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Old 05-26-2010, 01:09 PM   #118 (permalink)
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Join Date: Feb 2010
Location: CT, USA
Posts: 544

RaceJeep - '98 Jeep Grand Cherokee (ZJ) 5.9 Limited
90 day: 13.62 mpg (US)
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If you step up to only somewhat larger injectors, the computer will simply learn around them and reduce the pulsewidth. It's only if you go much bigger that you have to either reduce fuel pressure for less flow, or more optimally, have a new tune written for the ECU and loaded via an SCT tuner or other flashing device. I'd definitely upgrade the injectors (unless they can already flow enough fuel), even if you don't normally run to max RPM, that way if you ever do for any reason, you're covered and won't lean out too much.

For boost control, I'd suggest starting out with a wastegate on the turbo set to 5 psi or so. At 5 psi, you should have no issue running without an intercooler, although you might need to run 89 or 93 octane gas to avoid pinging.
Call me crazy, but I actually try for mpg with this Jeep:

Typical driving: Back in Rochester for school, driving is 60 - 70% city
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