Fuel Leak at Rear of Engine

New to forum. I have a 1999 996 C2 hardtop 6 speed. 130K miles. I have what has developed into a serious fuel leak coming from somewhere above the rear main seal and rear sway bar area. Here is one picture where I tried to capture the area where it's coming from: Here's a picture at the fuel pump end. As you can see in the photo above, the top fuel line is not connected to anything. I was under the impression my car would only have two lines, one high pressure line and one return line. Anyone know what the deal is with the unconnected line? Does anyone have a picture of what fuel lines run where? Also if the leak is indeed coming from the suspected area, is the only remedy to pull the engine to get to that area of the fuel line(s)? Thanks in advance for any help you might give me.

U need a new sending unit for the tank (see pic). That is the return line and the nipple has broke off. Use some needle nose plyers to extract the piece out of the black line. The quick disconnect should release when u squeeze the tabs. Do not start the engine as fuel will be pumping out of that line. The 3rd port is the vent off the round protrusion.

Quotes source post: 19764921

Thanks Jeeper. Is there a chance this pump was changed previously? I'm pretty sure the unused port not even having a hole into the fuel tank or even looking broken. Trying to keep from having to take that heavy battery out to look again. Do you happen to have access to a fuel layout diagram for the '99 996 or know if engine removal is required for fuel leak repair?

Anyone else have any comments that might help me? Thks.

So it looks like someone put a mk2 sending unit in your car. That would be for a 3.6l motor 2002-5. This pretty scarry and incredible. Probably one the most dangerous things i have seen. The black line that is not connected is a fuel return line and its job is to pump excess fuel back to the tank. So if u srill have the 3 4l in your car its just pumping it on top of your fuel tank. The 3 6l has the regulator in the sending unit and doesnt use the return line but because your fuel is regulated at the motor it needs the return line. I guess its possible that someone swaped the fuel rails or even the motor to a 3.6l?????? Take a pic of your motor and fuel rails best u can. Please do not start your car or turn the key. I dont think i can stess this enough until some things r figured out. Here is the mk2 sender.

What dejeeper said. That is a pump for a 3.6l car. I would confirm what fuel rails are installed. The 3.4l has a fuel pressure regulator mounted on the bank 2 fuel rail (someone correct me if wrong). The 3.6 does not. you may also need to confirm if you have a 3.4 or 3.6 engine. The easiest way I can think of to do that would be to look at the cylinder heads to see how many chains there are. This is a picture of the 3.6 head. The cam cover will have a lump above the cams for the cam chains on a 3.4 where the 3.6 is flatter.

Look for the engine number near the sump plate under the drivers side. It will start with M96/0. That will tell us the engine size.

Quotes source post: 19766740

Thanks Jeeper. I definitely then have the MK2 sender. Never considered that I could have a engine swap to a 3.6 l. I'm sure I still have a regulator on Bank 2. I'll try to get some pictures of the engine posted.

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Thanks I will check that out and post.

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Here is the engine number: M96/0366207218 Guess that says the engine is from a 2002 coupe, even though my car is registered as a 1999 coupe. Perhaps that explains the unconnected fuel line at the fuel pump. Still need to figure out where all the fuel lines go and pinpoint where fuel leak is coming from (somewhere above the rear main seal). And can be repaired without pulling the engine and/or transmission . Thanks for your help.

Yes, that’s a 996.2 3.6. You will also need the ECU, Immobilizer, and possibly wiring harness from a 2002+.

Well at least they gave u more hp...so we now know this has a 3.6l motor. U can start looking for images on what the top of the motor should look like to verify the fuel rail. U can pull the air box, throttle body and 2 plenums off and get a real good view of the top of motor. Then u can turn the key, but dont start it. The fuel pump will run for about 5 seconds and u should be able to find the leak. I would guess its the quick disco on the fuel rail. U can just leave the return line in the car unused. Did u have this car running before the fuel leak? If so the po did most of the swap correctly.

Yep, someone put a 3 chain engine into your 5 chain car.....the vario-cam systems are not comparable without a lot of conversion of wiring and electronic stuff. Like Tex said .. DME ,complete wiring harness, and even the A/C controller should have been changed..ie LOTs of work!! I think the fuel leak may be the least of your issues......there is a "BIG Story" behind this that apparently you are not aware of...

Quotes source posts: 19772097, 19764768

Wow! I'm surprised you haven't caught the car on fire driving down the road. Thanksgiving miracle! Not trying rub salt in your wound, but you've been driving this car with the M96.03 3-chain engine in a car designed for the M96.01 5-Chain for two years?? The M96.03 would be designed for e-gas. Your car was original designed for ol' school throttle cable. I assume this is running e-gas? Or, did the previous shop modify a '99 throttle body? Any chance you have a Durametric so that we can see what DME you have. A good look at the DTCs and live data would be interesting. I assume this engine was swapped by a previous owner? If so, wonder if the shop swapped out all the electronics (i.e. DME, Immobilizer, wire harnesses, etc.)??? So many questions. Hope you get it all sorted!

