Engine randomly shuts off, sometimes I can drive for 5 minutes sometimes an hour?

Tiny
96DODGERAM
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  • 1996 DODGE RAM
  • 3.9L
  • V6
  • 2WD
  • AUTOMATIC
  • 168,000 MILES
My truck shuts off at random I've replaced or cleaned a lot of parts. Sometimes I can drive for 5 minutes sometimes an hour and on some drives it doesn't shut off at all, but at least 3 out 5 drives it will shut off but it starts right back up. The last thing I switched was the ASD relay and I really thought that fixed it but the truck shut off on the way home from the store but didn't have any problems going there.
Sunday, January 3rd, 2021 AT 8:35 AM

51 Replies

Tiny
CARADIODOC
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When does this happen; only when idling or even when driving at a steady speed? Any history that led up to this? What have you done so far to identify the cause of the problem? Have you read the diagnostic fault codes? Has the engine ever failed to restart?
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Sunday, January 3rd, 2021 AT 1:46 PM
Tiny
96DODGERAM
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It mostly does it at steady speed. I have hooked it up to a few readers and they all just tell me faulty o2 sensors, but my upstream o2 has been cut off by the previous owner. Everyone I talked to tells me that wouldn't cause it to shut off. 1 reader said the throttle position sensor was bad so I changed it still shuts off.
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Sunday, January 3rd, 2021 AT 2:49 PM
Tiny
CARADIODOC
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You don't need a code reader to check the fault codes. Chrysler made doing that yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine. Leave it in "run", then watch the code numbers appear in the odometer display. You can go here:

https://www.2carpros.com/trouble_codes/obd2/p1500

to see the definitions, or I can interpret them for you.

Also be aware diagnostic fault codes never ever say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a sensor like the throttle position sensor, or other part is referenced in a fault code, it is actually the cause of that code about half of the time. First we have to check for wiring and connector terminal problems, and mechanical problems associated with that part.

You're correct that the sensors you listed won't cause stalling. The throttle position sensor has about the least impact on fuel metering calculations. It's the oxygen sensor that concerns me. Its main function is to provide information so the Engine Computer can fine-tune the air / fuel mixture. What worries me more is of the over 2,000 potential fault codes, about half of them refer to things that could adversely affect emissions, as is the case with O2 sensors, and those are the codes that turn on the Check Engine light. While oxygen sensor codes could be relatively minor, with the warning light already on, you'll never know if a more serious fault code is set. You won't know it so it's going to be ignored. That could lead to more serious problems.

To add to the misery, there is always a long list of conditions that must be met for the computer to set a fault code. One of those conditions is that certain other codes aren't already set. The easiest example to explain involves the coolant temperature sensor and the intake air temperature sensor. The Engine Computer knows that after the engine has been off for at least six hours, both sensors had better be reading the same temperature. Failures of temperature sensors are extremely rare because they have just one component inside them. Instead, most fault codes related to them involve the wiring and their connectors. If you were to unplug, lets say the coolant temperature sensor, with the ignition switch on, the computer would see that, set the appropriate fault code, and stop using it as a reference for the intake air temperature sensor. Serious defects with the IAT circuit will still be detected, but the more minor tests the computer constantly runs will be suspended since there's nothing trustworthy to compare it to.

It's not until the coolant temperature sensor circuit is repaired that the air temperature sensor tests will resume. That is when any minor problems that developed recently will finally be detected. In the case of your oxygen sensor, one example it's used for is when the computer commands the charcoal canister purge valve to open, it expects to see a rich condition reported by the front O2 sensor. With no valid readings from the O2 sensor, the computer has no way of verifying the purge valve opened as instructed. The rubber hose could be plugged, or dry-rotted and leaking, but you'd never know.

