E34 M50B25 power lost and doughy

[Stewart]

Hi,
I have an E34 with an M50B25 (Non Vanos) Engine. It has an Auto gear box in it. I have had a long continous problem since I replaced the engine with a low distance replacement engine.
It is slow of the mark and feels like I am pulling a trailer full of bricks !! Sometimes when I hit the pedal quickly it almost cuts out or may even stall.

I have also noticed that it tends to loose power when going up hills even on a freeway, going up a hill is a big issue...

However once I get the engine really reving above say 2 or 3k RPM it winds out really smoothly and goes like a rocket. Kicking it down in gear has the same effect.
Its not the type of car at the moment that you would pull out of in front of someone comfortably you really have to sort of let it roll off the mark then excelerate

I have undertaken the following work on the car as its been a project for quite a while.

Replaced Engine with new one with only 75K from half cut Jap import.
Remanufactured the transmission HP5-18 5 speed
New fuel pump
New fuel pressure regulator (on rail)
Replaced fuel filter
Had injectors professionally cleaned
New Cam sensor
New Throttle body position sensor
New Mass Airflow sensor
New Cats on Exhaust line
New Air filter
New spark plugs and tube leads

The car starts fine and idles smoothly.
Fuel is reasonably good depending on how you drive it?? Using 95 no ethanol

Just stuck as replaced almost everything and driving me crazy??
Appreciate any help.

[whiskychaser]

Your 'Premium' 95 Ron fuel is classed as bog standard unleaded here. I used to use it in mine so I don't think it is an issue. The engine coming on song at 2-3k rpm sounds right. Depending on what sort of a hill it is, the car should drop down a gear and not slow down appreciably. But bear in mind that at 70mph, it will only be doing about 2k rpm and top gear is overdrive. Not sure of your speed limit but try 75mph. Mine much preferred that on the motorway.

A few questions:
What is it like in sports mode?
You say you only had the problem since you replaced the engine. Was it OK before?
Are your compressions, fuel pressure and intake vacuum all ok?

[Stewart]

Your 'Premium' 95 Ron fuel is classed as bog standard unleaded here. I used to use it in mine so I don't think it is an issue. The engine coming on song at 2-3k rpm sounds right. Depending on what sort of a hill it is, the car should drop down a gear and not slow down appreciably. But bear in mind that at 70mph, it will only be doing about 2k rpm and top gear is overdrive. Not sure of your speed limit but try 75mph. Mine much preferred that on the motorway.

A few questions:
What is it like in sports mode?
You say you only had the problem since you replaced the engine. Was it OK before?
Are your compressions, fuel pressure and intake vacuum all ok?

Thanks whiskychaser.

The engine is more responsive when I use 98 Ron fuel
When in sports mode it seems better as the REV's tend to extend out more giving it that extra time to get going.
Our max speed limit is only 60 mph or 100KPH when over this goes like a rocket !!
The original engine was replaced due to rear crank seals leaking and big end bearing shot, but still ran better than this one.
Compression is good along with fuel pressure.
I have not checked the vacuum, but the instrument panel guage is stable with no fluctuations??

I have also replaced the torque convertor in the transmission, and tried a different ECU which made no difference ?

[Javier]

When you say fuel pressure is Ok it is because is High or is because its on value. I had once a similar issue with my 535i that had me nuts for a wile, and ended being an issue with the fuel returning hose inside the fuel tank (no fuel return). At that time I noticed also when reeving up the engine with the car parked, a lot of carbon residues at the exhaust.

[whiskychaser]

The key is that your old engine ran better than this one. Your fuel pressure should be 51psi +/- 1 with engine off and fuel pump relay jumpered. That goes down about half a psi for every inch of mercury vacuum you have. So if you have 18in HG, your fuel pressure will be about 42 psi with the engine running. It varies with altitude but as you are on the Gold Coast I'd suggest you can ignore that bit :-) I am thinking along the same lines as Javier - that you may have a fuelling issue. Are you using your old fuel rail or the 'new one'?

IIRC, the compressions on mine cold were 180psi. (I don't like removing spark plugs from a hot engine). Are yours similar?

One thing does occur to me. Japan has low speed limits like you do. Maybe your new engine had too easy a life? Perhaps it needs a heavy right foot to clear out the cobwebs?

