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F250 - exhaust

D

dhermesc

Well-known Member
I bought a 1996 F250 4X4 automatic with a 5.8 (351W) engine (105K miles). Crawled under it and found the exhaust had been removed from the manifolds back with dual pipes and glass packs muffles. When I bought it - the engine started horrible - had to hold the gas peddle to the floor to get it fire then it ran horrible until it warmed up. I replaced the IAC valve and it now starts at the turn of a key but it idles pretty rough until it warms up - lots of black smoke and when gunned it will backfire. When it warms up the backfire is gone and the smoke almost disappears except when gunned extremely hard.

Now for the question - anyone know what they did to remove the catalytic converters? The oxygen sensors are gone. The check engine light doesn't come on now that the IAC valve has been replaced. As stated it runs very strong once warmed up but the plugs we removed were black and sooty. I am assuming there is a tune that tricks the computer into thinking the oxygen sensors are still giving a read out - otherwise the check engine light would be on all the time. Should we run hotter plugs than standard or is that asking for more problems? Or just drive it like it is and don't worry about it cold running antics.

I bought it for my son and he LOVES the sound and is in the process of installing a flatbed on it. This summer it will be the main hay hauler.
 
I also had a problem with the evap system that I didn't feel like fixing at the time.
Light on and needed an inspection.
Cleared the codes and ran the car a few days to reset them.'Kept the gas tank full.
Every time I went 20 miles I would fill it.
The computer would not do an evap test with a full tank.
After two days one 02 sensor still wasn't ready.
After I drove the car that day I let it sit overnight and in the morning I started it and let it idle for 20 mins.
That reset the 02 sensor and went and got my inspection.
As soon as I got down below 3/4 of a tank the engine light came back on.
I fixed the problem when it was warmer out.
Too darn old to be working on cars in the cold weather.
I guess there is a trick to most everything.
 
The O2 simulator is not legal for on the road use.
May be a federal offense.
There are also ways for them to detect tampering in the system.
They know people are always looking for ways to improve performance.
 
I never knew such a thing existed. When you try looking this up for pickups you get lots of posts about don't do it - its illegal but little practical advice. Some of the Mustang websites are much more forth coming with information but most of it deals with 4.6 engines and their computer setups - not the older 5.0 engines from the late 80s and early 1990s.
 
The EPA leaves it up to the states to enforce vehicle emissions - Kansas has elected to not enforce EPA vehicle mandates. Kind of like how some states have elected to be sanctuary states on immigration laws and others have elected not to enforce drug laws (legalized pot).
 
Yea, I think they might not be able to purchased in the US anymore, or maybe I should say legally purchased.
You should see the tricks to get satellite tv.
Amazing!!!
 
Are you SURE the front O2 sensor(s) aren't still there? Typically, it's the BACK ones that get edited out, or replaced with "simulators" in those "butcher jobs".

The front sensor(s) are the ones that help the 'puter determine the fuel rate, the back one(s) don't actually CONTROL anything 'cept turning on the MIL if the cat(s) aren't doing their job.

Don't think the engine would run very well with no FRONT O2 sensor(s) or of they were replaced with "simulators"!
 
O2 sensor turns the injectors off and on, around 10 times a second in order to "trim" the fuel mixture. When sensors get "lazy" due to mileage and deposits, they cycle a lot less and your fuel mileage is in the tank. A slight ex leak will introduce air into the ex thus triggering a lean signal and the sensor will go full rich. I would certainly pick up an ex spud and weld it into one side at least. Ideally any set of headers should have a crossover or balance tube connecting them to help scavenge the exhaust. That's the ideal place to spot it. Something is obviously telling it to go stupid rich. I'm not sure if if the 351 uses the automotive mass airflow type of sensor or shares the 460s older EECIV speed density system. Either way try and correct the thing. Cat converter on this truck has no sensor in it, just the mixture one between the cat and the engine. Ford uses a heated sensor, because it's not in the manifold but further downstream so the right one..............
 
I was out in Kansas a few moths ago looking for ToTo. AKA Terry
Went through what looks to be a ghost town in the making.
It was Creepy.
Middle of the dayon main street, no cars, no people, no nothing.
 
Have no clue.
That is way above my pay grade. lol
I know they send a voltage signal that simulates the signal coming from an 02 sensor.
 
the computer does not look at O2 sensors on a cold start until a minimum engine temp is reaches somewhere around so your problem is more likely with a MAF sensor or something else, possibly even excessive fuel pressure, and when it goes in to closed loop it reads the O2 sensors and adjusts the mixture.
 