There's a more direct way the oxygen sensor can be involved here. Depending on how the previous owner hacked the wiring to it, if the wire for the sensor's heater circuit fell down onto hot exhaust parts, it could short to ground intermittently. That harness falling down is already a somewhat common problem on many car and truck models. With a direct short, a fuse will blow, then the engine can't be restarted until that fuse is replaced. With rusty exhaust pipes, the short might not be solid enough to cause the fuse to blow, but it can drag circuit voltage down enough to cause other parts of it to stop working. The O2 heater circuit is tied in as part of the "ASD", (automatic shutdown) relay circuit that also feeds the injectors, ignition coil(s), alternator field, and fuel pump or pump relay.

Now that I described what could happen, we have to figure out what is happening. We know fuses aren't being blown. We know some defects that could provide valuable information aren't going to be detected. Based on your ability to restart the engine right away, we can probably rule out the crankshaft position sensor or the camshaft position sensor failing by becoming heat-sensitive, which is pretty common on all car brands.

Depending on what you have for equipment, there's two things I would do if this was happening to one of my vehicles. The first is to connect a scanner so I can view live data. I have a Chrysler DRB3 for most of my vehicles. Under the "Inputs / Outputs" menu, it lists the crankshaft position sensor and the camshaft position sensor as "Present" or "Lost". Aftermarket scanners may list them as "Yes" or "No", or something similar to indicate those signals are showing up at the computer. Those signals will both still be present when the engine stalls, as long as it's still rotating as it coasts to a stop. What you need to watch for is if one of them switches to "Lost" while you're driving, and then the engine stalls a fraction of a second later. That can be hard to catch, so most expensive scanners have a "record" function that lets you capture about a five-second picture of sensor data. Since that data passes through the scanner's memory, the recording actually starts a couple of seconds before you pressed the button.

Another thing to look at is the state of the ASD relay, meaning "on" or "off", and what happened at the instant it turned off. If it switched to "off" on the recording, and then engine speed started to drop, it was switched off by the computer, usually in response to losing the cam or crank sensor signal. Instead, if you see engine speed slowly dropping to "0', and then the ASD relay switched off a couple of seconds later, it was likely due to loss of spark or loss of fuel pressure, but not both. This is easier to see on a scanner because as long as the truck keeps coasting at a high enough speed, the transmission and torque converter will keep the engine rotating, perhaps as long a five to ten seconds.

You can also get a better idea if either of these tests seems appropriate by observing how the stalling occurs. A fuel pressure problem will cause sputtering or gradual loss of power over a period of a up to a few seconds. With a spark-related problem, or if the ASD relay turns off, stalling will be instant, as if you had switched the ignition switch off.
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Sunday, January 3rd, 2021 AT 4:47 PM
Tiny
96DODGERAM
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Thank you for your reply. I haven't responded yet because it's hard for me to focus and read but I'm about halfway through. Thank you for your patience.
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Monday, January 4th, 2021 AT 4:42 PM
Tiny
CARADIODOC
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I'm here almost every day to impart my wondrous wisdom. I'll be back to see how you're doing.
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Monday, January 4th, 2021 AT 5:04 PM
Tiny
96DODGERAM
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Darn dude those experiences you've had are crazy. Okay, so what I've gathered from your reply is that I need to hook it up to an obd2 and record until it shuts off and look for "lost" signals (I'll send the picture or video of the results). And also hook up a fuel gauge to see if it loses pressure when it shuts off. And also I'm almost positive my engine light bulb blew cause it never comes on and the fuse is fine and I looked how to replace it and that's definitely a project.
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Tuesday, January 5th, 2021 AT 6:14 PM
Tiny
CARADIODOC
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Remember that there can be fault codes in the Engine Computer that don't turn on the Check Engine light, so we need to read those codes any time service is needed. Don't wait for the light to turn on.
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Tuesday, January 5th, 2021 AT 7:04 PM
Tiny
96DODGERAM
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Okay, cool. I'll let you know when I hook it up might be a few days though.
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Tuesday, January 5th, 2021 AT 7:15 PM
Tiny
KEN L
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This guides can help you get the codes as well as the on, off trick. Also I have seen the crankshaft angle sensor cause this issue as well.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