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going to follow this thread. Got many questions about compatibility other than the engines vario cam/valve/etc compatibility. question, can 996.2 dme and 996.1 immobilizer be correctly paired up.? With 996.2 wire harness, is it just a plug and play, or does the immobilizer need to be reprogrammed to the 996.2 dme and all keys/pills repaired..? Can plug and play 996.2 dme control the 996.1 dash cluster and other 996.1 car functions..? As for the fuel leak on back of engine, isn't there a fuel cooler there ?, piped into the ac suction line and fuel rail, on some 996.1..? Wonder if it or its connections could be leaking,? just a possibility with all the mismatched fuel system parts we all ready see at the fuel pump..?

^^^^^^ The 996.2 DME doesn't plug into the 99 996.1 wiring harness, the connectors are different so the entire chassis harness has to be changed.. Immobilizers are "married" to the DME's ....same immobilizer but it is not "married" so will either need a new one programmed, or a used "set" ie DME+immobilizer+ remote Also the 996.2 has a small CAN going to the A/C controller, so a 996.2 controller/wiring is needed.. Also the 99 has cable throttle, so the 996.2 DBW pedal and wiring has to be installed...Like I said..lots of work to do it "right".... Then the issue with fuel lines/leak...

Its really not that hard of a swap, rermember i did it with a mezger. 5 years ago an entire wrecked car was half the price of a rebuild. If u have all the parts from it (as i did) all u need to do is take it apart and put it back together, everything fits. It only took me 4 weeks of of evenings and weekends.

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OP, would your '99 coupe happen to be a Carrera 4? That would make better sense with a M96.03 swap since the '99 C4 uses DME 7.2 with e-gas.

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Yeah I know you did it, but how many more have you seen ? .......Its' like 1 in 100K !!!

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Second sentence says C2.

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Oh yea, but he didn't know that he had a M96.03 which makes me wonder if the car is truly a C4. This car obviously has a unique history of piece milling ... a coat of many colors.

[QUOTE=De Jeeper;19772450]Well at least they gave u more hp...so we now know this has a 3.6l motor. U can start looking for images on what the top of the motor should look like to verify the fuel rail. U can pull the air box, throttle body and 2 plenums off and get a real good view of the top of motor. Then u can turn the key, but dont start it. The fuel pump will run for about 5 seconds and u should be able to find the leak. I would guess its the quick disco on the fuel rail. U can just leave the return line in the car unused. Did u have this car running before the fuel leak? If so the po did most of the swap correctly.[/QUOTE ​​​​​​ Thanks Jeeper. Yes I've owned the car for 7 years and didn't put many miles on it, but was running fine until I developed this fuel leak. And recently due to some health issues, it's been sitting up on jack stands for about the last year. I've got the air box off, and tried to smoke test it a couple of times with no luck. I will get the throttle body and plenums off and try to find that leak as you suggested. Thanks again.

Quotes source post: 19772510

The car has manual throttle cable. And looking at the car it appears to be completely stock. Obviously if it had an engine swap that's not the case. But I've had virtually no mechanical issues until the fuel leak. Another interesting fact is that had a PPI done on the car back in 2017, and nothing much was reported. I still have the paperwork from that PPI and will report back with any relevant information. Thanks for your comments.

Quotes source post: 19773249

The car is not a C4, rear wheel drive only. And has the original red paint. Thanks for your comments.

I would say that if it has been running for 7 yrs whoever did the swap, did a good job. At least u now know what u have. I think u just have a connector or a split hose issue. Just get the top of the motor cleared off and u will get good vision on the fuel rail. Good luck. Also if u r in the mid-atlantic area and want to swing by DE i would be happy to look the car over. Odd ball stuff interests me.

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I'm more than appreciative for the offer, but I'm in Dallas Texas.

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Well if i ever make it to cota ill stop by.

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As Skip said, so much of the M96.03 Variocam+ associated components would need to be swapped out to make it work correctly. Any chance you could scan the car's DME you're running? I assume that if you've been driving the car successfully for 7 years, the shop that handled the swap did it right DeJeeper style?

Quotes source post: 19774291

I'd be willing to bet a Steak Dinner that the Vario-Cam System isn't working...The car will run fine with it not working except at full throttle on top end you wont get that "extra kick."... That is THE main difference between the M96/03 and the M96/01/02/04.. and to have the Vairo-Cam working on this coversion takes all the things mentioned..