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-   -   Starts cold but dies out when warms up (http://www.wranglerforum.com/f210/starts-cold-but-dies-out-when-warms-up-71075.html)

jeff98059 12-04-2010 05:44 PM

Starts cold but dies out when warms up
 
My 1998 TJ with a 4L starts right up cold but once it gets warmed up a little it starts running rough and dies, after that I can't restart it untill it drops down again. It's not overheating.

Any ideas? I did clean the throttle body, new fuel pump and filter last year.
Thanks.

jasonwrangler 12-04-2010 06:03 PM

when you clean the throttle body, did you clean the idle air control?
also when its warmed up, when you say it runs rough, is the idle correct? or its idling low?

jeff98059 12-04-2010 06:06 PM

Just put the straw inside the groove and shot as much as I could, didn't have the right torx driver handy to pull it, guess after the game I'll hit the store for a stubby so I can pull it off.

It runs fine untill it reaches temp, idle seems right and all that.

jasonwrangler 12-04-2010 06:13 PM

Quote:

Originally Posted by jeff98059 (Post 908152)
Just put the straw inside the groove and shot as much as I could, didn't have the right torx driver handy to pull it, guess after the game I'll hit the store for a stubby so I can pull it off.

It runs fine untill it reaches temp, idle seems right and all that.

if your idle is fine after warmed up but engine running rough, then its not the idle control
got CEL?
when you say dies it just dies suddenly or the rpm gets lower and lower?

rrich 12-04-2010 07:22 PM

Jason's on the right track. The IAC is only operational at closed throttle - idle. If you hold the throttle open and it still is rough, then for sure it has nothing to do with IAC.

Start with the ignition.

jeff98059 12-05-2010 12:18 PM

Not sure what you mean by start with the ignition.
PLugs, cap, rotor, and wires all fairly new.
Starts up fine cold then dies out when warm, no amount of throttle will keep it running.

JD Adams 12-05-2010 01:31 PM

Rule out fuel starvation first. Did you replace that fuel pump with an OEM or aftermarket product? Aftermarket pumps are notorious for this kind of thing.

Hook up a pressure guage to the fuel rail and start. Leave key on while the engine dies; pressure should remain constant. If not, focus on the fuel delivery system to find your problem.

I've seen defective fuel pump relays that cause fuel pump delivery problems as well.

rrich 12-05-2010 01:33 PM

When it's cold it's in open loop - the PCM richens it up (old way the choke is closed.) As it warms up the computer starts taking control and leans it down (old way the choke opens.)
Try holding your hand over the throttle body while it's warming up, blocking some of the air, if it's too lean it will richen it enough to keep running.

Sounds to me like a severe vacuum leak. A small vacuum leak won't keep it from running, it'll just run rough warm. This is a big one. Try pinching off the vacuum hose to the power brake booster to see if that helps. The booster may have gone south.

Look at the throttle body - is it loose? As it's running but warming up, spray some carb cleaner around the base to test for a big leak.

Once it dies and won't restart if you spray some BURNABLE carb cleaner like Gumout on the leak it should try to start momentarily. The carb cleaner will try to burn like gas for a few seconds.

Try spraying down the area where the intake manifold meets the head - the manifold may be loose or cracked.

Let us know what you find - or didn't find.

Also if you "didn't find" - when you say warmed up, do you mean after 2 minutes or so, or more like 15 minutes. The coolant takes 10 or 15 minutes to get up to temperature, but it goes into closed loop in about 1-2 minutes. It could give a clue to where to go next.

jeff98059 12-05-2010 04:58 PM

It'l run 15 minutes when cold then sputters out, if it restarts at all it wont stay running long after this.

rrich 12-05-2010 06:11 PM

Yeah, try choking off the TB when trying to restart. If it even tries to start it's lean.
Or better yet, just before it's dying choke it off. Don't fully choke it, just restrict about 60% - 80% of the air. If it stays running tht proves it's lean - for a reason yet to be determined,

Running 15 minutes before dying pretty much eliminates a big vacuum leak, that should make it die much sooner as soon as it goes into closed loop.

Need to know if it's dying from being too lean or from another cause not lean related.

