So about a year ago we were coming back from a 670-mile trip when we had a major overheat condition. We limped home, but I believe the heat damaged some components.
I replaced the stock copper radiator with an aluminum one.
But the engine idled rough when cold, and I traced this to a bad Engine Temperature Sensor, which I replaced, and the problem went away.
Later, the catalytic converter broke loose internally, so I replaced that.
An intermittent problem that I had was in times of high outdoor temps (95F+), when driving hard on the interstate and then slowing down due to traffic or surface streets, the RV would stumble and die. While dying if you tried to give it any gas it would pop and backfire through the intake. If you left it alone it would idle, barely, but then die anyway.
I assumed this was another bad electrical component that had been overheated.
So, I have since replaced the Ignition Control Module and the Distributor (PIP sensor), as well as the spark plugs and spark plug wires.
Last week, it did it again. This time we were running on the interstate about 63 MPH, with the AC running. Temps were near 100F. Time was around noon.
The engine died, we waited about 15 minutes, it started up fine and we went another 20 miles or so, did it again. Both times it died we had just gone up a slight rise in the road, and the engine temp went up to like 202F. Normally it runs 190-195F (I have a 195F thermostat in it).
We gave up on our trip and my wife came and got me and we went home, leaving the RV at a repair shop.
We went back on Friday night, picked it up around 8pm (temps now in the 80's), and I drove it home with no AC and not a single hickup.
I have run my codes with an ODB1 reader and get nothing with Key On Engine Off, and a code 67 (which I think is a neutral switch indicator for manual trans) from continuous memory.
I am now starting to think this may not be a component failure.
I believe this may, in fact, be vapor lock.
Even though this is an EFI system. I have had folks tell me that if the fuel boils in the fuel rail, then the pressure regulator will not correctly sense fuel pressure and thus will not route fuel back down the return line to the tank.
I also understand that with vapor lock, you will see a drop in fuel pressure when it happens.
So, I am going to install a fuel pressure gauge to monitor fuel pressure. My fear is that now that the weather is finally turning cool I won't see the problem again until next spring. This is the problem I had last winter when I thought I had the problem fixed when I replaced the ICM and it drove fine all last winter.
I also understand that ethanol gasoline has a lower vapor point than normal gasoline, and this engine, being from 1990, was designed before the advent of ethanol gasoline.
Now about 5 years ago the fuel pump in the tank burned up. And when I mean it burned up, I mean parts of it looked like molten slag. When it went, it took out everything in the circuit, including the fuel pump relays and the inertial switch.
However, I do not think it took out the high pressure pump, which I did not know existed until recently. I do not think it was replaced when the in-tank pump was replaced.
So it is possible that the high pressure pump was also damaged. Also I'm not sure I have ever replaced the fuel filter on this vehicle. It is 30 years old now with 85K miles. I will be replacing the fuel filter shortly.
Assuming I do have a vapor lock condition, will a fuel pressure gauge detect it?
Also, how would I eliminate it? Somehow I have to get additional airflow through the engine compartment. This weekend I removed the front trim panel and carefully and thoroughly washed the AC condenser grill with a hose. The fins are in good order.
I'm considering adding some rear-facing louvers to the back edge of the hood. What do you think of this?
Any other thoughts?
Steve
I replaced the stock copper radiator with an aluminum one.
But the engine idled rough when cold, and I traced this to a bad Engine Temperature Sensor, which I replaced, and the problem went away.
Later, the catalytic converter broke loose internally, so I replaced that.
An intermittent problem that I had was in times of high outdoor temps (95F+), when driving hard on the interstate and then slowing down due to traffic or surface streets, the RV would stumble and die. While dying if you tried to give it any gas it would pop and backfire through the intake. If you left it alone it would idle, barely, but then die anyway.
I assumed this was another bad electrical component that had been overheated.
So, I have since replaced the Ignition Control Module and the Distributor (PIP sensor), as well as the spark plugs and spark plug wires.
Last week, it did it again. This time we were running on the interstate about 63 MPH, with the AC running. Temps were near 100F. Time was around noon.
