Cabriolet: the un-fuckening begins

"I like cars: Jim Spanfeller is one ugly motherfucker" (qaaaaa)
06/16/2020 at 20:41 • Filed to: None

Hood up, the way they usually are

Ever since I bought my 1986 Cabriolet, it’s run kind of terrible. I’m talking “idles at 1600 and has a massive exhaust leak, also don’t try to drive it before it gets warm or else it’ll stall” terrible. That’s kind of not cool. Since I bought the car, all I’ve done was:

Change the oil with the wrong grade of oil, whatever

Put a fresh intake air filter in

Replace the cracked radiator

Change the brakes, find that one caliper was seized

Replace the badly worn out rain tray cover

I still need to replace that brake caliper. It’s fine as long as you give yourself adequate stopping distance, but sheesh, that explains the core support damage. (Nothing important is bent, just the bottom section of the support is pushed in, which might be why the radiator was broken when I bought it)

So, let’s commence. The car is from 1986. This means it has Bosch CIS with closed-loop lambda control. The oxygen sensor sends feedback to something on the fuel distributor called the “frequency valve”, colloquially known as the “buzz box” since it buzzes when properly operating. To adjust fuel mixture, one must insert a 3mm hex wrench into the adjustment hole in the fuel distributor, turning a small screw. You check the set point with a dwell meter (or some other way of measuring duty cycle). When set appropriately, the dwell meter will read 45° of dwell, or 50% duty cycle. However, I do not own a dwell meter and none of my friends have one, so I’ll do this the “right” way eventually. There’s also a small screw on the back side of the throttle body, located in such a place that you must burn you hand when adjusting the idle air bypass. Thanks, guys.

The screw was almost all the way out when I first adjusted it. This explains the 1600 ish RPM idle. But why was it set this way? With the engine hot and running (this is important), I turned the idle air bypass screw until idle was about 800-900. That seems right I guess, the tach wiggles a bit anyways. Whatever, it wasn’t choppy or high. So I turn it off and let the motor cool for a bit while I put the tools away. Job done, right? That was easy.

The next start attempt saw the motor fire a few times then turn off. Crap.

My assumption: One of the POs of the car (the guy I bought it from only had it briefly, said he inherited it. Seems legit) found the car to be running rough, so they removed the factory anti-tamper seal one must remove to adjust the mixture, adjusted the mixture, realized they screwed up, and cranked the shit out of the idle screw to compensate. It’s run well enough for me to drive it ~2000 miles, so whatever.

Not having a dwell meter, I just sort of guessed, made some adjustment, let it cool for a few minutes, made another adjustment, etc etc etc. Now it idles at ~850 and revs up and down without sputtering. When cold, I have to hold my foot on the gas for a bit to get it to not stall out. That’s fine for the time being.

CIS Lambda, formally known as K-Jetronic on this car, features the fuel distributor with air flow metering plate, a cold start valve which sprays fuel into the manifold when cold (instead of, you know, having a choke), a warm-up regulator, which measures the temperature to control fuel enrichment, and a few other components. Watch !!!error: Indecipherable SUB-paragraph formatting!!! if you want to have your mind numbed by the absurdity of CIS and the genius of the engineers who designed it. It’s pretty cool.

Pictured above on the end of the intake is the cold start valve. I didn’t take many other photos as my engine bay is pretty gross. I think what’s happening is when the engine is cold, the fuel mixture is enriched enough that the car will stall if the throttle isn’t open. This is not the only issue with the car. It runs and drives pretty fine as is, but vacuum leaks, the enemy of CIS, are non-zero. I found none on the intake air side, but manifold vacuum had a number of badly dry rotted hoses.

I replaced a bunch, all related to the vacuum advance for the distributor. So far this actually has a somewhat large effect on drivability. I also removed the windshield wash bottle, since this is a race car.

So, to do:

Hunt down a dwell meter or similar and get this running better

Replace V belts

Clean up the engine bay more

Fix the core support

Fix the brakes! This one obviously is more important.

Then I can move on to the fun stuff.

