Fooling the computer on a 2007+ JK Wrangler for mechanical diesel
#1
09-10-2015, 01:25 PM
Fooling the computer on a 2007+ JK Wrangler for mechanical diesel
Hi All,
I'm right in the middle of swapping a mechanical diesel into my 2007 JK Unlimited Ruibcon, and I'm researching and trying to understand how to best fool the JK computer into thinking the engine is running so I get the stock tach to function, etc.
My understanding is that most people use two trigger wheels and sensors on the front of the engine - one for the crank position sensor, the other for the cam.
JPJeeps.com sell such a kit here - JD Jeeps - Diesel Conversions - crankshaft
I'd like to keep this all as simple and straight forward as possible (and cheap!), so I'd like to understand if I actually need two sensors, or if feeding the cam wire the same signal as the crank will suffice. Here's some info from user redveloce on another forum who did exactly this in an earlier TJ
Which makes sense - we need the crank signal to be "accurate" to have the tach be correct, but the cam sensor just needs to think the engine is turning, and that's good enough.
It also appears the computer doesn't even care if the camshaft signal stops after startup, but again, it seems there is no reason to not leave it there.
My check engine light will be on, of course, but I'll just pull the bulb.
I'm going to lose cruise control and likely ESP will be strange, but other than that I hope everything functions as normal (air bags, lockers, a/c, etc.)
I checked the factory service manual for the JK, and both the crank and cam sensor have exactly the same wiring (5v supply / sensor ground / signal) so I can't see how connecting them together will hurt anything.
Does anyone here have first hand experience doing this on a JK?
Thanks very much,
-Dan
I'm right in the middle of swapping a mechanical diesel into my 2007 JK Unlimited Ruibcon, and I'm researching and trying to understand how to best fool the JK computer into thinking the engine is running so I get the stock tach to function, etc.
My understanding is that most people use two trigger wheels and sensors on the front of the engine - one for the crank position sensor, the other for the cam.
JPJeeps.com sell such a kit here - JD Jeeps - Diesel Conversions - crankshaft
I'd like to keep this all as simple and straight forward as possible (and cheap!), so I'd like to understand if I actually need two sensors, or if feeding the cam wire the same signal as the crank will suffice. Here's some info from user redveloce on another forum who did exactly this in an earlier TJ
Originally Posted by redveloce
"Here's one for anyone looking to do a diesel swap into a '97+ Jeep.
In order to turn on the tach, the PCM needs to see a signal from the cam sensor on startup. It's common for people to make or buy two sensor wheels, one for the cam and one for the crank sensor ($400+ from JD!). When I was building mine, I found that it doesn't check for accuracy of the cam sensor signal, just presence during startup. Some have used a relay to tie the disconnected cam sensor signal wire into the active crank sensor signal wire during startup, which is what I did and have used successfully for the past year and a half.
I was thinking about it last night though and couldn't see any reason why the cam sensor would need to be disconnected after starting. The actual signal from the cam sensor is used with the gas engines for checks related to fuel and ignition timing, but does not affect the gauge readout in any way after startup. It shares the same 5v power and ground output as the crank sensor, and is the same type of pickup, so there isn't any chance of overpowering and frying something.
I decided to try just directly connecting the cam signal wire to the crank sensor signal, and it worked! I managed to eliminate two fist fulls of wire, ties, and other junk in the process. "
In order to turn on the tach, the PCM needs to see a signal from the cam sensor on startup. It's common for people to make or buy two sensor wheels, one for the cam and one for the crank sensor ($400+ from JD!). When I was building mine, I found that it doesn't check for accuracy of the cam sensor signal, just presence during startup. Some have used a relay to tie the disconnected cam sensor signal wire into the active crank sensor signal wire during startup, which is what I did and have used successfully for the past year and a half.
I was thinking about it last night though and couldn't see any reason why the cam sensor would need to be disconnected after starting. The actual signal from the cam sensor is used with the gas engines for checks related to fuel and ignition timing, but does not affect the gauge readout in any way after startup. It shares the same 5v power and ground output as the crank sensor, and is the same type of pickup, so there isn't any chance of overpowering and frying something.
I decided to try just directly connecting the cam signal wire to the crank sensor signal, and it worked! I managed to eliminate two fist fulls of wire, ties, and other junk in the process. "
It also appears the computer doesn't even care if the camshaft signal stops after startup, but again, it seems there is no reason to not leave it there.
My check engine light will be on, of course, but I'll just pull the bulb.
I'm going to lose cruise control and likely ESP will be strange, but other than that I hope everything functions as normal (air bags, lockers, a/c, etc.)
I checked the factory service manual for the JK, and both the crank and cam sensor have exactly the same wiring (5v supply / sensor ground / signal) so I can't see how connecting them together will hurt anything.
Does anyone here have first hand experience doing this on a JK?
Thanks very much,
-Dan
#2
09-10-2015, 06:21 PM
Not on a JK. I tried Red's piggyback to crank signal method on my '98 xj and it did not work for me. I had success with a fakey cam signal with a very simple glued magnet set up and shooting at the existing cam sensor.
I don't see much in the $ cost factor. You already have both cam and crank sensors. Sounds like you are already using the stock OE crank sensor in the stock position? I guess depends on your transmission choice. So all you need is a tone for the cam sensor either accurate, fakey, or piggybacked into the crank.
have fun
I don't see much in the $ cost factor. You already have both cam and crank sensors. Sounds like you are already using the stock OE crank sensor in the stock position? I guess depends on your transmission choice. So all you need is a tone for the cam sensor either accurate, fakey, or piggybacked into the crank.
have fun
#3
09-10-2015, 06:27 PM
Thanks for the info.
We made the adapter before we realized it needed to be heavily recessed to fit the crank sensor in the stock location, so we're going to have to run a trigger wheel on the front of the engine somewhere for crank.
I'm interested to hear if anyone has "faked" the cam sensor signal on a JK, and how they did it.
Thanks,
-Dan
We made the adapter before we realized it needed to be heavily recessed to fit the crank sensor in the stock location, so we're going to have to run a trigger wheel on the front of the engine somewhere for crank.
I'm interested to hear if anyone has "faked" the cam sensor signal on a JK, and how they did it.
Thanks,
-Dan
#4
09-10-2015, 06:30 PM
I had to recess my crank sender into the bell housing as well, and cut notches into the Kubota flywheel which is a lot smaller diameter than the jeep. just trim the mounting ears off make a drop bracket and set the clearance . Are you using a stock transmission?
Last edited by dieselxj; 09-10-2015 at 06:36 PM.
#5
09-10-2015, 06:37 PM
The problem is the adapter we've made doesn't allow the crank trigger ring to fit over it - and to make it fit we'd have to machine off a large chunk of adapter, and completely change how it's all constructed, basically starting again.
At this point we've decided to just go for a wheel on the front of the engine for the crank.
-Dan
#6
10-28-2017, 10:07 AM
#7
10-30-2017, 08:00 AM
Wow, that conversion looks factory, nice work!
Sorry, my engine blew up before I ever finally sorted out the tach and computer issues.
I was just doing what all the 4BT guys do, and I see no reason it would not work.
Good luck, I'd love to hear about the mileage you get with that engine!
-Dan
Sorry, my engine blew up before I ever finally sorted out the tach and computer issues.
I was just doing what all the 4BT guys do, and I see no reason it would not work.
Good luck, I'd love to hear about the mileage you get with that engine!
-Dan
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