When the crank sensor goes out it may not leave a trouble code btw. Here is the sensor location. Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.
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Friday, January 8th, 2021 AT 8:53 AM
Tiny
96DODGERAM
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I located the crankshaft sensor and it's in a really hard spot to get to and I don't have the right extensions to go at it from the top so I'm trying to figure out how to get to it. Sorry it took so long for me to reply if I start it up today I'll take a video and show everyone what it does. A buddy is also going to let me borrow his obd2 code reader today. I'll also send video of those results as well. Thank you
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Wednesday, January 13th, 2021 AT 9:03 AM
Tiny
96DODGERAM
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I had to drive last night and when I was driving I had my lights on and it acted like it shut off and my dash lights went a little dim so I pumped the gas to see if the truck actually did shut off and the lights got bright again and tried to stay on and it did that twice until I just pulled over because I had cars behind me and then it shut off. I just got the fuel injector connector so I can take them off and clean them and make sure none of them our clogged but maybe I'm wrong. Do you think I would have a spark problem or electrical problem from what I told you? It does backfire every once in a while when it shuts off and it doesn't want to start up. I usually give it about a minute to a minute and a half and then it starts right up but sometimes I get inpatient and try it too soon. My battery gauge on my truck stays the same doesn't drop at all until it shuts off.
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Wednesday, January 13th, 2021 AT 9:16 AM
Tiny
KEN L
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It almost sounds like the battery is shorting out, how dim do the light go? Can you please shoot a quick video with your phone so we can see what's going on? That would be great. You can upload it here with your response.
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Wednesday, January 13th, 2021 AT 9:56 AM
Tiny
96DODGERAM
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It's a brand new battery and new terminals but the lights of to about 60%-70% bright. Okay, I'll send one in about an hour or so.
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Wednesday, January 13th, 2021 AT 9:59 AM
Tiny
KEN L
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Its like the battery cables or the new battery is bad. Use this guide to test the battery:

https://www.2carpros.com/articles/car-battery-load-test

Please run down this guide and report back.
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Thursday, January 14th, 2021 AT 8:18 AM
Tiny
CARADIODOC
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Sounds like the lights went dim because the engine was slowing to a stall. Cam and crank sensors that fail when they become heat-sensitive typically take at least a half hour to cool down and work again, and often up to an hour. Being able to restart after only a minute sounds exactly like the plugged strainer I described. Unfortunately I don't see that as being available separately as it was for me the four times this happened. The blue arrow is pointing to that strainer on the bottom of the fuel pump housing assembly. I've also found it is not available separately for my '94 Grand Voyager, but it was for my '88 Grand Caravan.

To add to the misery, many times this is diagnosed as a failing fuel pump, and replacements are usually available as just a pump and motor that get installed into the existing housing. Less-expensive replacement pumps might not come with a new strainer, but many do, then you're expected to pop the old one off and snap the new one onto the housing. If you do install that strainer, it's still assumed it was the pump that solved the problem.

Remember my comment too about nursing my van home by watching the fuel pressure gauge and momentarily lifting the accelerator pedal when pressure dropped to 20 psi. I was dragging a huge trailer at the time, but by keeping it going that way, anyone following me wouldn't even have known I was having a problem.

I suspect plugged injectors aren't the issue. That is not common, and it would not act the way you described. You'd have a lack of power under hard acceleration at first when they need to flow the largest volume of fuel, but it would have to get a lot worse to cause stalling, and then it wouldn't be intermittent, and the engine wouldn't be easy to restart at any time.

