Hi all,

My truck (see sig.) has been acting up for a few weeks. I've been trying to narrow down the potential problems before giving up and taking it somewhere. Here's the story: The truck first shut off for a split second while passing on I-75 in 3rd gear at 5000 rpm. I thought I blew a tire or the rear end but when getting off the interstate realized that the truck was trying to shut off. That same day it shut off on me about 6 times while trying to get back home. No engine light yet. The next week, no issues although I took it easy. Then, the same issues but not within the first 20 minutes or so of driving. Engine light came on with 3 codes: u0100 (loss of communication w/computer), p0335 (crank sensor malfunction) and p0300 (random multiple misfire). After checking for corrosion or looseness on connections under the hood I replaced the crank position sensor. I disconnected the (-) on the battery overnight. The truck acts the same. I now have a new code on top of the first three which is p0016 (cam/crank sensor correlation on bank #1). The truck will temporarily quit while driving without warning. Sometimes it begins to quit/come back to life a few times. The check engine light sometimes will start to flash/chime and when it does this the truck won't rev over 2500 rpms. It will also quit when in gear and hitting small bumps like a manhole cover. Here's the part of all my info that will hopefully help narrow this problem: Sometimes the truck dies for up to 45 minutes. Within this time, the fuel pump won't turn on and the truck won't crank (meaning it won't attempt to turn over). I switched the fuel pump relay with the a/c relay. No change. My current best guess is the computer(ECM, PCM, ECU) itself causing this. The engine would still crank even with a bad fuel pump, right? And the fuel pump would turn on with a bad cam sensor, wouldn't it? Other computers are programmed this way that I know of. Thoughts? I can't think of anything else that would cause this weird no-start condition or these crazy codes. This is not a battery/charging/maintenance issue like plugs, etc. I just finished cleaning every ground and the ECM connection is secure and clean. How hot is the ECM supposed to get and could something inside be loose or not able to handle the heat? I can touch the ECM case for maybe 4 seconds without risking a burn. Thanks everyone.

 

I've had the truck idling on ramps and been underneath flicking sensors and jiggling wires to see if I can reproduce this problem. No luck. The harness is in good shape and over the years I've replaced wire loom to protect the wires. By the way, I just installed a cheap 4-inch fan right at the PCM to see if keeping it cooler will help. Maybe something inside gets hot and breaks contact intermittently. A solder that is weak? I'll see if anything changes.

 

iam not an electronic expert. but my pappy always said check the cheapest and easiest things first. i would start with the grounds. check the grounds on elec boxes. one time i had a cable that went from the batt to the engine ground. and the wire was not connected to the terminal. a nice spark jumped. might be time for the VOM.

 

I'd have to agree with you on the ecu. It not turning over makes me question the ignition switch though. Shouldn't the starter engage regardless of the ecu?

 

I agree about checking everything simple first and that's been done. I've gone through every ground, checked fuses, etc....Everything is now clean and shiny with strong connections. What is VOM? Thanks for the response.

I really don't know what the ECU sequence is, or what has to commit before the next component will energize. The fuel pump not turning on and the truck not turning over is fishy. I wondered too about the ignition switch, but turning the key to run makes all my gauges turn on every time, reliably Do you think it's possible to get all of these crazy engine codes with just a bad ignition switch? I appreciate the input.

 

VOM = volt-ohm-meter, aka multimeter.

For the price of an ignition switch it wouldn't hurt to replace it and see.

 

Ignition switch (aka "starter switch") can be had for under $30 easily enough, and if it's going bad, you'll get a LOT of weird symptoms (consider that there's usually several sections to an ignition switch ... )

RwP

 

Ah yes, I should have known. It's been a long time since seeing that acronym. I've only heard multimeter for the past 10 years. I do have a good VOM. I am no stranger to using one either. If I knew a specific wire to check for continuity, or a resistance reading range on a suspected sensor I'd check it. What is the switch rate-of-failure for these 3g's?


I'll keep the switch at the the top of my list. What is a good diagnosis for them? I would've suspected it right away if it's ever given me an issue like the no fuel pump/no crank condition before the symptoms. I also would've questioned it if there were ever no gauge lights when in the "run" position.

 

well sounds like you know how to start. just remember the electrons DO know the color of the wires. LOL LOL

 

Dang those smart a** electrons !!!!!!!!!!!!!