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Stalls after starting?

Tiny
AVALOVER0816
  • MEMBER
  • 1992 DODGE DAKOTA
  • 3.9L
  • V6
  • 2WD
  • AUTOMATIC
  • 128,000 MILES
Hello, I bought the vehicle listed above at auction and it wasn't starting. I think it sat for a good 10 years; I will list below what was replaced.

Spark plugs and wires.
distro cap.
fuel pump.
Battery.

Started right up. Ran rough and was misfiring but cleared up right away. Cycled the start up a few times and everything was all good. Turned it off, secured the gas tank back up and walked away for a couple hours, tried to start it and it would only stay started (ran rough) if I had my foot on the throttle. Soon as I take my foot off it would die. Dropped the gas tank again and noticed the check valve barb had broke off and the vapor return line was disconnected. Also, noticed the vapor return tube on the filler neck was not seated properly into the gas tank. These may have happened when I secured the tank back up. Would these two things cause the issue I'm having?

Thanks
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Monday, September 9th, 2024 AT 9:45 AM

19 Replies

Tiny
AL514
  • MECHANIC
  • 4,795 POSTS
Hello, yes, they can cause running issues, if the vapor hose that goes to the Purge valve is broken then the engine is pulling in fresh air from that open hose instead of fuel vapors, so it's basically a vacuum leak at that point, it can be tricky when reinstalling a fuel tank, you really have to go slow and make sure not lines are pinched or being crushed. If it was running good before reinstalling the tank then make those repairs, and just watch when putting the tank back up. I assume you're probably working on the ground? I know it can be very difficult to do a tank laying on the ground. Can you post a picture(s) of the broken components?
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Monday, September 9th, 2024 AT 9:58 AM
Tiny
AVALOVER0816
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Yes, I am working on the ground. Pain in the butt. I'll post pictures when I get home later.

What would happen if I just didn't use that purge valve and plugged up the vapor return line?
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Monday, September 9th, 2024 AT 10:02 AM
Tiny
AL514
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Well, you may or may not get a code set in the engine computer, this is an older OBD1 system, so it doesn't have the circuit monitoring that newer vehicles have. But it's also good for the system to be working properly, on really hot days the gas vapors in the tank will expand a lot, this 1st diagram is of the Evap (vapor management) and vacuum hose routing. Having the Purge valve unplugged might set the check engine light on, I'm not sure what your inspection/emissions laws are in your state, they differ from state to state, but you might fail inspection or emissions if the system is not working properly.
I understand what you're saying though, we just try to give advice on repairing vehicles correctly.
The 2nd diagram below shows the canister that the fuel vapors are stored in before being purged.
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Monday, September 9th, 2024 AT 10:23 AM
Tiny
AL514
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I know how difficult it is working on the ground, I do it all the time during a mobile service.
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Monday, September 9th, 2024 AT 10:24 AM
Tiny
AVALOVER0816
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  • 8 POSTS
Thanks for all your help!

Would 10-year gas still in the lines (I didn’t clear them out) cause problems with maybe the injectors or anything else or would it just burn off? I mean it ran at first so I would assume not. The gas was so old and smelled so bad. I cleaned the tank out pretty good so I’m thinking maybe something is caught in the lines. But it wouldn't run at all if that was the case, I think. I can rev it, and it doesn’t shut off. Just when I let off the throttle. So, it’s still getting fuel.
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Monday, September 9th, 2024 AT 10:35 AM
Tiny
AL514
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It's possible some garbage got stuck in the fuel injectors, but it's good you cleaned out the tank ahead of time, most people wouldn't think to do that, then wonder why their vehicle won't run on gas that's a couple years old. Was there a fuel filter on the frame rail anywhere you could check/change and see if there's anything caught in it? I'll look and see if there's a fuel pressure spec listed in service info, it sounds like it was doing ok before securing the tank, so Id concentrate on getting that taken care of, and if needed you can run some fuel system cleaner through it. But I'll check on the fuel pressure spec for you.
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Monday, September 9th, 2024 AT 10:42 AM
Tiny
AVALOVER0816
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  • 8 POSTS
Yes, there is a fuel filter, and I replaced that. I forgot to put that on the original post.
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Monday, September 9th, 2024 AT 10:44 AM
Tiny
AL514
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Did you happen to get a look at the throttle plates? If they were dirty and needed to be cleaned, there is also the idle speed motor, if you take that off for inspection just don't force the pintle by hand in or out, that's how they get damaged, When the vehicle is first started up the engine computer will be using the coolant temp sensor to calculate its fuel strategy until the engine gets up to operating temperature, then it will start to look at the oxygen sensors signals to help keep it within the correct air/fuel ratio. So, if you notice a difference from cold to hot operations there could be a skewed sensor causing it, but this is a very basic system.
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Monday, September 9th, 2024 AT 10:48 AM
Tiny
AL514
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I would replace the PCV valve as well since the vehicle sat for so long, that will help to prevent premature oil leaks from too much crankcase pressure.
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Monday, September 9th, 2024 AT 10:50 AM
Tiny
AVALOVER0816
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Interesting. The throttle plates look good.

When I did get it started that first time and it was running, I noticed the temp gauge wasn’t working. So in between the time from when the engine was running, and it didn’t run, I found the connector and plugged it back in and the engine started up fine, so I don’t think it was because that current temperature sensor was unplugged. I’m rethinking that something happened when I secured the tank back up.

