So, during reving, acceleration, throughout the rpm range there seems to be a vibration and major lack of power....checked oil, it's fine, but I'm thinking a foul spark plug, or 2?? Any ideas?

spark plug? dirty afm? o2 sensor? those could all be causes....

mine used to do that. was a combination of the computer under the dash getting wet, bad cold start valve, and sucky injectors, may need to check all those things.

ah i knew i was forgetting something... the cold start valve and the injectors... thanks webb..
i was trying to remember the common issues off the top of my head...


keep us updated..

and you may want to wander over to BIGCOUPE.COM to get another opinion bunch of tech guys over there

wouldn't the cold start valve only come to play when your car isn't warmed up right? im knida just testin my knowledge lol

vibration=drive shaft issues??

vibration=drive shaft issues??

If the car isn't running well, the whole motor can vibrate pretty bad.

I had the same issue, swapped out the plugs, cap & rotor with only mild return (it was time anyway). Swapped in the new AFM and all was well...

This is what I ALWAYS do when I have a poor running engine (roughly in this order):

1. Check for air leak(/s) by spraying carburettor cleaner to all potential places where a leak may occur. If the engine revs go up all of a sudden you found the leak.
2. Compression check
3. Check spark plugs. They should look light brown after a longer run AND all alike. Eventually just replace them.
4. Check on every single spark plug cable if there is a strong spark (using a good spark plug).
5. Check / adjust valve clearance
6. Check throttle switch - eventually stuck at WOT position = fuel mixture way too rich.
7. Check fuel supply / fuel pressure. Especially on cars which have been sitting for a long time some residue may collect in the fuel tank and clog the fuel pump (had that recently). Note that the fuel filter is mounted AFTER the pump, so dirt can actually get into the pump.
8. AFM is a possibility but quite unlikely. The spring inside becomes a little weak over time but won't cause a really bad running engine.
9. Cold start valve may be stuck and additional fuel is supplied to the engine, but then you should have an ok running engine when it's cold.
10. Water temp sensor could be faulty giving the Motronic wrong temp. values
11. O2 sensor faulty delivering BS information to the Motronic.
12. If possible run a CO test.

@sixseries

drive shaft issues don't create a significant loss of power - unless something really brakes down :)

This is what I ALWAYS do when I have a poor running engine (roughly in this order):

1. Check for air leak(/s) by spraying carburettor cleaner to all potential places where a leak may occur. If the engine revs go up all of a sudden you found the leak.
2. Compression check
3. Check spark plugs. They should look light brown after a longer run AND all alike. Eventually just replace them.
4. Check on every single spark plug cable if there is a strong spark (using a good spark plug).
5. Check / adjust valve clearance
6. Check throttle switch - eventually stuck at WOT position = fuel mixture way too rich.
7. Check fuel supply / fuel pressure. Especially on cars which have been sitting for a long time some residue may collect in the fuel tank and clog the fuel pump (had that recently). Note that the fuel filter is mounted AFTER the pump, so dirt can actually get into the pump.
8. AFM is a possibility but quite unlikely. The spring inside becomes a little weak over time but won't cause a really bad running engine.
9. Cold start valve may be stuck and additional fuel is supplied to the engine, but then you should have an ok running engine when it's cold.
10. Water temp sensor could be faulty giving the Motronic wrong temp. values
11. O2 sensor faulty delivering BS information to the Motronic.
12. If possible run a CO test.

@sixseries

drive shaft issues don't create a significant loss of power - unless something really brakes down :)



we just got schooled by the master haha :D

still far away from that, but almost 30 years of experience as owner of various BMWs.

exactly, it was a positive compliment! haha

Started it yesterday morning, drove to work, and it ran fine like it had never ran rough before?? Now I'm really confused. I know for a fact the previous owner rarely drove it, and left it in his garage for long periods w/out running it. In addition to the mystery, it looks as if the thermostat is oscillating, just not working properly at all. Temp gauge reads on the cold side, then sometimes a hair on the warm side, heater fan works, but inconsistent on actual "warm" air. If I do get heat, it is only from the floor OR windshield defroster vents. The center air vents ONLY BLOW COLD, never have they blown warm air! I will start by replacing the thermostat and checking/replacing the spark plugs and then follow w/ the long list of what to check. Thanks for the advice guys!!

