Help! Strange Vapor Lock
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Joined: Sep 2010
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From: Kearney, NE; Cville, IN
Help! Strange Vapor Lock
1980 F250 400 w/ electronic fuel pump mounted on frame
So my truck is vapor locking, but only at speeds exceeding 55 mph. It just surges, and acts like it has no power. The confusing part is that it doesn't do this in town, in stop-and-go traffic, or just sitting there idling. The fuel line under the hood is a rubber line that does come close to the valve cover. I have had this truck for 2 years now, and it hasn't done this in the past. Though the heat and humidity is a little higher here in Kansas compared to Indiana.
I did notice that the bolts/nuts of the fuel pump underneath aren't completely tight, but didn't have anything to tighten them with at the time. Could this be the problem?
Any advice/knowledge/tips would be helpful.
Thanks fellas.
So my truck is vapor locking, but only at speeds exceeding 55 mph. It just surges, and acts like it has no power. The confusing part is that it doesn't do this in town, in stop-and-go traffic, or just sitting there idling. The fuel line under the hood is a rubber line that does come close to the valve cover. I have had this truck for 2 years now, and it hasn't done this in the past. Though the heat and humidity is a little higher here in Kansas compared to Indiana.
I did notice that the bolts/nuts of the fuel pump underneath aren't completely tight, but didn't have anything to tighten them with at the time. Could this be the problem?
Any advice/knowledge/tips would be helpful.
Thanks fellas.
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From: Denver Metro Area, CO
Given the amount of flow through the fuel system at 55 MPH I really can't see how a vapor lock could transpire during that time, the fuel isn't sitting in a static location and getting heated up and vaporizing because it's constantly flowing through the fuel lines.
I instead suspect a fuel delivery issue at higher RPMs and it can't supply enough enough - clogged filter, leak in the lines, crimp in the lines, failing pump, something like that.
I instead suspect a fuel delivery issue at higher RPMs and it can't supply enough enough - clogged filter, leak in the lines, crimp in the lines, failing pump, something like that.
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From: Kearney, NE; Cville, IN
I should specify. I can drive at 65 or 70 mph until it starts to really warm up, then it starts surging and I'm lucky to be able to run 55. I got a new fuel filter earlier, going to put that on as well as tighten the nuts on the pump and see what happens.
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From: Kearney, NE; Cville, IN
I changed the fuel filter and routed the line farther from the motor and tightened the fuel pump down. Took it out and after 5 min at 65 mph it started surging again. To which my top speed was then between 45 and 50 mph. I'm now thinking fuel pump is bad.
Also, fuel pressure gauge shows about 5 psi when idling. Who knows whether or not this gauge under the hood is accurate.
Also, fuel pressure gauge shows about 5 psi when idling. Who knows whether or not this gauge under the hood is accurate.
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From: Denver Metro Area, CO
IIRC that's about the right pressure for a carb.
Ignition modules are known to fail when they heat up, they can be tested at auto parts stores but the heating-up part is tested only by places that have a hair dryer-type of heater, might check into that, too.
Ignition modules are known to fail when they heat up, they can be tested at auto parts stores but the heating-up part is tested only by places that have a hair dryer-type of heater, might check into that, too.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
And, the ignition module usually fails completely, meaning the engine dies. But, it is possible that the module is providing a weak spark that is only able to light off the fuel every once in a while. So, when it does this pull the coil wire and check the color of the spark. It should be a fat blue/white.
However, I'm guessing the electric fuel pump is getting hot and providing just enough fuel to run 45-50 MPH. After all, they are just a motor running a pump, and as the motor gets hot the armature "grows" and if the bearings are worn can contact the windings or at least the field structure - just like starters do.
However, I'm guessing the electric fuel pump is getting hot and providing just enough fuel to run 45-50 MPH. After all, they are just a motor running a pump, and as the motor gets hot the armature "grows" and if the bearings are worn can contact the windings or at least the field structure - just like starters do.
