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Discussion Starter #1
I have a 2000 s10 zr2 blazer with the 4.3L Vortec
Only code is P0303
Due to low pressure issues and backfiring I picked up the engine and transmission out of a 80k mile 2000 gmc jimmy and my father and I swapped both in. We replaced all spark plugs and plug wires, new cap and rotor, complete fluid and filter change and after starting it up have a persistent cylinder 3 misfire. We have swapped spark plugs and plug wires and ruled those out. Checked fuel pressure and it's getting about 56psi of fuel running. We are debating swapping the fuel spider but I figured I would see if anyone else can maybe help us pinpoint this issue.
As I said before the old engine had a backfire if you revved it and let off, but I never diagnosed what it could be as the low oil pressure made me think I'd be better off getting a new motor(figured this one was worn out), but this has my dad thinking the issue is electrical and could have been part of the issue on the last motor and now this motor. We kept all the old wiring and modules.
Would a bad injector be a likely culprit, could it be distributor related even with the new cap and rotor (distributor shaft off the new engine)? Is the new motor not playing nice with some computer systems? Could a Vacuum leak cause this (We believe everything is hooked up right)?
The parts place that sold us the motor and transmission claimed they had the vehicle running and driving and it was perfect and they seem like a reputable place (Vehicle was only being parted out because of impound fees being more then the value of the vehicle or something), I'm really hoping it's not low compression in that cylinder but we haven't ran a compression test yet.
I'm not very knowledgeable when it comes to this stuff, my dads the shade tree mechanic not me and he doesn't have a whole lot of spare time to mess with this and he's not very good with electrical issues.
Would appreciate if anyone could point us in the right direction.
Also not sure if this is the right area to post this.
 

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Hi Patchett ,
I would definitely make sure the battery is all charged up & then use a good screw-in compression tester & test compression in all cylinders !
You have to have a good
foundation to stand on !! The next step could be doing a thorough fuel pressure test , this will be a solid foundation , knowing were those 2
tests take you .
 

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Discussion Starter #4
Hi Patchett ,
I would definitely make sure the battery is all charged up & then use a good screw-in compression tester & test compression in all cylinders !
You have to have a good
foundation to stand on !! The next step could be doing a thorough fuel pressure test , this will be a solid foundation , knowing were those 2
tests take you .
I can't do anything this weekend but hopefully monday we can try swapping the injector spider and maybe a compression test if that doesn't fix the issue.
 

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Been there Done it
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Did the old engine have a P0303 or just the new one? Have you done a Crank Sensor relearn? Your PCM needs to be in sync with the CKP sensor.
Did the newer engine come with the spider in it or did you swap in the one from the old engine?
One very common cause of a single cylinder misfire is a faulty new spark plug. Or the nut on the end of the wrench cracked the plug while installing it. We've all done it. Particularly on #3 because it is so hard to get at. Try looking at it in total darkness, if anything on that cylinders secondary electrical system is faulty you'll probably see it.
 
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Discussion Starter #6
Did the old engine have a P0303 or just the new one? Have you done a Crank Sensor relearn? Your PCM needs to be in sync with the CKP sensor.
Did the newer engine come with the spider in it or did you swap in the one from the old engine?
One very common cause of a single cylinder misfire is a faulty new spark plug. Or the nut on the end of the wrench cracked the plug while installing it. We've all done it. Particularly on #3 because it is so hard to get at. Try looking at it in total darkness, if anything on that cylinders secondary electrical system is faulty you'll probably see it.
Old engine had low oil pressure issues and a backfire issue, but I never diagnosed what was wrong with it. New engine has the p0303 cylinder 3 misfire. The old engine didn't vibrate and shake nearly as bad as this new engine with the misfire. It's possible the old engine also had a misfire of some kind but we yanked it out before I checked.
We replaced one sensor (I believe crank, I just fetch and hand tools not fix stuff) when the old engine was in because I had some crank/camshaft sensor position error code but that did not fix the problem and a new distributor did. We never did a crank relearn because it seemed to run fine (until the low oil pressure issues started). We unplugged everything and pulled the old motor and popped the new one in and hooked everything back up, so It would still be using the sensor we replaced I believe.
It's using the spider that came with the pulled engine, which has about 84k miles on it and I believe it to be original. I have the spider from the original motor still.
We inspected the spark plug and it seemed fine but we swapped spark plugs from one of the other cylinders that was firing fine and it did not fix the issue.
Alright so I guess I got my checklist, I actually ordered a new spider (conversion kit to MPFI, figured I might as well) and when that gets here It's going in. If we are going to have to mess with the spider anyway I would rather have a brand new part. My father was adamant when we installed the sensor it did not need a relearn but everything I'm being told and seeing online says otherwise (is it possible to be close enough to run ok but still cause issues?) so I assume even if the new injectors fix my issue I should bring it to someone to do a relearn.
 

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Discussion Starter #7
So got the fuel spider and went to pull it into the garage sunday to change it when I found my vehicle completely dead. Went to jump it and what do you know, the negative terminal is loose enough to fall out. Tighten it a bit and realize the battery is basically stripped out (only like 1.5 years old) but it starts up so we move it to the garage, still chugging away and shaking from the misfire. We swapped the fuel spider and tightened the terminal as much as possible as it had come loose again and got it pretty secure and started it to find the motor running perfect, absolutely zero vibrations and smooth as can be. No more misfire. We're still not sure if was the fuel spider or the bad ground that fixed it (We're leaning towards ground which makes me feel like a real idiot for not noticing). Took it for a test drive for a few miles including a mile on the highway at 70 and the issue still hasn't came back so I'm happy. Just gotta go get a new battery soon.
 

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Mr Goodwrench's Evil Twin
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Particularly on #3 because it is so hard to get at.
I unbolt intermediate steering shaft at steering box... #3 isn't a pain that way ;)
We're still not sure if was the fuel spider or the bad ground that fixed it (We're leaning towards ground which makes me feel like a real idiot for not noticing).
It was the spider that fixed it. A bad ground like that isn't going to cause a misfire on a single cylinder. Those spiders are a common failure too. And yes, like oldeerslayer said, the CKP needs a relearn. It needs to be relearned anytime the CKP sensor is replaced, the engine is replaced or the PCM is replaced.
 

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Discussion Starter #9
I unbolt intermediate steering shaft at steering box... #3 isn't a pain that way

It was the spider that fixed it. A bad ground like that isn't going to cause a misfire on a single cylinder. Those spiders are a common failure too. And yes, like oldeerslayer said, the CKP needs a relearn. It needs to be relearned anytime the CKP sensor is replaced, the engine is replaced or the PCM is replaced.
The motor has 84k miles on it so I figured it might be the original spider, and that after almost 20 years it might be suspect. The parts yard did claim they test drove the vehicle it was in before they parted it out and it ran "perfect", hard to believe if the fuel spider was bad....
Back to the CKP relearn, apparently it's the sensor that came with the new motor and we didn't touch it, just swapped the new motor in and hooked it up. Considering we have the pcm original to my vehicle with the new motor and CKP I still need to go get it relearned I assume? I'll have to call around and see if the garages near me can do that.
 

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Mr Goodwrench's Evil Twin
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Back to the CKP relearn, apparently it's the sensor that came with the new motor and we didn't touch it, just swapped the new motor in and hooked it up. Considering we have the pcm original to my vehicle with the new motor and CKP I still need to go get it relearned I assume?
You assume correct, it still needs to be relearned
 
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