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Is there anyone who could help me in translating the pages 15-20 of this manual? My B7 is experiencing an serious issue with the petrol pressure in the injection head, and we absolutely need to understand these pages to fix the problem.

Thanks in advance. Retribution possible. MP me.
 

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I have crudely translated it, but I have to warn you, don't get too excited. It gives you the design pressures/ranges for everything, but if your system falls outside of those values, it tells you nothing except "replace with new....". As far as adjustments, you can adjust system and control pressure on the regelventil (basically a warmup regulator, in Bosch terminology), and you can adjust the overall mixture on the main Pierburg DL unit, but that's about it for major mixture/pressure adjustments. Can you describe your problems in more detail?
 

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Thanks already Mike.
I know that the manuel does not say how to fix the problem, but atr least we should know where the problem comes from.

My symptoms are:
- lack of power - unability to let the engine run over 2500 rpm - Although, start up and idle of engine are OK.

This problem has very slowly evolved over years. I was unable to get all the power over 5500 rpm since the beginning (I had brutal engine "cut offs" and turbo depression if I tried to push the engine at "full speed").
Now the same happens but much quicker.

We already replaced the petrol pump.
We tested the engine by forcing the petrol cold injection ("choke") , noting that, when injected directly in the air intake, the engine is revving superbly. So no ignition issue.
We tested the ignition condensator ("bobine"?) (replaced by another one) , noting to progress.

THanks for any possible help.
 

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Yes, I remember an earlier post about your "cutoff" issue. I also have an intermittent problem with that under full load. I have so far attributed that to the turbo wastegate (bypassventil) sticking. Is it possible that yours has now stuck open = no boost?

Do you have a fuel mixture (fuel/air ratio ) meter on the car or any way of checking the mixture (emissions equipment at a garage?) to confirm that the fuel mixture is leaning out under boost or at other times? There is some boost enrichment that can be adjusted on the DL unit. Control pressure adjustment on the regelventil also likely affects this, but I am uncertain of the exact effects control pressure on this system.

Which fuel pump did you replace? Depending on your year, there should be an in tank pump (low pressure) and the main high pressure pump (under hood in mine).

I checked my system and control pressure and adjusted the control pressure on the regelventil. With a fuel/air ratio meter on mine, I found that my mixture was leaning out under part throttle/moderate load (high vacuum) conditions. Under full load mixture was fine. I sometimes get that full load pop/cutoff, but still believe that is wastegate/bypassventil related. My problems, I determined, were likely centered around the vacuum enrichment mechanism on the main Pierburg DL unit. The vacuum unit itself may be the culprit (not holding vacuum), and also the cam that this vacuum unit follows (raumprofil) was very worn in areas (shape worn off). I was going to machine a new raumprofil, but decided to send the unit off to Alpina for complete rebuild. The price really isn't bad, considering what a stock Bosch fuel distributor for an BMW of this vintage costs these days. Plus, with the unit completely renewed, I can take it out of the equation when troubleshooting/tuning.
 

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I agree with Mike - knowing the fuel/air ratio at the point where the problem occurs could go a long way to solving the problem. If it's too lean, it may point to a fuel flow issue. If too rich, you may be getting air in after the meter (not certain how the Pierburg system meters air, tho). Loose or cracked hoses can cause unmetered air to enter the system, or pressurized air to excape. Hopefully, these have already been checked. Also, his suggestion about the wastegate is valid, as well. Two years ago, mine was stuck open, and my car exhibited similar symptoms - no boost pressure was being made, it ran somewhat acceptable up to about 3000 RPM, and then burned very rich and stumbled a lot after 3000. We removed the gate to check the diaphragm action and found the valve stuck. Applying air pressure to the top of the diaphragm caused it to release. I lubricated the valve shaft with graphite powder and have not had any problems with it since then. Best of luck, and please post your findings...
 

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Thanks for weighing in there, JT, especially about the wastegate. I've been worried for a while that I was being glib with the "sticking wastegate" diagnosis on my car, but your experience there makes me feel a little more confident.
 

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Is it possible that yours has now stuck open = no boost? .
No, we tested the by pass valve when the issue was minor. Even with the valve open, the engine was able to rev up to 5500 / 6000 rpm. Now it's not anymore possible.

Do you have a fuel mixture (fuel/air ratio ) meter on the car or any way of checking the mixture (emissions equipment at a garage?) .
This is part of the programmed tests.