Rob's comment below is correct. Look at your coolant temp sensor too.

Have you looked to see if the wires to the O2 sensor are still present or have they been cut off. I'm not 100% sure, but I believe you only had upstream sensors in your "Y" pipe with no downstream sensors after the convertor. I may be wrong but if yours only had the upstream sensors, you may never get a check engine light.

Do a direct injection of seafoam through the intake and a can in the gas tank. You'll be surprised how much it will help.
 
No MAF sensor on a 1996 F250 - at least not one I can find. It does have a MAP sensor (manifold absolute pressure) sensor. But when they go bad usually the vehicle will refuse to idle and die at stop signs even when warmed up. This one idles just fine when its warmed up. Coughs and misses some when cold - like a old carbed vehicle does when its cold.
 
I'm curious, does the check engine light come on when you turn the key to run without starting it? If not the light was disconnected or the bulb was removed, a sophisticated version of putting black tape over the warning light.

I could suggest that truck would be a good candidate for a four barrel carburetor, but I had an '86 F150 with the last year of the 351HO-4V and it was trouble.

Search the web for Ford tuning tricks, pickup a magazine specializing in off-roading Ford pickups, or stop into a local shop that specializes in setting up off-road pickups. Your son will likely handle that himself.
 
I didn't see any wires hanging down - I doubt they were cut and capped - unless they did it real close to the hookup. I didn't go looking for the where the sensors hook up. Exhaust pipes replaced from the manifold back - no sensors or cats - just nice clean steel.
 
I think they send back a signal that is "spec" for the cats at normal operating temp. Possibly the reason why my runs so rough when the engine is cold. The "lying sensor" says the cats are nice and hot with typical oxygen levels but the engine is actually cold.
 
Check engine light works like it should. It comes on when you turn the key and it was coming on when the IAC would stick half open. When I replaced the IAC the engine light would only come on when key was put in the run position without starting it.

Actually when warmed up the engine run great with very good power (the 40' black marks attest to that). I was concerned about the carboned up spark plugs. I was wondering how they got the thing to run without a check engine light with no cats.
 
There is bound to be O2 sensor connectors up close to where the exhaust manifolds connect to the "Y" pipe. It's possible they tucked the wires in behind something. Glad they done a clean job of putting on the dual exhaust, better than most hack jobs.

By chance, does the exhaust manifolds have the O2 sensor threaded into the manifold?
 
You need the O2 sensor(s) to be there and working properly if you want your engine to run right and quit blowing black smoke.
 
You obviously don?t live in an area requiring emissions testing. Otherwise you would be solving the problem.
 
I've never seen one on an exhaust manifold for the 5.0 or 5.8. I've had 5 of these over the years and have ended up swapping the sensors out on all of them (what happens when you buy old stuff).
 
If I lived in an area that had testing I would never have bought the vehicle. Hard enough to remove the cats without creating a huge mess - reversing the process is probably even worse. The only other vehicle I owned that had the cats removed was a 1984 F150 and 5.0 engine. It had been done right with the EGR removed and an older Autolite pre-emissions carb (2100?) installed. It too had good power compared to other F150s.
 
Agreed - it looks like they did it mostly correct. I'm just checking their work as I hate to find out after the fact I've got a problem.
 
you need to get a scan tool on it and look at MAP, BARO, IAT, ECT, and see what is going on and if any of them are a little, or a lot out of normal. Also look really close at the PCV lines and elbows for a soft or sucked in spot or a hole. Fords were always notorious for PCV hoses leaking causing vacuum leaks and drivability issues.
 


This is the best forum I have found for getting good info and help on that eras Ford trucks- https://www.ford-trucks.com/forums/forum28/
 

I have a 97 F250 4x4 with the 7.5 eng and the cat got damaged and had no internals for a while but I never had a check engine light. There is a sensor at or near the convertor.
I had a vacuum leak once and caused idle at 1500 rpms but the check engine light never came on even though it comes on in run position on startup. My state doesn't require emissions on pickups of 8600gvw or more.
 
also try spraying carb clean or something along where the upper intake plenum meets the lower intake, those can leak and cause that type issue, especially if worse when colder out, as the engine warms up and the metal expands the leak becomes less and the computer compensates for it. If you could look at the fuel trim readings it would help your diagnosis
 
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