Poll about "surging" on K-Jet with Lambda models

Last 20 308QV and 328 cars serviced, zero to barely perceivable surge....

 

My 87 3.2 Mondial has no surge that I can note. I replaced the O2 sensor about 2.5 years ago as a matter of being thorough on the service and there was no record of it being replaced in the past.

I have driven my car about 20K miles over the last three years and as soon as it's warm it idles so smoothly and beautifully that I just love to sit for extended periods of time at stop signs and listen to it.

 

You know this is very interesting to me ---- thanks for bringing it up, Steve.

I've owned many, and a fairly wide variety of, different makes / models of cars employing CIS-E / CIS-KE systems over the years.

And, this problem of perceived "surging" only comes up with Ferraris. Therefore, it must be related to some problem / inefficiency with the Ferrari (Marelli) ECU electronics that are used ---- either directly, as with the earlier cars running everything out of the same Marelli unit (or) indirectly, as with the later cars using separate Marelli ignition units which "talked" to the separate Bosch injection units --- as all the other cars I've had experience with use integrated Bosch ECUs to manage their combined CIS systems and ignition systems.

 

The system that Ferrari used has nothing to do with MM, as the lambda control box is made by Bosch. Other than some very basic parameters and pin-configuration, the systems are identical. There is no cross-communications between the MM ignition unit and the Bosch lambda box. With the low miles that most Ferrari's see, versus the European siblings sporting the same lambda box, it is surprising to me just how many still have the original O2 sensor in place. I got started with an independent shop in the 80 and then taught diagnostics to other shop owners on the Bosch D, L and K-variants. The surging that you speak of was certainly experienced by many other marques. The lack of regular driving that most Ferrari's see, coupled with a large percentage of DIY service exacerbates the perceived (by some) major problem.

 

People created the 'Weber myth' by fiddling all the time, the same has happened with the Bosch systems. They are not tolerant of tweaking into the unknown, most times it is a matter or carefully resetting the basics, some changes are needed to properly use the modern fuel blends, but they are small, very small.

 

Very true --- if the system is working correctly and every component is left at "factory" performance specifications, and not "messed with", the CIS stuff works pretty darn well.

 

I have had the BOSCH diagnostic item which allows a series install with each individual feul port on distributor to allow for ULTRA FINE TUNING OG each INDIVIDUAL fuel ports delivery at at host of load and RPM test reference points-and found that if even slightly "off", the car would run like dog crap if at all....(FYI/FWIW: Finnerty),
What does play a huge factor is the corrct BASE idle setting, NO VAC leaks, and PROPER hot-cold fuel pressures and an accurately set duty cycle(bosch uses one, single, integrator circuit in ALL 1/3 wire K-Jetyronic UCUs. This is an ANALOG circuit, thus, much less prone to the precision seen in LH-Motronic cars!...of ANY manufacture....rember, the freakm valve is bleeding pressure off begtween the uper and lower chamber! This is ALL a mechanical manipulation and not nearly accurate enough for the 1986 revisions for the Clean Air ACT...(noe TR changes to Ke)
the surge has been seen in Ke in MB BTW....

 

Very good information to know --- thank you.

I've also always been curious about Ferrari choosing to run their (still a Bosch design of course) air flow sensor plates in the "down" position ---- meaning that when the sensor plate moves with increased intake air flow, it moves downward. All other applications (at least that I know of) do the reverse --- the plate is raised up with increasing air flow. As a result, the AFS plate on Ferraris does not utilize a "static free play" setting (i.e., the plate moves a small distance before it makes resistive-force contact with the plunger tip on the fuel pressure control plunger) ---- conversely, the other configuration (plate moving upwards) uses a free play gap. Therefore, on the Ferrari set-up, the plate arm is always in contact with the plunger, and even right off idle moves the plunger and affects fuel control pressure instantaneously.

So, I always wondered if that configuration (the one used by Ferrari) made CIS fuel delivery "quirkiness" better or worse ----- anyone have any thoughts on that ???

 

Nope, none here. Everything working perfectly.

