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Discussion Starter · #1 ·
Hopefully one of the many experts out there can give me a little advice concerning the following which would be most appreciated. The initial symptoms were a noticeable but not major loss of power which developed over a period of approx 1 hour to the state where I could only reach 3K revs before I struggled to maintain 40 mph on the flat, after that I just limped home.I then took it to the dealer and they recommended new air flow sensors which they quoted & £260+ . Unfortunetely after fitting that was not the cause of the problem. They Have now diagnosed (not by any data from computer as they say there is lack of communication ?) that the cat is defective and causing back pressure.
Now waiting on on price for that.
If that is the case, then no problem I will pay the price and hopefully all will be fine. But what bothers me is why! if the cat core is melted and causing back pressure is it because I have an additional problem, what is the root cause. Possibly over fueling but surely pre cat lambada sensors would have picked that up. Anyway, at present just in the hands of the gods, who will likely phone back in the morning with a huge bill. So any info or advice would be really helpfull.
 

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It is possible that the cat ceramic has broken up and blocked the exhaust system causing the back pressure. I had this on a subaru before and caused exactly the same fault. Does the car have one rear box?
 

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i agree with steve rather than fork out more hundreds on a hunch pop to a local exhaust centre and bung a guy £20 to take the cat off and inspect it visually, but it would give you a lack of power if the ceramics collapsed in the cat.
 

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Discussion Starter · #6 ·
Firstly, sorry for not getting back earlier and thanking you and the others for their input and advice, so thank you. Just to update, I decided to take the car to a main dealer for a second opinion before going in the cat direction. The initial diagnosis (air mass meter and possibly blocked cat) was given by an independant BMW specialist who did not have the old revision software to collect fault data for the 850. The main dealer came up with the same thing as far as the air flow meters were concerned, but then changed their minds when I told them that a new meter had already been fitted, made no difference and was then taken off again, I mentioned the possibility of a blocked cat causing a restriction so they were going to remove the cats and check. As that had already been done by the Indie BMW specialist I told them not to bother. Better to take it to an exhaust specialist and pay their hourly rate instead of the main BMW dealers. They also reported that they checked the load signal readings (which were too high, but could not really explain to me what that meant) So looks like its time to go to the exhaust specialist.
Thanks again, Dermot
 

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These symptoms sound very much like a failing cam/crank shaft sensor:thumbsup

I experienced these problems on my Motorsport engine and it eventually immobilised the engine, all happened within a very short period of time:frown
 

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Discussion Starter · #10 ·
Hi there, its just very sluggish while accelerating and while running on the flat. If I reach an incline speed will drop off to 25 MPH, I think they are saying that there is a fueling problem, but caused by the lack of flow, possibly due to a blocked cat, (they initially suspected a false signal from the mass flow meter) but that was eliminated by installing new ones just for a test. They reckon the lack of flow is causing the engine management system to calculate the incorrect fuel air mixture. So I suppose you could say that it is a fueleing problem (after effect) but not the root cause. Also they ran the engine at idle with the air filters disconnected, restricted the flow into one of the air flow meters and the engine stalled, (senced drop in flow) then restricted the flow into the meter for the other bank and there was no change, engine kept ticking over, not sure what that proves, but they say it means low flow through one bank. (now known not to be caused by faulty air flow meter) so they suspect a restriction in the system elsewhere, possibly the catalytic converter on the particular side. I think only sure way to verify or eliminate this is to try it with no cats installed. Thanks a lot, Dermot.
 

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Hi there, its just very sluggish while accelerating and while running on the flat. If I reach an incline speed will drop off to 25 MPH,

I think they are saying that there is a fueling problem, but caused by the lack of flow, possibly due to a blocked cat, (they initially suspected a false signal from the mass flow meter) but that was eliminated by installing new ones just for a test.

They reckon the lack of flow is causing the engine management system to calculate the incorrect fuel air mixture. So I suppose you could say that it is a fueleing problem (after effect) but not the root cause.

