Trans can't seem to choose a gear to be in during city driving.

9

93LINCMK8

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My Mark VIII has 245,000 miles. I just had the tranny rebuilt in Sept. 2005. It doesn't seem to be slipping but it can't seem to find a gear while driving in the city. It always drops down to what seem like overdrive, even when the overdrive is turned off. Also, there is a violent clunk or thud when kicking down to passing gear at or above 50 MPH. Maybe restricted cooler lines or TPS or shift adjustment is off? Maybe throttle body not working properly?
 
Try manually shifting it.........it sounds like the TPS took a crap to me. If you can manually shift it, and it shifts fine up to drive(and o/d) than its not mechanical. TPS isn't adjustable.....you should really scan the codes to see if you have any.
 
A bad TPS will definitely cause incorrect shift characteristics. You may also want to investigate the alignment of the MLPS.
 
What about a fluid pressure test to see if the lines or cooler is constricted. Could low pressure cause it to have to be at a higher RPM to produce enough pressure for the tranny to engage?
 
Naw...too early in the Diagnosing process for line pressure measurements....plus you'd have a ton more issues than just irratic shifting.

MLPS is located just behind the shifter linkage on the side of the transmission....see where the cable is on my trans, the black thing above that.

PIC073.jpg


That is on the drivers side of the transmission....there will be "notches/lines" on both the MLPS outide electrical piece AND the little "hub" that slides over the shift linkage. In Neutral(I think) the lines should be parallel with each other.

Seriously though...you're honestly wasting a ton of time "guessing" whats wrong if you haven't attempted to "pull codes". Go down to the local parts store and buy a OBD1 Scan Tool. $29!
 
Sweet, once you get the code #'s, post them on here and we'll get your car back to normal!
 
Here's something many ask about. Lining up the marks on the MLPS while the shifter is in neutral:

Image000.jpg


You are to loosen the 2 mounting bolts and align the marks with the tranny and shifter in neutral.
 
OK, I just got the OBD1 code scanner. I'm sure I don't understand how to read this thing. I did the self test part 2, I guess, and here is what I got out of it. 3 beeps, pause, 3 beeps, longer pause, 1 beep, pause, 3 beeps, longer pause, 3 beeps. That's it. I did it twice to be sure that's what I read it as. I don't have a clue how to interpret that. Does the 93 Mark use 3 digit codes? Well, test part 2 is as far as I got. What's next?
 
http://www.autorepairmanuals.biz/site/573683/product/CP9015

Is this the scanner you have? This is the one I use on my 95 and it was kinda confusing the first time I used it.

Based on what you described you performed the KOEO(Key On Engine Off, step2) test which won't give you running codes. You got a code 33(3 beeps, pause, 3 beeps, longer pause) than you had the "seperator" beep(1 beep/flash) another longer pause, and than it sounds like you had a history code of 33(3 beeps, pause 3 beeps).

Code 33 is the EGR pressure sensor....not going to cause trans issues.

You need to perform step 4, the Key On Engine Running(KOER) to figure out if the TPS is faulty and other sensors that only test while the engine is running.

Be sure to follow the instructions and watching for the "beep" when you're supposed to "snap" the throttle, this is crutial for you because you could have TPS issues.
 
HAha...not that easy, they want us to live like cave men! It was super hard for me to see/hear my light/beep when it was time to snap the throttle, so make sure you don't try the test in the sun.
 
OK. I don't know about the EGR, I just had it replaced when I had the head gaskets done. I haven't had a check engine light for a long time now, but who knows, anyway, here are the results of the KOER test step 4.

4 blinks for 8 cyl. I turned the steering wheel one half turn and then back, I stepped on the brake and then released and I toggled the OD switch on and off. I did not see the 1 dynamic response blink but I did the WOT thing and this is what it did...

4 blinks, 1 blink, 2 blinks, 4blinks, 1 blink, 1 blink. It did that twice. What's it translate to? I hope I did it correctly!!

My name is Tom by the way. I don't want to be all anonymous. Oh, is it normal for the check engine light to blink when the scanner does?
 
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Looks like you got a PO411 and a PO412...BOTH are "cannot control RPM during engine run self test" 411 being low rpm check and 412 being high rpm check.

PO411....

Possible causes:

Improper idle air flow set.
Vacuum leaks.
Throttle linkage binding.
Throttle plates open.
Improper ignition timing.
Idle Air Control (IAC) solenoid contamination.
IAC circuit short to ground.
Damaged IAC solenoid.

If your car is idling normally....you've got a BAD Idle Control Valve.

PO412....

Possible causes:
Open or shorted circuit.
Throttle linkage binding.
Improper idle airflow set.
Idle Air Control (IAC) solenoid contamination.
Items external to Idle Air Control system that could affect engine rpm.
Damaged IAC solenoid.
Damaged Powertrain Control Module (PCM) .


It sounds like you've got a bad IAC valve for one.....

The EGR code I specified isn't a bad EGR valve, its the EGR pressure sensor thats located on the back of the drivers cylinder head.
DPFE.gif


There are two hoses that should be attached to it...take a small mirror and see if everything is hooked up properly. If it all looks ok, go purchace a new one.

If you're going to attempt to tackle the IAC valve...I HIGHLY recommend you replace the TPS sensor at the same time, I'm thinking this might also be bad giving you the transmission symptoms.

So....you need.

Idle Air Control Valve and gasket
Throttle position Sensor
EGR Pressure sensor aka Differential Pressure Feedback EGR (DPFE)
And if you can get the right one, replace the throttle body gasket.


Now....as far as the check engine light being OFF....on OBDI cars, the light won't come on unless its a "hard" failure, but it will store any "failures" into its memory as a "history code". If the same part fails 3 times, than your light will come on. Thats why you haven't seen the light....but that doesn't mean you don't have failure codes.
 
Thanks alot for your help J. That's alot info to check out for this wanna be a mechanic. At least I know what to go on now. You've got to take the heads and plenim off to get to the IAC and TPS? That will probably require a proffessional based on my level of experience. I'll just be glad when it is running the way it is suppose to. It's been doing that since I've owned it. Could that cause the xmsn to have a burnt smell. I hope it's not slipping again. Anyways, thanks again all who gave input!
Tom
 
Tom, as far as the IAC/TPS repair goes....what a pain in the butt! You do NOT have to remove the heads, or even the intake manifold, but you do however have to...

remove the intake tube,

than remove the throttle cable linkage,

remove the throttle body bolts and pull the throttle body off, while removing the TB this will give you better access to unplug the TPS,

with the TB off you can easily replace the TPS(its on the side of the TB),

now with the TB out of the way, you can kinda get better access to the IAC, the IAC valve is a PITA to get to, but its doable....just be patient with it.

While you're back there farting around, replace that EGR pressure sensor too!

If the trans fluid smells burnt, you NEED to change it ASAP! Burnt smell, means slipping clutches, or super old overheated fluid.
 
I notice you guys talking about Mercron V as one of the mods you do. What is the difference between Mercron III and Mercron V and how much better is it? Will it really make a difference?
 
Mercon V is recommended by Ford for use in our transmissions. I believe it is synthetic(or a synthetic blend) and has special friction additives. It is a much better fluid for the lock-up torque converter clutch as well as the frictions in the transmission.
 
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