new vette owner/builder needs help!

E

erikv79

Member
Mr Grumpy, and all who read,
This is a long one so here we go.
Bought a sick 85 coupe, rods hammering and fuel system drowned in water. Got her for a song so I decided to rebuild, new everything, almost. Haveing never peaked under the hood of one of these things before, I stood across the shop, ran and took a swan dive into it.
Installed a rebuilt motor, 72 model 350 #2970010
Same heads 72 2.02/1.6 I think LT1
Everything new except rods, block, crank, and heads. All went to machine shop(used many times).
Got it all back together replacing all sensors and such along the way, fired her up like any other 350, got a couple of codes. Simple stuff, o2 senser, water sender and knock sensor backwards, stuff like that. Solved all of those, now I have no codes, but more problems! The thing wont idle down stays around 1000rpm, has a miss, and wont come to temp. So far, I have done all the setups and checks as per (grumpyvette). Now I bought the temp sender for the 72 heads because the 85 sender was too small, possibly wrong one?
When I drove it it would stumble off start and then surge forward still vastly underpowerd. Went over everything I know to check Timing,Cam gears,Fuel pressure(47),Compression,Valves,etc. Pulled the plugs all look dark like too much fuel except #7 Its shiny brand new! Now im at a total loss! I have a Snap on scan tool although I got it for the car so I really dont know how to use it. I checked everything I could, The computer goes open/closed, no codes, all the stuff seems to be working, at least I can see it working. Hit the gas IAC moves, TPS .56,o2 sensor changes, stuff like that.Any ideas where to even begin would be great! Thanks from Texas!
 
you need a CHEVY SHOP MANUAL

most of those problems could be caused by a defective MAF,and the temp sensor on the under side center of the plenum, or defective injectors, Id try testing those or swapping those out, keep in mind if the cams not designed for EFI and youve got the TPI installed the cam can drive sensors nuts that are programed to look for certain parameters, that the cam installed won,t provide, and if its been running rich for very long the cats could be restricting the exhaust so check back pressure

links/sub links in these threads should help

viewtopic.php?f=32&t=1401

viewtopic.php?f=32&t=596

viewtopic.php?f=32&t=661

viewtopic.php?f=62&t=882&p=5410#p5410

viewtopic.php?f=56&t=495

viewtopic.php?f=55&t=2055

viewtopic.php?f=50&t=609&p=3174#p3174
 
Many thanks Grumpy! Im going to look over all these tonight! The cam is a comp 12-268-4 thats for this car. I have not checked the cat and the car has 150k possible bad! New injectors, maf, and temp sender but I wont rule those out either. Thanks a bunch and Ill get back with the results!
 
Ive NEVER seen a standard 268 cc CAM work in a basically stock TPI without reprogramming the CPU
and if the back pressure measures over 2 psi at 4500rpm the cats ARE restrictive, verify and correct that if they are clogged.

now thats good cam IF YOU make the necessary changes to the programing and it really REQUIRES a 2000 stall converter and a 3.54-3.73 rear gear to work to its full potential in a TPI, but the TPI versions a better choice


standard 268 cam
http://www.compcams.com/Cam_Specs/CamDe ... id=86&sb=2

TPI designed for TPI (notice the different LSA, duration etc.)
http://www.compcams.com/Cam_Specs/CamDe ... d=128&sb=2
 
Ok let me start over:
.030 over 350 block #2970010
SLP flat top pistons
Comp cams #12-268-4 grind #xe268h ,best for 350 tpi modified chip,exhaust,intake,runners.
heads gm# 3973487 I think are Lt1
Cloyes double roller timing chain
Crane roller rockers/lifters/springs/stud girdles
Comp ratio 9.5:1 ~roughly~
24# ford SVO injectors
Computer reprogrammed by Tony Duncan Via F.A.S.T.
Delete items: air pump, cold start, security, egr,?
adjusted for cam and injectors?
I have the slp runners but I have not put them on the car yet, I was hopeing to buy the intake base first. I have yet to buy the throttle body (52mm) As you can see im in for a big chunk already!! Plus all sensors are new, including the maf. Its bound to be something simple that im overlooking im gonna tear back into her tonight!!
 
