Swapped engines,won't start...

danm

New member
Oct 17, 2021
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I put an 02 engine in my 03 2500HD. It starts and immediately shuts off. I also put in a different 03 Allison at the same time. I didn't change any control modules. Any help would be appreciated.
 

TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
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Mid Michigan
Used all the 03 sensors/wiring harnesses?
Crank/cam sensors plugged in correctly?
Checked all the pins in the bale connectors and made sure they arent pushed in, not making contact?
Are you getting any codes?
 

danm

New member
Oct 17, 2021
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We used the original 03 wiring and sensors that were in the truck. I will check the connectors. Do you think Im good on the ECM and TCM? Im getting tons of codes from the old motor and trans.
 
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TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
14,119
344
83
Mid Michigan
Used the 03 ECM/TCM/FICM, too? Cam/crank connectors can be accidentally swapped, so if you have a crank/cam code...look there.
Try to list whatever codes you can. It'll help us a lot. Right now, its just a shot in the dark.
 

bimmer95

Member
Mar 15, 2019
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Morgantown Pennsylvania
I don't think the engine will fire if there's a vats issue but could be wrong. With the key on engine off does the security light on the dash go off after a few seconds? What does the fuel rail pressure desired vs actual do when this happens?

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dndj

Boost!
Apr 13, 2019
292
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Oregon
Since the truck was an 03, and the OP stated all the original ECM, TCM, etc modules remained in place as the 02 engine was swapped in, I'm not thinking VATS since that normally only causes trouble (start, then die like James said) when the ECM and BCM aren't properly paired.

OP, please provide the DTC codes which would give us a better place to start helping.
 
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rfletes79

Active member
Mar 5, 2010
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Galt, Ca 95632
If you kept the original ecm with the truck then the vats, anti-theft, should NOT be an issue.

If, on the engine you installed, you installed the engine harness or the cam &crank sensors, you may have those transposed. The sensors OR the connectors. Those need to be correct for the engine to run. AND it’s possible to mix theses up. AND it will cause this issue.


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rfletes79

Active member
Mar 5, 2010
589
56
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Galt, Ca 95632
I read your post again, looks like you installed the engine harness, as the 02 one is different. In the process of installing the 03 harness you plugged in the cam and crank sensor, or you should have. Check those connections at the cam and crank sensor. Your issue is there. No doubt.

They’re either not connected or transposed. Or the sensors are in the wrong position.


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danm

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Oct 17, 2021
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The harness from the 02 engine was used, everything plugged in. We are getting 100+ codes mostly transmission related which I feel are from the old transmission. Here are a few codes, u1000,B0105, on the powertrain system I've got 50 codes on the transmission and 50 codes on the engine. Where are the crank and cam sensors located?
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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The harness from the 02 engine was used, everything plugged in. We are getting 100+ codes mostly transmission related which I feel are from the old transmission. Here are a few codes, u1000,B0105, on the powertrain system I've got 50 codes on the transmission and 50 codes on the engine. Where are the crank and cam sensors located?

you need to start by putting the correct 03 harness on the engine. thats part of your issue. lots of things changed from 02 to 03 electrically.
 

danm

New member
Oct 17, 2021
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Even though it all plugged in it still needs to be changed? Do I need to change the electrical box that has the fuel lines hooked to it also?
 
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danm

New member
Oct 17, 2021
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UPDATE while beginning to remove the wiring harness from the 02 motor a connection was found not connected. We put them together and it started up and runs great. It still has the 02 harness in the 03 truck.....
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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1,101
113
Phoenix Az
UPDATE while beginning to remove the wiring harness from the 02 motor a connection was found not connected. We put them together and it started up and runs great. It still has the 02 harness in the 03 truck.....

good for you and glad its running.

the lack of detail in these posts and lack of understand about what we are talking about makes this very hard for us to do much over text. at the end of the day, we dont know what you did, touched or if what you are saying is exactly whatyou are interpeting as to what is done. in the end, if you figured it out, thats all that matters!
 

danm

New member
Oct 17, 2021
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Now with the engine running, I took it for a test drive and the transmission is in 4th gear I believe, and it bangs when you put it in gear. Code po700. Thanks for all the suggestions and help for getting this far.