We replaced the thermostat on our 2002 Ford F150 Supercrew 5.4L V8, not a diesel. We let the engine run afterward while adding coolant. Unfortunately, we didn't take it for a test drive until later that evening. It idles perfectly normal, however upon taking it down the road, the service engine light began blinking and it was running quite rough. It kind of chugs and runs similar to when you have bad fuel or are running out of fuel.

We thought perhaps the gasket didn't seal up properly, so redid the process. It test drove fine for approximately 15 miles, then began running rough, chugging, etc. It does not leak coolant.

I find it hard to believe something ELSE could be wrong with the truck... too much of a coincidence.

Any ideas?

And, when I purchased the replacement thermostat, the parts store gave us a gasket that was far larger than the original. I went and purchased another, thinking he simply gave us the wrong part. There was no gasket between the housing case and the housing, just one inside. Should there possibly be one sitting on top of the case between the case and housing?

Thanks again!

The only thing that makes the check engine light flash is a class A cylinder misfire so first thing is to check it for codes and find out which cylinder(s) are at fault.

If it's cylinder 4 (rearmost on the passenger side), there's a longshot possibility that you may actually have a coolant leak onto the COP shorting it out. I don't remember if it applies to a 2002 but it happened to my 98 F-150 5.4L, however that failure would be unrelated to a thermostat job and pure coincidental. Hence why I say it's unlikely.

I would make sure I didn't bump any vacuum lines, and if it has some of those plastic vacuum lines, it is real easy to bump one and break it and not realize it. The check engine light came on. Just take it to advance autoparts or auto zone and have them run the diagnostics on it. And a cylinder misfire is not the only thing that will make a check engine light come on. Many things will.

Anything that could compromise the emissions will cause the light to come on but only a misfire DTC will cause it to flash.

Oh OK, sorry about that, didn't catch the part that it was blinking, thought it just came on.

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Originally Posted by 1979kawkz650c

just take it to advance autoparts or auto zone and have them run the diagnostics on it.

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Thank you all for your answers. Unfortunately, we do not live anywhere near an Advance Autoparts or Auto Zone to have diagnostics run on the truck. Not to mention we don't want to drive it very far so as not to damage the engine itself!

And, as Majoria mentioned, it would be odd that suddenly there is another issue unrelated to the thermostat, as in an emissions problem, unless it is the coolant leaking onto the COP (which, by the way, I have no idea what this stands for).

The service engine light is on nearly constantly with the truck... we've been told various reasons, and the service techs usually just reset it. I believe the last tech said it was because our coolant system was running too low of a temperature, but it was nothing to worry about. :rolleyes: This is the first instance of it blinking.

We will check the vacuum lines and whatnot to see if one was knocked loose. Otherwise, it looks like we're going to have to find someone nearby with a diagnostics computer to see what the issue is!

Thanks again... and any other ideas would certainly be appreciated!

COP = Coil On Plug. Instead of having a coil pack as with older distributorless ignition systems, this engine has the newer common approach of an individual coil right on top of each spark plug thus no high voltage spark plug wire. The COP will have to be removed to access the spark plug, they are black and the top (the coil itself) is cylinder shaped and a little bigger around than a quarter.

Right above the #4 cylinder's COP is a coolant line that could leak. Take a look for any indications of moisture around that COP, if none then check the other COP's.

Another option would be to wait until it is acting up and then disconnect one COP (should be a two wire electrical connector on the side of the COP) and see if the problem gets worse, this can be done while the engine is running. If it does get worse then the COP you disconnected is from a cylinder that is working fine since it became worse. If there is little or no change when the COP is disconnected then that cylinder is not contributing. Keep in mind that disconnecting COP's may also induce codes so once you are able to check for codes you may have false codes in addition to the valid original code(s) and you may not be able to tell which ones are valid. A dealership could by checking for a code that has freeze frame data but most generic scan tools may not have that ability.

Sad part is as long as it's blinking, you really need to find out which cylinder(s) is/are causing the issue. If you can pull codes then hold off on disconnecting COP's with the engine running.

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Originally Posted by Majoria

Another option would be to wait until it is acting up and then disconnect one COP

Sad part is as long as it's blinking, you really need to find out which cylinder(s) is/are causing the issue. If you can pull codes then hold off on disconnecting COP's with the engine running.

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The only time the engine acts up is after it's heading down the road. There are no misses or clunking when it idles, which would make it a bit difficult to test the COP. (And, thanks for the clarification on COP).

I forgot to ask the hubby if the light was blinking during his last trip. As I mentioned, he drove it about 10-15 miles before it started chugging. We also let it sit and idle for 15-20 minutes after he made it home... and nothing amiss.

Thanks again... we will keep working on it!

A misfire will not cause the truck to act up only after it's warm.

Take the truck to a certified mechanic with the proper tools and find out what's making the light come on to begin with.

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Originally Posted by this8384

A misfire will not cause the truck to act up only after it's warm.

Take the truck to a certified mechanic with the proper tools and find out what's making the light come on to begin with.

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Unfortunately, your answer is wholly incorrect and Majoria had it nailed... almost.

