Revving engine at neutral bad?

[Rick L]

I have few cars that are not driven during winter seasons. I do start the car once every two weeks and run for 20 minutes. To warm up the engine faster to operating temperature, I would rev the engine up. Is revving the engine with no load on it bad for the engine? I was told that it is...?

[BigKriss]

I dont see how its bad unless the oil isn't warm enough. But I dont see how without any "load" it would be bad.

[Rick L]

Friend told me this after seeing me rev my engine. I don't go over 3k rpm and take it easy. Maybe another myth? ;)



I dont see how its bad unless the oil isn't warm enough. But I dont see how without any "load" it would be bad.

[shogun]

Caveats about the ZF automatic transmission!

The automatic transmission supplied in the 745I (edit: in the later e24 also) is the ZF 4HP-22 EH. This electronic slush box is a marvel of engineering for it’s time, and is a good match for the turbo motor. It has a flaw however that many owners have discovered the hard way, and I will detail it as best I can.

The problem is that after starting the engine, and selecting any gear, forward or reverse, the front clutch pack in the transmission is pressurized, and that pressure is not bled off when park or neutral are selected.

This will cause premature wear of the clutch plates if the car is idled for long periods after engaging a gear, and can actually burn the clutch plates out if the engine is revved for a period of time. This high rev condition is particularly scary when you consider the process many states require in the process of emissions testing, and also might cause much concern when having the Air Conditioning recharged.

There is a BMW service bulletin (posted in full below) on this phenomenon, to summarize it is permissible to operate the engine at speeds up to 2000 RPM for up to 90 seconds in Park, only if the engine has been shut down for at least 60 seconds, and only if no gear has been engaged after starting the engine. Once shifted into any gear, the clutches pressurize, and stay pressurized until the engine is shut off for a minute or so!

When I go for Emissions or A/C service, I explain the concern to the shop, most have heard of it and are glad to be reminded. I then stay with the car during any high idle operations just to be sure!

I and most other owners swear by synthetic transmission fluid, Mobil1, Amsoil, or Redline. There has been a concern expressed by Brett Anderson, that if the transmission has not been serviced regularly, that the conversion to synthetic could do more harm than good. Apparently a non serviced transmission can have lots of particles floating around and sticking to internal parts of the transmission, and when the change to synthetic loosens all these particles they become a hydraulic abrasive that can cause even worse damage to the transmission. So if you are unable to verify regular service on your trans, you might want to stick to just a good grade of ATF, and change it more frequently.

Many thanks to Jeff Moser, Chris Koch, Prakash Maggan, Brian Mihalka, and Alan Chung for sharing their collective wisdom of this problem.

BMW NA service bulletin # 24 01 91 (3196) dated June 1991

Subject: Transmission Failure during Exhaust Emission Testing

Models: All 1984, 1985, 1986 with 4-speed automatic transmission, 1987 635CSi, 735i, and L7.

Situation: There have been reported isolated cases of automatic transmissions failing during a High Idle Exhaust Emissions Check. The failures have resulted from a preconditioning procedure where the engine is held at high rpm for a prolonged period of time. The following applies to all states which have a High Idle Exhaust Emission Check.

As the internal transmission components experience normal wear over time, the possibility of transmission damage exists if the vehicle is operated for extended periods of time at high rpm in PARK or Neutral. Such operation does not constitute normal operating conditions. If, in exceptional cases such as A/C recharging, injector cleaning, charging system tests, or emissions testing, vehicle operation at high rpm in PARK or Neutral is required the following setup procedure must be performed prior to beginning such operations.

Solution: The emissions test must be conducted with the engine at operating temperature. If the engine is not at operating temperature prior to beginning the test, it is recommended that the vehicle be driven for a short period of time to bring the engine to operating temperature. DO NOT run the vehicle at high idle to achieve operating temperature.

Once the engine has reached operating temperature, the following pretest procedure must be performed BEFORE testing begins.

Setup Procedure for I/M Emission Test

1. Shift to PARK.

2. Turn engine OFF.

3. Wait at least 30 seconds.

4. Restart engine, LEAVE TRANSMISSION IN PARK. After the engine is started, DO NOT move the gear shift selector through the Forward or Reverse gears before or during the test sequence. DO NOT EXCEED 2000 RPM.