DISCUSSION (18)

dieseldub > I like cars: Jim Spanfeller is one ugly motherfucker
06/16/2020 at 20:54

Oh man, I usually only adjust the fuel dizzy on those as a last resort.

It’s all about chasing vacuum leaks as step 1. Step 2? Check for more leaks.

Crumbling crankcase ventilation piping? Vacuum leak. Cracked dip stick funnel? Vacuum leak. Cracked intake boot between distributor plate and throttle valve? Also gonna mess with you. Intake manifold gasket leaking? Old injector o rings?

These old things do not tolerate vacuum leaks with the fuel injection system being as mechanical as it is. Also seem sensitive to less than perfect ignition system. I always seemed to go through more caps and rotors on CIS cars than more modern fuel injection systems due to this.

I’d also check injector spray pattern (yank them all out, aim them into a bucket, jumper fuel pump relay, pull up on air flow plate in the fuel distributor and make sure the patterns all look similar, similar flow etc. Then also check fuel pressure from the pump.

Once you’ve verified virtually everything else is infact correct, then go ahead and start messing with the fuel distributor’s adjustments.

I like cars: Jim Spanfeller is one ugly motherfucker > dieseldub
06/16/2020 at 21:01

I sprayed everything intake side with carb cleaner, no leaks there. Spraying the breather hose didn’t change idle, I suspect it’s clogged up somewhere. I have to hunt down a new hose set. Everything was out of whack on this. Idle air bypass was almost entirely out of the throttle body. When I got the car, most of the electrical connectors were disconnected. I don’t think I could have made it run worse and still run.

lone_liberal > I like cars: Jim Spanfeller is one ugly motherfucker
06/16/2020 at 21:22

For a dwell meter check with your local old guy. I’ve had one gathering dust since I got rid of my last points-style distributor and I’d guess a lot of my fellow old guys are the same.

I like cars: Jim Spanfeller is one ugly motherfucker > lone_liberal
06/16/2020 at 21:29

I rent some space in the back of a local museum that I keep some of my cars in. The museum is all British stuff, most with points, but somehow, not a single dwell meter to be found. I’m just going to buy one. Or borrow an oscilloscope from work.

dieseldub > I like cars: Jim Spanfeller is one ugly motherfucker
06/16/2020 at 21:32

Oof, sounds like quite the mess to untangle.

CIS just makes me appreciate diesels more. LOL

I like cars: Jim Spanfeller is one ugly motherfucker > dieseldub
06/16/2020 at 21:37

Yeah. I really can’t overstate how poorly it ran. Are you a VW mechanic? I’m having a tough time finding the valve cover vent setup. I would like that to work.

I have an 81 Rabbit diesel. The motor is in the machine shop right now. I briefly had a Mk2 1.6td, but I didn’t really want to work on it, too leaky. I got it because it was cheap and flipped it. Those motors are beyond simple.

MiniGTI - now with XJ6 > I like cars: Jim Spanfeller is one ugly motherfucker
06/16/2020 at 23:19

Sounds a bit like the Jettronic in my 85 Jaguar although I don’t think mine’s closed loop. Luckily apart from requiring somewhat excessive cranking especially on hot restarts it actually runs extremely well without the slightest bogging. Idle’s about right though I wish it was a little smoother.

dieseldub > I like cars: Jim Spanfeller is one ugly motherfucker
06/17/2020 at 14:24

I am, though I haven’t really messed with a CIS car in about a decade. I owned a Mk2 GTI 16V for awhile myself.

I do more TDIs than anything these days, with the occasional older 1.8T and direct injected 2.0 TSI or FSI thrown in for good measure.

I rarely touch the old IDI diesels anymore either, like those 1.6s.

There’s a late Mk2 diesel Jetta in my possession now (91) that will be getting a TDI swap in the not distant future. Should be a riotous little car.

I will say that old 16V GTI was reallly fun. When you get those old CIS gassers running right, they are some of the most responsive to your throttle input engines I’ve ever driven. Just feel so eager, even though they’re not supremely powerful on paper.

dieseldub > MiniGTI - now with XJ6
06/17/2020 at 14:26

If it was K-Jetronic or KE-Jetronic, then yeah, would be the same basic system.

