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Old 02-23-2003, 04:52 PM
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Question '86 300E with Voltage Problems and poor acceleration from a stop

Hello, I have recently purchased a '86 300E from a good customer of mine for $4000 (canadian). I have already put over $8000 into it and have almost entirely lost faith in my mechanic. I should have come to this site long ago!

Please excuse the length of this post, I'm trying to give as many details as possible to assist in anyones possible diagnosis. =)

Ok, as for the problems. It has numerous problems, all of which I firmly believe are closely associated with each other, possibly all from the same root problem, I shall list them all:

It accelerates acceptably if accererating lightly But unter heavy accelleration, the car will just about die, and accelerate slower than if I just eased onto the pedal, but then suddenly have a surge of power once the RPMs climb to roughly 2,000

The major issue is a very strange electrical problem that also seems to influence the mentioned acceleration issue. My heater fan is the most obvious place it influences. I'm not sure how to best describe this, but I shall try. the 'auto' setting for fan is very erratic, sometimes on, full blast of entirely off, never in between, so I use the low setting. When sitting at a light though, for example, the fan set at the low setting, will after a few minutes begin to surge higher. The longer you sit, the more frequent teh surges till it runs full blast consistantly. Any load such as headlights, seat heaters, or rear defrost will make it many times worse. In extreme cases my radar detector will begin flashing 'low voltage' though no dash light comes on.

Closely associated with that is that though much more strange, is that when I select 'high' speed on my fan, it will not go to high speed for a delayed amount of time, namely untill there is a load on the system. If I'm sitting at an idle it will come on immediately, but otherwise it will come on if I hit the brakes, turn teh seat heaters on, turn on the rear defrost, etc. As a side note, the rear defrost and seat heaters barely heat up enough to be considered on, but the lights on the car will dim noticably when either one is turned on. The accelleration problem I mentioned already seems to be closely related in severity with how bad the electrical problem is at teh moment.

I had trouble also with my ABS. The 'antilock' light would randomly come on, but the brakes would pulse seemingly randomy when at low speeds even if only stopping very lightly. I unplugged my abs module, covered up the 'antilock' light on my dash, and just live with regular brakes.

I also seem to get pretty pathitic mileage and rough idling.

Now, as for what my mechanic has done. The entire exaust system has been replaced, along with the O2 sensor. The transmission was rebuilt because it was toast. I regret spending that much money on this car, but now that I have I need to stick withit because I can't get my money back out of it. =^/ The spark plugs have been replaced. The fuel pump and fuel filter have been replaced. The heater fan has been disassembled and checked. (said there were dirty contacts that they cleaned up) And just a few days ago I replaced the 'overload relay'. The alternator has been rebuilt (they said it had been running on 2 of 3 windings. But the rebuild didn't help.

That's all that comes to mind at the moment, thank you very much for your help in advance! =)
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Old 02-23-2003, 05:21 PM
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Cruise Control

ALso, I should add, my cruise control surges terribly when on, causing it to be entirely unusable... Don't know if it's related, but thought I'd mention it.. Thanks!
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Old 02-23-2003, 09:46 PM
pesuazo's Avatar
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Join Date: Oct 2002
Location: Near Raleigh, NC
Posts: 580
1.- Try changing the OVP relay (Overvoltage Protection Relay) it is behind the battery (remove plastic cover), it is the silver one with the red top and the fuse on it. This relay has been known to create havoc on these vehicles when it goes bad.

2.- I was having the same problems with the climate control unit. I took it out and resoldered all the contacts related to the pushbuttons, as of today it still works like a charm.

3.- The cruise control is another problem with these vehicles. The amplifier, or the actuator may go bad. Since yours works at times, I imagine it can be fixed. Use the search in the forum and inform yourself before you spend any more money. I have saved hundreds, if not thousands by reading in this forum.

Right know I am going thru some problems with my own vehicle. I am going thru all the suggestions found here trying to solve it before bringing it to a mechanic.
I am suffering from high-oscillating idle (600-1000 RPM or fixed at 1200 sometimes) when in park or neutral. I removed and cleaned the Idle Control Valve twice (consecutive weekends), and still the problem occurs. I also cleaned the air intake and surrounded areas. The response is much better during acceleration.
I also checked for vacuum leaks with starter spray, and found none.

Believe me, you are in the right place if you enjoy doing some work in your car.

Search, read and work on your car.
By the way,
Welcome to the forum.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified
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Old 02-23-2003, 11:11 PM
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Join Date: Dec 2001
Posts: 571
It's possible that part of your electrical porblems are due to a bad voltage regulator. This is a $30-$60 part(depending on what brand you buy & who you buy it from). The ABS light issue raises this suspicion.

You mention alternator work. If a rebuilt alternator and by that I mean a good one that was designed for your was installed, then I would hope it came with a new voltage regulator.

In closing, I would suggest that you consider that you hired the wrong mechanic. It could be argued that he hasn't done well and should be held accountable, but that really means nothing if he's unskilled and it sounds as though he is just that.