5. Begin emissions test procedure.

6. If the vehicle fails the emission test, some states allow for an extended pre-conditioning before the repeat test. In this case the following procedure should be adhered to.

Precondition Procedure

1. Shift into PARK and turn the engine OFF for 30 seconds.

2. Restart engine, LEAVE TRANSMISSION IN PARK.

3. Engine may be preconditioned at a maximum of 2000 RPM for up to 90 seconds, at which time the repeat test must begin.

If the above steps are not followed, serious transmission damage can result.

Note: Due to the unusual nature of the emissions check, this type of failure does not take place under normal operating conditions.

The rebuild with lots of pictures:
http://www.bimmer.info/~rickm/trannyrepairs.htm

If the above link won't open, try the archive from the WayBack Machine:
http://web.archive.org/web/20071229041003/http://www.bimmer.info/~rickm/trannyrepairs.htm

Rebuilding the ZF4HP22 in the UK (with mention of "Hanging" in first):
http://www.cowdery.org.uk/zf.php

[Mr._Graybeard]

Great post, Shogun. I think the no-rev caveat also applies to the non-electronic 4hp22 automatic (no EH suffix), which is in the E30 325i models (but not the 325e) and some E36 3ers.

[whiskychaser]

Friend told me this after seeing me rev my engine. I don't go over 3k rpm and take it easy. Maybe another myth? ;)
I wouldnt rev a motor to 3k to warm it up. Over 1k and I'm getting giddy.:D I'd no more rev its b....cks off in neutral than drive around in too high a gear. Why? Because I think it will cause wear and strain on the engine. I cant point to any studies or other evidence so I will just call it empathy:D

[Rick L]

Thanks Shogun for the info. I didn't know about the auto trans. But I don't really rev my E34 at neutral. :) Both cars that I do rev are manual trans. I've been told revving engine with no load is bad. I don't see why that would be...

[Rick L]

Not sure what's worse... Taking longer to warm up by idle/low rpm or rev the engine slightly so it warms up faster?



I wouldnt rev a motor to 3k to warm it up. Over 1k and I'm getting giddy.:D I'd no more rev its b....cks off in neutral than drive around in too high a gear. Why? Because I think it will cause wear and strain on the engine. I cant point to any studies or other evidence so I will just call it empathy:D

[shogun]

that is clearly mentioned in the owners manual, immediately start driving the car and do not wait till the engine gets warm in idle.

[BigKriss]

Erich, in your experience how much payy in the transmission pump is acceptable before it goes bad?

When I changed the engine in my car, there was 1-2mm of play on the input shaft. When I told a mechanic this (one that has done a few zf-4hp22 rebuilds), he said the pump was going bad and I should get it looked at. He said 1-2mm isn;t good, there should be no play. the gearbox has done 260,000kms without a rebuild yet.

cheers.

PS. I'm in china now. There are no cars over 10 years old year. I've seen 1 e34 in shanghai and now e32s, one e39 and the rest are new BMWs. Plenty of longwheelbase cars in 3,5,7 series and x6's also. cheers.




that is clearly mentioned in the owners manual, immediately start driving the car and do not wait till the engine gets warm in idle.

[shogun]

Kris, about the play in the transmission pump check the online shop manuals, maybe something is mentioned there. http://www.bmwtechinfo.com/repair/main/

But that is a lot

the gearbox has done 260,000kms without a rebuild yet
Maybe soon it's time to do a overhaul
And how to manage a cold start, is clearly written in the owners manual. See here
under additional practical tips
http://luuk.xs4all.nl/bmwboeken/bmwe34manual/html/pg57.jpg.html


BTW: I just cleaned up my stock a bit and found a lot of new Bosch ignition coils, ignition distributors, - rotors, Hella voltage regulators etc.
If you need, let me know, have to dig in the old files how much I paid for them, bought them from Germany.

