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Lightbulb Let's discuss digital WURs and replacing K-Jet Lambda

I debated if I should post this topic here or in the engine rebuilding forum. I flipped a coin and posted here.

Background

Yesterday I broke out the CIS pressure gauges and found my old Bosch WUR is out of calibration yet again. The cold control pressure is way too low and it's overly rich on cold start. Warm control pressure is a tad high meaning I'm slightly lean when the engine is warmed up.

Frustrated at the prospect of getting the old analog WUR re-calibrated yet again, I started doing some reading on digital WURs. After I spent some time reading through product docs to get a better understanding of how the systems work, I started thinking this had some real potential to bring some good qualities of modern EFI to our old CIS cars. And maybe it wouldn't be that expensive. This is what I'd like to discuss.

Now some of you may be asking what's wrong with the old analog WUR approach? The answer is nothing. If you think your analog WUR is working fine for you, then no need to read any further. I don't really want to have an analog vs digital debate here. I'd like to discuss "the art of the possible" of going the digital WUR route.

Current Solutions

There appears to be two options in the marketplace: Reanimotion/Dkubus FrankenCIS and Unwired Tools UTCIS.

Reanimotion Engineering is a company based in Australia. They develop a system called FrankenCIS. As I understand it, they do the development and contribute software to the Megasquirt project. Reanimotion apparently does not distribute directly to customers -- instead they direct customers to another Australian company called dkubus which supplies either components or kits.

The other company is a US-based company called Unwired Tools based in Flagstaff, AZ.

Both systems appear to be similar in theory and have slight differences in implementation. I've never used either so I can't speak to support or product quality. I've reached out to ask some questions of both.

Analog WUR Theory of Operation

The original Bosch WUR is a rather simple analog device (in theory). But it's implementation is actually a pretty amazing little piece of engineering when you think about it.

Fuel flows from the fuel pump to the fuel distributor. The fuel distributor connects to the WUR which then connect back to the fuel distributor. The purpose of the WUR is one thing: it controls how much fuel pressure is bled off back to the fuel distributor.

When the engine is cold, the WUR keeps the fuel pressure low which enriches the mixture for cold start. After cranking, the WUR receives 12v which heats up the bimetallic strip inside the WUR. Three things are important:

(1) the cold control pressure should be set at a setting appropriate for cold starts

(2) the rate the WUR heats the strip should be roughly the same amount of time as it takes for the engine to come up to a minimum temp where the extra enrichment is no longer required

(3) the warm control pressure must be within spec

Note: some WUR models incorporate a vacuum line for extra enrichment and some do not have this feature.

Digital WUR "Basic" Operation

Both digital WURs I've looked at have very similar theories of operation.

The basic components are as follows:

A machined block (aluminum?) designed to approximate the dimensions of the original Bosch WUR and to be a direct bolt-in replacement. The block is a modular design that can accommodate several different components. The components can either be sourced by the DIYer or the companies apparently provide them as a kit.

The block fits (at a minimum) a fuel pressure sensor, an ambient air temperature sensor and a fuel injector. A separate control module is also required and it connects to the block. The block also has threaded holes to accommodate the supply and return line fittings from the original WUR which simplifies installation.

The fuel injector is what regulates the control pressure and it replaces the bi-metallic strip functionality of the analog WUR. It acts very similar to the frequency valve in K-Jetronic w/ Lambda cars by controlling the duty cycle of the injector. The duty cycle of the digital WUR injector is what sets the control pressure.

Power to the control module is suppled by reusing the same 12v electrical connector used by the original WUR . The control module can be mounted nearby on the left side of the engine bay. Note that an additional ground is needed for the module (which can be easily attached nearby).

The control module requires some software and this is where the two systems are different. The FrankenCIS system uses the popular MegaSquirt platform. I'm not sure yet what the UTCIS system uses.

Beyond the software implementation differences, both systems essentially work the same way. They use a map table (think of an Excel spreadsheet) to control the control pressure value at various temperatures. The table is used to look up values. When temp is X set control pressure to Y.

Bosch made a number of different WURs over the years and for many vehicles other than Porsche. The application of which WUR models were used in which cars was based on the engineering specific to that vehicle. That means that the initial cold and warm pressures were different and the time duration from cold to warm may have also different.

The beauty of a digital WUR here is that it can accommodate any different WUR design by simply changing the map table to mimic the appropriate values for a specific WUR. It appears that if you provide the vendors with the WUR model for your vehicle, they can ship the digital WUR with the correct map table preloaded so that the system can work right out of the box with no tuning required.

However, if you need (want?) to change your map table, they also provide an interface where the units can be programmed via a laptop.

