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Car Dieing, Trouble Starting -- Diagnosis of 96' Honda

So, for the last week or so my cars has started dieing while driving. First time it died randomly when approaching stop signs a couple years ago. Now it seems to have progressed and dies while on the highway and now has become more frequent to date. I checked for vacuum leak and spraying all visible lines that I could see from engine bay. Engine codes…the array of engine codes. P0420 catalyst system efficiency, P0706 trans solenoid ‘C’ clutch, and P0430 another catalyst system inefficiency to join it’s brother P0420. The car starts up fine in the morning. Car does not ride rough.

Today I changed the spark plugs and noticed oil in all 4 wells and a lot of oil in the 3rd one. I changed the spark plugs because they were 20k miles and figured I might as well replace them while I’m diagnosing the car. So turned back on the car after doing the job and got a puff of smoke…go to o’reillys and new codes. P108(MAP Pressure Circuit High Input), P110(Something about coolant being high input) and still the P0420. (Shop I took it to must have removed old codes. Not sure why).

So there shouldn’t be oil in the wells because my shop did head gasket job 2 years ago. I’m pretty confident in their work, so I’m thinking it must be blowby and because the amount of oil in all 4 wells. (But then again this is the cars second head gasket job, so who knows) If it is indeed the rings causing blow by, is it safe to drive around with oil in the wells? If I drain it regularly can I continue to drive it safely? Is there a test to determine if it’s blowby?

I ran car for oil cap off looking for smoke, nothing. I did feel a steady stream of air though, not sure what’s normal and abnormal on that front.

Thanks, I know this is a lot but it’s somewhat intermittent issue. Took it shop yesterday and they couldn’t figure it out.

Of course the historical issue is the main fuel relay giving out but could be anything else also like the crank sensor or coil etc. You have changed the distributor cap and rotor as well as the fuel filter, correct? Thats standard tune up with the plugs. Also there are gaskets and rubber grommets to seal the oil from the plug holes for that upper cam shaft cover. That’s all changed out when you do the timing belt or valve adjustment. You have done the timing belt on schedule, correct? I don’t think the codes from Pep Boys or whatever are telling you much and you really just need to get a diagnosis instead.

The engine stalling might be caused by the ignition module being effected by heat.

The oil in the spark plug wells is from the O-rings leaking at the bottom of the wells which can be fixed by installing a new valve cover gasket kit.


Concur w/Tester, the oil in the spark plugs wells is probably just the valve cover gasket needs replacement. A MAP sensor problem would certainly cause this symptom, but MAP sensors are not a common thing to fail, and I expect that recent code was b/c the engine was started at some point – probably as an attempt to diagnose this stall problem --when the MAP sensor had been disconnected. Double check that the MAP sensor is now firmly connected to its wiring harness connector. I doubt that code will re-appear. The coolant too high may be the same thing, the connector to the coolant temp sensor was disconnected during the diagnosis. Check to make sure it is connected now, and monitor the coolant temp on the dash gauge.

Does the car accelerate ok, easy to get up to freeway on-ramp speed? If so, the cat is probably not plugged up much. It would have to be really plugged up to cause idle stalls. A cat problem usually results in heavy acceleration symptoms, like freeway on-ramps, going up steep hills, etc. If you don’t have those, set the cat issue aside for now I guess.

The transmission code you need to find someone with Honda auto-transmission expertise, that could possibly be the root of this stalling problem.

I guess if this were my car the first thing I’d do, I’d bring all the routine engine and transmission maintenance up to date, then check the compression, the fuel pressure, the egr, and for any vacuum leaks.

Thanks for feedback. Distributor is 2 years old. All gaskets and seals were replaced when head gasket was done. Car drives great same performance, I’m at 277k miles and it drives the same when I got it. Except it’s a lot louder than it used to be. Exhaust is rusty as all get-out and there’s a lot of noise coming from the exhaust in the vicinity of the CAT

Maybe the coil. Maybe the valves, I don’t think they’ve ever been adjusted and I remember somebody saying this was routine maintenance at my mileage for Honda. Maybe the hole in the exhaust is so bad the extra air is creating a very high fuel mixture causing the engine to stall? I don’t know.

Exhaust leaks can indeed confuse the ECM (computer) to think the air/fuel mixture is incorrect. When it tried to “correct” the mixture, that can cause the engine to stall. Modern engine, they are sealed systems, and if that seal is broken either on the intake side or the exhaust side, there’s no telling what the symptom will be, but rarely will the engine run correctly until the sealed-engine state is returned to the way it came off the assembly line.