Also they ran the engine at idle with the air filters disconnected, restricted the flow into one of the air flow meters and the engine stalled, (senced drop in flow) then restricted the flow into the meter for the other bank and there was no change, engine kept ticking over, not sure what that proves, but they say it means low flow through one bank. (now known not to be caused by faulty air flow meter) so they suspect a restriction in the system elsewhere, possibly the catalytic converter on the particular side. I think only sure way to verify or eliminate this is to try it with no cats installed. Thanks a lot, Dermot.
Sounds like a air leak to me on the bank it had NO effect on.

Also if they suspect a fuel problem then they should test the fuel pressure when the car is running and with the revs held up e.t.c
 

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Possible air leak

A considerable air leak on the intake side of one bank adds up with the symptoms. This air will not be measured (so replacing the air mass sensors will make no difference) and lead to a very lean mixture in one bank and a general loss of power.

This type of fault is dangerous to the health of the engine and could lead to serious faults such as damage to exhaust valves. Hence, the vehicle should not really be driven much until the cause is conclusively determined.

The symptoms may also be caused by excessive back pressure in the exhaust system of one of the banks. This is very easy to test by installing a manometer instead of the pre-catalytic converter oxygen sensor in the side subject to suspicion. A special tool exists - part no. 99 00 0 001 855. (Simply placing a hand just behind the exhaust pipes will give an indication of whether the air flow through them is balanced from side to side).

Generally, in the case of lacking performance my first suspect would probably be the fuel system, e.g. something simple like a clogged fuel filter or even poor connections to fuel pumps or one of the fuel pump relays. Checking fuel pressure while (with the fuel relays removed) shorting between the terminals in the relay box connecting the switch inside the relay will detect fuel pump performance.

Hope this helps - remote diagnostics by email is an imperfect science :).
 

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Discussion Starter · #13 ·
Hi Talyinka, thanks a lot for the input its much appreciated. Started it today (first time for 3 weeks, Ive been away) After ticking over for about 3 or 4 minutes the drivers side exhaust was hot (all the way from engine manifold pipes to the tail pipe) but passanger side still cold to the touch, the pressure at the tailpipe from the drivers side exhaust is definetely a higher pressure. After ticking over for a further 5 minutes the passenger side exhaust gas pressure still weak compared to the drivers side but the manifold had starting warming up, but 'no where' near as hot as the drivers side. Also noticed some liquid, not much but just a little at the tail pipe (drivers side) it did not smell of petrol, no smell at all really and does not appear to be hydrocarbon based. Have already made arrangements to have the cats removed tomorrow and checked out at the local exhaust specialist, will also see what happens when I test it with no cats or exhaust boxes attached (no backpressure at all). Thanks again to you and all the others who have been kind enough to offer advice.
Dermot.
 

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Hi Dermot,

The clear liquid is water (condensation).

Have you had all the error codes read by a competent person (garage)? It is obvious from your explanation that one of the banks fails to operate correctly and of course there can be loads of different reasons for this, catalyst failure not being one of the most likely.

Do you happen to be familiar with the Motronic 'pedal' fault codes? These are fault codes that you can read out, yourself. If you switch the key to the engine run position (position 2) and subsequently depress the accelerator pedal to the floor five times (for the first bank, six times for the second), the CHECK ENGINE light will flash out any stored error codes. E.g. flash-pause-flash-flash-pause-flash-pause-flash indicates fault code 1211.

So, if you do perform this simple test and you do get an error code it is too early to start to take things apart :). Instead, investigate any fault codes first.
 

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Do you happen to be familiar with the Motronic 'pedal' fault codes? These are fault codes that you can read out, yourself. If you switch the key to the engine run position (position 2) and subsequently depress the accelerator pedal to the floor five times (for the first bank, six times for the second), the CHECK ENGINE light will flash out any stored error codes. E.g. flash-pause-flash-flash-pause-flash-pause-flash indicates fault code 1211.

