Missing at high rpm and WOT

#21

[quote=“Ranger” post=57371]Here’s some data for posterity.

Bottom line up front. By cleaning connections and defeating the small wire to the battery I increased DME voltage from 13.61v to 13.78v.

Background. The DME has the ability to adjust to a limited range of supply voltage change. That ability seems to be reduced at WOT and high rpm. Not WOT or high rpm, but WOT AND high rpm. We don’t have numbers for any of that tho. All I can say for sure is that 12.6V seems to be too low. So maybe 12.8 is ok? Maybe 13v is necessary? Likely we’ll never know.

This series of experiments was intended to find out how much voltage could be increased by simply cleaning connections.

Voltage measuring points.

  1. Big lug at kill switch. Goes to battery.

  2. Big lug at kill switch. Goes to big connector at firewall and from there to alternator via the starter.

  3. At firewall connector. Goes thru small fused wire to battery. This is part of the system giving DME it’s own route to batt.

  4. At firewall connector. DME connects here. This is the big enchilada for DME power.

Yes, that’s a little confusing. Think of a 2 pole kill switch, the big pole handling the big cable to the battery and the small pole handling the small wire to the battery. (1) and (2) are either side of the big pole and (3) and (4) are either side of the small pole.

There was a couple other measuring points I used to see if I would find out anything interesting.

All tests were done with the rpms at 1500-2k with no electrical devices running other then dashboard gauges.

Test 1 was the car as it came home from Mid-O.

(1) 13.73v
(2) 13.83v
(3) 13.68v
(4) 13.61v

Conclusions.

  1. The kill switch and the connections associated with it are costing me around 0.1V. (2) is higher than (1) and (3) is higher than (4).

  2. The small wire loses 0.5v. Both (1) and (3) go right to the battery, but the small wire (3) has less voltage.

Test 2 making the connections cherry. I disconnected every connection between the battery’s ground and the engine’s ground, and between bthe battery’s 12V lug and the alternator’s 12V lug. I cleaned every connection with a dremel wire brush and put on conductive grease.

(1) 13.87
(2) 13.87
(3) 13.78
(4) 13.71

Conclusions. All voltages went up by 0.1V or better. The charging voltage to the battery went up the most (0.14v) and the critical DME voltage (4) went up by 0.1v).

Note how (1) and (2) are the same, indicating no loss across the kill switch, but (3) is more than (4) indicating that there is some resistance in the kill switch’s small pole. This is irksome because it’s directly impacting voltage to the DME.

The small wire to the battery (3) still shows voltage loss vs. the big wire to the battery (1).

Test 3. I added a heavy gauge wire connecting points (1) and (3). This was an attempt to fix the small wire voltage loss.

(1) 13.87
(2) 13.89
(3) 13.87
(4) 13.78

Conclusions. This idea boosted small wire to battery (3) voltage by 0.09v so the idea worked. It doesn’t fix the fact that the kill switch is costing me voltage, but it does increase voltage to the DME (4) from 13.71v to 13.78v. Hard to jump up and down and holler over 0.07v, but at least the various ideas are working as expected and there weren’t any surprises.

A sad final note. Because I’m an asshole, I burnt the shit out of a finger in this test. I tightened up the big lugs on the kill switch without having the battery disconnected so the lugs were “live”. I figured that I’d just be careful about it an there’d be no problem.

I neglected to factor in my wedding ring. Which to my very great surprise, attempted to weld itself between mini socket wrench and sheetmetal. The resulting burns on my ring finger and adjacent fingers were quite “well done” so to speak. Later, getting my titanium ring off my badly burned and swollen finger was fairly challenging. It was a fine learning experience.[/quote]

I did 2 more tests. I swapped in a new voltage regulator and checked all the voltages, then I cleaned up the ground at the passenger strut tower anc checked them all again. No change in voltages.

Conclusions. My old voltage regulator was fine as was the ground at the shock tower.

#22

Is the problem gone or have you not been able to test? You should just run that thing down Whitaker street then around Forsyth Park!!!

#23

[quote=“FishMan” post=57443]Is the problem gone or have you not been able to test? You should just run that thing down Whitacker street then around Forsyth Park!!![/quote]No Wifi in jail.

