91 BMW 535i ASC+T Cruise Control

[kreine]

Are there any e34 guru's that understand the 91 version of eml asc+t and cruise control out there?

I have a 91 535i drive by wire version of the 535i. When I got the thing it was nothing but a pile of problems. Blown head gasket, wrong eml, wrong chassis computer, wrong/missing relays in the power distribution, jacked up wires in the trunk because someone had connected a subwoofer etc. The car runs and drives like a dream now. One thing that is frustrating me to distraction ... the Cruise control doesn't work. I've got a Bentley out and I run some preliminary tests. From what I can tell things are like they should be. No eml light, car has amazing pickup and gets about 21 to 23.5 mpg on the highway. Other than the cruise control not functioning the only other thing that doesn't work is the MPG AVG on the check computer in the dashboard. I guess I'm thinking that the two things might be related. I'm about to just give up and take it to a service shop. But I know a problem like this is going to cost thousands of dollars to troubleshoot. And I've already sunk about 3.5 K into a car that is only worth about 2K on a good day. Anybody out there got any ideas ... I could sure use the help.

[Binjammin]

At this point it sounds like you'd be more knowledgeable than whatever shop you took it to. It's not like there are a ton of EML 535s out there.

It had the wrong EML? I don't even know what would have worked in the place of the stock unit, got any pics of what was on there?

Look to see if the clutch switch is in place and functioning correctly to correct the no-cruise.

The MPG avg, you're talking about the OBC function or the gauge in the cluster?

[kreine]

Yeah ... i forgot to mention that it was an automatic. So no clutch sensor.

It basically had an abs and chassis control unit out of a non eml car. I've got the two eml units now and two chassis control units as well. I have a 89 535 and someone had stuck the same control units out of a non eml e34 in the car. Yeah it took me a while to sort out what was going on with my eml and ASC lights. I can send pics of what was in there and what was supposed to be in there.

It is the MPG avg on the OBC that isn't working. I guess my suspicion is that since both rely on the vehicle speed input to work ... maybe there is something wrong somewhere in the wiring. The instrument cluster works fine. I've observed no issues with it in the 10,000 miles I've put on the car since I got it running right.

[kreine]

Here is an update. It has taken awhile since I was traveling for work. I broke down and took it to German Imports in Parker CO. The technician said all of the right cruise control signals are getting to the eml control unit but for whatever reason the the control unit isn't kicking in. According to him it is a pretty primitive system and there isn't much he can measure. So has anyone else had this kind of an experience with an early drive by wire 535? His suggestion was get a new throttle body and eml computer. 2k worth of parts and I don't think you can even get the eml computer new. Does anyone know if people rebuild eml computers and if so can you send me a link or their contact info? Or does anyone know how I could test the signals coming from the eml computer to the throttle body control so I could verify what I need? I only have a volt meter and from what I read online you have to be careful with probing the wiring harness because you can short something out fairly easily.

Oh yeah ... one other thing ... I have a replacement eml control unit and throttle body and both sets of eml/throttle bodys do the same thing. Is why I suspect the wiring maybe???

[Mark185]

Here is an update. It has taken awhile since I was traveling for work. I broke down and took it to German Imports in Parker CO. The technician said all of the right cruise control signals are getting to the eml control unit but for whatever reason the the control unit isn't kicking in. According to him it is a pretty primitive system and there isn't much he can measure. So has anyone else had this kind of an experience with an early drive by wire 535? His suggestion was get a new throttle body and eml computer. 2k worth of parts and I don't think you can even get the eml computer new. Does anyone know if people rebuild eml computers and if so can you send me a link or their contact info? Or does anyone know how I could test the signals coming from the eml computer to the throttle body control so I could verify what I need? I only have a volt meter and from what I read online you have to be careful with probing the wiring harness because you can short something out fairly easily.

Oh yeah ... one other thing ... I have a replacement eml control unit and throttle body and both sets of eml/throttle bodys do the same thing. Is why I suspect the wiring maybe???

The first thing you should try is to measure the resistance of each wire going from the EML computer to the throttle body to make sure there are no short circuits or breaks. Unplug both of them and just measure resistance from connector pin on EML computer to corresponding connector pin on throttle body. Ideally, you want 0 ohms but meter leads usually add a small amount of resistance in tenths of ohms. Ignore a reading that low. It is as good as zero. You should also measure resistance between each wire in the connector to make sure none are short circuited to each other.

I am not familiar with your early version of EML. On later 525i models, there is a secondary throttle body for traction control and the computer actuates it briefly when ignition is switched on as a self test. You can see the cable linkage move if under the hood when someone turns the ignition key for you. Do you know if your system is also supposed to do this? On my car, there is a servo motor mounted to the strut tower and a cable goes from it to the ASC throttle body. Is the servo motor separate like that or is built into your throttle body? I ask because on E39 models, the servo motor is built into the throttle body and uses gears to drive the throttle plate. The gear drives and the servo motor are known to fail on the E39 although it is not common.

If the wiring checks out OK, the next piece of info you need is something I can't help you with because I don't know how the early EML is designed to work. You need to know if the drive voltage from the EML computer is an analog voltage from 0-5 volts or 0-12 volts or if it is a digitally switched signal called pulse width modulation (PWM). PWM motor control signals can only be seen properly with an oscilloscope. The way they work is to switch voltage off and on rapidly between 0 and 5 volts or whatever the car voltage is. It will look like square waves that vary in how long they are on. The longer the on time, the more the motor moves. Once you know what the signal is supposed to be, you can check to see if proper signal is going to the throttle body.

