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-   -   4.2 carb to 4.0 FI swap - starts, won't run (http://www.jeepforum.com/forum/f12/4-2-carb-4-0-fi-swap-starts-wont-run-1465370/)

JunkyardJeep 01-18-2013 07:02 AM

4.2 carb to 4.0 FI swap - starts, won't run
 
First of all I would like to thank Joe Dillard for pointing me in the right direction.
I recently swapped out the 4.2 carb. engine for a 4.0 FI engine. I installed the engine, trans., t-case, PCM, and all necessary harnesses & sensors from a 93 ZJ. The engine starts, but stalls almost immediately. It has proper fuel press. and spark. My research has led me to the possibility of needing a security module from the donor vehicle. My questions are as follows:
Do I need a security module?
Does it have to be from the donor vehicle, or can I get one at the junkyard?
Can the security module be by-passed?
Any advice/help will be greatly appreciated. Since this is my DD, and I am currently using my wifes vehicle, time is definitely a factor.
Thanks, Rob.

Mark05059 01-18-2013 07:53 AM

Yes your probably dealing with the security system thats in the ECU. There are 2 pins on the ecu that need to be grounded to get around it. Ill see if I can find the thread. Que may chime in on it before I get back.

skyj 01-18-2013 09:08 AM

have you read cevans thread on this. I know he mentions somewhere in there which wires they are.here is a link.http://www.jeepforum.com/forum/f12/4...build-1114875/

Mark05059 01-18-2013 09:23 AM

he is using an xj harness which doesnt use the security system. It does show which pin to ground if you have an auto trans however. Unless I missed it, I dont see a reference to the security system issue.

JunkyardJeep 01-18-2013 10:28 AM

Found the two wires, cut them where they come from the PCM, and connected them together on both sides like the thread explains and still the same. Starts and shuts off. I tried connecting them at the plug ends that went through the firewall of the ZJ also and still nothing.

Que89YJ 01-18-2013 10:37 AM

Pins 26 and 46 of the ecu are the 2 wires you want to twist together. No you shouldn't need a security module. When it dies are you losing fuel or spark? Have you tried jumpering the fuel pump relay between pins 30 and 87 in the relay socket? It hardires the fuel pump on.

JunkyardJeep 01-18-2013 10:52 AM

Pins 26 & 46 are the ones I cut and twisted together. There is a slight drop in fuel press. when it starts (from 39-40 to 34-35). Not losing spark either. I was jumping the coil wire during testing and it would still start and run for a second or two even while the spark was jumping 3/8". I even tried grounding pin #30 (bk/wt) and still no good.
It does stay running if I spray starting fluid in the throttle body.
When I turn the key to the on position it's taking a few seconds to a few minutes to get power to coil and fuel pump. Not sure if PCM is shutting down power due to a security issue, or what's going on. Also blew fuse #15 30A in power dist. center. Replaced, and still same.

JunkyardJeep 01-19-2013 02:14 PM

Well, this really has me stumped. I have spark when cranking, when it kicks over, and right up to when it stalls.
The fuel pressure is correct, the pump comes on to prime the system for a second, while cranking, and right up to a second or two after it stalls. I tried to jump the fuel pump relay at pins 87 & 30 and the pump will run, but it won't even start at all.
I also don't understand why it takes up to 1-2 minutes for the fuel pump to prime after turning the key on, and I also have no spark during that time. Then suddenly everything comes back on as if it were on some kind of automatic overload or reset circuit.

Mark05059 01-19-2013 04:05 PM

ahhhhhhhhhhh... Now you tell the rest of the story.. You have bad capacitors in your ECM. Either change it for a new one or change the capacitors. You can find the link here on the forum telling you how to do it if you search for brain surgery.

JunkyardJeep 01-19-2013 05:21 PM

Thanks Mark05059! I have a spare PCM/ECM that I'm going to try. If that doesn't work, I'll use it to disect for the capacitor change. I will post results. Thanks again.

uhohthe50 01-19-2013 05:56 PM

Quote:

Originally Posted by JunkyardJeep (Post 14809753)
First of all I would like to thank Joe Dillard for pointing me in the right direction.
I recently swapped out the 4.2 carb. engine for a 4.0 FI engine. I installed the engine, trans., t-case, PCM, and all necessary harnesses & sensors from a 93 ZJ. The engine starts, but stalls almost immediately. It has proper fuel press. and spark. My research has led me to the possibility of needing a security module from the donor vehicle. My questions are as follows:
Do I need a security module?
Does it have to be from the donor vehicle, or can I get one at the junkyard?
Can the security module be by-passed?
Any advice/help will be greatly appreciated. Since this is my DD, and I am currently using my wifes vehicle, time is definitely a factor.
Thanks, Rob.

Out of curosity, how much did it cost to do the swap? When my motor goes I still don't know what I want to do... either a v8 swap or a 4.0 swap. Seems like the 4.0 would be a lot cheaper so thats why its appealing to me

JunkyardJeep 01-19-2013 07:53 PM

Quote:

Originally Posted by uhohthe50 (Post 14817215)
Out of curosity, how much did it cost to do the swap? When my motor goes I still don't know what I want to do... either a v8 swap or a 4.0 swap. Seems like the 4.0 would be a lot cheaper so thats why its appealing to me

I got the donor vehicle for free. I had to buy a harness and throttle cable from the junkyard, along with a few other minor things, but only because I got rid of it long before the swap and didn't have the forsight to keep certain parts.
I would also suggest that if you go with the 4.0 swap, you get it from a YJ that had one originally. This way all the harnesses match up. With mine being from a ZJ, I had to marry the two harnesses together... alot harder.

JunkyardJeep 01-19-2013 08:20 PM

Update on the Junkyard Jeep:
I changed the PCM with one from the junkyard. Everything fires up when I turn the key on (fuel pump, relays, etc...), But it still only starts for a few seconds, then dies. I tried keeping it running by pouring gas into the throttle body instead of starting fluid and it worked. Ordinarily that would indicate a bad TPS, but the voltage input is 5.0v like it should be, and the voltage out to the PCM is .8v closed, and 3.8v at WOT, and is smooth without spikes or fluctuations. Does anyone know if those figures are correct? I searched TPS in the forum section, but found some conflicting data.


I have no words to describe how frustrated I am right now. A feeling shared by many, if not all Jeep owners, I'm sure.

Que89YJ 01-20-2013 06:46 AM

Jumper the fuel pump relay and see if it will run and stay running. Jumper 30 to 87.

JunkyardJeep 01-20-2013 07:04 AM

Quote:

Originally Posted by Que89YJ (Post 14819546)
Jumper the fuel pump relay and see if it will run and stay running. Jumper 30 to 87.

I tried that, and it won't start at all. (see post #8)


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