Explorer stalls when hot

Not Solved-Explorer stalls (hunts) when hot

I have been fighting this intermittent problem for a long time. I need help.

the vehicle is a 2000 Explorer 5.0 V8. I bought it with 30K on it back around 2003. Not long after we got it I was towing a trailer up the mountain and lost power. It seemed like it would slow down as I pressed down on the gas. We pulled over for a while and then it would go again for another 50 miles before stalling again. We made it to the camp site and didn't have the problem again. Next summer, in town on a 98 degree day, it happened again. let it cool down and it was OK again. I changed the fuel filter, having no clue what was going on. No codes by the way. Off and on though the years it has happened. Usually on a hot day after a long drive. The other day it happened on the way home from work. I work 25 miles away and it has been hot here. I happened to have my OBD scanner with me so I plugged in and looked at the live data. While it was trying to idle it would rev up and slow down, rev up and slow down. All I could see in the data that seemed wrong was that all of the short term fuel trims would jump up into the 40s and then go back down, up, down. At the same time the ignition advance would go up to around 20 degrees (my memory is a little fuzzy here) and then back down. All of the O2 sensors seemed to cycle with the revving. After I let it sit for an hour I drove home.

We are in for some serious hot days and I need to get this taken care of once and for all. Today I replaced the IAC. It seemed to be OK but after an hour of driving, the problem came back. It didn't seem to be as bad as it has been but it is still screwed up. I've cleaned the MAF sensor before but it is the original. The O2 sensors are original as is just about everything except one of the coil packs which I replaced a few months ago. I am thinking about a new MAF but I thought I would try asking here before I spend another 125 on a shot in the dark.

I should mention that I usually only have the problem when I slow down to an idle or near idle. When it is really bad, I can feel it cutting out while coasting down hill. It pretty much always happens for the first time when I am sitting at a light and I try to take off. Never when I am at cruising speed.

The first time it happened, I did replace the fuel filter (another wild ass guess).

The Explorer has 176K on it. Runs great as long as the temperature stays below 90 or so.

Looking for some ideas.

Tony

I've had the same exact issue with my 98 v6 SOHC. Really hot day, longer drive and it lost all power. After it cooled off 10 min or so it starts back up. Interesting that you have seen the fuel trims jump around when it happens. I'm curious to see if anybody has good input on this.

Well, I bought the MAF and I wasted the money. Still doing it's thing.

However, I looked at it with the scanner again while the idle is pulsing up and down. Tonight, the trims were not so wild. Only +5 or so when normal is a little bit negative. It seems to be happening more frequently now. I don;t know if it is the new IAC and MAF or if the problem is just getting worse. Tonight it was below 90 and it still happened. It is related to the idle somehow. It even backfired a little bit when I tried to take off while it was in the down part of it's up/down cycle.

Tony

My neighbor is a service manager for a GM dealership. He was out this morning while I was trying to figure this out. I had driven the car for nearly two hours before the hunting idle started again. We sprayed carb cleaner everywhere with no effect. Unplugging the IAC has no effect but unplugging the MAF sensor makes it start acting erratic. When we were done, he suggested some BG 44K injector cleaner so I went and got some and put it in the tank. It seemed to help so I let the car cool down and went to the mountains to escape the heat. It is over 100 again today. When I got back I drove it for half an hour. The idle is much smoother but when I pulled up into the driveway and was about to turn it off, wham, it started hunting again. The fuel trim slowly creeps up still. That has been pretty consistent. Before the hunting starts, the trims are down where they belong, near zero. When the hunting starts, the trims start creeping up.

Engine temp stays near 190, I've seen it as high as 198, but it typically stays betwen 190 and 193 or so. MAF runs at about .68 but I don't know what is normal for that. Inlet temp runs as high as 140 but usually more like 133. Advance is at 18-19 degrees normally but when the hunting starts it swings from about 15 to 25 degrees. Absolute TPS is at 19.

Tony

Well, I may have fixed the hunting. I doubt that this was my original stalling problem from long ago. I don't remember any hunting back then. I recall that the engine speed would go down to almost nothing if you pressed the gas pedal. If you held it down, it would eventually catch and go.

