Catalytic converter - safe to drive idling rough / possible misfire

So I had a misfire on cyl 1. I changed cap, rotor, plug, wires and checked the injectors with a multimeter, inspected obvious wires in engine bay. The DTC went away but it's now idling rough in a different way. Can't get CEL to come back on.

Bad gas occurred to me. Jeep has been mostly sitting for months. I put some seafoam in and filled her up. However, I was told by my mechanic and internet strangers I need to strictly limit how much I'm driving with a misfire because I could toast the catalytic converter.

Does anyone have any thoughts on this? I'll need to drive it around to test out the bad gas theory

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What year? Also yes driving with a misfire will overheat and internally melt a cat, plugging it.

1997 4.0

Do you think I need to be as concerned now that the misfire isn't registering?

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Any Check Engine Light (CEL) trouble codes should be promptly diagnosed and repaired.

The only time you should pull over and stop driving is if the 1997-2001 CEL is flashing.

Tim_MN said:

Any Check Engine Light (CEL) trouble codes should be promptly diagnosed and repaired.

The only time you should pull over and stop driving is if the 1997-2001 CEL is flashing.

Click to expand...

Currently there's no CEL

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If your concerned about the gas, drain and re-fill. You could try to top it off but that depends on how much you have in it now. A new set of injectors would not be out of the question, have you checked the fuel pressure?

RCP Phx said:

If your concerned about the gas, drain and re-fill. You could try to top it off but that depends on how much you have in it now. A new set of injectors would not be out of the question, have you checked the fuel pressure?

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Haven't checked the fuel pressure. That would indicate a bad fuel pump if low?

It had maybe a 1/16 of a tank, that's why I just filled it up and didn't bother to drain the old fuel.

I'd rather not shell out the money for new injectors if it's avoidable. I saw a set was something like $400 on quadratec. I have an appt with a mechanic two weeks out. My goal is try try all the cheap easy stuff before then. If it's something moderately expensive I figure save the money for their bill rather than throwing parts at it. Particularly now that the misfire code is gone.

So do you think I'd be alright driving it around some to get the fresh gas and seafoam through the system or too risky in terms of the toasting the cat?

The driving part depends on what's happening at the time, but you won't find out with it in the driveway. You can get good injectors for around $150.

$150 I could probably swing. What injectors would you suggest?

Also, if what's happening at the time is just the rough idle would you see that as safe? Only way I can get the code to pop back up is to remove the ignition or injector wire.

I've bought several sets from these guys with excellent performance, and that's with my oldest set going on 5yrs now.
https://precisionautoinjectors.com/collections/jeep-fuel-injectors

I'll see how the compression test shakes out and if it's good possibly pull the trigger.

Any advantages from the upgraded injectors or just putting in new ones generally (beyond attempting to fix the rough idle / misfire)? Like, does the spray pattern get messed up over time and I'll see some gains in power or something?

well if it was already driven a bunch with misfire, the cat(s) may already be shot. now you got good gas in there for the most part i.e. just over one gallon old gas, and near 14 gallons new gas. unless that one gallon was many years old, or contaminated with some really bad stuff, you should he ok now.

drive a short distance, if she is still rough, return home and diagnose more. if not rough, maybe she is ok now.

if still rough, yes check the injectors, first check the fuel pressure, bad pressure can be a kink hose, clogged filter, bad pump, failed regulator or such. if pressure good you can also check each injector, one at a time, remove from intake and check flow rate into a vial, and note for even spray pattern, and check for failure to shut off, or course pressure test is also a test for injector failing to shut off as you should make sure pressure holds high after engine shut off, if pressure drops fast, that indicates a leak, possible an injector not shutting.

if she is missing, rough, discontinue the test drive to save the cat(s)

also a clogged cat can cause rough running, loss of power.

if you replace cat, also replace O2 sensor, a bad O2 sensor can rapidly kill a new cat.

also after the test ride, if still rough, check spark plug color, as that can indicate which cylinder is bad.

also intake leaks can cause misfire, so do an intake leak test with a flammable aerosol carb cleaner spray, spray at the intake gasket, injector seals, hose fittings, throttle body base etc. do this at a stable idle. if idle changes with application of spray, then you have a leak this is a simple test to confirm intake sealing.

also make sure the coil,is producing a good strong spark, note spark gap jump length to ground, and spark color, should have blue color indicating a good hot spark.

also exhaust leaks upstream of the O2 sender will cause a rich mixture, make sure O2 sender is tight, and examine exhaust manifold for signs of leak such a black soot from joints or a crack.

good luck

All good info, the OP has got some work to do!

Yup, incredibly good info. Thanks!

Does it need new injectors ?

My 1998 has +284,000 miles and most of the original injectors. The only injectors replaced were cracked. I dragged some newer injectors home from the junkyard. This same 98 was wrecked and sat under a tree with no gas cap for two years. After I fixed it, I drove to the gas station and topped of the gas tank.

I ran some seafoam and other injector cleaners through my 91 4.0 and they melted my CAT.. I assume that the CAT was already toast and the injector cleaner made it worse by pushing a ton of heat that way. Once I replaced the CAT everything improved.. sound, heat, mileage, power..

whatwave said:

So I had a misfire on cyl 1. I changed cap, rotor, plug, wires and checked the injectors with a multimeter, inspected obvious wires in engine bay. The DTC went away but it's now idling rough in a different way. Can't get CEL to come back on.

Bad gas occurred to me. Jeep has been mostly sitting for months. I put some seafoam in and filled her up. However, I was told by my mechanic and internet strangers I need to strictly limit how much I'm driving with a misfire because I could toast the catalytic converter.

Does anyone have any thoughts on this? I'll need to drive it around to test out the bad gas theory

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Click to expand...

Is it possible you got the plug or injector wires swapped around? Pull the codes. Just because the lite isn't on doesn't mean there aren't stored codes.

whatwave said:

$150 I could probably swing. What injectors would you suggest?

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Try PMing jhc7399 over on CherokeeForum.com. He sells refurbished, flow matched Bosch 4-hole injectors for a really good price. He can help you with which injectors based on the year (Bosch 746 for Renix, and 703 for the HO engines). Beware that some of the online vendors are selling cheap chinese Bosch knockoffs.

lawsoncl said:

Is it possible you got the plug or injector wires swapped around? Pull the codes. Just because the lite isn't on doesn't mean there aren't stored codes.

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Oh, I "fixed" my check engine light long ago. When I say CEL is or isn't lit it's more metaphorical. I scan with Torque regularly. If it's throwing a new DTC I just call that a lot CEL

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