In the name of sanity, please help !

Banjo013

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Hi,

I recently bought a 1995 BMW 520i E34 auto model.

I knew when I bought it (very cheaply from an emigrating friend) that there was a problem with it. He told me he had taken it to his mechanic who diagnosed a faulty mass air flow meter. My friend decided to sell the car cheaply rather than getting the work done as he was going away.

So I got my hands on a new mass air flow meter today, and fitted it this evening in 30 minutes. Off I went for a drive, and it felt so much better - I was certain the problem was solved. But when pulling away from a set of traffic lights, the problem returned. Here's a description :-

The car runs fine for the first 20-30 minutes. Then suddenly this problem develops, whereby the engine seems choked up. It would be very sluggish on pulling away, then it would "loop" - accelerating and falling back, accelerating and falling back .... etc etc etc ..... It's the very same effect as if the driver was pumping on the gas peddle as the car moves.

If you step on the peddle, the car will accelerate like the clappers, then once the gear shifts up the problem is back again. It seems to only happen in or around the 2k rev range. Above or below that it doesn't seem to be such a problem, however it will stall sometimes upon braking.

Any ideas please ? Anyone else experienced this problem ? What on earth could it be ? Haynes don't do a manual for this model ... I'm completly baffled.

All comments/ideas welcome please - thanks.

lomb

could be anything from cracked head, damaged cat, defective injection, faulty sensors, faulty ecu, defective replacement mas, timing slightly out, vacuum leaks, absolutely anything. prob need a diagnostic probe in it on it even to begin.

Seth Brundle

Possible problems:-
Air Flow Meter (dirty or faulty)
Throttle Postition Sensor
Crankshaft Position Sensor
Lambda Sensor
Vacuum Leak (loose or split pipe)
O2 sensor (if present)

TBH, your best bet is to get it to someone who car read all the ECU faults and diagnose the correct fault. May turn out to be cheaper in the long run!

Banjo013

Thanks K ... any chance you could recommend somewhere on Dublin Southside ?

Seth Brundle

There are a few specialists (& parts suppliers, etc.) listed on http://www.bmwcarclubgb.co.uk/regions/irlnd/contacts.asp but you would need to phone them to check if they can hook it up to a pc.
There are also 3 dealers south of the river
Murphy & Gunn (Milltown)
Maxwells (Blackrock)
Frank Keane (Naas Rd)

lomb

i believe u can buy a diagnostic connector for 50 stg and download free software on the web if u want to do it urself. but i reakon a specialist or failing that a main dealer is best for something like that.

haynes manual is a waste of time.

maninaskirt

Hi, How does it rev when in neutral? I.E. when prob occurs knock it into " N " in a safe place and see if it revs ok, as its an Auto it could be the torque converter, and the ECU is trying to figure out what is going on!! also I had this problem with my GTIR Pulsar and it turned out to be the Plug leads breaking down and had a mini lightnening show under load on high boost, but could not be seen due to the intercooler, have you tried the BMW forums as that engine is also in the more popular 320i, are there any smells from the engine or exhaust when the issue is present?
hope this help,
cheers
G.

P.S. here's the URL for mentioned forum http://www.bmw-forums.com/

stratos

I had a prob with same bmw not as bad though, and it was a crack in the pipe from airflow meter to airbox. as the engine moved under accelleration the crack in the pipe opened. the symptoms were not drastic though, just like minor acceleration glitches.

stratos

I thought i had a manual when i had my e34's. I had a quick look yes there is a haynes manual. it's ISBN 1 85960 236 3. It covers the 3 and 5 series.

stratos

I just had a look in the manual. and under trouble shooting. Section for engine surging here is it's idea's.
1 Intake air leak.
2 fuel pump faulty.
3 loose fuel injector harness connections.
4 defective ecu.

Seth Brundle

stratos wrote:

I thought i had a manual when i had my e34's. I had a quick look yes there is a haynes manual. it's ISBN 1 85960 236 3. It covers the 3 and 5 series.