So, if you do perform this simple test and you do get an error code it is too early to start to take things apart :). Instead, investigate any fault codes first.
Cheers for all your helpful advice. IIRC aren't the pedal fault codes only applicable to US models?

Ian
 

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Discussion Starter · #16 ·
Hi Talyinka,
In answer to your first question (Have you had all the error codes read by a competent person (garage)?
The answer is yes, or at least I have done my best to do so!! competent or not. I first took it to an independant BMW garage who have a good reputation on Deeside Flintshire, some of their mechanics are actually eX local Main BMW dealer mechanics, (the results were non conclusive) possibly air flow meter and after that was replaced without any improvement they guessed back pressure due to a possibly defective cat. (they did not have the software to read the error codes on an old BMW 850!).
So next I took it to the main BMW dealer in Chester who had the required software.
No error codes except air flow (and that would have been because they had both been disconnected during the original testing by garage No 1 and not reset).
The original diagnosis (garage 1) was a faulty air flow meter, after replacement, that was not the problem. (but luckily they didnt charge me and put the suspect old one back on)

At the main dealer (I didnt tell them the other garages diagnosis) and they came up with the same potential cause. So naturally I told them not to go down the same road as the air flow meter had already been eliminated and made no difference.
Basically, then they gave up and said maybe a back pressure caused by the exhaust, In the overall process I was offered 2 new cats @ £1400 each from Germany. I was not confident that they were the root cause and took it back home. I am now going to use my local exhaust specialist to check out the exhaust system (they do not charge BMW main dealer hourly rates!)
Your next question:-
Do you happen to be familiar with the Motronic 'pedal' fault codes? the answer is No, extremely interesting and will give it a try and see what transpires. In the mean time I have already booked it into the local exhaust place tomorrow. I do not mind spending the money but refuse to waste it on so called experts guess work.
Thanks for your info, you are obviousally no amature and just what I (we all)need.
keep you informed, Dermot.
 

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Ian,

I think you may be right that this type of diags was only implemented in US spec models (being in possession of computer test equipment I have never used the pedal principle). I just went out and tried it on an EU and a J spec car and did not get any result. Sorry about that - I should have tested it before writing.

Dermot,

If you can find somebody in your area who has Autologic diagnostic equipment and knowledge of E31/E32 cars, particularly those fitted with M70 engines, try to get that person to update his software for these cars completely (Autologic supplies tester extensions on request to subscribing garages but I'm not sure these are subsequently distributed generally). I drove an 850 down to Forrester in Lincoln today and we played around with his Autologic for a while (btw, I can recommend that chap - former racing driver and BMW expert - try to keep up with the bimmer he has built for himself! :)). The Autologic will do the same as a main dealer unit but the chap operating it will often be more knowledgeable than your average BMW mechanic when it comes to these very special cars. (How anybody manages to keep an 850 running without wrenching on it himself is beyond me). NOTE: I have no commercial or other interest in Autologic.

Somebody suggested 'false' air entering your engine, possibly indicating a cracked intake manifold. I just noticed that a chap near Frankfurt has a set for sale on ebay.de. I shall be in Frankfurt week after next, partly to pick up parts, and partly to flog an LHD 850i I've been bringing up to scratch recently, so if you need these parts I can pick them up for you and make sure they are all right.
 

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Discussion Starter · #18 ·
Hi Talyinka,
thanks for the offer to collect parts but hopefully I wont need any intake manifolds. I am pretty sure that the problem really is back pressure due to a blockage in the exhaust system. By removing the pre cat oxygen sensors for a short time and driving the car the performance improves 100%, that is just by releaving the back pressure via the open ports where the sensors were located, this indicates that there is a blockage after these ports, the catalytic converters are most likely. I have just ordered two new cats which should be delivered on Tuesday next. Hopefully that will be the end of this particular problem, additionally I have had the fuel system checked out and all OK, I was a bit concerned as to why the cats had failed in the first place (over fueling & high hydrocarbon content into the cats etc) but all reported as fine. Will see what happens next, thanks again to you and all the others for the advice & support.
Dermot.
 
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