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Discussion Starter #1
Mercury Sable, 2004, 24 Valve, DOHC, 110K miles.

Recent to event, things done: Oil change, new spark plugs, checked ignition coils, cleaned injectors, new fuel filter, new PCV valve and good PCV-elbow tube, cleaned EGR valve - needle moves with vacuum applied and port is not plugged, cleaned TB, IAC and MAF.

Prior performance: car was running okay but often does not respond sharply to acceleration. It performed within 18 - 22 mpg. About two weeks before event, car would not start at first crank when cold, but after it warms up or during the day, it usually starts at first crank - battery determined not the reason. Also, some rattling sound from the heatshield/exhaust area by the engine wall.

The event:
While driving car suddenly began to dramatically lose power and would not accelerate as I give it more gas. Within about 3 minutes, it would not go beyond 10 - 20 mph, jerks and stumbles as if trying to accelerate but unable to, runs rough, and NO check engine light. To go up a slight incline on the road was like crawling at snail speed. While in Park or Neutral, it idles somewhat more stable than in Drive, but still runs rough and the rpm flunctuates around 800rpm. Checked for OBD2 codes and pulled P0442 as yellow.

After event, the following services were done but not exactly in order:
Checked spark plugs-ok, PVC valve and tube-ok, EGR valve and port-ok, cleaned MAF, checked TB and IAC-ok, replaced TPS, swapped out the EGR regulator solenoid and the fuel pressure regulator with used ones, the checked for vauum leaks-none found, rattling heatshield removed (was held in place by plastic). After these services, the problem still remains - rough idle, stumbling on acceleration and not able to rev up (and hold) above about 2500rpm before it stumbles down in rpm to as low as 200rpm sometime and may even cutoff. Still no CEL code. Car now starts usually at first crank, revs to about 1500rpm for about 20 - 50 secs, then goes down to about 800 rpm and flunctuates. Still rattling sound from the exhaust area.

Please your advice will be appreciated.
 

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Thanks for the response. I'll check the DFPE sensor and its hoses. I think it is behind the intake manifold facing the firewall? Any hints on how to test the DPFE? I don't quite know where the Cam sensor and synchronizer is and how to test. Further help is appreciated.
 

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Discussion Starter #5
Thanks for the info about Duratecs and cam synchronizer.

Could a bad catalytic converter or fuel pump be responsible for the event - severe loss of power, rough running, stumbing and unable to accelerate?
 

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A clogged catyltic converter could very well be the cause of the loss of power, unable to accelerate. You could take out the o2 sensor out of the cat where you can hear the rattle (or both) and see if the car runs/sounds better. The rattle you mention is indicative of failed catalytic converter
 

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Discussion Starter #7
Thanks for info Bull-Geek and others.

Some additional info:

Days before the event, I noticed that when I give it gas (open throttle the engine compartment), the plastic-top of the manifold (UIM) rises/flexes significantly. After the event, the manifold rise/flexing not as much, although the engine is now unable to accelerate beyond 2500rpm and cannot maintain the rpm.
 

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That is definitely sounding like clogged cats.
 

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I would want to check my fuel pressure.
 

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I agree with Tom...... Check fuel pressure first.
 

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Discussion Starter #11
DPFE quick test perforned:
Unplugged the vacuum hose from the EGR valve, and plugged the vac hose with a screw driver. Result - engine idles somewhat smoother at about 800rpm, but when I press the accelerator (give it gas), it is still unable to rev above about 1800rpm before stumbling /loosing the rpm immediately even though the accelerator is still pressed. However, the idle rpm does not flunctuate as wildly as before. Test was done for about three mins. Still NO check engine light and OBD2 code, except for yellow OBD2 light.

Regarding fuel pressure:
I earlier swapped the fuel pressure regulator (located on the injector fuel rail) with a used one from the salvage yard, but saw no noticeable difference in the car's rough/stumbling performance as described.

Any tips on a more robust yet quick DIY test for the fuel pressure? Thanks for the suggestions thus far.

Its raining today, so can't do more on the car bcos of the rain.
 

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Discussion Starter #12
Update:
Following Bull Geeks' advice, I removed the O2 sensor near where I think the rattle is coming from - it is the upstream one facing the firewall and behind the UIM. I reassembled and started the car.

Result:
1.) the car sounded loud and some smoke came out (due to the large unplugged hole for o2 sensor)
2.) the rough-running and stumbling were almost not noticeable
3.) when I gave it gas, it reved up high over 2800rpm and could hold the rpm without stumbling down immediately as before
4.) the idle was also relatively stable without wild flunctuations.
5.) when I put it in Reverse and Drive gears, it moved without noticeable hesitation.

Seems Bull Geeks' suggestion that the catalytic converter is clogged is onpoint. Thanks Bull Geeks and to all for their suggestions.

Wondering if I only need to replace that one catalytic converter, if cheaper options are available, and if it is a possible DIY thing to replace?
 

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Sure if you are not a California resident, you can order replacement exhaust sections from Rock Auto. Just undo the bolts for the exhaust piece you wish to replace.

If it was me, I'd replace both cats up by the motor. If something caused one to fail, whats to say with the poor operating conditions the car has had, it hasn't caused the other to be near the end of its lifespan?
 

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Discussion Starter #14
Update:
Had the manifold catalytic converter (one facing the firewall) and its O2 sensor replaced by mechanic. I didn't feel I could do it myself due to the seemingly tight space to work with. Also mechanic said it is a tough one to pull out and charged me for about 5 hours labor! Mechanic attested that the offending cat's honeycomb was degraded.

Car ran fine with more power, but still had a slight occasional miss/hesitation at IDLE, but not noticeable in DRIVE. After about two weeks driving it gave a CEL with P2196 code, signaling Bank 1, sensor 1 oxygen sensor failure.

I contacted mechanic and he suggested to change the O2 sensor on cat facing the radiator (Bank 2, sensor 1?) first, and if the code remains to go with PCM programming at dealer.

However, by the second day of driving, the CEL light is OFF but the P2196 code is still there and is now read as YELLOW by OBD2 scanner. Now I'm worried if this can degrade to the cat getting clogged up again, and how quickly can that happen if ever?

I notice also that the PCV valve on this car is housed in a grommet that is affixed to the manifold and is hardly replaceable. Could this be a source of leak that may result in this problem?

Also, I read somewhere about the Intake Manifold Runner Control (IMRC) potentially causing a miss/hesitation at IDLE. Could this be the issue here? Where is the IMRC on this car? (2004 Sable 24 valve, DOHC.)

Again, I appreciate the suggestions from everyone.
 
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