Cold Starting Fuel Exhaust Smell XJ

[jeepsrock]

I am not sure if this is somethin to worry about, but whenever i start the jeep when its been parked for a night it starts fine but the exhaust reaks a gas smell. I have the checked the obvious injectors o-rings / fuel filter. I am pretty sure its coming from the exhaust, whihc if left to idle usually goes away in a few mins.

Pete

 

[Yucca-Man]

What year / what engine / what thermostat, and do you have ANY indication of leaking fuel around those injectors?! If so, cease driving it now and get those repaired/replaced before you report yet another car-b-que...

 

[RTicUL8]

:chef:
I failed divination-101,

but I aced Wild-Guesses.

Therefore, I will diagnose your problem using my Wild-Guess magic toenail.

You have a broken, loose, or disconnected spark plug wire. One of the cylinders is not firing. It is filling up with gas and that is why you smell it – it’s being pushed out the exhaust.

 

[jeepsrock]

Well its a 94 xj with the 4.0HO /aw4/231. I have the 195 mopar thermostat in there and the motor has 112k miles on it. AS far as i can tell there is no fuel leaking anywhere including around the injectors.

pete

 

[Matthew Currie]

Does it smoke or run rough until it warms up? Possibility that an injector is leaking into the cylinder after shutting down. This wouldn't have much effect on running once the excess gas burns off.

 

[jeepsrock]

Well when i start the jeep in the mornings it acts a bit weird but i always attributed that to its age. When i first start it if i press the gas pedal it bogs down a bit unless i press it a bit hard. The idle is fine usually at 1k rpm until it gets hot where it drops to 700-800rpm. Usually after a min or so it works fine and does not bog and drives fine with no noticable issues.

pete

 

[Matthew Currie]

Well when i start the jeep in the mornings it acts a bit weird but i always attributed that to its age. When i first start it if i press the gas pedal it bogs down a bit unless i press it a bit hard. The idle is fine usually at 1k rpm until it gets hot where it drops to 700-800rpm. Usually after a min or so it works fine and does not bog and drives fine with no noticable issues.pete

I still think it might just be a little flooding from an injector. It's pretty simple to have those tested for leakage with an injector tester and a pressure gauge. But you might want to run a bottle of Techron or something like that through it and see if that helps.

 

[jeepsrock]

Well is funny that you say to run that stuff thru as i have already ran one last month with little to no effect. Actually it was a black and blue bottle , the chevron techron stuff.

How and what exactly do i need to test the injectors?
pete

 

[RTicUL8]

You're not listening. :twak:
My magic toenail still says its a spark plug wire :exclamati

 

[jeepsrock]

If it was a spark plug wire then wouldnt the engine misfire at all times. And especially under load the engine would hesitate/ vibrate a bit ?

I will check the wires tonight for spark at the ends ?

pete

 

[jeepsrock]

I havnt had time to check the wires for spark tho i do remember a while back that aline to my charcoal canister was a bit messed up so i kinda repaired it, if the line has deteriorated again would this casue that in the exhaust ?

Also when checking for leaky injectrs where exactly on the injector do i check and is it hard to see or is it apparent ?

pete

 

[jeepsrock]

ok guys...sorry for the long time update....I checked all spark plug wires , replaced them and replaced plugs.

I checked for leaks around the injectors and there apears to be none. I repaired the canisters hose and the problem is stil apparent.

During a cold start the whole vacinity smells like raw fuel out of the exhaust. I have to close all the near windows of the house when i start the jeep bc it gets into the house and bothers everyone, its pretty bad- tho it lasts only for a few min .

Pete

 

[HossHoffer]

I believe you need to look at the coolant temp sensor. That usually will explain burning rich at cold start.

 

[jeepsrock]

I replaced that last week as per suggestion from a auto friend and it didnt do a difference. Can it be bad ? OR should i get the one from the dealer ?

IS there a test for it ?

pete

 

[corbinafly]

Possibility that an injector is leaking into the cylinder after shutting down. This wouldn't have much effect on running once the excess gas burns off.

x2

check for this problem.

K

 

[corbinafly]

I replaced that last week as per suggestion from a auto friend and it didnt do a difference. Can it be bad ? OR should i get the one from the dealer ?

IS there a test for it ?

pete

I don't think that the cts is your problem. Your motor is supposed to run rich at startup if your motor is cold. On cold startup your PCM uses a preprogrammed injector pulse width. I think this preprogrammed pulse is influenced by the signal from the map sensor but I'm not sure.
The point is that it's going to run rich until it reaches a predetermined temperature. Once it reaches that temp it uses the signal from the O2 sensor to adjust air/fuel ratio. But if you're smelling raw gas, I'd suspect maybe flooding from an injector. Or maybe a bad map sensor..?

K

 

[HossHoffer]

I replaced that last week as per suggestion from a auto friend and it didnt do a difference. Can it be bad ? OR should i get the one from the dealer ?

IS there a test for it ?

pete

Make sure you're changing the coolant temp sensor and not the coolant temperature sending unit. Not that I ever did that. :banghead: There isn't a check you can do for the CTS other than check for codes. As for the injector leaking. That would be checked by pulling the spark plug after its cold and looking for fuel.

The most obvious things are the CTS and injectors. From there you would have to start checking the TPS, O2 sensor, MAP sensor and EGR. If none of those work then you might need new injectors. I would start with the O2 sensor as they sometimes act that way when they are near their service limits. Do you get raw gas coming out of the tailpipe?

Just so you know. Raw fuel at start-up is the #1 sign of bad CTS.

 

[jeepsrock]

Actually there is no liquid that comes out of the tail pipe just the bad gas fumes. The CTS i replaced was the one on the thermostat. And as far as an EGR i dont think my year has one.

Do you think i need a OEM mopar CTS sensor from the dealer ? As far as the other sensors(o2 and map), do they have a big effect on this issue ?

pete

 

[HossHoffer]

Hmm. I'm at a loss now. The injectors are still a possibility but I would doubt that all of them would go bad at the same time. Just from what you have described my next move would be to change the O2 sensor.

There are ways to check the O2 and MAP sensors if you're handy with an ohmmeter. And you need to check the MAP sensor and hoses for vacuum leaks.

Don't forget to let your computer reset. When you change a sensor then take the ground off the battery for a few minutes. Replace the ground then start the engine and let it idle for about 10 minutes.

I wish I were there. Finding sensor faults on these systems is a royal pia.

 

[corbinafly]

Hmm. I'm at a loss now. The injectors are still a possibility but I would doubt that all of them would go bad at the same time. Just from what you have described my next move would be to change the O2 sensor.

There are ways to check the O2 and MAP sensors if you're handy with an ohmmeter. And you need to check the MAP sensor and hoses for vacuum leaks.

Don't forget to let your computer reset. When you change a sensor then take the ground off the battery for a few minutes. Replace the ground then start the engine and let it idle for about 10 minutes.

I wish I were there. Finding sensor faults on these systems is a royal pia.

If the gas smell goes away and the engine runs fine after it warms up I wouldn't suspect the O2 sensor. The PCM ignores the O2 sensor signal on cold startup. And I highly doubt that all the injectors would go bad at the same time. It could be just one that's leaking down after shutdown. Check it out.

K