engine likes to buck

[lincster2]

Hey there... my 92 mtx was knocking, knocking really badly, loudly banging. I guess 1 too many races to the redline done her in. So I bought a used engine from a local wrecking yard. Had my mechanic compression test it, all good so out with the old and in with the new....well new to me. This engine seems to run a little rough..just like the old engine..bought the car about 2.5 years ago. Question No. 1 are the sho yamaha engines suppose to be a little rough running? Question No. 2 there is a little bucking between 1,800~ 2,400 rpms every gear. New spark plugs, timing belt installed. The former boy racer owner had a performance chip installed....pulled a 511 code k.o.e.o. so I removed the chip, tested again no code...does this mean that the chip is bad or just non ford chip was installed? The master plan is to take the sho the a dyno tuning/custom chip shop to see what they can do. They told me that they have all sorts of testing equiptment so if it has a bad sensor of some sort it come to their attention. Please chime in with some thoughts...I report back after the dyno experience. Thanks

 

[93rev2sev]

any time a chip is installed (to my knowledge) you will get a 511.

Since your rough running spans two separate engines in one car, I'd be looking hard at the coil pack, DIS module and grounds. I'd also make sure there was a decent fuel filter (if it hasn't been changed...change it). Clean your MAF sensor (do a search)

 

[shobote]

SHO engines are extremely smooth; one of the biggest attractions. Revving it to redline will not do any harm either; actually lugging it is what eats rod bearings. You have some issues other than the motor itself; either DIS or soiled MAF sensor. Bucking is what mine did before cleaning the MAF; smooth as silk afterwards. Hope you installed new rod bearings before for the replacement motor too.
Pull the chip and keep it out; probably what fried your motor as most of these screw up the A/F. I have not heard of any shop that does custom chip and dyno tuning on a SHO motor. If it is mostly stock you do not need to tune it anyway, just clean the MAF sensor most likely and youll be good to go.

 

[lincster2]

Thanks for the thoughts

Sounds like all good info....the shop said the computer was bad, so I ordered a good used one from RCM. Hummm makes me think that the crappy computer might have screwed up the old engine. I'll post an update after I slap the good computer in. Wished there was a icon with fingers crossed...