!

UrS4boy

2. You have to do the boost leak test at at least 15 psi. Anything less and you won't find your leak. Re-read my boost testing link.

4. If you are down to 12 psi on max boost, you have a boost leak (or an N75 WGFV issue depending on the spring in the waste gate, if 1.9 Bar spring, you have a non-functioning N75.

Mance found that he could only drill out the orifice if he had a special jig (which he built). Otherwise, it was impossible to drill the hole out without fatally damaging the FPR.

andydoody

Hi Dave. I will do the boost leak test per your suggestion. The wastegate is still on stock spring and I was able to test the N75 using an old VAG 1552 and it was clicking away. Are there any other tests I can do on the N75?

I was able to find the text of Mance's instructions and he said the orifice could be enlarged up to 0.125" on a DIY basis using a battery operated hand drill and two drill bits. He further stated that to achieve a 0.140" orifice size of the A series FPR would require a jig. I have some machine shops close to home so I was thinking of sacrificing one of my C FPRs for drilling out to 0.125". Ultimately an AFPR with proper orifice size is my goal. Hopefully someone will share their experience with AFPRs real soon.

Have a good weekend!

UrS4boy

I did some searching on Bosch 0280160516 ( = Audi 534A) and found some used ones (e.g. in Germany or Russia). No idead of quality, etc. Lots of suppliers want to supply the "equivalent" 0280160517 (= Audi 534C) so you really have to watch out. I am running a 534C and thought I was doing a good thing to go to the latest and greatest. Obviously that was wrong. I have NO idea whether I kept the old 534A - which was (at the time) working fine. Live and learn.

beepbeep

Are you sure your return line isn't blocked/pinched? If return is restricted, fuel pressure will rocket despite fully functioning BTR and pump.

andydoody

Hi Dave. I checked that by undoing the return line coming from the fuel rail. There was a lot of fuel coming out of the line but I wasn't able to measure it (volume). With the return line disconnected the fuel pressure was still at 94 PSI.

This morning I tried doing a "Mance" modification on one of my C series FPRs. I took it to the machine shop and followed the instructions to achieve an orifice bore of 0.125". It was a bit dismaying to find that the pressure was still at 69 PSI (with the new original fuel pump). I did notice that the idling was better and exhaust was rich but seemed to be substantially lessened.

I also checked the exhaust for leaks because it seemed to be different. There was a leak from the ABT muffler and another one at the junction of the downpipe (after the 02 sensor). Will get these leaks fixed and retest.

You know I totally failed to ask about vacuum readings. The boost gauge I have reads 20 when cold and then increases to 15 when the engine is warm. Is this normal?

UrS4boy

Well that should prove to you (and us) that the issue is not in the return line, it was the fuel pressure regulator that you have now opened up. (I have no idea why the pressure is still so high).

Vacuum is measured in inches of mercury (Hg). Your numbers are very strange (and this could lead to the solution of the problem). When I first start my 93 UrS4, when the engine is cold and the rings haven't full expanded, I get around 10 in. Hg vacuum (which is about -4.912 psig (side note: 4 Bar is 58 psig so with 10 in. Hg, the fuel pressure in the rail with a 4 Bar pressure regulator should be about 53.088 psig (say 53.1)). When my car is warm, idle vacuum is about 16 in. Hg (as shown in the photo below (-7.859 psig)(fuel pressure should read about 50.141 (50.1) psig).

The only time I see 20 inches of Hg vaccum is when the engine is hot (running temp 89 C) and I have been in the throttle and then back off quickly. Then I get 20 in. Hg or more, momentarily.

Starting at 20 in. Hg cold then warming up to 15 in Hg doesn't make sense to me.

andydoody

Hello Dave. I will check the boost gauge again to ascertain the levels of vacuum at idle when cold and at operating temperature. It will have to wait a day because the car is at the exhaust shop getting the leaks fixed.

Did a little research and found a couple of websites with information on vacuum. I honestly don't know if the info is relevant to our vehicles but would like to share the same with everyone. Here are the links:

http://www.linnbenton.edu/auto/perform/vacuum.html

http://www.gregsengine.com/using-a-vacuum-gauge.html

Of particular interest is the "Chart of Vacuum Readings" on the second website.

Gt back to you. Thanks