In summary, this could be a simple approach to replacing the analog WUR.

Digital WUR Advanced Operation

But what if you have a car with K-Jetronic with Lambda? K-Jet with Lambda was designed to provide additional closed-loop fuel control. This is where I think this starts to get interesting.

Both digital WUR systems appear to also support what I'm calling an "advanced" mode of operation. By that I mean they can take additional inputs to better control fuel delivery. In what I call basic mode, the control pressure is regulated based only on ambient air temp. The advanced mode could possibly replicate everything K-Jet does and possibly go further. On CIS cars that never had K-Jet, this could be seen as improved functionality.

This advanced mode can utilize a wideband O2 sensor (or possibly the existing narrowband sensor) in cars with K-Jetronic Lambda to better control the fueling under different conditions (idle, cruise, WOT). In addition, it appears that the control module can also control the normal lambda frequency valve. These inputs can be used to further refine the fueling characteristics.

At worst, this would seem to replace the K-Jet brain functionality. At best, you'd get the benefit of modern programmability plus the ability to do data logging.

I have also thought about the merits of the Classic Retrofit CDI+ coupled with this approach. By locking the dizzy and controlling the timing advance through the CDI+ software -- couple with a digitally controlled WUR -- it seems to me you would have 99% of the value of a full EFI conversion with less cost and less hassle. No need to modify the airbox, fuel delivery system, etc. and it would look mostly stock.

What inputs would be needed to eliminate the Bosch K-Jet?

- Throttle position (could original TPS be retained?)
- rpm/tach signal
- engine temp
- manifold air pressure (looks like a sensor would need to be incorporated)
- O2 (either stock narrowband or wideband)

Thoughts? Does this sound plausible? Are there any holes in my thinking?

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'83 911 SC 3.0 coupe (NA)

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Last edited by tirwin; 05-27-2018 at 09:03 AM..
Old 05-27-2018, 07:55 AM
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You shouldnít lock the distributor- 3,2 motronic and even the 964 used advance weights to put the rotor in the right position, even though spark timing was controlled by the Motronic control unit.
Old 05-27-2018, 08:14 AM
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Quote:
Originally Posted by 304065 View Post
You shouldnít lock the distributor- 3,2 motronic and even the 964 used advance weights to put the rotor in the right position, even though spark timing was controlled by the Motronic control unit.
I'm only referring to my understanding of how the CDI+ unit works. My understanding is they supply an (optional) locking collet that allows the additional advance to be controlled by software. I would have to let Jonny comment on whether locking is required for his system since it is his design.

My real point was that between the two systems you'd have the ability to programmatically control both the fuel delivery and additional ignition timing.

The disadvantage is you'd have 2 systems to configure versus 1 with a single EFI system but I don't see that as a major obstacle. Less convenient perhaps. Unless there was a way to interface the two.
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Old 05-27-2018, 08:32 AM
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Tim, thanks for creating this thread.....very interesting and well explained; I will be following along. I've checked-in on the FrnakenCIS thread a number of times and would like to see a modern solution for what seems to be the most frequent failure point in the CIS system. I understand that we have the luxury of experts like Tony in Philly to repair and calibrate existing units, but (quality) options are always a good thing, especially to those of us who a) appreciate the inherent mechanical (if not visual) elegance of CIS and/or are too poor/cheap/stubborn to go to either something like the Bitz kit or something fancier, like ITB's with Rasant, both excellent options in the own right(s). I'd think there would be enough old cars running around the world with CIS (Porsche, BMW, audi, Benz to name a few) that a universal solution rendered via digital WUR would be worth someone's time. Easy for me to say, of course! Best, John in CT.
Old 05-27-2018, 09:10 AM
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I'll be watching as well. Thanks!
Old 05-27-2018, 09:24 AM
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Good point, John!

CIS was used quite extensively back in it’s time. It appears to me the digital WUR idea is being used with success with other marques — notably Mercedes — but hasn’t seemsd to quite catch on with the Porsche community.

What is intriguing to me about the idea is it seems to give you options. Let’s say someone is in a situation like me and need to get their along WUR calibrated. If the cost difference between sending off the old WUR and a digital WUR is not substantial, then I think the investment could be justified.

Here’s what I mean. If you started with the “basic” digital WUR you’d have equivalent functionality to the analog WUR but also the option for future expansion. Let’s say on down the road you wanted to modify the engine. Bigger displacement, hotter cams, etc. The cost of changing to EFI or ITBs or both is fairly substantial. Not saying it’s not worth it. It’s just additional cost. This seems like a promising option for those that have a hard time justifying the cost of more drastic changes.

