Pls help a new 1991 750il owner, acceleration issue.

[beymapl]

Hello to all of you fanatics. I just purchased a 1991 750il with a good maintenance history and 340Km, engine resealed, valves done, about 16000$ in documented maintenance, plus more. The car runs perfect, looks great, idles great, everything last thing works like it should, except for this problem which puzzles me and the mechanic at the local BMW, here in Edmonton, Canada. I have owned quite a few BMW's in the past and do a lot of my own maintenance, I prefer the older ones as the last E46 I had wasn't as enjoyable as this V12. The problem I have is the car will accelerate madly from standstill, pound of the first shift at 5700rpms(tranny in S3)keep going strong up to about 130km/h and then bog out as if the speed limiter came on, or something similar. I thought it was the tranny not shifting up, but tried putting it in manual 3rd and accelarating at full throttle and I don't get past 150km/h most of the time, with the accelerator at half throttle I get 180-190 max and that's where the fun ends. We did scan the car after a few runs and no faults came up anywhere. The previous owner did have performance chips installed for both ECU's and tranny, and according to hip there should beno speed limiter, and he also says that it has never happened to hip. Please help, as I really would like to know how I can go about fixing this annoying problem. Thank to all of you

[shogun]

Ask the same question here, there are many 750 drivers and we can help together.
http://www.bimmerboard.com/forums/e32/page/0
Some questions:
is the EML light in the dash on for about 2 seconds when you start the car (ignition in position 2).
Thereafter it should be off and never be seen during driving, otherwise the car runs in limpmode.
Can you see in the dash the selected gear mode?

The speed limiter might be out, if they also changed the chip in the EML, the chips in the 2 MOTRONICS are only for more performance. But that does not matter, speed limiter comes in at a speed more than 250 kmh.

What kind of scanner did you use?
What is the VIN number so that I can have a more detailed look into the wiring diagrams? Last 7 numbers is enough. Or Go to my website below and use the VIN decoder as I need the month and year of production (not the first registration date), to see which MOTRONIC is installed.

Do you get a warning for LAD? There is a speed limiter for the LAD in case of failure, maybe the sensor is misalligned.

Have you checked both fuel pumps if they are working?
When have you changed distributor caps and rotors?
Remove one plug from one side MAF and see if engine dies, then the other side the same procedure.
If engine dies completely, you found out that one side is not working. That is already a good starting point.
Remember that if you remove the plug from the MAF on drivers side in the engine room, actually the cylinders on the other side in the engine room are affected.
What is on the right hand side in engine room for the intake, works on left side and vice versa.
To understand this, click on the explosion view of the engine on my website below.

[beymapl]

Thank you for the quick reply Shogun. I did as you said first checked the EML light, it comes on briefly and goes of and stays off throughout. The selected gear mode shows in the dash display. And the chip in the EML was changed at the same time the ECU's were changed, I have all 3 originals. I really couldn't say what scanner was used as it was scanned in the BMW dealership with their equipment. The last 8 #of the VIN are MDC79615, no warnings or errors for the LAD either. The fuel pumps are working(took out one fuse while car was running and then the other, and the car stayed running.) From what the previous owner tells me the distributors were changed recently, the wires about 5 years ago, and the lugs recently. I did as you said and also removed the plug from one side and then the other from the MAF boxes, the car just fluctuates slightly in RPM but stays running. The mechanic seems to think that it has something to do with the transmission shift points chip(or something rather)and ordered a new one, it's only a few bucks and there was a service bulletin for some models(but not mine according to the VIN)I honestly don't believe that the tranny would cause this unless it's not shifting up at the limiter, and in 3rd gear it's got a long way to go to hit the limiter at full throttle(I am not sure what the speed should be at 5700rpm in third but I assume it should be higher than 150km/h)I am supposed to pick up the chip tommorrow and install it, but really doubt it will solve the issue. The only think I can think of is replacing the chips for the originals, which I will probably do today, and maybe checking the fuel pressure on both pumps?? Any suggestions from anybody would be greatly appreciated, I will also post my original thread in the other forum. Thanks again, Luke

[shogun]

Maybe to change the chips back to original is an idea just to check if that is the cause.
The signal from the accell pedal is transfered fly by wire. Maybe you can measure this one, I think it works like a potentiometer.
Should be in the Bentley Repair Manual mentioned how to check it.
If you do not have one, let me know and I will have a look into it.