Which fuel pump did you replace? .
The second pump, under the hood.

I checked my system and control pressure and adjusted the control pressure on the regelventil. With a fuel/air ratio meter on mine, I found that my mixture was leaning out under part throttle/moderate load (high vacuum) conditions. Under full load mixture was fine. I sometimes get that full load pop/cutoff, but still believe that is wastegate/bypassventil related. .
How did you adjust this on the "regelventil" (petrol pressure regulator)?


My problems, I determined, were likely centered around the vacuum enrichment mechanism on the main Pierburg DL unit. The vacuum unit itself may be the culprit (not holding vacuum), and also the cam that this vacuum unit follows (raumprofil) was very worn in areas (shape worn off). I was going to machine a new raumprofil, but decided to send the unit off to Alpina for complete rebuild. The price really isn't bad, considering what a stock Bosch fuel distributor for an BMW of this vintage costs these days. Plus, with the unit completely renewed, I can take it out of the equation when troubleshooting/tuning.
According to my mechanician, it's indeed either the enrichement on the DL unit, either the regelventil. Do you confirm that Alpina in Buchloe is able to fix these problems ? Do they replace the parts or repair them? Is it possible to have an idea of their prices?

Many, many thanks.
 

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Two years ago, mine was stuck open, and my car exhibited similar symptoms - no boost pressure was being made, it ran somewhat acceptable up to about 3000 RPM, and then burned very rich and stumbled a lot after 3000. We removed the gate to check the diaphragm action and found the valve stuck. Applying air pressure to the top of the diaphragm caused it to release. I lubricated the valve shaft with graphite powder and have not had any problems with it since then. Best of luck, and please post your findings...
Exactly my symptoms.... How is it possible that the engine stumbles as of 3000 rpm with the valve open? Anyway, this will be checked tomorrow. :lightbulb:
 

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Exactly my symptoms.... How is it possible that the engine stumbles as of 3000 rpm with the valve open? Anyway, this will be checked tomorrow. :lightbulb:
Unsure. Mine is the Motronic version, so there are certainly differences. It's possible that with my Motronic version, fuel mapping may have caused it to run extremely rich (it was blowing black smoke out the back). I'm not certain if the Motronic was sophisticated enough to do anything more than associate RPM to a certain amount of injector duration. I do not think it has any (electronic signal) input for boost pressure. I am just unsure if and how it may relate to your Pierburg controlled engine. It's worth a look, though. Again, knowing your fuel/air ratio (too lean or too rich) at the RPM it's failing at should help you diagnose.
 

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I was assured that I would be getting back an essentially brand new unit, (although cores are no longer available, and so Pierburg will be rebuilding my actual DL unit (regelanlage)). They do not bother diagnosing any specific issues with each unit, just rebuild/replace everything.

I am in the US, and with our currently bad exchange rate it is ~$2000US. Considering a similar Bosch part for an old E21 323i is I think ~$1500, I thought that was a bargain.

Adjusting the regelventil is pretty simple. You must hook up the gages to get the appropriate pressure readings first. Then, you dismount the regelventil from the mount bracket at the front (one bolt). There is a screw in the front that will now be exposed. Turn to increase/decrease control pressure. If you look at the cross section picture in the manual, and if you already understand old Bosch CIS systems, I think this should make perfect sense. As I said before, though, I am not certain of the role control pressure plays in this Pierburg system (vice the Bosch system), so I don't know if control pressure will effect the mixture more on the top end or at idle yet (I will eventually, though!)

You can make sure this is set to within the specs in the manual, but then I wouldn't play with anything else until you understand where the mixture is leaning out. You really need to run the car with an air/fuel meter hooked up to see what the mixture is doing at different times. You drive it around with lean mixture too much, you'll burn a valve or something.

Also, have you checked all vacuum hoses? This is a mechanical CIS system. The first step in diagnosing a vacuum controlled CIS system should be FIND ALL VACUUM LEAKS first. Then see what you have. Do NOTHING until you are sure you have no vacuum leaks in any hoses, even ones that you don't think would make a difference. If the rubber hose from the big screw cap on the DL unit to the regelventil is *******, maybe you don't get full boost enrichment?

