1998 Ford F-150



December, 4, 2009 AT 12:09 AM

Engine Mechanical problem
1998 Ford F150 V8 Two Wheel Drive Automatic 125k miles

This one is a little strange (aren't they all) My 98 4.6L has a Karr 2040 aftermarket alarm. A month ago, leaving Home Depot it would crank but not start. The alarm has been a little flakey so I reset the alarm (thinking that there might be a fuel pump shut off connection to it) and then engine started. A few weeks later it happened again - same remedy - set then disarm alarm. Happened a week later, then a few days later all with the alarm reset remedy working. Now finally - same symptom - cranks but won't start - but alarm set and disarm no longer solves the problem. The alarm still seems to be working.

Diagnostics so far:
Checked Fuel pump fuse - good
Swapped Fuel pump relay with horn relay (same part number) - no effect
Checked emergency fuel pump cutoff switch - ok
Intentionally triggered alarm and tried to start - engine would not crank - this is actually good - starter disable is exactly what a tripped alarm is supposed to do per the Karr manual. There is no fuel pump connection mentioned.

At this point, don't know if alarm involvement is real or coincidence but for the life of me I don't understand how it could be involved.

I am fairly mechanically proficient - have in the past done drum brake jobs, manual trani fixes & done short-block level engine swaps, but don't have the test equipment for these new electronic beasts - and can't afford a high dollar dealer repair after over a year unemployed. Help!


3 Answers



December, 4, 2009 AT 4:08 AM

Security light on the dash with no key in ignition, should blink one blink every 3 seconds, turn key to on light should go on steady for three seconds then go out, truck is now startable, if security light does not operate this way you have a problem with the key, or key sense in ignition, or the security module. If this is your problem, do you have a second key to try? Do you have a remote starter?



December, 6, 2009 AT 4:53 PM

Thanks Merlin2021 for the reply and my apologies for the delay in getting back to you.

My F150 has no dash light (THEFT) for the alarm as it is an aftermarket install. Checked the red lights on the Karr 2040 units and none of them blink - the valet light does indicate properly (steady red light on the valet button) when that feature is activated.

Also, did try another key - but still get the crank - no start issue. The vehicle does not have a remote starter.

Finally decided to deactivate the aftermarket alarm by pulling both fuses in the wiring leading to it.

Net result - still have the same crank with no start isssue.

Any further diagnostic help would be appreciated.




December, 9, 2009 AT 2:15 PM

Start with the basics, and work your way up, Last tune up was? Wires plugs ALL filters? If all that is ok, check for a stuck EGR, then test fuel pump pressure, If it won't restart, determine what's missing, the engine needs three things to run, Spark at all plugs, gas to all cylinders, and compression in all cylinders, tho an engine may run lacking one in one cylinder, it won't run very well!
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