picking ignition timing method (Jeep crank trigger)

bleoh · Post by **bleoh** » Mon Jul 03, 2006 7:25 pm

Sounds like you are getting there.

Just though I would throw this out as an FYI for those with 4.0L as another option.

The distributor from a 4.2 will drop right in. It has a VR sensor with 6 triggers. You need to lock down the mechanical advance and you can also put the large cap and rotor on it from a mid 80's 300 cid Ford.

Here is a pic of them side by side (4.0 and 4.2)

http://pg.photos.yahoo.com/ph/bleoh/det ... pg&.src=ph

Good luck with it. Brian

Fastest95PGT · Post by **Fastest95PGT** » Mon Jul 03, 2006 8:45 pm

czb83 wrote:Is it possible to see from the measurement from an oscilliscope? On the first page of this post I posted a measurement the two hall sensors on my vehicle. The top one is the crank sensor and the bottom on is dizzy sensor. The bottom of the wave is 0V and the top is 5V.

Sounds like you don't need a pullup resistor then.

czb83 · Post by **czb83** » Tue Jul 04, 2006 3:22 pm

I have good news! (and some bad news)
I went out today connected the power, grounds and the two hall sensor inputs to the MS. First I was happy that nothing was smoking. I was running megatune under wine and it was acting kinda funny so im assuming my results are right.

Anyways, I connected the sensors and starting cranking the engine. I was getting a consistant ~1050 rpm reading which is not good. I noticed that the engine would not start. I had spliced a wire in each of the hall sensor wires going to my existing ECU. I guess that the signal only takes one path, which happened to be to the MS instead of my stock ECU which is why it wouldnt start. Im also assuming that both the signals went to the MS and not just one.

Im guessing its good that I got a consistent signal while cranking and nothing caught on fire

I suppose I need to double check my MS settings, the megatune interface seems weird. I know that all values are changed in RAM on the flash and that "burn to ECU' puts them in flash, but there is no timer on if its completed or not, im sure its not instananious. ALso, when I power up the MS after to the "burn" how long does it take to put whats in flash to RAM?

Well, any thouhts on my I might try? Im happy that I got a signal and nothing broke, but somewhat dismayed that the signal I got was the wrong rpm. I need to go find out what my cranking RPM really is. Anyways, thanks for all the help yall provided. I would have not even made it this far without yall.

shaqjeep · Post by **shaqjeep** » Wed Jul 05, 2006 8:04 am

I thought i'd let you know what I did with my Jeep I6 258. It comes stock with a six trigger VR distributor. Instead of that I used the 4.0L distributor because it is locked and has a hall sensor which I prefer (I like trigger return during cranking for the -35 degree cold starts). I machined a six window wheel to replace the original single window cam synch wheel. I pulled up the hall sensor to the +5v line with a 330 ohm resistor. I can't remember my exact figures but it is about 12ma through the sensor and 4 ma through the opto isolator. Obviously I used the hall input on the MS. I took the MS spark output and ran it to a GM Delco 4 terminal HEI type ignition module coupled to a 12v HEI type separate coil (off a 1989 type 4.3L gm). The modules and coils are cheap and easy to find. I didn't use the internal coil driver (VB921) because I like to keep my potential problem areas accessible and easy to diagnose and fix, thus an external reliable module. Note that the HEI module is normally connected to a VR distributor, but it works with one terminal grounded and the other connected to MS output and to an external 12v 10k pullup (thus varying from 12v to ground) it fires on the downward going voltage. You can try a module, coil, plug and battery on the bench and create sparks in this manner. I really find this module handy....

I was concerned about how much current the distributor's hall sensor could handle reliably, recognizing that I had to have enough current to light the opto isolator LED in the MS. If you pullup the sensor to straight battery voltage you have to have enough current in cold weather/low battery voltage (10v) and therefore have excess current at high voltage (14v). Makes it tougher to choose the best pullup resistor. I wish I knew for sure how much current the sensor can pass and the absolute minimum required to drive the led in the optoisolator...I have the original jeep computer and intend to set it up and measure how much current flows throught the hall sensor in stock form.

