heat-induced misfire with a twist

I totally realize the late-model heat soak issue has been beat to death. However I'd had something come up this week that initially felt like that same thing but has gotten much worse so I figured I would ask about it.

Vehicle and History:
- '00 Sport with the Cali emissions package (2 pre-cats)
- On second engine due to 0331 head issues, 4 years old
- Hood vents 3 years ago
- Fan override switch 3 years ago
- Stock fan configuration with heavy duty fan clutch 2 years ago
- The useless #3 injector insulator installed 7 years ago

I normally run around 210 on the dash gauge, a little under if I'm moving. I have a winch up front, but I usually run cooler if I'm moving (even in the mountains) so I don't worry about the winch impeding airflow.

The problem:
I've had heat soak issues before. Walk into a store for 5 minutes, come out and it would misfire for a couple minutes, then smooth out and off I go. This is way worse. It's been mostly in the 90's during the days around here.

A few weeks ago it started where I would shut it off for 10-15 minutes, then come out and it was misfiring. But it doesn't clear up after a few minutes. One day I drove home 15 minutes with it misfiring the whole time.

Yesterday was the worst and most unusual. I was sitting in traffic and it was baking, so I turned on the A/C to cool off a little. The fan kicked on with the A/C but within 15 minutes the temp climbed to about 225 and the engine started misfiring while I was moving!

Today I only shut off the engine for 5 minutes in the shade and it still started misfiring. Today it was while I was trying to get my emissions done and the problem make them fail me out, so that was not fun. Then it happened again after being in the doctor's office for almost half an hour, and the temp gauge even said it was under 210 when I started it.

Now:
I had planned on putting in a shutoff fan timer, but this seems to be worse than a fan timer can solve, especially when it happens with a running hot engine. What should I look at? Replace? Upgrade?

This kinda sucks since I'm out of town for the next 2 weeks on business and now I'm guaranteed to be a month late on my registration because of this emissions issue.

Things I've considered doing:
- New radiator (mine's stock), to try to keep the engine cooler to begin with
- New injectors, apparently this has helped other people
- Shutoff fan timer

You didn't mention the cooling system service history.

Maybe time for a flush, fresh coolant, and a pressure test/new cap.

That said, few have ever "fixed" hot/heat soak without adding a timer to the efan.

Try parking and opening the hood, see if that relieves if not eliminates the symptoms--if it does, install the timer.

The Datsun F10s got so hot there was a little fan in the engine compartment to blow cool air on the carb.

DOZENS of modern vehicles have efans that kick on, engine OFF/key OFF, when the underhood temps climb too high. The best Chrysler could do was a .03 cent wrap for an injector.

Back on topic--make sure the system is in good condition, serviced, and put in a timer.

Yeah, that's pretty much what I was planning on. Stopping and running the manual fan override or opening the hood for 10-15 minutes fixes the issue when stopped. The thing that stumps me is the misfire in traffic with high temps without ever turning off my engine.

Say, would bad or plugged pre-cats make this issue worse? I replaced the pre-cats with a used set a few years ago.

Fully service the cooling system as suggested. If that fixes the problem, you're done.

Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a slipping mechanical fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller or even a defective radiator cap.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others, and your engine will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic, points to a weak or failing mechanical fan clutch or worn out water pump fins.

The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.

-Use a flushing/cleaning solution to remover mineral buildup or rust, and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

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Update.

Due to the order of parts arriving, I installed the new fuel injectors first. I had ordered them on a recommendation of a mechanic I talked to who said the Siemens injectors tended to fail at the mileage my rig is at. Replaced those and the heat-driven continuous misfire was gone. I flushed my cooling system really well, replaced the radiator, and bled it. I still get the occasional 15-minute heat soak misfires that everyone with late-models deal with, but nothing like before. I am working on a fan timer design that I'm going to build that incorporates some features I want to have. That will solve the heat soak issue for good.

Oh, side question. I know everyone says to keep the coil in the lower hose. Problem is, I pitched mine years ago before I knew any better. Any places to buy a new one?

Mopar hose comes with the spring in place.
Tim_MN mentioned thermostat, I had one flake out a couple of years ago.
Overheat issues where a nightmare until I changed it out. I change them yearly now.

You can always replace the lower hose with a UNIVERSAL FIT HOSE--those will never collapse, you never have a spring rot away.

Remember--they are "ribbed" for your pleasure!