We are the original owner. The car has very low mileage for an eight year old vehicle, between 75 & 80 Kmiles. When car was new it immediately developed a simular problem and the Ford dealer eventually had to replace the main computer. It has been trouble free until this past fall when it started this problem, usually on very hot days. As soon as the outside temps go down it starts right up. We have been at a loss because it does not always fail making it very difficult for any mechancic to diagnos.
I would have your local dealer reflash/update your PCM to the latest calibration. I would also have the IAC replaced, I have attached the TSB explaining what can happen.
Some vehicles, may exhibit drivability conditions. These may include:
These conditions may be intermittent with no Diagnostic Trouble Codes (DTC) and no Malfunction Indicator Lamp (MIL). In some cases DTC and MIL may be evident.
Trouble cannot be identified with 95% of returned Idle Air Control (IAC) valves. The following procedure is supplemental information to normal diagnostics to facilitate accurate identification of malfunctioning valves. These symptoms would include engine stall, hard start, crank/no start, idling problems, and Idle Speed Control System related DTC's.
If the service writer uses the attached worksheet (Figure 2) for all drivability concerns including stalls it will assist the technician making a correct repair the first time.
Perform normal diagnostics.
Never clean an IAC valve. Carburetor cleaners and other cleaning agents may temporarily repair the drivability concern, but the long-term functionality of the valve is compromised.
For all drivability concerns, make certain the service writer obtains as much information as possible from the customer as to the conditions causing drivability concern. Attached is a drivability concern check off sheet (Figure 2) that if used, can help reduce the time required to diagnose a vehicle.
At stabilized engine speed and temperature, verify that the IAC duty cycle is between 27-36% with no purge flow (EVAPV duty cycle is 0%).
If no DTC's present check the following items in this order before examining the IAC valve:
Examine IAC valve under these conditions:
For IAC valve noise concerns check for obstructed or potentially damaged IAC valve from backfire.
What is the PCM and what's its function? What is the IAC and what is it's function?
Our vehicle runs really well and never stalls, surges, or fast idles. The problem only manifests in the it simply will not start after being driven around on hot days. Even that is intermittent.
The PCM is the main computer (powertrain control module) and the IAC is the idle air controller.
The idle air control (IAC) valve assembly (Figure 117) and (Figure 118) controls engine idle speed and provides a dash pot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.
The IAC valve (part of throttle body assembly) has an internal diode on some applications. If the internal diode is measured in crossed terminal position with a digital multimeter, there will be an incorrect or negative reading. It is important that the mating component and harness connectors correctly oriented. Diagnostic procedures emphasize this importance.The PCM uses the IAC valve assembly to control:
Assuming I got lucky and was able to get my vehicle to a dealer with the problem present ( engine will crank, but not start ) would they be able to get a code to verify what was going on?
The problem occurred yesterday and I noticed that when I laid down next to the vehicle on the side of the fuel tank and had my wife turn the key to the on position, I could not hear the fuel pump turn on. We went back last evening after the outside temperature had cooled and I had my wife turn the key to the on position and the fuel pump could be heard pressurizing the system and when she cranked the engine it started right up and we drove the vehicle home. Would a faulty IAC valve and the PCM not being updated cause the fuel pump not to pressurize the the system prior to starting? Are electric fuel pumps known to be sometimes intermittent in these vehicles?
If I took this vehicle into the Ford dealer, what would the approximate ballpark cost be to reflash or update the main computer PCM and have the IAC valve replaced based on the current labor and parts price? We are on a tight budget as many folks are right now and any repairs to the car have to be planned for if possible.
The next time it does not start, lets check voltage at the inertia switch in the right front kick panel. I have a feeling that the relay is failing. There should be 12v going in and coming out.
Is this under the hood or under the dash? Is there any general location picture for the pillars of the vehicle that I can look at?
Where does the voltage to this relay come from? Is it fed from the ignition switch when the key is in the on position or does it come from some logic source in the main computer? How would I measure the voltage.......by pulling the plug and checking the source side of the plug?
The "A" pillars are the front windshield pillars. The inertia switch is at the bottom behind the kick panel, by the passengers right foot. Check voltage with your volt meter on the incoming side, simply unplug it.. This could be as simple as the fuel pump relay in the battery junction box, that is the fuse box in the engine compartment.
On the diagram showing the inertial switch and the fuel pump relay, which line actually goes to the fuel pump? If it's from the fuel pump relay which appears to be activated by the ignition switch in the start or run position, does this mean the fuel pump pressurizes the system in the start.rum position without any other signals from the main computer or is there more to it than that?
I will keep you posted.
The temperature today did not get not get over 83 and the vehicle did not fail. We are supposed to have warmer days from Wednesday on so I suspect that I will not be able to check the inertia switch until then. One day at a time we wait until the thermometer goes up. It needs to reach 88 or higher. This problem started in September of 2009 during our Santa Ana season. The weather cooled and the vehicle ran good all winter until just about a month ago when we got a few days of warm weather................and bingo the trouble returned.
In keeping you posted, the temps yesterday did not go over 83/85 and the vehicle did not fail. The 4th of July forecast has temps to remain cool for us thru the weekend so I suspect we will still be waiting. I'm having my wife drive directly home from work each day instead of stopping at the store first so, if it fails, it will happen in our own driveway at home. One small note..............I located the fuse box where the fuel pump relay is located just to be ready in case it turned out that the relay was suspect. Suspiciously, the cover on the box was open. I do not know if this would cause the relay to be heated up more than normal, but I latched the cover closed. More to come...........I may try and buy some "cooling spray" commonly used to troubleshoot electronic circuits. I could use this to spray the fuel pump relay when the car fails to see if that component may be causing the problem. George Santee, CA
C1000 & C1050 right next to it.
Okay, just like clock work the weather was in the mid to high 80's yesterday and when my wife pulled into the driveway from work and shut the vehicle off. It would not start.
The fuel pump was not turning on when the ignition key was turned to the pre-start on postion. I pulled the plug off the inertia fuel shut off switch and found 12 volts at the input pin when the ignition switch was placed in the on position. I also went to the fuse/relay box under the hood and had my wife cycle the ignition switch and I could feel the fuel pump relay engaging, which it had to doing in order for the 12 volts to show up at the inertial fuel switch plug.
I made a jumper and very carefully jumpered the pins on the inertial switch plug, basically routing 12 volts to the fuel pump past the inertia fuel shutoff switch. If this voltage goes to directly to the fuel pump, it tells me that it's likely the pump is suspect? Please advise me on what's next, in your opinion, so we can complete our session and I can get this car repaired. It's going to be hot for the next few days, so I can get the car to reliably repeat the problem.
If you have more checks for me to do beyond what we have done thus far, please let me know..................Thanks, XXXXX XXXXX CA
I know this is a little late, but I want to thank you sincerely XXXXX XXXXX me with this very difficult problem. My mechanic did not even want to believe the fuel pump was the problem. I told him it was myu call and he replaced the whole fuel pump cage assembly. I also had him replace the fuel filter as it was due. The problem was totally solved and the mechanic has the case down in his notes for the future. Without your trouble shooting help, this would have cost me a whole lot more time an money.
George Nochta Santee, CA