Hey it sounds like a cool setup almost like my camaro but im using the zz3 roller cam with slp runners. What are you using for your water pump the tpi motors use a reverse rotation water pump.
 
Ok,
Last night I started over again to see where im at. The complete mechanical assy. is intact and correct! I have between 180 and 185 on all 8 cyl. All seems to be working correctly, I put it all back together and plan on attacking the fuel system next. Perhaps some hidden trash has clogged some of my injectors? #7 in particular! I opened the cold start inj. plug in the end of the fuel rail to see what would come out, Clean fuel, no trash. Can a maf be bad and not give a code? Mine is new but perhaps bad? Its a bosch and it has in yellow letters on the side (New Unit) Kinda suspect? Anyway I have eliminated all mechanical problems so must be the TPI sytem somehow. Any Ideas?
 
TPI intakes are well known for frequent vacuum leaks so ID start by verifying you don,t have that issue, and ID verify the fuel pressure regulator maintains 38PSI minimum fuel rail pressure and the oil pressure is at least 15 psi at idle before working on anything else.
 
Ok,
Last night I spent a few hours with the car. I tried two ways to look for vaccum leaks and found none. A small propane torch and a can of starter fluid. I did find that the o-ring on my brake master cyl. was a little worn from the hose pulling on it but it still did not leak. I put the fuel pressure guage back on and again tested 47 psi running at idle, With the vaccum hose attached, without vaccum hose she's 50 psi. I have been running with the vaccum hose attached. My digital dash assy. was kaput when I got the the car so I built a custom manual gauge assy. My oil pressure runs about 26 psi idle after 5 to 10 minutes. I cant say at temp because according to my guage and the scan tool she never gets over 109, 110 deg! I did a few checks to the fuel system to make sure it is working properly, so far so good. The oil switch works, and the fuel relay works, fuel pressure from 47 psi bleeds down over 35 minutes. Im leaning toward the injectors? These I bought from a guy on the internet, Jon Banner@ FIC. I have not ohmed them yet but its the next step I guess. Although Ill try whatever you think is more likley. Thank you Erik Valdez.
 
Mr. Grumpy,
I think I may be out of the woods at last! I found a plugged cat, stuck t-stat and broken injector wires on #7. All repaired and running smoothly! My t-stat is the weidest thing though, it has some brass clips that catch the plunger when it opens fully and will not let it close. Ive never seen one like this, I tried bending the tabs out of the way but I think it was no good since it still would not come to temp, so I replaced it with a new one and viola temp is right on. During checking the injectors I checked the plugs with a noid light and found #7 wouldnt fire and #3 was intermittent. I solderd the connections and checked all others and all was well. I also pulled the cat to find that the center was melted closed and the surrounding edges were plugged here and there so I left it off for the time being to test only. After all this I went through the normal set up and she came right into her own and pured like a kitten! I have not driven the car since without a cat she's awful loud and im sure the nieghbors would not approve! Now back to an ealier post you said that a cam such as this needs a stall and lower gears, does this apply to the cam that I have?
 
the cam you have will run much better with a 3.54-3.73:1 rear gear and a 2500-3000stall speed converter, but neither is MANDATORY if your willing to put up with a slight low rpm delay in response , and a slight tendency to surge or jump into gear which is common with a basically stock tpi with that cam,with the current set up, keep in mind the cam will pull higher rpms than the stock tpi intake can efficiently feed the intake runners
and you sacrifice a bit of low rpm torque, its not a bad trade off but you loose a bit of the potential at both ends of the rpm band if the only change is the cam swap
 
Thanks for the help! I planed on changing the intake and runners but might go the tunnel route? I already have a set of slp runners but for the money I could buy a whole diff. setup. Anyway evrything seems to be coming along and ill see where it leads :?: You are a well respected person for good reason, any suggestions? Just thought ide ask. Thanks a million, Erik. :D
 
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