Believe me when I say I feel bad for those who do experience "surging" in whatever capacity it shows up as. My 2002 BMW motorcycle had similar problems and it turned out to be a combination of factors, not just the O2 sensor/ECU system.

 

My 3.2 kJet proper only ever had a problem with the O2 protection relay, which was rapidly progressive. The rest of the system worked as advertised. While it may seem a bit extreme, in K Jet cars that still are running on their original relays, not just the O2 protection circuit, I think it would be a good idea to pre-emptively change them all out - all of them.

Another obvious thing is clean gas and regularly changing the fuel filter. If there is a disparity between injectors due to clogging, the system may hunt, as well if the control pressure injector is clogged or not working properly.

Lots of German and Sweedish cars are still running well with KJet, albeit with good maintenence and regular driving. K Jet does what it was designed to do pretty well.

Jmho.

 

YES-this is a little known and even less understood design quirk..
in a 3 liter us car, the relay has a solder strip fusde ENCASED within the realy and can okly be changed by replacement of a 2-300 dollar item-or-expert Dias assemble repair, and reassembly....not for novices, believe me...
the 3.2 has a GM red(10A) spde fuse, typically car wont run-start really, but if you can get it running, it runs like crap and loops amomgst a host of quirky ailments, and, if hit with a 36-48 volt jump, its possible to exceed the capacity of the alndslide zener diode aftger the fuse and even if replaced with a new fuse car can run like cvrap
Typical giveaway here-in MB for example-would be total loss of operational voltage to ABS with dash light NEVER going off, despite the system tester otherwise saying all mis well)(oem tester)

FWIW-this item is designed and its sole reason for existence is to protect ECU for FI, and ECU for ABS(probably 2-3 times money of a FI ecu!!!) against voltage spikes caused by "JUMPING" the battery-especially from tow trucks which frequently use a 24 volt tandem circuit as most ar diesls

 

all MB V-8 cars since 1976 that used K, Kjet, Ke have plate which go down, thus pivoting in air flow housing and pushing the core plunger upwards on the slits sleeves/central plunger...I have 300SE and cant honstly remeber! But am willing to say/guess ALL Benzs which used any variant of K from76 on will have the downward travel..
chime in if im wrong-it happens everyday!

 

All cars with K-jet and lambda control surge. As the oxygen sensor measures the exhaust gases it causes the fuel mixture to cycle between lean and rich, and the idle speed will rise and fall. It is worse when the car is warming up, but still present even at operating temperature.

I listen for it to make sure that the system is operating correctly. As an oxygen sensor gets older, the response time gets slower, and the cycling is more pronounced. With the car at operating temperature, the system cycles so fast, that you should not be able to feel it surge when cruising at a constant speed. If you can, then it is probably time for a new oxygen sensor.

If the car is out of tune, and the fuel mixture is way off in open loop mode, then the surge will be worse. Carbon on the intake valves, dirty fuel injectors also contribute. Even the type of gasoline will have an effect.

Early cars with unheated single wire oxygen sensors (BMW 320i, VW Rabbit) were worse. Heated three and four wire oxygen sensors get the oxygen sensor up to operating temperature quicker, and surge less.

 

I got to thinking about this over the weekend and went out to check some milages on my 3 Sciroccos with K Jetronic and my 308. All of the O2 sensors were unplugged when I bought the cars going back past 20 years (one 27 years ago but I am nearly 100% certain it had no O2 sensor. That model year only the California package had it and I have one of those too). Over the years I tried them with and without and never noticed any difference except the 308. The surge was subtle but I could not stand it. After about 12 years disconnected I decided to hook a new one back up and try that for a while. I made it about 350 miles total. We worked as much through the basics as we could but could not totally shake it off. Finally on the way to work one Friday morning I pulled over, popped the engine cover, reached in and disconnected it. I had put 45,000 miles on it with not single hint of a problem - ever - before installing a new one and decided I had had enough from that point forward. The second I unhooked it, it ran silk smooth instantly. I had my old car back again and I loved it.

