3.2 Liter Stalling Out. Please Help!

[EMJ]

My 88 911 Carerra stalls out intermittently at low and hwy speeds, then starts right back up again when started. Apparently a common problem, but the car has been to a noted motorsports shop and a local dealer and still the problem persists.

Here's what's been checked and fixed so far without success:

-DME relay, coil ignition connections, relevant fuel pump connections - Corrosion was sanded off of the various connections, and all connections were snapped, fastened, and tightened. Worked at first, after a couple of days, problem reoccurred.

-DME relay - tested fine

-Cylinder head temp sensor - tested fine

The car has an Autothority Mass Flow Sensor and Chip -- the dealer is wanting to replace these to stock DME and flow sensor to see if this is the problem. Very expensive! Don't know what else to check -- definitely an electronic issue somewhere

Any help is greatly appreciated!

[450knotOffice]

I'm sorry that I can't really help you but I noticed that this is your first post. Welcome to the forum! I am sure that many others will chime in with ideas. Some will probably suggest you do a search using the "search" button in the upper right corner. There is a huge pool of knowledge in the archives. It has helped me many times.

As is tradition on this board, you must post some pictures of your car when you are new to the forum. We always look forward to seeing new members cars.

By the way, where do you live, at least generally speaking? You may want to add that to your profile because many times fellow board members that live near you will offer help, or may ask for help from you someday.

Good luck with your engine problems.

On a side note, your ID - EMJ - do you happen to fly for a living and if so, do you fly the EMJ? I ask because I fly one out of LAX.

[ZOA NOM]

Replace the DME relay regardless of your test. They can test good and then once installed, tiny stress cracks in the solder joints can be flexed enough to fail intermittently. As a short-term fix, you can re-heat the joints to flow the solder and hopefully seal the cracks. It's also possible (but highly unlikely) that there are similar soldering issues within the DME itself. Eliminate everything else before you replace the DME. Swap with a known good one before you believe it.

[EMJ]

Thanks for the replies.

The DME relay was actually replaced and tested, as well as the cylinder head temp sensor. The dealer did find corrosion and loose connections and corrected, but this hasn't worked. I'm skeptical about swapping out the aftermarket DME and mass flow sensor. I agree that these should be a last resort.

They claim that there are no other corroded or loose connections that could be causing this shut-off issue. Anything out of the ordinary that should be checked? Besides the standard electronic connections?

BTW, EMJ are actually my initials. Didn't know I had an airline named after me. Cool.

Thanks for the help.

[nhromyak]

The DME's ignition control is known for doing this as they get older. It can be refurbished, but as I recall your DME will be modified for the MA sensor.

It could also be a coil going bad, or the flywheel sensor(s).

Was your CHT sensor replaced?

My DME did this, and it even bench tested fine! I finally replaced the DME with a known good and I didn't have anymore issues.

Good luck.

[jtratza]

EMJ, I have the same Autothority mass flow and had the same problem. It took a while to track down and find the potentiamoter in the wireing harness to the mass flow was bad. Cost to replace a few years ago was about $90. Call Autothority and if they don't have th replacement they should be able to give you a number where to find one. Mine BTW had about 90,000 miles on the system before it went bad. LOL

[EMJ]

Guys, thanks for the replies. Very helpful.

The coil and its connections tested okay but I don't believe there's been a flywheel test. The CHT was replaced, same issue. Same with the DME relay.

The potentiometer in the wiring harness to the mass flow I don't believe has been checked. The focus has been on corrosion in the connections and securing connections, CHT, and DME relay, etc. Would be great if this is the problem and a new DME isn't needed. This sounds promising.

Only problem is that Autothority is out of business. Jtratza, Any ideas of where we could get a replacement, generic part -- potentiometer -- for the wiring harness of the Autothority mass flow?

