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In that case, I think your 0.9 bar ( negative 0.9 bar strictly speaking since 0 bar gauge reading = atmospheric pressure) is highly suspicious since it's close to complete vacuum. Our engines just cannot produce that much vacuum at idle. You should read about -0.58 bar (17 inHg) if you are at sea level. http://www.renntech.org/forums/topic/40898-need-help-with-intake-vacuum-gauge-reading-from-more-cars/#entry241744

Yes, and an incorrect amount of vacuum applied to the fuel pressure regulator would directly affect the amount of fuel being delivered, which is exactly the fault being generated. If there was no or little vacuum, then I would have a leak, and I could check for that. But what can cause excessive vacuum?

That said, I T'd into the line going to the fuel pressure regulator as it seemed like I wouldn't want zero vacuum at the fuel pressure regulator. Was that correct? Or is it safe and was I supposed to take the fuel pressure regulator out of the equation entirely and just measure the vacuum on the line? If it is safe to run the car at idle with the fuel pressure regulator's line detached, and if the excessive vacuum pressure is reproduced with the warm motor, then I would to see if there is a difference with the fuel pressure regulator applied. If so, then maybe the problem is with the fuel pressure regulator...?

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Can't imagine how you can get excessive vacuum. That kind of vacuum you will only get if you snap the throttle and close it abruptly. When the engine is only idling, it can't generate that much vacuum. Can you test your gauge on another vacuum port directly off the intake manifold or on another car just to make sure it's accurate?

Also, if the vacuum is trully excessive, you should see a lower fuel pressure based on how the regulator works. However, your idle fuel trim is Removing fuel so that's not consistent.

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In that case, I think your 0.9 bar ( negative 0.9 bar strictly speaking since 0 bar gauge reading = atmospheric pressure) is highly suspicious since it's close to complete vacuum. Our engines just cannot produce that much vacuum at idle. You should read about -0.58 bar (17 inHg) if you are at sea level. http://www.renntech.org/forums/topic/40898-need-help-with-intake-vacuum-gauge-reading-from-more-cars/#entry241744

Yes, and an incorrect amount of vacuum applied to the fuel pressure regulator would directly affect the amount of fuel being delivered, which is exactly the fault being generated. If there was no or little vacuum, then I would have a leak, and I could check for that. But what can cause excessive vacuum?

That said, I T'd into the line going to the fuel pressure regulator as it seemed like I wouldn't want zero vacuum at the fuel pressure regulator. Was that correct? Or is it safe and was I supposed to take the fuel pressure regulator out of the equation entirely and just measure the vacuum on the line? If it is safe to run the car at idle with the fuel pressure regulator's line detached, and if the excessive vacuum pressure is reproduced with the warm motor, then I would to see if there is a difference with the fuel pressure regulator applied. If so, then maybe the problem is with the fuel pressure regulator...?

OK, it works like this: You first test the vacuum line disconnected from the regulator for vacuum level at idle with the engine warm (there is relatively low fuel demand on the injectors at idle) looking for around 15 inches of vacuum; this test the vacuum supply line, which often is holed or disconnected. If you find it, you then reconnect with a T to see the vacuum level with the regulator connected; if the diaphragm on the regulator is blown, you would see little or no vacuum.

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Sorry for the delay in replying, but life has been a bit hectic.

First, sorry but false alarm about excessive vacuum pressure earlier. When I converted my vacuum readings to BAR, I didn't realize that my vacuum gauge measures in in.Hg for vacuum but PSI for pressure. Thus, I converted BAR from PSI instead of in.Hg. In my defense, I did say I was a newbie in the topic of this thread. :)

Attached are pictures from my Actron vacuum gauge with the 996 at operating temperature, as well as a reference image to show the base reading. As you can see, I get about 14 in.Hg (0.474 BAR - for real this time) of vacuum at idle at 680RPM. When the vacuum gauge is T'd into the vacuum line attached to the fuel pressure regulator, the vacuum measured drops to 12 in.Hg (0.406 BAR). That puts it within the 0.4-0.6 BAR specifications from that 986 diagnostic PDF Ahsai provided.

