I own a 93 AWD 4.0 Aerostar with approx. 225,000 miles that has historically gotten around 19mpg with my usual mix of in city/hwy driving. That recently declined to around 16. I decided it was time to have a tuneup as it was beginning to run slight rough as well.

The tuneup was done by my usual mechanic using Ford parts - new wires, platinum plugs, pvc, air/fuel filters and an oil change. Post tuneup the mpg have declined to between 12-13 with the same useage and continues to run somewhat rough? I've had it back into the garage and the mechanic says there's nothing wrong with the work they did. I have noticed that the transmission seems to be running up to slightly higher rpms before shifting gears since this work was done. Coincidence? I don't know. Any ideas? Suggestions? Thanks!

 

He displaced a vacuum hose during the plug/wire change or mis-routed two plug wires.

 

I had a hard time rerouting the plug wires on my 3.0 you would think the distributorless ignition box wire on the drivers side back went to the plug in the back and the middle went to the middle plug. But after looking at the old wires I was wrong the drivers front and middle were criss-crossed. These were factory wires and were never replaced so I just installed them the same way they were.

As Aero said check the order of the plug wires in your Haynes manual and trace them from the distributor to the plugs make sure they all go to the right plug.

Since I think the 93's were distributor models look for the round plug wire diagram in the manual.

 

I would think that two switched plug wires would give you more of a problem than "running a little rough".

 

any PCM codes?

 

Well, a vacuum leak could do this, but you would be surprised how little shacking can com from switch plug wires, especiall if they are across from each other. This creates a balanced miss, which creates little shaking.

 

Yes, I agree, displaced a vacuum hose during the plug/wire change or mis-routed two plug wires

or mechanic dropped in the wrong set of spark plugs.

 

or "mechanic" cracked a plug insulator with his "special" Ford Aero plug installation tools. 100 ft lbs of seating torque...oops...or he accidently dropped a new one while inserting, forgot to recheck gap and put in a plug now gapped at ZERO due to flat rate shop on commission.

I'd pull all plugs and check if vaccum lines and plug wires are OK.

 

A mechanic usually has a warranty on all work he has done. I think it's 90 days or maybe 30 days. Take back to mechanic and have him run a dianostic as to why truck is running worse than when you took it in for the repairs.

 

That could be true. Would have a definite lack of power I would assume.

I mis-wired side by side plugs on another vehicle one time. The thing backfired like it just ate a huge Mexican dinner.

 

Actually, on the electronic ignition 3 & 4L Aero engines, one can switch the two wires on any coil pack pair and will run perfectly.
Coil pack has 3 ign. coils, each fires two cylinders at a time-one on compression stroke and opposite on exhaust stroke.

 

welcome!

I agree with everyone else, the mech messed up somewhere.

Also you did not mention if he decarboned the engine. This might be contributing to your issue.

 

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96 4WDR, 100% correct!!! I have seen this happen, and a possibilty. Aerostar is up on a rack. The mechanic is putting the plugs in from underneath. A plug slips out of his hand, bangs on the rack, suspension, or worse yet, falls on the ground. Cracked insulator, or gap is reduced. It is not intentional, but it happens. This happened on a neighbor's car, 7-8 years ago. Same as you, she had a tune-up done at a tune-up speciality shop. This was in a Chevy Lumina. Came home, the car ran, but not like it should. Slightly harder starting. Took the car back a few days later, they "checked" it out. Said everything was okay. It was not. It would start and run, but with "issues". Long story short, 2 weeks later on a Saturday morning, I took a look at it, for her. Pulled a plug. It was one of those "Mighty" plugs, which is a common, generic, aftermarket plug used in tune-up shops. Another thing, I noticed immediately. The insulator and tip of the plug was coated with grease. Not clear dieletric grease, but black grease. This tells me, the mechanic was putting in the spark plugs with greasy fingers. Obviously, you are using the tip of the plug, when threading the plug to the head. I removed 4 more plugs, same thing. Black grease on the tip of the plugs! Told the neighbor what I found, went and bought the correct AC Delco plugs. Checked gap. Took a long Q-tip, sprayed in WD40, to clean the spark plug boot, as I thought it the plug has grease, then the boot connector does to. Installed all 6 AC-Delcos. Plug wires on secure. Started the Lumina, it ran like a million bucks. Peppy. Accelerated normal, and idled warm at 900rpm, in gear. The neighbor lady thanked me several times for a month, saying her car ran like normal once again. However, it's one of those things, if I didn't pull a sparkplug out, I would not have discovered this. Plus, most people (myself included) would think: "The plugs are new, and have just been changed. It MUST be something else?!" I'm not saying this is what is wrong with your van. Only that, if the plugs have been replaced, and you don't like how it's running, I would pull the plugs out again, check them closely along with other good suggestions as stated by others. Good luck. ED PS A plug might be loose in the head, or the boot not properly "clicked" on. Those kinds of things happen. A good shop will correct their problem, and you will be satisfied. Flakes, will try and blow you out the door. If you start hearing a bunch of "oddball" lame excuses, requiring extra work, more parts, or $ for additional diagnosis, hold your ground. They are fleecing you, and they know 90% of people will say "okay, and hand them their Visa or MasterCard, Good luck.