1999 5.7 4x4 Hesitation and Miss

[miked79928]

My wife's 99 Surburban with the 5.7 has been hesitating when she drives it cold. It starts fine but when we go to accelerate with the engine cool it hesitates badly almost to the point of backfire. Once warm, this issue goes away. I am thinking this may be due to the engine coolant temp sensor.

Just yesterday I noticed that it has developed a miss under acceleration with the engine either hot or cold. What could this be?

Also, occasionally when we stop the truck I can notice a strong odor of gas coming from the rear of the truck near the tank. I have a feeling it could be the fuel pressure regulator as the fuel pump was replaced only a year ago.

Any help is greatly appreciated as this is the vehicle we use to move our family of 7 around town. Thanks so much!

[j cAT]

Originally Posted by miked79928

My wife's 99 Surburban with the 5.7 has been hesitating when she drives it cold. It starts fine but when we go to accelerate with the engine cool it hesitates badly almost to the point of backfire. Once warm, this issue goes away. I am thinking this may be due to the engine coolant temp sensor.

Just yesterday I noticed that it has developed a miss under acceleration with the engine either hot or cold. What could this be?

Also, occasionally when we stop the truck I can notice a strong odor of gas coming from the rear of the truck near the tank. I have a feeling it could be the fuel pressure regulator as the fuel pump was replaced only a year ago.

Any help is greatly appreciated as this is the vehicle we use to move our family of 7 around town. Thanks so much!

have the service engine /check engine failure DTC's checked out. then post back what was found. with your issues this will help narrow the problem down.

[miked79928]

Thank you for the reply. I actually had the codes pulled and none were present.

[j cAT]

Originally Posted by miked79928

Thank you for the reply. I actually had the codes pulled and none were present.

with no dtc's the fuel pressure should be checked with a pressure guage . should be 60-65psi with key on engine off. then with key left on should hold within a few PSI for a few minutes. If low or pressure drops rapidly the pump is most likely bad.


Injectors fouled/leaking can also give you those issues . usually its with DTC failure codes.

If the pressure is good then the other componet would be the ECT sensor. this reports to the PCM/computer the engine temp. this could be reporting incorrectly giving too much fuel or too little fuel to the engine..

not very expensive to replace / could be the connection also..

[miked79928]

Thanks. I was kind of thinking it was starting to go bad. I am going to change that first thing tomorrow morning and see how it goes. Thank you!

[miked79928]

I replaced the ECT this morning and I saw a little improvement. I made sure to disconnect the negative cable and made sure there were no codes. I also noticed the truck only seems to miss when the trans shifts into overdrive going at highway sppeds. After this shift, the miss is very noticeable if you keep a constant oush on the pedal. The miss does not appear to be present at idle or any other time, or if it is it is not very noticeable. I am planning on checking the fuel pressure this weekend, but is there anything else I should be checking? I checked the plug wires and none seemed to be loose. Thanks so much for the help!

[j cAT]

Originally Posted by miked79928

I replaced the ECT this morning and I saw a little improvement. I made sure to disconnect the negative cable and made sure there were no codes. I also noticed the truck only seems to miss when the trans shifts into overdrive going at highway sppeds. After this shift, the miss is very noticeable if you keep a constant oush on the pedal. The miss does not appear to be present at idle or any other time, or if it is it is not very noticeable. I am planning on checking the fuel pressure this weekend, but is there anything else I should be checking? I checked the plug wires and none seemed to be loose. Thanks so much for the help!

this could be multi problems..

with this miss at ALL temps it can be a bad distributor. these engines at this age have many that the bearing failed causing random miss fires .

thats why the fuel pressures need testing..