[beymapl]

Thanks again guys, I guess I got some digging to do this weekend. I don't have a Bentleys manual for this car or any other since I haven't seen them on shelves in our stores. I will see if I can find one if not I wonder if Chiltons will be of help, I know I can get them here. I did change the EML chip back to the original and the car seems to shift more abruptly and stay in gear longer(I thought it should have been the other way around, oh well) but the issue remains, dissapointment. I will change both of the other chips and clean the throttle bodies using the system Brian sent me links to. One other thing I noticed yesterday but not any other day that I smelled fuel in the cabin for a few minutes until the car completely warmed up. It has not happened today at all, I wonder what would have caused that, according to the previous owner (which by the way turns out to be the shop supervisor for Edmonton BMW, go figure) he changed most of the hoses etc. when he had the engine up, the engine does look really dry, top and bottom. Anyway I will tinker with this tonight and tommorrow and hopefully get closer to solving this annoying issue.(Got burned today by an infinity G35 because I ran out of breath again at 120km/h:-)Cheers, and thanks again, Luke

[shogun]

Luke,

look into your private messages on top right of this page. There is something for you what you need.
As for the fuel smell, that are usually the small hoses which come up at the firewall on drivers side. They are about 10 centimeters long between steel pipes as flexible items between chassis and engine, which moves in it's mounts.
Look under engine fuel pressure hoses replacement, there is a detailed pdf file here
http://www.e38.org/e32/
Maybe tightening the clamps will do. If there are the old clamps, replace the hoses and clamps, see the info in the pdf.

[beymapl]

Ok, thanks again Shogun, and here is what the current standing of my situation is. I have taken apart all of the air intake hoses, air filters, distributors and whatever else I could get my hands on that would pertain to what I assumed would be of importance and could be checked easily without getting in deep and incapacitating the car completely over what was a gorgeus weekend here, perfect for a cruise in my freshly power polished and tinted 750il:D . Here is what I have found:
Taking the air boxes apart I have found a wasp nest in one of them! The filter was fairly clean but completely filled with dried wasps(or bees or whatever)I contacted the owner and he said the car has sat for about a year after he did the work on it so it is a fairly easy conclusion there. I have also found a couple of pretty big cracks in one of the hoses leading into the throttle body, the hose was a bit weathered and had lost its elasticity. Not being able to find any replacements on short notice I cleaned it bought a tube of 450deg gasket maker and neatly filled the cracks after which I put 3M electrical tape around the siliconed parts. While I was waiting for this to dry I inspected the throttle bodies, they looked really good, the motors had good tension on the plates but one of them had a LOT of black soot or oil that looked like it was there for a while. Got some throttle body cleaner for that and cleaned as good as possible trying not to put any marks or else on the plate itself. After that took apart the connections and put electrical drying fluid on all of them. Took apart the disributors and noticed some carbon buildup on the points(the whole assemblies and wires were replaced 5 years ago according to the maintenance records)cleaned them with some 120 grit paper and dried off with electrical cleaner. Checked the fuel hoses all were replaced judging by the rubber and new clamps. As my silicone dried I put back the main air assemblies and the mafs(the little wires inside were all intact and the inside looked clean and original)and also put on a couple of polished aluminum intake pipes and K & N cone filters properly oiled(I know there is an issue here of the oil damaging the little wires that some members were mentioning, but I do not drive this car very much as I own others that I don't care as much about and besides I used to own a accessory store and after I closed it I have so much of this stuff lying around that I couldn't resist hearing the sound of a V12 with a deep resonance sound:D ) Put everything together checked for vacuum leaks with the plastic bag over the oil filler(looked good)and went for a test run. The engine sounds amazing and accelerates at full throttle past 150km/h now! It still does not pull as hard as I would like it to past that point or maybe I am just overly optimistic and can't feel the speed in a 2 ton beast. But now I have an idea of what was causing the problem, the car sat for way to long and all the wiring, connections and hoses must be cleaned so I will spend another day doing that next weekend. If you have any suggestions as to what else I might clean or take apart I would love to hear them in the meantime I have found a place to share my BMW experiences with people that are true fanatics to the name and engineering that goes behind it. I will post a few pictures once I figure out how and hope to be able to post advice and ideas here in the future. I owned a couple of detailing and accessory shops where we only worked on European cars, BMW as much as possible, so I am sure I can be of help in that department. Thanks again to you and whoever else took time out of their day to offer advice. Luke