heat soak or something else?

I've been reading a bunch of threads on this. I've just ordered the elk timmer for the fan. which I think is a good idea whether it solves my problem or not.

but I'm not sure if I have the notorious heat soak issue or something else.

first of all it's a 99. and it seems to be a 2000+ issue.

I have no starting issues. I have no cold running issues. I have no CEL. I've had this problem for years it hasn't gotten any worse just keeps happening. it's pretty minor so I haven't bothered to fix it. but it's getting annoying.

it happens 80% of the time on hot starts. (year round even in below freezing outside temps) I have a bad idle / no power issues. however the problem starts 1-2 mins after start up.

does the normal hot start issue happen immediately after startup ? or cause tough starting? I couldn't find any posts with actual symptoms.

so I'll start the car (after it sat hot for 15-45 mins) it'll start and run fine. I'll get 3 blocks down the street. I'll lose all power. car will barly move forward and run like garbage. if I don't give it gas it will occasionally stall out as I roll down the street. 30 secs later it's running fine.

same thing happens if I don't move. start car. idle in park for 2 mins. then idle goes to cr*p. push the gas pedal down a bit so it doesn't stall. 30-60 secs later it runs fine.

if it stalls out. no problems restarting. and runs fine after restart.

no problems running for long periods in hot weather. problem only happens on hot restarts.

What have you cleaned/inspected/tested/replaced so far ?

How old are the O2 sensors ?

Based on my heat soak, I don't think that's your problem. After lengthy run in 95 degrees and sitting 15 minutes, I have lengthy cranking for a rough restart. Takes a minute or more to run smooth, but then all is good.

Just throwing a few things out there. It seems to be something heat related. Try turning the key from off to run a few times, trying to get some cooler fuel to the rail. Any XJ without a fuel return line can heat soak.

Ignition coils can do this, try pulling a plug wire; number two is handy and putting a used plug, gapped to around .060 in that spark plug cable, then look and see what kind of spark you are getting.

A timing light can be an indicator of a CPS issue, you hook it up to a random spark plug cable and watch the light for misses. If the CPS is marginal it may miss random beats and this will show up as a miss to the spark plugs. Spark plug cables, distributor cap/rotor, coil and the general health of the high voltage delivery system may also be an issue.

The trick is to catch these intermittent problems in the act, then work from there, trying to figure out if it is fuel or ignition causing the problems.

Best guess is it is a CPS issue, my 96 would do much the same in the early stages of CPS failure. For me it always seemed to happen right at the transition from open loop operation to closed loop operation, just when the motor would hit around 140-160 degrees. Mine never did throw a CPS code and eventually failed completely.

I've changed the plugs, wires, cap, rotor a couple times since the problem has started (4+years ago ?) last time 2 weeks ago.

doesn't sound like it's the common heat soak problem if it normally effects starting and happens right away. also sounds like it happens mainly in hot weather. mine did it twice this morning and it's 30F outside. though it seemed to not last long today.

it'll be hard to catch and monitor while happening.

I've read the coil will cause issues while running in the heat? and requires cooling off before it'll run again. which is different then mine. but might cause multiple issues I guess.

Have you tested the coil ?

What you describe is not heat soak. Based on your limited diagnostic info, I would suggest you test the O2 sensors and inspect their wire harness and plugs. A lazy O2 sensor can cause bucking or stalling when the ECU switch from open loop to closed loop. You should also test the Coolant Temperature Sensor.

is the test info in the FSM? the copy I have is only half compleate I'll have to take a look.

wouldn't those issues come up on every start though? as it would be switching from open to closed even when started cold as well.

my problem is still only on hot starts. 0 issues first start of the morning or after sitting all day.

Been my experience almost anything is possible with high voltage. I had an issue with a hot motor, it would start just fine cold, but hot it would miss like crazy. Turned out to be some water under the sync sensor plate in my distributor, it would get hot turn to vapor and cause random arching inside the distributor. Not saying this is your issue, but just a story to illustrate what can happen with high voltage and heat.

I have an idea for a low tech troubleshooting method that may help nail down the problem. Next time you park it hot for a short period, dump a small bottle of water on the CPS and see what happens. Try the same thing with the fuel rail. Maybe seal up the coil well, with some dielectric grease and pour some water on the coil. May take a few repeats but eventually you may be able to isolate the culprit.

I had a CPS do that, it would crap out when it got hot. I suspected it was the CPS. One day on a hunch I poured a bottle of water on the CPS after a no start and it fired right up

Coils that get hot and act up are fairly common. Jeep supposedly redesigned the coil to withstand the temperatures when mounting the coil on the block. But who really knows how well redesigned it was?

as an update I installed an e fan timer for 3 mins but it didn't effect my problem. but it's a cool mod and I'm glad I did it.

it appears it was the upstream 02 sensor.

since the stumble / trying to stall / no power happen about 30-60 secs after startup I'm guessing there was a glitch when switching between open and closed loop.

I replaced the whole exhaust as the muffler was barley hanging on. with new upstream 02, left old downstream

hasn't done it since.

never had a CEL

I think my millage went up 20% on the highway too. but haven't driven it to far yet to really confirm.

still have a cracked exhaust manifold....