List (partially complete, have more stuff as you know):
ignition coils, OEM Bosch rod type (round) 0 221 118 335 5 pieces

fits BMW

318i (E30, E36) M40 B18
320i (E30) M20 B20
325i, X (E30) M20 B25
325E (E30) M20 B27
520i (E34) M20 B20
525e (E28) M20 B27
525i (E34) M20 B25
530i (E34) M30 B35
535i (E34), (E28) M30 B34
635 CSi (E24) M30
730i (E32) M30 B30
750i (E32) 87 - 90 M70 B50
M5 (E28) 85 - 87 S38 B35
M535i (E28) 84 - 87 M30 B35

Porsche
928 GT , GTS 89 - 91 M28.47, 49, 50

Volvo
740 Series Turbo 84 - 90 B230ET

according this this list from Bosch Australia http://apps.bosch.com.au/products/saa/ignition_coils.pdf maybe even more, but that is listed by Bosch Australia

ignition coil Bosch 0 221 502 009 = BMW ring type ignition coil
BMW :
12 13 1 720 877 - 12 13 1 742 925

fits
M70 engine cylinder 1-6, 5 pieces

Part Cross-reference RealOEM.com Home

Part 12131742925 (Ignition coil) was found on the following vehicles:

E31: Details on E31
E31 850Ci Coupé, Europe
E31 850CSi Coupé, Europe


E32: Details on E32
E32 730i Saloon, Europe
E32 730iL Saloon, Europe
E32 735i Saloon, Europe
E32 735iL Saloon, Europe
E32 750i Saloon, Europe
E32 750iL Saloon, Europe
E32 750iLS Saloon, Europe


E34: Details on E34
E34 520i Saloon, Europe
E34 525i Saloon, Europe
E34 530i Saloon, Europe
E34 535i Saloon, Europe
E34 M5 3.6 Saloon, Europe


Z1: Details on Z1
Z1 Z1 Roadster, Europe

http://www.realoem.com/bmw/partxref.do?&part=12+13+1+742+925+&lang=en



Bosch ignition coil 0 221 502 010 for M70 cylinder 7-12, 3 pieces, ring type

BMW 12131742926

Part 12131742926 (Ignition coil) was found on the following vehicles:


E31: Details on E31
E31 850Ci Coupé, Europe
E31 850CSi Coupé, Europe


E32: Details on E32
E32 750i Saloon, Europe
E32 750iL Saloon, Europe
E32 750iLS Saloon, Europe

http://www.realoem.com/bmw/partxref.do?lang=en&part=12131742926


distributor cap, BMW 12111725070, Bosch 1 235 522 365, many

Part 12111725070 (DISTRIBUTOR CAP) was found on the following vehicles:


E23: Details on E23
E23 732i Saloon, Europe
E23 735i Saloon, Europe
E23 745i Saloon, Europe


E24: Details on E24
E24 635CSi Coupé, Europe
E24 M635CSi Coupé, Europe


E28: Details on E28
E28 535i Saloon, Europe
E28 M535i Saloon, Europe
E28 M5 Saloon, Europe
E28 520i Saloon, Europe
E28 525e Saloon, Europe


E30: Details on E30
E30 320i Touring, Europe
E30 320i 4 doors, Europe
E30 320i 2 doors, Europe
E30 320i Convertible, Europe
E30 325e 2 doors, Europe
E30 325e 4 doors, Europe
E30 325i Convertible, Europe
E30 325i 4 doors, Europe
E30 325i Touring, Europe
E30 325i 2 doors, Europe
E30 325ix 4 doors, Europe
E30 325ix Touring, Europe
E30 325ix 2 doors, Europe


E31: Details on E31
E31 850Ci Coupé, Europe
E31 850CSi Coupé, Europe


E32: Details on E32
E32 730i Saloon, Europe
E32 730iL Saloon, Europe
E32 735i Saloon, Europe
E32 735iL Saloon, Europe
E32 750i Saloon, Europe
E32 750iL Saloon, Europe
E32 750iLS Saloon, Europe


E34: Details on E34
E34 530i Saloon, Europe
E34 535i Saloon, Europe
E34 520i Saloon, Europe
E34 525i Saloon, Europe
E34 M5 3.6 Saloon, Europe


E38: Details on E38
E38 750i Saloon, Europe
E38 750iL Saloon, Europe
E38 750iLP Saloon, Europe
E38 750iLS Saloon, Europe
E38 L7 Saloon, Europe


Z1: Details on Z1
Z1 Z1 Roadster, Europe


http://www.realoem.com/bmw/partxref.do?lang=en&part=12111725070


distributor rotors for above distributor, Bosch 1 234 332 347, BMW 12111734110

http://www.realoem.com/bmw/showparts.do?model=GC81&mospid=47354&btnr=12_0052&hg=12&fg=05&lang=en

[Ferret]

Daft question, but why does the V12 use a different coil on each bank, never got that?