Now this is a car that I practically over maintain. EVERYONE that knows me here knows this too. In the past 15 years, I am on my 6th set of belts/tensioners (last done 11 months ago) and I am so picky about my fluids I change the brake and oil before AND AFTER every track event. What I can't do myself I let Ron do in Atlanta and he sees this car at least every other year. Those examples are just the tip of a list of maintaince issues I don't skimp on. This is why I have a car with 109,XXX miles that during the course of 15 years and 52,000 miles I have beat the **** out of in about 50 track events and have driven all over the southeast and I would have no problem driving it across country this very second.

But I refuse to spend another single penny on that ******* O2 sensor surge treatment.

Back to those other cars. This past weekend I figured I have driven about 225,000+ miles total on K-Jet cars with the O2 unhooked and this goes back to about 1985. Zero problems. None. Not one. I am walking talking 100% positive-proof that the O2 can be unhooked on K-Jet with 100% dead on reliability from that point forward.

So IF you have the surge issue like very many of us do - or we obviously would not be having this discussion to begin with, take your car in to a good experienced mechanic and have him do what he can do. At some point you will have to decide how far you want to take it. If you are still unhappy do not be afraid to just unhook it and save the money for your next belt service which I recommend you do every 3 years like I do.

 

1. No and this is a point that really gets to me. Anyone that is actually truly concerned about emissions and the environment needs to park a 308 altogether and buy a new car. I don't care how legal it is to drive a 308 in spec, it produces far more environmental toxins and get FAR less fuel economy than ANY new car. That plus we drive them for pure enjoyment only, not because the grocery store is too far to walk to.

2. See #1

3. When I bought the car one of the bank's tubes had rusted off and had been welded closed. I didn't do it, someone else did. This brings me to my issue of how much are you going to spend to tweek it. I am not going to pay to restore that part of the car. No way in hell. If someone else thinks I should, send me a check and I'll get it done tomorrow.

4. Slightly, but surprising little.

If you live in an area where the emssions testing is an issue I guess you have to deal with it on a different level than I have to. Good luck to everyone that does. I wish them success.

 

I have records for my car since new. The car was returned within the first week for surging. It's minor but you definitely know it's there. In Illinois we have only OBDII testing now. Cars 95 and earlier are no longer tested. I'm curious though; can unplugging the O2 sensor cause any problems?

 

I didn't mean to sound harsh.

The thing is I am not anti-lambda. Not at all it's just one of those little things that really bug me but i am just that way with my cars. For example, I cannot stand for my steering wheel to be even one degree off center. Drives me crazy. I can feel if one tire is just a tiny bit out of balance that probably no one else would even notice. So that "surge" may not be even noticed by someone else driving my car but I notice it. It isn't THAT big of a surge but to me, and probably only me, it is. I tried to work around it in the shop but it beat me. It won and I made a decision to just unplug it. Frankly after really never having one hooked up it made no sense to me to pour money into something that did in fact have a zero dollar cure that I have seen be completely harmless in over a quarter century with my other cars.

That's why when someone asks is it ok for the O2 sensor to be unplugged, the short answer is yes. There are other factors to consider such as where you live, the tune of the car, etc. but other than that, yes, you can leave it unplugged if you really want to.

That's all. I still love all ya'll

 

None that I have ever seen and I am one of the few around here that has pushed his 308 over 100,000 miles and drive it regularly including dozens and dozens and dozens of track days.

 

Based on your experience, I'm in agreement with you that disconnecting the sensor should be considered an option rather than spending enormous time and money of trying to tweak things.

But, in regards to emissions, it's not about personal feelings regarding emissions or the environment. All that matters is that some of us live in places where we MUST meet strict requirements regardless of our opinions of emissions generally. So the question is whether disconnection of the sensor makes the difference between passing and not passing.

 

I understand that but really the only question beat back and forth here was could you unhook without a problem otherwise with the car itself. If you have emissions to deal with do what you have to do.

 

Then unplug that mutha truckin O2 sensor and ROLL TIDE ROLL!

In all seriousness though, it's quite possible your car has never run properly and you wouldn't be able to fix it to know the difference if you didn't repair the test port. It's folly to compare the system on your Ferrari to the system on a car with MUCH lower tuned performance.