I’d note that Fred Cook made CIS work with his 3.3SS build. He set it up so that the CSV fires when at WOT for extra enrichment. This is a different approach to the same thing.

With this approach, you could extend the lifespan/usefulness of CIS and get the added tunability down the road if needed.

Plus I’m a digital guy so I like the fact that this would eliminate some of the analog “guesswork”.
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Last edited by tirwin; 05-27-2018 at 01:01 PM..
Old 05-27-2018, 10:57 AM
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Hi Tim,

I had briefly looked into the digital WURs and it seemed to me that you still end up with a whole bunch of other CIS parts that are old and could be suspect. For our cars, you can do the Bitz EFI for about $2,000 and eliminate a whole ton of old stuff and get a lot of tunability.

Of course there is a bit of a learning curve to programming it.

Best,
Rutager
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Old 05-27-2018, 11:00 AM
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Hi, Rutager -

I have some emails out to the vendors so I will post my findings as I get more info.

I did talk to a friend yesterday who bought the UTCIS for his ‘76 911. He said it was plug and play - no programming required for the basic WUR functionality. He simply provided the vendor with his WUR model and the controller module came preloaded with the correct map table. No muss, no fuss.

Here is a thread by another Pelican that covers his experience.

Note: I’m not suggesting either brand right now. I am a bit more intrigued by the Megasquirt since there is a broad base of support around MS.

As far as the other CIS parts, there is some truth to that. But the only other CIS component that needs to be calibrated is the AAR. I’m wondering why the AAR couldn’t be replaced with something digitally controlled too? Decel valve isn’t necessary. Other than the plumbing and airbox there isn’t a whole lot else. And if you did want to go full EFI later, you would already have the MS control module.
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You can't buy happiness, but you can buy car parts which is kind of the same thing.

Last edited by tirwin; 05-27-2018 at 12:59 PM..
Old 05-27-2018, 11:35 AM
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Many folks on PP's own 930 forum were early adopters of Unwired's WUR, because it appeared to offer a way to laptop tune CIS fueling to match the needs of modified turbo cars, without needing to replace or twiddle with a whole bunch of stuff.

Unfortunately, reports are not very positive. I'm not aware of anyone who ended up with a working unit with no issues. Many (myself included) sent their unit back for repair/replacement/upgrade - usually at Unwired's suggestion - only to never receive any unit at all back, much less a functional one or their money.

Digital WUR - Success stories?
Digital WUR UTCIS-PT poll

Unwired apparently continue to advertise and sell units, but there's some customers of theirs out there that they apparently have no intention of even talking to, much less repaying them or repairing/shipping the units they promised.

Many in the forced-induction forum started toying with FrankenCIS (running MS to modify control pressure via an injector, much as the factory did with the SC frequency valve, or the very late turbos):

Digital WUR plus? ( FrankenCIS )

Which is a very flexible/interesting approach, and in my view a much better bet than a company who have a product with a long history of bad software/hardware fails and appalling reliability issues.

Or just install EFI instead... What I ended up doing...
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Old 05-27-2018, 12:56 PM
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Tim, I'd forgotten that thread ˇou linked us to. For Gomez it sounded like a real success; for the Turbo guys, not so much. I wonder if perhaps the unit in question can handle the narrower window/requirements of being a replacement for a stock part in a naturally aspirated motor, but that for those Turbo applications it was insufficient? I'm wondering if the 930 guys who spoke up were running stock-spec 930 motors or if they'd been modded for more power and were looking for this device to deliver the extra fuel flow needed to feed more boost, better charge cooling, etc? If the latter, then perhaps more sophistication is needed on a hotrod 930 engine to offer the extra gas under heavy boost while still maintaining reasonable AFR's under light loads...i.e., a full EFI set-up.

Certainly any shortcomings in the vendor's promises as to what results the part would deliver, poor customer handling, or failure to communicate with paying customers are all red flags unless one can hear anything to refute the complaints. I too would be PO'd to lose $500 and/or not have my calls returned. John.
Old 05-27-2018, 01:13 PM
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Spuggy answered my question. Thanks!
Old 05-27-2018, 01:15 PM
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Quote:
Originally Posted by jjeffries View Post
perhaps the unit in question can handle the narrower window/requirements of being a replacement for a stock part in a naturally aspirated motor, but that for those Turbo applications it was insufficient?
The only difference between the UTCIS-V and the UTCIS-PT version is that the SC version has a 0-1 bar MAP, while the 930 version has a MAP that covers positive (> atmospheric) pressures, and the software has extra cells for > 100 kPa.

