Pinging 1992 Cherokee Sport 4.0

[WilliamK1974]

Hey all,

I recently bought a 1992 Cherokee Sport with auto, 4x4, 4.0, and a/c with just over 174k miles on the odo. It passed our local smog test but seems to have been the victim of some negligent maintenance.

When I first bought the vehicle, it sounded like something was rattling just before the trans shifted, especially when shifting from 1st to 2nd when accellerating from a standstill. This reminded me of a car I had years ago that would ping under certain load conditions because its EGR valve had failed. Cherokees didn't have EGR in 1992, but it made me think that I was experiencing a preignition situation.

Something else that seemed odd was that the temp gauge rarely got even as high as the 1/4 mark, so I tore into the cooling system. PO claimed to have installed a new water pump and radiator, but the t-stat was in 4 pieces inside the housing. All pieces were present, but still... The coolant seemed dirty and rusty. I replaced the t-stat and flushed everything as best I could. The gauge now tends to stay between the 1/4 mark and 210.

After it sounded like the engine was pinging at 65mph uphill on the freeway, I did a Seafoam treatment, following all directions except for pouring it in the oil as I'd just changed it. I had experienced a fuel starvation issue, so I changed the fuel pump and filter. I've also changed the distributor cap and rotor and plugs and wires. A couple of vacuum hose connections were split, so I fixed them. Does the hose from the valve cover to the air intake box need to have a tight fit?

The engine blew *alot* of smoke when I started it after it had sat for 5 minutes and I was holding the idle close to 2500RPM.

What happens now is that the engine is ping-free until it gets close to NOT. Then, it pings at the shift, especially the 1st to 2nd shift. But it's quiet until then.

One of my friends theorized that the broken t-stat may have caused the engine to run cold for a long time, leading to the cylinders becoming carbonized, which would hold heat and causing pinging. But we really don't know.

Any other suggestions would be appreciated.

Thank you,
-Bill

[bigjim350]

When it smokes, what color is the smoke? To me it sounds like the timing may be too advanced.

[WilliamK1974]

When it smokes, what color is the smoke? To me it sounds like the timing may be too advanced.

It only smokes immediately after doing the Seafoam treatment. Otherwise, it's smoke-free.

The timing could be too advanced, but I'm not sure what to do about it. In 1992, timing was controlled by the engine electronics and not adjustable.

[4.3LXJ]

I am thinking timing too.

[WilliamK1974]

I am thinking timing too.

But this still begs the question of how to remedy a timing situation when there's no way to adjust the timing because of how it's controlled by the PCM.

[4.3LXJ]

The PCM needs a reference to work off of. So there is a timing procedure to disconnect the PCM from the distributor. When you get a smog check, they do this every time.

[WilliamK1974]

The PCM needs a reference to work off of. So there is a timing procedure to disconnect the PCM from the distributor. When you get a smog check, they do this every time.

Where I live in TN, the only thing they do during a smog test on a car as old as mine is a sniffer test. They also check the gas cap for leaks. But no wiring is connected or disconnected.