Idle issues when hot

['98chili]

I have a 98 Xj, 4.0. Was having typical vapor lock issues.

I have done a complete return style fuel system and replaced every component in the fuel system. Aeromotive 310lph pump, boostwerks billet fuel pump module with return fitting, -6 a feed and return lines, nrt billet fuel rail, adjustable fuel pressure regulator, and 4 hole injectors. I also have new plugs, wires, distributor cap and rotor.

I was still having issues where the jeep would die if I was driving long distances, interstate driving, sitting in traffic, or turning the jeep off for short periods and then resuming driving.

I have since deleted the evap system to rule out a clogged charcoal canister. I haven’t been able to replicate the crank no start like previously, but when the jeep gets hot there is still a constant pinging i can feel in the exhaust that feels like a misfire but the engine doesn’t seem to be running poorly or shaking. This pinging used to appear right before the jeep would die so it is worrying me.

I don’t know what this could be or what to look for. I suspect this could just be caused by excessive underhood heat. With that being said, the jeep does NOT run hot it doesn’t get over 205-210.

Would a cowl hood help?
Would exhaust fans help??

 

[Anak]

I had a pinging issue which I worked on for over a year. It was different from yours in that it did not occur at idle but rather under load (when you could expect pinging on poor fuel or some such thing). It wound up being a matter of injectors flowing at substantially different rates. The XJ computer system has no way to measure or compensate for that. Sending the injectors out for service got them balanced and solved the problem. And yes, I tried the Berryman product. It didn't fix them.

Varmint #1 had a similar injector problem, but his was a matter of one injector which would never close and thus would essentially flood his engine. Again, sending injectors out for service fixed the issue.

In both cases it was remarkable how much variation in flow there was from one injector to another. 30 years of use adds up. If your injectors are original to the Jeep it might be worth it to send them out for service.

 

['98chili]

I had a pinging issue which I worked on for over a year. It was different from yours in that it did not occur at idle but rather under load (when you could expect pinging on poor fuel or some such thing). It wound up being a matter of injectors flowing at substantially different rates. The XJ computer system has no way to measure or compensate for that. Sending the injectors out for service got them balanced and solved the problem. And yes, I tried the Berryman product. It didn't fix them.

Varmint #1 had a similar injector problem, but his was a matter of one injector which would never close and thus would essentially flood his engine. Again, sending injectors out for service fixed the issue.

In both cases it was remarkable how much variation in flow there was from one injector to another. 30 years of use adds up. If your injectors are original to the Jeep it might be worth it to send them out for service.

They have less than 10k miles on them, but they are not Bosch. They are k suspension 4 hole injectors which I have seen mixed reviews about… I might find myself a set of Bosch oem replacements.

 

[Anak]

With that few miles on them I certainly hope the injectors are not the problem, but I will grant that with modern quality standards it is a possibility.