Engine failing at low rpms in every gear.


Tunnermann

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hi there,

I've got a 94 4.0L v6 Ranger.

It idles at around 800 rpm. And when I accelerate normally it struggles a lot to get past the 1500 rpm range as the engine fails a lot. It makes some "buble poping noise" come from the exhaust.

I run it on Gasoline and on LIQUEFIED PETROLEUM GAS. It is like your home gas. I can turn a switch and I change fuels.

So when I take of on gasoline, that problem happens. When I take off on LPG it runs fine. I would drive only on LPG if it was as powerful as gasoline...

So, since in one system it runs fine, and in the other it fails... I'm wondering what could be the cause...


any ideas?
 


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Bgunner

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As a shot in the dark because I have never worked on a propane engine, I would think that issue would be air fuel ratio for the gas side. Be sure you are not getting any unmetered air inside the engine. A nagging question I'm having is, is it possible to run both without having to remove some components?
 

Tunnermann

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Unmetered air... Like the O2 sensor is not working properly or there's too much/little air coming in?

I dunno about you... But I had this on plus a lot, like 5mm thick, of eletrical tape covering this.
Photo editing_Cloud20190610.jpg



Since then I used 2 coke plastic bottles with the ends cut off and used it as a sleeve ober it. Then used the hair dryer to heat shrink to shape. Then I silver taped it. I guess there's no air escaping anymore.


But I think the unmetered air, or at least the air hipothesis is good.


As in removing some parts to run on Propane...

You don't have to remove, but you do have to add some other valves and things... But I guess you don't remove anything... Otherwise you wouldn't be able to run on petrol anymore.


But previous owner have done a pretty shitty job... Wiring is a mess... And I'm not a mechanic... And this is my first truck... So I'm kind of lost 🙈
 

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What's the fuel pressure on the gasoline system?
 

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What's the fuel pressure on the gasoline system?
Good question. How do I see that?

Recently my fuel pressure regulator's hose had come out (the little black one) ( I think that's the name).

So it could be related also.

Photo editing_Cloud20190611_1.jpg


How do I see the fuel pressure? And what's a good pressure?
 

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Unmetered air in this case would mean that there is some sort of air leak leading to the intake. Yes your intake hose would be a big, and common, culprit of this. Because for the petrol system needs all air to flow through the MAF sensor, located on the air cleaner box, if there is a leak (vacuum, intake gasket, air cleaner tube ect.) the air getting into the engine will change the air fuel mix. The O2 sensor will read the mix as thin and try to richen it but ECM can only add so much more fuel before it reaches its programmed maximum.

To test the fuel pressure you will need a fuel pressure tester, for fuel injection systems not for carbureted systems, to check the fuel pressure. ON the fuel rail there is a Schaider valve, looks like a tire valve, where it hooks up. These links to the HOW To's here on this site should help you understand and help diagnose the issue. https://therangerstation.com/tech_library/pdf_documents/Ford_Fuel_Injection_Book.pdf AND https://www.therangerstation.com/how-to/engines-fuel-systems/
 

Tunnermann

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Unmetered air in this case would mean that there is some sort of air leak leading to the intake. Yes your intake hose would be a big, and common, culprit of this. Because for the petrol system needs all air to flow through the MAF sensor, located on the air cleaner box, if there is a leak (vacuum, intake gasket, air cleaner tube ect.) the air getting into the engine will change the air fuel mix. The O2 sensor will read the mix as thin and try to richen it but ECM can only add so much more fuel before it reaches its programmed maximum.

To test the fuel pressure you will need a fuel pressure tester, for fuel injection systems not for carbureted systems, to check the fuel pressure. ON the fuel rail there is a Schaider valve, looks like a tire valve, where it hooks up. These links to the HOW To's here on this site should help you understand and help diagnose the issue. https://therangerstation.com/tech_library/pdf_documents/Ford_Fuel_Injection_Book.pdf AND https://www.therangerstation.com/how-to/engines-fuel-systems/
Very good!! I have done some work to my air filter box recently too. I had some backfires which I think caused an explosion inside the air filter box... The box had a belly, like it had been expanded. So I tied a string around its belly and used a hair dryer to soften the plastic back to its original shape. It still had some minor cracks, which I will into it again.

I've seen that 'tire pressure valve" before.

Another question:
Let's say those holes on the air intake were made gradually. Is it possible that the ECU learnt and regulated itself to a richer/poorer mix? And when I fixed it it was still running on the "broken air intake setting"?