The engine died, we waited about 15 minutes, it started up fine and we went another 20 miles or so, did it again. Both times it died we had just gone up a slight rise in the road, and the engine temp went up to like 202F. Normally it runs 190-195F (I have a 195F thermostat in it).
We gave up on our trip and my wife came and got me and we went home, leaving the RV at a repair shop.
We went back on Friday night, picked it up around 8pm (temps now in the 80's), and I drove it home with no AC and not a single hickup.
I have run my codes with an ODB1 reader and get nothing with Key On Engine Off, and a code 67 (which I think is a neutral switch indicator for manual trans) from continuous memory.
I am now starting to think this may not be a component failure.
I believe this may, in fact, be vapor lock.
Even though this is an EFI system. I have had folks tell me that if the fuel boils in the fuel rail, then the pressure regulator will not correctly sense fuel pressure and thus will not route fuel back down the return line to the tank.
I also understand that with vapor lock, you will see a drop in fuel pressure when it happens.
So, I am going to install a fuel pressure gauge to monitor fuel pressure. My fear is that now that the weather is finally turning cool I won't see the problem again until next spring. This is the problem I had last winter when I thought I had the problem fixed when I replaced the ICM and it drove fine all last winter.
I also understand that ethanol gasoline has a lower vapor point than normal gasoline, and this engine, being from 1990, was designed before the advent of ethanol gasoline.
Now about 5 years ago the fuel pump in the tank burned up. And when I mean it burned up, I mean parts of it looked like molten slag. When it went, it took out everything in the circuit, including the fuel pump relays and the inertial switch.
However, I do not think it took out the high pressure pump, which I did not know existed until recently. I do not think it was replaced when the in-tank pump was replaced.
So it is possible that the high pressure pump was also damaged. Also I'm not sure I have ever replaced the fuel filter on this vehicle. It is 30 years old now with 85K miles. I will be replacing the fuel filter shortly.
Assuming I do have a vapor lock condition, will a fuel pressure gauge detect it?
Also, how would I eliminate it? Somehow I have to get additional airflow through the engine compartment. This weekend I removed the front trim panel and carefully and thoroughly washed the AC condenser grill with a hose. The fins are in good order.
I'm considering adding some rear-facing louvers to the back edge of the hood. What do you think of this?
Any other thoughts?
Steve
Just to let folks know how this ended up.
The root of the problem is a failure of the in-tank fuel pump.
I did not think to check it, because I had replaced it just a few years ago.
These early 1990s vehicles were early transitions from carbureted engines to fuel-injected engines. The small in-tank pump was not sufficient to push the fuel up to ~40 PSI needed for fuel injection, so they simply added a high pressure pump in the circuit. The high pressure pump is mounted on the frame rail under the driver's seat.
The way the system works is this: The in-tank pump pumps fuel out of the fuel tank towards the high-pressure pump, which then boosts the pressure up to around 40 PSI to the fuel rail on the engine. The injectors drink what they need to supply the engine at any given throttle/RPM, and the excess fuel not used by the engine is routed back on a return line back into the fuel tank.
When the in-tank pump fails, the high pressure pump is strong enough to suck fuel all the way from the back of the vehicle, through the dead pump, and run just fine - under most conditions.
However, I installed a thermocouple sensor on the return fuel rail just as it leaves the engine compartment. On a hot day, that sensor was reading about 125F. If you stopped the vehicle and sat for 10 minutes, that sensor would run as high as 145F. After you start the engine and fuel gets flowing through the line again, it quickly drops back to around 125F.
I used an infrared thermometer to read the temperature of the fuel tank itself after extended (hours) running at interstate speeds. The tank wall was reading about 110F.
Here is what I believe is happening:
Ethanol-based gasoline starts to boil at around 175F. The boiling temperature of liquids is directly depended on ambient pressure. This is why it is hard to heat water hot enough to cook with on top of Mt. Everest - water there boils at only 154F. This is because the air pressure there is only 4.89 PSI as opposed to around 16 PSI at sea level.
