My car has what feels like fuel starvation when driving with "light throttle" it jerks and feels like it is missing,but,a session on the sun diagnostic threw up o2 sensor control fault and i had already changed the lambda sensor
I am hoping somebody has experienced this problem with a positive end
Also the car drives fine on full throttle if a little bit reserved
Love this car so no intention to cut any corners but want to rectify asap
Mine is doing something very similar: Idle is fine, full bore is also fine, but if I criuse slowly and steadily at, say 40mph in 4th (about 1500 to 2000 rpm) there is an occasional and slight hesitancy (if there is such a word). However, higher steady speeds are fine. So I am not too worried.
Bentley manual for 5 series suggests it could be carbon deposits on the injectors, poor air intake measurement (E.G. due to holes in intake piping between intake manifold and hot wire) or a poor ground connection.
I am running the car 100% on optimax, so I hope that will clean the injectors a little, I have also but a few ml's of redex in the last tank as well for good measure - seems to be running better already, but it hasn't gone completely - I might even do a little overhaul of the injectors soon. Given a moment or two over the next few days I will check all the ground connectors and intake hoses (I have recently changed the main rubber tube between the hot wire and manifold).
Is problem worse or better when the engine is cold ?
Have you pulled out the spark plugs to visually inspect their condition? are all six in the same condition ? is any one them covered in black oily deposits ?
Check the air intake trunking from airflow meter to inlet plenum for any craks or leaks
Check the all six inlets for posible signs of air leaks
lastly if none of the above helps and the car has covered a great deal of mileage it might possibly be the injectors suffering from gunge build up and no longer atomising the fuel, which would requiere to have them ultrasonic cleaning.
Hesitation? These engines do not like to pull from such a low RPM in a high gear, I have expienced this is two different M5s, and it was just due to the gearing and engine characteristics.
SEE REPLY IN CAPS FOR MY CASE: DON'T KNOW IF THAT HELPS STEVE THOUGH. PAUL
Quote:
Originally posted by jrturbo hi there
Question is it a 3.6 or a 3.8 engine
3.8
Is problem worse or better when the engine is cold ?
COLD
Have you pulled out the spark plugs to visually inspect their condition? are all six in the same condition ? is any one them covered in black oily deposits ?
NO. THEY ARE NEW, BUT I WILL CHECK ANYWAY
Check the air intake trunking from airflow meter to inlet plenum for any craks or leaks
HAVE JUST REPLACED THAT
Check the all six inlets for posible signs of air leaks
GOOD IDEA
lastly if none of the above helps and the car has covered a great deal of mileage it might possibly be the injectors suffering from gunge build up and no longer atomising the fuel, which would requiere to have them ultrasonic cleaning.
I would like to think that between us all we might be able to shed some light on your problem.
I gather from your post that the engine check up was not done by BMW dealer, which also means that the diagnostic equipment used by them might not pick up the fault correctly, to give you an example another member of this board, from memory I think it was kurt Ramsden, had a problem with the engine and the non BMW diagnostic equipment kept showing as a fault a Crank sensor, which he replaced, and kept coming up faulty again, in the end when he took it a BMW dealer they found a couple of the ignition coils which where faulty. I am not saying that this is necesarily the case with yours, but it just adds another posibility.
Althought the engine is designed to perform at its best at mid to high rpm, there is no reason why it should not cleanly at low Rpm as well, my 3.8 will pull from 1000 rpm in 6th gear cleanly and without hesitation.
I would recomend you have the fault checked out by either a BMW dealer to diagnose the fault or at least by a BMW specialist
Never the less there are certain things you can do to eliminate possible causes.
Check your throttle linkage, make sure it moves smoothly without sticking, and visually check that all six butterfly open at the same time, although this adjustment is done from the factory and in theory should not require readjusting, there is a posiblility that one of the adjusters might have worked itself loose. check that no vacum pipes have come of, check condition of vacum pipe to servo, etc.
If youre mechanicaly minded, remove coil cover, check visualy all six coils, for posible cracks on the insulation coating, when they beguin to fail you usually see black marks where there has been high voltage leaks also check the wiring to the coils.
Remove the spark plugs and check the color and apearence, do they all look the same
Check the compression of all 6 cylinders, they should be even, with no great variation, if one is low this could a possible problem with one of the cylinders.
Remove cam cover and check the valve clearences, (in most cases you can reuse the cam cover gasket with out a problem), if the valve adjustment varies a lot between valves this could be the cause of your engine running badly at low rpm. (adjusting the valves is something that tends to get neglected on these engines)
I am sorry to say that there so many possible causes to your problem that there isnt an easy answer, I would also add a couple of fuel injector cleaning additives to the tank and see if there is any improvement. if there is, it would point to the injector being dirty, but the only method I would is to remove them and have them cleaned and overhauled and refit with new O rings
I thought this would affect the starting but not what i experienced
Paul it might pay you to check this out as mine was minimal to begin with then got worse
Now the bi**h is on heat and flying
Thanks guys for all your input it was much appreciated as my next step was my main dealer £££££s but was prepared to go the whole hog fortunately not needed
jrturbo,de witt and PSB
Also the engine has not long undergone a full rebuild
A very happy Steve Mac
Last edited by Steve Mac; 9th October 2002 at 00:18.
I know I (well the Bentley manual) suggested that you should check the ground connection, but I didn't actually believe that that would be the problem! Well done for fixing it.
I shall be checking said connections on my own car asap - mind you, having tipped a load of Optimax and Redex into the tank, the last time I drove the car it was as smooth as could be, so I might already have fixed it.
Glad to hear your problem was easy and inexpensive to remedy ! Joe (JRTURBO) was correct in saying I had a problem with non-dealer (but BMW specialist) diagnosis - I went to a dealer in the end who solved the problem quickly, but not quite as cheaply as you ! Two new coil packs required.
I don't subsibe to the view held by some that these cars (in 3.8 guise at least) lack bottom end grunt. Maybe if compared with a lazy big cc V8, but not much else ! As Joe says, 1000rpm in top shouldn't be a problem - 221lb/ft from 1800rpm is the quoted figure from BMW and that will do fine thanks.
Paul - I had a similar experience to you in that some days the car seemed fine, and others not. I couldn't correlate it with fuel, weather, driving conditions, or anything else, which made diagnosis even more frustrating without the proper equipment. My local dealer (NE England) has a E34 M5 enthusiast for a workshop foreman - which is nice.....
I have a -95 M5 and had exactly the same boring hesitation problems!
I did service II, cleaned the injectors (didn't needed to be cleaned) and so on and got no improvements at all!
After that I tuned my engine with an UNICHIP ( http://www.dastek.co.za/ ) on a rolling road and the car is like a completely new car to drive.
No hesitations any more!
It pulls strongly on 6:th gear from 800 rpm if I want!
It is easier overtake at 2000 rpm on 6:th gear without shifting down!
It was expensive but nessecary if you want to enjoy driving the car and if you use it as an everyday car.
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