Is the pressure that’s built up inside the fuel tank part of the vacuum system?
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Monday, September 9th, 2024 AT 10:52 AM
Tiny
AL514
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So, the way this Purge valve operates is not conventional. This ECM will energize the purge valve which closes it, this is opposite of modern purge valve operations. Service info here states that when the vehicle gets up to operating temperature it will de-energize the Purge valve which opens it, again opposite of conventional operations. But yes, vacuum is pulled from the canister which stores vapor, at operating temperature the purge is opened, this causes fresh air to be pulled into the vapor canister threw the Tank vent, and then into the intake manifold where it's burned to help keep emissions down.
Modern vehicles operate where the ECM will ground the Purge valve which opens it allowing for vapor to flow, which is why this system is different. It looks like the EGR valve is on the same vacuum line as the purge valve that goes to the intake manifold.
And your fuel pressure spec is 31psi key on engine off, so that's the fuel prime, then running it will be somewhere between 31-39 PSI roughly.
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Monday, September 9th, 2024 AT 11:09 AM
Tiny
AVALOVER0816
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Thank you. I’m going to drop the tank again and connect everything again, make sure nothing is broken and come call and post results.
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Monday, September 9th, 2024 AT 11:16 AM
Tiny
AL514
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Sounds good, at least this way the truck will keep running good for you for a while longer, especially after so much hard work.
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Monday, September 9th, 2024 AT 11:19 AM
Tiny
AL514
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Sorry I forgot to add this diagram, just showing the Evap system parts highlighted better.
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Monday, September 9th, 2024 AT 11:34 AM
Tiny
AVALOVER0816
  • MEMBER
  • 8 POSTS
Update.

Didn’t drop the tank. Lifted the bed up. Much easier to service the fuel pump.

The vent tube into the pump from the filler neck must of come out of its hole on the fuel pump. Real pain to get it back in due to new grommet but got that back in. I replaced the vent valve and grommet. I also replaced the filler neck tub grommet on the gas tank. Started it and same problem of only staying started with some throttle, once foot came off pedal it would shut off. So, I started it up again and just kept my foot on the pedal and the RPMs around 1,500-1,800 for probably close to 2 minutes let foot of pedal and it didn’t shut off. So, I’m thinking the pressure just needed to build in the tank. Obviously wouldn’t if filler neck vent tube was dislodged. Or the replacing of the vent valve solved it. Or there was still old gas in the rail that needed to be cleared out. Haven’t had any issues with it starting or staying started.

Idle is a bit erratic by only a couple 100 rpms. Surges a bit the same. Only in Park and idle. In Drive there are no erratic RPMs when stopped. I’ve got a new distributor on the way so hopefully with that and cleaning the injectors I can solve the RPM issue and also the possible misfire. There is oil in the distributor so the seal must be bad and it’s a bit rusty in there.
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Saturday, September 14th, 2024 AT 10:21 PM
Tiny
AL514
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It could have been some old fuel in the rail, but what I've found more with vehicles that have sat a long time is fuel injectors that stick closed, or at least have some build up on the tip of the spray nozzle, which can clear up once some fresh fuel gets spraying at a higher rate. I have even seen tapping on the fuel injectors get them to start working again. There was a V8, I don't remember the make, maybe a Lincoln, which had sat for a few years and all 8 fuel injectors were stuck closed, but eventually were able to clear up and it started up, that was a complete Crank, no start condition. I don't remember if the injectors were replaced or not, it was a long time ago, but that's a common issue when they sit for a long time.
The oil in the distributor is also going to cause misfires, so once you get that installed hopefully it will make a big difference in performance.
You might want to take a look at the idle control motor, everything is kind of getting moving again the more it warms up and has been driven, so the idle control motor might be sluggish as well. But it sounds like you're making some good progress.
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Sunday, September 15th, 2024 AT 3:07 PM
Tiny
AL514
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Okay, I just looked and there is no base timing to be set on this engine.
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Sunday, September 15th, 2024 AT 3:11 PM
Tiny
AVALOVER0816
  • MEMBER
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Yea, I think you just make sure you are at TDC and the rotor is positioned correctly. Or just pull the old one out and reinstall the same way.

I got the A/C working this morning. It’s an r12 system. Had to use an adapter to put the refrigerant in. The clutch on the Compressor looked all rusted up and stuck a few days ago, so I sprayed some penetrating fluid on it and let it sit and when I added the Freon today made a couple pop noises, but ended up spinning And the AC started getting cold. Not sure how long it will last because I know the oil is different between the two systems but for now it’s cold. Probably this week I’m going to throw all the injectors in one of those ultrasonic cleaners, and see if I can just get them cleaner than they are. Sad some of the suspension being worn out she’s a good little truck.
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Sunday, September 15th, 2024 AT 3:17 PM
Tiny
AL514
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If you have one of those injector pulse tools, I use one and a can of carb cleaner adapted to the injector, then pulse the injector for the longest setting it has and spray the carb cleaner, makes a huge difference in the spray pattern after a couple of cleanings. Then just replace the injector seals. The injector pulse tool is about $30, its the one used for doing an injector balance test.
If the injector has screens inside also, check out "theinjectorshop com". He sells kits to replace the seals, screens (if they have them), and a tool to remove the screens as well for a really good price. I use him all the time now. He does ultrasonic cleaning and flow testing as well.
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Sunday, September 15th, 2024 AT 6:26 PM

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