Valve clearance: that can get out of adjustment in two ways. the preferred way )(if it has to happen at all), the clearance is too great, which means the valves don’t open as much as they should. This will cause the engine to be sluggish, esp in acceleration or at high speeds. The other way – the more common I think – is the valve clearance is too tight. This can damage the valve and valve seat, esp the exhaust valve. If that has already happened, it would usually show up in a compression test.

Dying at random can also be caused by an intermittent fuel pump, main relay, or ignition switch. Those 3 things are all directly related too.

The oil in the plug wells is a concern and that is something you should not be going through right now.
If the head gasket was replaced 2 years ago the valve cover gasket should have been part of the procedure and should not be leaking so soon afterwards.


The valve cover gaskets are not automatically replaced when doing a head job.

Remember? Honda has a scheduled valve lash adjustment. This means that the valve cover gaskets are resilient. Meaning, they’re meant to be removed and reinstalled without required replacement.

So it’s not uncommon to remove the valve covers and see no evidence of oil leakage and reuse the gaskets after the head job has been done. But a couple years after the head job, they start leaking.


I suppose everyone has their own methodogy but I would never, ever consider not replacing the valve cover gasket while doing a head gasket job.
The OP says the HG was done 2 years ago and the car was probably built n 1995. That means the V/C gasket was 17 years of aged rubber old.

A head gasket set includes a new V/C gasket (unless someone was cheaping out with HG only) and if the V/C gasket had been replaced 2 years ago the OP would not be posting anything about having all 4 plug wells full of oil.

To me anyway, this falls into the same category as a rubber thermostat gasket and I would never reuse one of those either.

Anybody reusing old valve cover gaskets is asking for trouble, as the others have said

OP said the exhaust is very loud, especially near the cat

In my opinion, it’s very possible the exhaust leaks are “confusing” the oxygen sensors, thus generating the P0420

If it were my car, I would install a new valve cover gasket kit and take care of all the exhaust leaks

An evap/smoke machine is especially useful in this situation . . . dump smoke into the intake manifold and you’ll find any leaks. Dump smoke into the tailpipe and you’ll find those exhaust leaks

I fully concur with both Tester and db4690 on this one. The only way that oil gets into the spark plug wells is through the gaskets (o-rings) that fit into the valve cover at the base of the spark plug wells. The leaking exhaust may be throwing the rear O2 sensor so far off that it is not only causing the P0420, but also the poor performance.

I don’t see how he got a P0430 with a 4 cylinder engine though. The exhaust leaks would be the top priority at this time. The oil in the spark plug wells does not affect performance in any way and is not caused by blow by. That would be a low priority fix.

“I ran car [with the] oil cap off looking for smoke, nothing. I did feel a steady stream of air though, not sure what’s normal and abnormal on that front.”

I’d also check the PCV system. If blow-by is pressurizing the engine, oil in the plug holes might be the first clue.

I looked under the car today and there’s a 2 x 2 hole after the cat where the metal bar hugs the exhaust to the frame. The rust is deep red in many places, I’m sure there are other smaller invisible exhaust leaks

Here’s where I stand. I need to know my engines good before I proceed to put any more money or time into the car. I know how to do a compression test, will I get an accurate reading considering the state of my exhaust? Or will I have to repair the hole in the exhaust first?

A hole in the exhaust will have little to no effect on the compression readings.
Make sure that after the plugs are removed that you prop the throttle open. (Brick on the pedal if need be.)
Write down the reading for each cylinder.
If there is an anomaly then redo the compression test with a squirt of oil into each cylinder; also notating that on the paper.

insightful, “steady stream of air” to me implied that the airflow was into the engine and would be normal. A plugged PCV and/or excessive blow by would be a puffing of air out of the engine, but it would be a steady puffing so who knows what the OP meant.

HondaHonda, your picture doesn’t show anything of value. The O2 sensor is mounted at the back of the Cat, is your hole at the back of the cat or further back in the exhaust pipe. I tried to get a new pipe for my 97 Accord from Rockauto but both pipes they sent me had the wrong bend radius in the rear bend of the pipe so they just refunded my money. You might try a Walker pipe instead or have one made at a muffler shop instead.

If the hole is far enough back from the O2 sensor, it may not be the cause of the P0420 code, but you may have other leaks you haven’t found yet.

Are we confusing front and back? The front of the cat is toward the front of the car and the back of the cat is toward the back of the car. I replaced the whole system on the sons 96 from the cat back for about $150 from Rockauto. So really if you have a leak, it needs to be fixed for safety too. Now if its in front of the cat or the cat itself, that’s a little more expensive.


With the oil cap off engine was steadily puffing air OUT of the engine. Thanks for raising the point, so I could clarify.

You might try driving for a short time with the oil cap off (hillbilly diagnostics). Any change?