I have a S-10 Blazer with a 355 with holley 670 TBI . How can I tell if it is running lean at wide open throttle. Does not seem to have proper power above 3500 RPM. I was using a ADS 350 chip and had problems running rich with 15 lbs. fuel pressure. Changed chip to stock 305 chip and lowered fuel pressure to 12 lbs. performs better at low and high RPM. Engine has 9.8 comp ratio 208-214 dur 455-470 lift. Stock truck tbi
intake machined out to 2 inch.
I would appreicate and tunning tips
Thanks

 

You'll need to find out what size injectors you have: 55, 65 or 80lb/hr? You may simply have too much injector.

I had the same problem on my last RS with a heaviliy modified 305 (vette heads, cam, Holley 670TBI, and just about everything else). It always ran rich no matter what I did. Fuel pressure anywhere between 8-15psi did not lean it out enough. 3 different custom chips didn't change much either. I never did figure it out. I think I only had 55 or 65lb/hr injectors.

If your injectors are 55 or 65's, then you may want to look at a different brand of injectors. Holley uses Chrysler injectors, which I've heard are not as accurate as GM.

You may simply need a custom chip. I have a 350 with the same cam specs and Holley TBI as you do. I will not use anything but a custom chip. Even a stock "350" chip will not give your ecm the correct fuel and timing settings.

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'92 RS, ZZ4 10:1 350, Edelbrock 6085 heads, Crane 208/214 467/482 cam, GM/LT4 1.6 true roller rockers, Holley Projection TBI intake, Holley 670 TBI, SLP/Jet-Hot 1-5/8" headers, Catco 3" cat, Flowmaster 3" catback, Hughes 2500 stall converter, stock 700R4, Auburn Pro posi w/3.42, 17x9" SS rims w/BFG tires, Medium Quasar Blue w/white SS stripes, 48,000 miles....

 

Tuning is just all about chips there isnt really much else you can do to tune

To find out if you are running lean, there are two ways that will get you started in the right direction, the first least accurate way, is to watch the voltage from your O2 sensor... generally above .8vdc is where you wanna be but these sensors are really innacurate
if you notice it DROP off the chart then you have a problem with it going lean OR rich (if it goes to rich it reads low) so you wanna watch that for some drastic differences.. drops below .8 usually indicate leaning out

the BEST way is to simply pull a plug from a WOT run
the way to do this is find a deserted road to do some testing, and take off at WOT foot to the floor and the instant you hit the spot that you think the car is not running right, turn off the ignition and throw the car in neutral and just coast off to the side of the road. Remember to bring a glove and a spark plug socket and wrench, then pop the hood and pull out an easy to reach plug. Ideally it should be a light coffee color, if its black its too rich, if it looks shiney like its wet, its REALLY rich.. if its lighter than a light coffee color its lean.. the lighter, the leaner


Pablo

 

don't turn the ignition all the way to the lock part of it or you'll get a nice pucker factor when the steering wheel locks !!

A chip is a must for a modded engine and ADS isn't a good choice...I've got one in my 93 S-10 but my dad bought the chip when it was his truck. Have you bumped your timing up to around 8 degrees? Any codes being set in the computer?

Have you pulled the plugs at all to see how they look under normal driving conditions? If they are really rich then, more than likely they won't be lean in the upper rpms. Also when you say it seems to loose power above 3500rpm, have you checked the coil and distributer on a scan machine to see if it's getting the proper dwell time, sending the right amount of spark to all the cylinders and how about the cil's voltage output. I had a friend check mine and I didn't even realize I had a bad (going bad) ACCEL coil and GM distributor. I had low voltage output and my distributor wasn't managing the spark very good at all. It was hard for me to believe but the machine didn't lie. I didn't notice they were going bad but after I replaced both and took it back to him (for free) I saw the difference easily on the machine and noticed the hp I was loosing.

I'm running around 14 psi with my setup. I did have to replace my injectors when I first got the unit 4 years ago b/c the injectors were 80lb/hr instead of the 65#. I couldn't get it to lean up no matter how low I turned the fuelpressure down. I was also fouling sparkplugs like crazy.

Another thing, what manifold are you using? I hope it's not a stock TBI intake b/c they give out around 4500 rpm that's why I'm changing mine out now. How about your aircleaner? Is it an open air cleaner or the stock one. If I used my stock aircleaner w/o at least flipping the lid upside down and getting a bigger element, it would starve the motor of much needed air on upper rpms.

hope some of this helps.

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1988 TA 300+hp 350 w/ TBI and Holley TB unit, Holley projection intake,
WC T-5, 3.42 gears w/ Auburn posi. MSD 6A, edelbrock TES headers, dynomax 3" cat and cat-back system, ACCEL coil, polyurethane bushings all around, aluminum driveshaft, Mr. Gasket open air cleaner.

1993 S-10 w/ 4.3L V6 TBI, slightly bigger cam, Mild polish job and 3 angle valve job on heads, Edlebrock TES headers, Dynomax cat back, MSD 6A, ADS chip

2000 Kawasaki KX 125

[This message has been edited by badbird88 (edited October 04, 2000).]

 

Thanks for the help. I have checked with holley a while back they said I had either 55 or 57 injectors can not remember which.
What do you think about installing stock 350
injectors and fuel regulator on Holley TBI and what fuel pressure would you recommend?
Maybey going back to the 350 ADS super chip with stock 350 injectors.
Thanks for your help.