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Ford Ranger idles roughly, stalls out during hot weather

I am trying to troubleshoot this problem before paying for a new fuel pump in the hopes that it fixes the problem. I recently purchased a 1996 Ford Ranger with the 4 cyl. engine. The first 10 days I owned it it ran just fine. I then took a an hour drive to another city. After the first few stops there, as the temperature outside reached about 90, It started to sputter and idle very badly. After I got rolling it would would run fine. I decided to try to make it home. It ran fine at freeway speeds of about 70 mph. I had to stop once; it stalled out and would not start again. After waiting about ten minutes I tried again. It was still running rough, but I was able to get rolling and drove the rest of the way home without any problems until I was in town and had difficulty keeping it running at idle. The next morning it ran fine again. A local mechanic changed the fuel filter, but the problem came back as soon as the temp neared 90 degrees. A mechanic friend who witnessed the problem said that it definitely sounded like a lack of fuel and not an electrical problem. Is there a way to troubleshoot without swapping parts? If the fuel pump is failing in warm weather, how is it possible that it runs fine at 70 mph, but not at idle? Engine temp gauge looks good. I did get one code after it died the first time (lean mixture, I think he said).

There must be a check engine light involved - yes? If so there are error codes. Many auto parts stores will read them for free if you don’t have them. The format is “P1234” - folks would need the exact P number, not something that someone said it means.

It doesn’t sound like a fuel pump issue to me - but didn’t this mechanic who replaced the fuel filter just put a pressure gauge on it? This takes 5 minutes and eliminates any need to guess about the fuel pump. So no - you don’t have to just swap it to find out.

You just bought it, and didn’t really say anything about the state of basic maintenance items, so I’ll assume you don’t know. If I just bought something and didn’t know then I would do the following before anything else:

  • new spark plugs and wires, unless it was obvious that they are fairly new. Even so I’d check them carefully visually and with an electrical meter (resistance). If they are newish wires, but cheapo then I’d just get Motorcrafts. They’re not much more expensive than the bargain basement stuff.
  • check compression while spark plugs are out.
  • clean the throttle body, idle air control valve, and MAF sensor.
  • inspect/change air filter
  • check the fuel pressure
  • service the cooling system including a new thermostat.
  • put a vacuum gauge on it and look for any evidence of issues - vacuum leaks, valve issues, potential compression issues, exhaust issues…

All of that is dirt cheap stuff to do (mostly time) and is just good maintenance. The plugs & wires, TB/IAC/MAF cleanings may actually help.

As to other things that are also cheap/easy and may give you this issue:

  • pull the vacuum line from the fuel pressure regulator and look for liquid fuel. If you find any replace the regulator. (This should show itself while checking fuel pressure, but you never know).
  • check air and coolant temp sensors with an ohmeter for correct resistance specs

…and I’m sure some other stuff that other people will chime in about

Thanks for your quick reply. Of the above areas, which are most likely to be affected by ambient temperatures? It runs great in cooler weather. I know that the fuel pressure tested good, but it was not acting up at the time it was tested. Is it possible that it is failing just at warmer temps?

On most cars the fuel pump is cooled by it being immersed in gas. When they get older, I’ve seen failures where the pump just doesn’t work as well when there’s not much gas in the tank. Eventually they fail altogether because they overheat. With ambient temperatures being higher, one would assume that this would make the situation worse.
I guess its bearings seize.

Could it be that your problem is less pronounced when the tank is not full? If so, that would point to the fuel pump as a possibility.

There are lots of possibilities given the heat - the fuel pump could be one but not all that likely, and the thing is that a borderline fuel pump would not be acting up at idle. It would act up under load, so your symptoms are somewhat backwards. If anything your symptoms fit the opposite - which is too much fuel. This is no reason not to check the fuel pressure when its acting up.

In general , heat related failures very often affect ignition components - like the ignition coil. As far as I know those are very hard to test - but easy to replace. For testing you’d need an experienced tech with a good electrical scope, and the conditions that make it happen. But in general, any borderline electrical part will show issues when hot.

Start carrying a spare spark plug or plug tester. The next time it stalls and won’t start, check it for spark.

If you find spark, shoot some starting fluid into the intake. If that gets it to fire a bit then that will tell you that you’re lacking fuel.

At those times when it wouldn’t start do you remember smelling any fuel as if it was flooded?

Problem Solved

Short Answer: Fuel pump
Long Answer: My favorite mechanic has not been available for years, since he took a job as head mechanic for a government agency. He recently started taking side jobs again. I left work the other day when it was 97 degrees, and it started acting up almost immediately, before the engine had time to warm up, confirming that the problem was not related to engine temperature. I limped it over to my mechanic, who got to see it acting up. He saw that there was fuel in the fuel rail, and at first suspected the ignition module. He then put a pressure gauge on the fuel line and restarted the truck. At first it had decent pressure, but within a few seconds the pressure began to drop, even as he gave it more throttle, eventually dropping to zero.

The fuel pump, strainer and filter were replaced, and the problem appears to be solved. He said that the fuel pump looked original. At 250,000 miles, I guess it was due.

Hello, I am posting this to help those that I can from going what I went through.

Vehicle: 1994 Ford Ranger, 2.3L, Manual Trans, 5 Speed

Symptoms: Idles roughly, lack of power, dies on days hotter than 80 degrees after driving around for 20-30 min.

Possible Diagnosis: Bad Ignition Control Module (ICM), Bad Fuel Pump, vapor lock on fuel rail, or Catalytic converter clogging up.

So as stated above, my ranger was idling roughly and dying after driving it around for a little while, but only on hot days. I would have to let it sit for a little while it cooled down and could get it running until it would heat up and die again. At first I thought it was the fuel pump even though I was getting fuel to the rails and it would test fine with a pressure gauge(needed to change it anyway since the sensors had failed). However, this did not fix the problem. My next attempt at fixing this problem was to change the ICM as it could possibly be overheating and not working. This also did not keep it from dying. I then experimented with the issue being vapor lock in the fuel rail and the catalytic converter getting too hot and clogging up. These did not help resolve the issue either. I was kind of at wits end and was almost ready to just call it a lost cause. Then it dawned on me, especially since I hadn’t checked it in the four years I had the truck, I should really check the timing belt. Upon opening up the timing cover, which was way harder than it should have been, I found that the belt had jumped one tooth out of time. So I went and replaced the belt and set it back into time. After reassembling everything, I said a small prayer and started it up. This had solved the rough idle and it has not died even when the days are getting up above 90 degrees. So before you spend all your money and time with replacing fuel pumps and such, give the timing belt a look and see if it is out of time.

That’s a very interesting finding @joshmota66 . Thanks for posting, hopefully will help others here w/similar problems. I wouldn’t have a guessed a single cog-tooth slip on a timing belt would cause temperature related stalling. I’d have guessed the symptom would be a somewhat noticeable loss of power, a little backfiring, pinging, poor mpg, perhaps a little bit of rough idling, etc. . I’m wondering I on your Ranger the belt was too loose for some reason, and it was actually that looseness that was causing your more severe symptoms. i.e. the valve timing was sort of swaying back & forth in the proverbial breeze. And then your fix of a new belt not only got the cogs lined up again, but also completely fixed the loose belt problem.