1998 Pontiac Grand Prix Engine swap

JECLARK1982

MEMBER
1998 PONTIAC GRAND PRIX
6 CYL
FWD
AUTOMATIC
134,000 MILES

My original motor stoped working so I came across a 3.8l engine from a 2005 impala police interceptor with only 20000 miles. I have the 2005 motor installed and it installed rather easily. My problems lie with not getting any spark. I have tried both computers and neither provides any spark. I have not installed the 2005 wiring harness because it appears to be the same. Can the problem lie with some of the 2005 sensors not being compatabile with something from the 1998. Any help would be greatly appreciated

6 Replies

MMPRINCE4000

MECHANIC
8,549 POSTS

Call a local junk yard and see if the 98-05 can be swapped.
If they are not listed, then you will most likely have to swap the harness.

When you consider an engine swap, it is a good idea to call a junk yard to see if they are listed as interchangeable.

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Wednesday, January 7th, 2009 AT 5:45 PM

JECLARK1982

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3 POSTS

I have found they are not 100% compatabile. If I change the wire harness, can I expect any other problems? Any idea how much a shop will charge me for this job? If I do this myself can you offer me any suggestions into what quirks I need to look into.

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Wednesday, January 7th, 2009 AT 9:56 PM

MMPRINCE4000

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I will be honest with you, this will probably be a large undertaking. You are going to have to "marry" the two harnesses' together.

You will probably be better off removing the doner harness (everything) from the 05 and start from scratch to the 98.

What you may try is calling a company like Painless wiring and ask the techs if they make (or can make) a harness that will integrate the two together.
You may have to provide them with a schematic of both harnesses'.

There are custom shops that make complete harnesses' but they tend to make them for more popular swaps.

I would not want to guess at the cost.

I will foward this to a moderator who has more electrical experience than I.

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Wednesday, January 7th, 2009 AT 10:57 PM

MMPRINCE4000

MECHANIC
8,549 POSTS

One approach is to remove all sensors, manifolds, everything from the 98 and transfer to the 05. The harness should then plug in, but The 05 is a different series than the 98, so there may be some (or many differences between the two). So strip the 05 down to the longblock and put it back together with the 98 manifolds, sensors, alt. AC compressor, fuel rail, EGR, exhaust etc.

Not trying to be vauge on this issue, but generally, when you swap engines, they are generally interchangeable for 1-2 or 2-3 years, in other words, you could probably swap a 99-01 with much fewer problems, but when you skip 7 years you are pretty much in experimental mode.
Also you generally want to swap a transverse engine into a transverse application, not a longitudinal engine into a transverse.

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Thursday, January 8th, 2009 AT 7:46 AM

JECLARK1982

MEMBER
3 POSTS

We took everything but the crank position sensor and ignition coils off of the 98 and put it on the 2005motor. We then put the 2005 motor in. The cranksensor is very difficult to change and will require us to almost remove the whole engine again. We have been debating wether we should do this or go another route. We are considering buying another motor from a 98 which will have undoubtedly have high miles. The original 98motor has been junked. Ideally we only want to pull the motor one more time. We used a code reader and it said bad ecm.