Doug E.

I had a similar problem with my 1984 911. I went through many of the same steps. In frustration, I took it to a really good local Porsche mechanic. It turned out to be the intake manifold gasket. It was old and dried out, so it was letting air in and running the car much too lean (acting like a vacuum hose leak). The part didn't cost much, but the labor was expensive.

I've heard of people diagnosing these types of problems by CAREFULLY spraying a LITTLE starter fluid around the gasket while the engine is running. If the engine revs up, then you've found your leak. But be careful, because this stuff is very volatile.

bott63

Doug,
Thanks for the suggestion... Already been there, done that, and paid for that $$ Unfortunately, this didn't fix the problem...

Ian~ I did drive the car about 150 miles this weekend, after doing the Intake Cleaner routine. The bog has moved up to the 4300-4600 rpm range now, and when under full throttle.... The demon has apparently found a new home

Also, while cruising on the highway, at or around 3k rpm's, there is an intermittent surge. Nothing like the bogging sensation previously noted... I'm still running the K&N Filter, but will be soon replacing it with an OEM unit. At that time, I will attempt to again clean the intake, and sensor's/element to see what happens next. After this, I will be contacting my Priest to see if he will perform an Exorcism on the car....

Did you try anything new on your car this weekend Ian?

Pat

Dan Cobb

Could the electrical connections on the MAF be questionable when the motor shifts under load?
It almost sounds like an intermittent ground or +12V.
Disassembly relocated the wire a bit and now the current path is different resulting in a new location w/ respect to RPM.

Just a wilda$$ guess, but I have been witness to stranger things.
+++

bott63

Thanks for chiming in too Dan, as ALL guesses - big, small, smart, wilda$$ are welcome and encouraged to remedy this strange problem

At this point, anything is possible... Because of the way the symptoms changed, one would think that it might be due to what I just tried.... However, as the problem has been present more lately than not, it still is one of being intermittent... As my mechanic did run the EFI 8400 piggybacked on the harness for the computer while the problem was happening, it did not show any inconsistencies in voltage from any sensor, or any of the other 32 pins that are on the DME... My frustration is not aimed at anyone, other than the phkin Demon that has taken up residence in my car...

Eye thinks that it is highly likely there is some sort of a grounding issue somewhere.... At either one of the harnesses, or at a sensor? This is hard to believe, as the diagnostic tool used SHOULD have identified any voltage inconsistencies in the entire system, as the problem was occuring. The other possibility, is perhaps the AFM sensor element might be gunked up with dirt or sludge from the K&N Air Filter. As the original bogging under light load disappeared, it moved to the 4200krpm area as a bog under full throttle. WHY? Find the answer, and I shall dub thee "Von GudenWrenchen!!"

Pat

rbcsaver

Pat,
I know how frustrating and expensive this chasing is, as I have been there. I will just type some thoughts. I not saying they will or will not solve your problem. Double check and re-clean all of your grounding, including battery. How is your copper tranny/motor ground strap? I replaced mine at a the last motor drop just because of age. A number of years ago, I read a tech article on one of the Porsche Racing Motor builder's sites (CDW, CRW or something like that) about how ineffective the chasis/body grounding is and they dynoed some increased HP by running a ground directly from the neg battery terminal to both heads. I connected mine directly to thv valve cover bolts. Brandand octane of fuel. If chipped you should be using only 93-94 octane and preferably the latter. Check the intake manifolds for tightness. Check for good seals/leaks/tightness around throttle body, Your coil is OK?
regards
Steve

