the car.
91 Z28 SD tpi
I recently installed a fresh 355 with flat tops, ported and polished heads Lunati cam etc. I need to have the car tuned for the new engine as the car originally came with a 305.

The problem.
After all was installed, it fired up and ran fine while we broke the cam in and sounds great. I can fire it up and as long as it doesnt run more than 15 minutes its fine and takes throttle without a problem. After that it starts sounding like its running on 4 cylinders and WILL NOT throttle up .

I checked the fuel pressure, its at 43lb and does move up and down with a vacum pump on the regulator. Timing is at 8 degrees. has new plugs, cap, rotor, and wires. Set the tps to .45

I checked the injectors and cold they run 14 to 16 but when it heats up 3 of them drop below 10. I figure they are the problem but wanted an opinion before I buy new ones just to make sure I dont have other issues.

Donny

 

You "figured" right.... if the resistance on your injectors is falling below 10 then you have coil failure....which is a common problem with the stock multec injectors. Unfortunately you are going to have to replace them.

 

thank you for the response. I got a stock set of 19lb injectors from my brother just to check and see if that was the problem. put about 60 miles or so on it and that cured the misfire after running for a bit.

What size injector would you recomend or what specs do you need to make a recomendation?

Donny

 

U still using the 305 ecu ??

 

Stock replacement would be the 19lb injectors, it depends on what you want to achieve. If you do not have any mods that have bumped up your horsepower i would just stick with the 19's

www.southbayfuelinjectors.com
516-492-6504

 

22lbs are the factory size for a 350. But you can use 24lbs on a modded 350 just make sure you tell whoever does the tune what size your new injectors are and you should be fine with either injector. But it will run lean with the bigger injectors until you get the tune done.

 

thanks for the replies.
her is what I have, all suggestions are welcome. what I'm looking to do is get any and all parts before any tuning is done. I'm planning on getting my own tuning equipment but for now I got a buddy that will burn me a prom to get started with.

the motor is a 4bolt 350 punched 30 over with flat top speed pro pistons. the heads are 801 castings, port matched and cleaned up under the valves to match the new 1.94 1.60 valves. intake has been matched to the heads, runner have minimal work done and the plenum is matched to the runners. stock throttle body. fpr is stock but I can convert it to adjustible if I have to. the cam is a lunati 10002LK.

 

yes, until I get everything I need to get it tuned.