Hello,
I have a 1990 F150 with 300-6 & E4OD. I've been trying to figure it out for over 2 years now. Here's a summary (it's long):
1) Often stalls when coming to a stop or during something like a K turn (on & off the throttle) or jockeying a trailer. IAC valve does work. ECM does bump up cold idle speed & returns to normal idle after warm up so I know the ECM does have control of the IAC.
2) Hard starting when less than operating temperature. Long cranking times makes no difference. Best way to start it is 3, 4, or 5 normal length cranks. Cycling the fuel pump several times before cranking makes no difference. Fuel rail holds pressure over night. A shot of starting fluid & it starts up first try. Starts fine when up to operating temperature. Fuel pressure 48 psi @ 20”, 52 psi @ 10”, 54 psi @ 0”. After putting a couple thousand miles on the truck, this problem went away for no apparent reason & the truck would start up like new. Five hundred miles later, the problem returned, again for no apparent reason.
Check engine light is OFF. No codes. Passes KOEO and KOER test. I don't recall the exact procedure but there is a procedure for testing if the ECM has control of the timing. I did that test and it passed. Engine is mechanically sound. Acceptable oil pressure. Acceptable compression (1) 160 (2) 150 (3) 160 (4) 140 (5) 150 (6) 155 Timing was set per the manual. No vacuum leaks. Steady, good manifold vacuum reading. For an old school straight six the engine pulls pretty good especially considering the 3.08 axle. I only have a simple code reader. Nothing with live active readings.
When I got the truck, the check engine light was ON with codes for the TPS and the EGR position sensor. Verified they were bad & replaced them. No more check engine light and the truck then passed the KOEO and KOER test. The TPS has a linear voltage output to wide open throttle. The 5 V. output from the computer measures 5.00 at the TPS plug. The ignition module was suspect so I replaced it; made no difference.
Temporarily blocked off the EGR valve: made no difference.
Tried several different good used parts just because I had them and couldn't figure out the problem: coil, ignition coil radio capacitor noise filter, IAT sensor and MAP sensor; made no difference.
All grounds clean and present.
Correct ECM: F0TF-KA Nothing obviously burned up inside. No leaking capacitors.
Transmission works great. Obviously has been rebuilt at some point because the shifts are slightly firm as they should be in a truck. Not a mushy slush box like Ford built them.
Smog pump and associated parts present, original, and working.
Also inspected the vast majority of the engine harness and associated plugs. No defects found.
Local repair shop replaced the coolant temperature sensor; made no difference and I already knew there was nothing wrong with the original sensor as I had tested it at several different temperatures & the ohm readings were correct.
New IAC valve. I couldn't verify that the one on the engine was correct and the new one was a little different.
New distributor pickup (I was really frustrated & desperate at this point). Distributor shaft and bushing are like new . New cap, rotor, spark plugs, plug wires, fuel filter, air filter, PCV valve. I have an OTC 7448A Fuel Injector Cleaner Canister. Injectors were cleaned twice, once with OTC injector cleaner and once with SeaForm; made no difference. Under hood condition is (mostly) stock and unmolested. Any new parts were good name brand parts, not off-the-wall Amazon stuff.
I really wish I could get this truck running correct. I like it & I need it.
Dave
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