#24

geez ranger… be careful playing with electricity :slight_smile:

#25

[quote=“Ranger” post=57371]I neglected to factor in my wedding ring. Which to my very great surprise, attempted to weld itself between mini socket wrench and sheetmetal.[/quote]The head greenskeeper I worked for at the world renowned Bristol Country Club (think of Bill Murray’s character in Caddyshack - only less polished) had that same scar.

He learned to use shorter wrenches when working around golf cart batteries.:blink:

It’s a great scar for telling people what a b@llbuster your wife is. “She didn’t trust me to keep my ring on when I went out of town, so she did THIS!”

#26

I finally went to the doc on Friday, 6 days after about burning my finger off. A lymph node was starting to get angry so that meant that it was fighting an infection. I figured the doc could get me an oral antibiotic to help out the topical antibiotic I’d been using.

The doc and the nurses got kinda excited. By the time I got out of there they had my whole hand swathed in bandages.

Any goatscrew you walk away from just makes you smarter.

#27

Another point to add to this thread.

I thought, after fignting a high rpm cut out problem for almost two years that I had finally gotten rid of it with the last engine harness change. But a month or so back it started up again very sporadically. It was pretty bad at the HOD DE at Barber, as Eric Palacio can attest. So I started doing the usual replace one component at a time. After Barber I had done a single replacement of everything except the harness with essentially no affect on the problem (main & fuel relays, CPS, DME, 60a substitute for the fusible link, AFM). Since all of those swap in parts (excpet the fuse) were used I put the newer part back in when the swap didn’t help.

On a whim, I changed the CPS and DME this past weekend when I was at Hallett. And the cut out went away! My suspicion is that that the coax in the harness that routes the CPS signal to the DME is somewhat degraded, the CPS was a little weak, and the input section of the DME was a little off. The combination was enough to cause cut outs in summer temperatures.

#28

Hans Ackerman, a relative newby in our forum, and I have been talking about grounding the alternator. The other day I read something in some E30 manual that alluded to a ground strap that went to the alternator, something I’d never heard of.

Based on that reference I made a ground strap last night for the alternator and attached it to the second bolt hole on the frame rail where the oil pan ground attaches. Hans found a RealOEM reference to it. http://realoem.com/bmw/showparts.do?model=1113&mospid=47309&btnr=12_0145&hg=12&fg=22

If you Google the part # for the ground strap you’ll find folks selling it. Easy enough to make your own tho. Note in the pic how the groundstrap connects to the voltage regulator, even if it’s not our voltage regulator. That’s probably the clever way to do it, so I may redo mine.

You would think that the alternator is attached to the block solidly enough that grounding wouldn’t be an issue. But last winter I painted the alternator, it’s mount and all the sheetmetal at the front of the engine. I was bored. It didn’t occur to me that I might cause alternator grounding problems.

#29

[quote=“Ranger” post=57371]A sad final note. Because I’m an asshole, I burnt the shit out of a finger in this test. I tightened up the big lugs on the kill switch without having the battery disconnected so the lugs were “live”. I figured that I’d just be careful about it an there’d be no problem.

I neglected to factor in my wedding ring. Which to my very great surprise, attempted to weld itself between mini socket wrench and sheetmetal. The resulting burns on my ring finger and adjacent fingers were quite “well done” so to speak. Later, getting my titanium ring off my badly burned and swollen finger was fairly challenging. It was a fine learning experience.[/quote]

It’s been 4 weeks since I burnt the crap out of my finger. The damage was deep enough that heeling has been slow. Thur it all the sudden started looking worse. Lots of new redness and leaking various types of yuckage. By the end of the day I’d seen my doc and then spent the afternoon at the hospital. The “wound specialist” decided that instead of an infection what I was seeing was a reaction to the “Mexico trip in 2005” topical antibiotic.

So no flesh-eating bacteria.

#30

I’ve had the same problem for a year also. I was suspicious of the kill switch so I decided to solder the wires to the side post connectors i have on the killswitch. I had to use a propane torch to get it hot enough and then i replaced the lead connectors with beefier ones after melting the first ones. Then I basically rebuilt the entire top end of my motor and found that the tube connecting the charcoal canister purge solenoid to the bottom of tb was nearly gone. Today I fired it up and took it up through third gear without a missfire.