Engine frustration- help

[tiger9297]

Just built a 388 stroker for my '90 K5. 9.5:1 compression, XE262 cam, Vortec heads, and Howell MPFI. We have tried everything, but it just won't run right. It's doesn't idle smoothly and when you crank it you have to give it some gas to make it run. Running down the road it seems to smooth out and do ok. Timing is currently set at 9*. Everything on the truck is brand new except the starter and the alternator. The only thing that seems to make a change is unplugging the MAP sensor. Sometimes it will crank right up and idle smoothly when it's unplugged. However, after it warms up it won't idle at all with the MAP sensor unplugged. Does anyone have a clue what could be wrong with this thing? Oh yea, Howell burned a new chip for it.

 

[odin]

Have you contacted Howell? Is the chip correct for your combination? Sounds like its running rich.

 

[tiger9297]

I called Howell and they told me to check the "block learn number", which we did and they were perfect. I have no idea what that is other than I think it tells whether the engine is running too rich or too lean. It's almost like it's a different engine each time you crank it. Yesterday it ran decently well. Try to go out and crank it this morning and it will hardly run at all, blowing smoke everywhere. What the heck happened? It just sat there all night and now it runs completely different. GRRRRRRRRRRR!!!!

 

[shaun89]

damn computers! but it sounds like a nice engine though, check you plugs and see if its running rich or lean. maybe trying doing some timing changes. if there is a hot rod/muscle car shop near you, they can re-curve your dizzy so it will work with the cam and vortec heads. i had to get mine done. they actually cut off the vac. advance and curved it all just with weights. runs a lot better now. if you do,do that, make sure u tell them that you have vortec heads, because they change the number of total timing degrees. other then that, maybe a vacuum leak? intake manifold leak? throttle body leak?

 

[mnstrburbon]

I would get a pyro or a wide band then you can see if it is rich or lean and at what point in the power band.
also i would check for vacume leaks, try spraying starting fluid wd-40 or some thing around mating surfaces intake throttle body so on.
check all the grounds espically motor to frame and cpu.