ok, i just purchaced an 86 t. it has a cpt66 turbo, a 38mm wastegate, 60lb injectors, big poston headers, 3in downpipe, alcohol injection, frontmount innercooler, and an ls2 maf. my question is, why at 4000rpm does it fall on its face? please help! also has a turbo tweak chip that was programed for a pt51 turbo but had same injectors.
ls2? mass air?
- Thread starter gnguy84
- Start date
bmackinnon
Active Member
- Joined
- Feb 24, 2005
Uhhhh... it's not tuned properly??? Gotta' give more info than that... do you have a scan tool of some sort? If not, you need one.... What's the fuel pressure set at? Does it rise lb. for lb. for every lb. of boost? What's it doing when it 'falls on it's face'? Popping? Breaking up? How much boost?
bmackinnon
Active Member
- Joined
- Feb 24, 2005
What are the O2 numbers on the SM when it starts to fall down?
bmackinnon
Active Member
- Joined
- Feb 24, 2005
OK.... those are good numbers.... assuming the fp is rising properly.... can likely eliminate a fueling problem. Is it breaking up/missing? or just kind of nosing over/going soft? Are you using an aftermarket tach for the 4000 rpm figure? The factory ones are worthless and inaccurate. How many miles does the car have? Could be simply the valve springs are weak if they are original. They are NOTORIOUS for giving out over time.... even with low miles.... like 25k. Lot's of people after replacing orig. valve springs are like, OMG!!, feels like I hit it with nitrous!! ... but that's another discussion..... maybe.... :wink:
PS - I didn't mean to sound rude at first.... just, need at least a little info to get a start in the rite direction... sorry! :redface:
PS - I didn't mean to sound rude at first.... just, need at least a little info to get a start in the rite direction... sorry! :redface:
bmackinnon
Active Member
- Joined
- Feb 24, 2005
Hmmm... no, never heard of too much spark.. 
Sure have seen a lot of too little spark, though. Coil packs are always likely suspects on these cars.... followed by ignition modules. You never answered whether is missing/breaking up or just losing power. Ohm the towers of the coil packs between the 2 cylinders on each coil. Should be 11-13 kOhm... anything less, and the coil pack is going south. The ignition modules are too expen$ive to just 'throw parts at it'. OEM GM module is req'd, as the aftermarket Wells are junk and work about (maybe) 1 out of 3 times. Check the coils first. If they appear good, you may want to try and find someone near you to swap in their module and see if it fixes it.... I see you're in Indy, so there should be plenty of folks around there that will lend you a hand. (I'm orig. from Carmel). Also, how about some other scanmaster #'s around the crap out zone. Check M(AF) and Knock Retard (KR - should be zero or near) and post up the numbers...
Ooooo... edit.... hopefully the 'brand new lt1 springs' didn't wipe your cam... the flat tappet cams are VERY spring pressure sensitive, and wipe easily with a heavy spring.... (thus my 'another discussion' bit above about valve springs)
Sure have seen a lot of too little spark, though. Coil packs are always likely suspects on these cars.... followed by ignition modules. You never answered whether is missing/breaking up or just losing power. Ohm the towers of the coil packs between the 2 cylinders on each coil. Should be 11-13 kOhm... anything less, and the coil pack is going south. The ignition modules are too expen$ive to just 'throw parts at it'. OEM GM module is req'd, as the aftermarket Wells are junk and work about (maybe) 1 out of 3 times. Check the coils first. If they appear good, you may want to try and find someone near you to swap in their module and see if it fixes it.... I see you're in Indy, so there should be plenty of folks around there that will lend you a hand. (I'm orig. from Carmel). Also, how about some other scanmaster #'s around the crap out zone. Check M(AF) and Knock Retard (KR - should be zero or near) and post up the numbers...Ooooo... edit.... hopefully the 'brand new lt1 springs' didn't wipe your cam... the flat tappet cams are VERY spring pressure sensitive, and wipe easily with a heavy spring.... (thus my 'another discussion' bit above about valve springs)