The Unwired unit is (supposed to be) managing control pressure, not flowing fuel to the injectors.

Frankly, if you're itching to spend money/time/effort and insist on hanging on to all that 60 year old tech, i'd put it into FrankenCIS.
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Old 05-27-2018, 03:07 PM
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Quote:
Originally Posted by 304065 View Post
You shouldnít lock the distributor- 3,2 motronic and even the 964 used advance weights to put the rotor in the right position, even though spark timing was controlled by the Motronic control unit.
You are referring to 'rotor phasing'. In practice, the rotor arm end is wide enough to accommodate being locked. At idle, the rotor will be almost at the end of the post. As the RPMs rise, the rotor 'moves' towards the centre of the post. I've run my own car for 25,000 miles with a locked distributor and never had an issue.

Tim, I have a FrankenCIS system to play with here. I was hoping to try and drive it direct from the CDI+ box to achieve a fuel map. Big project though and not enough time at the moment.
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Old 05-27-2018, 04:13 PM
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Happy Memorial Day! To those veterans out there, thank you for your service!

Here’s an update. It seems there are some dissatisfied customers with Unwired Tools. That is unfortunate. I only found out about them 2 days ago when I called my buddy with the ‘76. He has been a happy customer with his UTCIS so far. But looking back on some of the older threads sure doesn’t paint a great picture.

I received a reply to my email from Dkubus last night. I have not replied yet as I have not been able to stop laughing. They offered 2 approaches.

1) DIY where I buy the block from them and source the rest myself (they provide docs and part numbers). Cost is estimated at under $1000 US.

2) Turn-key from them for $3500 US. Day-um.

So I got up this morning newly motivated and I re-calibrated my WUR myself. Car runs great.

I still think this idea has merit but the prices are RE-DONK-ULOUS. There is no way it should be that expensive to build this.
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Last edited by tirwin; 05-28-2018 at 02:40 PM..
Old 05-28-2018, 02:37 PM
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Wow. What do you say to that?

To Spuggy's point, I need to drive an EFI-converted car and see how it feels. I think the Bitz kit is cool but I'd want to do some junkyard hunting to come up with a better-looking intake, maybe using some pieces from a newer VAG/Bosch-equipped car.

It's academic right now because my CIS is working nicely...but I may be tempting fate by writing that. Besides, we have Tony!
Old 05-28-2018, 02:55 PM
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I wonder if you could do something with an Arduino or Raspberry Pi? Check out github - you never know what you might find there.
Old 05-28-2018, 03:12 PM
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Quote:
Originally Posted by jjeffries View Post
Wow. What do you say to that?

To Spuggy's point, I need to drive an EFI-converted car and see how it feels. I think the Bitz kit is cool but I'd want to do some junkyard hunting to come up with a better-looking intake, maybe using some pieces from a newer VAG/Bosch-equipped car.

It's academic right now because my CIS is working nicely...but I may be tempting fate by writing that. Besides, we have Tony!
My opinion for what itís worth... EFI is a slippery slope for a CIS car. I have looked at this a lot.

You can take a very mild approach and do something like Bitz or Rasant. They are basically bolt-ons. Letís say you were faced with spending a bunch of money on CIS. Maybe you had a bastardized motor with the wrong CIS parts or were missing parts. Thatís a clear case where the cost to retain CIS isnít worth it and EFI makes a lot of sense.

But if the reason you want EFI is to hotrod the motor, youíre really talking about a lot of money. Intake, cams, pistons, ignition and fuel delivery probably needs to change. Machine shop work. My napkin math says itís the cost of a rebuild plus another $7-8k. Now if you were at the point of needing to do a rebuild anyway, maybe itís not so bad. Then itís just the incremental cost.

It might be cheaper to just get another one that already has Motronic.
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'83 911 SC 3.0 coupe (NA)

You can't buy happiness, but you can buy car parts which is kind of the same thing.
Old 05-28-2018, 07:45 PM
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I wonder if you could do something with an Arduino or Raspberry Pi? Check out github - you never know what you might find there.
That’s a good idea. Heck, the code for the FrankenCIS is open source.

You still need the block which Dkubus sells for $300-400 US. Still spendy for a CNC’d chunk of aluminum. They need to recover their R&D costs, but still... This is not rocket surgery.

A Microsquirt ECU is $300-400. All the other parts are probably ~$100 plus the wiring harness. It looks like the vast majority of the cost is in the block and the controller. Address that and I think you’d have a winner.

I’m not really up to speed on 3D printing. Are the materials safe for use with solvents like gasoline?
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Last edited by tirwin; 05-28-2018 at 07:55 PM..
Old 05-28-2018, 07:48 PM
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Hi Folks,
I just wanted to jump in and wave our flag before reading the first post fully.