My 2 cents.
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Old 02-23-2003, 11:12 PM
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Join Date: Feb 2003
Location: Ottawa, Canada
Posts: 126
Check the contacts on the coolant temperature sensor (located at the far end of the engine valve cover with two connection on top). They might be old and loose. Also check the resistance of the coolant temperature sesnor at different temps to make sure it works. Its resistance should be about 6000 ohms at 0 degrees C and abot 300 ohms at 80 degrees C. Also use Fuel Injection cleaner in your tank and then change the fuel filter if you have not already done so.

'86 300E (5-speed)
'88 260E
'84 944
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Old 02-23-2003, 11:42 PM
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Dash Disassembly

Thank you for your reccomendations so far! I have replaced the OVP relay already. As for further diagnoses of my climate control module.. When I change a fan setting, I can hear what sounds like a relay clicking at a fast rate (once or twice a second) untill it finially responds to my selection..

How does one go about getting access to that module? I'd be glad to do it if I knew how! ;-) I assume teh dash comes apart?

Thanks again!
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Old 02-23-2003, 11:44 PM
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Voltage Regulator

Also, I will check into the voltage regulator as to weither it was done, but may I be so unknowledgeable to ask where it is? ;-) The alternator out of the car was what was rebuilt and put back in, by the way...

As for teh rest of teh ideas, I shall try them out as soon as I can and post my findings, thanks again...
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Old 02-23-2003, 11:52 PM
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Join Date: Dec 2001
Posts: 571
The voltage regulator is on the botton of the alternator as seen from it's mounted position. Two phillips screws set an inch or so horizontally apart are removed, then the voltage regulator comes right out. It slips back in very easily. The brushes are what wears. They are carbon-like and about 1/2 inch long when new.
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Old 02-24-2003, 12:02 AM
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Join Date: Sep 2002
Location: So. Calif.
Posts: 323

DIAGNOSE FIRST . . . REPLACE parts as needed LATER . . .

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Old 02-24-2003, 12:22 AM
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mpyne makes an interesting point - his profile indicates 29 yrs. MB experience - can't argue with that.

I'll throw this in for what it's worth. It's what I call a poor mans electrical system test. It does not "load" test the system, but gives some indication as to the general health of the charging system. If you do not understand what I'm about to describe, find someone who does and to the originator of this post, this would not include the mechanic you've given 8 grand to.

Buy a digital voltage-ohm meter, more commonly known as a VOM. The ones sold at Wal-Mart are pure crap as most everything else they sell is.

Set it on the 20 scale - DC side. Start car. Put red VOM prong on the + terminal of the battery and the black prong on the - terminal of the battery.

What voltage reading are you seeing? Your MB is likely equipped with Bosch electrics and this sytem for whatever reason doesn't put out what Asian and many Americam models do. Your MB may only be putting out 13.5 or so. When the brushes in the voltage regulator start to wear, this reading starts to look more like 13.3 or lower.

If you perform this test on a cold engine and all is well, you may see 13.95 or slightly higher, but not much more. The reading drops when the engine has been driven. I get suspicious if it falls below 13.5 when testing a warm engine.

One of these days I'm going to experiment with the adjustable Transpo regulators. They make a model that an be turned up in .5 volt increments, all the way to 14.4. This sort of reading is what you see on Asian cars.

Last edited by Mike Richards; 02-24-2003 at 12:28 AM.
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Old 02-24-2003, 12:36 AM
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Join Date: Sep 2002
Location: So. Calif.
Posts: 323
Let's discuss another issue . . .

Does the vehicle have an aftermarket HI-POWER audio system with external amps?
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Old 02-24-2003, 10:42 AM
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Join Date: Dec 2001
Posts: 571

Interesting point. I have an external amp in the trunk along with a CD player and an after-market stereo + alarm that I have switched off, but wired into the ign. circuit anyway.

I suppose these external amps are a major source of drain while the car is running and the stereo is on. I would hope that the external amp is not always hot like brake lights.

I need to explore this as I have a current drain issue - losing approx .001 volts every hr. or so.

Granted the battery is getting old - it's now 3.5 yrs. old, but this issue has been with me for quite awhile, even with a fresh battery.

Pulling the factory fuses under the hood doesn't dim a 12 volt test light connected to a disconnected battery grnd. strap.

It could be that it takes less current than I realize to activate a 12 volt test light. Need to go ahead and use the amp scale on my VOM to test for actual draw.

I've always suspected the alarm, but I may be looking in the wrong direction.

Thanks for the tip.
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Old 02-24-2003, 11:27 AM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
chasm, i think it is time for you to visit the dealership
for evaluation of your problem. they charge 1.5 - 2.0 hours
for it and you get a printout of the problem/s.

take that with you to your independent mechanic
and sort it out.

if you need another mechanic call RJ motors in
capstan way, richmond. they are listed in the phonebook.

good luck.

Prayers bring forth enlightenment.
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Old 02-24-2003, 01:32 PM
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Thank you everyone for the advice, and thank you Joel for teh reference of RJ motors. I have definitely been enclining toward taking it to the dealership and having them hook it up to thier computers and run a full diagnostic test on it... What are peoples experience with the Dealerships diagnostics? Are they the best thing since sliced bread, or are they faulty and nothing more than a 'good try'?
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Old 02-24-2003, 01:35 PM
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Join Date: Sep 2002
Location: So. Calif.
Posts: 323
It's kinda like goin' to Denny's . . .

The food's worse in some than others . . .
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