Greetings I'm new on the forum and hope a basic question's ok (chiltons manual is on the way from mail order).
I have a 1994 4.0L that's developed a knock. Last week I noticed a knock going uphill and that the temp gauge was a little high (the "a" in "normal"). Filled up that day with half a tank of 90 and a half tank of my more usual 87 octane and it's been better but I'm not sure what to tackle first in solving the knock. The truck had new plugs and wires 5 or 6 months ago, filters and oil all done regularly, generally I go easy on it. What should I check first?

 

Welcome to the forum

Run a can of Seafoam or similar fuel system cleaner in the gas tank, I do this once a year
It cleans up dirty injectors and any carbon inside cylinders, either can cause ping/knock

Next time you hear the ping/knock push gas pedal to the Floor, see if it goes away or gets worse
When computer sees WOT(wide open throttle) it no longer uses O2 sensors for fuel mix, it dumps extra duel in for maximum power, so if pinging/knocking stops then it was caused by Lean mix.

 

Thanks! Seafoam in the gas got rid of the knock in a quarter tank, pretty amazing I guess the detergent they sell me in my gas isn't what I thought. The overheating then actually get worse so I finally got some weekend hours and replaced the thermostat which completely fixed that. Now, I have a warm start question (and tell me if this should be a different thread or subforum).

If I leave my 1994 4.0l stopped for 7 or 8 minutes come back it starts and runs fine. If I wait 10 or 12 (but not longer then 30, longer then 30 it starts and runs fine) it turns over and kicks like it wants to start, sometimes backfiring. But in the 12-30 minute window it usually won't start first try. In that window, if I try to start it kicks like I mentioned and if I sit ten minutes after an attempt it usually will start if I give it some gas. Any ideas? Air filters fairly new, I've run MAF cleaner over the wire screen, and (as I said in previous post) wires and plugs were done in the previous 6 months.

 

Fuel injected engines don't have a "gas pedal" they have an "air pedal", when you press down on the pedal it allows more air in, Computer controls the fuel flow, Driver controls air flow
With a carburetor there was a "gas pedal", when you pressed down on the pedal extra gasoline was squirted into the engine right then.
So you need to think of things a little differently when diagnosing fuel injected engines

Because adding more air seems to help, check for fuel leaking into the intake, which is fairly easy

After it sits for 15-20min(hard to start time) turn on the key, press gas pedal down to the floor ALL THE WAY and HOLD IT DOWN
Now try to start engine
It should NOT start or fire at all, if it does then fuel is leaking in

Test above is using Clear Flooded Engine routine, which is part of every fuel injected engine computer's software
Key on
0 RPMs
TPS(throttle position sensor) at WOT(wide open throttle)
Computer enters Clear Flooded Engine mode, which simply means it shuts of fuel injector pulses but spark stays on

I use this every morning to pump oil thru the engine before I release gas pedal and it starts up.

If engine fires or starts in Clear Flooded Engine then you may have fuel leaking in from an injector or FPR(fuel pressure regulator)
On the 4.0l the FPR is behind the alternator, on lower intake, it has Return fuel line attached and a smaller Vacuum Hose.
If it leaks the vacuum hose sucks raw gasoline into the intake which can cause flooding on startup.

Just after shut down the gasoline will evaporate pretty fast in hot engine
After 15-30min it may stick around, past that it will slowly evaporate so no fuel left

This is all just guessing