[kreine]

Hi Mark,

I tried to post the 91 535 engine management diagrams from my Bentley in the thread but I'm limited to 150 MB. What you say about continuity makes sense. I wanted to post the diagrams because I'm not very smart about electrical notations and thought having the diagrams might mean more to you and help you with suggestions about what I should test. I guess I was hoping they might make more sense to you than they do to me.

Anyway, I have a supposedly good eml brain that I purchased online. Before I installed the thing I wanted to test my system to ensure there wasn't some underlying fault causing a bad eml. I talked to the tech and he said he could see through the scanner that all the right signals were getting to the eml controller but the controller didn't respond. So he suggested replacing the controller. I'll test continuity using my manual and put the new controller in when it arrives and see what happens I guess.

As an aside, I have a 95 525 and I know exactly what you are talking about when you mention the secondary throttle body. My 91 535 uses the M20 and is totally drive by wire. The throttle body sits directly above the intake with the maf and air filter on the passenger side. It isn't the same set up as the later 525's have. Thanks for the help and let me know if you are interested in me emailing the EWDs to you. I would be happy to send them from my yahoo account.

[Mark185]

I have a Bentley manual. You could just tell me which page(s) you are looking at and ask questions. I will help if I can. I am a little confused by you saying your 91 535 uses the M20. If you are talking about engines, the 535i uses the M30.

[ross1]

If the cruise unit is seeing all the right signals it makes sense that the unit is bad or perhaps the cable is disconnected or broken.
I have a spare cruise unit FS if you care to throw parts at it

[kreine]

Mark ... your right ... it is the m30 ... fingers are too fat for my phone I'm looking at EWD 73 & EWD 74 in my Bentley. I can't interpret what pin is responsible for producing the cruise control signal ... furthermore on my hour commute to work this am, I noticed my avg mpg and mph on the obc aren't working. My speedometer works fine ... is there a secondary speed circuit with a bad sensor possibly?

Ross1 ... my particular car is all eml ... it doesn't have a cruise control module ... unless you mean the eml controller ... and if you do lets verify the numbers and I would totally be interested in taking it off your hands.

[ross1]

Ah, yes, I neglected to consider the EML throttle bit. I parted an EML car a while back, will check for remaining parts and advise via PM.

[kreine]

Ok, well I tried the Mechanics suggestion of just getting a new EML and putting it in. No luck. Same results, no cruise. So I did notice that the speedometer isn't generating the warning when I leave my headlights on, and the speedometer does some strange things from time to time so, I have a spare. I'm going to put that in this weekend and check the wires. I'll update the post if I find anything interesting.

[Mark185]

Ok, well I tried the Mechanics suggestion of just getting a new EML and putting it in. No luck. Same results, no cruise. So I did notice that the speedometer isn't generating the warning when I leave my headlights on, and the speedometer does some strange things from time to time so, I have a spare. I'm going to put that in this weekend and check the wires. I'll update the post if I find anything interesting.

Sorry I did not get chance to look at EWD pages you asked about. Wife is out of town and I've been busy with the kids after work. I will try to look tonight. Here is a link to a really good E34 website that does not get mentioned much on this forum. The page I am linking is specifically about gauge cluster problems.

http://www.bmwe34.net/E34main/Mainte...Capacitors.htm

The only secondary speed signal I am aware of, is from the automatic transmission on later models with M50 engine. That signal goes to the anti lock braking computer module IIRC. I don't know if same applies to your car. There should be some evidence of it in Bentley if there is a speed signal from tranny on your car. That speed signal is probably important to cruise control function if your car has it.

[kreine]

So here is the deal. I checked the Bently EWD 74 and found that the cluster does in fact have a VSS out. My assumption is that VSS is vehicle speed sensor. And guess what it hooked directly to pin 3 of the EML labled VSS. So since I've had some pretty erratic behavior from my speedometer and the OBC AVG MPH and AVG MPG wasn't working and it is also connected to the VSS Out from the instrument cluster. I swapped it out. I now have cruise, AVG MPH and AVG MPG. I'm making progress. Took the car out for a spin and the tranny shifted much smoother. So I assume it was shifting hard because it relies on the VSS out as well. The last little gremlin I have to work out is the cruise is cutting out periodically. So I'm driving along and it has to accelerate to maintain speed and bang ... it cuts out. I think that might be related to the VDO motor on the throttle body. I'm going to follow Shoguns tips on how to do a quick recondition of it and see how it goes. Man ... when I got this car I thought it was a simple sensor problem. A head gasket, all the general maintenance stuff like new thermostat, water pump, DME, EML and ABS control. It is finally running like it should. I dont' know how the PO had anything working with the wrong controllers in the thing ... but hey ... it is purring now!

[Mark185]

Glad to hear that you are working it out. I ran into a bit of bad luck since last Friday and forgot about looking at the schematic for you. The S52 in my touring suffered some kind of catastrophic failure while waiting in line for NJ vehicle inspection. It suddenly started misfiring and making knocking/crunching sounds. It was purring like a kitten prior to failing and no warning signs of impending failure. Compression is zero on cylinder 1 and low on 2 others. Spark plug on #1 was obviously hit by something. Looks like foreign object got sucked in or a valve train failure of some kind. I am thinking if timing chain had failed all cylinders would have suffered valve/piston contact and compression would have been down in all. Regardless, the engine has to come out. Adding insult to injury (actually injury to injury) I threw my back out working on it Saturday and have been barely able to walk before today. My 535i never gave me trouble like this and I drove that very hard for over 100K miles after buying it with high miles on it. The only engine issue was that it was starting to burn a little oil and puff blue smoke on full throttle when it was over 200K miles. It continued to run reliably for another 20-30 K miles after that and the only thing that killed the car was rust. Hope yours is just as good.