Or possibly it's too rich. Getting lots of black smoke as it dies?

I suspect a faulty temperature sending unit - without looking, I think it's right on the thermostat housing. Not expensive. If you know someone with a good scanner that can see the computer's interpretation of the block temperature, you may find the temp is "stuck" and doesn't change as the engine warms up. The expensive elaborate scanners can do that.

Although somewhat rare, a possibility is the cat's plugged. When it heats up it plugs worse. Try standing behind the rig and listening while it warms up, then dies. You may be able to hear it progressively choking the exhaust off. Typically it'll whistle or hiss.

jeff98059 12-05-2010 06:50 PM

Choked it off when warn and starts up, stays running for a bit with my hand on it but not when I pull hand away.
No black coming outta tailpipe, the exhaust is original, so cat would be also. 12 years old with 110K.

rrich 12-05-2010 07:03 PM

Then that shows it's way too lean. Something is telling the PCM it needs to be super lean.

Like the block temp sender unit.

I'd think if it was fuel pump related it would still run bad even with it choked off, in that case it would not be able to get enough fuel.
Running better shows it has the fuel but the command to the injectors is to go lean.

How's the battery? Does the volt meter on the dash show it's low? Low volts to the PCM does strange things.

jeff98059 12-05-2010 07:08 PM

I did trade my kid batterys on the trail and still have his in mine because mine was new and his was dead due to alternator, my gauge shows its sitting at 14 volts when it's running.

JD Adams 12-06-2010 04:33 PM

It's always interesting how people panic and begin replacing parts randomly and/or soliciting dozens of different opinions from strangers when a machine ceases operating properly, rather than using established troubleshooting methods set forth in most repair manuals. LOL...human behavior continues to amaze me even after five decades of observation.

jeff98059 12-06-2010 05:57 PM

Quote:

Originally Posted by JD Adams (Post 911007)
It's always interesting how people panic and begin replacing parts randomly and/or soliciting dozens of different opinions from strangers when a machine ceases operating properly, rather than using established troubleshooting methods set forth in most repair manuals. LOL...human behavior continues to amaze me even after five decades of observation.

Seems random, personally I like to study up and pick peoples brains before I start buying parts if I'm clueless.

rrich 12-06-2010 07:33 PM

JD - at least he's asking before throwing parts at it. Service manuals are cheap compared to a stack of parts. Chilton and the home types are useless - many times even wrong!
Ebay has them on disc, the cheaper discs are a rip-off - they only cover a few chapters, not the entire manual. But the more reputable places have complete ones for a little more.

Logically eliminating potentially defective parts by step by step diagnosis is always the best - and cheapest.


Try jumpering it to another vehicle's battery and let it warm up to see if it dies - to eliminate it being a battery problem.

Check the bottom side of the relay box under the hood. Look at the bottom of the sockets for loose wires or corrosion.

jeff98059 12-16-2010 06:20 PM

Quote:

Originally Posted by rrich (Post 909675)
Yeah, try choking off the TB when trying to restart. If it even tries to start it's lean.
Or better yet, just before it's dying choke it off. Don't fully choke it, just restrict about 60% - 80% of the air. If it stays running tht proves it's lean - for a reason yet to be determined,

Running 15 minutes before dying pretty much eliminates a big vacuum leak, that should make it die much sooner as soon as it goes into closed loop.

Need to know if it's dying from being too lean or from another cause not lean related.

Or possibly it's too rich. Getting lots of black smoke as it dies?

I suspect a faulty temperature sending unit - without looking, I think it's right on the thermostat housing. Not expensive. If you know someone with a good scanner that can see the computer's interpretation of the block temperature, you may find the temp is "stuck" and doesn't change as the engine warms up. The expensive elaborate scanners can do that.

Although somewhat rare, a possibility is the cat's plugged. When it heats up it plugs worse. Try standing behind the rig and listening while it warms up, then dies. You may be able to hear it progressively choking the exhaust off. Typically it'll whistle or hiss.

The temp sending unit did the trick, was nice to be able to go through this without dumping a pile of money into it, part cost 15.99, heading up to the pass this weekend to play in the snow. THANKS!


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