996 3.4 rough running issue

[Revolution996]

Installing fuel pump tomorrow, will update then.

Ahsai, if the fuel pressure regulator was bad, wouldnt the car run too rich with way too much pressure? I have lean running condition codes and i am getting 18PSIG with pump switched on, engine off, and 27 PSIG at idle.

[Ahsai]

I was thinking if the regulator is leaking hence reducing the fuel pressure. E.g., stuck in idle high vacuum condition.

[Revolution996]

Right but when the engine is off, there is no vacuum correct? And the fuel pressure is less than half of what it should be. Either way, we'll find out today whether or not the fuel pump will fix it. I removed the bad one, but I haven't bench tested it and I'm not really sure how one would do so, but I am installing the new one in the next few hours, and I'll let you guys know how it goes. Thanks for all the help thus far, it is much appreciated.

[Ahsai]

Look forward to your update and hope the fuel pump is the culprit. My points was a faulty pressure regulator can also reduce the pressure even when the engine is off. The proper way to test the head pressure is to crimp the return fuel hose to block any fuel from returning to the fuel tank. If you get proper pressure that way, the regulator is bad. If not, either the fuel filter or the fuel pump.

[Revolution996]

UPDATE: They sent the wrong fuel pump. They sent for the pump for the 99 C2 instead of the 99 C4. So while waiting for the new pump, I decided to change my oil. Bad news. In the filter I found little metal flakes. The bigger ones weren't magnetic, but when i took a magnet over the filter I found little pin-head size pieces. So I pulled the sump, and I didn't find any noticable metal pieces, but I did find about 10-20 small pieces from the chain rails. Not sure if this is part of the issue, or something seperate entirely. I would think that this engine wouldn't have an IMS failute because it is a factory rebuilt M96 engine which supposedly has an updated bearing in it. Also, the engine only has 40,000 miles, and it wasn't babied either. The car was daily driven and has been to many DE's and Autocrosses. Next step would probably be to separate the transmission and take a look at the bearing. Any other ideas? I haven't put new oil in yet, but I have that and a magnetic drain plug ready to go.

[Ahsai]

Does sound like something more is going on. I think it will be wise not to run the engine anymore until the metal flakes have been addressed.

[Revolution996]

Update: fuel pump installed. Fuel pressure is about 35 PSIG now at both idle and engine off. The car still has the same issue present, but it is doing a little better. I reset the codes before I started it, and took it for a test drive, and I haven't gotten any codes back yet. Installing a new fuel filter and checking fuel pressure regulator today. Will update on the results.

[Ahsai]

FYI, the spec fuel pressure is 3.8 bar +/- 0.2 bar with a stationary engine and 3.3 bar +/- 0.2 bar when engine is idling. Sure you want to keep running the engine with the metal flakes you found?

[Revolution996]

Yeah I am going to just run it and change the oil very often and see how it does. Pretty soon I'll have to open up the engine and put in new tensioners and chain rails, and when I do that I'll open up the engine and check the IMS bearing and the rest of the engine. If worst comes to worst, I'll just rebuilt the engine with better parts, and go all out with new pistons, etc

[Revolution996]

Update: got lean condition codes again, but this time I also got misfire on Cylinder 3, so next up for replacement is coil packs (which are all cracked) and spark plugs

[Revolution996]

Update: changed the plugs and coil packs and noticed smoother throttle response, but did not fix the issue. Also I installed a new fuel pressure regulator, and it helped the problem a lot, but it was still there, so I cleared the check engine codes, and it started running terribly again. Driven about 50 miles now since the code clear and it is still running worse than when I put the new regulator in. Any help would be appreciated. I can get numbers off an auto logic If that would help you guys to help me diagnose also. Thank you.

[Ahsai]

Have you verified the fuel pressure and flow rate again after all the new parts on the fuel system? Your fuel pressure was below spec (35 PSIG vs 55 required) even after the fuel pump replacement. I don't have the spec flow rate but you could probably google it.

[Revolution996]

Not sure how to measure flow rate, but the fuel pressure is still low and only put out 24 PSIG at idle and with ignition on. There is no change in fuel pressure whether at idle or with the engine off. Not sure how I still have low pressure when I have a brand new pump, new fuel filter, and new fuel pressure regulator. No visible kinks in the fuel lines under the car either.

EDIT: I tested the pressure at the pump by taking off the fuel line from the top of the sender unit and putting on an adapter to fit the little nozzle. I got 23 PSIG with the pump on, and you would think that since it doesn't have any way to return, the pressure would skyrocket, but it just stayed constant at 23. Any insight? The pump is brand new.

Edited November 8, 2014 by Revolution996

[RFM]

I would consider to replace the fuel pump relay, the resistance of the relay can became probably too high. It does not cost much and in time he still fails.

[Ahsai]

Do you have another gauge to try or you are sure the gauge itself is accurate? I like RFM's theory as well. Can also check the voltage at the pump terminals when the pump is running. Should be very close to the battery voltage.

Edited November 9, 2014 by Ahsai

[Revolution996]

Just read another thread on rennlist and I think I might have the answer to my problem. Haven't checked my car yet, but I will be doing so today or tomorrow to update. I believe one of the end caps has come off of the Venturi tubes and/or there is a crack/hole in the pressure line going to the Venturi tubes, so the pump could be working perfectly, but just pumping gas back into the tank without going up to the sender unit with correct pressure

UPDATE: This is what I found.

Edited November 10, 2014 by Revolution996

[Ahsai]

Wow, that looks promising. Someone tried to fix that with a zip tie?? My goodness.

[Revolution996]

Yes they tried to melt the plastic together too actually. Pretty janky job. Looks like I need a new one. Anyone know the part number for the drivers side Venturi tube? Is it stamped on the part somewhere?

[Ahsai]

Part #20 here? http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99-05&section=201-01

Ouchy price. Better be the culprit...

[Revolution996]

I'm 99% sure it is the issue so I will report when I install the part. I have a wholesale hookup, so the price won't be as bad as that I believe. It stinks that I've replaced all this other stuff too that wasn't causing the issue. Sure they were probably due sometime soon, but I think it was about $500 for the spark plugs, fuel pump, coil packs, and fuel filter together.

Edited November 10, 2014 by Revolution996

[Ahsai]

$500 is a smoking deal for all those parts!

[Revolution996]

Also, TBH I can't believe the car ran at all with the fuel pickup leaking like that. Seems crazy to me how it could still deliver enough fuel to drive reasonable between 2k-4k rpm. Most other people that have had this problem couldn't even get their cars to start.

[Revolution996]

Replaced and fixed!!! Thanks for all the help and support you guys gave me.

[Ahsai]

Glad to hear that and good job tracking down the culprit!