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Username Post: Hesitation or miss in 4.3L        (Topic#357269)
Redspad 
Poster
Posts: 88
Redspad
Loc: South West Florida
Reg: 08-15-09
07-18-19 03:55 AM - Post#2770962    

Have a 1997 S10 3door automatic. Here about 2/3 months ago the motor got extremally hot. Had it towed in and replaced the radiator, pump, thermostat, and lower hose, done a pressure test on motor and it pumped up and held. Ever since there has been a miss or hesitation. Changed the plugs, wires, distributor, distributor cap n rotor, mass air flow sensor, still there. Have never found any condensation [water] on ground or out of the exhaust. Temperature is normal but after driving a while and shut down at times it does want to start hard. I want to sell it but I feel this should be fixed first. Oil has never had a burnt smell. It idles smooth and when running at about 50/60 mph in cruise you can feel a slight hesitation but when you step on the gas it runs like a scared rabbit. Also had fuel filter changed and pressure on the fuel pump and that is good. Sure could use some advise.



 




gchemist 
Senior Chevytalk Moderator
Posts: 24929
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-18-19 07:24 AM - Post#2770972    
    In response to Redspad

The problem may be under the intake, the FI spider. Extreme heat could have damaged one of the poppets. Check your fuel pressure. It should be above 55 PSI. The ECM is not detecting something or it would set a code. Scan it anyway. It may have a pending code. Check all the vacuum hoses. One could be broken or loose. Remove and clean the ERG valve. At night, check under the hood with the engine running. Check if any spark plug wires are arching. What were the cylinder pressure readings? Have the lower intake gaskets ever been replaced?

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Redspad 
Poster
Posts: 88
Redspad
Loc: South West Florida
Reg: 08-15-09
07-18-19 08:11 AM - Post#2770975    
    In response to gchemist

Have not done a compression test as of yet. The shop I took it to said they did a pressure test on the pump and said it was good. Question, if I had a broken or lose vacuum hose wouldn't I have a rough idle. We did find a couple of plug wires arching and that is why we changed them all and as of right now none are arching. To the best of my knowledge NO the intake gasket has never been changed. Thanks for the come back and info.



 
gchemist 
Senior Chevytalk Moderator
Posts: 24929
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-18-19 12:00 PM - Post#2770990    
    In response to Redspad

A failing head gasket may not show up until it's hot. The head may have warped cause cylinders to bleed into each other. When they do that water does not leakF into the cylinders or air into the cooling system. Some vacuum lines are not used until the engine is hot or under high RPMs. GM did away with vacuum lines at high RPMs by using electric EGR valves. Emission stuff is all temp and vacuum operated. The most annoying part is going to be finding a bad poppet. GM updated the FI spider in late '01. The poppets were removed for hose end fuel injectors. I upgrade my old 96 to the updated spider. It did wonders for running good. It took 6 months of troubleshooting to eliminate everything down to bad poppets.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 




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