Symptom/Solution: Running Hot, Poor gas mileage, high idol, stumbeling

[Akira28]

Hello Pelicans,

This is the second post in an attempt to thank everyone for being so kind in providing information for those of us trying to repair our newly acquired 911’s. Here is the problem I found and how I solved it.

911SC (1983) 3.0L – Purchased 6 months Ago
CIS and Loop Cooler..

Symptom(s): Started running hot by about +15 to +20 degrees (and climbing when stopped in traffic). Poor gas mileage, stumbled occasionally at stoplights, idle running about a grand too high (9.5 rather then the typical 8.5).

After reading through the “101 Projects” book I received for Christmas, I noticed on page 100 that replacing the oxygen sensor could potentially help the current gas mileage I was seeing (about 12 MPG). As I am new to the 911, I dove into the maintenance records of the previous owner and discovered no info on when the unit was last replaced. So I jacked up the car, pulled the drivers side rear wheel and replaced the unit.

The end result is that the idle was instantly corrected.
The gas mileage increased by 3-5 miles per gallon
No more stumbling when you step heavy on the gas pedal.
And most unusual of all, the car stopped running hot.

It’s weird that replacing this unit would have such an effect, but considering I was about to start taking drastic measures to cool down the oil (external oil cooler), just to drive to work and back, this was a pretty fortuitous side effect.


Side Note:
The “101 projects” book is absolutely invaluable for we first time 911 owners. There are a few points that I would like to add for 911SC-er’s out there who look at the pictures in the book and go – “Umm wait, it doesn’t look like that on my car”. Actually it does but the pictures are taken with hoses and covers removed and you have no land mark references with tight shots of parts. Once you actually find the unit then the pictures make conceptual sense.

1. Jack up the rear end of the car and pull that tire. With my 83 SC, you can not get to the Ox unit (before the Cat) from underneath without removing the rock guard, and considering the beating this thing takes that is a big pain in the butt. So instead just pull the rear drivers tire and work over the top of the guard. The job becomes 100 times easier and the less you have to remove the better.

2. Once you have the Ox unit removed trace the cable to it’s plug in the fire wall, the rubber plug pulls right out, but do not pull super hard or it will disconnect the plug from it’s nipple above (in the engine compartment where you can’t see it). Take a flash light and aim it in the hole, this will make it easy to spot when you go to trace the wire to its origin point.

3. Open the rear deck and look on the left hand side for the light you’re shining in from below. My engine has two large black air intake hoses that make it impossible to reach the wire and cover the final plug-in point from being visible. The wire goes to a black rubber boot that connects to a (orange-ish) nipple on the left hand wall of the engine bay about halfway up the wall (right below the silver beer can like fuel filters and such). Remove the retainer band from any hoses that get in your way and use a zip tie to attach the free end to anything on the decklid to keep it up and out of the way.

4. Replace the Ox unit with a C shaped sensor tool, don’t purchase the full round socket style unit if you can avoid it, (Santa -wife brought mine so I didn’t have a choice) they make no accommodation for the rubber boots or the wire.

5. The hardest part of this project was putting the rubber firewall plug back in. What took two seconds to remove took 10 minutes to replace. The only way I managed to get it in was to start it and twist the unit over and over until the rubber grommet was secure. There is no way to make this any more practical that I could find. But if you just start an edge and push while twisting (then turn the wire itself in the opposite direction to remove any tension) eventually it will seat itself.

The job itself is simple in retrospect and while I respect Mr. Dempsey’s work to the utmost, the project time estimates are based upon someone who actually knows what the heck they are looking for and not a complete newbie. It took me longer to find the sensor then it did to change it out. Perhaps we could get him to include a retarded monkey scale of difficultly.

But once the job was done, it had such a significant impact on performance and temperature that I hope other first timers find this post.

P.S. A suggestion for the wonderful, tough old birds out there, who have become the gurus of our group and the book writers. One of the hardest things to explain and to gain a perspective on is the idea that finding things on the 911 is not as intuitive as you might think. I’ve had my car for about 6 months and I have spent just about every weekend tinkering on what ever I can find and I even have a few friends that will come over to lend a hand. The one thing I’ve gotten used to hearing is “What the heck is that?”- and many of them know far more about cars then I do. So my point is please forgive our naivety and understand that even with a picture, finding the part is often more complex a task then actually fixing it.

Pictures need easy to identify landmarks like (tires, air intakes, mufflers or fans) and for the love of all that is good and feathered, will someone please post up a picture with an arrow pointing to the location of a major land mark and the Warm Up Regulator. There are at least 50 people on this board reporting the identical cold idol problems I’m having and I can’t be the only one that can’t find a picture of the little sucker (installed on the engine).

Thanks so much folks.. Hope you all had as fun a Christmas as I did, Akira28


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1983 911SC
1984 944-NA

[stlrj]

"...Started running hot by about +15-20 degrees (and climbing when stopped in traffic). Poor gas mileage..."

"...I was seeing (about 12 MPG)"

After replacing the 02 sensor: "The end result is that the idle was instantly corrected.
The gas mileage shot up by 3-5 miles per gallon"


It seems that replacing the 02 sensor corrected a too rich mixture problem that made the engine run hot.

My experience with too rich mixtures also confirms the elevated engine temps I have seen which goes against what most would expect...very interesting.

[burgermeister]

Hee hee ... glad I'm not the only one that has time-dilation issues. After my first valve adjustment I learned to budget 3 times the advertised project time, and I've exceeded that on occasion. There must be a way to use this 3:1 ratio to determine how many retarded monkeys I get on my mechanical ability scale???