My thermostat thermal sensors had a slight leak due to the O-rings compressing over 170,000 miles. I tried to find O-rings but the right size does not seem to be available. Solution, buy new thermal sensors.

The sensors are under the intake manifold and the job is easier if the intake manifold is lifted or removed. I decided to remove the intake manifold because those gaskets are also probably compressed and would not seal properly again without installing new gaskets. I thought it would be a good time to clean the build up on the inside of the manifold also.

Everything was pretty straight forward but just took a while to complete. The problem started when I went to start the engine. It would not fire. I tried repeatedly and not even hint of firing. I checked all the electrical connections and the vacuum fittings and tied again, no fire. I could tell it was getting fuel because I could smell unburned fuel in the exhaust pipe.

I tried cycling the ignition switch and it did try to fire once. After I disconnected the battery for a while, it fired up for about 5 seconds and shut down and would not fire again. I cleaned the MAF, idle control valve, and checked out the EGR valve. This time it started normally and ran about 15 seconds and shut down. I could not get it to fire again. At that point it was getting late and I was convinced I would have to take it to a Ford dealership so they could run their diagnostics. I was not feeling very good about that because I have never had this kind of problem even with much more complicated repairs.

Since I had been using the battery a lot by cranking it so much, I put a charger on it overnight.

The next morning I decided to try to start it one more time. I got a backfire in the intake and it blew the PVC elbow off of the intake. A lot of dark smoke blew out too. I tied again and it would still not fire. I then disconnected the battery again and went to work.


When I got home that night I hooked up the battery and tried to start again. It fired up like there was never a problem and continued to run without even a slightest misfire. I drove it to work today and it is running great.

The only thing that I can think of that may have caused the problem is some of the throttle body cleaner may have gotten trapped in the intake somewhere and was giving some of the sensors a false reading. I know I sprayed a lot of stuff though it. I did drain it by rotating it and shaking it and then let it set several hours in the sun before reinstalling.

There was a lot of gelled antifreeze in the block valley. I flushed it out of there with water but was very careful not to get water on any of the electronics or connectors. I taped off the head inlet ports to make sure nothing got in there. It just didn't act like this contributed to the problem.

Anybody got any ideas on possible causes of the no start. BTW, it would turn over just fine, it just would not fire.