Hi everyone new to the forums here hoping i can find some suggestions on what is wrong with my truck.
Some information on the truck:
1993 K1500 Sierra 350 TBI with 174k miles
Engine has been rebuilt with around 35k on the rebuild. It has an RV cam and high volume oil pump. Other than that it is stock.
I just received the truck from my dad and im trying to diagnose some issues it has had for some time. When turning the key to the "on" position the fuel pump primes for around 10 seconds before shutting off. Is this normal? I remember years ago when i used to drive the truck the pump would only prime for 2-3 seconds before shutting off.
After the 10 seconds of fuel pump priming, it starts right up but immediately runs very rough where the engine, tailpipes and doors shake if open. The exhaust sort of flutters out the tailpipes and smells very much like un-burnt gas or as if it is running rich. I have so far changed the spark plugs, map sensor, o2 sensor, fuel filter, egr valve, fuel regulator, both temp sensors, thermostat and cleaned the IAC with no improvement. I checked for any vacuum leaks or bad vacuum lines and can't find any. The truck will continue to run rough even when warm and at a stop light the idle will drop to almost wanting to stall but then will surge back up and then drop to almost stalling and so on until i start driving again. I have to hold the brake and give it gas to about 1000 rpm so it wont have the surging idle. It has a 195 degree thermostat but seems to never reach full operating temp. From the gauge cluster it looks like it stops at around 175 degrees or so.
I will be checking the ignition timing this afternoon to verify that it is correct and plan to test the fuel pressure as well. Do you guys have any ideas what might be the problem?
Thank you for any assistance and i'll post back with my ignition timing findings.