993 backfire/intake separation -- causes & questions
 

Hi Y'all,

(Long unnecessary lead up, so skip to end if you wish.)

The other morning as I was putting my kids and their gear in my targa to take them to school, a neighbor asked me about Porsche mechanics -- other than the famous old name shop here in New Orleans. See... she's got a Porsche dead in her driveway and she's un-inclined to dump more money into it.... She said it was a 1995 911. What happened? Loud boom and then wouldn't run.

Sounds like the problem in either of these threads:
http://forums.pelicanparts.com/porsche-964-993-technical-forum/498455-help-motor-blew-apart.html or http://forums.pelicanparts.com/porsche-964-993-technical-forum/587841-having-some-major-engine-problems.html

Anyway, I wanted to find out more, but had to get the kids to school. I was distracted all day at work. I stopped by her house after work to discuss and learned that she's the second owner of the car. Got it when it was 8 months old. Has been taking it to one of the known good p-car shops here (just as she had with her first car, a '71 914). She's had electrical issues, mainly with brake sensors over her years with the car. Had it tuned up just days before the "boom." That was 8 or so months ago. Car has 100,000 miles. I'm sure she has all the records, but they were not available the other night.

I want to help her get it running. I know my sc engine pretty well, but don't know much about a 993 other than what I read here.

Any initial thoughts about what to look for other than something loose in the intake? What are known causes for a backfire that would separate the intake from the engine (if that's what happened)? I'm guessing dizzy belt failure could be one cause. Any precautions to take with an engine that has not been cranked in 8 months?

Thanks in advance. I'll keep you posted. I'll probably go look at the car tomorrow afternoon.

Shawn

Not sure what the "boom" could be. If she had it tuned only days before, I wonder why the shop was'nt contacted that did the tune and talk to them. But, if it's been sitting for 8 months and you think it could start, there is a startup procedure that should be followed. Pull the DME relay and crank the engine over till you get oil pressure. Then put the DME relay back in. Then start it. I was told to do this when I got my 95 993 and have been following this procedure after every winter storage. This is to make sure all internals have oil instead of starting dry.
http://forums.pelicanparts.com/uploa...1314495551.jpg

I don't know the whole story on why she didn't take it back to the shop. Something about the shop owner suggesting she needed to inject a bunch more cash into it -- new "computer" or something -- and then she had to go out of town and then a month passed and then and then....

Probably optimistic to think it'll start, much less crank over. I haven't even seen the engine. But thanks for the direction on pulling the relay.

Shawn

I would check the dis belt. Just pop off the caps & see if one is not lined up.

That'll be at the top of the list.

Thanks.

Update...
Yeah. Intake had been popped open. I was able to push the right side back together, but the left side was all the way off, above and below.

Is there a trick to re-connecting these things? I can't seem to get the left side back together.

http://forums.pelicanparts.com/uploa...1314581646.jpg

http://forums.pelicanparts.com/uploa...1314581659.jpg

Pulled the dizzy caps. Not sure if these are aligned correctly. The belt-driven one has considerably more play. Don't know if you can tell from the two pics....


http://forums.pelicanparts.com/uploa...1314581958.jpg
http://forums.pelicanparts.com/uploa...1314581973.jpg

In other news. I was wrong. The backfire "boom" experience happened in June of this year (not 8 months ago). It was not a tune-up but a repair for which she brought it to the shop prior to the backfire. Car had been driving fine then died en route to somewhere. The shop changed the DME relay and/or the fuel pump relay (sounds like fuel pump to me) and all seemed okay until trying to start it some two days later when it backfired, and all ended.

It had backfired enough to break loose the intake once before -- in 2005... 10,000 miles ago.

BTW, I plan to shop-vac out all the leaves

I would just remove the secondary distributor cap and see if the rotor is free to turn. It can only do so if the belt is broken.

I'd also check for a leaking fuel injector.

No free spinning on the secondary.