Started it yesterday morning, drove to work, and it ran fine like it had never ran rough before?? Now I'm really confused. I know for a fact the previous owner rarely drove it, and left it in his garage for long periods w/out running it. In addition to the mystery, it looks as if the thermostat is oscillating, just not working properly at all. Temp gauge reads on the cold side, then sometimes a hair on the warm side, heater fan works, but inconsistent on actual "warm" air. If I do get heat, it is only from the floor OR windshield defroster vents. The center air vents ONLY BLOW COLD, never have they blown warm air! I will start by replacing the thermostat and checking/replacing the spark plugs and then follow w/ the long list of what to check. Thanks for the advice guys!!

your ventilation system is ok. The center vents never blow warm air. Strange but true. If you have warm air your thermostat is ok. But your oscillating temp gauge might be a sign for a screwed up sensor.
Besides that definitely check fuel pressure.

Wolf

Chech out this diagram on the vents:

http://bigcoupe.com/phpBB2/viewtopic.php?t=4805&highlight=center+centre+vents

Chech out this diagram on the vents:

http://bigcoupe.com/phpBB2/viewtopic.php?t=4805&highlight=center+centre+vents

You seem to be a living encyclopaedia when it comes to E24 issues. To every problem you know the correct article or thread. AMAZING. Good to have you on this board.
:alright

your ventilation system is ok. The center vents never blow warm air. Strange but true. If you have warm air your thermostat is ok. But your oscillating temp gauge might be a sign for a screwed up sensor.
Besides that definitely check fuel pressure.

Wolf

What sensor? O2 sensor, located where? Sorry....I'm a little far from a decent mechanic, lol.

your ventilation system is ok. The center vents never blow warm air. Strange but true. If you have warm air your thermostat is ok. But your oscillating temp gauge might be a sign for a screwed up sensor.
Besides that definitely check fuel pressure.

Wolf

I have "warm" air sometimes....and how will checking/replacing the sensor help? What about the heater core?? Does it have a heater core?

What sensor? O2 sensor, located where? Sorry....I'm a little far from a decent mechanic, lol.

You have some sensors on the thermostat housing. One is for the engine ECU (Motronic) while the other one is for the temp gauge in your instrument cluster. Disconnect them one by one and you will find out which one is the temp. gauge sensor.
Your O2 sensor has nothing to do with engine temperatur. It is located in the cat and you can only reach it from underneath.

http://www.wokke.de/BMW%20E24-635CSi-85%20delphin%20grau/Motorraum/06.JPG

You have some sensors on the thermostat housing. One is for the engine ECU (Motronic) while the other one is for the temp gauge in your instrument cluster. Disconnect them one by one and you will find out which one is the temp. gauge sensor.
Your O2 sensor has nothing to do with engine temperatur. It is located in the cat and you can only reach it from underneath.

http://www.wokke.de/BMW%20E24-635CSi-85%20delphin%20grau/Motorraum/06.JPG

Wokke.....YOU ROCK!!! When I make that vacation trip to Europe, I'm takin' you out to a steak dinnner and buyin' u some drinks!!! Thanks for the help!

sounds good. Looking forward to it :drink1

Does anyone have some step-by-steps on replacing the o2 sensor located underneath? Pics are helpful. I asked about this earlier as a precautionary fix, but, I didnt follow up as I should of.

Does anyone have some step-by-steps on replacing the o2 sensor located underneath? Pics are helpful. I asked about this earlier as a precautionary fix, but, I didnt follow up as I should of.

Jack up your car and just have a look. If you still think you need instructions have someone else do the job :)

I think it may depend on the car, or the manufacturer of the down tubes. But, i picked up a bolt-on cat unit from haygood for a VERY good price. You can see the bung where the O2 sensor threads in just below the Y in the down tubes...

http://i43.photobucket.com/albums/e370/jbd5015/IMG_0682.jpg

So, its going to be after the Y in the tubes on your car, which is easiest to access from underneath. Might actually be easier to replace the down tubes then mess with a 20+ year old 02 sensor haha...

-Jeff

kitty has downpipe ftw

I think it may depend on the car, or the manufacturer of the down tubes. But, i picked up a bolt-on cat unit from haygood for a VERY good price. You can see the bung where the O2 sensor threads in just below the Y in the down tubes...

http://i43.photobucket.com/albums/e370/jbd5015/IMG_0682.jpg

So, its going to be after the Y in the tubes on your car, which is easiest to access from underneath. Might actually be easier to replace the down tubes then mess with a 20+ year old 02 sensor haha...

