Hello everyone,this is my first post to this site. The tips coming from you guys are great,you can't find this stuff anywhere else!
Our problem is the '91 4.0 AWD Aerostar (130,000 miles) is stalling when starting out from a complete stop. If we use a real light touch on the accelerator to get the van rolling then apply more pressure to speed up,it works okay. But if we step on the pedal normal or hard to pull out in traffic, the engine will shut down.This just started happening the last month or so. About 2 years ago we replaced the FPR because we were getting 5 mpg at the time. Since that was replaced, fuel milage averages 11 city,18 highway,so we figure the FPR is still good. Along the way we have also replaced MAF,oxygen,PCV,fuel filter and air/coolant temp sensors. We don't see any loose vac hoses. Idle Air Control is clean and functioning. Soooo,what's left? Any votes for the Throttle Position Sensor? Thank You for any ideas you may have!!!

 

I would check the fuel pressure regulator again. I had the similiar problem and it turned out to be the FPR.

 

Hello and welcome to FTE, always nice to have another Aerostar fan.

I have the same year/model as yours, with much higher mileage and still average 18-19 mpg combined driving. I would vote to replace the TPS sensor as all the other usual suspects have been addressed. A simple cleaning of the contact surfaces with an electronics cleaner may be enough to restore function. There seems to be a rash of TPS replacements lately on this forum, so perhaps yours is also due for one. Replacement is a simple remove and replace scenario - two screws to remove.

If you have a multimeter, check the resistance pre and post cleaning. A good TPS will show a nice resistance gradient from stop to stop. A poorly functioning one may show dead spots or high resistance spots. It sounds like yours has a dead spot just off idle that is confusing the EEC unit.

To tweak that mileage, you may want to consider plugs and wires replacement if not done within the last 60-80,000 miles. With all the advice on this forum, surely we can get that mileage up a bit

 

Thanks for the comebacks! I just tried a new TPS,went for a drive and it stalled out once in the begining (may not have been up to temp yet),but from then on I was able to take off fast from a dead stop with no hesitation at all. However....when I parked it I revved the engine a few times,and there was the dreaded black smoke. It looks prettty hard to get to the FPR just to see if there is gas in the vac line,so I figure if I am going to go that far I might as well have a new one ready to put in. I hope to get to that job soon and will post the results soon after. Thanks again guys!

 

Well,just installed the new FPR and still have the same symptoms as above. Any other ideas out there?

 

It is still obviously running overly rich. When you replaced the TPS, did you disconnect the battery for 5-10 minutes to reset the EEC? If not, you may still be operating on an old profile. Otherwise, rich mixtures could be from O2 sensor(replaced recently, should be good, perhaps loose connection?), vapor cannister drawing raw fuel, displaced, dirt/grime fouled or loose connection at the crankshaft position sensor or else just plain bad EEC unit running the injectors at too large a pulse width.

 

aerocolorado, I did disconnect the battery when I installed the TPS,and cleaned and checked the plugs at the same time. However I did not disconnect the battery when I swapped the FPR,maybe I should give that a try? It's just frustratrating when you do things and see no change whatsoever. For instance,a neighbor stopped by and actually found a slight vac leak at a rubber plug at the PCV. So,I replaced the PCV (used the plastic cap that comes with it to replace my leaky one) and just about every vac hose in there. No change at all.... This whole problem started out way back when suddenly one day the van would stall out if the enigne temp was only showing 1 bar on the gauge. When it went to 2 bars there was no problem. Then a few months later it wouldn't run right until it hit 3 bars. Now even if it goes to 4 bars (normal temp) the problem is still there. Has tons of power once you get it rolling! Thanks again for your help!

 

Scca,
You seem very knowledgeable about your engine and I hesitate to ask this question for fear of insulting you, but are you certain the previously replaced sensor was the engine coolant sensor and not the engine temperature sensor? The former feeds data to the EEC (2 wire connector) while the later (single wire) merely runs the temp gauge.

From what you described in the last post, the problem is almost certainly temperature related and indicative of a failing coolant sensor. Sounds like the sensor has finally completely failed, providing no input to the EEC, which in turn thinks the engine is still cold and provides a rich mixture. Once the engine is warmed up, the overly rich mixture causes the stumble and stalling when coming off idle.

Of all things discussed so far, this makes the most sense to me. I discounted it from the range of possible causes in the previous post as you had already replaced it, but the latest post made me wonder. I can sympathize with your frustration at this point in the process. Hang in there, you're close to solving the problem. Invariably, it will turn out to be something simple.

 

Thanks for the kind comments. I think I could recite the Haynes manual in my sleep from going over this engine so much! :^) The sensor I replaced is at the top,front of the engine,under the throttle body,slightly off center towards the drivers side. It has a two wire plug. Is that the right one? There is another one in the same area that is more towards the passenger side,also with two wires.
A few days ago a mechanic neighbor brought home his analyzer
(a nice gesture,that's an expensive unit!) and we did not get any codes,which would be correct since I have not had any "check engine"lights. Also,while the engine was running,we could watch everything working as the temp changed,etc. From his view it looked like all the sensors were doing thier jobs,which makes it more frustrating. He is leaning toward a vac leak and will be taking it to his shop tomorrow,where he has a couple of other guys who want to look at it. I will post the results as soon as I hear something. Stat tuned!

 

Aerocolorado is the winner!!! I picked up a new coolent temperature sensor today,checked the resisitance on my workbench hoping to compare it to the old one in the vehicle. Turns out the old one was completely open. This part was only two years old,so I overlooked it in my initial troubleshooting. Oh well, this is one I won't forget next time. Thanks to everyone who contributed to this post,and I hope this helps someone else out there. P.S. Part was only $18.99.