exhaust sniffer?

I was wondering if anyone has an idea of where I can rent/borrow an exhaust sniffer if that is possible. I have about 4 different fuel pressure regulators that I can switch between for my new injectors. I went to 4 pintle 19LBS injectors, over the factory 1 pintle 14.5 LBS injectors. The 19LBSers are running way to rich at 3 bar of fuel pressure(black soote all inside my new exhaust), so I am switching to a 2.5 bar FPR. I am just wondering if there is an easier way than driving around for a few days, and checking my exhaust(not to mention this is pretty inaccurate). And I am not in the market to buy a wideband o2, unless you are going to me for free. Thanks