i have a 1979 euro 280ce w k jetronic injection. recently, I installed a wideband o2 sensor and gauge for tuning purposes. this gauge tells me that under partial load its running lean- around 16, 17,18 to 1. under full load, the control pressure circuit kicks in like its supposed to and drops it to around 15,16 to 1. i set the co at idle to 14.7 to 1. my question is: how can i get it to run richer? i have tried everything- new injectors, new filter, cleaned out the fuel distributor, cleaned out the pressure regulator, had my mechanic tune the control pressure regulator, tested fuel pump delivery (almost a gallon a minute at the return line). i even removed the little screens that are in line to each injector because they were clearly clogged, and redundant as there is a similar screen at the line in, which i replaced. am i wrong in thinking it should run richer? i'm thinking no because i cant even set the timing to specification (30 btdc) because the motor then pings because (i believe) its running too lean. [:-]whew- a mouthful i know but i hope someone can help. i am seriously considering yanking the whole thing for an efi system.

 

The key question is whether you are experiencing any problems with your vehicle e.g. poor start, poor gas consumption, hesitance etc.
Maybe you are worrying unnecessarily because your mixture gauge is either wrong or in fact the readings are intended.

You appear to have investigated and found some potential problems from your post. Do you understand how your system is supposed to work....or is controlled? I guess you do.

Your K Jetronic is a hybrid electro mechanical system and is extremely sensitive to line pressures etc since this is how the system controls mixture. Current full electronic systems use a software fuelling map and basically check datum every time the engine starts. Unfortunately your map is to a large extent implicit in the design of the mechanical system components in your system and cannot be altered.

The following URL gives a fair outline of the system and a Google search will reveal many others. http://www.auto-solve.com/mech_inj.htm

Suggest you start by getting the ignition correctly set. Then move to idle CO. If the system then runs lean under load you need to ensure the various enrichment devices are working correctly. For instance as load increases so should fuelling otherwise you will get pinking. If it remains weak (pinking) then I suggest the MAF (mechanical in your system) combined with the manifold pressure sensing control system cannot be correctly determining the load due to faulty MAF or control valves.

Sorry can't help much more for the moment.
Let us know how you get on.

Stuart

 

thanks for the reply- and in answer to the first question its mostly an issue of power- since i have to retard the ignition almost 20 degrees from spec just to keep it from pinging (on 92 octane) the car is sluggish. not good! otherwise the car runs fine, beautifully even, if all im doing is motoring around town. so you basically re-inforced my suspicions that i should replace the k-jetronic w a later electronic fuel injection system, because i just cant see anything else i can do to it- the air flapper seems to have full travel without anything hindering it. i was mostly wondering if anybody had a similar experience w these- if they just wear out irrepairably at some point or even if its a []design flaw. after all, when this thing was made wide-band 02 sensors, with their ability to show air/fuel ratio across whole the range of rpm/load, didnt exist.

 

Your response is not what i intended to convey.

It is not really feasible to upgrade to electronic so youre stuck with what you've got.

The electromechanical worked fine on millions? of cars so its just a matter of working out what is wrong with your installation.
If you need +20 degs of retard to stop it "pinking" there is something seriously wrong. No wonder it is "sluggish" with this amount of retard.
Is 92 octane recommended for use in your car? Maybe you are using 92 ilo 95 which is bad news. Vehicles which use low grade fuel have lower compression ratios than those that use higher grades. You can't change the compression ratio on an engine without a total rebuild. prolonged pinking will burn a hole in your pistons. Suiggest you use 95 octane.

Although simple your system should have feedback to modify fuelling. This uses the O2 sensor to determine amount of unused oxygen in the exhasut gas which in turn operates a control valve to enrich or weaken the mixture. The degree of control however is somewhat crude to current all electronic systems but this shouldn't be of concern to you (i.e. it will not be noticeable) unless you take "GREEN" issues very seriously.
O2 sensor technology has improved but the ones in your system were designed to give the required characteristics to work your system adequately.

I stated that the control system needs to be set up carefully and that system pressures are key to this.

Your assertion that the vehicle pinks due to weak mixture may not be correct. It is more likely a fuel quality /compression ration issue which has been incorrectly addressed by backing off the ignition.

Hope this reinforces my previous post.

Stuart

 

you could be right about octane but to me that cant account for all of it. my car is euro spec so it does have 9.5/1 compression rather than the 8/1 of us models. the k-jetronic in my car is a really basic one-it has no 02 sensor. it only has the thermo-time switch, cold start injector, and the control pressure regulator (otherwise known as the warm-up regulator). all fuel metering is handled by the air flow sensor, modified by those 3 things. the 02 sensor i installed is an after market wide band sensor connected only to a gauge. i have checked this gauge against diagnostic machines in local garages- it is accurate.
anyway-yer right, 20 degrees of timing is a lot. hence my frustration. a 3 octane difference isnt going to fix that. as i said i have been through, cleaned or replaced every last component in that system. its true i havent checked control pressure to see if it is in spec but i trust the mechanic who did. but maybe that is worth another look.

 

OK. I now have a better picture of the system.

Has the engine ever been rebuilt? It is possible that cam and distributor timings are incorrect (within the engine assembly). If not then compression ratio is your number one suspect. 9.5 vs 8:1 without electronic ignition and modern knock sensors(to automatically retard the ignition in moments of "stress" /temporarily) is a MASSIVE difference. Is there no fuel better than 92 availabl anywhere?

I hadn't appreciated that 8:1 was the MB USA norm. No wonder you guys always want more power!

Has the car ever run satisfactorily whilst it has been in the USA?

If you want the enrich the mixture you will have to alter the characteristics of the MAF + the base/datum idle setting. Its all you have on your system.

What capacity is your car? Is there a MAF from a larger capacity car you could try, but this approach is definitely a needle in a haystack trying to get appropriate settings.

You appear very knowledgeable on the subject so I guess you have already tried everything available from the outside of the engine.

Stuart