What is the Difference between BMW & Porsche K-Jetronic

[Vincent Hill]

I am puzzled by “1” Thing! The 82 BMW 320i has almost the Same “K-Jetronic” Fuel Injection As the 1982 Porsche 911. It can sit for a month and start and run smooth in 10 seconds.

The Porsche starts like a WWII Radial Aircraft Engine after 1 over night! Why!!

New Injectors Porsche not the BMW

New Accumulators Porsche not the BMW

2 one way Valves Porsche “1” on the BMW.

New Fuel Pump on the Porsche not the BMW.
See what i mean.

When Warm or Sitting a Few hours, No Difference

I have “2” Large Accumulators On the Porsche to Resolve the Not Hot And Not Cold After Sitting for 2-3 Hours.

[Superman]

Remember the story about Goldilocks? She finally found what she wanted, but everything had to be just right. When a K-Jetronic CIS system is adjusted and working correctly, the car will start instantly at any temperature and immediately run as if it were already warmed up.

[Vincent Hill]

Originally Posted by Superman

Remember the story about Goldilocks? She finally found what she wanted, but everything had to be just right. When a K-Jetronic CIS system is adjusted and working correctly, the car will start instantly at any temperature and immediately run as if it were already warmed up.

YUP! Sometimes I cannot turn the key Back Fast Enough Because it is Already Running. This is After Sitting for Days!

Somehow the BMW Retains Fuel In all Of the Lines And gets Instant Pressure. The Porsche has to Build Pressure.

“IF” I use my “Modified” Relay That starts the Pump as soon as the Key is on, the car starts well.

I think that maybe having to Fill “2” Accumulators does not help this situation BUT Choosing between being unable to ReStart after 2-3 Hours or a Slow start at the beginning of the Day, Not even Close! The Car Needs to Start when your wife is in the Parking Lot Trying to get back Home

[RWebb]

the difference is Lederhosen vs. monocle

[Vincent Hill]

Originally Posted by RWebb

the difference is Lederhosen vs. monocle

?? Do not understand!

Also my next plan is to pull all of the Injectors and see if any are leaking. I know even New ones can leak. I use Chevron with Techron and keep Additives For Ethanol.

But the BMW has has ZERO WORK on it for at least 5 years.

[pmax]

Originally Posted by Vincent Hill

The 82 BMW 320i has almost the Same “K-Jetronic” Fuel Injection As the 1982 Porsche 911.

Well, looks like the BMW has an all metal airbox, what Porsche should have done in the first place, no toilet seat valve needed.

[RWebb]

Originally Posted by Vincent Hill

?? Do not understand!

Also my next plan is to pull all of the Injectors and see if any are leaking. I know even New ones can leak. I use Chevron with Techron and keep Additives For Ethanol.

But the BMW has has ZERO WORK on it for at least 5 years.

Lederhosen vs. Monocle is a play on the regional stereotypes in Germany - Bavaria vs. Stuttgart or northern Germans

[Vincent Hill]

Originally Posted by rwebb

lederhosen vs. Monocle is a play on the regional stereotypes in germany - bavaria vs. Stuttgart or northern germans

👍🏾👍🏾

[Vincent Hill]

Originally Posted by pmax

Well, looks like the BMW has an all metal airbox, what Porsche should have done in the first place, no toilet seat valve needed.

Crazy! But you are 100% Right but this is the First time it has Registered to me that difference Between the “2” AirBoxes. 👍🏾👍🏾

[manbridge 74]

I have found easier starting and general running to be better when the base fuel pressure is set at the upper limit at the PRV located on the fuel distributor. The O-rings on the PRV need to be in good shape too...

[fanaudical]

It's not the "airbox". My old Audi Fox had CIS (all metallic intake manifold but had a rubber boot connecting it to the air flow sensor, just like the BMW) and it never did start well when hot. I never could get the WUR dialed in.

My 911 continues to start well at all temps. It really is about validating the control pressures and getting the WUR adjusted correctly. +1 on adjusting the relief valve in the fuel distributor.

[Vincent Hill]

Originally Posted by fanaudical

It's not the "airbox". My old Audi Fox had CIS (all metallic intake manifold but had a rubber boot connecting it to the air flow sensor, just like the BMW) and it never did start well when hot. I never could get the WUR dialed in.

My 911 continues to start well at all temps. It really is about validating the control pressures and getting the WUR adjusted correctly. +1 on adjusting the relief valve in the fuel distributor.

I have the “WUR” Perfect. The Relief Valve in the Fuel Distributor I remember dealing with it in my 1976 But not this one.

From Starting this Thread and thinking about EVERYTHING, i KNOW Fuel Pressure at the Start up “IS” the Problem. So in the Next few days
“#1” make sure No Injectors are leaking

“#2” Bypass my second Accumulator and see if it starts Better.

I am Hoping #1 is the Problem because if it is #2, Then I will need to install a Switch
(Either Manual Or like a 5 Second Timer) to Run the fuel pump before starting the car.

[pmax]

Originally Posted by Vincent Hill

Crazy! But you are 100% Right but this is the First time it has Registered to me that difference Between the “2” AirBoxes. ��������

Perhaps Porsche selected the plastic version to save weight ... the turbo version is metal as well.

Check for air leaks especially around that valve, assuming you have one.

[Rawknees'Turbo]

Originally Posted by pmax

Perhaps Porsche selected the plastic version to save weight ... the turbo version is metal as well.

Check for air leaks especially around that valve, assuming you have one.

Whatever the reason, their use of plastic there is truly a joke.

