random missing loss of power

[tdkd99]

Hi all. Sorry for the long post,
I have searched the forum and can't find anything that matches up exactly to my problem. 93 4wd with 195,000 miles on it. The truck will start and idle perfectly, then sometimes within 50 feet or 50 miles of my driveway the problem will begin. At any speed, 35 or 65 (its not particular) the truck will jerk like you turned the key off and back on quickly. The check engine light will come on for about two seconds and go off. This has been happening about once a week for over 3 months. Today while sitting at a light the idle suddenly went from 600 to1000RPM and the check engine light came on and remained on. When the light turned I went to take off and it accelerated to about 15MPH and then bogged down and would not run any faster than 25MPH. The engine was missing, sputtering and with my window down, the inside of the vehicle filled with the stench of sulfur. If I let up on the gas to say 1/2 throttle it would accelerate up to speed, just slowly. I pulled off the road shut it off and restarted it. Check engine light was off and it ran smoothly and accelerated to 55 mph with plenty of power. 2 miles down the road the light came on again and it fell flat on its face with the same symptoms. Ran the KOEO and KOER and got 512 on KOEO and 111 on KOER.

In the last 20k miles I have replaced as normal maintenance the plugs, wires, fuel and air filters, cleaned the MAF and the IAC and changed the trans fluid. I also replaced the fuel pump assembly 4 years ago to fix a faulty float that made my gas gauge read empty all the time. (I installed the complete assembly). At that time, I also replaced the FPR as I had heard they like to act up sometimes. Today, I tried swaping the EEC relay for the AC WOT and it made no difference. When I first noticed this months ago, I exchanged the fuel pump relay with the blower relay. No change there either.

If anyone has an idea on where to begin looking for this I would love to hear it. It's been a good truck, I have owned it since new and have always kept it well maintained. Hate to see it go now.

Thanks

 

[larrydd999]

Was the FPR new? It sounds to me like a fuel problem or perhaps the TPS. I don't have my code book handy but as I recall 111 is ok.

 

[tdkd99]

Was the FPR new? It sounds to me like a fuel problem or perhaps the TPS. I don't have my code book handy but as I recall 111 is ok.

Thanks for your reply. The FPR was new and 111 is all ok. 512 has to do with power loss to the PCM keep alive memory. Now that I think about it, that code was not there a while back when I checked them. I checked the codes today before exchanging the the EEC relay.

 

[trashtruck]

have you checked grounds? sounds like something is only making a partial connection.

 

[tdkd99]

have you checked grounds? sounds like something is only making a partial connection.

Thanks. You are probably right. It was really bad driving today. I pulled over and shut the engine off and then turned the key to the on position just to see if I could hear the fuel pump run. To my surprise not only was it running, but it didn't stop! It ran for about a minute or so while I sat there and then I heard the relay start chattering under the hood. The pump was going on and off while the relay was clicking so it is definitely fuel related. Anyone know where the ground for the PCM is located? I want to go through and clean and tighten them.

I promise if I fix this thing I will post the resolution for others to see.

 

[larrydd999]

To me, that sounds like the fuel pump is running but either not pumping fuel or for some reason it's not building pressure (bypassing back to the tank, perhaps?). There's a test port on the fuel rail, it might be useful to check the pressure. Sorry to seem to be chasing you in different directions, but we all have a different troubleshooting procedure and we all have different experiences, so our suggestions will follow the same way.

 

[tdkd99]

To me, that sounds like the fuel pump is running but either not pumping fuel or for some reason it's not building pressure (bypassing back to the tank, perhaps?). There's a test port on the fuel rail, it might be useful to check the pressure. Sorry to seem to be chasing you in different directions, but we all have a different troubleshooting procedure and we all have different experiences, so our suggestions will follow the same way.

No problem, I appreciate the response and any ideas of things to check. My local parts store has a loaner tool program. I'll see if they have a fuel pressure gauge.

 

[trashtruck]

pcm is grounded right there behind the pass kick panel. there is also another 4-6 ground spots under the hood on both fenders and the firewall.

 

[tdkd99]

pcm is grounded right there behind the pass kick panel. there is also another 4-6 ground spots under the hood on both fenders and the firewall.

Just an update. Removed the PCM opened it up and looked for any obvious signs of failure. I saw the capacitors had a small amount of what looked like green corrosion under them but that's all. I removed and cleaned all the grounds I could find and took it for a test drive. It stumbled backing out of the driveway but then ran great. I have noticed this problem is at its worse when the the vehicle is cold. Seems to get over it after about 15 minutes of driving. Stay tuned.

 

[tdkd99]

Just an update. Removed the PCM opened it up and looked for any obvious signs of failure. I saw the capacitors had a small amount of what looked like green corrosion under them but that's all. I removed and cleaned all the grounds I could find and took it for a test drive. It stumbled backing out of the driveway but then ran great. I have noticed this problem is at its worse when the the vehicle is cold. Seems to get over it after about 15 minutes of driving. Stay tuned.

PROBLEM SOLVED!! I hope.. Found the rest of the grounds and cleaned them with sandpaper. Drove it off and on all day today and it runs perfectly. Hopefully one of those was the issue.

 

[trashtruck]

glad its back up and running. the ground on the firewall near the brake booster gives me the most problems.

 

[larrydd999]

Thanks for the feedback, my two are probably going to have these issues soon.

 

[natenkiki2004]

Glad you got it fixed. For a bit of preventative maintenance, slather on some dielectric grease on all grounds and connectors you come across. You'll thank yourself later.

 

[tdkd99]

Glad you got it fixed. For a bit of preventative maintenance, slather on some dielectric grease on all grounds and connectors you come across. You'll thank yourself later.

Well folks, I wanted to bring this old thread up as I believe in posting the resolution to a problem, even if you thought you had it resolved before! I had thought cleaning every ground cable I could get my hands on solved my problem with the loss of power and stalling issues I was having. Guess I was wrong, as the problem came back with vengeance several weeks later. It turns out those leaky capacitors I saw in the PCM was my problem after all, because after I replaced them I can say with as much confidence as you can put in 23 year old vehicle pushing 300K miles the problem is solved.

In case you need to replace yours, there are three that leak green goo out of the bottom. Two are 47uf 16 volts and the third one is a 10uf 63 volt. I got them for under $10 bucks at Digikey. www.digikey.com.

Happy Holidays

 

[natenkiki2004]

If you go that route, make sure to clean up all the corrosion you can find and then cover it in dielectric grease. Just like rust, once corrosion sets in, it's difficult to stop it. Wouldn't hurt to toss a packet of desiccant in the computer.

 

[larrydd999]

Be careful, however, since some dielectric grease (mostly the dark gray or black stuff) is conductive. We use both types where I work, depending on where it's used. Most types of 'bulb grease' are light colored or clear and are not conductive.

 

[natenkiki2004]

Be careful, however, since some dielectric grease (mostly the dark gray or black stuff) is conductive. We use both types where I work, depending on where it's used. Most types of 'bulb grease' are light colored or clear and are not conductive.

I'm not sure what kind of special sauce you're talking about but dielectric grease, the clear silicone paste, is, by it's name, non-conductive. Are you talking about anti-seize?

 

[larrydd999]

You're right, of course. I wonder if someone re-used the container? Need to check on that...