i just inherited my farther in laws 93 aerostar .it runs great motor seems nice and strong.. has a few issues oil pan gasket need to be replaced and the a/c compressor is out. My diy skills are pretty advance and those repairs i can handle. But this one in need some help diagnosing...it's a 4L engine auto trans the gauges are electric and work but the speedo does not work until you hit about sixty and then it says your running about 5miles per hour...the odometer does not register miles it stays the same....at highway speed the overdrive will cycle on and off rapidly...but drives fine if you turn it off....also the cruise control does not work...I was wondering if this could all be related to a bad cable or speed sensor...If any one could give me some advise i would be grateful

 

For the speedo/cruise issue, the first thing to check and/or replace is the Vehicle Speed Sensor, located at the top of the rear differential. One bolt and some wiggling. You'll want to spray some cleaner all around it before you remove it, you don't want any debris falling inside. An o-ring seals it to the case.

(click on any image for larger)


Next, if that doesn't change the symptom, you might pull the diff cover off and check the tone ring ("exciter") to see if it's damaged. I've never heard of one being damaged, but if other fingers have been in there, you wouldn't know. Plus, you'll probably want to change the rear axle lube anyway, and you've got to pull the cover to do that.



Beyond that, you're into PSOM territory. Search this forum on "PSOM".

 

Al, this is a great diagnosis if I ever did see one. Couldn't ask for more and I don't even drink!

 

I didn't give any resistance spec for the sensor, so it's not like I gave him a great diag chart. I just happened to have some pics of a spare diff that I took a few years ago, a quick bit of arrows-n-text, and some links.

Oh, for the OP: your OD issue is probably related to this as well. The OD operation is toggled by the electronics, and if they think you're going too slow for OD, it drops out. So, if you can figure out the speedo issue, it's likely that the CC and OD problems will fix themselves.

 

well asavage your diagnosis was right on the money... changed the sensor today .... the first thing i noticed when i pulled out of the drive way was the speedo and the odometer were working.....pulled out onto the highway and the over drive engaged, locked in and stayed there no more cycleing on and off ...... set the cruise control and drove about 20 miles down the road and it preformed flawlessly....it's amazeing what a 12 dollar part and a little elbow grease can do.. got a buddy that owns a tranny shop he was trying to sell me a new tranny.... hahahaha guess the jokes on him now.... thanks for the great advice i was hoping to get it fixed and keep this van.....now it has a new home

 

The VSS seems to not have been dead reliable in the Aerostar years. Glad it was an easy fix for you.


Change the coolant!

That, and changing the ATF in the trans will save you the most money in the long run.

 

Yeah, I've had a VSS go out before. Its not a high failure item, but its not uncommon either. Glad you got it fixed and that it wasn't a major issue.

I second that, get the trans fluid changed. If you keep on top of it, you don't need to do a dynamic exchange. Just drop the pan and drain what comes out, install a new filter, and call it good. If you fail to change the fluid, the trans will fail prematurely.

And yes on the coolant. Make sure not to use any tap water when you change the coolant, I've seen many a vehicle work fine on old coolant that was as much as ten years old, then fail in less than a year due to cooling issues caused by corrosion due to minerals in tap water. Use either RO or distiller water, its cheap enough, or you can buy premixed coolant. Just don't put tap water whatever you do.

For the record, unless you have a lot of experience with repairing AC systems and have all the tools and equipment, leave AC service to a pro. I have seen too many people waste a lot of money ruining AC systems because they didn't know what they were doing. You can make it worse unless you know how to service them, and the end result is a system that is even more expensive to repair than what you started with.

 

thanks again guys and as far as the atf and coolant the first thing i did when i brought it home was change the oil, atf fluid and coolant....

And for the record khan i am a certified hvac commercial technician...so the pro will handle it

 

Perfect, just making sure. As you are an HVAC pro, I'm sure you know exactly what I'm talking about i.e. fixing a DIYers screw up.

 

Yes sir... i have seen many of my friends and family destroy their ac systems over the years....usually be adding to much refrigerant or trying some kind of cure in a bottle....my nephew actually crack the housing of his compressor by overloading his system ...

On another note was just wondering if anyone had any tips on accessing the plugs and wires. I am thinking it would not hurt to do a good tune up and would like to change them out....Have not done a lot of work on vans
so was just curious if there are any tricks of the trade to make this easier.

Thanks again for everyone's help

 

There are many stories on this forum of people's struggles with changing the plugs and wires. There really isn't an easy way. They will all involve accessing some plugs through the wheel wells, and others from underneath. One plug will require the use of a box end wrench on the hex head of a spark plug wrench. If these are the original plugs, the hardest part may be to pull off the plug boots without destroying them. However, since you're replacing the wires anyway, you may not care about that. Replacing the wires may require removal of some of the stuff on top of the engine to gain access.

A couple of years ago I did a full overhaul of my AC system, including a new condenser core, accumulator, flushing all the lines, new seals. Then after assembling everything, evacuating, and filling up with an R-12 replacement, got no cold. It turned out the compressor had actually wore out, was no longer compressing, and had a shaft leak that allowed all the refrigerant to escape. So I had to get a new compressor, and try again. The new compressor worked, and has been working great for almost 3 years. The only problem I have now are slow leaks in all those little Schrader valves on the new accumulator. I've tried tightening the cores, but they still leak. I keep the aluminum caps with O-rings on them, which seems to slow down the leakage. I haven't had to re-charge the refrigerant yet, so it's not too bad.

 

What he said

The driver's side plug wires were no fun at all. They seem to be threaded through the intake manifold -- no joke.

I used some mechanic's wire (baling wire), connected a 6' length to one end of a spark plug wire, and pulled the old wire out, fishing the baling wire in its place. Then connected the baling wire to the new plug wire, wrapped with some electrical tape to make the junction smooth, and fished it back through. One at a time, I got there.

The doghouse has to be removed to connect the plug wires to the coil pack (unless you remove the alternator). To remove the doghouse, the ABS module has to be unscrewed I think, and on mine anyway, I had to remove the cupholder from the floor.

The two rearmost plugs are toughest. Jack it up, use extensions and one wobbly, via the wheel well and above the tire. Worked for me.

The right rear (on the 4.0) is best done, as he said, using a combo wrench on the flats of a plug socket.

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I've cut up an old 12k BTU window AC and am going to make a poor-mans mini-split out of it. It's an R22 rig. I picked up a Mastercool AC evac pump last week, have two sets of gauges, and I'm going to put one of those snake-oil blends back in (R22a from http://autorefrigerants.com/22a.htm , Enviro-Safe). I know the original system capacity and the conversion ratio for the new working fluid; the only real variable is the length of my extension lines. My AC training & certification was 30 years ago, and I almost never used it in subsequent careers, so I feel like a novice. Fortunately, there's a lot more readily-available info than 30 years ago.