elgy

This thread details what I have done with the CIS system on my ‘78 928 euro:
https://rennlist.com/forums/928-foru...is-system.html

For those that have not read the thread here is a summary of where I am.
- replaced all hoses from the fuel tank forward.
- new fuel filter and accumulator.
- cleaned the injectors and screens in the FD and the WUR.
- replaced the Mercedes FD with the correct Porsche spec FD (bought off eBay, not rebuilt but the car runs better than with the Mercedes unit).
- at the same time as the FD change I replaced the original WUR (Bosch # 0438140036) with a very similar rebuilt Mercedes unit (Bosch # 0438140068) that I was able to adjust to get the proper pressures (the original WUR is in sad shape – I intend to rebuild it)

Next I went through the 928 Classics baseline procedure… (available here if you want to understand what follows)
https://928classics.com/bosch-kjetronic-cis-fuel/
... with the following results:

System pressure is good at +/-72 psi.

Leak down pressure...
10 min = 42 psi (should be 29 according to the document)
20 min = 40 psi (should be 25)
30 min = 40 psi (should be 23)
Adjusted the WUR for CCP to 20 psi at 52 degrees F.
Plugged in the WUR heater and the pressure started to rise as it is supposed to. It topped out at 46-47.5 psi (second test was the lower number), which is limit (normally 41 to 46 psi).
Set the air/fuel ratio baseline as outlined in the procedure, backing off the AFR screw till the injectors were quiet. I didn’t count the number of turns but I think it was in the 11 to 15 normal range.
Adjusted the idle screw.

At this point I went for a short road test, the car was responsive, didn’t stall but wasn’t running perfectly. It seemed to have more power than with the Mercedes FD. There was some popping in the exhaust and to me it felt as if it was running a bit rich.

The engine run test…
Today the temperature is about 64 degrees F and I got a CCP of 21 psi
With the engine running, WUR heater element attached and no vacuum line I got to a HCP of 46 psi
With the vacuum attached this went up to 51 psi
So all of this looks fairly good.

When I started the engine run test with the heater and vacuum disconnected it took a couple of tries to start and almost stalled, but settled into a less than perfect idle after several seconds.
While waiting for the HCP to rise to its limit there was some minor popping from the exhaust. Idle was about 500 rpm.

What next????
Would adjusting the air/fuel ratio lean it out and get rid of the exhaust popping or should I be looking elsewhere?

Things that I am aware of but have not done.
- have not checked the timing – will do that soon.
- fuel pump flow test – but I am getting good system pressure
- injector flow test.

elgy

Went for a short neighborhood road test with the following results.
- It stumbles a bit from a stop if I am gentle with the gas pedal... a bit more gas and it pulls away nicely.
- The idle is more like 400 rpm at stops... it comes up to 500 after a few seconds, but "lopes".
- Once it is warmed up there is no more popping in the exhaust.

When I got back I pulled a couple of plugs and they look OK, perhaps a bit dusky.



I still need to try it on the highway to see if the bothersome "flat" feeling is still there at cruising speed.

drooman

Read your other thread... you got a lot of stuff done that needed doing.

Assume that anyone who would paint injector pipes should not have been in there. Anything they may have touched needs to be checked. Before chasing the fuel tuning around you must complete the following:

Check the cam timing, correct if required.

Ignition: check and set correct timing and check for correct advancing. make sure vacuum lines to distributor are in correct ports on throttle body. check ignition wires for resistance. replace cap and rotor and make sure you have a nice hot blue spark.

Vacuum system: Entire vacuum system must be absolutely air tight for proper running. This is a bit of a commitment to go through.. every hose, intake gasket, boot, etc should be replaced at 40-plus years old. The system "starts" at the sensor plate and "ends" at the intake runner gaskets on the heads. A quick estimation is that there are around 40 places in the intake system can develop leaks, this includes both ends of any hose attached and external components operated by vacuum. . There may not be a single significant leak point but the accumulation of minor leaks add up to sucking lots of false air. find a way to vacuum check the brake booster these can make a huge air leak. A hand pump vacuum tester is cheap and very useful here.

