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The customer described a progressive problem when I received the vehicle. He stated that initially the pickup would idle rough but ran good at high rpm. The last time he drove it he said it was running pretty poorly even while driving. He arrived at his destination and when ready to leave it would not start. I was able to get it to run a couple of times for a few seconds if I floored it as soon as it fired. It ran terribly and smoked profusely black and grey. It seemed to be severely over fueling. There we and still are no codes. I checked the alcohol content which was registering 40% but he was running no ethanal premium. I reset the alcohol content with no change. I unplugged the MAF with no change. I then drug it to my shop for further diagnostics. It was only maintaining maybe 10 psi fuel pressure. Dead head showed 60 psi. The oil was half a gallon over full due to fuel dilution. The plugs were fouled. I replaced all plugs and injectors with oem parts as well as changed the oil and filter. I now have 60 psi on the rail and it drops just slightly when it fires. It only fires occasionally and idles for half a second or so when it does fire. I checked the throttle position and sensor 1 shows 3.5 v and sensor 2 shows 1.5 v at throttle closed. The spec is above 4 v on sensor 1 and below 1 v on sensor 2. There is one spot of delay part way up when I ease it up and wot reads correct voltages. The pedal sensors are reading correctly. I cleaned the throttle body with no change. I am inclined to replace the throttle body but am unsure if this is what's causing my no start issue. Other throttle body replacements I've done have always thrown codes and messages on the dash. Any input would be appreciated as I've already got some money into this thing and don't want to just throw more parts at it.
I wouldn't sweat the throttle body for now. Even if there were something wrong with the throttle body, the engine should still start and idle low.
I know that you've replaced the injectors and plugs, but I'd still recommend checking for spark and injector pulse with an incandescent test light during a starting attempt. If you get it to fire while testing, does it lose injector pulse or spark when it stalls?
I'd also suggest taking a fuel sample from the rail, to rule out bad gas/diesel/water. Fuel contamination would very neatly explain many of your symptoms (smoking, start/stall, no codes).
As a quick check of engine breathing, you can watch the MAP sensor signal during a starting attempt. Don't touch the throttle during this test. The MAP should show a few inches of vacuum while cranking. More vacuum than that suggests an intake restriction. No vacuum suggests an exhaust restriction or base mechanical issue.
Thank you for your reply. I just got back on this thing today. I checked everything you suggested, and everything checked out. Your comment about fuel contamination stuck with me and I contacted the customer. He was pretty certain that wasn't the case. I decided to do a compression test and the plugs were quite wet from all of my other testing. I hit one of them with a little torch and no fire. I put a little bit of the fuel in a metal container and lit it with a torch. It acted much more like diesel fuel. Ironically, I recently read a couple of articles talking about gas station gas tanks getting diesel dumped in them and the symptoms of the victims were identical to this vehicle. I pumped out the tank and it foamed up in the bucket. Your initial thought was spot on. I dumped 10 gallons of gas in and it runs just fine.
Bad gas happens to good people, unfortunately.