jerking, poor milage and high emissions

I have a problem with my 996 C2 2002. I have just installed a "new" (a used engine) into my car. It works but now and then it is jerking under acceleration, it takes about twice the normal time to crank it to start, it has poor milage and emissions on the verge of being illegal. I also get fault codes for the cam shaft sensors on both cylinder banks (intermittent fault codes). I have replaced both cam shaft sensors, but the problems remain. What could be the problem?

timing

Ok, I put the engine in TDC and checked the exhaust cam on the left side. The cam looked like it was perfectly aligned. Do I need special equipment to check the timing more accurately? Or what else could be wrong? I don�t get any CEL. Robert

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From what little I've learned from the RL experts, your timing could still be off even if the cam slots are visibly in line with each other. Do you have a Durametric? If so, you need to evaluate the cam deviations for both banks, if they're more than 6% off, than I'd say the engine needs to be dropped and timed properly. You also need to evalutate the fuel trim and closely look how each piston is performing. Jake Raby did a YouTube video on the subject called "ECU Interrogation using a Durametric Diagnostic Tool".

You installed a new (used) engine in your 2002 car. Why was the original engine replaced? Where did you get the new (used) engine and how did it run in the donor car? Was the donor car also a 2002? What version DME...the same or different? Was this a straight up replacement...meaning dropped the original engine and installed the donor engine? Was any work done on the donor engine before it was installed?

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Thank you. I'll check out the video and how to move forward. I don't have a Durametric, but i'll buy one if I have to. I don't know how well the new engine worked before I got it. The reason I replaced the engine was that my old engine had a seized con rod bearing that destroyed the engine completely. All cables and intake are from my old engine. The new engine is from the same engine generation M96/03 as my old engine. Robert

Without codes or a durametric it will be a fishing expedition .Good place to start is to recheck all ground connections .The hard start could point to a bad connection or possibly failing fuel pump .If you transferred over the engine harness it might be a good idea to verify connectors are tight and where they should be .

one question - is the tachometer functioning correctly ?

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yes, it works fine.

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Did you use new intake runner/manifold gaskets? New Vacuum lines, hose clamps all seated and tight on the intake connections? Are you sure it's a 3.6 that went back in? Buying a used motor without seeing it run first is a risky gamble.

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I only replaced the gaskets that I deemed necessary. Some gaskets were pretty new. Yes, I am sure the engine is a 3.6. I checked the engine number. I got the engine cheap, so I can rebuild it if necessary but it seems to be pretty fine.

"It seems to be pretty fine"? That statement completely contradicts reality at the moment...I do hope it's something simple for you. Get the proper diagnostics done (otherwise we're just all pissing in the wind) and keep us posted.

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One of my close friends gave me one of his Rolex watches. It's very sentimental to me. One day while I was playing with my girls on the trampoline in the rain (great memories btw), my watch got moisture inside. Apparently, I forgot to tighten the crown which must be tightened or it doesn't provide the proper weather seal. Unfortunately, my watch filled up with moisture and it became very cloudy. Instead of sending it off to Rolex for service, I took the advice of people online and put it in a bag of rice to dry it out. It appeared to work, but after a few weeks, I noticed it wouldn't keep time. I'd wind it up, but after a few hours of not wearing it, it would stop. Rolex watches are supposed to work at least 48 after being wound. Eventually, it stopped completely. I sent it to Rolex and they said the internal gears had lost lubrication and rusted. Cost me a lot of money to service it. But It has worked flawless ever sense. The point I'm trying to make is these Porsche engines are precise machines. A few degrees out of time and all havoc can occur. For example, if a new flywheel is installed without being balanced, then harsh vibrations can occur at certain rpms. If cam shaft timing is off more than 6% (as noted by Porsche), then timing issues will occur and you'll get poor performance even if it doesn't throw a CEL. I've heard of engines that are off time, shake uncontrollably. They used to say "tune up" a lot in the ol' days, but after studying mechanics as a hobby, I've learned the beauty of the word. Even though modern cars are controlled by computers, everything still has to be "in tune" with each other or crap hits the fan. Again, my best advice is to get the car scanned with a Durametric or PIWIS. It can be something simple as Bill mentioned like a vacuum leak or something more serious, like a timing issue. All you can do is speculate based on the evidence on hand. Good luck!

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When I said "pretty fine" I meant that I don't think the engine needs a complete rebuild. Something is wrong of course and I just want to know if somebody has a clue what might be wrong. I haven't got a Durametric reading, but I have used a universal fault code reader. As I wrote above, I get two fault codes, one for each cam shaft sensor. I talked to a Porsche mechanic and he didn't think it was a vaccum leak. He thought it was electrical or possibly mechanically related. Robert

If you are still getting fault codes -suggest you post them .There are some knowledgeable people on here ( not me ) who would know what conditions trip the codes .Actually the shop manual will also provide diagnostic steps as well .

It took some time to figure out how to proceed (and I had my car in winter storage until now). The fault codes are P0344 Camshaft position sensor 1 - open circuit and P0349 Camshaft position sensor 2 - open circuit. I finally decided to go to a Porsche Center to find out for sure what is wrong (other companies seemed to just guess on different things). Their verdict was that for some reason, the rotors, used by the position sensor, attached to the camshafts are broken/damaged. That means I have to replace both intake camshafts... I got the camshafts and am planning to replace them myself. I just can't understand how they managed to damage the rotors. Robert

Someone awhile back posted about finding those rotors bent and it caused problems. Maybe search for intake rotors bent....

There is a LOT of information that only specific readers can access. Durametric is one and The Porsche PWIS is another, there are a couple other aftermarket testers that have special code available to get a lot of the functionality. If your going to DIY much of anything just buy one before you break expensive parts. If you read-a-round on this forum its a common event, someone keeps asking the forum to remote diag and there are just too many variables not to use the right tool. mistakes on a 996 can destroy the expensive parts you need to rebuild the engine. Or just drive you crazy chasing gremlins.. Information is power..