Well, deal is, this is my dad's truck, and i'm just learning to drive on it, and i LOVE it...

that sounded flaky, i know.

The truck has been great all these years. it's got over 200k miles on it, and until about 2 months ago, it purred like a kitten.

It has the 5.0 V8 in it, and a standard transmission. The problem is thus:

Whenever you start driving the truck, it runs fine. after about 2-3 minutes of running, the engine starts to choke. It runs rough, and threatens to die. Often (although not consistenly) you can smell the catalytic converter really strong. The engine's getting too rich a mixture, and eventually the engine dies if you let it idle too long.

My dad checked the air filter, which is brand new...

'bout a week ago, it wouldn't start, so he had it towed to a mechanic, who replaced the coil, and called it fixed. Well, it stalled again, and wouldn't start, so the mechanic replaced the distributer cap and rotor (that problem was burning out the coil) and he put in a new coil, too. The mechanic didn't think the coil problem was related to the rich mixture, but i thought i would mention that anyway...

Yesterday, we took the EGR valve off, and cleaned out the carbon buildup with STP's carbon buildup remover fluid. While we were at it, we cleaned out what we could reach of the entrance to the intake manifold. When we replaced the EGR valve and started the truck, we let it idle, then it started to choke again. It stayed running for about 5 minutes in the choking idle state, then we drove it around the block. After the first few rounds around the block, the engine started running great. Then we came to a stop sign, and the engine started running rough again. We noticed a new sound. A kind of whistling coming from the engine compartment. When the engine was running good, the whistleing wasn't there, so it seems the rich mixture has something to do with the whistling.

This morning, my dad drove me in to class in the truck, and it ran rough basically the whole time. Black smoke comes out the exhaust whenever it's running rough (not solid black, just really strong exhaust).

Well, i've explained the whole problem. if you made it through the whole post without falling asleep, i congratualte you, i know I don't write with a gripping style, as such.

I really need to fix this problem. I hopeing it's just a dirty intake manifold. If it is, i'll take it off and clean it. Only other possibility I can think of is that some thing that was bolted on for the new smog regulations is now malfunctioning and giving the engine too much gas.

It's either fix this old truck or have it towed to a junkyard, which i REALLY don't want to happen, but since i'm not contributing any money to the project, i don't have any control of what's going on. Hope I can get it fixed, cuz my dad says it can be mine when i get my license

Thank you for all your patience and time in reading this exorbitant post.

-Mike

 

I'm just guessing here, but check the O2 sensor. The computer doesn't start taking info from it until the engine has reached operating temps (2-3 minutes after a cold start). If it's off it can cause the engine to run rich.

 

Could also be a problem with the idle air control solenoid. If it's sticking in the cold (i.e. rich) position it could cause your problems. Pull it and clean it.

 

Thanks. i'll try both of those. My friend also says it could be the PVC valve, so i'm probably gonna clean that too, if neither of these work. thanks!

 

You really ought to pull the codes, before you start throwing parts at it. But if I had to guess I would say either coolant temp sensor or IAT(intake air temp.) sensor.

 

I could understand a coolant temp or iat sensor for running rich but not dying. When was the last time you replaced the fuel filter?? Another thing you might want to try is unbolting the exhaust before the cat converters. When you do that if it is a plugged converter you willl eliminate it. Run the truck if it runs fine then there is your problem. But the converters are my guess. Another way to check them is with an IR thermometer, take the temp in front of the cat and behind it (this is once the truck is up to operating temp) If the cats are goo, the temp AFTER them will be hotter then the temp in front of them. If they are bad, the temp in front of them will be hotter. Hope this helps.

 

Some other things you can check that can cause the engine to run too rich. Check the fuel pressure, should be around 35-45 psi at idle. Too high fuel pressure will cause the injectors to flood. A bad fuel pressure regulator will cause high fuel pressure. Also since your year engines fuel contoll is speed densisty, you could have a vaccumn leak in the vaccumn hose to the Map sensor. This could be the whistling sound your hearing when it's running rough. I'd also have the Map sensor tested. Ford Map sensors are frequency type sensors, so you will need a Map sensor tester to test those. Good Luck!

 

I would definitely start with pulling the codes and doing some diag. If the whistle is a bad vacuum leak it could make the truck run lean which would cause lean misfire (running rough) and cause the dead cylinders to just pump the raw fuel out the exhaust which can cause the black smoke and overheated cat.

You can also test the cats just by hooking up a vacuum gauge. Try doing a search on this forum, i know me and Pkrwud have posted the procedure before.

-Jon

 

hi,
Just went through the same problem....other are right ck codes to save time....

My problem was the throttle positioning sensor...
ck you motor manual ...it only has the wire s going to it

my wires were touching each other engine did not know if it was coming or goinG!!!!....
I changed mine wires were raw ....runs great now

just a idea rsvp it it works
mine was agrivate by rain water

 

Check the TPS. I had the same problem with my '90. I replaced it and have been runnning fine ever since.

 

Okay, i pulled the IAC valve out and cleaned it, but it doesn't really seem to be the problem. I got a new O2 sensor, and that didn't help, although we needed a new sensor in there anyway, so it wasn't a complete waste.

What we've been trying, and this works: We took the intake hoses off the throttle body and sprayed STP Throttle body cleaner in there in case the butterfly valves were getting stuck, then reconnected the hoses, and started the truck. After we sprayed that stuff in, the truck ran fine. We drove it around about 30 minutes and did not have the problem. I'm starting to think it's just a dirty intake manifold.

I don't understand some of your suggestions, but Ford4ever, your suggestion makes sense. it could be a vaccuum leak.

Also, i don't have one of the machines that reads codes from the computer so if one of you could tell me where to get one of those that'd be great.

Anyway, spraying that cleaner into the throttle body makes the truck run great, but after it's set over night, the truck misbehaves again. I'll ask my dad when the fuel filter was replaced last, cuz it might just be that simple.

Thanks for all your time and suggestions. I hope i can get this resolved.

Also, when you're mulling it over in your head (if you care to) remember that the problem only starts several minutes after the truck has been started. It starts fine, but after about 3 minutes of driving, it starts to run rough and rich.

Again, thanks for all your time.

 

I had almost the same problem on my 95 f150 with 5.0 v8...
"whistling too"!!!

After taking it to a shop to get the codes pulled... then at their suggestion I swapped out the TPS and O2 sensors, as well as cap & rotor and it still did not fix it.

After poking around on it for a bit I found the problem!!!
It turned out to be a leaky gasket between the plenumn and intake manifold. When I pulled the plenumn off, the gasket was all craked to pieces and missing in a few spots. Replaced the gasket... Life is good again!

I even went back to the shop that did the diagnostic and showed them the bad gasket... They gave me my $70 back for the diagnostic. Bad part... I was still out $95 for the TPS and O2 sensors that could not be returned.

Hope this helps,
Don