Rough idle-black smoke

[BigVicXLT]

Hi all.

I have a 1992 XLT 4.0L with 100K plus miles. Just tuned up within 3 months, and replaced the IAC and TPS sensors too. Also cleaned the MAF (MAS?) filament.

Truck has been running great until last week. The idle goes from 500 to 1100, and some black smoke from the exhaust. On the road, it runs great (and shifts OK) at any speed (except idle)? What gives? No check engine light either.

I checked the easily accesible vacuum lines, and they look OK.

Any help would be appreciated

Vic

 

[88vert]

How is your cat

 

[BigVicXLT]

Not sure...how can I check?? It does have good power on acceleration, which would rule out a bad cat, right (or not). Thanks

 

[88vert]

I am not sure on the cat

Sounds like you have a fuel problem starting,have you ever checked the fpr or changed a o2 sensor?Mine got black smoke when my fpr went out.But I got a check engine light thats weird

 

[BigVicXLT]

What is an fpr, how much, and where is it?

Thanks for the quick replies!!!

UPDATE: Wife says the check engine light DID come on once, but went out.

 

[88vert]

Im sorry Fuel pressure regulator its located on passenger side fuel rail on metal line and one vacume line,if it goes on too long it will fry your o2sensor too Check the vacume line for fuel there should be none,they cost about 70 bucks through autozone very easy to install,check everything close first.Does it smell like raw fuel coming out your exhaust?

 

[BigVicXLT]

Thanks for your help...appreciate it

Will check out your suggestions.

Does it smell like raw fuel coming out your exhaust?

No, not raw fuel, but she's REAL rich (black smoke, bad enough to leave a black mark on the driveway).

 

[88vert]

Check the fuel pressure regulator mine left black marks on the pavement too,check the vacume line close

 

[BigVicXLT]

Will do...thanks for your help

 

[88vert]

good luck

Keep us posted

 

[oceanworker]

Black smoke from the exhaust usually indicates (in a gasoline fueled engine) too much fuel in the mixture.
Probably your fuel pressure regulator. On the 92 check the vacuum hose (a small diameter hard one) coming to it from the "vacuum tree manifold" near the firewall driver side on the air manifold.
Fuel pressure, attach a pressure gauge to the Shraeder valve on the fuel-air plenum which should be near the FPR. Test the pressure with the key ON but not started. The fuel pump should pump about 42-44? psi. Then start the engine. The pressure should droup to about 34-36psi. If it doesn't, and your vacuum hose is OK, replace the FPR and the O2 sensor or sensors.
BTW, the OEM pressure regulator comes in two flavors: depending on the fuel connection, a quick/snap fuel connector or a screw on type.
Just for kicks, check that you are getting air to your air filter, no leaves, squirrel nests etc. in the intake.

 

[BigVicXLT]

Problem solved!!!

It was the fuel pressure regulator! Replaced it, and it runs fine. Thanks all!!!!!!!!!

I did NOT replace the O2 sensor...do I have too?

The only other thing I noticed is the battery light is now on...weird...volts look OK...maybe not related.

Truck is running OK though

 

[88vert]

Cool

Glad you got your truck figured out

 

[88vert]

Sorry

I would replace the o2 sensor in the future just for piece of mind they are pretty cheap anyway

 

[BigVicXLT]

Will do...thanks again.

BTW, any thoughts on the battery light on all of a sudden...belt OK, battery 6 months old, cables 6 months old. Volts OK....weird?!

 

[88vert]

What about your altenator,you didnt by chance knock something loose while putting in your fpr.

 

[oceanworker]

sounds like you jarred sumpin loose messin around with the fpr. If I were you I would spend the $$ for a new O2 sensor. What happens when the FPR goes, is it dumps too much unburned fuel in the system and sort of blacks up the o2 sensor. If your check engine light goes on, that is probably it.

 

[BigVicXLT]

Thanks folks....been a great help!!

Still have the battery light on, but I put a voltmeter on the battery and the volts are OK (with and without a load). Checked connections, all look OK...who knows?

How much is a new O2 sensor, where is it located, and do I need any special tools? I will take your (good) advice and replace it...good insurance

 

[88vert]

o2 sensor should be about 35-40 bucks to disconnect the harness is the hard part if you slide under the truck on the passengers side front tire and follow the exhast you should see the o2 sensor I think i used a 7/8 inch wrench disconnect the harness first then unscrew it out of the exhaust,its pretty self explanatory,there just is not a bunch of room

 

[oceanworker]

About the O2 sensor, you should note how many you have. On the 91 there is only one. I think the 92 may have 2, on the same exhaust manifold. Make a call to ford parts. Also double check the length of the wiring harnes attached to it. they gave me the wrong sensor twice before I brought in the old one to match up. that's Pep Boys for you.