Unfortunately, this means it is most likely leaky fuel injector(s). This makes sense, given the fact that one bank is running richer than the other, the low mileage of the car likely meaning it or its gas sat for long periods of time, etc.

I'll talk with Reno Rennsport regarding options of having my injectors refurbished/cleaned, but should that be cost prohibitive or the injector be not salvageable, does anyone have any experience with Beck Arnley refurbished fuel injectors? Looking online, it seems like I can replace the whole bank of injectors with them for the price of one new Bosch injector. And since the fuel rail would be removed, I'd prefer to clean or replace all three rather than guess which injector is the problem based on the burn condition from reading the spark plug.

Thank you!

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Sorry for the delay in replying, but life has been a bit hectic.

First, sorry but false alarm about excessive vacuum pressure earlier. When I converted my vacuum readings to BAR, I didn't realize that my vacuum gauge measures in in.Hg for vacuum but PSI for pressure. Thus, I converted BAR from PSI instead of in.Hg. In my defense, I did say I was a newbie in the topic of this thread. :)

Attached are pictures from my Actron vacuum gauge with the 996 at operating temperature, as well as a reference image to show the base reading. As you can see, I get about 14 in.Hg (0.474 BAR - for real this time) of vacuum at idle at 680RPM. When the vacuum gauge is T'd into the vacuum line attached to the fuel pressure regulator, the vacuum measured drops to 12 in.Hg (0.406 BAR). That puts it within the 0.4-0.6 BAR specifications from that 986 diagnostic PDF Ahsai provided.

Unfortunately, this means it is most likely leaky fuel injector(s). This makes sense, given the fact that one bank is running richer than the other, the low mileage of the car likely meaning it or its gas sat for long periods of time, etc.

I'll talk with Reno Rennsport regarding options of having my injectors refurbished/cleaned, but should that be cost prohibitive or the injector be not salvageable, does anyone have any experience with Beck Arnley refurbished fuel injectors? Looking online, it seems like I can replace the whole bank of injectors with them for the price of one new Bosch injector. And since the fuel rail would be removed, I'd prefer to clean or replace all three rather than guess which injector is the problem based on the burn condition from reading the spark plug.

Thank you!

That looks more like it. Be careful with aftermarket injectors, they are not always what they claim to be. There are firms that do excellent refurbishing of the injectors all over the country that will tell you quickly if one or more cannot be saved, but that rarely happens if the car is just off on mixture. I would suggest that while you have the car apart. do them all as you don't want to be doing this twice.

Before you take it apart, if you have not done so already, run out the gas in the tank, and then dose the new tank of fuel with a bottle of Techron (get the large one for 20 gallon tanks), and take the car for a prolonged hard run at highway speeds. You could just have varnish on one or two injector pintles that is causing the issue, and the Techron dose may clean it out.

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Before you take it apart, if you have not done so already, run out the gas in the tank, and then dose the new tank of fuel with a bottle of Techron (get the large one for 20 gallon tanks), and take the car for a prolonged hard run at highway speeds. You could just have varnish on one or two injector pintles that is causing the issue, and the Techron dose may clean it out.

Since it took 90 miles for the fault to re-trigger last time, and since the car is running rich as opposed to running lean, and since everything else checked out, I will definitely give this a try.

Well, that and it's so hot that I really don't want to spend hours in the garage tearing apart a near-perfectly running car... :)

Thank you!

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That makes a lot more sense. Your fuel trim numbers seem to suggest both banks are affected, maybe more so in bank 1 so I won't be so sure about leaky injectors. In addition to the techron cleaner I think it's a good strategy to wait and see till the CEL comes on again, which will make diagnosing the problem easier.

