My previously dead reliable truck has recently started giving me grief. Every once in a while it will go into what I assume is limp mode, i.e., acts like its running out of gas and will barely pull itself along in first gear and idles ragged at about 300 rpm. If I turn the engine off and let it sit for a few minutes it will crank and drive normally for a few miles and then suddenly loose power and do the same thing. There seems to be a direct correlation between how much I let it cool off and how long before it looses power again. There is no bad catalytic converter smell and all the gauges read well within the normal ranges whenever it does this. The engine seems to be running hotter than it used to, though. Even back in Georgia in the summer I could usually open the hood and grab the upper radiator hose indefinitely and the radiator would be almost cool to the touch but now I can barely keep my hand on either for more than a few seconds. Spit on the head seems to sizzle awfully fast, too, but the temp gauge never gets above 'o'.

I had a CEL (for the last ten years ) but had to finally fix it with a new EVP sensor to pass emissions here in Anchorage, which it did with flying colors. I pulled the codes a few minutes ago and got a 522 (not in park or neutral even though it was) and 334 (DPFE or EVP circuit above the closed limit of 0.67 volts) for the KOEO test and for the KOER test got 111 (system pass).

Searching for similar problems turned up a few threads where the issue was either the power supply to the ECU or PCM or simply a bad computer board or possibly a bad ground or bad air intake temp sensor. Any other ideas?

 

Here's a little something you might want to check from another site.

Click on this link:A9x ECM's (and same years ECM's) Failures Due to Age


I just did this repair on my (ecm, pcm, computer, whatever term you'd like to use) and it corrected a mysterious miss that I'd been chasing for about 3 years.

This COULD cause the symptoms you're having.

I'm not saying that this is the "cure all for everything", but it's something to check.

Good luck !!!

Bob

 

Every time I work on my '95 4.9 I seem to over think the problem and go off the deep end. So I'll try to start simple for your sake.

Your symptoms are a dead ringer for a bad coil. The coil heats up and the truck doesn't run. The coil cools off, and the truck runs until the coil gets hot again.

Try to get a coil off another truck if you have one and test. If not, coils are pretty cheap from the usual auto parts stores. If you haven't replaced it in the last 5+ years... it wouldn't hurt to replace.

 

Not being able to put your hand on the radiator hose for more than a few seconds doesn't necessarily mean the engine is running too hot. It's probably a good idea to look at the cooling system to figure out why it's running hotter than previously though. I would also check to see if the added under hood heat is also affecting the TFI module

 

So this morning on the drive to work it did the same thing after a couple of minutes of 65-70 mph highway driving after five minutes of stop and go surface streets. I pulled over and, without shutting down, the engine cleared up after a few seconds and I continued on. A couple of miles later, it did it again. I pulled off onto the shoulder, turned off the engine, popped the hood, and felt the radiator and hoses for excessive temperature, but everything seemed normal. However, when I touched the coolant temp sensor to make sure the connector was secure (force of habit at this point) the plastic top half of the sensor broke off. I was able to drive the rest of the way into work by sorta sticking the sensor back together and keeping the speed down. Good thing I commute against the flow of rush hour traffic! Anyway, I stopped by the parts house and picked up a new coolant temp sensor and replaced it before driving back home (I had a short day today). I don't know if the sensor was the culprit, but I had no problems during the 15 minute run back down the highway running about 70 mph. So far so good.

The coil is a 2.5 year old MSD unit. I suppose it could be bad, but I tend to doubt it. Well, there kinda looks like there might be a little discoloration in the epoxy. If the truck goes limp again, I'll try a new coil.

 

I'm wondering if i have the same problem as you, today it was running fine then as soon as i started the ac mine started missing, idling low, and would die in under 5 min idling, and now it wont idle for more than 5 min and has no power when i drive

 

did you think about the fuel pump?? its very common for one to go bad.

