Rough idle/no rev problem

[muscatty]

This is a great picture of the intake cam. Could you post a picture of the exhaust cam so to see if the notches are straight up and down?

See post:

DIY: Setting Cam Timing on M96

[Smallblock454]

Originally Posted by tada

It never ran right, yet. In other threads in the General Discussion area I explained I bought a non runner and am trying to get it going.

Hi Tom,

to me that looks OK. Even there is a little deviation, the engine should run - and not in the way it runs on your video. Also the problem in general isn't a bent crank at this engines. Mostly it's a chain that sprung over – caused by a failed chain tensioner, broken chain ramp or anything related to ims mechanism.

Do you have any infos from the preowner how the car stopped working and what he or his workshop did to fix the problem?

From the symptoms i'm still on the clogged catalysator or intake side.

Regards, Markus

[tada]

Originally Posted by Smallblock454

Hi Tom,

to me that looks OK. Even there is a little deviation, the engine should run - and not in the way it runs on your video. Also the problem in general isn't a bent crank at this engines. Mostly it's a chain that sprung over – caused by a failed chain tensioner, broken chain ramp or anything related to ims mechanism.

Do you have any infos from the preowner how the car stopped working and what he or his workshop did to fix the problem?

From the symptoms i'm still on the clogged catalysator or intake side.

Regards, Markus

Hi Markus,

I'm just following ideas and eliminating variables. Below is what I bought to check the catalytic converters. Screws right into the O2 sensor holes. But, I'm running out of time tonight and I will save it for tomorrow.

As for the previous owner, he bought it in Glenwood Springs, Colorado at a used car lot in July 2015 for $8000 and had 94368 miles. Drove it to Sierra Vista, Arizona. Parked it. Would not start. He tried changing plugs. It was obvious his girlfriend (the actual owner on the title) had had enough of it. Their prospects were towing it to a Porsche dealer or Indy in Tucson, 100 miles away. So getting history from them was useless. They didn't know it had a toolkit (I needed the tow eye for the flatbed). I ran carfax and autocheck. 7 previous owners. Was a lease car for its first four years with 4 owners in those first four years.

Tom

P.S. Before this is all over, I think I will own every specialty test tool available. It would be great, but my other cars actually run dependably and need little maintenance. I guess I will be setup for servicing Porsches for life.

[tada]

One last update. Did the chopsticks test. Difference between TDC and BDC on all six cylinders was 2.25 inches. No variance.

So at this point, I'm going to rule out a bent connecting rod and bad timing on bank 2.

On to cat testing tomorrow.

Thank you all for all your help and suggestions. I'm learning more than I ever thought I would.

Best regards, Tom

[tada]

Well I got the appropriate O2 sensors out and tested in front of and back of each cat. The gauge read almost zero on all four openings, so I will assume that back pressure is not the problem. On to checking for intake restrictions. Something may be blocking that side. Hoping it's not something long dead.

[Smallblock454]

Hi Tom,

well zero means, that something is blocked. Right?

Please also check if the left side header and all connections points of the exhaust system on that side for new gaskets and screws - so the question is if some parts were removed lately. I've seen idiots that put in gaskets without holes. And because we don't know what the workshop did…

Regards, Markus

[911monty]

Originally Posted by tada

One last update. Did the chopsticks test. Difference between TDC and BDC on all six cylinders was 2.25 inches. No variance.

Best regards, Tom

Good result! Might check your measurement though. 2.5 liter has stroke of 72mm or ~2.8".

[tada]

Good result! Might check your measurement though. 2.5 liter has stroke of 72mm or ~2.8 in.

Hey, you said approximate!

Hi Tom,

well zero means, that something is blocked. Right?

Please also check if the left side header and all connections points of the exhaust system on that side for new gaskets and screws - so the question is if some parts were removed lately. I've seen idiots that put in gaskets without holes. And because we don't know what the workshop did…

No, it actually means the cats are free flowing. The gauge reads pressure in psi. I saw puffs on the gauge at all four O2 sensor holes but the pressure was negligible . If the cat was plugged, the readings in front of the cat would be higher.

So I'm running out of ideas. I'll go ahead and remove the throttle body and intake manifold, clean it, and look for any air restrictions to bank two and any vacuum leaks that may be present after getting the parts out of the way.

Any chance this could be a bad DME?

[78F350]

Maybe I missed it, but did you check the cam timing already from the link that "muscatty" posted?
The check is easy enough to do with the engine in.

