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Discussion Starter #1
Hi, I recently picked up a 04 pt cruiser non turbo manual transmission that has 102k on it and freshly rebuilt other than sitting for 5yrs. It runs good other than a p0420 code and when ever you let the rpms drop when coming to a stop or when you start it sometimes it will stumble or die. I have had it on a scanner and all sensors seem to be operating like they should. It does have a hot smell and oil smells like gas. It doesn't have a Schrader valve on the fuel rail so unable to check fuel pressure. Does anybody have any ideas what could cause this? I'm leaning towards a vacuum leak or something fuel related. Thanks
 

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Assuming P0420 is the only code stored.
Warm the vehicle to normal operating temp, with the scanner connected bring the RPM to 1500 and watch the Voltage of the Downstream O2 Sensor, what is the voltage reading?
 

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Discussion Starter #3
I didn't do the reading a friend did but they didn't do what you just described. So I don't know what the reading was. But it's getting a hot smell coming from cylinders and plugs are burning hot and I checked for vacuum leaks and replaced the fuel rail along with the injectors that came on the fuel rail and harness with one that has a Schrader valve so I can test the fuel pressure. I will post back once I get a chance to do a fuel pressure test. The exhaust doesn't seem plugged at all but it acts up worse once it's warmed up or after driving for a while.
 

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Is the CEL illuminated?

Code P0420 is Catalyst Efficiency meaning the Cat is not doing its job.
The upstream O2 sensor voltage should be constantly moving between .1 and .9 volts indicating the controller is making fuel corrections.
When the exhaust moves through the Cat all pollutants are converted and all oxygen is used so the voltage on the downstream O2 sensor should read approximately .45 volts and not move.
If the down stream O2 sensor is reading what the upstream O2 sensor is reading the Cat is not doing its job and a P0420 is set.

My Son's subscription to Alldata for his 2003 Caravan expired or I could have given you the exact diagnostics



 

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Discussion Starter #5
Ok so I found my Bluetooth code reader. Only code is p0420 and while cold both o2 sensors read the same basically. Once warmed up, upstream bounces between .1 and .9volts like it should and the downstream stays at .7 to .8volts but once I hold the rpms at 1,500 the downstream begins switching like the upstream. So would that be a bad cat or lazy downstream? Thanks, oh and I have tested fuel pressure and it hangs at 58psi all the time.
 

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My Son renewed his Alldata subscription for their 2003 Dodge Caravan.
Give me some time and I will send you the Code P0420 diagnostics.
His vehicle is a V-6 but diagnostics should be the same.
 

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Discussion Starter #7
  1. I'm having a hard time understanding this why can't they explain it in laymen terms lol I'm going to attempt pulling the cat off today and hollow it out and put a spark plug de-fouler in the downstream o2 see if that helps. It's bound to be better than it is if it's worse I will just replace it.
 

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Discussion Starter #9
I don't understand the way they word it. lol It's a lot simpler than the way they word it. I didn't go to school to be a technician and learn all the technical terms. I do however understand that the upstream o2 is working properly and the downstream o2 is functioning also but it's not keeping a constant voltage like it should so that being said, the catalytic converter isn't functioning properly and needs replaced. The catalytic converter is also discolored from getting too hot, it smells hot and I did notice after driving it yesterday there was an abnormal amount of heat coming from above the catalytic converter along the firewall. All signs point to a bad cat in my opinion. Please feel free to correct me if I'm wrong.
 

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98% of the time there is a Code P0420 the cause is a faulty Cat, however...let me explain and hopefully this will help you to understand more clearly.

