Staggered Tooth Tach Signal?

Hello its been awhile, I have been spending many months engineering some stuff for my engine swap. No one as far as I know have done this swap and I can't wait for it to be done!

But one hurdle I'm trying to over come during my 1998 XJ swap is I want to use the stock tach. After sending an email to Dakota Digital about there converter I wanted to use to convert a gear sensor on my engine to a signal for the tach. The guy at Dakota told me that...

" While we have the DSL-2 that can read the teeth, there is a problem with the way Jeeps reads the tach signal. Jeep used a staggered tooth crank sensor that indicated RPM and TDC for the ECM and in 1996 started using CAN bus to feed a signal to the dash cluster.

If your use the DSL-2 the Jeep tach will not work right. You could use the DSL-2, a with adapter from Novak to feed the ECM with the proper signal - http://www.novak-adapt.com/catalog/e...h_emulator.htm "

Now if I use Novak's adapter and then the DSL-2 I will be down about $300... and that sounds a little much to me to be honest... I can get an AutoMeter Diesel tach that runs off the alternator for $130 http://www.ebay.com/itm/290552814748...84.m1423.l2649

So this gear I plan to get a tach signal has 50 teeth. And it spins at half the speed of the crank so I get 25 pulses per rev of the crank.

Now what do I have to do to get the factory tach to operate properly? Any way around using the Novak adapter?

Thanks for any help guys! :looney:

Came across some info but lead to couple more questions.

What info does the computer need to see to operate the factory tach?

I have heard that when they went to coil packs (1999 or 2000) that the computer needs to see a signal from the CPS and Cam Synchronizer. Also heard that if you don't get both not only will your tach not work but your A/C won't either.

Now can I just use the CPS to run the tach?

you are trying to swap what into what year xj

1998 ax 15

I plan to use most of the stock wiring harness to run water temp, oil pressure, volts, fuel obviously and the speedo. I bought a NP241 and SYEd it with a Jeep speedo housing so I can use factory stuff.

I am just trying to find out how to get this stupid tach signal to work, being as Jeep had to do something complicated and send a staggered tooth pulse to another computer to run the tach... whyyy?

I think the only way I will be able to run the factory tach is by taking a stock Flywheel (I'm using a 5 speed) or even a flex plate. And cut center out and mount it to my new flywheel and machine my bell housing of the 2002 NV3500 (MG5) to accept the Jeep CPS or machine the bell housing adapter to accommodate it.

98 motor into what year xj?

no no my Jeep is a 1998 the motor is a D722

Here is a picture of a 1997 TJ 4.0 which uses the same P/N flywheel.




P/N 53020519AB Flywheel (4.0)

91-01 Jeep Cherokee (XJ)
93-96 Jeep Grand Cherokee (ZJ)
97-04 Jeep Wrangler (TJ)
91-95 Jeep Wrangler (YJ)

They are wrong about CAN bus, the XJ uses CCD bus to run the IP. In fact all the gauges in a 98 run via the ccd bus...

Your best bet is to read up on the CCD bus and build a device that reads the CPS, CTS, voltage, OPS, and fuel level sender and encodes them into the proper data packets, then sends them via CCD to the instrument panel.

This page may help a bit: http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm

You may be able to just run the jeep ecu and not connect it to any of the engine stuff, but your check engine light will definitely be on and your tach may not work, I'm not sure.

That sounds like a lot of work for a 20 horsepower motor.

cal said:

That sounds like a lot of work for a 20 horsepower motor.

Click to expand...

20 Horsepower?!? My 87 XJ has at least 35HP... I'll sell you the motor!

Are you really doing all this for a Kubota engine swap?

I have no input, but a buddy is doing a similar swap... Kubota diesel into a late 90's TJ, I'll ask him what he plans on doing about this....

kastein said:

They are wrong about CAN bus, the XJ uses CCD bus to run the IP. In fact all the gauges in a 98 run via the ccd bus...

Your best bet is to read up on the CCD bus and build a device that reads the CPS, CTS, voltage, OPS, and fuel level sender and encodes them into the proper data packets, then sends them via CCD to the instrument panel.

This page may help a bit: http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm

You may be able to just run the jeep ecu and not connect it to any of the engine stuff, but your check engine light will definitely be on and your tach may not work, I'm not sure.

Click to expand...

Thanks for that info. But I'm not an electrical engineer and looks a bit much of a project for me to tackle right now ha ha

jrowell said:

20 Horsepower?!? My 87 XJ has at least 35HP... I'll sell you the motor!

Click to expand...

ooo I may be interested! haha

shelbyluvv said:

Are you really doing all this for a Kubota engine swap?

Click to expand...

Nooope, just said that cause the motor is irrelevent to my question. If I ran that engine it would be "The Little XJ That Couldn't"

Found some more info---

Okay here we go.

The crankshaft position sensor is mounted to the transmission bellhousing at the left/rear side of the engine block. Engine speed and crankshaft position are provided through the crankshaft position sensor. The sensor generates pulses that are the input sent to the powertrain control module (PCM). The PCM interprets the sensor input to determine the crankshaft position.

The flywheel/drive plate has groups of 4 notches at its outer edge. The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM. There are 3 groups of 4 pulses generated on 4.0L 6-cylinder engines, and 2 groups of 4 pulses for 2.5L 4-cylinder engines. The trailing edge of the fourth notch, which causes the pulse, is 4 degrees before top dead center (TDC) of the corresponding piston. The engine will not operate if the PCM does not receive a crankshaft position sensor input.

So the notches are in time with the pistons. 2 pistons are at TDC (top dead center) for each set of notches. Then they use the cam position sensor to time the injectors. The cam turns half the speed of the crankshaft.


So I now know what I'm going to do. From the research I've done... The only signal the PCM needs to see to operate the tach is a CPS signal. So I am going to be reverse engineer and CAD up a CPS wheel that mounts to crankshaft of my motor and will send a signal via my factory CPS.

Quick question... How come I can't upload pics on this forum? I can only post links to images?

have to be a member to upload images, and then, not in the tech forums.

you know, i'm actually dissapointed.

20 horsepower is retarded, but i was really looking forward to seeing that 3 cylinder diesel running in an XJ.

A paid member?

Your not allowed to post pictures in tech forum? oooppps

sorry to of dissapointed you! but yeah that little kubota would have very interesting though haha

lol, Naxja is a Club, not a forum - the forums are free, certain forums and privileges are left to members of the club though.

You can post pictures, not upload pictures. Upload them to photobucket. Next to the photo in Photobucket there will be a series of urls, one of them starts with [ IMG ] ... copy that url and paste it here to the forum.

Note from DJ
Why can’t you just hook up a Kubota tachometer?

djgrayxj said:

Note from DJ
Why can’t you just hook up a Kubota tachometer?

Click to expand...

Cause I want to use my stock tach, using that would look hack. Atleast to me it would

On a side note, I reverse engineered the flywheel. Hopefully it will help someone else out.



Also got the 2 parts CADed up that will be creating the signal to my factory PCM.