I love 1999 Tahoes, I have four of them. One is driving me nuts. Mileage is about 230,000. 5.7 L gas engine. Intermittently it will not start. It cranks fine, fuel pressure is fine, have checked spark at the plugs, but it won't start. Sometimes in this mode it will cough a little while cranking and sometimes after cranking it will putt along for a few seconds before stopping. The exhaust smells rich when the failure to start happens. When this problem first started it was occasionally throwing a Bank 2, O2 sensor 1 code for heater circuit issues. Replaced the O2 sensor and since then there have been no codes. I thought the problem was tied to the O2 sensor and was confident enough to take the vehicle on a trip where it worked fine until the day planned for return. After trying for over an hour had the vehicle towed to a dealer and made other arrangements to get home. The dealer could not replicate the problem, but found a loose battery terminal that he thought might be the issue. Picked up the car and drove home where after just a couple of days the problem repeated. Battery terminal is definitely not loose. But then the next day started fine and has worked every time I have tried since. I don't have the confidence to take it anywhere.

There are no codes and no obvious problems (to this not totally skilled shade tree mechanic) in the fuel trims or anything else a code reader spits out. It seems most likely that it is some sort of fuel issue, but I don't know where to look next. Replacing the injector assembly is expensive and a pain in the butt so I don't want to do that just on speculation. I have replaced the fuel pump several times on this vehicle, I am aware of that weakness in the design, but the fuel pressure seems fine.

Any suggestions?

 

I'd start out with Techron Complete or Seafoam. Might be an injector issue. Believe it or not, not all types of gasoline are the same even in this day and age. I personally won't use unbranded gasoline or ARCO, unless I must. Their ads look nice, but their fuels have never been all that good.It's not like I don't know anything about fuels. I used to sell and have them delivered. Also in all my years as a shade tree mechanic that was studying the trade, I've seen the difference in cleanliness between using cheap fuel and good fuel. That's not to say that is your issue, but it might well, be. If so these two additives might well do the trick.

 

Spider injectors are a issue in those motors. Had the leaky injectors in my '99 Yukon making it hard warm starting. Easy test if it's hard starting when warmed up is to floor gas pedal when cranking and see if it fires up faster.
Fuel pump relays go bad over time and can be intermittent and yours may be bad as you've had several fuel pumps replaced. That tells me it's relay has been stressed.
Relay is a cheap fix. Relay failures will not set any codes either.