I've not seen an email so if you have specific questions not covered by this thread, throw them in here

I'll go back and read the thread now and respond asap
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Old 05-28-2018, 10:25 PM
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OK,
For many reasons CIS / K-Jetronic is both cool and weird, but simply a means to an end. It gets fuel into the Cylinders and makes things go bang.
If it's working properly the bang is good.
If it's unloved or broken the bang can be very bad.

As most journeys into options for CIS equipped vehicles begin with some sort of fault being found with the system, there is an important set of questions already being asked
usually "Can I repair it ?" and "What do I replace it with ?"
Less common, but also important is "how can I make it better ?"

My first 928 had probably the worst condition CIS system I'd seen, every line filter was plugged with junk, the fuel head was trash, it ran but only barely.
EFI was considered, but seemed like a whole lot of unnecessary work, repairing CIS was worth a go at least.
So during the revival process, I reasearched a lot and found UTCIS, but I also found the mentioned threads above.
And after a close look at both the user comments and photos of the product back in '09, I went back to simply refurbishing the Bosch system.
A couple of dudes with a soldering iron, vs the Wizards from Bosch way back when, was pretty much a no-brainer.
After fixing the Bosch system, the car ran well, and the whole CIS/EFI thing was simply filed away

My second 928 was an accidental purchase ( I swear )
Now this one was in pieces, but everything was in good condition, so it was a simple restoration with some assembly required
Happy days, another toy to play with after disposing of 928 #1

A couple of years of driving and enjoying the end result, the brain started to wander, could it idle nicer, could I get better than x cruising range, etc.
So, I got bored one day and created FrankenCIS, which turns CIS from a simple mechanical system into something complicated but flexible.

To go back to your initial post I think it's important to clarify a few points

UTCIS has been around for a fair while now and essentially replaces the WUR, from what I can gather it's also now self contained with the electronics and the mechanicals all in the one unit.
UTCIS is ostensibly plug-and-play, using the original WUR Power feed, a vacuum connection and the two fuel lines as the only external connections.
There is a simple RPM reference input as well as the internal pressure and temperature sensors
UTCIS control of CIS is limited to Control pressure only, so suitable for WUR based systems only
Essentially Digital WUR "Basic" or an electronic version of the BL WUR
I don't think UTCIS can do your "Advanced Operation"

FrankenCIS on the other hand is definitely not plug and play
FrankenCIS was never really intended to be used as a WUR only system, although it can do it, WUR control was not the goal from day one of the design
Like MegaSquirt beginning as an educational tool, the WUR only mode was only ever intended as a starting point, growing with the owner as they learn CIS, ultimately leading toward CIS-Lambda or CIS-E as the final goal on a modified engine. Spark, Boost Control, Wideband O2 closed loop etc. are all there in the basic design
FrankenCIS was really started to prove a point, CIS worked but needed a user tuneable version 4 (v1 is WUR only, v2 is CIS-Lambda, v3 is CIS-E)
FrankenCIS is overkill really, 90% of CIS based vehicles don't need it, and of the remaining 10% there is a good case for going straight to EFI, however boring that might be

FrankenCIS has over 100 "genuine" units out there somwhere with no known negative feedback apart from two CIS-Lambda turbo 911's that had issues with the eWUR injector getting stuck closed at near 100psi system pressure. As they are both CIS-Lambda, there is really no need for the eWUR in the first place as FrankenCIS does most of the control via the Frequency Valve in this mode

The last development iteration on my 928 was CIS-E based which worked really REALLY well in comparison the original Bosch WUR based system.

So at this point four years after the crazy journey began I would summarise CIS in the following order depending on your skills and preferences


If you are good with tools but a little off on the electronics side
#1 stock CIS in good condition
#2 Maybe a Brian Leask WUR
#3 an EFI Kit from Bitz or Turbokraft ( I think there is a third one too )

If you are good with tools and electronics, and patient or crazy
#1 stock CIS in good condition
#2 Maybe a Brian Leask WUR
#3 FrankenCIS (CIS-Lambda or CIS-E)
#4 an EFI Kit from Bitz or Turbokraft etc.

__________________
Steve
1981 928S 4.7 ROW with KE3-Jetronic and Franken8 (AEM Inifinty) "Be the man your dog thinks you are."
Yes! mechanical/hydraulic constant flow injection can be managed by a modern EMS

www.FrankenCIS.com

Last edited by Reanimotion; 05-29-2018 at 12:08 AM..
Old 05-28-2018, 11:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)
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