Age: 15 1/2
Join Date: Apr 2008
Bill Wheats is offline
Re: 1998 gmc sonoma problems
So your 99 4.3 won't start without the help of starter fluid....
Your symptoms are common to fuel pressure issues. The key is to troubleshoot with the use of a fuel pressure gauge. The injection system needs between ~56 to 60 lbs at the fuel rail to start the engine. Then you need a little less to keep it running.
When you first turn the key to RUN (not start), the fuel pump relay turns on for ~4 seconds. The system is expected to have held at least ~35 lbs from the last time it ran. If you have a leak (fuel pressure regulator, fuel pump check valve, spider, injectors) the system may not be able to pump enough gas that quick to reach ~58 lbs. To test for this, you would watch the gauge after turning the engine off. Ideally it should hold pressure for at least a day.
A rapid drop would point away from the pump, but not the pumps check valve, FPR, Spider or injectors.
If it holds good pressure but fails to come up to a high enough pressure to start; expect Suspect plugged fuel filter or weak pump. Continue by supplying fused +12volts to the fuel pump test lead found on the pass. side fire wall (Tan, Brown or gray some times found by the brake boster on 4wd's) for 5+ seconds. If the pressure comes up to par: then replace the fuel pump primer relay. Often when they wear out it takes them longer then needed to energise the contacts.
If the pressure bleeds off too fast; open the veiw cover on the upper intake (covers the fuel injectors) and look for signs of washing. Where gas leaks wash the build up away. You can post a pic here and the experts will point out the leak.
If you don't have a leak but it drops fast, then suspect the check valve at the pump. 3 options; replace the pump. Install an inline check valve. Supply fused+12v to the test lead until the engine starts.
Post you pressure results. Key on run, after start, and leak down after turnned off.