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1994 gmc sonoma running rough?
- Thread starter aron ft
- Start date
epiphaknee
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CPI W Engine or TBI?
Are you getting any codes? Like maybe P0172 or P0171?
Now would be a good time to pull off the EGR valve (two 10mm bolts and check out the carbon situation). Typically though you would have gotten a code with a bad EGR or a tired EGR valve. Replace the gasket with a screened gasket form NAPA or Autozone. This will capture the carbon in the future.
Last time you changed your fuel filter? If more than 15,000 miles ago change that first.
However, this sounds like either the fuel pump (time will tell) or the fuel pressure regulator (time will also tell). Does it take longer to start? Longer cranking times? Is the fuel pump really noisy now (different from before)? Is the fuel pump really quiet now (it used to whine)? So just buy a fuel pressure gauge and test the fuel pressure at the fuel rail. This is on the drivers side, very near the firewall with a screw-on dust cap on the valve. Test pressure at prime, idle, WOT (wide open throttle) and with the key off. Fuel pressure at prime and idle should be around 54 psi to 58 psi. WOT should go up to maybe 62 psi and then the vacuum should pull it down, a little. With key off, fuel pressure should drop a little and then hold. Does it hold or just keep dropping?
If fuel pressure is too low or does not hold the pump is probably bad.
The easiest way to check the fuel pressure regulator (FPR) for a CPI (under the intake plenum) is to check for washing after you pull the plenum. The plenum attaches with about 10 bolts and nuts (all 10mm). Washing is caused by the gas leaking from the FPR and washing an area clean in the intake. Upon assemby the plenum must be tightend consistently with a torque wrench and the tightening of the bolts is sequenced.
Well, you are off to the races.
Both the fuel pump and FPR will go totally out with time. It will never get better. So better to address now than wait to be stranded somewhere. However, generally with both the pump and FPR you will get an early warning P0172 or P0171 code. Read codes for free at Autozone.
Are you getting any codes? Like maybe P0172 or P0171?
Now would be a good time to pull off the EGR valve (two 10mm bolts and check out the carbon situation). Typically though you would have gotten a code with a bad EGR or a tired EGR valve. Replace the gasket with a screened gasket form NAPA or Autozone. This will capture the carbon in the future.
Last time you changed your fuel filter? If more than 15,000 miles ago change that first.
However, this sounds like either the fuel pump (time will tell) or the fuel pressure regulator (time will also tell). Does it take longer to start? Longer cranking times? Is the fuel pump really noisy now (different from before)? Is the fuel pump really quiet now (it used to whine)? So just buy a fuel pressure gauge and test the fuel pressure at the fuel rail. This is on the drivers side, very near the firewall with a screw-on dust cap on the valve. Test pressure at prime, idle, WOT (wide open throttle) and with the key off. Fuel pressure at prime and idle should be around 54 psi to 58 psi. WOT should go up to maybe 62 psi and then the vacuum should pull it down, a little. With key off, fuel pressure should drop a little and then hold. Does it hold or just keep dropping?
If fuel pressure is too low or does not hold the pump is probably bad.
The easiest way to check the fuel pressure regulator (FPR) for a CPI (under the intake plenum) is to check for washing after you pull the plenum. The plenum attaches with about 10 bolts and nuts (all 10mm). Washing is caused by the gas leaking from the FPR and washing an area clean in the intake. Upon assemby the plenum must be tightend consistently with a torque wrench and the tightening of the bolts is sequenced.
Well, you are off to the races.
Both the fuel pump and FPR will go totally out with time. It will never get better. So better to address now than wait to be stranded somewhere. However, generally with both the pump and FPR you will get an early warning P0172 or P0171 code. Read codes for free at Autozone.