Hey guys, I really need some help here.

While accelerating it will sporadically fall on its face. When it first started it would back fire through the throttle body, hasn't done that since the beginning. Doesn't seem to do any of this in the cooler months of the year, but as soon as it gets over 90 deg she'll start acting up again.

So in the beginning I had the injectors replaced along with the throttle body gaskets and 02 sesor. Ran fine for 2 days.....back to the shop.
Next trip...... the coil got replaced. I had already done the cap, rotor, plugs and wires before they got it the first time. Ran good for 2 weeks........
Next.....me and my dad jumped on it. Couldn't find the issue but we replaced the pick up coil and cooling temp sensor.Ran fine all the way through winter with only 1 or 2 hiccups,but both times it cleared up quickly.
Currently..... Just replaced every sensor on the throttle body, installed new fuel filter. I checked fuel pressure and its a little low, 11 psi. Did some test from the haynes manual. With the gauge connected, when I pinch the fuel return line closed, the psi shoots up to 30 and it seems to run great. The book claims that the fuel pump should be good but the regulator is bad. It's brand new. So I reinstalled my old one with the same result.

Could it be a fuel volume problem? How would I check that?

I welcome all feedback.
I've never been this stumped...........

 

Not sure about 1990 but for later models these vans have two temperature sensors. The 1-wire one is for the dash gauge, then there's a 2-wire one for the engine computer. The computer uses the sensor to control the air/fuel mixture, so if the sensor is bad then the mixture could be off.

 

yes the '90 has 2. I've just changed the 2 wire last week.

 

Fuel pressure should be 14.5 psi. Also look at the EGR valve, They like to stick. Not familiar with the vans but my 90 pick up had an external fuel filter.

 

Thanks @Moparite My egr has been disconnected since i was battling this problem last year. Or at least the vacuum line has been. I think I am ging to put a fuel pump on it and see what happens. " throw MORE parts at it"

 

looking for updates

 

@nibroc no updates yet.Works been crazy,but I am putting a fuel pump on it currently. Hopefully this will take care of it. I'll keep you posted.

 

Are you having the same issues?

 

no -- both my vans run well-- I just like to try to keep up with this old stuff

 

Update.......... New fuel pump and the pressure is back to normal. Still no change in how it's bogging down when I press on the accelerator. Still when I close off the fuel return line it seems to run fine. I noticed that I have no vacuum on the fuel pressure regulator. The vacuum line comes off the throttle body and goes into the fuel pressure regulator. I can't find my vac tester but I should be able to feel a vacuum there like everywhere else, correct? I connected another vacuum line to the regulator but it kills the motor immediately, but that perticular line has a lot of vacuum on it. Too much?

Any help would really be appreciated!
Thanks