MERRY CHRISTMAS FORM TH ELAND DOWN UNDER!

O.K. This is a long one so bear with me.....
I bought me new vette 1988 in QLD Australia, and decided to drive her down, we live in Wollongong NSW Australia, approximately 1200 klm's away.
She's is a beautiful thing, ground up rebuild new new everything, not over the top or anything would idle like a kitten the Vette was built for cruising, i.e.
L98 TPI ( Tune Port Injection ) 350 Chev V8. Currently doing 11.5 Ltrs Per 100 Kilometers.
Aluminum Heads ( Normaly L98 Had Cast Iron )
Crane Cam 214 Deg & 220 Deg @ 050
Part Powermax # 2032 @ 270 Deg & 276 Deg Duration.
Fuel pressure Regulated. ( Increased fuel pump and 26 pound Injectors )
400 Flat Top Pistons and ring set @ J100F8-4165-5. 30 Thou Oversized.
Water cooled Oil Filter.
Marty White Race Motors was the engine Builder with Quantum Racing providing the parts.
HPC ( Ceramic Coated ) Hoaned and polished inlet manifold and runners.
Gonzo Customer Headers HPC
Gonzo Full 2 & Half Sainless Steel inculing CATS & Pollished Mufflers with HPC

Gear Box

Turbo 700 4 speed Auto.
Full rebuild with HD Reaction Shell
HD Shift Kit
Larger Stall converter.

Any ways, 2hrs into journey I noticed she started to develop slight miss cruising at 110klms.... got progressively worse into the trip so much so that about 4hrs into trip she was missing and running real rough, hesitating only under load. Lead or plug I thought, so pulled into servo and seeing I was new to the Vette game thought I'd ask one of the local mechanics if he could have a look.... At this stage the miss had gotten so bad she was hardly able to idle... Yeap, the local mechanic than proceeded to adjust the idle screw and them worked out that the little map sensor thingy on the side of the throttle body was like a timing adjustment and the rest of the story is all down hill from there.
Well we eventually got her home and I enquired locally who best to send her to, Came up with some local hot shot with a dyno and he researched the map sensor and idle adjustment and set her back up as the book specifies. New leads and plugs and she's running better but still doesn't run like when I first got her. She still surges when in over drive at times and doesn't like knocking back a gear until you really boot her and then it's a savage kick back. Also when she is hot 98 (200 degrees) she has a tendency for idle to vary 300 r.p.m from 700 - 1000rpm

Told you this would be a long story!
P.S forgot to mention she was originally set up & still is with a new delco computer chip based on VR Commodore V8 with modifications to run the vette.

Thanks for taking time to have a read of my post and looking forward to some assistance.

 

Hi Jethro, I can't help very much with the EFI and other computer related problems but every internal combustion engine needs the same basic ingredients to make it run. I would check the compression on all cylinders to make sure it didn't burn a piston or eat a valve, if all eight are the same or within 10% of each other then you have a fuel or ignition issue to track down. Good luck, let us know what you find.

 

I have to agree, check the basic mechanical condition of the engine with a compression and cylinder leakage test to make sure nothing went wrong, no matter how good your engine builder and parts supplier are something could have gone to pot. With the computer chip you have will the engine still set trouble codes and turn on the check engine light? And are there codes stored? When stock these engines were prone to mass air flow sensor problems caused by bad relays that did not porperly burn off the MAF sensor wire when the car was shut off. If there is nothing wrong with the mechanical condition I'd try disconnecting spark plug wires one at a time with the idle air control valve disconnected to see if all cylinders cause about the same amount of RPM drop. Watch out for the spark, you may want to disconnect the wire with the engine off and jumper it to ground before starting the engine. If all cylinders are working equally the engine should idle at about the same speed, plus or minus about 50 rpm, regardless of which cylinder is disconnected. If still no fault has been found,remove the O2 sensors one at a time and connect a pressure gauge and measue exhaust pressure at a steady 2500 rpm in park, if pressure is more than about 1 1/2 PSI (10 kpa) the catalytic converter may have been damaged from the misfire. If you still hae not fopund any problemyou probably should find somebody wou has the scanner needed to read your computer data to figure out what has happened.