Can these cars run on the primary dizzy alone? At least just to test it?

Yes, just as it would to get you home if the belt broke on the road. You would disable the secondary though.

To check if the rotors are in synch, look for the two pointy notches on the body of the distributors. Each rotor should line up with the notch on each distributor body. I can't see this being the problem though.

Thanks. Yeah that makes sense. Find TDC.

No work done this weekend (tropical storm, tons of rain, car in open driveway). But went over there this evening to see if dizzies are aligned by getting them to TDC marks.

Soooo... here's a really, really stupid question: How do you hand-turn this engine? My 13-year older 3.0 engine is turned by a special tool on the pulley. No such tool in the 993 tool kit. And the pulleys are different. I thought the 993 was turned by the turning the 24-mm(?) nut on the fan pulley, but that just turned when I tried.

Stupid question #2. I do turn it clockwise, right?

Thanks,
Shawn

A lot easier to see what's going on in the daytime. Got to TDC, and here's what I found....

http://forums.pelicanparts.com/uploa...1315672215.jpg

Looks like the belt is bad.

If I were to try start it on the primary dizzy, is there a right or wrong way? Should I just pull the primary lead off the secondary distributor? Disable that coil?

Well if TDC is set to cylinder #1 at the top of compression, then the primary distributor is set correctly...note the rotor pointing to the point in the casting at the edge of the distributor body.

But the secondary distributor is way off. The secondary rotor should be pointing to that point in the casting at the edge of the secondary distributor.

Here is a pic of the distributor cap wire numbering...note the position of the #1 wire on the secondary distributor...90 degrees CCW from where it is located on the primary distributor. The top of the pic is the fan housing...the pic was taken from the left side.

http://edelweiss.smugmug.com/Cars/Po...sor-Cap-X2.jpg



Maybe. Can you rotate the secondary rotor with your hand? If so, the belt is broken.

Maybe someone just did a distributor rebuild and didn't know what they were doing.

Disconnect the wiring to the secondary coil; tape them up and do not let them short to each other.

BTW, tell her to clean up that engine...what a mess. :eek:

The points where both rotors should be pointing when at TDC of #1 - Compression.

http://forums.pelicanparts.com/uploa...1315675079.jpg

Thanks y'all.

Yes. I saw the TDC point for the secondary and saw that it was not close. In fact, as I hand cranked the engine, it seems to have stayed in the same general place as in the earlier pics. I should have had both caps off when turning the engine to see if the secondary moved at all. When I get back over there, if I can hold the dizzy caps out of the way, I'll crank it around some more to see.

Anyway, the secondary rotor does not spin, but it does have a lot more movement than the primary one. I'm guessing the broken belt is binding it somehow.

I guess I'll read up on changing the belt (or get it to where she can drive it, limping, to the shop).

I do not believe she had the distributor serviced. She didn't mention it. It couldn't have been recent; the caps and rotors are due for replacing.

And yeah... there's a ton of leaves in there. She has a shop vac. I'll use it before putting anything back together.

Possible seized bearings which would cause the belt to break?

Edit: Don't know how I posted the same post twice. Sorry 'bout that.

Maybe.

The rotor moves some. It just doesn't spin freely. We'll know when the dizzy comes out and apart, I guess. I had mine on my '82 re-bushed last year. No fun, but not too hard.

Thanks,
Shawn

Or the 100,000 miles.

Over that 100 grand, I'm not sure if it was maintained well or just bought to the shop when it needed fixing.

Just saw this thread...I'm the guy from the one referenced in your original post. Sounds like you have the exact same problem as I did. It was quite a PITA for a cheap little part.

The second rotor likely isn't moving because you have the torn up belt fragments mashed in there, blocking the shaft from rotating. Has the belt been replaced before? If not, then it was probably just old age and not a bearing seizing.

