Proving the power.
If you tuned in last issue drooling to see the final installment of our Golen Engine Service 4.6L stroker swap, all we can say is sorry. It's pretty common for magazine writers to have the occasional story go completely awry, but this author had three stories in one issue disintegrate into a series of setbacks. Rather than half-ass the final part of this story and leave you with unanswered questions, we decided to kick the story back an issue so we could have the vehicle properly tuned, smog tested, and dyno'd. Unfortunately, the G-Tech performance meter we had hoped to use to give you some 1/4-mile times was on severe backorder, so those numbers will have to wait for another day.
Turbo City Tune After getting the new stroker installed into the engine bay, we fired it up, checked for leaks, double checked the coolant level, and took it for a blast down the road. Even with 91-octane fuel in the tank, there was severe knocking upon mildly hard acceleration. Full throttle use was out of the question. The stock 19 lb/hr injectors just weren't capable of supplying enough fuel to feed the extra cubes and the engine seemed a bit lazy out of the hole.Rather than fumble for our asses in a dark room with both hands, we took our 1999 XJ to Turbo City in Orange, California, to have the fuel injection experts tell us what we needed to do. Turbo City has a vast amount of experience with fuel injection systems and really goes the extra mile to provide the customer with top-quality work. For example, rather than sending us packing when we unknowingly dropped off our XJ with a cracked and leaking header, the guys tore it off, welded it up, and reinstalled it without a whimper.
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Although our OBDII computer basically wants to do what it wants to do and Turbo City said the correct way to dial in our system was to reflash the computer, we asked that they just put the scan tool to our system to see where they could go with the factory settings. After replacing the fuel injectors with larger Accel 24 lb/hr parts, they modified our crank position sensor to advance the ignition timing 3 degrees. With their modifications complete, another scan revealed that our fuel system was pulling back fuel both at idle and during normal cruise, trying to get the air/fuel ratio down to a lean 15:1. However, under acceleration the computer was allowing more fuel, with air/fuel ratios back to stock levels of 13:1 or richer. Compared to how lean our engine used to run with the stock 4.0L and our modifications (see Sidebar, Power Play) the fatter fuel curve on our stroker as dialed in by Turbo City nearly mirrored that of our unmodified 4.0L. Although the fatter air/fuel ratio we're running is most likely costing a bit of power, there's no pinging even with 89-octane fuel and full-throttle blasts.