New to forum w/ question

DogDoc · 09-10-2002, 11:23 AM

Hi everyone!
Great forum with a lot of useful info.
I just bought a '87 944 NA which at the time seemed like a good deal. After replacing the clutch, timing belts, water pump, ect.,(the previous owner led me to beleive that they all were changed "a few thousand miles ago" - caviet empitor) I can see why owning a 944 is, at times, a love-hate relationship. Luckily, I have found a very sympathetic mechanic. One problem that persists is a knock or rattle that I think is coming from the exhaust. I had my mechanic check the muffler for and exhaust for loose hangers, damaged muffler, ect. but he wasn't able to find anything loose. I had to replace the cat (the previous owner had a straight pipe - passed the emmissions but failed the visual; I should have checked more closely before the inspection) and the exhaust sound is improved but not eliminated. I was wondering if the timing was changed (being new to the Porsche Ownership Club I haven't poked and prodded the car yet) with a different chip or if this is something more serious. The mechanic did not find anything that he thought was life-threatening (like a blown timing belt) to cause the noise, but he only occasionally works on Porsche's. Is there anything that I can check without replacing the muffler? While at rest, if I rev the engine, no knock or rattle can be heard - but if the car was dieseling I don't think that I would hear a rattle. Being a novice, I'm not sure. I would be appreciative of any advice.
Thanks in advance!
Mike

AFJuvat · 09-10-2002, 03:09 PM

Welcome to the group.

First place I would look for a rattle is in the exhaust headers/heat shielding. Looking for cracks in the pipes or other loose parts.

Can you be a little more specific as to where it is coming from (front/center/rear/left/right) and when you hear it (high speed, low, all the time, only when moving etc.)

If the PO chipped it, I'm sure he would have told you - it is about a $200 upgrade and the car will not run well on regular (87) octane gas if it was.

AFJuvat

Taz's Master · 09-11-2002, 06:35 AM

DogDoc, I didn't post, because I am experiencing a similar problem and am interested in the advice you get. I get a rattle at 3000rpm, and suspect a heat shield that waits for the proper vibration frequency. I intend to live with it until this winter, when I plan to fix several little items and will have the 944 up on stands.

DogDoc · 10:39 AM

Hi,
Thanks for the quick replies! The rattle or sound appears to be worse when the car is first started and appears to be coming from the left rear. It usually begins at about 1000 rpms and dissipates but doesn't entirely disappear at around 3500 rpms. I ran the car yesterday and manually advanced the throttle but I didn't hear any obvious rattle from the engine with the hood up. I suspect, based on the previous posting that there may be a loose heat sheild since that appears to be a common problem. When I had the cat re-installed, the mechanic did not mention anything loose, although not being a Porsche mechanic I can't blame him for not specifically looking. I can take the car back to have him inspect it (having a pneumatic lift is a bonus). Is a loose heat sheild that obvious or is it a problem that someone needs to specifically know what to look for and how to manipulate it to see if it's loose? I'm running 87 oct. gas right now; is it safe to add an octane booster to see if the rattle clears with increased octane? The tank is pretty full (about 7/8th).
Thanks again for the prompt postings!
Mike

Bob's944 · Bob's944's Garage

if you can't find anything loose on your exhaust, prolly have something loose inside your cat converter.

DogDoc · 09-11-2002, 11:46 AM

Hi Bob,
Just replaced the cat and the noise was there previously but much louder. I have read post about having a damaged cat and also the post about having a loose ball of metal in the muffler. I think that if there was a loose piece in the muffler, shaking it would produce some noise, wouldn't it? I guess that the hangers could be loose although it seems that on inspection you problably could identify it pretty easily.
Thanks,
Mike

Bob's944 · Bob's944's Garage

if yer cat was falling apart, a piece could have travelled down the exhaust to the muffler and might be stuck in there now.

Scott R · Scott R's Garage

Welcome to the board! Good to see some other Colorado residents on-line.

I do work on the side on some of the local 944's and 951's. I am an x-GM wrench. I keep seeing an exhaust rattle on the NA's after they have clutch replacements, check this:

There is a test pipe for factory mixture calibration, this pipe attaches to the exhaust line under the car. You can locate this pipe along side of the valve cover and towards the rear on the passenger side. It has a tiny "blue" cap on it. It attaches with a nut that is kind of a pain in the butt to reach, I keep finding these pipes missing the nut.

DogDoc · 09-11-2002, 01:53 PM

Thanks for the info!
Bob, that may be what happened - the car came with a straight pipe w/o a cat. The PO may have ditched the cat since it was falling apart, replaced it with the pipe and ignored the rattle. When I test drove the car it sounded loud but I thought it was the muffler or a loose tail pipe cover. I would have thought that shaking the muffler would have produced some noise, but not being a mechanic I'm not sure.

Scott, thanks for the input. I haven't been able to get under the car very far. Not having a garage is a pain since there isn't a stable area on the street to use jack stands or a ramp to prop the car up safely. Is the test pipe nut in a difficult location to access or is it pretty obvious? The only reference I have right now is a Haynes manual - pretty basic. I may need to invest in a more detailed shop manual, any suggestions? The problem again is that without a garage, it's pretty hard to get any work done myself without a lot of pain and suffering. I'm trying to get as much info as possible on what to look at when I get the car to the mechanic and on the lift.

Thanks all!
Mike

Scott R · Scott R's Garage

It connects to a flange just below the head, then it attaches via pipe thread coupler to the actual exhaust line.

DogDoc · 10-07-2002, 08:36 AM

Hi all,
I finally was able to get the car to the mechanic today. A couple of items worth noting:
#1: Scott R may be right! The test pipe is missing the connecting nut. The question I have is where can you get the cap/nut other than a Porsche dealership special order?
#2: O2 sensor was not properly placed and is hitting the exhaust.
While I don't think that this is the source of the problem, could a faulty O2 sensor cause decreased acceleration and knocking when accelerating? I'm assuming yes (given my less than adequate mechanical knowledge). Anyone know where I can get an O2 sensor relatively cheap? If not I may patronize the sponsor of this board and purchase through them (not necessarily a bad deal considering that they are sponsering an excellent forum!)

Thanks for the input!
Mike

mike944 · 10-07-2002, 11:15 AM

There was in interesting post a few months back, about oxygen sensors by someone who worked at bosch, do a search, you'll probably find it. Apparently the universal sensors are not really as universal as we are all lead to believe. The poster mentioned a specific bosch part number as being mechanically and chemically interchangable with the one on the 944, but i think you needed to cut the electrical connector off, and replace it with the 944 one.

I'm kind of busy at work right now, and don't have time to really go searching for the post.

Mike

Dougster · 10-09-2002, 05:46 AM

Welcome to the wonderful world of Porsche's! Yes, not having a O2 sensor could cause some issues. I would look around and see if their might be another local 944 guy you can become friends with to learn from and work on each others cars. Also check out the Rennlist for area people...I am sure you can find someone who has one by you. Keep an eye on the streets where you like & make friends with someone if you see one too! Good luck, you will learn to love her!

Lawrence Coppari · 10-11-2002, 04:33 AM

Hi Dogdoc. I assume you are a veterinarian. This is off the subject but where can my wife and I obtain a cockapoo. Our beloved cockapoo of almost 16 years passed away this spring and we are now ready for another. They seem very hard to find.