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From: Kearney, NE; Cville, IN
And, the ignition module usually fails completely, meaning the engine dies. But, it is possible that the module is providing a weak spark that is only able to light off the fuel every once in a while. So, when it does this pull the coil wire and check the color of the spark. It should be a fat blue/white.
However, I'm guessing the electric fuel pump is getting hot and providing just enough fuel to run 45-50 MPH. After all, they are just a motor running a pump, and as the motor gets hot the armature "grows" and if the bearings are worn can contact the windings or at least the field structure - just like starters do.
However, I'm guessing the electric fuel pump is getting hot and providing just enough fuel to run 45-50 MPH. After all, they are just a motor running a pump, and as the motor gets hot the armature "grows" and if the bearings are worn can contact the windings or at least the field structure - just like starters do.
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From: Denver Metro Area, CO
IOW it is still up to you to diagnose your truck.
BTW in my experience, ignition modules eventually die altogether but they give plenty of warning. Here is a quote from another FTE member on the topic:
The 3 step scenario of a failing DuraSpark ignition module.
1) Module overheats, engine dies. Module cools down, engine restarts almost at once.
2) Module overheats, engine dies. Module cools down, engine restarts in an hour...or so.
3) Sooner or later, usually sooner, the module overheats, BURNS OUT. Now the engine will not restart.
Since these modules only fail when they overheat, taking it to a parts store to be tested: Will test OK unless the little charmer has burned out.
Engine heat is the mortal enemy of these modules which are located on the left fender inner apron just in front of the firewall (across from the red hot left exhaust manifold on V8's).
.
When replacing the little charmer, use some washers to space it further away from the apron, cuz the more air flow, the better.
Inside the dizzy is the stator aka magnetic pickup coil. The same symptoms can apply to this as they do to the module. Ford techs used to replace both at the same time.
Cheap "miracle" modules sold by chain autoparts stores are made in China CRAP. If they last a year, it's a miracle! Replace with an OEM (Original Equipment Manufacturer) Motorcraft module.
Modules have a colored plastic square above where the wires feed out used to ID them. The most common module used 1976/97 has a blue square.
1U2Z-12A199-AA (replaced: D6AZ-12A199-A, D8VZ-12A199-A, D9VZ-12A199-A) .. Ignition Module-blue (Motorcraft DY-893).
MSRP: $120.84 // FTE Ford Dealer Parts Dept sponsor tousleyfordparts.com online price: $73.11 / Tousley Ford = White Bear Lake MN
1) Module overheats, engine dies. Module cools down, engine restarts almost at once.
2) Module overheats, engine dies. Module cools down, engine restarts in an hour...or so.
3) Sooner or later, usually sooner, the module overheats, BURNS OUT. Now the engine will not restart.
Since these modules only fail when they overheat, taking it to a parts store to be tested: Will test OK unless the little charmer has burned out.
Engine heat is the mortal enemy of these modules which are located on the left fender inner apron just in front of the firewall (across from the red hot left exhaust manifold on V8's).
.
When replacing the little charmer, use some washers to space it further away from the apron, cuz the more air flow, the better.
Inside the dizzy is the stator aka magnetic pickup coil. The same symptoms can apply to this as they do to the module. Ford techs used to replace both at the same time.
Cheap "miracle" modules sold by chain autoparts stores are made in China CRAP. If they last a year, it's a miracle! Replace with an OEM (Original Equipment Manufacturer) Motorcraft module.
Modules have a colored plastic square above where the wires feed out used to ID them. The most common module used 1976/97 has a blue square.
1U2Z-12A199-AA (replaced: D6AZ-12A199-A, D8VZ-12A199-A, D9VZ-12A199-A) .. Ignition Module-blue (Motorcraft DY-893).
MSRP: $120.84 // FTE Ford Dealer Parts Dept sponsor tousleyfordparts.com online price: $73.11 / Tousley Ford = White Bear Lake MN
But, again... the symptoms you describe here (rough-running at high RPM, exacerbated by being warmed up) sound more like a fuel-delivery issue than an ignition problem but there is no way for any of us to know for certain what your problem is, all we can do is point you towards places to go look.