[bubba966]

Do believe that the V12 is run like it's a pair of I6's. Hence the 2 coils, 2 DME's, 2 batteries, etc.

[Ferret]

Do believe that the V12 is run like it's a pair of I6's. Hence the 2 coils, 2 DME's, 2 batteries, etc.

I know :P I'm just wondering why they have different part numbers for the right and left bank coils.

[whiskychaser]

Not sure what's worse... Taking longer to warm up by idle/low rpm or rev the engine slightly so it warms up faster?
TBH I was going to say what Shogun said - drive it to warm it up. But if your car is iced up this isnt practical; its much safer to see where you are going! As far as revving in neutral is concerned, the best analogies I can come up with are that you wouldnt let a bow string go without an arrow or run your amp without speakers. Maybe its an age thing? If you are 50 odd like me you say dont do it - if you are not you say wtf?:D

[e34.535i.sport]

tbh i was going to say what shogun said - drive it to warm it up. But if your car is iced up this isnt practical; its much safer to see where you are going! As far as revving in neutral is concerned, the best analogies i can come up with are that you wouldnt let a bow string go without an arrow or run your amp without speakers. Maybe its an age thing? If you are 50 odd like me you say dont do it - if you are not you say wtf?:d

wtf!

:d

[632 Regal]

I know :P I'm just wondering why they have different part numbers for the right and left bank coils.
dont forget the 2 sets of over priced wires, rotors, caps... different coils huh? brb

Maybe the position of the terminals to where the coil wire goes in? Too cold out to check it personally.

http://www.realoem.com/bmw/diagrams/e/o/2.png

[Ferret]

dont forget the 2 sets of over priced wires, rotors, caps... different coils huh? brb

Maybe the position of the terminals to where the coil wire goes in? Too cold out to check it personally.



Yeah, I hit the jackpot with the ignition wires, a friend of mine was breaking a 750i and it had an almost brand new set of Magnecor Blue leads on it - ended up getting them for a couple of pints at the local! After doing some research they retail over here (uk company) for about 300USD with a brand new set of impulse sensors pre fitted! I was quite surprised, I thought I was just going to get handed a set of clapped out bog standard leads...

It's made one hell of a difference to the running of the car changing them over - I've got a theory that putting the wrong plugs in can fry old/fragile leads due to the increased breakdown voltage across the plug. Call me a conspiracy theorist, but it's only a thought.

[Mordan]

try to punch as hard as you can in the air and see how your arm likes it :)
try pedaling down a hill on a bike with a slow gear.

Now are those analogies valid for an engine? Will the crankshaft and bearings suffer? hmmm I would say yes if there is a play due to age wear.

[shogun]

I know :P I'm just wondering why they have different part numbers for the right and left bank coils.

the brackets are different, that is why they have 2 different part numbers.

The ring type ignition coils as used on E30, E23, E24, E34 etc. were also used on the M70 till 09/1987 built year.

[Rustam]

In case of ZF 4hp22 and 4hp24 as found on e32 and e34, the practice of revving the engine in "PARK" may be damaging to the transmission gear. There was a bulletin about this some years ago. I did rev my engine with the 4hp24, not knowing this, and soon after had to change my transmission, because it could not engage 1st gear. If revving is mandatory it should not exceed a minute - this is a part of the stipulations mandated by the bulletin I remember. I do not remember the maximum allowable RPM range for mandatory revving...

[shogun]

Hi Kriss
3 years have passed, is your pump still o.k.?

[BigKriss]

yes, I have 295,000kms now and it's still running okay.


Hi Kriss
3 years have passed, is your pump still o.k.?