bott63

Thanks Steve~
I did have one of those "quick disconnect's" on the battery for when you are going to have the car parked for extended periods(definitely added from P/O.) Removed that P.O.S., installed new terminals, NEW battery. Then checked the ground strap at the tranny. Good call - as there were barnicles growing from that nether region... Ground off the uglies, put some aircraft quality grease, of dielectric standard!, and put new strap on.(Not that kind of strap-on...) Keep in mind we did this about 2 months ago... The problem while not completely gone, cleaned up considerably - I'd say about 80% better.... Then it all came back about 3 weeks ago... The car did get driven alot in the rain this year, as we had record rainfall in SoCA this last season 33"+?? I'm intrigued by the suggestion of running a ground to "both" heads...Makes total sense!!! Did you run one line back to engine, then split it? or 2 lines from the neg. battery terminal???? I gotta know!! I might have to give that one a go...
Coil checked out perfect... Intake manifold is tight, and has a new gasket we just put on ... Throttle body is good and seal is good too... But... would it be likely that the problem would be intermittent if there was a leak of vacuum, or at the intake or throttle body gasket?? Wouldn't that be a constant problem?? I've had other vehicles that have had vacuum leaks, and the problem would always remain constant until the leak was corrected!

I run Union76, and Chevron which unfortunately on the left coast is only 91 octane. I do have an Autothority Chip installed... This was before I knew about Steve Wong, or even the Rennlist BBS for that matter!(5 years ago...) The chip was removed and replaced with the OEM, & the problem still remained... I have the Autothority chip back in now... I could Fill up the tank with Union76 Race fuel (100 oct.) as I am not running a Cat... However, I might try the new grounding approach first, as I'm not sure that the fuel has anything to do with it...

Thanks for pointing me in a different direction!!!

Pat

rbcsaver

One heavy 6-8 gauge wire then split to each side with long flat ended battery straps. Will try and get a picture later. This is only just a thought.
Steve

bott63

Thanks Steve

rbcsaver

Pat, Best picture I could get. The area is so narrow, dark and my arm still doesn't bend well enough. It also occured to me that there was recently a very similiar discussion on a Subaru forum and bought the wire to do it, just haven't gotten around to it yet. The concept is the same, the motor is just in the rear of our Porsches.
http://forums.nasioc.com/forums/show...ight=grounding

The heaviest wire that you can fish from the batterty to the motor the better. You can get some pretty good braided and well insulated wire and connectors at Lowes or HD as well as electric supply. Auto supply won't have heavy 6 gauge or so. After I got the wire to the motor, I connected it to 2 black battery cables with "terminal to starter" ends together(package descript according to the Advance Auto packing this AM), then one lead to ech side of the motor.See the attached pic of the left side. Each end has a flattened connector with 3/8 or so hole, that you can place under on of the The come in lengths up to 6 ft or so, but buy the correct length. Certainly try iut a different way I you have a better way. The Porsche I did probably 8 years ago.
regards,
Steve

bott63

Thanks for the info Steve! I just checked out the Ubu link on the topic... Very cool. Honestly, I would probably pay $500 for a mod kit if it fixed this problem.... But $10-20 to start is even better! Hard to believe that .3 to .5 ohms less resistance could really make a difference, but stranger things have been found on these cars before... I suppose that under load, maybe the ohm difference might be even greater? Another project lies ahead...

Pat

Dan Cobb

BTW,
I would place a flat washer between the nut and the terminal. It will make for a tighter connection and it won't bugger up the connector when it gets tightened.
+++

ian911

Pat,
Sorry I haven't responded quickly. I am in the middle of a move. I was really hoping that trick would work. I haven't had a chance to try it myself yet. The fact that it did move the hesitation seems like you are on the right track.
The 928 is a fun car. Much faster in a straight line at high speeds than the 911. It has a great driving position as well. The 911 is more fun in the twisties though. The 928 also can be expensive to maintain, so get a good one.
Ian

bott63

Thanks Dan, and Steve... It will probably be a couple of days before I can try the new grounding method. Definitely the next plan of attack!

Ian~ read the last couple of posts... Looks like an alternate method of grounding the battery lead might be the issue here???? I'm crossing my fingers!!

I'll be sure and let you guys know as soon as I make the change!

Pat

bott63

correction... Grounding is the issue... Possible solution - alternate method of grounding!

bott63

Any updates?

Ian?

Problem is still ongoing with my car...
I've installed new CHT, speed and reference sensors at the flywheel.... Still runs bad...
Considering having the distributor curved?

Any body else have any luck to report??