ffspiel

Hello All,

I've been battling an intermittant stalling problem for about two months now. When it initially started stalling, my Civic EX (165k) threw a: P0420 code. This code was erased and never returned through phase 1 of repairs.

The stall would occur when the throttle was released/relaxed after an acceleration.. around 1500 rpm while slowing down. More recently, I was driving it about 35 and it cut out... dieseled down without any backfire... as though there was no spark/electrical; just died. When it stalls, it might be started after the 5th or 6th turn over; this car will always start in the morning. Weather has not been very hot yet, so I doubt if this is the "main relay interior temperature issue" in this situation.

This is a family driver, no mods, and timing belt was done about 2 years ago.
This is what I've done thus far to attempt a remedy:

Phase 1:

(Igintion switch replaced about 2 yrs ago... recall issue, similar problems then... ignition switch resolved the stalling issues. I have no idea if the similar code was thrown at the time).

-New plugs, rotor, coil, cap.
-New catalytic converter (old one WAS hammered), new upstream sensor (Denso), new downstream sensor (NGK) replaced. Prior to replacement, I tested the downsteam sensor, which was found not to be in it's operational window (wasn't working within the electrical perimeters). This prompted me to order it and the upstream sensor too.
-Fuel main relay was taken apart, resoldered.

The above actions didn't seem to correct the intermittant stalling issue, but the code didn't return until today. This is what I did to it last night, prior to the code...

Phase 2:

-Replaced Ignition module (aftermarket, Duralast)
-Replaced fuel/Main relay (aftermarket, Duralast)

Drove car for nearly 15 miles in all situations, slow... fast.... off/on then run... reverse... u-turns; no stall... no engine light.

Today, as mentioned above, the check engine light came on after a ten minute drive to my son's school. I checked to see which code was thrown, and sure enough... P0420 code again... this after the above two things were installed; no stall however.

I'm kinda at wits end. Any thoughts on what else I can check or consider in conjunction with a thrown P0420 before I wrap this up and gather some money together to take this to a Honda qualified mechanic? Thanks... ~ rob

ekb16

iTrader: (1)

p0420 is for a cat..i would replace the cat and 02 sensor

Meyerman015

p0420 would be "Catalyst system efficiency below threshold" So if you have not yet replaced your cat, you should go ahead and do that. You may also change the o2 sensors if you have not already done so. I'm not sure how well o2 senensor extenders work, but for like 10 bucks, might be worth trying. If anyone can tell me how well (or bad) those extenders work that'd be great.
you can get a Magnaflow resonator for under $100 and i have been told it won't set off the CEL.
OEM replacements would be the best, but they are costly.

I hope that helps!

waaBAAH

p0420 wont stall the car. so you proably got two problems going on here. you will have to look at the second 02 voltage on a scanner. what year is the car?

alot of problems could cause a stalling condition. when the stalling condition happens you have to be quick to eliminate some potential causes.

lets start with some basics first......do you hear the fuel pump priming after it stalls? any way you can get your passenger at the moment to check for spark?

ffspiel

Hi Guys,

Thanks for replying.

Yes.... the catalytic converter was JUST replaced (Honda OEM)

Yes... the upstream O2 sensor was replaced (Denso type).

Yes... the downstream O2 sensor was replaced (NGK type).

Course of events:

I replaced the Cat and sensor about a month ago. Drove the car and it stalled a couple of times; no check engine light or code thrown. After it stalled, I just let it go for a bit and didn't drive it: it and sat in the driveway because I didn't have money to do further changeout of items (rotor cap, spark plugs and coil).
When I got some money about a week later, I replaced: rotor, distrib cap, coil and spark plugs) and resoldered the contacts on the main relay on the off chance it could have been contributing to the problem... no change, still an intermittant/unpredictable stall.

After I had put together a few more dollars, I replaced the ignition module in the distributer and the main fuel relay yesterday. I drove it and so far it hasn't stalled... but this time the check engine light came on and the same code popped up... the P0420.

As it hasn't stalled, I can't reproduce or check for lack of spark immediately after (I drove around last night with a plug in my pocket.. just in case).

Q: Any other thoughts? I read somewhere about coolant sensors being flawed or inoperational, causing a fuel/air mix problem that could cause the thrown code issue. Also vacuum leaks... where should I look first? Also, my radiator fluid level has been irradic lately (I'm not sure why)... I read also that an air bubble in the system could cause the temp/coolant temp sensor to also read irratically, perhaps causing problems.... any experience with this?

I'm currently looking for an exhaust manifold leak or crack in manifold that can cause a bad O2 sensor read.

Anything else?

waaBAAH

what year is the car?

waaBAAH

Defective Catalytic Converter
Leaking Exhaust System
Oxygen (O2) Sensor — If equipped, one or more may have a problem.
(coolant sensor being bad wont set this code)


those are the only things that would cause p420.

(Napafix vvvvvv)

1. Monitor the front and rear Oxygen (O2) sensors while driving at a steady cruise. If the front O2 sensor is operating normally (switching rapidly from 0.1 to 0.9 volts) and has a good pattern, check to see if the rear O2 sensor signal is steady and not switching correctly from rich to lean.

2. Verify that the outlet temperature of the catalytic converter is at least 100 degrees hotter than the inlet temperature.

3. Check for an exhaust leak, it could set a false code P0420. If there is an exhaust leak, repair it before replacing the catalytic converter.


The catalytic converter uses the oxygen in the exhaust to clean up the emissions. If the rear O2 sensor switches like the front one, the catalytic converter is bad and needs to be replaced. Keep in mind that the catalytic converter is covered under the 8 year/80,000 mile factory warranty. 1996 Civic has a 14 year/150,000 mile warranty.

ffspiel

It's a 99.

Also something that's been happening lately: I've noticed the radiator being lower on fluid when I've checked it, yet the reservior is full; the reservior doesn't seem to be allowing for flow back to the radiator. Finally, a year ago, I've noticed a darker discoloration to the inside of the normally clearer radiator reservior. I'm starting to put twoandtwo together... I hope I don't have a head gasket leak. Oil consumption is pretty mild and the oil in the dipstick looks normal, not milky. Perhaps the radiator is the culprit?

waaBAAH

check your radiator cap or just replace it for the coolant to flow back to resivoir. when pressure builds inside the raditor it will open the cap to allow expansion of the coolant into the overflow.

if your low on coolant (its a sealed system) your either burning it or leaking it. do a pressure test or look for leaks.

darker discoloration could be that it is time for a coolant flush. coolant does break down over time.

ffspiel

I'll try a new radiator cap and check for an exhaust leak; I've read that the exhaust manifold also frequently cracks... so I'll look specifically for that too. Thanks for your replies, WaaBaah.