I had a flex fuel Renault that its ECU would adapt to some conditions, as my mechanic said.


Thanks for the tips.
 

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No, every time the engine enters a warm running state, the ECM uses the sensors and adjust the fuel mix to what is read at that time, no memory in this case of what it ran before.
 

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No, every time the engine enters a warm running state, the ECM uses the sensors and adjust the fuel mix to what is read at that time, no memory in this case of what it ran before.
So I probably have an air leak after the o2 sensors or my fuel pressure is too low/high?

Does it make a difference if the problem is intermitent? I think it runs better when the engine is hot.
 

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After the O2 would be to late in the system, ( O2 sensors are located in the exhaust, the last part of the system, an exhaust leak between the heads and the O2 sensors could change the air fuel mix just FYI) after the air fuel mix is burned is when the O2 sensor actually get a reading. If there is an air leak it would be at the air box, intake tube, intake gaskets, vacuum leak ect.. OR fuel pressure is to low.

EDIT: When the engine is first started it runs on a basic start up setting, after the engine reaches a certain temp the ECM switches over to use the sensor readings to adjust the air fuel mix and timing of spark. this could explain why it runs a bit better after warmed up.
 
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Tunnermann

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Ok, to check for a hole in the air box and intake tube is easy. But how do I check the intake gaskets? I'll probably would have to remove lots of parts around the engine that I'm not very comfortable doing... I'm afraid of deregulate something and damage it. And where could I have a vacuum leak? It would be inside the engine right? In the piston chamber?

I'm getting a fuel injection mechanic to have a look at it... but the more work I do to it, the cheaper it will be...

I've checked my air box the other day and inside on the bottom of the box there were 2 holes, looked like they were factory made, and of course air could leak out of there. But I thought it was for any water to escape in case the intake sucked any water in.
 

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intake gaskets can be checked by spraying a mixture of detergent and ATF at the mating surfaces of the intake, heads and block. If there is a leak you will see white smoke out the tail pipe, alternatively though, you can also use carb cleaner. Spray it around the gaskets and if the RPM goes up then there is a leak. (be careful with this one though, since carb cleaner is highly flammable.)

https://www.therangerstation.com/how-to/engines-fuel-systems/ford-ranger-engine-vacuum-hose-diagrams/
This link if for the vacuum diagram for your engine, last one on the page. Take a arms length of vacuum hose, can be shorter but be prepared to have to lay on the fender to reach, and stick one end in your ear... the other end in your nose... ok joking but seriously put one end in your ear and with the other run it along your vacuum lines and connections and listen for a hiss/sucking type sound. This would most likely indicate a leak at that spot. The hose amplifies the sound because it directs it strait to your ear and its movable.
I actually found a vacuum leak at my air cleaner box a couple weeks ago using this exact method so it is tried and true method.

There is a vacuum tree off the back side of the motor where the majority of the vacuum connections start from. The tree is a fitting with a bunch of vacuum connections protruding from it, though many of them may just be capped off and not used.
 
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Tunnermann

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Lol, if you had said to blow one end and stick the other end in my ear, maybe I would have considered doing it 😅

I don't have any ATF but I have some carb cleaner... (Dangerous) with this method I should probably grt a friend to watch the rpms or it will be noticable like reving?

Photo editing_Cloud20190611_2.jpg


My engine bay looks like this one. Should I spray carb cleaner where that gray/silver meets the engine block? It's kind of confising this setup. 🤔

And the vaccum hose you refered to is a hose from a vaccum cleaner right?
 

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The engine will rev quite a bit higher, then drop back down to normal, for it. It is best to spray the cleaner just after the engine starts as to not be spraying carb cleaner on a hot engine. 🔥

Yes that silver "thing" is part of the intake. These engines have a 2 part intake: The top, called a plenum, I think I spelled that correctly, is bolted to the lower, second part of the intake just below what we can see in this pic. There is a gasket between the plenum and lower intake so you would want to spray there and, the best you can without a lot of over spray on other things, where the lower intake meets the heads and across the front and rear of the engine where the intake meets the block.

EDIT: now I think about it the engine may stumble also when spraying the carb cleaner, it will be noticeable, so watch for this behavior also and double check spots that may have a stumble. Most times It's rev'ed when I have done it and found a leak.
 
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Bgunner

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And the vaccum hose you refered to is a hose from a vaccum cleaner right?
Sadly no, I'm not referring to that type of vacuum hose I was referring to Automotive vacuum hose, although a chunk of garden hose will work also if you have a a bad hose kicking around.
 


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