I have searched the old threads but what are the symptoms of a cat becoming plugged??
I have a 90, 199,000 miles, with the 2.9 and 5 speed that I drive 15 miles one way to work every day. As I get closer to work, I have a noticeable loss of power and an increasingly louder puttering noise from the exhaust. Like a miss. Same symptoms on the way home. It was running so bad on the way home Thursday I thought the engine was going south!! I took the other truck to work Friday. I pulled the plugs today and found one finger tight but all were burning evenly. Oil is clean as I changed it recently. No CEL on. A plugged converter is what I am leaning to but how can I be sure if that is the problem?? Whatever it is, it is heat related as the engine runs fine when it first gets started.

 

You need to put a vacuum gauge on it

"Low vacuum can be an immediate clue to a clogged exhuast. To check further run the engine at 2500 RPM for 15 seconds. If vacuum drops during this period and does not increase when you close the throttle, the exhaust is clogged.

 

drive it for good run and then look at the cat. if it's glowing cherry red then it's plugged.

 

A plugged cat will be restrictive right from the moment you start the vehicle. I would say a fuel pressure test is in order to check for a weak fuel pump. The pump may get weaker as it heats up, which is why you loose more power towards your destination. Also your cat will not plug itself, a plugged converter is only found where the vehicle has either excessive oil consumption or has an obvious tuning problem. Also if the cat is glowing cherry red, the cat may be plugged, but in order to generate that much heat, a misfire or otherwise incomplete combustion is required. Fix the source of the problem. Leave the cat as a last, not the first thing you jump to.

 

I like all of the ideas so far.

Well it sounds like you may have found the "puttering" sound, with the finger tight spark plug, maybe it was loosing compression & causing the rough running & power loss too.

I agree, the vacuum gauge test for a clogged cat converter is a good one.

Another way to check for a clogged exhaust, is to put your hand over it when the engine is first started, to feel the back pressure, then do it again at the same rpm, after it's warmed up & acting out, to see if exhaust pressure has changed.

Another power loss cause that's come up over the years, that fits the number of miles driven when the power loss problem begins, is a fuel cap that's not venting properly, such that the fuel pump is slowly drawng a vacuum on the fuel tank & can't suck hard enough to provide the neeed fuel delivery.

SO, the next time it's power lays down, pull over & loosen the gas cap to equalize fuel tank pressure & see if it'll suddenly wake up!!!! If so, suspect the fuel cap.

If no joy, as has been suggested, maybe do a fuel pressure test, perhaps one of the fuel pumps is getting hot, or lazy & laying down on the job.

 

I did 2 of the suggestions as I don't have a vac gauge. The converter doesn't glow red after driving and the exhaust pressure seems the same.
I drove it to work today, ran fine all the way there but here's the kicker I didn't get above 55 as the roads were icy. When I came home, I varied the speed 60-65. By the time I was within 5 miles of home, loss of power, puttering exhaust and it felt like a miss. Parked it, came back out an hour or so later as I had to run some errands here in town and it ran great.
Another clue, it does have some lifter noise when it is cold, the noise goes away mid-range and comes back with a vengeance (LOUDLY) when it is warmed up.
Maybe this truck should be just a run around town only vehicle.

 

Well it kinda sounds like a collapsed lifer, or sticking valve.

Do you have a lot of deposits under the valve covers????

 

Did it do this before the oil change. If it didn't I would probably try changing the oil filter again.it sounds like you are losing oil flow (pressure) after warm up. Could be a bad filter or the oil pump and or bearings are wore out. If the lifters lose there oil then they collapse and the valves don't open very much causing a loss of power and the noise you are hearing. Remember the factory gauge on this is an Idiot gauge 5-7 lbs oil pressure will keep it a half range.
It has been awhile but I have seen this exact thing on another Ford truck changed the filter and all was good again.

 

I still sustain that a fuel pump problem can be the culprit. Fuel pumps can and do become temperature sensitive. I had a pump that would work fine driving around town, but when it was a hot day over about 95 or higher, the fuel pump pressure would drop and it started making a strained noise. The noise wasn't always there, but the symptoms were consistent with yours. Mine required hotter ambient temps to show up, but the issue is about the pumps internal temperature. It can get hot enough internally to misbehave without the outside air being hot at all. I would hook a fuel pressure gauge and see what is happening while this problem is occurring and see if the pressure drops when this starts to happen.

 

Probably not any more than what would be under there with that many miles on it. I did change the valve cover gaskets this past summer and there was maybe 1/4 inch of gunk I cleaned out.

It happened after I changed the oil but that was 1000 miles ago. The filter is a Fram and I put in 10w-30 for high mileage engines.
If I come across a gauge I will check it.


UPDATE!! I have been driving it to work this past week and a NEW noise has popped up. A rod knock!! It only does it fully warmed up and at idle. Give it a little throttle and it goes away. The factory idiot gauge fluctuates between halfway and nothing. I am thinking about changing the oil to 10w-40 this weekend maybe with some STP, too. Looks like I may have to change the oil pump if I can get it to last until spring. Weird, this engine doesn't burn or leak oil between changes and has been super dependable. Thanks for all the replies!!

 

Try a Motorcraft filter on it & see what happens.

 

Good idea!! Looks like they are the best to use. Engine Oil Filter Study

 

From what you're saying, You had better check your oil pressure, and soon!
The factory "oil pressure gauge" is not a gauge at all. It's just an idiot light hooked up to a gauge face, and it functions just like an idiot light: it shows "full" pressure at the same point at which an idiot light would go out. So you, might have 5 psi and not know it...

 

You are doing the opposite of what you need. Switch to ordinary 5W30 oil and stop using Fram filters. Get a Wix, Purolator, or Motorcraft.

You need a light oil, heavy oil is harder to pump, so you get less oil flow to the valves and lifters and other moving parts when you use the heavier oil, and it takes longer to get the oil to those parts on startup. Those fram filters do not have good anti-drainback devices, if they have them at all, this makes the problem worse.

The proper weight is 5w30, and you should stick with that regardless of the mileage or oil consumption.

 

Thanks Pawpaw!! I did switch out the filter this weekend to Motorcraft. I drove to and from work today and what a difference!! No noise on start up and just a tad of noise when warm. Turning up the radio and you couldn't hear it. No power loss, missing, or puttering. I haven't heard it this good in a long time. The oil "gauge" was reading a little higher, too.
I know one thing, Fram filters are JUNK!!


Khan, was 5W30 recommended from Ford in 1990? I tried a search and came up empty.