Backfires

Tiny
CHADPAM3944
  • MEMBER
  • 2000 CHEVROLET IMPALA
  • 3.4L
  • V6
  • AUTOMATIC
  • 170,000 MILES
I have a 2005 3.5L out of Saturn relay I bought engine to replace my worn out 3.4 in my 2000 Impala. I changed the plenum and fuel rail and injectors and all the sensors to use the Impala 3.4 engine wiring harness and now it backfires. Do I use the 3.5 crank sensor on the back of the motor or can I use the 3.4 crank sensors? How do I wire the 3.5 crank shaft sensor to the 3.4 engine harness for engine to run?
Sunday, March 31st, 2019 AT 8:33 PM

6 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

It looks like the two different engines use two different types of strategies for their Camshaft Position Sensors (CMP)(s). The answer here is to run the original 3.4L CMPs to make not only the wiring harness, but more importantly the Power-train Control Module (PCM) which is going to use the information any ways, to work effectively in providing Electronic Fuel Injection (EFI) control. I have included the descriptions of the two different CMP operating systems in the diagrams down below for comparison.
Get back to us with how it turns out or if you have additional questions, please, don't hesitate to ask. That's what we are here for.

Thanks,
Alex
2CarPros
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Monday, April 1st, 2019 AT 10:48 PM
Tiny
CHADPAM3944
  • MEMBER
  • 4 POSTS
Well I did use the original 3.4 cam sensor because it was new. I think it was like $35.00 I paid for it the cam sensor in 3.5 was made different it came to an almost point like shape. When I change them around I thought this shouldn't be an issue and put new 3.4 cam sensor in its place. The crankshaft sensors are completely different though my 3.4 has two crankshaft sensors one under harmonic balancer and one back of the engine. This is where my problem is this crank shaft sensor has two wires to run to ignition module the 3.5 crank shaft sensor has three wires and also it is maybe a half inch shorter than the 3.4 crank shaft sensor. The three wire sensor ran to the engine wiring harness somewhere in the Saturn relay. The coil packs are made completely different from each other.
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Monday, April 1st, 2019 AT 11:41 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

You can also tear out the 3.4L wiring harness and PCM and replace it with 3.5L wiring harness and PCM, This is really going to be your only solution short of fabricating your own CMP's.

Thanks,
Alex
2CarPros
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Tuesday, April 2nd, 2019 AT 11:29 AM
Tiny
CHADPAM3944
  • MEMBER
  • 4 POSTS
If I can't figure I'll haul it to the scrap yard. I will not put anymore money into it. I'm already flat broke with no money not even change. But thanks anyways.
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Tuesday, April 2nd, 2019 AT 7:23 PM
Tiny
CHADPAM3944
  • MEMBER
  • 4 POSTS
Update: The 3.5 is not backfiring now. Turns out that the 3.5 lower intake manifold was causing the backfire. I took it replaced it with the 3.4 lower intake manifold no more backfire. Now it's turning over like normal, but doesn't crank. Changing 3.4 sensors around tomorrow praying it cranks and runs prayers it does. I bought this car last year three months after I bought it, head gaskets blew, down for six months I fixed it three months after the first repair. Original motor started to knock finally found a suitable motor after four months. I pray I'm on the road again. Scwickedstang thank you for all the help you are offering.
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Tuesday, April 2nd, 2019 AT 10:48 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

I understand how frustrating it can be to do a project like this. It seems like you will get one problem ironed out and then two more will pop up. I have gone through the same frustrating, aggravating problems on rebuilds more than one person should have to go through in ten lifetimes. Keep your head down though, and if you need to walk away for a day or two. Sometimes a fresh perspective will make all the difference in the world. It sounds like you are getting close to the finish line though, and we will always be here to help, so you have a friend to help, and that's always a good thing.
I'm pretty confident that it will make a huge difference when you swap these guys as they are two completely different strategies on how to get the same thing done. Keep us in the loop and let us know what we can do to help.

Thanks,
Alex
2CarPros
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Wednesday, April 3rd, 2019 AT 1:01 AM

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