This combo is working great and for a few bucks I carry around a spare coil, module and distributor. Everything can be changed in 20 minutes !

czb83 · Post by **czb83** » Wed Jul 05, 2006 11:04 am

Yeah, I had actually thought about doing the machining of another wheel for the distributor, but I was really exicted about getting MS to work with the vehicles stock sensors requiring no modifications.

You said that you pulled up the sensor to the +5V area. My hall sensor gives a 5V reading when passing over a window. Wouldnt doing that make it 5V all the time?

Im not sure what you mean in the second part about pulling up the voltage. You still talking about pulling up the voltage from the hall signal, but to 12V? I assume your just trying to figure out where to get the 12V from? I would imagine that once the engine is running you would be getting more than 10V since its connected to the alternator. Also, wiring it to the battery wouldnt give to much noise?

You talked about how much current through the Hall in stock form. I could measure the amperage from the the hall sensors signal wire in my vehicle and let you know what I get, thought it would have to wait till this weekend when I go home(where my tools are).

Let me know if I misunderstood you.

czb83 · Post by **czb83** » Mon Jul 10, 2006 6:49 pm

Well, i thought I would offer an update. I have my MS mounted and all the cables run, except for fuel and igntion, as I'm making sure all the input signals are good first. I connected the two hall sensors to the MS, added a 1kohm resistor in series with the 2nd trigger input as I had forgot to previously. Upon cranking I was reading a fairly constat 175 RPM. I just going to assume that this is correct

I was hoping it would start, but apparently me reading the hall sensors with MS stops the stock from reading it so it wouldnt start. This left me with only reading cranking RPM.

So, if its cranking rpm correctly, then hopefully it will read all other rpms good as well. This is great news. This means that people with fuel injected jeeps wont have to resort to other methods to get a viable tach signal into their jeep, and they can keep there stock sensors.

oh, and shaqjeep. I tried measuring the current from the hall sensors and there was so much noise I couldn't pick up a signal, it must be really low current.

Hopefully i can end this thread with saying that my jeep is running MS fuel and spark using stock jeep sensors.

Fastest95PGT · Post by **Fastest95PGT** » Mon Jul 10, 2006 7:20 pm

That sounds like you have a good tach signal! Now the only thing to do is play with trigger angles unless you already know your wheel's angle.

czb83 · Post by **czb83** » Sat Jul 22, 2006 6:01 pm

I've been fighting with this for a while and havent got much done. I'm getting a RPM signal of 180 but its not perfectly smooth, i see it drop to like 50 for split second ever second or so. I cant see to get any spark. I've got the coil connected to MS but it never grounds. Ive got everything set up as indicated above. Im not sure if its a hardware problem or software problem.

Another thing. The MS only recognizes my two hall sensor inputs whenever i have them spliced into the original ECU. SOmehow the original ECU modifies the signal. Any thoghts?

czb83 · Post by **czb83** » Mon Jul 31, 2006 3:40 pm

If I stop sharing the hall sensors between my stock ECU and MS, then MS can no longer read it. I put a scope on the hall with it just connected to MS and saw no signal. I tried wiring a pullup to both inputs. I read 5V on one and 0V on the other with very little flucuation on both. Im using a 1k resistor between the wire and 5V. Should I try a smaller or larger resistior?

Project7 · Post by **Project7** » Sun Aug 06, 2006 6:02 am

On the two jeeps I tried to install a megasquirt in for fuel only. I never had a problem sharing the the OEM sensors with the megasquirt. YOu should be able to start the jeep with the MS attached.

czb83 · Post by **czb83** » Sat Aug 12, 2006 4:22 pm

just wanted to update this. I stopped trying to share hall sensors between stock and MS. It wouldnt work just connecting hall sensors straight up though. I put a 5V pullup on both with a 220Ohm resistor on each. I had a seperate thread on the method.

It seems I get a stable RPM now, so this method appears to work.

czb83 · Post by **czb83** » Sat Aug 19, 2006 8:28 pm

UPDATE:
Set 10 Degrees BTDC timing, and got my timing light out. I got it to match up with a 67 Degree trigger angle. I don't know if its exact, but its really close.