Help or ideas from any and all appreciated!

I have a 93 Aerostar 4.0L (95,000 miles). Recently it has started running EXTREMELY poorly - can not hardly accelerate at all, the engine just stumbles along, makes no power and hardly revs up at all. I can get it up to highway speed in about 1/2 or 3/4 mile but it runs so badly I can't stand to do it. It does start fine but it idles rough. If you are in neutral or park and step on the gas to rev the engine it stumbles a little and then starts to rev more freely but still it is running rough even held at a steady higher rpm.

The problem is getting steadily worse - first I thought it was missing on one cylinder - maybe a bad plug or something (only owned the van a few months). The problem has continued to get worse over the last two weeks until now it is barely drivable. Here is what I have tried to date:
- Changed all the plugs to new - no difference.
- Someone suggested Throttle Position Sensor - I tested this and thought it was working fine, threw away the money and bought one anyway but no difference.
- The O2 sensor tests out okay and since the problem occurs imediately on starting the van it is not even into the closed loop cycle so even a bad O2 should not be able to affect the running at that point. Also the "check engine" light is not on.
- Checked the intake and the MAF for restrictions but found nothing.
- The vacuum is at 19 - 20 inches so a vacuum leak seems unlikely. The needle holds steady at 19 - 20 so if I remember right this indicates no substantial problem with valve springs or clogged muffler??
- my Ford code reader turns up only a 565 "Canister Purge Circuit failure" and a 538 "insufficient RPM change for Dynamic Response test"

If you know what a carburated car felt like when it was flooding out under acceleration then you know what this feels like. The difference is the carburated cars would eventually clear themselves and then start to make power - my van does not ever clear itself. The plugs I took out all looked pretty normal (medium tan colour) so flooding does not seem like a problem. This made me think perhaps not getting enough fuel for load conditions?

The ideas I have left - clogged catalytic converter (muffler is new), or bad fuel pump or regulator, or bad fuel filter (if it has one) or a bad MAF sensor.

Anyone know how and where to test for fuel pressure? Or how to test for a clogged converter? Or how to test a MAF sensor? Can a "Canister Purge Circuit Failure" cause the van to run so badly? I think it is only there to vent vapors from the gas tank.

Or better yet any one have similar experience or a another great idea to try?

Thanks for reading all the way to here! You can tell I am stumped!

 

Spend the $30 and get a fuel pressure gauge/test setup. Shadetreee MEchanics brand is what I got. Hadda A* 4.0 using gas like crazy. 10mpg. Black cloud and lousy idle. Fuel pressure was 80psi !!!!!!!
spozta be about 30-40. New (expensive) regulator made run fine, doubled the mileage, and passed emissions test w/flying colors.
Your MAF could be dirty- causes lousy idle and bad throttle response. Has a wire that can get covered with junk. CAREFUL!! dont mess up the wire. I hear you can use a 'gentle' carb cleaner-the kind that won't remove coatings and does not mess up O2 or catalytics to clean it.
DUh. didja check the air filter... and loose/clogged PCV?
just a few wandering thoughts.
tom

 

[updated:LAST EDITED ON 08-Jul-02 AT 11:07 PM (EST)]Tom

Thanks for your "wandering thoughts"!

Yeah I looked at the air filter - no problems there.

Yeah I looked at the MAF seems to be clean and not broken.

No I did not think of the PCV - will check tonite.

Will be happy to buy a fuel pressure kit if I can find one. Can you tell me where to attach it to?

Idle is actually the only rpm where the van runs somewhat normally but it is somewhat rough even there. I have no black cloud and the exhaust pipe is just the normal soot - not real black like running too rich would normally show. And the spark plugs looked pretty normal too.

What about clogged injectors - can this actually happen? Would a cylinder not getting fuel not show up on the spark plug?

Would love to simplificate, it's the van that won't cooperate leaving me to explicate - again!

Any more ideas welcomed!

 

The fuel pressure regulator is a black cylindrical object on the passenger side of the engine mounted on the side of the intake manifold/fuel rail assembly. Look just behind the throttle cable connection down a little lower about 1/3 of the way back. It has a vacuum line connected to it and a fuel line connection. It is held on by 2 screws and once they are removed you can pull it out of the fuel rail. It has a schrader (bicycle tire valve stem) connection where you hook up a fuel pressure/delivery volume tester.
If you have no black smoke, and it misses the way you describe, I'd check the fuel filter and pump volume if you haven't done so. A pro mechanic would use the amp draw of the fuel pump to check its condition. Draws more amps as the brushes, etc wear out...
The fuel filter is located on the 'frame' rail. Looks like a real small coffee can connected in-line with the fuel hoses. Has a mounting clamp and 2 'duck-bill' connectors at each end. Be ready for a slight shower. Don't smoke, etc. Pull the duck-bills out, and the fuel line will pull off each end. Replace. Re-clamp.
done.
best guesses for the day
tom

 

You're thinking too hard and missing the obvious - the plug wires are bad.