After getting the truck hooked up to the diagnostic computer, it is misfiring on cylinders 5 & 6. It is totally unrelated to the thermostat replacement... just one of those quirks of fate.

After cleaning the corrosion off the terminals and re-gapping the spark plugs, it was STILL idling perfectly normal and the code cleared. However upon backing it out of the bay, it began to chug again and the service engine light began blinking. The plugs need to be replaced, and possibly the coils. He is going to replace the plugs and see if that remedies the problem. Otherwise, the coils get replaced as well.

Our service tech advised spark plugs usually have a life of around 100K miles... we're at 121K. Also interesting to note is the tech typed in our VIN for the truck, and it comes back as being a "bi-fuel" vehicle.

NOTE TO ANYONE WITH A FORD F150 AND A BLINKING SERVICE ENGINE LIGHT: DO NOT continue to drive the vehicle for any extended period. With the misfire, fuel can get into your carburetor and torch your catalytic converter. In other words... BIG BUCKS!

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Originally Posted by lgehner

Unfortunately, your answer is wholly incorrect and Majoria had it nailed...almost.

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Actually, it's not. You indicated that your truck only ran poorly after it had been driven for awhile. A misfire will be present whether the vehicle is warm or cold. It may get worse after warming up, but if it was that bad then you can't tell me it ran 100% when you first started it. I've had customers tell me that their vehicle is "running perfect" and when I go to pull it into the service bay, it's skipping and missing. People either don't pay attention to their cars, or they get so used to them running poorly that they just get used to it and think it's normal.

As for the blinking engine light, that applies to ALL vehicles, not just F-150s. When the light is flashing, that means a code is being set into the computer. If you don't fix what's wrong in the first place, you end up costing yourself even more money, just like you indicated.

Just out of curiosity what is bi-fuel?

Just out of curiosity, what is "bi-fuel"?

Ford offered two bi-fuel options for this eninge in this vehicle, LPG (liquid propane gas) or CNG (compressed natural gas). The engine could run on two different fuels, gasolone and also either LPG or CNG, whichever it was set up to run. Other vehicles were set up for strictly CNG operation and could not run gasoline.

I've seen many COP's only act up under certain conditions, some of which make no rational sense such as intermittent failure yet they are the root cause. Misfires can be intermittent, the one on my 98 F-150 was and it had a coolant drip onto it so one might think it should be constant.

Kind of falls into that "fix it now and explain it later" category. In this case, internal COP wiring would explain everything except the coincidence of when it started, that's gets chalked up to just bad luck. Still other possibilities like the plugs of course.

The blinking light means the code is likely a P030X with X being the cylinder number of the misfire, so P0305 and P0306 in this case. The P0 level codes are universal to all OBDII vehicles.

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Originally Posted by this8384

Actually, it's not. You indicated that your truck only ran poorly after it had been driven for awhile. A misfire will be present whether the vehicle is warm or cold. It may get worse after warming up, but if it was that bad then you can't tell me it ran 100% when you first started it.

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It IS incorrect and your answer is ALSO incorrect. The certified service tech started our truck and it idled fine. After idling for 10-15 minutes, he then took it out on the road and about 2 miles later, it began chugging. He hooked the truck to the diagnostic computer and came up with the code. He cleaned the plugs, re-gapped them, etc. AND IT IDLED PERFECTLY FINE. He thought all was well... UNTIL he backed it out and drove it a little way. It began chugging again. Thus, the replacement of the coils, plugs and wires.

So, if a certified service tech thought there was nothing wrong with it and thought it ran perfectly fine, how would the average Joe know any different? And, I'm NOT the average Joe...

:)

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Originally Posted by lgehner

It IS incorrect and your answer is ALSO incorrect. The certified service tech started our truck and it idled fine. After idling for 10-15 minutes, he then took it out on the road and about 2 miles later, it began chugging. He hooked the truck to the diagnostic computer and came up with the code. He cleaned the plugs, re-gapped them, etc. AND IT IDLED PERFECTLY FINE. He thought all was well...UNTIL he backed it out and drove it a little way. It began chugging again. Thus, the replacement of the coils, plugs and wires.

So, if a certified service tech thought there was nothing wrong with it and thought it ran perfectly fine, how would the average Joe know any different? And, I'm NOT the average Joe...

:)

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Unfortunately She is a 100 percent right. You just took it to a dumbass. Some money hungry jackass whose sole purpose is to make money, not fix cars. A misfire will be present all the time. People don't clean and regap plugs on a 5.4l ford because they're a pain in the to do. That was the first indication you took it to someone who didn't know what he was doing. If it only happened after you did the thermostat, have someone draw a vacuum on the coolant system and refill it.

Another note on Ford Trucks. If equipped with the electronic 5 speed automatic O/D transmission, all electrical components must be in working order!! My 2002 Ranger had a burnt tail light bulb. The trans stopped shifting properly, burnt the fluid badly and would not go into O/D mode. Changing the bulb corrected the problem. I saved the transmission, only because we were still in town and near a parts store. I carry spare fuses and bulbs with me now ! If it hadn't actually happened to me, I would have not believed it.