Hello, I have a 99 TJ 6cyl 4.0 with 172k miles. I was in head gasket denial for 1.5 years and replaced the radiator, water pump, thermostat (all needed replacing) and it ran better for a while until coolant started running onto the intake manifold between cylinder 3 & 4. There was no evidence of coolant in the oil.
I have taken the head off & was concerned it was an 0331 with a crack. Turns out it has a 0630 head. The jeep was manufactured in 5/99. I purchased it in 2017, so a lot could have happened before I bought it, but I have no reason to believe it was not the original head. I had a machine shop test for cracks, valve leaks and installed new valve seals. All good.
I reinstalled the head with a Fel-Pro gasket kit and new head bolts. I followed the TJ shop manual for torque and pattern. I reinstalled the intake and exhaust manifold with the existing bolts.
There was not a heat shield by the intake manifold, and the exhaust header has the 2 accordion sections. This may indicate a previous owner installed an aftermarket header and failed to reinstall the heat shield.
One of the exhaust connection flange bolts was corroded, but still had thread left at the end. It being late and me being tired, I went with it and reinstalled the existing flange bolts.
Initial start up went well. Driving it around the block went well, but as it warmed up, it would buck several times. Then the check engine light. The P0171 (lean) & P0133 (slow O2 sensor response) codes were detected by my scanner.
I removed the flange nuts and corroded bolt on one side (pain in the butt) . Installed a new one and cranked down on the nuts (i had previously replaced the gasket). It drove much better, but after 15 min, it bucked once and then the check engine light. P0171. The p0133 code never came on again.
I have since checked all vacuum lines, rechecked the manifold torque, and tightened the flange nuts some more. This time it drove longer just fine, but eventually bucked and threw the p0171 code.
When doing the head gasket, I cleaned the intake manifold really well (extremely gunky inside) replaced the TPS (it would occasionally throw that code, especially when wet for a while) and the throttle body gasket. I did not add any rtv to the gasket, just applied dry.
So I am trying to figure out if
A) there is an issue with the head gasket install (temps are great and no bubbling in coolant resevoir)
B) issue with manifold gasket or install - i installed it dry, no sealant, followed the torque sequence and values, rechecked, head and manifold surfaces were prepped
C) issue with oxygen in-leakage in the exhaust upstream of O2 sensor 1. I am confused on this, it would seem like any crack or leak would expel exhaust gas and not suck in ambient air. But I have read this can happen and believe it. Cranking down on the flange nuts did seem to help. Could I have a cracked exhaust header? I inspected it when it was off the head and saw no visible signs.
D) some other intake leak or a bad o2 sensor? I have sprayed wd40 all around the intake manifold and did not detect an increase in RPM. I do not here a sucking sound. As for the O2 sensor, this is a new code and condition since the head job, so I am ruling it out for now.
Thanks for reading through this. I wanted to be detailed. Any assistance would be appreciated.
I have taken the head off & was concerned it was an 0331 with a crack. Turns out it has a 0630 head. The jeep was manufactured in 5/99. I purchased it in 2017, so a lot could have happened before I bought it, but I have no reason to believe it was not the original head. I had a machine shop test for cracks, valve leaks and installed new valve seals. All good.
I reinstalled the head with a Fel-Pro gasket kit and new head bolts. I followed the TJ shop manual for torque and pattern. I reinstalled the intake and exhaust manifold with the existing bolts.
There was not a heat shield by the intake manifold, and the exhaust header has the 2 accordion sections. This may indicate a previous owner installed an aftermarket header and failed to reinstall the heat shield.
One of the exhaust connection flange bolts was corroded, but still had thread left at the end. It being late and me being tired, I went with it and reinstalled the existing flange bolts.
Initial start up went well. Driving it around the block went well, but as it warmed up, it would buck several times. Then the check engine light. The P0171 (lean) & P0133 (slow O2 sensor response) codes were detected by my scanner.
I removed the flange nuts and corroded bolt on one side (pain in the butt) . Installed a new one and cranked down on the nuts (i had previously replaced the gasket). It drove much better, but after 15 min, it bucked once and then the check engine light. P0171. The p0133 code never came on again.
I have since checked all vacuum lines, rechecked the manifold torque, and tightened the flange nuts some more. This time it drove longer just fine, but eventually bucked and threw the p0171 code.
When doing the head gasket, I cleaned the intake manifold really well (extremely gunky inside) replaced the TPS (it would occasionally throw that code, especially when wet for a while) and the throttle body gasket. I did not add any rtv to the gasket, just applied dry.
So I am trying to figure out if
A) there is an issue with the head gasket install (temps are great and no bubbling in coolant resevoir)
B) issue with manifold gasket or install - i installed it dry, no sealant, followed the torque sequence and values, rechecked, head and manifold surfaces were prepped
C) issue with oxygen in-leakage in the exhaust upstream of O2 sensor 1. I am confused on this, it would seem like any crack or leak would expel exhaust gas and not suck in ambient air. But I have read this can happen and believe it. Cranking down on the flange nuts did seem to help. Could I have a cracked exhaust header? I inspected it when it was off the head and saw no visible signs.
D) some other intake leak or a bad o2 sensor? I have sprayed wd40 all around the intake manifold and did not detect an increase in RPM. I do not here a sucking sound. As for the O2 sensor, this is a new code and condition since the head job, so I am ruling it out for now.
Thanks for reading through this. I wanted to be detailed. Any assistance would be appreciated.
