Need help! idle and breaking up on acceleration problem

[beamer]

I have a 97 GTP and it was running great, but I broke a flex plate and after re installing the engine It idles rough. the motor shakes, but I can't tell if it is misfiring. It is not throwing any trouble lights, of course. the car runs smooth on normal driving but under any acceleration it breaks up, and sounds like it is making a sneezing noise. That is the best way I can describe it. It seems like a vacuum leak or something, it is only getting 13-15 pounds of vac at idle. I tested all the plug wires, and it has new plugs and air and fuel filter. I put a brand new supercharger gasket on it today hoping that would fix it. It has the newer metal lower intake gaskets.
The mods on the car are SLP headers, cat and magnaflow exhaust. short ram air intake, Gen V supercharger, 3.2 pulley, 42 lbs injectors, Intense racing PCM, 150 degree thermostat, 8mm plug wires, autolight plugs.
The car is a 97 GTP 2 door with 97k

Any help would be greatly appreciated but its driving me insane and about to go for a tour on craigslist.

[Fivefingerdeathpunch]

Can you run a smoke test to check for any leaks?

[beamer]

I don't personally have one, or know anyone with one around me. I tryed the old starter fluid trick hoping to get a spike in RPM, but I cant get it to rev up anywhere. I also put new gaskets on the TB and adapter plate just as a long shot, and the EGR is blocked off so its not that tube. And I did check the MAP and other sensors on the top of the car.

[Fivefingerdeathpunch]

A scanner or something like a aeroforce gauge or tuner can watch fuel trims. If the trim changed when you sprayed the fluid, you'd find a leak. Sometimes the rpm will never jump.

It's kinda hard to diag alot of problems without being there or without a data log file to watch stuff.

[Scottydoggs]

did you spray the starting fluid right into the TB? if so you may have killed the maf.

try unplugging it, then start the car, see if it runs better. if so the maf is bad.


make sure all your plugs are plugged back in and all grounds are bolted down tight and that no wires got damaged during the work.

[BillBoost37]

When you say the motor shakes.. can you describe it a little better?

When you swapped the flex, did all of the 8 bolts start easily by hand and then they all kept going in easy by hand?

[beamer]

I will have my buddy check out the fuel trims with the scanner, thanks for that Idea and check all the grounds and stuff again. The engine shakes back and forth and you can feel the vibration in the entire car. As far as the flex plate bolts go, I think they all went in normal. Does it only go on in a certain way, and could I have put it on wrong causing the weights to be off and possible out of balance? And if so would that cause the breakup at acceleration and weird noise it makes? it seems like that would just be a vibration issue (still important) but I don't know how it would effect the other stuff.
Thanks for the ideas I will let you know what I find. I might pull the motor back out today and investigate.

[BillBoost37]

Reason I asked the way I did is....because I had a trans done at one point..and flex swapped etc. When I tossed the flex back on the motor.... I was able to get the bolts to thread in 180 degrees off. One hole was egged slightly allowing it to happen. All it takes is one fuggin hole.

I was searching for the vid of it. Hilarious headlights bounce up and down at idle.

[beamer]

Now I am concerned lol it does shake pretty good, and i dont believe it is misfiring....... dang
Also the maf is good checked that and no i didnt spray it directly with carb cleaner

[beamer]

Could the flexplate installed wrong cause the other problems?? I really dont want to pull the motor again, but if you guys think that could be doing it its worth a shot I guess.

[BillBoost37]

Found it!

[BillBoost37]

I never revved/took it off the jackstands. Yes..that vid shows about 1/4 of the actual speed it was happening and it was on jackstands.

Here's where I marked the flex and crank. Undid the bolts.. found where they lined up


Here's where that flex mark ended up


I undid it all..lifted enough to get to the flex bolts. The key here is .. that was in a Bonneville where there's room to push the engine about 4 inches to the passenger side. I'd probably think of some reason to pull the trans and subframe and do it that way.

Here's a w body with trans out

[beamer]

thanks for the help, I am pulling the motor out now to see if i can find anything suspicious and at least I will have piece of mind that that is not the problem.

[beamer]

Hey guys. we got it fixed. turns out one of the rear spark plugs had a hairline crack in the porcelain. (I pulled the motor to discover this so if you want to laugh its understandable. But I got some wiring cleaned up and looking and routed better while I was at it so it was not a complete loss. But she is up and running. LOTS of boost :0 thanks for all your help and input.!

[Scottydoggs]

buy your self some spark plug sockets, they have a foam insert, helps keep the plugs from breaking.

and damn that blows.