That book covers the E30 & the E34 till 1991
Get a Bentley manual

stratos

Don't think they changed the 5 series that much mine was a 95, mechs as I remember seemed much the same. was a while ago though.

Seth Brundle

different engine though! [M20-B20 to M50-B20(24V)]

AMurphy

Previous suggestions which I think I would follow initially.

I also think it may be a leak in the intake manifold piping, or that's where I would first start looking.
Check for any and all leaks on any rubber/plastic piping to the intake.
Just jiggle things about and see if anything makes a difference.

What does it do when reved in "N" or "P"

Get a Bently manual.

Check the fuel pressure regulator for fuel leaks. (the diaphram in them can crack)

Check the auto idle adjust motor function.
given you mentioned it will stall on braking, assuming it has a vacuum booster, any possibility it may be leaking. Listen to it for possible airflow. Or it's simply running lean and the extra air from the vac boster is swamping it.
typically your Auto Idle adjust should take care of these blips.. assuming it is not already 100% closed doe to a continuous lean condition.
Or possibly block it off for a test.... just remember you will have poor/no brakes, so best done on a Sunday morning early.

That fact that you get full acceleration on Wide open throttle, where the fuel is increased, suggests you do not have a fuel supply problem or the failing pump kind, but perhaps is running lean most of the time.

Put a DVM on the O2 sensor (if it has one) and see if the voltage fluctuates properly.

How many miles on the current O2 sensor, (again assuming you have one)

lomb

id replace the o2/lambda sensor personally, they never last anyway. its a heated wire and it operates under bad conditions.

AMurphy

lomb wrote:

id replace the o2/lambda sensor personally, they never last anyway. its a heated wire and it operates under bad conditions.

I'm pretty sure the BMW has a Bosch and it is not a heated wire, even though it may have a heater in it. (3 wire).
and they typically last about 60K mls. but 45K to 120K is possible.

stratos

kbannon wrote:

different engine though! [M20-B20 to M50-B20(24V)]

True, lol the engine was fine everything else broke down. :eek:

lomb

AMurphy wrote:

I'm pretty sure the BMW has a Bosch and it is not a heated wire, even though it may have a heater in it. (3 wire).
and they typically last about 60K mls. but 45K to 120K is possible.

id say the car has 120+ miles on it. 95=10 years @12000 per year is 120000. so replacing it is good maintainence.

Banjo013

Thank you so much everyone.

Problem seems to be solved - looks like it was the throttle position sensor (well spotted kbannon) ... had it changed on Thursday by my mechanic and the problem has disappeared. Took it for a 2-hour spin last night after work and no jolting.

Thing now is that the engine still seems a bit choked up - tends to be very slow on acceleration. Is this normal ? I suspect it probably needs a good service at this point and maybe some adjustment to the fuel/air mixture ......

Don't think my mate (the previous owner) took the best of care of the car to be honest - but I do think that with some TLC now it can be brought back to full health.

Thanks guys - I'll be back again if I get more problems !

lomb

how much was the throttle sensor?
def change the lambda sensor next. theres only a few sensors that need changing at high miles- the maf, throttle body, and the lambda. uve done 2 no point in doing things by halfs. also change all the plugs and renew the airfilter. should drive like new then oh one final thing: poor engine running may be incurable if the car engine has lost compression. this is possible with the old alum blocks. if this is the case drive it till it stops. no point in proceeding further with it. hopefully its not this anyway.
how many miles does it have?

Banjo013

The part was 70 squids. Been driving the car around all day today and old problem def seems to be gone.

But it is still sluggish, and the fuel guage moves towards the "E" mark alot quicker than I can believe - ie it seems to be drinking petrol.

That diagnostic connector you mentioned earlier - any idea where I can get my hands on one of them ? And the software ?

lomb

sounds as it may be overfueling it low in the revrange. ie not enough air and too much fuel. il look up the diagnostic thing and get back to u.

tapest

Banjo013 wrote:

The part was 70 squids. Been driving the car around all day today and old problem def seems to be gone.

