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Hi guys, I bought my first Aerostar in October 2025 and have been a reader of this forum ever since. The van is a 1993 with a 4.0L. I've been able to find many answers to my questions from searching through older threads, but this time I'm a little stumped. I've read other fuel and fuel pump related threads, but can't seem to find a similar problem to what I'm experiencing.
Every now and then my fuel pump won't prime the engine with fuel when I turn the key forward to accessory. So it'll just crank and crank and no start. I checked the Inertia switch, it was fine. I replaced the fuel pump relay, it didn't help. So I figured I'd replace the fuel pump.
I read reviews on pumps, everyone seems to say Motorcraft ones are the best. However I can't seem to get one. I went with a Carter. I installed the new pump and for about a week the van worked excellent. Primed and started every time.
Now, again I'm having the same non priming issues to start the engine. If I cycle the key back and forth, sometimes I get lucky and can hear the pump starting to run. Sometimes I just give up, take my wife's van and try again when I get home and it'll start right away. Very hit or miss it seems like.
During my fuel pump review research, I read every fuel pump other than the Motorcraft's is junk. But I didn't really have a choice. I've driven the van roughly 1000km's since changing the pump. Could it have really failed in that amount of time? Or is there something else I should be looking for?
Are you saying that when you turn the key to the "ON" position, you don't hear the pump running for a couple of seconds? Do you hear the relay clicking on and off for that time?
Yes that's correct. I also noticed, when you turn the key forward and all the lights on the dash light up. If the "check engine" light doesn't come on, then the fuel pump is not working.
Sometimes, after cycling the key a few times (or a lot of times) once I notice the "check engine" light come on, the van will start.
I thought I needed another set of hands to touch the relay while I crank the engine over, but your saying if I leave the key in the "ON" position, with the fuel pump not pumping I should be able to feel it click still?
Either way, I have replaced the relay and the problem was still present immediately after.
I did put a new fuel filter on the van at the same time the fuel pump was replaced.
I should probably include the fact that, once the pump does kick in and the van gets going it will keep running. Not once has it died on the road, while idling, anything. It’s just the initial starting which it sometimes struggles with.
I can usually hear my fuel pump relay click on and off. But it would be more definite if you can put your fingers on it to feel it as you turn the key on.
Have you tried to run a self-test of the EEC? That should still be the old type (not OBD-II). With the key off, ground the STI pin (48), turn the key on, and watch for blinking codes on the CEL. I don't have full instructions or code list with me, but I'm sure they're readily available on the net.
The other thing you can do if you're careful is use a volt meter to try to tap into the wire from the EEC that activates the relay. It's light blue with orange stripe. Most devices have +12 on one side and activated by grounding the other side. So if the relay is not activated, that blue/or wire should see +12v when the key is on. When you JUST turn on the key, it should read 0 for a couple of seconds as that pin is grounded, then go to +12. When the engine is running, that pin should read 0.
As for the inconsistent readings you're seeing with the CEL that seems to coincide with the relay not working, that leads me to suspect the EEC itself.
Last edited by xlt4wd90; Feb 20, 2026 at 10:53 PM.
Thanks for the detailed response.
When you say "Ground the STI pin" I'm not quite following you there. I would need to probe the wire in order to do that without unplugging the computer? Or are you referring to grounding the EEC Test Plug to get the codes?
I did check codes, I got a 16 and 14. Which google tells me is; 14 - Profile Ignition Pickup (PIP), 16 - IDM signal not received. Sounds like I'm onto something here.
I removed the EEC to get a part number just incase. I took the cover off, I didn't see anything to my knowledge that looked bad. No leaking capacitors or broken tabs, or other things in there?
Put it back together and reinstalled.
Also, with a helpers hand on the relay's and me turning the key the relay's could be heard, but not felt. I'm not sure if that's normal or not.
I'm starting to believe I never had a fuel pump problem in the first place, most likely electrical like @xlt4wd90 stated above.
I was reading on another Ford forum, 80's Bronco I believe? About disconnecting the battery for a certain period of time and that will remove the long term codes stored in the ECU.
My question to anymore reading, could this be why my van ran without any starting issues for a week or so after I had installed the new fuel pump (battery disconnected for a few hours)?
Also, this past weekend I had the battery disconnected for an hour or two while messing around with the ECU. Since then I've had no troubles with starting.
Does this make sense as to why I'm not seeing the symptoms I was experiencing before?