 

Actually something in the fuel tank is now on the list of suspected causes. Last weekend, after I replaced the Engine Coolant Temp Sensor, I drove 300 miles including going over Turnagain Pass (sea level to 900ft in ~5 miles) at 65-70 with zero issues. It wasn't until I got down to 1/4 tank of gas did the engine start suddenly loosing power again. I was able to drive for four or five miles at a time until I got to the next gas station. After putting 20 gallons in the tank I drove the rest of the 40 miles back home without incident. By the way, I swapped in a 32 gal Bronco tank a couple of years ago. I'm now wondering if there might be something loose on the sending unit/pump assembly in the tank. Or is it possible that there might be water or trash in the bottom of the tank that's getting sucked up when the level gets low?

I think I'll go ahead and install a new fuel filter and drop the tank and replace the fuel pump since I reused the the original one that's been pumping for 212k miles when I did the tank swap.

But wouldn't a faulty pump cause the engine to not run at all? I mean, when it starts dying, I can pull to the shoulder of the road and let it sit for a minute and it clears up. However, if I try to drive away, it immediately does it again. Like I said up-thread, the longer I let it sit and cool off, the longer it will run fine before acting up again.

 

So after more research, it seems that the ecm might be the culprit. Apparently, the resistors leak electrolyte onto the circuit board and cause corrosion and bad connections. Well, here's what mine looks like:

http://www.flickr.com/photos/86607937@N00/4918163147/
Can the ecm be tested or is this one definitely bad? I've also read that a sign of a bad computer is the lack of the cel flashing momentarily when the ignition is turned on. Since replacing the egr position sensor a couple of weeks ago to pass emissions I've not seen the cel at all. Well, it came on when I unplugged the egr vacuum line, but went out again when I hooked it back up so at least I know the bulb is good.

 

Tom92F150,

Your computer is most likely still o.k.

As in my previous post, My computer had the same thing happen.

I did my repair with a few capacitors from Radio Shack and a little bit of time.

I suppose if you aren't comfortable with the removal and soldering that needs to be done, you could find a reliable electronics repair shop that still does "board level repairs" at a minimal cost.

If you decide to tackle this yourself, be sure to read and then reread the repair link and pay special attention to the fact that the capacitors have a positive and negative polarity and need to be replaced as such.

P.S. I'm sitll running without any misses or stumbles since my repair !!!

Good Luck,

Bob

 

I've been reading everything google will give me on bad ecm capacitors and it does sound like it fairly easy to fix with the right parts and the know-how. The guy at my work who fixes the radio modems and circuit boards and things in our survey grade (read: really expensive) GPS equipment said he would take a look at it and sounds pretty confident he can fix it. I know I'd rather give him a couple of cases of beer than pay the parts store $150 for a remanufactured unit.

 

Atta' Boy !!!
It will be a VERY easy repair for him.

Just don't give him the beer 'till AFTER the repair !!!

Let us know how your truck runs after "the repair".

Bob

 

Well, he soldered in new capacitors, but it ain't fixed. Now the computer thinks its in diagnostic mode. Any ideas before I just buy a reman?

 

Perhaps I spoke too soon. While tearing back into it just now I found a tiny flake of metal sandwiched between the big connector and the computer. It must've been stuck to the nozzle of my dielectric grease can and somehow just happened to short the self-diagnostic wire. Anyway I got it out of there, buttoned everything back up, and the truck runs great. I haven't had it on the road yet, but the cel comes on until the engine starts just like it's supposed to and it seems to idle smoother and respond better to throttle. It had recently developed a habit of dropping rpm for a fraction of a second when I would press the gas pedal. We'll see how she does on the highway tomorrow, but so far so good!

 

There you go....sounds like a success !!!!

Don't forget your computer may take a little while to re-learn it's optimum settings under load, idle, and everywhere in between.

Give a little time to re-learn itself and you'll be a happy camper !!!

Good job !!

Bob