Oxygen Sensors produce a small amount of voltage when exposed to oxygen, the more O2 present the lower the voltage reading.
The upstream O2 sensor should show constant voltage changes between .1 and .9 (.450 volts is middle ground, below is lean, above is rich) since the O2 content changes as the controller makes small fuel corrections to attempt to keep the A/F mixture at Stochiometric (14.7/1).
As the exhaust enters the Cat the first part of the 3 way Cat removes O2 from the exhaust thus eliminating/reducing NOx emissions (Oxides of Nitrogen, a photo-chemical smog produced when cylinder temps are above 2500 degrees), it then uses the additional O2 to reduce/eliminate CO (Carbon Monoxide, a byproduct of combustion) and HC (Hydrocarbons, unburnt fuel) emissions.
In doing this the exhaust leaving the Cat should have virtually no O2 left, the downstream O2 will reflect this by voltage sitting in the middle and not moving.
When the Cat is no longer doing its job none of the O2 in the exhaust stream is removed/used so the downstream O2 see's the same amount of O2 as the upstream and they virtually mimic each other.
A Cat that is getting excessively hot or smells like sulfur (rotten eggs) is usually caused by the Cat working too hard, attempting to convert a large amount of emissions which are usually caused by another issue, either running rich, burning oil, coolant entering the exhaust, lead (from gasoline or an additive) or another containment that has entered the exhaust stream.
Your Cat may now be faulty causing the P0420 code to set, however, you need to determine what if anything actually killed the cat.
If the Cat did not die from natural causes but was killed by an outside source and you do not find and correct the outside source issue the new Cat will die a similar death.

1)What do the spark plugs look like, any signs of fouling of any kind?
Link - 2)Is there any Blowby with the engine running and the oil cap off?
(Indicates worn internal engine components)
3)Is there any oil in the Air Cleaner housing?
4)Is the PCV system functioning properly?
5)Does the oil smell like fuel?
(Running Rich)
Are the O2 sensors contaminated?
Link - 6)Is there/was there any loss of coolant from the radiator or overflow tank?
(Clyinder Head/Block/Head Gasket Issues)

If you do not see/find anything obvious checking from the list above and suspect there may still be a problem a Cylinder Leakdown Test will tell you if you have any major issues.

If you have any questions/concerns or there is something you do not understand Please ask.
 

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Discussion Starter #11
The catalytic converter was bad it had the internals rattling I hollowed it out and put a spark plug de-fouler on it. It runs dramatically better, has way more power. But it's still not running perfect and still smells slightly hot but not as bad. The oil smells like gas and is even separating from dipstick instead of coating it like oil normally does. Before the engine was rebuilt I think it had a blown head gasket so it's very possible that the o2 sensor is contaminated and for sure the oil is contaminated. So I plan on changing the oil and filter. Do you know the proper procedure to check fuel pressure on this car? The upstream o2 sensor is reading in the lower numbers a lot between .1 and .6 volts and the down stream is staying solid now unless I'm driving it and it's under load then it will bounce around some but I think that's just because of the de-fouler and gutting the catalytic converter.
 

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.450 volts is middle ground for the O2 sensor, as long as the voltage is crossing above/below .450 volts you are fine.
Recheck voltage after you change the oil and filter.
If the oil is fuel diluted I would suggest you avoid driving so you do not damage the engine.
 

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Discussion Starter #13
So I changed the oil and have put close to 100 miles on it. No longer smells hot and o2 sensors seem to be operating fine and operate the same as my mother's car which is the same car as mine and same year but when I first start it when cold it will fire right up but then as the rpms drop it will die. The second start it will stumble a little bit when the rpms come down then stable out. Also anytime the rpms drop to idle while driving it will stumble or fluctuate briefly then stables out. There still is no codes coming up either. Any ideas?
 

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Sounds like carboned throttle plates and AIS Pintle.
Was the base idle screw tampered with?
 

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Discussion Starter #15
Not that I know of is there a base setting for it and that's simple enough I will take it off and clean it up I should of thought of that lol
 

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If the base idle screw has not been tapered with do not touch it.
Be sure to remove the AIS and clean the AIS Pintle and Bore in the TB.
Do not forget to get a new gasket.
 

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Discussion Starter #17
I cleaned it all up and 1 can of carb cleaner later and it's running smooth as butter no stumbles or dying what so ever couldn't be more pleased! The idle screw didn't appear to be tampered with. Thanks NAJ you've done it again. Have a great day!
 
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