Then, do the volume test on the fuel delivery. Pressures can be fine with low volume, but low volume can show itself under sustained revs. I do the volume tests at the fuel tank end on the return line, this tests for blocked return lines as well.

Then revisit mixtures.

Jadz928

Glad to hear the baseline tuning procedure got you up and running!
Keep in mind, the idle setting is just a ball-park. Each 928 can vary quite a bit.
First get your idle up to spec (or even slightly higher).
Then set ignition timing (which may change idle, so may have to re-adjust idle afterward).
Finally set AFR (I like to use Gunson Colortune). I use 2 (one in each bank), but one is sufficient.
If you are feeling lucky, you can do it analog by sound and smell.
AFR affects idle too, so followup with a final idle tweak to spec.

Petza914

Popping is usually a lean condition and bogging is usually a rich condition. Your description suggests you have both, but from the plugs (especially the top one), looks a little rich and that could explain the light throttle hesitation. Very small changes to the mixture screw result in a fair amount of mixture change. Don't do more than about 5 minutes of change (referencing a clock face) at a time. By now you know that just turning the top allen screw doesn't do anything and you need to press it down through the spring travel so the point of that adjuster actually engages the mixture screw. When pressing down and actively making the adjustment, it throws off the mixture because you're forcing the air plate open so you have to adjust, allow it to stabilize and adjust again - it's not like carbs where you can leave the screwdriver on the screw and keep making changes.

I'm a big believe that a wideband AFR gauge is very useful in these CIS cars as it allows you to really see what the ratios are under different driving situations. They're mandatory with forced induction and that's where I really started to appreciate it as a tool from my supercharged '79, so much so that although my '81 Euro S is staying normally aspirated, I'm going to be adding one into it also when I redo the interior shortly.

As Jim said, pick up the idle a bit, then check the timing, then play with the mixture in that order.

drooman

Both of these guys offer very good suggestions, but mixture and idle speed tuning is the LAST step in the process. Unless you ensure that the ignition health and timing/advance, cam timing, fuel volume test, and that the guaranteed-to-be-leaky intake/ vacuum system is tight, you will never achieve optimal running. So many of these cars are driving around at 80-ish percent and people think they run fine....until they drive one that's tuned correctly.

elgy

Thanks to everyone for the suggestions. I will work through them. The cam timing is good. I will check the ignition timing tomorrow. I have already started working on the vacuum leaks... I removed the A/C electric air valve (my car is A/C delete) and already it seems to be running a bit better on light throttle starts. I also used pliers to close the hose to the brake booster... and the idle dropped, so there must be a leak there. Tomorrow I will try to isolate it to the booster or the HVAC system.
I am not ready to start taking the whole intake apart so I will start with the connections and hoses that I can get to easily. The garage is going to be tied up with a Boxster engine change soon, disassembly of the 928 input will have to wait for that.

GregBBRD

One of those spark plugs has a very black center porcelain (the top one.)
One of those plugs is not black.....and looks relatively proper.

In a CIS system, all of the spark plugs must be all the same color (assuming there are no air leaks in individual cylinders), since a correct fuel distributor provides equal portions of fuel to all of the cylinders.
One or several black spark plugs, with a relatively clean spark plug indicate a problem....low compression in a cylinder, ignition system issue (spark plug wire), bad injector, bad fuel distributor.

I always toss in a brand new set of spark plugs, when working on CIS injection. This allows me a "clean" slate to pull spark plugs and make absolutely sure all of the cylinders are getting the same amount of fuel.

Petza914

Greg is absolutely right on this (of course he is). I had the same issue when putting a different engine into my 928. My original fuel distributor worked perfectly, but couldn't get the car to run when I reinstalled it. Put in a different one from someone else's car and it fired right up, but was fouling 2 spark plugs (6 and 8) in short order. Compression was good in all cylinders and the previous engine owner didn't have the issue. I never would have found it if I didn't swap which ports on the fuel distributor were feeding which cylinders when I installed some of Greg's fuel lines. The foiling plugs moved from 6 and 8 to 5 and 7. Sure enough, in looking at photos of how the fuel lines were routed, the lines from those two FD ports moved from 6 and 8 to 5 and 7. I figured out was was wrong with my old fuel distributor (pressure piston got stuck), freed that up, reinstalled it, and problem gone.

