Goldhawg

iTrader: (7)

I am giving up on getting my E38 ECM to give a tach signal (for now) and want to just take the signal of a coil wire. But which one? Any pics from anybody that did this?

BP Automotive

iTrader: (3)

You have to add that to the e38 ecm connector. Or are you having trouble getting that signal to read?

Goldhawg

iTrader: (7)

Yes. I have the Pin 48 on the J1 connector going to the tach. I have added a 12V signal thru a 680ohm resister per suggestions. I told my tuner to do

" GEN IV E38 Tach Settings for aftermarket tach (autometer)

Correct HPTuners tach settings for E38 ecm with 58x crank sensor.
Tach Output = Crank
Resolution - High =14
Resolution - Low =15
This will make the ECM output the correct frequency for a 2 pulse per revolution tach. "

Per the guidance found here. He says he did it and I have no reason to believe otherwise. I have a Speedhut tach. I would love it thru the ECM; much more elegant. But for right now I just want a tach w/my 6 speed, so if I can find out exactly which coil wire to connect to, I will do that. Anybody done this?

85MikeTPI

iTrader: (9)

FWIW, that HPTuners thread was using a 2pulse-rev aftermarket tach. The factory tach is 1 per rev and I had to use 7 for both high and low resolution settings. I'm not familiar with the speedhut, but if its programmable you may need to change the tune and/or the input to the tach...

Goldhawg

iTrader: (7)

I tried every one of the speedhut settings to program it. I'm skeptical I'm getting a signal out of the ECM at all. I will be getting a friend w/a nice multimeter to help me check the signal. Of course my tach could have been bad from the factory, but I'm doubtful. I'm still not sure I know of anyone w/E38 VVT engine/T56 that has actually gotten a signal out of the ECM.

85MikeTPI

iTrader: (9)

Well you don't know me, but you can say that someone has.. Me

Of course I do my own tuning and wiring so I'm positive of what I'm working with.

Can you get and post your tune?

Goldhawg

iTrader: (7)

Probably; but I'll wait until I can get a good multimeter to verify nothing is coming out of the ECM. If something is coming out, then perhaps my tach is bad. I've had at least three other supposedly good parts bad on this build--would be just my luck! If I knew which coil wire I'd also try tying in there just to see if I could get the tach working.

My tuner had been posting ??s to (Chris?) on HPTuners during my dyno tuning (last year), but never could get answers to his ??s. So now that Spring has returned to Ohio I'm trying to get the car ready to run.

Goldhawg

iTrader: (7)

Update. I talked w/Speedhut and they informed me that of the four wires that go into each coil, one is different colored than all the rest (so therefore is different on each coil while 3 wires are the same color) and the one wire that is different on each coil is the one to tap into for the tach signal.

So I go out to the car with my power probe III to see if it picks up signal. On the suggested coil wire it would read .1 then .2 alternatively for maybe a second or less then back to .1 then .2 and so forth. About every 5-10 secs I would see a spike up to 4.1 or so volts. Does this seem normal for a tach signal?

Then I verified my lead into the J1 connector pin 48. Once the key is on it reads 12V (or a little less) and upon starting it goes to 13.5 and stays steady at the 13.5. Recall I have the 680 ohm resister connecting this line to a 12V under the dash, so electricity flowing backward. Does this sound right or did I do something wrong with the resister? If right, does the steady 13.5 suggest that nothing is coming out of the ECM?

Thoughts? I haven't tried splicing into the coil wire yet; waiting on advice here from some of you electrical gurus.

85MikeTPI

iTrader: (9)

The E38 signal just grounds the tach line during each pulse, so if yours is remaining steady then something isn't correct. Verify all your ECM grounds are on and secured, you have the correct ECM pin (X1-48), and that the tune is set to crank and not frequency. The resistor should be about 1k ohm, but make sure it's 680 and not 680K ohm! (What are the color stripes on the resistor you used?). It just connects between 12v and the X1-48 wire to bias it to 12v except when the ECM grounds the line and it keeps too much current from flowing and burning up the ECM .

71403

A voltmeter likely will not be able to pick up the pulses on the tach output (X1-48), they're happening way faster than the sampling rate of your basic DVM. One of the fancier automotive meters with frequency measurement could help show signs of life.

The schematics are posted on lt1swap if you want to pick up a coil signal.

http://www.lt1swap.com/geniv_schematics.htm

Goldhawg

iTrader: (7)

I dug back to last fall when I was trying to figure this out (yes, Cutlass goes into hibernation here in Ohio in winter!), and had this post where you tried to help me earlier:
https://ls1tech.com/forums/conversio...l-no-tach.html
here is the pic of the resister wired in

Question, before I go bug my tuner about what's on the ECM, I'm thinking about just tapping into the coil wire. Does that signal also need the 680 ohm resister? I'm hoping it will at least work with it, even if it doesn't need it. Cuz I'd really like to not cut that out in case I'm ever able to figure out the ECM programming and don't want to have to solder another tiny resister inline.

