PontiacBonnevilleClub.com

Last week I did a motor swap. The motor was a supercharged 3.8 out of a 98 Grand Prix. I dropped it in my 99 Naturally aspirated Bonneville. I have the PCM flashed and fuel codes removed. Everything is in place every bolt is counted for and every ground secured. New oil, plugs (autolites... I know not good, but tried doing this on a budget), coolant, plug wires and all the vacuum lines have been replaced. There are no leaks, and it started right up. Then the shake came. Oh boy what a shake and my MIL flashed. So I hobbled her to local auto parts store. Checked the code, and it gave me a P0300 (Random/multiple misfire). I cleared the code and have driven the car maybe 6 miles. Just to see if the monitor would put it back up and no I has not, but the misfire still occurs. Now I was suggested that the fuel pumps are different from N/A to SC. We checked the specs and the pressures read identical, but the Gallons per Hours are way different (At wide open throttle: NA: 20-30 gph and SC: 70-75 gph ). Now the question comes up, is it the fuel pump? The shake smooths out after higher rpm and faster speeds, but it's still there. It occurs at idle and everything in between. Any input, diagnosis ideas, anything is welcome, because I would like to spend as little as possible, and as things sit right now if it is the fuel pump, that's $300.... So if anyone has any ideas, please let me know! Thank you all very much.

bump for a good guy.

Jesse, I can't see the fuel pump causing the shaking issue at idle. The NA pump has plenty of flow at idle, so you probably have a spark issue.

Have you triple checked the plug wire order?

Azu had the same problem code P0300 ended up the problem was bad plug wires. How old are your wires?

He stated that new plugs and wires were installed on the swapped engine.

I also had the same problem when I dropped my engine into my 00. I had the plug wires crossed. Like Andrew said, make sure you triple check them. Do you know anyone who has a tuner or an aeroforce so you can see which cylinders are misfiring?

Jesse texted me and stated that he used an NA flexplate on the L67 he dropped in. Thats a problem. He needs to get an L67 flexplate, right?

I don't know what the differences are, as I have never dealt with a series II L36 but they do have different part numbers. Whether that could cause the misfire problem is another question. I'd say it is possible.

hahahaha, none of you remember when Boosty swapped an engine into his '97, do you?
Does it sound like this?
http://s20.photobucket.com/albums/b246/ ... I_1706.flv

Ok guys, finally got to my computer, here's what went down in full today. And thanks Andrew for relaying all the info and bumping my thread

petraman do you happen to have a link to the post regarding his video? OR even just a general description? Thanks!

The plugs are new. All the wires run to the correct spot and everything has been checked over and over again. All the injectors are hooked up, and plugs are new and gaped correctly. Now when I started the motor it shook, and then after letting it warm up to bleed the cooling system, the mil flashed, indicating my Type a misfire. Well as I said I got it to the parts store. Cleared the code, and it has not yet come back on. So I was confused, it shook, misfire right? (And this isn't a small shake, billboost's video is very similar to what mine does. It shakes a a consistent frequency at idle (almost like the car is camed and loping) and when I speed up it masks it cause of the high frequency.) Well not the case. The monitors have all ran, and I'm going with it just missed since it hadn't been ran in a while.

When I pulled it in, our shop teacher, said there's no misfire. Said listen, she sounds perfect. And I noticed, though it shook I didn't hear a misfire, or power loss, and I felt the exhaust fumes, and there was no missing showing up there. So we checked with a Tech 2. Nothing no misfires of any kind on any cylinder, past or present. The only off thing was my fuel trims, but they were still within parameters....

SO he started asking me questions, and finally brought up the flexplate, and I said I used the one from my NA motor. He said the SC motor should be weighted different to account for the power difference. Sure it has balance shafts inside, but that doesn't fix everything. And if the flexplate I put on was bolted on incorrectly, then of course it's gonna shake. Sure it's a fetch out there, but I can't hear any chain or anything rattling around for the balance shaves to be broken. Gm lists two different part numbers, so does our local parts stores, and Andrew verified that the flexplates are different. So I think this would be the best route to go first, cause if it's not right, at least the right part is in there. If you guys think otherwise let me know, I'm welcome to all suggestions. I mean doing this flat back in the garage doesn't put me next to a gm tech so everyone's input is truly appreciated, and helpful! Thanks!

Yeah, sorry, I was trying to look for an explanation but I'm in the midst of studying for finals so I kinda dozed off... What happened was that the flexplate was rotated 180 degrees and that disrupted the balance of the engine causing the vibration.

Also, the balance shaft is run off of a gear from the cam gear.

Thanks petraman! I think let alone it being the wrong flexplate, I wouldn't be surprised if I placed it on wrong...I was in such a hurry Well I have one coming and should be here by the weekend. I'll put the correct one in and report back on my shake. I still plan on swapping those fuel pumps. It may get me by, but I'd prefer to put myself in the best position for (slight) performance tuning.

And 00Beast, thanks for the info. I guess I just assumed they were chained. I haven't dissembled a 3800 before, so my knowledge is slim on the internals. I plan on changing this now that I have a motor to tinker with. My next swap plans to come in five years with a complete rebuild and a turbo setup. But those are future plans and now is focusing on getting this running properly ha. But again thanks man!

Flexplate shipped. That sucks you have to pull the engine again.

I'd definately have that new fuel pump in before any WOT runs. You will run lean real quick with an NA pump.

Very nice, thanks man!
And no real serious pulls yet, I'm willing to be patient lol

Good luck, man. I wish I had the balls to swap an engine, the last time I tore apart my car, it ended up sitting in a friend's garage for a week... (thank you parents of Gonneville, lol). If anything came from my post, just remember to triple check the installation of the flexplate.

Definitely swap that pump unless you want to pull the engine yet again for popped pistons.

my engine shook really bad once before and i thought it was a miss...luckily i work in a gm dealership and had them check it out, come to find out it was a bad injector making the engine rock like that and it was shaking really hard, put the new injector in and it runs great

are we sure this is a flex plate problem? The series II/III Plates are interchangeable IIRC, what will matter is the Torque converter size... what you should have right now is a 245mm and what you may get is a 258....

I am not 100% the flex plate is your problem...

Well I got everything back in and started it up yesterday. The shake is gone. It runs perfectly now, with the exception of the fuel pump. I did figure somethings out though!
1. The flexplates have different weights on them.
2. The torque converters are different depending on the motor (L36 or L67). I got the flex plate bolted to the motor and dropped the motor in, got the trans bolts and engine mount all secured. I went to bolt up the torque to flexplate and it wouldn't fit. The holes on the flex plate were closer to the outside of the flexplate than the N/a flexplate. As as result I couldn't even thread the bolts in the torque converter. Pulled the motor back out die grinded the holes a little longer to fit, and problem solved....

Wow, sounds like a lot of work, but I'm glad you got it figured out.

Still havent found a pump, sorry. Maybe put up a wanted ad here?