DIY: Setting Cam Timing on M96

[tada]

Originally Posted by 78F350

Maybe I missed it, but did you check the cam timing already from the link that "muscatty" posted?
The check is easy enough to do with the engine in.

DIY: Setting Cam Timing on M96

The timing on bank 1 was right on. I posted a pic of bank 2:

[Smallblock454]

Hello tada,

i have a wiring diagram for the 99 986 dme. It's too big to post it here.

Looks like every ground point for each fuel injector runs seperately, but has an internal node.

The ignition has 2 ground points on the DME. But they are connected. The wiring loom runs to one central ground node, but there is a wiring running to each. Maybe a broken wiring loom cable? Did you recheck the ground connection on each ignition coil?

Don't know DME outs for one bank could be shot all at once. In general each out has his own power transistor.

If you pm me your e-mail address, i can send you the wiring diagram.

Regards, Markus

[tada]

Going through the vacuum system for a bit. I have a question about the secondary air injection pump. I do not hear any sound coming from it during cold startup (not like I ever have warm startup). I left my windows computer at work, so my Durametric is helpless right now. Can a failed SAI pump cause this bad a problem? Thanks, Tom

[Smallblock454]

Hi Tom,

in my opinion the engine should run proper just with a failed SAI. Maybe it will run too fat, but that wouidn't lead to a not working cylinder bank. Also the SAI blows air into the complete intake system – not only in one cylinder bank side.

Could a failed o2 sensor lead to a problem with one cylinder bank. I would say yes, but i don't think it could block the bank from running. And that is what it sounds like.

There must be a more fundamental problem.

Regards, Markus

[tada]

I finally found time to remove the throttle body and intake manifold. I expected to find it filthy, but instead it is pristine clean. Strange. I am still hunting a vacuum leak. When taking off the intake manifold, the vacuum tube to the fuel pressure regulator snapped at the point where it enters the "bellow" of the intake manifold. It may have been weak or leaking to begin with. I'm still going to clean the IAC valve and do some more smoke testing on the vacuum parts

[Gelbster]

Interesting.
If one vacuum lie is so brittle it cracked ,what about all the others if they are the same age & have endured the same heat cycling ?
Pelican sell a vacuum hose kit but I had wanted to find a set that are a better grade of plastic. In theory silicone may work for the small diameter hoses if you get a thick wall? It has a tendency to collapse under high vacuum when hot. So the cheapo EBAy ,thin wall silicone hoses would be a bad choice.
For smoke testing the vacuum system I recent;y upgraded to a better quality paint+can+baby+oil system.It works well because it pushes ut a lot of smoke for a long period consistently.
Thanks for letting us all follow your progress.

[tada]

Originally Posted by Gelbster

Interesting.
If one vacuum lie is so brittle it cracked ,what about all the others if they are the same age & have endured the same heat cycling ?
Pelican sell a vacuum hose kit but I had wanted to find a set that are a better grade of plastic. In theory silicone may work for the small diameter hoses if you get a thick wall? It has a tendency to collapse under high vacuum when hot. So the cheapo EBAy ,thin wall silicone hoses would be a bad choice.
For smoke testing the vacuum system I recent;y upgraded to a better quality paint+can+baby+oil system.It works well because it pushes ut a lot of smoke for a long period consistently.
Thanks for letting us all follow your progress.

I'll replace them all if I could find that kit. I've searched for hours for the part number of the rigid vacuum line I need that goes from the intake manifold to the fuel pressure regulator. Porsche Atlanta shows it on a diagram as part 16, and then does not list it. Pelican has rigid vacuum line sold by the meter that is listed as 4.0 x 1.0 mm. If anyone knows the part number, I would appreciate it. Otherwise off to my local Porsche dealer.

[Gelbster]

For the hard line, try Sunset??? They have an excellent rep for helpfulness.

[Smallblock454]

Hello tada,

is the part you're looking for on the chart, or am i on the wrong chart. If it's on the chart, which number has it. Could you alternatively link to the chart from Porsche Atlanta. Than i can look for the parts number.

Regards, Markus

[tada]

Thanks Markus and Gelbster. I was finally able to find the part number for the vacuum line - 00004320501. I appreciate the help, Tom.

[Need_for_speed]

Just throwing this out in an attempt to be helpful: any chance that the variocam solenoid on that bank has failed? And if it did, would it throw a code or light the CEL?