99 SHO runs horrible when warmed up

[gearhead847]

Hi my name is Gavin i'm new to SHOforum and my 99 SHO runs absolutely amazing for the first minute or so after i start it but once it warms up it runs like complete crap. It has new spark plugs, 8 new ignition coils any ideas on why its doing this? Any help would be greatly appreciated thanks

 

[gearhead847]

i should also add that the cams are welded and i have a code p1414 but i heard that code is just for emissions and doesnt hurt any performance

 

[Siman]

can you describe what "complete carp" is?

 

[gearhead847]

it runs really rough and acts like it is kind of misfiring

 

[Siman]

if you have new spark plugs given they are gaped right and the cams were welded properly it sounds like a vacuum leak or MAF. Im still a bit new to the V8 though but thats what im throwing out given since the cams were welded and the V8 has hydraulic lifters i really dont think its timming since its all chain driven. What do you guys say?

 

[Daedalus]

I briefly had that problem on my '99 and it turned out to be a bad coilpack. The coilpack would spark gradually weaker as it got hot. Mine ended up being right up front and easy to change without pulling the intake. I ended up changing all 8 when the cams were welded, as you say you did as well.

Unfortunately if you're not throwing a code you're probably going to have trouble figuring out what your problem is. Does it smooth out if you raise the RPMs off of idle?

(V8 SHO engines don't have hydraulic lifters BTW. They use similar shims to the V6 engine.)

 

[gearhead847]

it is really rough until the secondaries open up. after that is smooths out but it still has a little power loss

 

[Siman]

hmm thought it had them just antoher item to add to my wall when i get my v8... but have you checked your vacume lines for leeks?

 

[Brydakidz]

There is a chance that at least one of your new ignition coils is defective. When my car started to miss i replaced all of them. About a month or two later I had the same problem again so i just took one of the old coils and swaped it with each of the front ones until I found the problem. Luckily it was in the front, and it was under warantee.

 

[gearhead847]

i think i have multiple coils goin out. there were two on the fornt that i would unplug when the engine was idling bad and they didnt make any change in idle speed. i still have to check the rears