[Frank87]

Completely different idea here but could it be possible that your lockup clutch is permanently on?

Test this by trying to get some slip in your RPM. Put the autobox in D and accelerate. While accelerating slowly, press the pedal a bit further suddenly. Not far enough for a downshift.. but far enough to see the revs rise while the speed stays about the same.

If you can simulate that, your lockup is ok. If your car feels permanently coupled like a manual = revs don;t jump up... you have a lockup malfunction leading to a car that runs as slow as **** through a tube.

[shogun]

What does the owners manual mention for minimum RON for that engine? Australia has quite low specs, when I check that
Australia: "regular" unleaded fuel is 91 RON, "premium" unleaded with 95 RON is widely available, and 98 RON fuel is also reasonably common. Shell used to sell 100 RON fuel (5% ethanol content) from a small number of service stations, most of which are located in major cities (stopped in August 2008).[27] United Petroleum used to sell 100 RON unleaded fuel (10% ethanol content) at a small number of its service stations (originally only two, but then expanded to 67 outlets nationwide) (stopped in September 2014). All fuel in Australia is unleaded except for some aviation fuels.
https://en.wikipedia.org/wiki/Octane_rating

Here in Japan: Since 1986, "regular" is >=89 RON, and "high octane" is >=96 RON, lead free. Those values are defined in standard JIS K 2202. Sometimes "high octane" is sold under different names, such as "F-1".

The German owners manual for the E34 mentions: all engines with cat unleaded fuel min. 91 ROZ, E34 520 EURO version ROZ 95 unleaded minimum, allowed is 3% Ethanol. see here page 4 https://forum.e34.de/thread.php?threadid=55555&sid=ad53a3fcff3788f28e9a558645661c74

Octane rating conversions http://www.pencilgeek.org/2009/05/octane-rating-conversions.html

Octane: (R+M)/2 vs. ROZ, US vs. European in Ferrarichat http://www.ferrarichat.com/forum/technical-q-sponsored-algar-ferrari/108761-octane-r-m-2-vs-roz-us-vs-european.html

BTW: the Ferrari guys like my E34/E32 interior light dimmer also :D triumph
quote... tested many dimmers and studied several electronic schematics. None of them where satisfying enough to be implemented in a Ferrari and especially behind the M032 ECU. Dirtly electronic modules would seriously mess up this ECU! My specs were quite severe: I wanted it programmable and configurable, ground based control (I initialy thought that we would need a +12V based control), almost no power consumption in standby mode, limited heat at the heat sink and a PWM based control (Pulse Width Modulation).

On a good day, I discovered on a BMW forum a guy from Japan who is making what seemed to be the perfect dimmer. I got in contact with him and after many email exchanges and studying his schematics, I got convinced that we have here the right product. His module is entirely programmed using a PIC12F629, just perfect! The MOS FET used is a 2SK3140 using a 4V gate and is attached to a small heat sink. unquote
http://www.ferrarichat.com/forum/360-430-sponsored-yellow-compass-group/319055-f430-diy-improve-interior-light-dimmer.html

[genphreak]

I had this exact problem with mine. The PO gave it to me cheap because it drove him batty.

The damn thing was a Japanese import and someone had gone over every single host and connector in the engine with cable-ties (rather than replace any hoses).

I was stumped for some time changing things too. Was sure it was fuel pressure as that proved sporadic. Changed the pump, no change. Then it blew the transmision.

I put in a manual cogbox and then found the fault... it was the ECU. After that it was the best (but worst... LOL) e34 I ever owned (... and still is).

To check, use a spark plug LED tester or;

1. Remove the ECU, I bet you have a Siemens... your M50 will probably have the Siemens MAF if so.
2. Open the box and inspect the spark plug output transistors (big ones, located down one side). One or two may be overheated or just show signs of cracking.

If so, find a new ECU or swap the transistors. I still have the old one here, I could post it to you if you need some good ones to strip out and use. Tehy are different to the BOSCH ones used on other BMWs, so can be hard to find. They must be 1990-1992 non-vanos E34 525i to be Siemens equipped, or similar early E36 325i. Not sure about 320i/520i but the ECU would certainly be very, very similar- probably can use by swapping the old EEPROM chip.