5.2L hesitation

[Curtis_H]

I installed a 5.2L from a 93 grand cherokee in my cj. I have had jeep on the trail since spring and have got most of the bugs worked out except one.

When I try to go from idle to wide open throttle like say at start of a hill climb many times engine will hesitate and not rev for a split second and kind of pop back then all sudden takes the gas and goes fine. Runs fine through rest of rpm range. Also if I am cruising around with rpms 1000 or higher it will take wide open throttle with no problems.

I have verified fuel pressure is around 38psi, I have set the cam senor sync with voltmeter, I have changed tps twice and seems to be responding on scanner, I have cleaned throttle body and replaced iac. I have not found any vacuum leaks.

One thing I know of and may be a problem and would like someone to confirm either way is motor and harness are out of a 93 zj. Zj had a alarm system on it so when I first started using that computer motor would start and shut off due to security system. I could not find any clear answers on if any 93 zjs came with out alarms and of so which ones. So I installed a computer I found off a 95 1500 pickup. Motor fired right up and ran good. I have been over scmatics and researched and only real difference I found is on the 95 truck it used 2 o2 sensors. The 93 zj only used one. My harness is only set up for one so that's all I have installed but computer is looking for 2. Looking on scanner both banks for fuel injector pulse width looks like they are tracking exactly the same. And engine runs great other then Initial hesitation.

Could this be the problem or do I need to look somewhere else. Also wondering if maybe timing chain could be stretched.

 

[retroedaddy]

I had a similar problem on my 5.9. I tried a lot of different things then finally talked to a guy who worked for Chrysler for a lot of years. He suggested it was the lower intake gasket, I replaced that and it fixed it. Here is a pic of where it is.

 

[Curtis_H]

Ok thanks I plan to put a full set of gaskets in it after the shop ride to fix some oil leaks any way so I will make sure to change this one also and see if it helps.

 

[NCJeeplover]

I agree with retroedaddy. The plenum plate is a consistent problem with these engines. I HIGHLY recommend upgrading while you do it or it will happen again.

Hughes Engines

 

[Curtis_H]

Thanks for the link. I was reading it and it says that this gasket being blown can cause engine to smoke. I do have blue smoke that seems to come and go. I have been thinking about a complete rebuild but wanted to make sure I could get the bugs worked out first before I spent the money. But this gasket may be the cause of both the hesitation and smoke. I will definitely get it replaced in a few weeks after the next ride and report back.

 

[Curtis_H]

Well I decided to go ahead and replace gasket before the shop ride. Looks like yall were right. I have only drove the jeep around my neighborhood, but seems to be running much better. It does not hesitate or pop back now and feels much stronger. Thanks for the help.