But it is still sluggish, and the fuel guage moves towards the "E" mark alot quicker than I can believe - ie it seems to be drinking petrol.

That diagnostic connector you mentioned earlier - any idea where I can get my hands on one of them ? And the software ?

Hi
diagnostic connector
New Car shop,Harfords, I think beside LIDL ,mahahide road. I saw them there, maker = Gunsons.....If memory serves me right(Check by phone) €50.
t

lomb

i think that gunson one is a service light reset. cant find a cheap bmw tool only a vag.com one. have a look here though http://www.unixnerd.demon.co.uk/motronic.html

i think u may need to employ a trained bmw technician possibly like kbannon suggested. could get very expensive otherwise.

AMurphy

Good work on the TPS.
re the sluggish and drinking petrol bit.

You did mention the past owner did not do a great job wrt maintenance.
Therefore, I might be inclined to follow another piece of prior advice.
Do a compression check.
If you have good compression, we have something we can work with. If not, you got a decision to make, is it a valve or ring job and/or is it worth repairing.

You might also do a Ex back-pressure test to check for a blocked CAT. (assuming this vehicle has one), or simply remove the cat for a while.

Assuming the compression is good.
I'd give this thing a complete check out.
I'm assuming the A/T is OK at this point and not slipping, etc.
btw, is it a mechanical or Electronic A/T?.

Plugs, cap, rotor, O2 sensor, fuel pressure & regulator, check all the temp sensors relating to the EFI, Thermostat. You can check the O2 sensor with a DVM.
With a good manual and a DVM you can check all these sensors, no need for access to diagnostic connectors, etc. although $50 is less than what you'd pay for a good DVM.
replace any and every vac tube with a crack in it, particularly if it has that external woven thread, where you cannot see any cracks underneath.

A EFI temp sensor that is registering the engine temp as cold or an O2 sensor that is stuck on lean will cause rich running.

lomb

http://f2.autospeed.com/cms/A_2362/article.html

lomb

AMurphy wrote:

You did mention the past owner did not do a great job wrt maintenance.
Therefore, I might be inclined to follow another piece of prior advice.
Do a compression check.
If you have good compression, we have something we can work with. If not, you got a decision to make, is it a valve or ring job and/or is it worth repairing.

very good advice.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=30921&item=7949217054&rd=1&ssPageName=WDVW

AMurphy

Thanks for the link LOMB.
That looks line a generic OBDII or ISO OBD connector.

I would never have thought of looking for it unde the H'brake. Do you have any idea where the same connector is hidden on a Pug 307. I looked all over, but not there or under the seats, boot, headliner, door, gas cap/spare tyre, etc.

Here are some useful links;

http://www.onboarddiagnostics.co.uk/obdcodes.htm

http://gendan.co.uk/diagnostic/index.shtml

http://www.onboarddiagnostics.co.uk/obdcodes.htm

actron

byw, compare this to this to this

and here is one for the DIY/PC expert.
As for the books, get ISBN 0-9715411-4-0 and 0-9712411-5-9 as a set.... they should really be one book.

However, I tried a USA 3100 on a 2000 EU Toyota and it did not work. Worked on Ford and VW

lomb

i know for a fact there is very good vag.com freeware software out there and a dongle to go to a laptop can be had for 40 quid. ive lost the link but theres a guy in the uk who sells them. they look rough and ready but they do the job.but thats vag.com i know little about bmw diag but a multimeter as u suggest is just as good in most cases

lomb

hmm check if its using oil if it is, ur bore is gone. therefore the oil would foul up the o2 sensors. in the short term replace this long term drive it till it dies or sell it in merlin car auctions thats where they all end up anyway

AMurphy

Oil burning typically has no acute effect on the O2 sensor, Grose oil consumption would clog the CAT before it dispatched the O2 sensor.
However, common "Form a Gasket" silicone paste/glue will instantly kill an O2 sensor... Even if you use it on a sump or oil/valve cover traces will get into the combustion and downstream.