97 Taurus misfire stumble @ idle & load 1-2K rpms

[cannoner]

Car has 95K miles on it. Originally thought bad trans (replaced trans oil & filter - car had bad motor mount) Less than 20K miles on plugs & wires. New fuel filter, fuel pressure 35PSI steady. DTC P0420 cat efficiency below threshold bank 1. PCV OK, Pulled EGR vacuum line no difference. Car runs 2200 rpms on hwy just fine.

What else could it be? Aunts car & she needs it back

[wrightz28]

That pressure sounds a tad low

[shorod]

The fuel pressure is about right for key on, engine off (should be 37-43 psi). With engine running, fuel pressure should be 26-45 psi according to the factory service manual.

When you pulled the vacuum line off for the EGR, did you plug the vacuum line or leave it open? If you left it open and there was no change in the way the engine ran, you probably have another vacuum leak elsewhere which may be causing your stumble and P0420 code.

Do you happen to have access to a scan tool with the component parameter feature that will allow you to check individual cylinders for misfire counts, even if they are below the threshold to set the CEL?

-Rod

[cannoner]

I plugged the EGR line. I noticed there is some vacuum on the line when hot and at idle. I have an OTC scanner that is for ODB 1... I thought this pushrod Taurus is not sophisticated enough to feedback individual cylinders.

In any case I put in brand new plugs and wires and had no change. The middle rear cylinder plug is a little darker the other 5 are perfect light grey.

Vacuum is a steady 17" at idle, no sign of backpressure from cat or stuck EGR, mis is definitely a beat

When engine temp is cold it does not misfire. At operating temp idle and accelerating (uphill is worse) in 3rd @30 or OD at 45 it misfires.

Is the DTPF a suspect for this condition?

[shorod]

As you're probably aware, your '97 is the OBD II system and your OBD I scan tool will not read the codes. However, even the OBD I Ford system would allow a cylinder balance test which could help pinpoint a misfire.

With the proper OBD II scan tool (I use an OTC Genisys) you can review the misfires on specific cylinders, even of the Vulcan engine. It would be beneficial to monitor oxygen sensor bank 1, sensor 1 and bank 1, sensor 2 to see how well the catalytic converter seems to be working. How rich does B1S1 indicate the bank is?

Have you used fuel injector cleaner regularly?

If you'd like, I can provide you with the factory service manual steps for troubleshooting a P0420 code. If you'd like that, send me a private message with the request and an e-mail address for you that can accept PDF attachments.

-Rod

[cannoner]

I have the OTC ODB1 system and have not tried it as I thought it would not work. My software ends 1995.

Tossed in a bottle of inj cleaner and sprayed the MAF and temp sensor with no change to conditions.

Will drop it off at a repair shop tomorrow with scan capability as a side benefit the check engine light came on, after getting into a construction zone

[cannoner]

Took it to a local 3rd party shop - He scanned it and replaced the TPS Sensor... NO Difference

Said it might be a camshaft position sensor he does not have the tool to align replacement.

Took it to a FORD DEALER with the tool.

They replaced the CPS and the distributor said the bushings were shot. They could not do a power balance test they tried 2 different machines. Gave me a bill for over $500 and said it might be something wrong with the PCM.

Now the engine stumbles so badly at idle in gear, the oil pressure lamp flashes on. Car is sitting in the barn with the battery disconnected because the dome light refuses to time out & shutoff...

Does not stumble at idle in neutral or during 30-40 mph acceleration.

If a FORD DEALER cannot fix a Taurus is there anyone on the planet that knows how to fix it? ???

[Salty25]

Sounds like the Ford dealer charged you $500 to make it worse.

[shorod]

Originally Posted by cannoner

Took it to a FORD DEALER with the tool.

They replaced the CPS and the distributor said the bushings were shot. They could not do a power balance test they tried 2 different machines. Gave me a bill for over $500 and said it might be something wrong with the PCM.

Now the engine stumbles so badly at idle in gear, the oil pressure lamp flashes on. Car is sitting in the barn with the battery disconnected because the dome light refuses to time out & shutoff...

Does not stumble at idle in neutral or during 30-40 mph acceleration.

If a FORD DEALER cannot fix a Taurus is there anyone on the planet that knows how to fix it? ???

So the stumble only occurs during load? I wonder if the dealer either broke/damaged a couple of plug wires, or for some reason took a few wires off the spark plugs and didn't put them back on the correct cylinders. Maybe the reason it cannot do a cylinder balance test is because when it thinks it's shutting off fuel to one cylinder, the mis-wired/damaged plug wires cause too many of the cylinders to misfire and the engine stalls. Or, maybe the PCM realizes that the idle is too low and aborts the cylinder balance test.

A professional scan tool should be able to monitor cylinder misfires and point you in the direction of those cylinders with high misfire counts, even if the misfire counts are not high enough to trigger a Check Engine Lamp (CEL). That knowledge could certainly help you/us narrow down the search.

-Rod

[cannoner]

I took the PCM out & found pin 12 bent outside the rubber insulator. date tag says 10/3/1996.

Put it back together and no difference.

The engine definitely stumbles at idle in gear. Neutral idle and at any road speed and load it's smooth as butter. I doesnt appear any plug wires were messed with or crossed wired.

The distributor and CPS replacements by the dealer improved the roadability, now it's just at idle. I'm into this problem almost 1/3 of the car value so not too excited at going back to the parts replacers who did not fix it the first time especially the FORD DEALER who should have noticed the failure driving out of the shop yesterday...

Could it be one failing injector only showing at idle under load?

[brokenantimatter]

I suggest getting a vacuum gage and having somebody turn the engine over while you monitor it, it sounds more like a leak than anything else to me. I would also get a can of sea foam or other reputable all purpose crankcase/fuel system cleaner be cause it also sounds like it could easily be a clogged or wrong size fuel injector.

That should run you less than 30 bucks.

[cannoner]

At idle the vacuum reads 17" steady. Motor is smooth untill the stumble.

Dumped in a second can of inj cleaner no difference.

How easy is it to replace the rear bank injectors? Fronts seem to be exposed does the whole intake have to come off?