When the in-tank pump dies, the high-pressure boost pump is sucking hot fuel through about 4-5 feet of fuel line, and a dead pump. Since the high-pressure pump is pushing 40 PSI downstream, it is capable of sucking that much from upstream. We can't be sure exactly how much resistance there is to suction so we can't be sure what the actual pressure differential is. But my suspicion is that the high-pressure pump is causing enough of a pressure drop in the upstream fuel line that the fuel there boils. Once it boils, the high-pressure pump cavitates and can no longer pump any fuel. With the engine off for about 20-30 minutes, the fuel cools enough to turn liquid again, and the engine will again run until the situation repeats.
You will see this with a very low PSI reading on the fuel rail. When I finally caught it in the act, I was reading around 11 PSI or less. Less than 20 PSI and the engine won't run much, if at all.
I ended up installing digital ammeters to both the high-pressure and in-tank fuel pumps, with readouts in the cab, so that I can monitor the current draw of each pump independently. I also have installed a digital fuel pressure gauge which picks up from a sending unit on the fuel rail.
Ultimately, the Airtex pump I had replace five years ago had died. When we got it out of the vehicle and I disassembled it, one of the brushes was gone, and the other was just a tiny nub. We replaced it with another Airtex pump, and I still had erratic running.
I finally located a new old stock Motorcraft fuel pump. This completely fixed the problem. Not only that, but because the sending unit was properly calibrated for my tank, my fuel gauge read correctly once again.
This problem is very hard to diagnose because the high-pressure pump completely masks the problem until extended operation at high temperatures. High temperatures with short-distance driving won't trigger the problem. If it's cold out, you may never see the problem (although I finally did catch it with the digital fuel pressure gauge in the middle of winter, with snow at one leg of the journey, after an 11-hour drive from Virginia to Alabama).
Because of the highly intermittent nature of the problem, very few complaints of this nature you find on the internet end up being resolved. Although, I have found a few posts after more intense searching where others have found this same root cause.
The root of the problem is a failure of the in-tank fuel pump.
I did not think to check it, because I had replaced it just a few years ago.
These early 1990s vehicles were early transitions from carbureted engines to fuel-injected engines. The small in-tank pump was not sufficient to push the fuel up to ~40 PSI needed for fuel injection, so they simply added a high pressure pump in the circuit. The high pressure pump is mounted on the frame rail under the driver's seat.
The way the system works is this: The in-tank pump pumps fuel out of the fuel tank towards the high-pressure pump, which then boosts the pressure up to around 40 PSI to the fuel rail on the engine. The injectors drink what they need to supply the engine at any given throttle/RPM, and the excess fuel not used by the engine is routed back on a return line back into the fuel tank.
When the in-tank pump fails, the high pressure pump is strong enough to suck fuel all the way from the back of the vehicle, through the dead pump, and run just fine - under most conditions.
However, I installed a thermocouple sensor on the return fuel rail just as it leaves the engine compartment. On a hot day, that sensor was reading about 125F. If you stopped the vehicle and sat for 10 minutes, that sensor would run as high as 145F. After you start the engine and fuel gets flowing through the line again, it quickly drops back to around 125F.
I used an infrared thermometer to read the temperature of the fuel tank itself after extended (hours) running at interstate speeds. The tank wall was reading about 110F.
Here is what I believe is happening:
Ethanol-based gasoline starts to boil at around 175F. The boiling temperature of liquids is directly depended on ambient pressure. This is why it is hard to heat water hot enough to cook with on top of Mt. Everest - water there boils at only 154F. This is because the air pressure there is only 4.89 PSI as opposed to around 16 PSI at sea level.