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After reviewing all the data you posted I agree with Ahsai and do not think you have leaky injectors. Without having the car in front of me my hunch is you have 1. the 02 sensors connectors have dirt or corrosion 2. vacuum leak 3. unmetered air just after the MAF or at the exhaust just before the o2 sensors that is fooling the o2 sensors to command more fuel. If you look at your screen shots the o2 sensors are switching at 0.4 mV to 0.74mV and giving a lean bis or low voltage command to the DME it see that as the motor is too lean. The DME now commands the injectors to add more fuel by making pulse width longer. Also the fuel trim on your car is 24% and 19% normal should be no more than 10%.Before you start looking for vacuum leaks I would also revisit the TSB on the 02 sensors as it is a quick and simple test to see if they start switching at normal rate. If the connectors have any dirt or corrosion this could add resistance thus giving a lower voltage to the DME. Porsche hates to admit any fault but this TSB shows that 1999 was a bad year for 02 sensors.

The TSB states Proper care of oxygen sensor connections It is extremely important that the oxygen sensor connectors be clean and dry at all times. Contact cleaners, contact enhancers (such as Stabilant 22A), oil or water based sprays, and even die-electric compounds MUST BE KEPT AWAY from the oxygen sensor connections, or permanent SENSOR DAMAGE will result! Always clean oxygen sensor contacts in a dry fashion, being careful not to allow any type of substance or debris into the connectors.

Note: The connections at the oxygen sensor can often be improved by simply unplugging and re-plugging the connector several times.

Edited by binger
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I'll talk with Reno Rennsport regarding options of having my injectors refurbished/cleaned, but should that be cost prohibitive or the injector be not salvageable, does anyone have any experience with Beck Arnley refurbished fuel injectors? Looking online, it seems like I can replace the whole bank of injectors with them for the price of one new Bosch injector. And since the fuel rail would be removed, I'd prefer to clean or replace all three rather than guess which injector is the problem based on the burn condition from reading the spark plug.

Being a Parts professional at major parts chains for several years while in college I would strongly suggest you avoid anything re-badged by Beck-Arnley.

When companies like RCInjector and Marren are easily reachable through the internet I don't think anything besides cleaning the injectors off your engine make any sense. I used to have access to an injector cleaner at school and I brought back injectors that were so bad that they didn't react to any pulse at all. (I got that set to flow within 10% so it is very doable)

Just my input. :)

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Being a Parts professional at major parts chains for several years while in college I would strongly suggest you avoid anything re-badged by Beck-Arnley.

When companies like RCInjector and Marren are easily reachable through the internet I don't think anything besides cleaning the injectors off your engine make any sense. I used to have access to an injector cleaner at school and I brought back injectors that were so bad that they didn't react to any pulse at all. (I got that set to flow within 10% so it is very doable)

Just my input. :)

Much appreciated (same to everyone who has replied).

I drove it low on gas today, and the check engine light turned off without me resetting the code. I haven't verified that the code is still present, but is that possible? Or did the bulb burn out? It's not an AUDI so I doubt the light has been illuminated for that long...

I did add a bottle of Techron concentrate at less than 1/8th of a tank and filled it to about 3/4th tank. So far, I put 110-130 miles on it and haven't noticed any problems. I will reattach the Durametric when I get a chance, or should the check engine light re-trigger, sooner to get additional information.

Thanks again, all.

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Being a Parts professional at major parts chains for several years while in college I would strongly suggest you avoid anything re-badged by Beck-Arnley.

When companies like RCInjector and Marren are easily reachable through the internet I don't think anything besides cleaning the injectors off your engine make any sense. I used to have access to an injector cleaner at school and I brought back injectors that were so bad that they didn't react to any pulse at all. (I got that set to flow within 10% so it is very doable)

Just my input. :)

Much appreciated (same to everyone who has replied).

I drove it low on gas today, and the check engine light turned off without me resetting the code. I haven't verified that the code is still present, but is that possible? Or did the bulb burn out? It's not an AUDI so I doubt the light has been illuminated for that long...