Junior User
Joined: Jul 2012
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From: Marlborough CT
id lean towards the pump. ive had issues with ignition modules and at high temp the motor would just die and not like to start back up, and progressively gets worse over time (running for a shorter amount of time, and not wanting to start back up). what type of pump are you using? how long have you been using this pump? most electric pumps that are aftermarket are only rated to last roughly around 60,000 miles. unless you spend more money then the rating for the pumps go up. check the wiring and ground for your pump too, possibly too much movement/vibration being mounted to the frame that is shaking the wires loose at speeds? maybe grounding the pump out? also id suggest following the wires all the way, if the wires are rubbing metal it could ware down to the bare metal of the wire and ground out. this is just my experience. good luck.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
No, Gary isn't saying that at all, he is only giving you suggestions as to places to look for the cause of your problem. Nobody on the Internet will know what's causing your problem, the only thing anybody can do is give you things to look at the could be causing the problem you describe.
IOW it is still up to you to diagnose your truck.
BTW in my experience, ignition modules eventually die altogether but they give plenty of warning. Here is a quote from another FTE member on the topic:
But, again... the symptoms you describe here (rough-running at high RPM, exacerbated by being warmed up) sound more like a fuel-delivery issue than an ignition problem but there is no way for any of us to know for certain what your problem is, all we can do is point you towards places to go look.
IOW it is still up to you to diagnose your truck.
BTW in my experience, ignition modules eventually die altogether but they give plenty of warning. Here is a quote from another FTE member on the topic:
But, again... the symptoms you describe here (rough-running at high RPM, exacerbated by being warmed up) sound more like a fuel-delivery issue than an ignition problem but there is no way for any of us to know for certain what your problem is, all we can do is point you towards places to go look.
And, that points to fuel delivery - as Chris also said. Not having enough fuel can easily cause an engine to not be able to run above a certain load, like 50 MPH for instance. But, a further symptom in that case usually is that if you give the engine more throttle than required to run properly at 50 it falls on its face. IOW, if you floor it the engine dies or runs very roughly. So, if that fits your situation then I'd bet it is fuel.
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From: Kearney, NE; Cville, IN
And, that points to fuel delivery - as Chris also said. Not having enough fuel can easily cause an engine to not be able to run above a certain load, like 50 MPH for instance. But, a further symptom in that case usually is that if you give the engine more throttle than required to run properly at 50 it falls on its face. IOW, if you floor it the engine dies or runs very roughly. So, if that fits your situation then I'd bet it is fuel.
Mountain Pass
Joined: Oct 2000
Posts: 180
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From: Backwoods Massachusetts
When it "fails" is it running smoothly, just not enough power? Or is it coughing and fighting?
I had a lot of trouble with Carter Chinese made electric pumps on my carb'ed 84 Bronco. Went through a bunch of them until I found another brand. Usually though they were a complete fail.
Good luck,
- Jeff
I had a lot of trouble with Carter Chinese made electric pumps on my carb'ed 84 Bronco. Went through a bunch of them until I found another brand. Usually though they were a complete fail.
Good luck,
- Jeff
Fleet Mechanic
Joined: Jul 2011
Posts: 1,916
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When it "fails" is it running smoothly, just not enough power? Or is it coughing and fighting?
I had a lot of trouble with Carter Chinese made electric pumps on my carb'ed 84 Bronco. Went through a bunch of them until I found another brand. Usually though they were a complete fail.
Good luck,
- Jeff
I had a lot of trouble with Carter Chinese made electric pumps on my carb'ed 84 Bronco. Went through a bunch of them until I found another brand. Usually though they were a complete fail.
Good luck,
- Jeff
"Foreign parts? WHAT DO YOU MEAN FOREIGN PARTS? Get that $@&* out of my ENGINE BAY!"
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From: Denver Metro Area, CO
Now that I'm older - combined with more offshore manufacturing - I'm finding it's the exact opposite, and I'm going out of my way to purchase Ford NOS parts when I can get them. In my experience, they're of a FAR better quality than today's minimally-constructed, foreign-made, cheesy substitutes.
Speaking mostly of ignition & fuel parts.
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