When the in-tank pump dies, the high-pressure boost pump is sucking hot fuel through about 4-5 feet of fuel line, and a dead pump. Since the high-pressure pump is pushing 40 PSI downstream, it is capable of sucking that much from upstream. We can't be sure exactly how much resistance there is to suction so we can't be sure what the actual pressure differential is. But my suspicion is that the high-pressure pump is causing enough of a pressure drop in the upstream fuel line that the fuel there boils. Once it boils, the high-pressure pump cavitates and can no longer pump any fuel. With the engine off for about 20-30 minutes, the fuel cools enough to turn liquid again, and the engine will again run until the situation repeats.
You will see this with a very low PSI reading on the fuel rail. When I finally caught it in the act, I was reading around 11 PSI or less. Less than 20 PSI and the engine won't run much, if at all.
I ended up installing digital ammeters to both the high-pressure and in-tank fuel pumps, with readouts in the cab, so that I can monitor the current draw of each pump independently. I also have installed a digital fuel pressure gauge which picks up from a sending unit on the fuel rail.
Ultimately, the Airtex pump I had replace five years ago had died. When we got it out of the vehicle and I disassembled it, one of the brushes was gone, and the other was just a tiny nub. We replaced it with another Airtex pump, and I still had erratic running.
I finally located a new old stock Motorcraft fuel pump. This completely fixed the problem. Not only that, but because the sending unit was properly calibrated for my tank, my fuel gauge read correctly once again.
This problem is very hard to diagnose because the high-pressure pump completely masks the problem until extended operation at high temperatures. High temperatures with short-distance driving won't trigger the problem. If it's cold out, you may never see the problem (although I finally did catch it with the digital fuel pressure gauge in the middle of winter, with snow at one leg of the journey, after an 11-hour drive from Virginia to Alabama).
Because of the highly intermittent nature of the problem, very few complaints of this nature you find on the internet end up being resolved. Although, I have found a few posts after more intense searching where others have found this same root cause.
Do you know for sure the pump is running? Might try changing out the relay for it. They are a known failure point at higher mileages.
Some shops always replace the relay when they replace the pump.
When the in-tank fuel pump burned up 5 years ago, it took out the inertial switch and the relays with it. So the relays have been replaced within the last 5 years.
I don't have a way to know right now if both pumps are running or not. I will be installing a fuel pressure gauge shortly.
When they started to modify fuel that put lots of accumulated junk in the fuel filters. Changing fuel filters isn't expensive and something that the Ford dealer recommended on my 91. Changing fuel filters would be high on my list when it came to anything that appeared to be fuel starvation - not much downside.
Agree. After I get a baseline reading with the stock setup, I'm going to replace the fuel pressure regulator, fuel filter, and high pressure pump.
Steve
maillemaker wrote:
Evidently the fuel filter is designed to last the life of the vehicle.
When they started to modify fuel that put lots of accumulated junk in the fuel filters. Changing fuel filters isn't expensive and something that the Ford dealer recommended on my 91. Changing fuel filters would be high on my list when it came to anything that appeared to be fuel starvation - not much downside.
When I was a kid in the 50's, probably half the cars on the road had clothspins clamped on the fuel line to radiate heat from the fuel easing vapor lock.
I have heard of this, and even seen it in a YouTube video, but I find it hard to believe this actually works by radiating heat.
First, wood is not a very good conductor of heat. And even if it was, given the high under-hood temperatures, the result would actually be to wick up heat and put it into the fuel line. This is because heat always moves from hotter-to-colder.
What I suspect is/was actually happening is that wood, being a relatively good insulator was actually insulating the fuel line from the ambient heat in the engine bay. If you clamp a dozen clothes pins onto the fuel line, then all that area is now encased in wood, effectively insulating it.
Carburetor engines often put a phenolic block of plastic between the carb and the intake manifold to try and insulate the carburetor from the heat of the engine.
Steve
Check this out:
http://www.429-460.com/t18331-460-fi-problem
Sounds like my problem exactly.
http://www.429-460.com/t18331-460-fi-problem
Yes. In fact, after I replaced the tank pump (low-pressure), we had the problem again, and a shop replaced the high pressure pump on the frame rail below the driver's door because they said it was running a little low. They subsequently tested all the pressures, and they were fine.
