Mechanics

ENGINE STUMBLING

1998 Mercury Sable • 193,000 miles

Okay, we're back. This is from the 98 DOHC engine.

I have since replaced the Fuel Pump, Filter, Plastic hoses from the Fuel Pump, replaced the wires, plugs, EGR Valve, EGR Valve gaskets, all other emission control items seem to be working, and I replaced the hoses running from the elbow under the intake manifold as the hoses had melted so I didn't have EGR or Fuel Pressure regulator control.

However,

Upon going up my hill the car continually acts like it's not getting the gas and also idles rough. There is a faint odor of gas coming from the rear, and I did replace the carbon filter element in the rear, as that had fallen off, though I wasn't able to use a new one, as they don't make them anymore. When I sit at a stop light the engine rumbles as if it's misfiring, but no SES light has appeared. The SES light did throw out a code 420, but I surmise since the engine was running rough that this code is a result of that, not the cause.

There is no smoke coming out the exhaust pipe, and you can't smell unburned fuel in the pipe, just in the general vicinity of the car.
The car runs down the highway just fine, it experiences heavy hesitation while in the 30-40mph range, while running at 1000-1500 RPM. You have to give it more gas to get it to not run rough, but it doesn't throw out any hard line codes to fix. I'm at a loss on this one.
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Bravestar1
April 10, 2012.




If it's a code p0420 that's a catalytic converter ineffeiciency bank 1, shouldn't cause the rough running though. Clean the throttle plate on both sides as well as the iac then check for a vacuum leak including going to the evap cannister, it might be leaking while at idle. Check your hoses and if you can talp the intake with a vacuum gauge do that as it would be low. Also check the fuel pressure just to be safe, as it could be a regulator as well.

Tiny
Hmac300
Apr 10, 2012.
Also try unpuggin egr hose see if that helps and try cleaning egr valve as well and clean maf sensor with choke cleaner too.

Tiny
Hmac300
Apr 10, 2012.
Yes, I've wondered about the Fuel Pressure Regulator, since it's not an electrical one, just a mechanical diaphragm. Nothing you can really check I suppose. Well the EGR valve is new, and I also replaced the MAF sensor like an idiot, due to the hoses to the EGR valve being busted. Which I also replaced, got lucky at a Junkyard on those.

Someone informed me that I should replace both Cats. Something about possible blockage if the honeycomb fell apart due to a backfire. I would think if this were the case I wouldn't be able to go anywhere, and it would throw O2 sensor errors (which there are 4 of) all over the place. It's not like these are the old sand filled ones of GM relics.

Tiny
Bravestar1
Apr 12, 2012.
One other thing the 420 code CAN be a bad converter or an air leak in he exasut system before the cat.
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Tiny
Hmac300
Apr 12, 2012.
Well I'll try cleaning all the things today, and when I have the transmission fluid replaced see what they say about the Cats while their underneath. Very vexing problem, considering all the work I've done to it to replace various engine components. I was toying with getting a new engine I saw for $900, but then I remembered the A/C pump died (even full of fluid) and summer's coming.

Tiny
Bravestar1
Apr 14, 2012.

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