(repost for daytime crowd)
I figured it was time for an update post on the SC, since I didn’t get into any details of the work I’ve been doing in the “intro” story. I’ve been a busy boy because cheap 911's inevitably have a mountain of needs. Mainly I’ve been working towards solving some rich running issues and setting a maintenance baseline, as well as getting the car ready for the drive to Luftgekuhlt in LA. That last bit is important, as I’ve thus far only done local driving in it, without the sustained higher speeds and temps that Southern California roads can bring. So, without further ado, this is what I’ve been up to.
First up was an oil service, spark plugs and valve adjustment. A few exhaust valves were slightly tight, but not nearly as bad as I feared given the mileage. As we did the top end of the engine about 60,000 miles ago, this indicates it’s doing fine. I also cleaned the PCV breather trap. Basically just a metal pipe with some steel wool in it, the trap was almost completely blocked with sludge. The previous owner of the car did much of his own service work, so the oil had not been changed since some time well before he passed away. I sent that sample off to Blackstone Labs and await their report, and I’m looking forward to seeing how the next sample compares. This car has run Castrol 20w50 its whole life, so that’s what I put in it with a splash of Lucas Zinc additive to make up for the reduced ZDDP content in the modern formulation of GTX. Going forward I may switch to Kendall GT-1 20w50. During the valve adjustment, I found a stash of acorns atop the oil cooler on the right side of the engine, so I’m glad to clean that out. Makes me wonder what else is hiding under the engine’s top cover though, I’ll have to drop the engine for that sometime down the road.
Next up, the rich running issue, which turns out to have been much more involved than I expected. The car had always run a little rich, but suddenly became much worse and started misfiring on tip-in due to badly fouled plugs. It was also mostly unresponsive to mixture adjustments. This would not only fail to pass smog, but would destroy the catalytic converter and wash down the rings in short order. This is the famed Bosch CIS/K-Jetronic system (OOooh voodoo, witchcraft, dark magic and sorcery wooOOooo!), specifically early K-Lambda as it has an oxygen sensor and frequency valve for mixture adaption. First I checked that the injectors were holding pressure (they’re completely mechanical and have a specific opening pressure) and that their spray patterns were good. Next I checked the control pressure and found it out high and out of spec, i.e. it was not being regulated down from system pressure correctly. This meant it was time to remove and disassemble the Warmup Regulator (also known as a Control Pressure Regulator), which is basically a heated bimetallic spring acting on a diaphragm to regulate the system’s basic fuel pressure. The oxygen sensor/frequency valve combo then adapts around load. When I got it apart I found corrosion everywhere, so it went in the ultrasonic bath. Fortunately, the heating coil around the bimetallic spring met the resistance spec. I also disassembled the diaphragm plate and cleaned the fine screens to the input and output ports with brake parts cleaner until I got clean streams through both, which was the real problem.
With this done and the warmup regulator back in the car, the control pressure settled down to spec nicely after warmup, running about 52psi (system/supply pressure is around 78psi). Still, it ran too rich, so I looked elsewhere, which is where the fun begins. First, I found the cold start injector miswired and the airflow plate lift sensor disconnected and plugged into some kind of a jumper harness. After correcting these issues, I moved on to the Fuel Distributor (also known as the metering head), which I like to call the fuel spider, shown below with a Volkswagen factory service bulletin.
I looked through the records and realized that about 8 years ago I had diagnosed the car as having a bad fuel distributor because, surprise! It ran too rich. I really should have remembered this, but I are dumb sometimes and have worked on and written up a lot of cars since then. The owner didn’t have us fix it at the time, and either did it himself or had someone do it for him. This also explains the wiring issues mentioned above. It must have worked for awhile because the car passed smog in the years since, but the issue came home to roost for me. I removed it from the car for inspection and found its plunger and bore badly scored, worse than any I’ve seen, and better yet, it was glued together.
Below, the plunger. These surfaces need to be perfect. Obviously, they were not. This plunger moves up and down via the airflow sensor plate through a sealed bore in the fuel distributor, changing the pressure relationship between upper and lower chambers of the fuel distributor depending on height. On this updraft-style system, the higher the plunger, the more fuel goes to the upper chamber and thus out to the injectors, which are constantly fed (hence C-I-S, Continuous Injection System).
Turns out, whomever “rebuilt” the unit seems to have done nothing more than strip it and put it back together with RTV or similar. This, as you may guess, is a big no-no. Bosch’s service information is very, very serious about this stuff and basically says DO NOT FUCK WITH THESE EVER. I had really wanted to take it apart myself to see how bad it was, but as it was so thoroughly glued together I didn’t want to risk damaging the unit because they’re very finely calibrated, not exactly easy to find, and are very expensive when you do. I decided to order a really nice rebuild kit from CIS-Jetronic.com, $125 with a laser cut stainless diaphragm and Viton seals, and sent the unit off to the good folks at Fuel Injection Corporation in Tracy, CA for a rebuild, who we’ve used for years at the shop. A little more than a week and $400 later, I had it back:
Worth every penny. After installation, the car settled into running much better after warmup, so I tuned it on the 5-gas with my multimeter watching duty cycle on the frequency valve, and it came right into spec, running great. I was elated. With that, I was off to smog, where it passed nicely.
I have not been that relieved about something in a long time. The great injection battle consumed several of my limited weekend days, including Easter afternoon after playing bunny and hiding eggs for the kids in the morning. It was a bit of a tight timeline, because I bought my ticket for Luftgekuhlt 6, and damnit, I want to drive this car down there so I needed the tags up to date by May 11. I’m still sorting out some uneven running during warmup ( I think the Warmup Regulator may have been adjusted around the bad fuel distributor, but there’s no way to know visually and it’s also something not normally messed with), but after the first minute or so it runs perfect. With smog done, I moved on to sorting some smaller issues. The first of those was the steering column bearing:
The bearing itself is fine, but they have a plastic sleeve in the center which crumbles, allowing the steering wheel to wobble around about 1" in any direction. Replacing the bearing requires removal of the steering column, which is a pain in the ass, but the aftermarket has come to the rescue with an easily installed metal repair sleeve that presses in place of the plastic one. The helm is so much better now! Next I’ll need to rebuild the shifter or save up my pennies for a Wevo unit, the 915's gates are a little squiffy so it’s hard to get first sometimes. In other news, wheels & wings...
Check that stuff out. I scored a set of 7 & 8" polished Fuchs off of a client’s old 944 that he’s parting out to turn into a race car, for the low low price FREE.95! Actually, I have of to take the engine and driveline out of another parts 944 for him, but still... big, fat, dished and delicious Fuchs, an inch wider than mine, for no dollars! I’ve test fitted the rears to make sure that 245's don’t rub (they don’t), and I need to find new rubber because the perfect-looking Dunlops are in fact well past the expiration date. This is a slight bummer because 245/50R15 tires don’t exist in anything other than full race gumballs so I’ll have to drop to 40 series out back. This won’t look as cool, but the BFG G-Force Rivals I want are a well regarded tire nonetheless. I also scored a Craigslist hoard of parts (see back of truck above), including a fat rear swaybar, spare rear muffler to experiment with, Turbo whaletail and fiberglass IROC tail for a few hundred bucks. I plan to clean up and resell the wings to make up for the cost of the lot and put some coin back in the car fund, though I have an idea for a bike rack for the rough Turbo tail...
Lots more to do on the ever-growing list on this car, but that’s all for now. Luft6 here we come, fingers crossed.