There is also a screw on top of the DL, on the air outlet side of the unit that adjust how much air bleeds from the engine side of the air flap (drehschieber) in the DL to the control side of things. This pressure bleed screw adjusts, I'm told, how quickly the boost enrichment will come on. Along those lines, there is a rubber bellows on the back side of the air flap that, if damaged or *******, could be effecting the air pressure differential inside the DL unit and thus, affecting onset of boost enrichment.
>>> See note!

The basic mixture is adjusted by removing the big screw cap on the DL unit (the one with the hose going to the regelventil in it) and then you can see the little screw that adjusts the mixture (again, if you understand Bosch CIS systems, I found this very simple and similar). A little adjustment (1/8 turn) makes a big difference. If you open up the other big screw cap on the forward side of the DL unit, you will see the vacuum control unit and the raumprofil (if you make a little clear plastic cover for this, you can watch it work with the engine running to better understand it!). You may be able to see (as I could on mine) that the raumprofil is worn. There is a machined profile on there, and on mine it was worn down flat in places where it rides a lot. These were some of my lean spots.

My problem was lean mixture at light to partial load/throttle. Full boost I was fine. Note that it has little to do with rpm. 3000rpm with my foot down was fine - 3000rpm with light throttle was lean. So you may have one problem with the sticking wastegate at times, but this stumbling above 2500-3000rpm, is it only when you are trying to accelerate hard, or does it not want to run above 3000 even sitting in the garage? If it's only under hard accelaration, then it would appear to be a boost enrichment problem. If it's any time over a certain rpm, then it's something more.


>> Edit note: This description since found to be incorrect. Upon complete disassembly, it's clear that neither this screw nor the bellows should affect boost enrichment. Per the Pierburg manual, this screw is only an air bleed/bypass for adjusting the mixture at idle.
 

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but this stumbling above 2500-3000rpm, is it only when you are trying to accelerate hard, or does it not want to run above 3000 even sitting in the garage?
Even in the garage. The engine works more on less fine at idle, climbs up hardly to 3000 rpm, then the rpm falls suddenly down until its turns off completely.
 

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My mechanician has ordered the manometers to perform the tests mentioned in the service manual. Last week he dismounted the waste gate to check it.

I will keep you posted.
 

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Here's an update of work done:

- the waste gate has been dismounted and overhauled, as well as the KKK27 turbo. No issues were found except a leak in the connection between the turbo and the intercooler (connector replaced)
- injectors have been cleaned up;
- new petrol pump has been installed, connectors have been replaced for Aerokit connectors
- the entire Pierburg injection head has been swapped with a similar one (spare part) noting no improvement in the symptoms (engine not revving above 3000 rpm).
- the initial injection head back in place, manometers have been mounted to test the pressure at the entry of the injection head, at different rpm.
- it showed that the pressure was between 550 grams (idle) and 220 grams (3000 rpm).
- the cause was therefore the Pierburg regulator (Regenventil), apparently not providing sufficient pressure .
- by shunting the Pierburg regulator, and working with its manometers as "temp" regulator, my mechanician was able to obtain a stable pression and a smooth engine rpm up to 5400 rpm. This was tested on the road , the car was able to a 180-200 km/h at 5400 rpm and with turbo charge at 0,5 bar, which confirms a normal output.

Now here the dilemna, as presented by my mechanician:

- sending the Pierburg regulator to Alpina in Buchloe for refurbishment (hoping they still do this type of work)

- installing a variable regulator instead, allowing to change the petrol pressure according to the needs (lower for a smooth idle, higher for a top high end performance).

My mechanician tells me that, alghough it is always better to have original parts (and therefore I should somehow have the Pierburg regulator fixed) , there are now better solutions than in the years 80 , which he can afford for this car (he speaks about special regulators used in competition, in which he is specialized) which can even be controlled from the cockpit. He is suggesting me to go that way, for a maximum of engine's output.


Hope you found it interesting (for those of you who struggle with the Pierburg system) . Any thoughts are welcome.
 

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My thought would be to stay with the original. Alpina/Pierburg should still be offering a rebuild, although I would get a clear explanation of what they will or will not do (I was not happy with my recent injection head rebuild).

I have faced this question of whether or not to modify, and so far I have decided that if I wanted a faster turbo car, I should build another turbo 635, not change the Alpina. Someday it will become necessary to modify due to parts being unavailable or unmaintainable, but that time hasn't come just yet (maybe next week).
 
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