1989GTA

I take it the pink wire is +12v and the purple wire is the tachometer signal? If so that looks good to me. I have also used a 1K ohm resistor but the car is not running yet. The car is going into the shop today for the whole drive train transplant.

Goldhawg

iTrader: (7)

Hmmm...curiouser and curiouser. Talked w/Speedhut (after not getting a tach signal off any of the four wires going into the coil--some confusion over which one is actually the trigger wire--just plugged into them all) and they said I needed to bypass the 12v/resister line--their tach should read w/o it. So last nite I pulled the tach out of the dash and disconnected the tach input wire (leaving power and ground applied) and I put a wire directly between the coil and the tach, and when receiving no tach signal, went to the next until I had tried all four. Started w/Tach set a 2 pulses/per rev, but then changed for several settings (1, 4, & 6) just to see if that would make a difference--but no signal w/any of them. The tach needle does do exactly as it should moving to the correct location as you set the number of pulses/revolution.

Then my partner hooks up his scan tool (fancy snap on) and yes, the ECM still reads 13.5v w/car running. But he has another mode that reads a PULSE on the signal. I'm beginning to think that my tuner did exactly what he was supposed to and I have yet another brand new part on this install that came DOA. I'll call speedhut later today to see if there is any more testing I can do before I send it back.

1989GTA

Please keep us posted as to the outcome. I am in doing the same thing as you are with the same compents. I should know in a couple of weeks on mine.

BBC632Camaro

iTrader: (82)

Bumping this up... Goldhawg did you find the problem? I'm having the exact same problem with an autometer tach on my e38. Crank 15/15 or 14/15 seem to be the way to go so I've read.. Been calling back and forth between autometer and the harness manufacturer and still no solution. Autometer told me sometimes when the computer is 'flashed' it gives a weak signal and I need to buy there tach adapter??? Ok so I did that and still nothing. The tach when hooked up with either a 1K ohm or a 470 ohm resister both make it glitch every so often and then freezes in that position when you rev the motor fairly high which leads me to believe my tach is bad as well. Its a brand new autometer C2 tachometer. When I hooked up their tach adapter off the coil wires it does the exact same thing. They have very well defined instructions on how to do this on a 2010 Camaro and they cut the pink wire and tap into both sides of those on the coils for the adapter. Also I have HPtuners myself and have played with all the tach setting with no luck.

IMHO autometer seems to be a little behind on technology through my experiences and to the people I've spoken with.

Goldhawg

iTrader: (7)

Well, I sent the tach back to speedhut, and they checked it out and it worked just fine. But they said some of the late model LS motors had problems, so they worked over the internals (what I don't know) to allow it to pick up a weaker signal. Tried it with the E38 signal thru the resister, w/2 pulses per rev and initially no joy. Waited till this weekend and tried the coil wire w/no resister. After getting ~100 rpm and stepping on throttle (maybe 1500-2000 rpm) giving me 3-400 rpm, I started playing w/different pulses per rev. I was able to get a signal that appears right w/1/2 pulse per rev. Engine idles around 700 rpm and will go up to 2-3000 rpm when I rev it up. The needle appears very notchy and wooden--doesn't seem to flow as it goes up. I'll try later w/my scan tool to verify accuracy across a wider range of settings.

However I also tried it again on the ECM; and I was getting some signal Unfortunately it would go to 2-300 rpm on 2 pulse/rev, but if you buzzed the throttle, it would go down to zero. And it bounced around a bit at idle--sometimes shooting up to 1000-1500 rpm. So I seem to be getting signal from the ECM.

I'll call speedhut tomorrow and talk to them; not sure why it works with 1/2 pulse/rev and why the ECM now does something but doesn't read right. In an ideal world I'd use the ECM--but I'm certainly ready to splice into a coil wire and declare victory.

1989GTA

Keep us posted. Hopefully in about a week I will have my motor up and running and I shall see if the tach works. Also running Speedhut gauges and the E38 ecm.

Goldhawg

iTrader: (7)

Mike--When you were using the other settings, were you getting tach signal just at wrong rpm levels, or were you at no signal and then once you got it to 7 it all worked?

85MikeTPI

iTrader: (9)

My factory tach was initially running half as much with the 14/15.
It always worked, just not correct reading.

Goldhawg

iTrader: (7)

OK, I've declared temporary victory and here are pics for anyone needed to duplicate. I traced the lead off the coil wire back (my coil wire was a red one on drivers rear coil); on the other side of the main connector it was orange, see pic). I decided to splice in there so I'd have more room to get a good solder. I added a short small wire w/weatherpak connector so I can disconnect tach from main harness. On the inside of the car, I just added a male bullet connector to the tach, and then two female bullet connectors to the ECM connection that has the resister and the new wire that goes to the coil. So if I ever figure out the ECM I can still go that route fairly easily. But since the coil works, I'll probably leave it alone. Re the tach, it still feels heavy and notchy when it moves, not smooth like tachs normally do, but it works. I may still be sending it back to speedhut for some more tweaking later, but hey--I have a working tach. I also hooked up my scan tool and it read ~100rpm higher than the tach did everywhere. Not sure it matters--I'll be keeping shifts no higher than 6k ever.