So My 91 Aerostar 4.0 liter
Is having problems starting. At the beginning it didn't want to turn on right after I turned it off. I began to think that the Fuel pump was going bad so I went out and bought a new one. I installed it and the first couple times it turned on but then it went back to the same problem. After reading about the problem I saw that the fuel pump relay could of been the problem so i went out and got my self another one. The first time i started the car again with the new relay the truck turned on right away but after turning it on and off a couple of times I started to get the same problem again(Cranked but didn't turn on).Then i went out again and exchanged the fuel pump thinking the one they sold me was bad, and once again turned one quickly the first time and after that It didn't turn one again.
You guys have any idea what it could be? Thank you in advance.

 

Did you check the fuel pressure before/after you installed the new fuel pump? How about the fuel filter? Your van is old enough that it probably could use a new one.

Your problem sounds almost like some electronic component is heating up and failing. If you leave the van overnight, is it easier to start in the morning? The first things I would suspect would be the EDIS module (screwed to the inside passenger fender), or the crank position sensor. Check to see if you're getting spark at the plugs the next time the problem shows up.

Also, run an EEC self-test to see if any codes show up.

 

Sorry I forgot to mention I indeed changed the Fuel Filter.
Another thing I forgot to mention that with starter fluid the truck starts.

I ran test with and Obd Scanner and everything comes out good.
And we are getting spark in the spark plugs.

 

How is the fuel pressure?

At idle it should read 30-40 psi, and under load it should read greater than 40 psi. This is at the schrader port on the fuel rail.

 

Check the inertia switch or the fuel pump cutoff switch. On occasion, these things are know to have intermittent problems.

 

Have you fix the problem? Check the Engine coolant temperature sensor. One of the symptoms on a bad ECT is that it starts right up the first time (like in the mornings) but if you turn the truck off and try to start it back on, it will give you a hard time. My 92 Aero is doing this and ive found this information online. I still haven't got the chance to try replacing this sensor though. I hope it helps.

 

I can see two major problems that could be contributing or causing your issues with hard starting. If you have a head gasket issue, you could have coolant seeming ito the cylinders when the van is off, and fouling the plugs enough that it is hard to start. Alternately, you could have an injector that is leaking down. This causes a no fuel pressure at startup issue that could make the van very hard to start. Fought an issue much like this on my mom's 1992 3.0L for over a year and a half, never was able to condemn the specific culprit. We retired the van, it had too many other issues as well.