Problem after head replacement

1999 XJ had the infamous head crack and got antifreeze into the oil. I replaced the head and am having some issues. It idles great but when throttle is given it back fires through intake and runs rough. The head was purchased from a local rebuilder but i do not know what was done to it. It also has some knocking noises coming from the valve train. Rechecked torques on rocker assemblies and seems good. Should I have changed the lifters or is there a problem with the head. Intake leaks would result in bad idle would it not. Oil is good. What do you people think it can be thanks in advanced for your help.

The first thing that comes to mind is 153624, with #1 at about the 4 to 5 o-clock position on the cap....meaning verify that you've got the plug wires going to the right plugs. I was taught that anytime you replace the head, you replace the lifters and pushrods. Many dont and are ok afterwards but were it me and I were this far in, I'd put in new lifters and pushrods. Did you catch the leak in enough time so that it didn't wipe out the cam? Hows the cam lobe lift looking? There is a chance that your upstream o2 sensor is fouled because of the coolant running through the system. They dont always throw codes and at about 35 dollars for a replacement and knowing that they get crappy after about a year or so, you might consider springing for a new one just to rule it out. You sure you have all the sensors hooked back up...including the vacuum lines? almost forgot...are you getting any check engine light and if so, what are the codes?

^^^Agree, my first thought was firing order or timing. Did you verify the timing marks?

The cap and rotor was not touched and the wires were labeled per cylinder. The sensors were all plugged back in checked all to ensure they were snapped in. The jeep ran good before shut down just had the milkshake oil problem. I will try the o2 sensor someone else suggested this also. Might put some Seafoam in to see if it will clean the remainder of the crap out. Will keep this post up to date let me know if there is anything else to try.

Check the preload on the lifters. How many times have you tried to fire it and how long did you let it run? Lifters may not have bleed down yet.

How do you check preload on lifters it has ran for at least an hour. I have started it at least 10 times.

Verify the basics and troubleshoot forward from there. Dont assume anything is correct with the swap at this point. Here are a few easy things to check that will take about 30 minutes. 1. You labeled the wires to ensure they would not get crossed. Now verify that the wires are in the correct order by confirming the firing order sequence 153624. 2. Verify each spark plugs is good and is in working on each cylinder...pull each plug and verify its firing. If in doubt, put in new sparkplugs and or put on new wires. 3. verify that the fuel injectors are fully hooked up and hooked up in the correct sequence...Injector 1 Dark Green/Orange-White/Blue, Injector 2 Dark Green/Orange-Tan, Injector 3 Dark Green/Orange-White/Yellow, Injector 4 Dark Green/Orange-Light Blue/Brown, Injector 5 Dark Green/Orange-Pink/Black, Injector 6 Dark Green/Orange-Light Green/Black. 4. Verify the ohm reading of each injector...10-15 ohms is good. 5. Doing a head swap means you move wires and harnesses around that don't often get moved. With age, its easy to bump something and break continuity and not realize it. A broken injector wire in the harness could mean an injector might not be getting firing commands and you have no visual indication of a problem. As such, get an injector "noid" light and verify each injector is getting firing orders from the PCM while the engine is running. 6. Verify correct fuel pressure is correct. 49PSI +-5. 7. With all of the above correct, disconnect each electrical sensor on the intake manifold and reseat the connectors. Pay attention to the TPS sensor and the MAP sensor. Make sure on the MAP that the little rubber elbow underneath has not been dislodged. 8. The PCM only uses the o2 sensor for fuel management purposes when in closed loop mode. If you have stumbling trouble immediately from a cold start, know that you are still in the open loop mode and the o2 is not likely contributing to the problem. If you have been running the engine and its warm, you need a scanner to verify which mode you are in at a given time. (FYI, suspects at play in the open loop mode are battery voltage, coolant temp, air temp, cam and crank sensors, MAP and TPS). 9. Verify each of the sensors on the intake is connected and if so, consider troubleshooting each of these with the mindset that there could be broken wires in the harness preventing the sensors command signal getting back to the PCM. I'm not comfortable that you dont have a good feel for the quality of the head rebuild, so I am questioning the head rebuild too. Did the shop miss a crack? Did they break a valve spring? 9. consider performing a cylinder leakdown test on each cylinder to confirm its holding adequate pressure for proper running. You need to have low leakdown and good balance between each cylinder. 10. Consider measuring each valves lift to isolate lobe / lifter problems.

n5xl said:

8. The PCM only uses the o2 sensor for fuel management purposes when in closed loop mode. If you have stumbling trouble immediately from a cold start, know that you are still in the open loop mode and the o2 is not likely contributing to the problem.

Click to expand...

Closed loop happens a lot sooner than you may think. Pretty much as soon as the O2 sensor is up to temp. Typically with in a minute.

Yup...somewhere between 15 to 45 seconds on a cold engine. If he has the problem immediately from a cold engine start, its not likely o2 sensors playing into it...also why I said it would be helpful to have a scanner to verify what mode his is in.