 

[updated:LAST EDITED ON 10-Jul-02 AT 00:28 AM (EST)]Thanks Tom & Colorado

Picked up plug wires and a fuel filter today but probably no time to try them till Friday nite or Saturday - will let you know how it works out!

Thanks for the input Colorado! It certainly could be plug wires failing but it feels so bad it would have to be more than one now. Seems like a coincidence they are failing one at a time in a short time frame as the problem has grown worse over the last few weeks. On the other hand I was pulling them off and putting them back on when checking/changing spark plugs and they do appear to be the original ones so maybe...?? It does start (easily) and it does idle (but rough) and it does develop reasonable vacuum for our elevation so my thinking in not changing the wires yet was that a bad wire would be bad all the time not just under load conditions. Do you not develop less vacuum with less cylinders firing? Also all the plugs appeared the same colour/carbon/wear - none appeared "fouled" as I would expect with no spark. Or perhaps my thinking is off??

Tom thanks for the info on the regulator and schrader valve locations. Thought I would try the plug wires and the fuel filter first since they appear to be original and should have been changed before now anyway.

If no success there then straight to the shop for the fuel pressure test kit I saw today ($ 54.00) to try that route. How would a person know if it was the pump or the regulator failing?


Thanks again guys!

Any more ideas, suggestions (other than taking it to the scrap metal dealer), opinions, advise, recommendations, propositions, admonitions, warnings, or plain old helpful hints still welcomed!

 

Regulator: Pressure too high (or too low but not normally)
doesn't raise pressure when vacuum line is removed with running engine
doesn't lower pressure with vacuum line connnected -engine running
pressure leaks down after a short while
Pump: pressure too low
leaks down after a short while
volume delivery below specs- tester has tube to allow collecting gasoline into a container...

Leakdowns: there is a check valve built into the pump.. would normally cause hard/slow starting, much as the leakback from the regulator would cause pressure drop, and slow starting

tom

 

Vacuum generated from the engine is the same whether the plug fires or not. You've aptly described a familiar experience; a complex set of symptoms therefore the cause must be something equally exotic. Speaking from experience, one certainly feels rather sheepish when the cause turns out to be something so simple.

 

Tom & Aero

Success!

Turns out it was a spark plug wire as Aero suggested. I should have just changed them in the first place but managed (also as Aero suggested) to convince myself that it had to be something tougher to diagnose.

The passenger side middle plug wire was broken or corroded somewhere. It was obvious as soon as I pulled it off the coil pack as that end was all cover with some green corrosion junk. Of course it was also the 5th wire I changed and since I was testing them as I went along I was still believing it was going to be something else causing the problem.

Thanks for all your help guys!


Gord

 

I read this sordid tale with interest, as the symptoms and trials and tribulations of trying to solve the problem mirrored my recent experiences almost to the letter.

Unfortunately for me, I was paying my friendly mechanic to try these different fixes... anyway after I read this, I printed it off, gave it to my guy... and told him to replace the spark plug wires...

He was doubtful... said the wires "scoped out"... but did it anyway and to his astoundment, and my satisfaction the long running problem has been irradicated!

Thank you so much for helping.

regards,
Steve H.
Calgary

 

 

I just wanted to post my addition to the excellent information in this thread.
I too, was getting overly complicated in my search for a lack of power and missing under load in my '97 4.0.
And, as some of the other posters, I went on a wild goose chase for a difficult solution.
Guess what? It was the plug wires.
After reading this thread I thought "what the heck. Try it."
As one of the other posters stated, I was missing the obvious.
I have been fooled before by bad plug wires, and I should have know better.
After working on this Aerostar to change the plugs and wires, ( it took about 1 and a half hours ) I sort of wished for a van with the dreaded dog house for engine access. HA!

 

Just wanted to add my two cents to the comments here.

I was experiencing similar problems, except that I was getting a check engine light also. (Code 173 & 179) I also noticed that the exhaust smell was stronger that normal. Above codes indicated that the engine was running rich. After checking/replacing IAC valve, O2 sensor, spark plugs, S/P wires, the thing that finally cleared the check engine fault was replacing the fuel pressure regulator. Got it used from a great U-Wrench it place $3.50. Normally $90 new.