V-Fib

There are definately advantages to having the old fashioned mechanical fuel injection, much simpler to diagnose and repair, IMHO.



NOT THIS YEAR! Sorry Dennis, I am from Norman.

Anthony Tate
79/928 Silver Metallic
(Hill Country or BUST!)

ViribusUnits

I disagree Anthony.

With the mechenical system, there are plenty of annoyances. If you don't know how it's put together, you'll never figure out exactly whats wrong. The WUR is a black box of sorts, you have the exact same cold start, idle control.

The old school EFI's the same way. If you know what the deal is, it's rather easy to figure out, and test. The basic ideas are all the same, it's just a matter of knowing what is what. With the EFI, start with a wireing diagram, and go through the various connecters on the ECU, if anything is out of spec, you go check the actual sensor. From there, it's easy to figure out if the sensor is bad, or if the wireing is bad. You can repair some AFM problems, but the temp sensors have to be replaced, and they're not that expensive, expecaly when compared to the WUR, the K-jetronic version of the Temp II sensor. If you still have problems, you can have bad injectors, and the issues with them are similer with K-jet injectors. Stuck open, stuck closed, cloged, and cracked are pretty much your only choices. Unfortuently, J-jet injectors are more expensive. Finaly, if you just have a mixture problem, it's easy to check the fuel rail pressure on an L-jet. The last thing is the ECU, but that fails very rarly, as electronics pretty much don't wear out. The K-jet has the fuel distributer which does same thing for K-jet, and it can wear out, and is even more expensive, IIRC.

It is not, IMHO hard to adjust the mixture on an L-jet. On the L-jet AFM, there are three adjustment wheels. One for accrost the board mixture, one that will enrich WOT while leaning idle, or visa versa, and one that pretty much only effects the idle mixture. They are covered to prevent nonqualifyed people from messing with them, as required by the law. I'm not sure if the K-jet is so flexable. And yes, I've done it to my car, as someone else screwed with the mixture before I bought it. I bought a new AFM, and then I took my old one apart. Interstingly, I've readjusted it to about where it should be. Neat uh?

The final thing, is the L-jetronic allows the car to avoid haveing an EGR valve, with it's attendent complexity, and still pass emissions.

All this is besides the point though, as her issues seem to be ignition relates, and the K-jet and L-jet have the exact same ignition system.

Dennis Wilson

Anthony,

Here's hoping it doesn't happen (OU letdown when playing OSU), but too often I've watched OU beat Texas, Nebraska and other powerhouses then lose to OSU. Anyone know if the Salukis won this weekend?

Dennis

V-Fib

VU, some very good points, I guess it's all what you prefer(or in my case, what you know more about), but I'll keep the CIS. The 79 just passed inspection, but from now on, will be emmissions exempt. The Euro S (M28.11) engine I'm preparing doesn't have the EGR set up on the exhaust manifold or upper plenum, so that will go too. It is interesting that the K-jet system was used on Alfa Romeo, Audi, BMW, Ford, Lamborghini, Mercedes, Porsche (911,914, 924, 928 and Turbo Carrera, Chrysler, AMC, Fiat, Saab, Peugeot, Renault, Volvo and Volkswagon. I'm sure the L-Jet was used on several makes and models other than the 928 too, don't know what they are, but would be interested in knowing.



Anthony Tate
79/928 Silver Metallic

ViribusUnits

The L-jetronic system was used on many many diffrent makes of cars. For Porsche, I know the 928, and 914. I have a list, that says Alfa Romeo, Audi, BMW, Citroen, Ford, Jaguar, Lancia, Mercedes, Opel, Renault, Saab, Volvo, VW. I know that a similer system, probably an unlicenced copy of sorts was used on some Crylser cars. There was a Asian parts manufactor that sold basicaly unlicenced copys. I belive some of the versions of the Nissan Z used the one of the Asian copys.

