Hey guys...thanks for all your previous help...need help again. I have got a 2000 Blazer, V6, 4x4, 4dr, 190000 miles. put in a new fuel pump in January/February because of low pressure it also wouldn't hold the pressure that it could get. New pump in...done. No problems until last month, it would crank awhile before starting (like it was flooded). Hooked up fuel pressure gauge...key on engine off - 62 lbs for two seconds then drops down to 58 lbs and holds. watched it for a couple of minutes and the pressure increased to 62lbs (slowly over about a minute). Once it reached 62lbs it would drop rapidly down to 58lbs and start all over, doing this for approximately 15-20 minutes. It happens more frequently after reaching normal operating temperature. Vapor locking maybe? The line doesn't touch anything that I can see/feel. Any ideas?

 

4psi isnt really going to affect anything, i cant explain the fluctuation. Have you tried a different gauge? Does the truck run poorly?

 

Idles and runs fine, slight hesitation during accel. Can the pressure open the injectors, dumping fuel into the cylinders causing it to start hard? I have to crank it at least 20-30 seconds before it fires. It fires right up in the morning. This only happens after I have driven it awhile. I dont think the tester is bad it's made by OTC.

 

The initial drop in pressure from 62psi to 58psi is normal. The reason it increases is engine heat radiates to the fuel pressure line at the rear of the engine, and inside the plenum. This causes the pressure to rise. Once it reaches regulated pressure, (62psi) the regulator opens and drops the pressure back down rapidly. Check fuel pressure and leakdown with the engine cold, you won't see that happen. As long as the fuel pressure remains above 55psi for at least 10 minutes after the pump shuts off, it's fine.

No such thing as vapor lock on this system... the fuel is constantly circulating, and pressure is regulated when the pump is running. Also, the 2 second pump prime eliminates any air that might be in the lines.

If an injector were leaking, the leakdown test would not pass, and yours passes. Make sure the fuel pressure needle moves instantly when the relay kicks on. I've had a few where you can hear the pump run, but it doesn't build pressure instantly, like it should.

 

my blazer does the same thing but it has aftermarket throttle body on it so its normal