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Problems with starting when hot

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Hey y'all. I am new here and searching for a solution to my starting problem. I have a 96 351 XLT. Had for about half a year. Lately it started getting hard to start after I drove somewhere and parked. It would crank over fast but would barley start and showed fuel smoke. I became convinced it must be Fuel Pressure Regulator, the fusible link, or the Throttle position sensor. I tried the Regulator first and it seemed it worked...while heating up in the driveway. It was starting fine. I took it to town on a short trip and the same happened but even tougher to restart. Still cranking over quickly but I thought that it might not start this time. When it did it had trouble keeping idle and I had to push to 4000 rpm before it quit trying to die. It really acted flooded.  I could smell fuel when cranking for sure. Any suggestions. I intend to check the fusible link tomorrow. Could I have gotten a regulator from AutoZone that was bum and failed quickly? A little stumped here.

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Hey Big Welcome.


First check for any codes and post here.


When the engine cranks but doesn't start check for spark at any plug or connect a test light between the + and - terminals of the coil and look for a flashing light.


A flashing test light indicates everything is ok with the primary ignition.   No flash and the coil is not getting a "fire" signal.  Suspect the ign. module.  This is a common problem with the module failing when hot.


If all is good with ignition, check the cranking fuel pressure.   


Post any findings here.

Good Luck

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Yo bigorange,


Would like to you have it scanned for codes; know anyone with an OBD II scanner? Or get it done for free at a local parts store if closeby.

Check Engine Light (CEL) comes on when the electronic engine control system is not working properly. The check engine warning indicator comes on briefly when the ignition switch lock cylinder is turned to ON, and should turn off when the engine starts. If the check engine warning indicator does not come on when the ignition switch lock cylinder is turned to ON or if it comes on while the vehicle is moving, the system is malfunctioning
If the CEL does not light up at all when starting it; then suspect that bulb is burnt-out or loose, socket was damaged by PO or shop, etc. or someone removed it. 

Does it light up when engine is running?

Same for:
Transmission Control Indicator Light (TCIL) , it is a LED and overdrive on/off switch at end of the Transmission shifter stalk; flashing OD light is an indication of a transmission related trouble code in the Powertrain Control Module (PCM).


Long Crank Times may be traced to a sticking Idle Air Control (IAC) valve, TSB 97-9-5 for 95-96; "...After a 1-4 hour engine soak time, long crank times and/or long crank to start followed by a stall may occur on some vehicles. No further stalling or rough idle will occur after the engine is running. The long crank and/or stall may be due to the Idle Air Control (IAC) Valve sticking. Replace the AC Valve with a revised AC Valve if no Diagnostic Trouble Codes (DTCs) are present." 

Source: by Ford


Maybe we'll see DTC P1506 & P1507 Idle Air Control Overspeed Error & Overspeed Error; "...A vacuum leak, a damaged IAC assembly, a stuck IAC valve or throttle valve typically sets one or both of these codes. The IAC can be checked with a scan tool, sensor tester or multimeter. A vacuum leak is one of the most common causes and can be checked with a vacuum pump..."


Idle or Noise Problems & Troubleshooting; including HIGH IDLE Conditions; "...For high idle problems, try unplugging the IAC motor. If the idle drops, its usually due to an input signal to the computer which results in the computer raising the idle speed. If this is the case, look at all of the computer inputs to make sure everything is up to par. If the engine RPM does not drop when the IAC motor is disconnected, then either the IAC motor is not functioning properly, or, there is a vacuum leak in the engine. Stop the engine, remove the IAC motor and block off the passages. Restart the engine to see if there is any change in engine RPM. An idle speed higher than base idle specs indicates a vacuum leak. If the engine RPM is at base idle specs, then the IAC motor is bad. Resistance specs are 7-13 ohms. A good resistance reading does not necessarily mean that the IAC motor is good. Occasionally, an IAC motor will become weak, and will actually bypass too much air, causing a high idle condition even though everything else is operating properly..." 


Idle or Stalling Problems & Troubleshooting; "...The IAC is usually a cylindrical unit attached to the upper intake manifold. This unit electrically controlled by the computer, and allows air to flow into the intake at idle, bypassing the throttle plate. The extra air is accompanied by extra fuel to bring the idle up to proper speed, and when cold, allows a high idle condition. These units may become dirty, and need cleaning. Many idle and stalling issues tend to be blamed on these units. Cleaning is achieved by removing the electrical connector, and two screws holding it on. Once off of the vehicle, clean with throttle body cleaner (or a good carburetor cleaner). Continue cleaning until unit is clean, like new; reinstall unit. This is also a good time to clean the intake, and EGR ports (if applicable). Testing may be achieved by bringing the engine to operating temperature, noting the idle speed (should be within spec). Unplug the unit’s electrical connector, and the idle should drop to about 650 RPM. When the unit is reinstalled, it should return to normal idle speed. If the vehicle does not idle at proper RPM (too low), there are no vacuum leaks, and the TPS calibration is correct, than the unit is most likely fault..."


Removal & Installation in a 96 from 1996 F-150, F-250, F-350, F-Super Duty Series & Bronco Vehicles Workshop Manual; "...Disconnect negative battery cable. Disconnect the idle air control valve assembly connector from the wiring harness. Remove the two idle air control valve retaining bolts. Remove the idle air control valve (IAC valve) (9F715) and gasket. Installation: NOTE: If scraping is necessary, be careful not to damage sealing areas of idle air control valve or throttle body gasket surfaces, or drop material into throttle body, or intake manifold. Make sure that both throttle body and idle air control valve gasket surfaces are clean. Install gasket and idle air control valve on throttle body (9E926) or intake manifold surfaces. Install retaining screws. Tighten to 9.5 Nm (84 lb-in). Connect electrical connector for the idle air control valve. Reconnect negative battery cable..." see depictions 
Source: by Ford


BTW, see my vacuum leaknow test at Help with dtc codes and idle
Post #11

One way to do a quick check is to grab a vacuum gauge. Bring the engine to normal operating temperature. Connect gauge to the intake manifold tee. BEWARE OF FAN, BELT, PULLEYS & HIT ENGINE. 

The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .

When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

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Well I don't have a code checker so I have to wait on that, but no lights are on the dash. Used the test light on the coil . Good when starting and good when it is hard to start. Next thing is to check fuel pressure. Will look on the internet to see how to do that. I assume you have to have a gauge. I did mention it was blowing a bit of black smoke and you can smell raw fuel. I sort of doubted the coil because I do manage to get it running even when hot, it is just tough.

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Check with local parts stores for a loan a tool program, refundable deposit for Fuel Pump Diagnostic Kit, spark tester, etc.

Fuel pressure;

Engine Running 30-45 psi

Key on engine off 35-45 psi

See http://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-test-the-fuel-pump-2


Ok on the check engine light as long as it comes on momentarily when starting.



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