I mentioned that when it is hunting, unplugging the IAC has no effect. It occurred to me that this is a closed loop system and the IAC is one of the main tools that the computer has to control the idle speed. What if the computer was trying to reduce the idle speed but ran out of range on the IAC? The control loop would break and the system could be unstable and hunt. So tonight I put the stop screw out a half turn to allow a little more room for the IAC to reduce the idle speed. Now, when I unplug the IAC, the idle drops. I drove it around with the AC on in the 100 degree heat and it did not hunt. I didn't drive all that long so we will have to see. Hopefully that was it.

Hunting is fixed. Unscrewing the idle stop screw by half a turn is all it took.

Well, it was good for a week of driving to work in the heat. Today we drove up into the mountains. After climbing out of Denver for about 20 minutes, we exited the highway and wham, the idle started hunting again. Trying to pull away from a stop and the vehicle jerks until it catches and then goes. So much for that fix.

I'm not sure what to try next. I've tried IAC, spark plugs, wires, coil packs, MAF sensor and fuel filter. I also ran some BG44K through the fuel system. I've tested the EGR valve. The Oxygen sensors are original with 176K on them but there are no codes. Things I have not tried:

O2 sensors
Fuel pressure regulator
fuel pump (it's an IDLE problem... probably not the fuel pump but who knows)
PCV valve
ECU

My '00 Explorer did the same thing to me yesterday. It would hiccup at stops. I live in Greeley and headed to Denver. On Quebec I lost all power for about 10 sec. It caught again and I had no further probs. Later, when the temp dropped to about 80, I drove back to Greeley with no issues. I spoke w/local Ford dealer. They think it could be fuel pump or filter.

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when you encounter this issue try adding fresh cool gas to the tank ,if it starts running correctly right away then your fuel pump is going bad from overheating .
i have this issue .
on long drives on a hot day (90 and above)my 2000 sport will lose power ,want to stall,buck and carry on but it has always got me home .

i suspected it was a fuel delivery problem and on a whim i pulled into a gas station when it was acting up .i put fresh gas in it and whalla it ran fine all the way home .
the fresh gas cools the pump and lets it run normal again for awhile .i been limping mine along near 2 years now on that pump as it only gives me trouble on 90 degree and up days on long drives (out driving around town a hour or more)the hotter it is out the sooner it will act up .
i have discussed this before in other threads .

i suspect you have a fuel pump issue .

good luck.

You say it only does it when it's real hot so I wonder what would happen if you put in a cooler thermostat?

jremington59 said:

You say it only does it when it's real hot so I wonder what would happen if you put in a cooler thermostat?

Click to expand...

do not do this..............

engines are required to run at certain temps for good reason.like emissions,driveability ,proper combustion ,ect,ect

jremington59 said:

You say it only does it when it's real hot so I wonder what would happen if you put in a cooler thermostat?

Click to expand...

The thermostat would not affect the temp of the gas in the tank or lines. The pump is in the tank so I would think that it is the temp of the gas in the tank that causes problems. Hot gas expands which also expands the air bubbles trapped in the liquid. Possibly installing a FASS (fuel-air separation system) may help with the stalling but won't help with the pump.

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In a sense I had a very similar problem. It started out with the problem the OP posted. I tried so many things (fuel treatment, tune up, oil change), and did not help. I had to drive the tar out of it for a period of time until it threw some codes finally. I got a misfire in #2 and lean on the right bank, later the next day both banks. I replaced all the injectors, tune up again, connectors, and still no change. It ran horrible..

When I originally bought mine, 1998 Sport, last month (59,000 miles on it), I was told that they had it sent out to have the fuel pump replaced as well as some other work. So I assumed it was done, and done correctly. Come to find out as I was tearing through it, I found that there were things that were claimed to be done that were not. So now I have to safely assume nothing was done.

