What if I have a dual battery system? Do I unhook both batteries?

 

Not sure how you hooked them up, normally they are diode isolated so unlink them if possible so the ECU can relearn everything from scratch.

 

So this year model came with dual batteries as this use to be an old handicap van. But for an update i disconnected both batteries for about 4 hours yesterday and after i reconnected them she had the same symptoms. I would drive, she would stall, i would coast for 5-8 seconds then she comes back alive and drives fine again. I am slowly coming to a loss on what's going on. Could i have a bad ECU?

 

Something we should have done prior to replacing the MAP and that is checking the 3-pin wiring.
Do you have a DMM (digital multimeter)? How about the service manual, or wiring diagram on the ECU and MAP? If you have a bad wiring, your MAP sensor can't communicate with the ECU properly.
Basically any MAP/MAF sensor consists of 3 or 4 terminals. Yours should be 3 and one is signal input to the ECU other is ground circuit and the last one is 12v power supply.
On all 3 pins of MAP you will need to disconnect the MAP and the ECU harness (disconnect battery ground first) and check continuity between the harness side of the ECU with the 3 pins on the MAP side, then check resistance and make sure the ohm is very low, like less than 2ohm. If the wiring is good plug the ECU harness back in. You check the voltage with your DMM on 2 of the 3 pins. The pin for 12v power supply you should get very close to battery voltage. The pin for signal, with ignition in ON position, you should get less than 1V, start the engine and idling, above 1V, if you rev to 3000RPM, there should be linear voltage rise to like 3 or 4V. Last pin on the MAP is the ground, you check resistance+continuity on that pin with body ground. These steps should tell if the wiring and the ECU, as well as your MAP sensor are good.

 

I do have a digital multimeter so i will test the terminals.

So i bought this van right before Thanksgiving and it drove totally fine with a little hiccup at 65-75. So the owner decided to take it in for a complete tune up with new plugs wires, dizzy cap, rotor, etc. He then replaced the O2 senor as well. Don't know if he did something else to it or if any of that would cause this issue or not.

And since then the amount of parts i have replaced tracking this issue down is insane. At this pace I'll have a new car in a month.

Once i got it i didn't do anything to it but it slowly started to stall while driving and I have been chasing it ever since. very frustrating. Thanks for the help.

 

Note the MAP sensor only sits in between the airbox and the ECU. Assuming your air filter is clean, there is throttle body in between the airbox and intake manifold.
I saw your earlier message in this thread that you already replaced the TPS, so I assume your throttle body is functioning properly as well. You can do a quick check on your throttle body and your 91 e350 should be dbc (drive by cable), so simply remove the doghouse, get a flat head and remove the intake hose clamp, pull the hose out, watch and see if your throttle body opening and closing smoothly while stepping on the gas pedal (not pressing the cable by hand by your throttle body), make sure your throttle body is not stuck open or closed. I personally clean the throttle body every 2 years on all my cars, for your case you should ONLY IF it doesn't open/close smoothly, don't waste time on it if it's not necessary to resolve the stalling problem. But since throttle body sits before intake manifold it can also be something to look into.

 

Let us know how you make out with this,thanks.

If you still have the problem we could suggest some checks you can do before spending any more $$$.

Pretty sure at this point we don't know if the problem is fuel or ign related.

 

Just got alldata installed and I found the MAP wiring for you. Pin 46, 45 and 26. Unplug your ECU harness (disconnect battery first) and test continuity and resistance.

Let me know if you also need another diagram.

 

Good afternoon,

So i haven't had much time to work on her over the last week but i did decide to check the timing and she WAS WAY off. So she is now at TDC. Question to you would be since i fixed that timing should I unplug the battery for the computer to reset? She idles great but when i took her out to drive i had the same issue but the stall didn't last as long as it had in the past. Should i reset her?

 

So i have been doing some additional work to her. went back to the basics and started looking over things again. One thing i found is that the previous mechanic installed the plug wires in the the wrong firing order. I have since corrected that as of yesterday and reset the time after i was done. 10 degrees from TDC and then disconnected the batteries so the computer would reset. Now that the timing is correct i took her out for a drive and she still stalled but minimally compared to times before. This time when she stalled while i was driving there was a stronger smell of gas. I am possibly now leaning to my catalytic converter going out? The owner did replace the O2 sensor before I took over. Thoughts? or because i have the timing and firing order finally correct it will just take some time to work out those kinks?