-Jeff


You know, I recall that from your build mod thread. You did say that the down tubes can be replaced without a welding torch? They just come off by unbolting it? I am interested in doing that eventually.

that was sent to my house from Haygood (or wherever he drop shipped it from). No welding, not cutting, no modification. 'simply' take the old unit off, and 'simply' install the new unit. Couldnt be any easier than and cost effective.

I sold the old cat converter on ebay as scrap and made back most of the cost for the new one.

Id highly recommend doing that if you need a new cat and just want a 'stock' replacement. The cat on there is a stainless steel DEC cat, so it performs and sounds better than original.

-Jeff

or be like me and hollow your cat out...

hehe

its just for looks now

...it sounds interesting now.... im looking to do fully custom exhaust this coming fall/winter headers and all...

good call! Thats what i was planning on doing, but i got nailed at inspection for my cat.

It had a crack in it, and even though the car didnt need to pass emissions (low mileage over the past year), the safety inspection failed. I guess they dont want the cats to be open and leaking death all over the place? haha

-Jeff

Does anyone have some step-by-steps on replacing the o2 sensor located underneath? Pics are helpful. I asked about this earlier as a precautionary fix, but, I didnt follow up as I should of.

my O2 sensor was on a small crossover just before the cat.


I soaked it with wd40, disconnected the wire, put a large wrench on it, then used a floor jack to push the wrench up to unscrew it out of the bung.

Had to repeat a few times, but it finally came out of there and then I took it to NAPA to find a replacement unit to rewire back in... think it was a 1986 Ford E150 4.9L O2 sensor I used.. exact sensor, just had to splice the old connector on it.

Seeker, what did you find? How's it running?

So, I replaced the temp. sending switch w/ a new one, and the temp gauge in the instrument cluster is still reading an improper temperature(stays in the blue area for the most part). And I'm still not getting any warm air from the lower heating vents and when I do, it's not really that hot, and not often at all. Maybe it is the thermostat??

could indeed be that the thermostat is stuck open. This way the engine never reaches proper operation temperature. What's your mileage? Should be substantially higher than normal. Since a new thermostat is really cheap plus easy to replace I would just go for a new one - can't hurt and may be the root cause. Make sure the big rubber O-ring comes with it.

Wolf

Have you tried bleeding the air out of the system?

mileage is 179k.....who knows if it's ever been replaced...no idea?
Thanks for the "O-ring" advice....I will make sure. It's kind of funny when I go to the parts store...I always wander between saying it is an '83 633(same year, not same model) and an '85 635CSi(really an '83 635CSi).

No.....have never tried bleeding the air out.....how do I do that?

Have you tried bleeding the air out of the system?

since he has not reported an overheating engine bleeding wouldn't change anything. If you have air/exhaust gas in the cooling system the bubble typically "parks" at the thermostat and prevents it from opening. For a to me unknown reason these bastards only react to hot liquids and ignore hot gases and therefore remain closed. This results in the overheating engine because the large coolant circuit through the radiator remains closed.

@Euro635CSi

Bleeding is super simple:
On top of the thermostat housing you have an M6 screw (10mm head).
Run the engine until it warms up and then open the screw. If there is any sort of gas in the system it'll escape now. Keep it open until you have a steady flow of coolant. It helps to have the car parked uphill, i.e. eventually lift the front of the car slightly.

Please keep us posted on your success :)

I used to drill very fine pilot holes around 1/3 of the outer lip of the stat and orient it on top. That helped pass the gas and let the TT get full coolant to it. Nowadays I crack the bleeder..

So, r u saying to bleed out the system and replace the thermostat....or just bleed the system and leave the thermostat alone?

I used to drill very fine pilot holes around 1/3 of the outer lip of the stat and orient it on top. That helped pass the gas and let the TT get full coolant to it. Nowadays I crack the bleeder..

that's indeed a good trick and some thermostats actually have a little hole already.

@Euro635CSi

Although I don't believe that you have any air in the system (judging from the symptoms you're describing), bleeding the system won't hurt.
If you replace the thermostat you need to bleed the system any ways.