I'd follow the instructions here for replacing the belt: http://p-car.com/diy/dualbelt/ (or send it to a shop, there are a few that do it for you for about $250-250) Replacing it wasn't too bad, but you need the tools to do it, so make sure you have everything before you tear it all apart. A bearing puller is probably the main thing, so you can pull the gear off the main shaft. And make sure to take the opportunity to check the bearings while you're there.

Also, before you pull it, make sure the engine is at top dead center and the car/engine aren't going to be moved. There ARE marks for this, but somehow my previous owner had moved the m, and I had a huge problem re-aligning the distributor.

It's also possibly that leaky fuel injectors could cause the same problem, however, if you've already found the distributor belt to be faulty, then that's the obvious problem.

As for getting the air intake manifold back on, just loosen all of the metal straps, get another guy, and push the things together and down, and maybe have a third person to tighten them again. The main thing is to be SURE they are on, and there isn't one still open. I couldn't get mine to start, even after a dist rebuild and fixing the timing, and it was because there was a small opening in the seal of the passenger's side forward one (hardest to see/reach), and it was causing a pressure leak which messed everything up. If you take it to a mechanic, they can blow smoke inside the air intake and see if there's a leak.

Thanks. I pulled the secondary rotor and the belt's definitely gone. Pictures later.

Shawn

wish I have a good neighbor here who can do my dizzy belt too...

Funny.

I don't think I'll be the one to rebuild the neighbor's distributor. There's some labor in that. And the need for a better timing light.

I took my '82 sc distributor apart last year. I had a machine shop cut bushings to fit. (It's documented somewhere on the 911 tech forum.)

I was just happy to get the neighbor's car to run on the primary dizzy today (taped up the leads to the secondary coil and wedged them between the plug wires on the secondary cap). The neighbor seems to really appreciate Porsches and I hated to see her car just sitting abandoned. I pulled the DME relay to crank it a few times, hooked up a charged battery, opened the unlocked door and promptly set off the alarm. Fun stuff.

Shawn

Just kidding. I rebuilt mine at 84k miles and it was about to break.

The right way to disable the secondary is to disconnect the final stage ignition control unit just below the coil. This way, the coil will not generate the high voltage spark.

In that case, since you cannot spin the secondary distributor rotor, the bearings must be seized. Let us know.

I know you said the rotor rotates a bit. That is because it is rotating about the shaft.

You do not need a timing light.

I unbolted the two leads from the top of the secondary coil (under the rubber cover) and wrapped them up in electrical tape. I don't recall seeing anything below the coil.

Don't you still have to re-set the timing after you put the thing back in?

I have a variable timing light (cheap harbor freight one) that I don't really trust.

Nope!

The distributor installs in one position only. Gone are the days where you'd rotate the distributor and then tighten a hold-down.

Well... that's cool. Maybe I should just trade engines with her. ;)

Meant to post this last night. Apparently there was water in the secondary. (This car leaks some. The tool kit was sitting in a puddle of water up front, some tools rusted badly.)

Anyway, this pic is not for the faint-hearted...


Ain't pretty.


Arrows point to the belt.

http://forums.pelicanparts.com/uploa...1315877131.jpg





I cleaned it out as well as I could. Oiled it down. Oiled under the felt of both dizzies.

OMG, looks like it suffered from Katrina.

Now that the belt is confirmed broken, put the rotor back on. It should spin freely with just your finger spinning it around. If not, break out the wallet. At this point, I'd check eBay for a used distributor.

Yep, distributor pretty much only picks which cylinder, the computer does the timing.

Also, because of the shape of the gear, be careful when re-inserting the distributor, as the rotors will twist a bit clockwise when the gear mesh.

After seeing that picture, I wouldn't even try fixing the thing, just get a used one on eBay or from the used parts forum.

Yep. If it were my car, I'd drill the pin and pull it apart just to see. Twenty bucks vs nearly a thousand or so. The thousand could wait another day.

But, or course, it's not my car.

Shawn