It's a very elegent system, and for the time, rather cheap. It is, in my opinion, a vastly more addaptable, and accuret, system than the speed/density. It's more accuret than the MFI, and is simpler than the so called electric smog carbs. The biggest problems where with the AFM and the ECU. The AFM is sensitive to atmosptheric pressure, tempeture, and humidity. The 928's AFM is corrected for temp, but not pressure or humidity. Some of the lititure I've read indicates some of the VWs were shiped with pressure compensaters. Thus the replacement with the MAF. The MAF is completely insensitive to changes in atmospheric pressure, and is reletivly easily corrected for changes in temp. However, it is sensitive to humidity, possibly even more so than the barndoor style AFM.

The ECU baiscly isn't programable. The launage of a Bosch mannual on the thing leads me to suspect the L-jetronic ECU is analog, but I'm not sure. If it's digital, then it's probably something even more primitive than the 8 bit computers used on the early LH-jetronic. It has no capasity to store, or even reconize, errors. It also has no ability to learn. The later digital systems are better becuase if you drive around where it is humid, and the MAF indicantes a false high reading, the computer can use the O2 sensor to adapt.

Personaly? I prefer the new style, fully programable, self diagnosing, seqencial EFI systems. Expecaly if it's part of an engine mannagelemtn system. A computer can tune the the a/f mixture to control detonation, while at the same time, set the timeing to optimal, for each cylinder. If any sensor starts going realy wild, the computer self diagnoises the problem, and can give me an error code. It learns, and compensates for humidity, false highs, or lows from the from the MAF. I really like Saabs ion sensing anti-knock control. Basically, it should be far more accuret than the current anti-knock sensors, and simplier to boot.

V-Fib

Interesting stuff, to me anyway.
Thanks!



Anthony Tate
79/928 Silver Metallic

928and944

Thanks to John and Dennis, new post-ers, as well as newest reply from Viribus!!

I will relay everything to Chris (who is Internet-dumb).

As he has just finished putting a timing belt on my 944, he will now turn his mind back to the 928.

As to money, as someone asked me, he sold me the car, so he is fixing it for free.

I will write again when I have him with me.

LOVE TO ALL FROM AUSTIN, TEXAS
Only a Girl

928and944

Ignore the above message. Don't know how I got on this thread -- this reply goes to "Engine Stops After 20 Minutes."

Pat

928and944

Thanks to John and Dennis, new post-ers, as well as newest reply from Viribus!!

I will relay everything to Chris (who is Internet-dumb).

As he has just finished putting a timing belt on my 944, he will now turn his mind back to the 928.

As to money, as someone asked me, he sold me the car, so he is fixing it for free.

I will write again when I have him with me.

LOVE TO ALL FROM AUSTIN, TEXAS
Only a Girl

928and944

CONCLUSION OF THIS TOPIC:

Chris has fixed the 928 problem. Apparently the PermaTune box (isn't this the computer?), was replaced last year, at which time he replaced the Bosch box that was in the car at that time.

At the same time he replaced the coil (PermaTune requires that he do when he purchased it).

During this current problem, Chris had always suspected that the box was malfunctioning (it is still under warranty). Therefore, after running other checks (many of which are described in this post), he finally pulled it out, and put the Bosch box back in (and the problem described in this POST -- after 20 minutes the engine stops cold, and the tach is jumpy -- is corrected). He SPECULATES that the original problem was the coil all along and perhaps the Bosch box did not have to be replaced to begin with.

Thanks to all for your replies to this Post.

928and944
Pat (Chris's customer)

ViribusUnits

Like I said before, there is no computer in the system. It's a "dumb" system. You can't "chip" it because it's not a computer.

The box is a complex electric switch of sorts. It's sole reason in existance is to turn the weak signles from the magnetic pick up into a properly dwelled break in the ground for the coil. It and the magentic pick up are dirict replacements for points and condensers on realy old cars. The advance in hannndled in the exact same mannor at on those old cars.

It's good to know you got it fixed. Those old Bosch boxes die hard.

Bad coils can be difficult to diagnose.