4.2 to 4.0 swap almost done; starts but shuts down - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-12-2002, 11:40 AM Thread Starter
 
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4.2 to 4.0 swap almost done; starts but shuts down

OK, it's been awhile since I've been here, when did this new software show up? And why did I have to register again? grrr.... But then I didn't like the old format anyway, maybe now I'll visit more often.

Nevermind that [img]images/icons/wink.gif[/img]

Here's the issue with my buddy's swap:
A buddy just swapped his 4.2 in a '79 CJ for a 4.0 from a '94 GC. Computer is wired
in, O2 sensor, CPS on new damper. Fuel pressure is correct. Engine starts, runs for
2 seconds, then shuts down. Adding fuel to the throttle body will keep it running. It
seems that the injectors are shutting down from the ASD relay.
The VSS is not hooked up, we think it should stay running without the VSS.
The other thing is that when he heard this engine run at the boneyard, it did the
same thing while still in the GC. The guy said it was the Sentry Key, he had to lock
then unlock the door with the key, then the engine ran fine.
So, if it's not the VSS, is it this sentry key crap? Any ideas on how to get around
that? I've heard one recommendation to dump the GC computer for an XJ or YJ computer, the pre-OBDII computers should be the same except for the sentry key stuff. Is the sentry key only on the GC? Is there any way around it?
Thanks,
Lynn
'71 UNIVRSL
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post #2 of (permalink) Old 04-12-2002, 12:19 PM
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Re: 4.2 to 4.0 swap almost done; starts but shuts down

Hey Lynn,

Welcome Back....

Here is a link describing Chrysler's sentry key system:
http://www.1-800-pdq-keys.com/sentry_key.htm

Good Luck,
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post #3 of (permalink) Old 04-12-2002, 12:28 PM Thread Starter
 
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Re: 4.2 to 4.0 swap almost done; starts but shuts down

Thanks for the link, (and the welcome back [img]images/icons/smile.gif[/img] ) but the link says Senrty Key was '98/up.
This 4.0L came out of a '94.

Hmmm, if that link is correct, then it shouldn't be a Sentry Key issue. But, my buddy saw it work on the original GC before they pulled the engine. It started then stopped, the yard man had to get out, lock the doors, then open the doors with the key. After that it ran fine. If not Sentry Key, it had SOMETHING to do with the security system. Any ideas??
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post #4 of (permalink) Old 04-12-2002, 02:23 PM
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Re: 4.2 to 4.0 swap almost done; starts but shuts down

Lynn, welcome back... long time no hear!

As to the engine... humm... the fuel pump comes on for 2 seconds and shuts down... so it's being told to shut down for a reason. You need to find the reason or jury-rig the 12 volts to the fuel pump to work off another source... which wouldn't be too hard... like the oil pressure feed voltage. This point is hot at all times and is unaffected by the moving the key from one mode to another. I'm suspecting that there is a mis-wire on the computer "Keep alive" memory voltage. So when you move the ignition from Start to Run the circuit's interrupted and the computer becomes brain dead, halting the fuel injection and the igniton..
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post #5 of (permalink) Old 04-12-2002, 07:07 PM
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Re: 4.2 to 4.0 swap almost done; starts but shuts down

It's not the century key, it is the VTSS, vehicle theft security system. The Door lock module supplys an input to the pcm to allow the injectors to continue to work. You will have to change the pcm. You can verify this with a scanner. Go to the page that says security and see if it is on. Once it has been turned on, there is no way to shut it off. You are going to have to change the pcm to make it work. One from a Grand will work if it didn't have the VTSS turned on. Your best bet is having the guy at the yard swap it out for one from a '94 or '95 YJ or XJ. Get one from a 5 speed, it should rum better and not set false codes for torque converter lock up.
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