Vehicle in question:
89 S10 pickup with a 5.3 LM7, (truck LS) carbed. It has two cats on it but no emissions equipment. It has an MSD 6LS spark box for the LS1 coils.
Conundrum:
Best way to pass the two-speed-idle emissions test with a Holley 4-bbl on a V8
Current research:
So far, leaning out the carb has proven pointless. The LS-type carb intake is a single plane intake and the vacuum signal doesn't support leaner mixes. Long before I get lean enough, it runs like crap.
Hypotheses:
- replace the carb with a 454 TBI and MS
- replace the intake with a stock EFI intake and run it with MS
- replace the intake with a stock EFI intake and a stock PCM
- find someone with a 2-gas analyzer who is better at tuning Holleys than I am.
Which MS would I need? Has the MS3 become more available? Last I checked it was still in development.
Which Holley do you have? Do you reset the idle after leaning it out? What kind of FP/system are you running? Does the E36 M3ty MSD box support different timing maps, IE- programmable?
To pass emissions, the easiest way is to just go back to a stock truck intake, injectors, PCM, etc... But then you have to change a LOT of stuff. I just don't see why, even with caveman technology, you can't pass emissions either once tuned in.
I haven't pulled the numbers off the Holley, but its a 600 cfm manual choke. Probably the cheapest one he could find :)
Fuel system uses the stock in-tank TBI pump with an adjustable Holley FPR. No fuel pressure gauge so I don't know what pressure, but it seems to run great.
So, cheapest probably is a used up pos?
I had a 650DP on my wife's car that needed a rebuild. Rebuilt it. Put it back on one of my shelves, after putting it on, because it was a worn out POS. I put a brand new one straight out of the box and cleared up all the driveability problems I was having, bog on accel, overly rich idle mixture no matter what the idle mixture/speed was . Plus ran a PB the next week at the track.
If you go a simple MS route, and can afford a basic O2 sensor- if you just get it to control via it, you should be good to go to pass.
If you find the analyzer, you could fine tune the closed loop fuel to run best. But so that it does not make it drive too funny, the steps back and forth should not be too big.
I know pretty much nothing about carbs, so can't help if you can make that work. Good luck, either way.
Ranger50 wrote:
So, cheapest probably is a used up pos?
No, actually brand new... but in my hands a Holley ends up being a POS 
Depending on which intake fits under the hood of the S10 you may be able to break even on the intake/fuel rails/injectors. The truck intakes are relatively cheap because they don't fit in the car applications most people swap them into. Then its a matter of choosing your computer system.
MS3 is readily available, no worries there. The code is actually in 1.0 release as well.
You can always add injector bosses to your intake and just use the carb as a throttle body until you work out something more elegant. We did that on a 454 and it worked pretty well.