I did add a bottle of Techron concentrate at less than 1/8th of a tank and filled it to about 3/4th tank. So far, I put 110-130 miles on it and haven't noticed any problems. I will reattach the Durametric when I get a chance, or should the check engine light re-trigger, sooner to get additional information.

Thanks again, all.

Many (but not all) codes, and emission related ones in particular, are capable of clearing themselves once the triggering event is gone. Often takes a couple drive cycles to accomplish, but they do clear.

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Many (but not all) codes, and emission related ones in particular, are capable of clearing themselves once the triggering event is gone. Often takes a couple drive cycles to accomplish, but they do clear.

Good to know. I checked soon after to ensure the light illuminates when the ignition is in the on position with the engine off, so I know the bulb didn't burn out. I just wanted to double check that the fault clearing itself is normal.

So far I have put 150 miles on the Techron filled tank without the CEL re-triggering. I'll post again if the fault re-triggers and provides any additional information, or if it doesn't re-trigger, in a couple hundred miles with the future FRA and TRA values.

Thanks, all!

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  • 2 months later...

As I said, I'd check back in after a while. It took a couple hundred miles, but the check engine light re-triggered. Given the low mileage for the age, I'm inclined to believe it's a clogged injector or a failing O2 sensor. In either case, refurbishing six injectors and/or replacing four O2 sensors without completely identifying the problem is too expensive and too much work for my taste, so I'll take it to my local independent Porsche mechanic sometime shortly and have them properly diagnose the problem. I'll report back then with what they find.

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Did you ever test the fuel flow rate for the insufficient fuel flow under load? The spec calls for 850mL/30 seconds (in the same pdf I mentioned before). You said you replaced the fuel filter and the car was fine for 5 months though. I'm curious to see what they find.

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Did you ever test the fuel flow rate for the insufficient fuel flow under load? The spec calls for 850mL/30 seconds (in the same pdf I mentioned before). You said you replaced the fuel filter and the car was fine for 5 months though. I'm curious to see what they find.

No, I did not. I stopped after the fuel pressure test as the fuel pressure reading was well within spec, and it seemed to me like the pressure would have to be either high (clogged) or low if there was fuel delivery problems, especially given that one bank is running richer than the other where fuel pressure should affect both banks. Weather depending, I might try that this weekend before taking it to the shop. The car is running fine, and it takes a while for the CEL to re-trigger, so I doubt it is a major problem and don't mind driving it a bit while trying to track down the culprit.

Thanks for the idea!

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  • 2 months later...

Just a check-in. The fuel flow rate measured fine, so I continued with the adding fuel injector cleaner and just driving it approach. Eventually, I had one hard start and took it into Reno Rennsport. They ran the same tests I did and ultimately came up with "Try fuel injector cleaner! That will be $220!" which honestly was worth it to ensure I wasn't misjudging anything that might potentially cause more severe problems. I told them, if you just drive the car 100-700 miles, it will retrigger! But they passe on that, and said they would gladly start replacing random fuel related components hoping that it solves the problem, but at this point there is no guarantee. So, with the car seeming to run great and me not in a position to drop a quarter of the value of the car replacing every fuel related component, I'm continuing to just drive it with Techron added at each fill-up. Hopefully, either the issue resolves itself or more symptoms arise that can help identify the culprit. For safety reasons, I would like to start checking weekly the long-term FRA and TRA values to ensure that, while they are not ideal, they aren't at levels that could potentially cause harm. Does anyone know what levels should cause concern enough to stop using the car as a daily driver (no track time or aggressive/spirited driving)?

Thank you!

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  • 4 months later...

My passenger side cat is gone and I'll be replacing. My research has lead me to the following from FVD (I'm told M&M manufacture these):

996 Sport Catalytic set (200 cell) X-Design OBD-221011122 210 111 22 $2,175.43 Add to cart 200 Cell German HJS Sport Catalysts with “X Torque” design made by M&M in Germany. The "X torque" design in is a ... more info

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