CIS/CIS lambda/CIS-E is just the VW/Audi terms for it.

I like cars: Jim Spanfeller is one ugly motherfucker > dieseldub
06/17/2020 at 14:34

After the guesswork adjustment I did yesterday, my Cabby is much more responsive than it was before. I can’t wait to find out what it’ll be like when adjusted the right way.

Are you doing the full TDI swap or the mTDI version?

I’d love to find a clean GTI 16v. So hard to find one in the rust belt....

Akio Ohtori - RIP Oppo > I like cars: Jim Spanfeller is one ugly motherfucker
06/28/2020 at 14:36

I forget... do you have a copy of the Bunny Book? Has some great explainers of CIS (sounds like you’ve got a handle on it but still.... CIS mysteries abound!) and is generally a good reference. I can shoot you a link to a PDF if not.

I like cars: Jim Spanfeller is one ugly motherfucker > Akio Ohtori - RIP Oppo
06/28/2020 at 14:53

I have a few books- one that goes over CIS Basic, another that goes over Lambda. If you have a link to another it might be helpful. There’s so many variations and oddities.

I'd like to say I understand it but I really don't. It's very odd and esoteric. On the border of magic.

Akio Ohtori - RIP Oppo > I like cars: Jim Spanfeller is one ugly motherfucker
06/28/2020 at 15:10

Fair enough. I have a PDF copy here . Let me know when you pull it and I’ll kill the link/share.

CIS is bit of magic for sure, but it really all comes down to pressures and flow. Fuel pressure dictates everything in that system. The warm up regular is stupidly named because it is working all the time to adjust pressure based on engine temperature. In my Saab the output is as low as 8PSI cold (REALLY cold) and around 50-60PSI with the engine warm. Higher PSI = less fuel to the injectors , confusingly.

Similarly the “cold start injector” is stupidly named because it is in operation all the time with the Lambda system. I don’t recall the exact figures, but I think it is capable of delivering up to 10% of your fuel (or A/F ratio, I guess) while running. Basically it leans/richens the system based on signals coming from the O2 sensor. It also, as mentioned, shoots fuel into the intake on extended or cold cranks.

Sorry if you already knew all this haha. I went through hell getting my Saab running (also CIS Lambda) so I learned way too much about how it all works.

I like cars: Jim Spanfeller is one ugly motherfucker > Akio Ohtori - RIP Oppo
06/28/2020 at 15:36

Oh wow. I hadn’t heard that book name and assumed it was a CIS specific book. I’ve got it saved now.

I need to build a fuel pressure test setup. The car runs fine as is, so I think guesswork got me close to where it needs to be. I’ve got Bentley Manuals for Diesel Mk1s, a Fox book that covers CIS, CIS Lambda, and Digifant, and a Mk3 book that covers Motronic, Mono-motronic, and TDI diagnosis. Between those three, there’s really nothing that isn’t noted. But having another reference source is never a bad thing. Thank you!

Akio Ohtori - RIP Oppo > I like cars: Jim Spanfeller is one ugly motherfucker
06/28/2020 at 15:45

Np! Don’t let the goofy art fool you it is a really solid reference.

I have both a CIS specific pressure testing kit, which works OK but is shockingly limited for the price, and a massive generic one I’ve never used. I’d recommend the generic one if you could be sure it had the right fittings but... hard to say haha.

Kinja'd!!!

I like cars: Jim Spanfeller is one ugly motherfucker > Akio Ohtori - RIP Oppo
06/28/2020 at 15:48

Wow, that’s a lot of coin for a single purpose tool. I’ll probably put one together with the appropriate fittings. I’m not afraid of plumbing together converters and such, so I can probably get it done a bit cheaper.

Akio Ohtori - RIP Oppo > I like cars: Jim Spanfeller is one ugly motherfucker
06/28/2020 at 19:32

Yeah larger kits can be found for a lot cheaper.

BrooklynEagle > Akio Ohtori - RIP Oppo
06/29/2020 at 12:04

That book is a MARVEL. Hadn’t seen it since I sold my last Rabbit in 1989.