Ford Taurus misfiring after start-up - head gasket problems?

Ok…long story here about my 2001 Ford Taurus.

Right before Thanksgiving, I had my coolant flushed and changed after not doing so in way too long…so of course I had “gunky”, brown coolant. Car drove fine on the highway - about 180 mile roundtrip, but started overflowing coolant and overheating pretty much as soon as I got it home from visiting family. Took it to the mechanic and was told that my thermostat was shot from all the coolant gunk and that I needed a new belt tensioner as well - also told that I needed some sort of air sensor, but that it was only critical when I needed my next inspection. However, the air sensor was apparently causing my check engine light to stay on. I had the thermostat and belt tensioner changed (swapped out the idler pulley as well).

Car drove better VERY briefly after replacing these parts, then started overheating again and overflowing coolant. Went back to the mechanic and was told my coolant system was really dirty and that the water pump was shot. They flushed/conditioned the coolant system and replaced the water pump.

Since then my car has driven fine (it’s been about 3 weeks) - no overheating or coolant leaks. However, I started it up today after not driving it for 3 days and it began misfiring almost immediately. Drove slowly for about 2 minutes and the misfiring stopped and everything seemed fine again.

One lingering problem I’ve had is that my heater in the cabin doesn’t work - I had absolutely no heat up until I had the water pump replaced (along with the thermostat and belt tensioner), and now if I turn the heater on, I’ll get heat at first, but then after a few seconds, the vents are blowing cold air. I only get consistent heat if I leave the vents on very low. Still, no overheating since the water pump was replaced.

Not sure what my next step should be - do I need to worry about a leaking head gasket? I asked the mechanic both times I brought in the car and they said it was “very unlikely”. I know they pressurized my coolant system but not sure if they did a compression test on the cylinders. Spark plugs and wires were changed about a year ago.

Can anyone help a poor grad student out? Only 89k on my car…I need a few more years out of this thing!

I should add that my check engine light has stayed on the entire time (air sensor, allegedly) and that the engine didn’t overheat or run hot during or after the misfiring.

Go to a big box chain-type auto parts store and ask them to read your trouble codes. They do this for free. Write down exactly what the codes are (format: P1234) and post them here. Don’t bother with whatever the parts store people say and don’t let them sell you anything. Just report the codes here.

For the heat, this is probably because your heater core is clogged up with all of that gunk in your cooling system. Did you ever mention this to the mechanic doing the cooling system? Do you know if anyone attempted to flush it out?

Cross your fingers about the rest of your cooling system. As you’ve now learned long term neglect can kill the car.

A head gasket issue is always a possibility. Check you coolant frequently and note any loss. Check your oil frequently and note its condition. Fresh clean oil will resemble thin honey. Older, dirtier oil will resemble maple syrup or old coffee in color (but not sticky). Every time you check your oil pull the oil cap and look underneath and inside of the valve cover. Look for signs that your oil is turning into something that resembles a chocolate shake.

Yeah…I’ve definitely learned my maintenance lesson. I usually just drive around town (and Chapel Hill, NC is very walking-friendly too, so not a heavy driver). Guess I took it for granted.

I was told my coolant system was flushed thoroughly (several times - once when the coolant was replaced, again when the thermostat was replaced, and a third time after that. Coolant was totally brown again after being replaced the first time). After I was in last to have the water pump replaced, they mentioned that the heater core might be gunked up too…I figured that was almost a “see you real soon!” kind of statement. All of my hoses and the radiator were apparently fine.

I’ve actually been watching the coolant and oil out of paranoia for the past 3-4 weeks. Coolant level is fine and it hasn’t gotten muddy again. Oil looks good too - had it changed with the coolant. No frothing, no gunky-ness.

Thanks for the quick reply! I’ll be sure to post those codes ASAP.

During the flush, the mechanic needed to make sure that the heat was on in the car (not the fan, just the heat) so that the heater core was included in the flush.
I’m not a big fan of flushing, but if you have to you have to. I think the mechanic owes you a free flush that includes the heater core.
It’s also very possible that either flush was just too short. Ten minutes isn’t long enough (it says so on the instructions), especially for a neglected cooling system. Forty minutes should do it. Hopefully the heater core is salvagable. Even if you can’t get the mechanic to reflush the whole system for free, bring it somewhere else and have it done again.
As for the misfire, it could be any number of things and may be a completely unrelated issue. Do try to get a diagnosis prior to doing anything and post the codes.
I don’t think you have a head-gasket leak. Only because the coolant loss and overheating has stopped.

Alright, so I went to one of the chain stores and had them pull the codes off the engine. All I got was one:

“P1405 DPFE Upstream Hose OFF”

Isn’t this just the O2 sensor the mechanic told me about? Could it have anything to do with the misfiring? I thought it was kind of weird that there weren’t any misfire codes…I’m not that knowledgeable about cars, but thought there would be something…

The guy at the parts store suggested that I might have oil in the air filter and that this could have caused the misfire. I had the oil changed when I had the coolant initially changed (along with the transmission fludi - everything was old). Any thoughts?

That code has to do with the EGR system. If the EGR valve is staying open because this hose is off then that can cause rough running problems.

Locate this hose problem and your car ills may be fixed. Maybe someone inadvertently knocked a hose off or broke a vacuum nipple while doing something else around the engine. Keep in mind that an engine can run rough with no codes at all. It depends.

These are pretty good cars and 89k miles is a comparative baby on one of these.

No, this isn’t just the O2 sensor your mechanic told you about.

Look on your car’s engine towards the firewall, near the windshield, on the passenger’s side, for an object that looks a bit like a silver UFO - a round shaped disk. Very nearby is a black or silver rectangular box (maybe 1.5" x 4" in size) that is mounted to the intake manifold. That box should have two hoses and an electrical connector attached to it. That is your DPFE sensor.

This code very likely means one of the following:

  1. One of the hoses is disconnected or cracked/split
  2. The EGR valve is faulty and the DPFE sensor is not detecting proper pressure from the EGR valve
  3. The DPFE module has gone bad.

Ford had plenty of problems with the DPFE sensor - if yours is silver/metallic and not plastic, I’d bet the problem is with the sensor and simply replacing it will solve the problem. The good news is that the part is cheap and trivial to replace, even for an untrained mechanic. The bad news is that the car, having been neglected, might throw a whole bunch of problems at you…

So I took a look, found the sensor, and immediately noticed that - well - the upstream hose is just disconnected (duh!).

Here’s my issue though - it looks like the hose won’t even reach where it’s supposed to go…I tried briefly last night but didn’t have a lot of time. Going to re-attempt today.

Is there anything obvious I’m missing? Can anyone offer some practical tips?