Sure as $$$$, I went ahead and replaced the fuel filter just for good measure. I had to cut it out because the line removal tools could not access the filter neck. When I got the filter out, on the pump side, there was serious heavy mud coming out of it and it weighed about 5x the weight of a normal filter. Now it runs like a champ.

With as much crap that was trapped in the filter, I am going to replace the pump, strainer and tank. I would recommend looking at the pump.

This is not my first Explorer. I have owned a 95 4.0 SOHC, a 97 5.0 AWD and now my 98 4.0 OHV Sport. On all three of them I have had serious fuel pump issues and had to replace them. All in all, looking at the stats, right around 90,000 miles these fuel pumps fail. Some sooner then others, but they are the weak link to these vehicles. (that and the electronic transmissions, lol).

For the $140-150, I would try out a cheapy fuel pump, or go ahead and get the Motorcraft one. I have even taken mine into the dealership where they replace the DPFE sensor, thinking that was the problem, and it wasnt.

Yours could be overheating, and more so when it reaches 1/2 tank or less. Pay attention to your fuel levels when it happens in conjunction with the outside ambient temperatures. You may get your answer!

joe doe said:

do not do this..............

engines are required to run at certain temps for good reason.like emissions,driveability ,proper combustion ,ect,ect

Click to expand...

I have a 180 degree T stat in mine and he says his is running at 195. Do you know what temp T stat is stock?

Thanks for the discussion. It's nice to hear some fresh ideas. I am leaning towards the O2 sensors at the moment with the fulel pump a close second.

I bought a fuel pressure gauge from Harbor Freight and the pressure is good, near 65 PSI and it stays at about 60 with the engine off. Of course it wasn't failing when I checked it so the hot fuel pump is still a possibility.

My plan is to replace the O2 sensors, run for a while and then do the fuel pump whether it needs it or not. 176K is a long time for both of these parts. Even if they are not the cause of the problem, I will be doing myself a favor by replacing them.

I did the PCV (what a pain on this engine) yesterday just because it was cheap and relatively simple to do. Ford managed to turn a 30 second job into a 20 minute job with scraped knuckles by placing the valve at the back of the intake, invisible and accessible only by feeling for it. I removed the big electrical connector and bracket that they put right above it and I still had to lay on top of the engine to get it back in there. The old one was pretty clean and rattled like a new one so I don't think that this had anything to do with my problem. I don't recall ever replacing it though so it was a good thing to get out of the way.

I don't think that 200 degrees for the coolant temp is a problem at all when I've been driving all over in 100 degree heat, thats not bad. The radiator was replaced last summer and I can drive around in the heat with the AC on without the temp gauge climbing.

I have not noticed that this problem is associated with a low fuel condition but I wasn't really paying attention either. I'll keep that in mind. It happened in the mountains last time and I don't usually head up there without filling up first.

Tony

I had this issue for the last few days... 115 degrees outside driving on 1/4 tank of gas.. NO BUENO!!! The beast was trying to vapor lock on me!!

Filled up the tank today with some fresh COLD gas and it started purring like a kitten!!! Told the wife DO NOT let it get past 1/2 tank with this heat!

Somebody asked about the t stat. I think stock is 190. That is where mine sits most of the time.

Tony

Edit: I just opened up my Haynes. It says 192 to 199 for the opening temperature and 212 for fully open.

I replaced the fuel filter and fuel pump today. The weather has been a little "cooler" so I will just have to drive it and see how it goes. The pump was original so it needed to go anyway.

Do you have any engine codes? Does it idle rough in normal weather?

First I had the same issue towing a boat through mountains. The problem was the MAF. I replaced mine and that was the issue. The Exploder never had issues at sea level only in the mountains. I ascertained that the air was thinner at altitude and my sensors would make adjustments. Could totally be off base, but that's my opinion. So I would start with a high flow air filter, check your vacuum, and change your thermostat. If it's running at 190* it's stuck open and not getting up to proper operating temperature. O2 sensors measure emissions. If they are rich or lean they throw a code, so save your money. As a gentlemen said before, these beasts are designed by an engineer to run warm and they like it warm. Just my two cents.