I kept a FP gauge attached to the Schrader valve on the fuel rail during one trip after that. It ran at the correct pressure (I think it was 50 psi, but that was a couple of months ago, so that may not be exact); however, as soon as I climbed a long hill in heat over 85 degrees F, the pressure dropped to zero and stayed that way through multiple attempts to restart. When I pressed the release valve on the gauge, I got nothing more than a few spurts and drips of fuel; I was halfway expecting to get a high-pressure burst of boiled fuel, but got nothing like that.
After about 45 minutes, though, I was able to start it just fine, the pressure went immediately back up to 50, and we were on our way again. That happened three or four times in one trip, and it was always the same: a drop to zero FP in a hot climb, a 45-minute wait, and a no-problem start with FP at specs until the next big climb. It has never happened except when very hot, and then only when climbing long hills. No engine overheat, though.
I got as far as removing the fuel lines from the single-function reservoir (small canister that holds fuel between the low-pressure and high-pressure pumps, similar to the function of a carb bowl in non-EFI systems); however, by the time I got all that figured out, it was working again, so I could not isolate the point at which fuel is failing to flow. And now the weather is cold, so it will probably not happen until next summer. There seems to be no way to check for the problem except when it is failing.
Sounds like my problem exactly.
What was your fuel level?
Full tank of gas.
With fuel systems pressurized from the tank to the injectors, vapor lock is a thing of the past. Your pressure regulator will bypass the excess fuel and keep the fuel rail cool. A good fuel pump will pump far in excess of your engines needs.
I used to think this, until very recently when I started hearing stories, like the video above, of EFI systems experiencing vapor lock.
It is true that EFI systems are a closed loop and route unused gasoline back to the tank. However, what I am hearing is that it is the Pressure Regulator that controls pressure by determining when and how much fuel to allow to return back to the tank. If your fuel boils in the rail, this pressure regulator evidently can't deal with that and fails to route fuel back to the tank - it senses this vapor as a pressure drop and so restricts/stops flow of fuel back to the tank. This allows the fuel to sit in the rails and get even hotter, resulting in more vapor.
In addition, I am learning that ethanol gasoline has a lower vapor temperature than pure gasoline. This is a 1990 engine. This was designed before the era of ethanol gasoline. It may well be that the system was not designed to handle heat loads with ethanol gasoline's lower vapor temperature.
I'm not saying that is the problem, but, what is the change interval on the fuel filter? Wouldn't it be common sense to replace the filter per the manufacturers recommendations? You have many of the symptoms of low fuel pressure and/or a restricted fuel line(s).
Yes, I agree. Honestly I don't think I've ever replaced the fuel filter in any vehicle I've ever owned, and we buy ours new and drive them about 13-15 years until they are just no good anymore. I've just never given the fuel filter any thought before. But I am going to replace this one for sure. A restriction in the fuel line could result in a decrease in pressure.
Long story a bit shorter we found that the catalytic converter. came apart and got red hot. Changed the converter and the engine picked uppower like before but the engine wouldn't idle right and would die at idle. Finally an ace mechanic found the issues. He said both oxygen sensors were bad which was dumping gas into the exhaust (I was getting 4 1/2 mpg)and burned up the catalytic converter. Also. the throttle position sensor was faulty which allowed the engine to die at idle. Also I found out that there is no way to set the idle speed without going into the computer and resetting it. Good luck.
My cat converter recently died - you could hear a piece of the internal honeycomb banging back and forth with the exhaust beat at idle. So, it has been replaced.
I have no problems idling, other than when the system gets hot as described above in which case it will not run at any throttle position, idle or otherwise. I have run my ODB1 code reader and have a clean bill of health so I do not suspect the O2 sensor at this time. However at 85K it may be due for replacement anyway.
Thanks for all the responses.
Steve
I found this very interesting video that sounds exactly like my problem:
https://www.youtube.com/watch?v=g6rf9oPDq1I
Pressure regulator failure.
Steve
https://www.youtube.com/watch?v=g6rf9oPDq1I
Pressure regulator failure.
Steve