[jtratza]

Call Performance Products. They gave me the name and number of the company taking over the mass flow. Trob;e is I didn't write any of it down after I talked to them. I think it was A.P.E. Try a search for them but Performance should be able to help. I'll bet a couple of beers its the potentiameter. My car was doing the same thing as yours and causing me and my mechanic fits tracking it down. Finally he said its gotta be the potentiameter. I bought a new one from Autothority and replaced it myself and car has worked fine ever since. Well except for that rebuild due to the head stud, oil leaks and cam upgrade.

[EMJ]

Thanks, jtratza. I'll give them a call!

[EMJ]

I was able to track down the maker of the AutoThority Mass Flow Sensor -- GPR Parts & Restoration, but am having some trouble getting in touch with their Porsche guy (Out of office).

Anyway, the dealer tech is asking for the location of the potentiameter on the mass flow wiring harness. They say the only non-P-Car part connected to the wiring harness is a black box. Is this the part that would need to be replaced? The black box?

I may get the answer from GPR, but I'm not sure when I'll be able to get in touch with them. jtratza, is this what you replaced when you fixed your issue? Would you happen to have a part number?

Thanks for all of the help.

[jtratza]

EMJ, Attached is a pic of where the potentiameter resides. Its hard to tell from this pic but its the small part that is taped up between the two connections between the Mass flow the wiring harness. Its about onehalf inch wide and a cople of inches long. I wrapped it in tape to clean things up a bit. Mine began intermittantly failing a few years ago like yours. I'll look for the receipt tomorrow.

[EMJ]

jtratza, thanks so much for the picture. It's a big help. Hopefully, I can get in touch with the GPR P-car today so that I can order this potentiameter part.

Keep you posted!

[jtratza]

No probelmo. BTW what year is your MAF. I think they made a change in the system about 5 years ago. Mines about 14 years old.

[EMJ]

It was on the car when I bought it a year ago, and I understand it was just installed, so I think it's about a year old.

[jtratza]

Found it! The part is WIR.911.100 MFS Wiring Harness. I bought it from Autothority June of 2002. Also try calling A.P.E. at 703 323-0919

My potentiameter lasted about 8 or 9 years before it failed. Seems odd that it would crap out after a year or two. There is an adjustment on it but unfortunately I cannot remember what it was. A.P.E. will have the adjustment data. Looking at your fixes to date you did just abot the same replacements as I did, cylinder head sensor, DME, O2 except for one which was to replace the throttle valve switch.

Good luck

[EMJ]

Excellent -- THANKS! Will let you know!

[EMJ]

Issue seems to be fixed! Whew!

So I got a hold of the A.P.E. folks who gave me the number to the company that bought AutoThority here in northern VA. I called up the shop and spoke with the owner about the MFS possible issue, and the potentiameter possible fix. After a few minutes -- the guy was extremely helpful -- he told me to bring the car down, he thinks he knows what it is.

I take it down, and would you believe it, he pulled out the DME relay, popped open the cover, and there it was: some burned out tips on the relay! Long story short, the relay was never replaced it turns out -- the other shops used "test" relays and never bothered to put a new one in. Still, the DME relay was the final piece of the work it appears -- the issue was a combination of loose connections in several places, buildup of corrosion around several connections, etc. He checked the connections tightness and corrosion -- looked good. He test drove it, tested good. I drove it home 35 miles -- good!

So, all in all, the electronics, connector stuff that would go bad sooner or later has been done (Maybe a little sooner than needed). Hope she doesn't act up tomorrow.

jtratza, THANKS SO MUCH for all of your help. And THANKS to everyone who helped out. I'll let you all know how it goes over the coming week.

[jtratza]

Glad to hear all's well. Especially since we're fellow Virginians. My folks live in Keswick and my sister and her family lives outside of Richmond. Keep us advised.

[ZOA NOM]

So you have a new spare relay in your glove box, right?

[jtratza]

Zoanas,
Wish I had a spare set of those in glove box. In addotion to my foks now living in Virginia before Contra Costa County. My grand parents lived in Livermore back in the 50's. Not country nor nuke anymore is it.