And just for the sake of idle jibber jabber, the Turbo box is only a housing for the air filter (is under neither pressure nor vacuum) - a big ol' honkin, in the way, mailbox looking thing that many owners, including myself, replace with a simple filter installed directly on the air metering assembly's throat (the Turbo's version being a draw-through design, where the metering arm travels downward as air is sucked over the disc/plate, on its way to the turbocharger's compressor intake). And let me tell you, the intake noise is glorious then, especially at sudden closing of the throttle.

[Rich76_911s]

Are you sure you don’t have an air leak or some other problem that has been getting “solved” with the tinkering on the CIS? Could you have a timing issue?

What was the original issue that had you start repairing the Porsche CIS? Why have 2 fuel accumulators? That sounds like a modification for another problem not a cold start issue.

Have you ever tested the fuel pressure on the car? If so you should see that the fuel pressure rises quickly to the cold start pressure. If you need a 5-second switch you have a problem that your just hiding by adding a switch.

I seriously compliment you on finding fixes to the problems, but I think for your enjoyment of the car going forward you ought to repair whatever is wrong. There’s no reason you need 2 large accumulators or a dedicated fuel pump switch. End of the day there are 1000’s of SC’s running perfectly without either. CIS isn’t an easy fuel system to diagnose and repair when it’s not working. And it seems like you can adjust one thing which throws three others out of whack. And then you adjust those three only to find out it was an air leak that was causing the problem now you have to go undo the 10 CIS changes you made to make the car run right with the air leak.

Good luck, Wish I was more helpful.

[T77911S]

my 77 started, ran and idled perfectly. so does my 930
its just a matter of fixing air leaks, fuel pressures and mixture.

you HAVE to make sure you don't have air leaks.
you can smoke test it or do as I did, pull the CIS off and replace ALL rubber that can leak.
including injector sleeves.
I also have a hand vacuum pump. I tested EVERYTHING for air leaks.
including and very often overlooked is the vacuum hose to the brake booster AND the brake booster.

I did not see where you said anything about the O2 sensor unless I missed it.
either replace it or bypass it.

next is a tune up.
plugs cap and rotor. make sure wires are good.
check timing advance. set timing.

set system pressure to spec, leave it alone.
check control pressures warm and cold.

I don't know what 2 accumulators would do, may not be good for it, in fact, it may make it worse.
the ACC has 2 jobs. it smooth's out pulsations from the FP and the other is to hold pressure once the FP is turned off. if you have 2 ACC's the FP may not push the diaphragm up far enough to provide residual pressure. just put one on that does not leak.

set idle and mixture with it warm.

make sure the CSV is working.

a bad WUR can also cause hard warm starts.
there is also a "pull up valve" in the system pressure reg (SPR). its job is to help with residual pressure. most people don't know about it. it closes off the return pressure from the WUR once the system pressure drops to a certain amount.

you could have fuel distributor issues.
its work and I would perhaps do last but I would check the fuel balance out of the FD along with checking for leaking injectors/ FD ports
pull all injectors and place in containers. with the FP on lift the sensor plate.
then compare fuel volume.

[dannobee]

Does the airbox have the fuel diffuser pipes? With the older airbox, the cold start valve just threw in some fuel, which puddled up in the bottom of the airbox, often causing the backfire. The later airboxes with the diffuser tubes pointed the cold start valve squirt right into the intake tubes.

[Coastr]

An SC can start and idle perfectly. You just have to keep going until you find the problem.

[Vincent Hill]

All Good Information Here!

BEFORE I Start about Individual things, please understand, that this Engine has Mostly Started up this way since I bought it. Second, I “JUST” finished a Total Rebuild Of this Engine. (All New Studs, Gaskets And Everything As Posted here on another Thread.

First, Air Leaks. I found that spraying Carb Cleaner at the base of the Intake Runners And Injectors will make the Engine Run Faster “If” There is an air LEAK.

Second, I have a New O2 Sensor and the Under the Passenger Seat all Working.

Third, the Reason for the “2” Fuel Accumulators is the 1974 to 1983 911 has a Cold Start System for when Cold And works Well. The Hot Start also works well but there is a time usually more than 3 Hours but less than 5 Hours where there is a Problem. Too warm for the Cold Start And Too Cool for the Hot Start. With the additional Accumulator it keeps the System Pressure High Enough To ReStart

Boy Toy Tony Saw my WUR Pressures And Temps Which were excellent.

Now what have I done and what have I found. Even though The Injectors are only a few years old (vs the BMW Which are about 10 years old), I tested them today. I pulled them all out and cleaned them with brake cleaner and put a small piece of Paper Towel under them. The Results are I just Bougbt a New Set Of Injectors. 1 was totally Dry. 3 had a Very slight leak and “2” were Horrible (Pretty good Leak). So when these are replace, I will see how it goes and get Nack to everyone

Also I do not have a switch to turn on and off the fuel Pump AND after replacing the Fuel Pump Relay with the Modified one I found that charging the Fuel System “Did Not Help the Cold Start Issue!

I plan to take my time and Investigate every possible system until this is Resolved.

If the Injectors do not resolve this, My next move is to check the Lift Plate Adjustment.

[Vincent Hill]

Originally Posted by dannobee

Does the airbox have the fuel diffuser pipes? With the older airbox, the cold start valve just threw in some fuel, which puddled up in the bottom of the airbox, often causing the backfire. The later airboxes with the diffuser tubes pointed the cold start valve squirt right into the intake tubes.

I will use my Borescope through the Pop Off Valve And see. Did not know about this but being and 82 I would think it does.