So, the fuel distributor could certainly account for this type of uneven plug colorin and performance issues. Could be as simple as some crud in the tiny filtering screens. The good news is that once you get a K-Jet system sorted out and performing properly, it's a very stable platform that doesn't require constant tinkering and doesn't have electronic modules that fail.

Having learned what I did about K-Jet with my engine swap, when buying my 2nd 928, I specifically looked for a 16v 300 HP Euro since it uses the same fueling system I'm now familiar with. Well, actually I didn't look for one, one found me.

elgy

I checked the ignition timing and it was OK except at idle, either I don't understand the test instructions or there is a problem. Decided to come back to that after going through the vacuum hoses.
This is the front of the engine before I started, as it was when I bought the car.

Looking at the vacuum line that comes from the air guide housing (under the intake distributor) to the auxiliary air regulator and than to the intake distributor I found the following:
- a short length of hose that lead to a manifold with 3 branches, 2 of them plugged and the 3rd connected to the A/C electric air valve mounted on the shock tower (which has since been removed, as mentioned in an earlier post)
- another short length of hose to the auxiliary air regulator
- the long loop of blue hose in the above photo from the auxiliary air regulator to a "T" connector where the output from the A/C electric air valve attached.
- a short length of hose to the intake distributor.
The 3 branch manifold was eliminated and I bought the proper curved hose from the auxiliary air regulator to the intake distributor, which means I went from 16 hose connections (and possible vacuum leak points) to 6.
While the auxiliary air regulator was out I tested it and found it functions correctly.
Current photo


Next I installed a new hose to the brake booster and replaced the rubber grommet and vacuum valve in the booster (with VW parts). For testing I left out the "T" fitting in this line that goes to the HVAC system.

At this point when warm the engine does not idle as well as it did previously, so I will have to redo the initial steps in this thread.

What stands out in the above photo is the rat's nest of wiring on the front of the engine. It all works... sort of, but is difficult to work with since all that tape is stiff and hard to move around, I am afraid of breaking a wire and it looks ugly. I am condidering making a replacement mini-harness to clean this up.

elgy

The CIS system has taken a back seat to other work on the 928, mostly electrical, but a new problem has me scratching my head. In the last year, since the previous post, I have changed the spark plug wires, rotor and green wire. A week ago, while on a short trip to pickup parts, the car died, like a fuel pump failure. I was able to restart and continue, briefly before the same thing happened again. I had hoped to make it home but finally the engine would not run for more than a minute. A failing fuel pump? CAA got me home and I installed a backup pump and tried a test drive around the block... made it halfway before it died again. I was able to restart and make it home.
I attached my fuel pressure gauge and redid the baseline procedure.
Initially I got a system pressure of about 70 psi and the leak down pressure is excellent but my cold control pressure was low at (25psi at 80 degrees F where it should be more than 30 degrees), the HCP went up to 50 psi (should be max 46psi).
Next day I redid the tests and I was not able to get a SP of more than 50 psi and the gauge moved up and down from 35 to 50. I tried three different fuel pumps with the same results.
I get the feeling that some element of the system is rapidly degrading. As mentioned in the first post my WUR has been rebuilt but the FD has not. My understanding is that the FD acts as the pressure regulator so logically if I cannot get the correct SP the FD needs to be rebuilt. I already have a rebuild kit but was hoping to not have to use it... I am a bit intimidated I must admit.

Petza914

Replace the fuel pump relay with a jumper wire and repeat the tests. Connect terminals 30 and 87 which will force the fuel pump to run all the time (even with the key out) so don't connect until you're ready to test.

elgy

Already done.

karl ruiter

If you SP is not holding you can either look at supply or the regulator. You can work on the SP regulator without pulling the whole FD, so it might be worth while to pull the SP regulator from the FD and inspect it. Also, I find the fuel volume in the WSM test easy to do and a good way to confirm fuel supply is, well, up to spec.
Some to the things, besides, pump that can go wrong with supply:
-Fuel Strainer
-Fuel filter
-Accumulator
-Secret filter
-Fuel lines