I'd suggest doing this first:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Fish the hose under the rear edge of the hood where it won't be cut. That way you can see what happens to fuel pressure when the problem occurs. You can find the gauge at any auto parts store that rents or borrows tools. In my city, they make you buy the tool, then you get a full refund when you take it back. If you choose to keep a tool, you still take that used one back, then they give or order you a brand new one.
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Thursday, January 14th, 2021 AT 5:29 PM
Tiny
96DODGERAM
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I'm sorry, it takes me so long to reply. I replace the fuel pump and it ran fine for about a day and a half and then back to the same. I bought a cheap obd2 from Walmart and it says no codes were detected and it only does a freeze frame when a code is set off, but this is what it does tell me:
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Sunday, January 31st, 2021 AT 4:36 PM
Tiny
96DODGERAM
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I have not been able to get to a fuel pressure gauge but I figured it would be good since I changed the pump.
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Sunday, January 31st, 2021 AT 4:39 PM
Tiny
CARADIODOC
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You've been describing symptoms very much like when the strainer in the fuel tank becomes plugged. When you replaced the fuel pump, if you replaced the complete housing assembly, you got a new strainer as part of it. Most people just get a pump and motor that has to be transplanted into the old housing. The more expensive ones come with a new strainer that has to be snapped on separately, but they can't be replaced separately on some models. This is where you need the fuel pressure gauge to see what's going on. If the strainer is plugged, you'll see fuel pressure slowly drop until stalling occurs. It will pass fuel again after sitting for a few minutes. Stalling is also more likely to occur when the highest volume of fuel is being pumped, which is during coasting.
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Sunday, January 31st, 2021 AT 5:18 PM
Tiny
96DODGERAM
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This is the one I got and took it to the mechanic he changed it all said he test drove it for a few on his drive he shut it off turned it on 3 or 4 times then headed back to the shop and like I said when I got it back I drove all over town no problem til the next day but I feel like it does do what you just said but it also dies when I let it idle to long and I cleaned the idle air control sensor which helped it out alot I cleaned the fuel injectors today thought maybe 1 was clogged but it shut off after about 30 minutes of idling and it came right back on left it on until it shut off after about 20 minutes then wouldn't turn back on so I went back inside.
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Sunday, January 31st, 2021 AT 5:50 PM
Tiny
CARADIODOC
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Dandy. That's the complete assembly including the strainer at the bottom. I did have a second strainer become plugged on my '88 Grand Caravan, but that was after another 200,000 miles.

I haven't run into this for quite a while, but repeat fuel pump failures used to be not uncommon. You'd buy an aftermarket pump, stick it in, then it would fail after a week or two. Get it replaced under warranty, and it too would fail after a couple of weeks. Try one from a different auto parts store, and it also failed after two weeks. By the time you got frustrated after the fourth or fifth pump, you'd buy one from the dealer and have no more problems.

The cause actually had nothing to do with where the pumps were coming from. In fact, Napa gets their Chrysler pumps from the same supplier that sells them to Chrysler. What was happening was microscopic debris had collected in the tank, and that was plugging the impellers in the pumps. It was just coincidence that by the time you bought the one from the dealer, all that debris had been collected and was no longer in the tank.

This was common enough that a service bulletin was issued telling us to have the tank steam-cleaned at a radiator repair shop any time the fuel pump had to be replaced. That did indeed stop the repeat failures.

After discussing this with a friend who runs a small engine repair shop, he showed me a sample of how mold grows in the ethanol in today's gas. I have to wonder if that contributed to the fuel pump problem.

We've also found that GM and Chrysler fuel pumps almost always fail in different ways. GM pumps slow down or lock up after you've been driving a while, leaving you sitting on the side of the road. They're also relatively noisy and easy to hear running, especially on their trucks. It is extremely rare for a Chrysler fuel pump to stop running once it has started up. They are built to tighter tolerances which makes them real quiet, but more prone to locking up from debris. Their pumps fail from worn brushes in the motor. That causes them to fail to start up, leaving you sitting in the parking lot or driveway. If they do start up, or if you get them going by banging on the gas tank, they'll keep running until you stop the engine.
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Monday, February 1st, 2021 AT 10:53 AM

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