High Revs at Highway Speed

[termnalvee]

Hi all!

New to the forum. I have a 92 with 210k on it. recently started revving about 500-600 rpm higher at highway speeds. had the tranny rebuilt with no change. Also, have had a noticeable drop in power lately. Plugs, wires, fuel filter all replaced within 10k. any ideas?

 

[Nate1]

Try cleaning your MAF and checking your TPS. If you do a search for both you should find all the info you need.
MAF is metered airflow (sensor) and TPS is throttle position sensor.

 

[Alec]

Sounds like your torque converter isn't locking up. Those sensors could be causing it, or it could be something else.

 

[termnalvee]

Thanks for the input. I cleaned the MAF recently after the problem arose and there was no change.

I will look into the TPS.

As for the torque converter, it was replaced with the rest of my transmissions guts last week.

Again, thanks for the help!

 

[MrShorty]

They may have replaced the torque converter, but did they either miss something electrical? Torque converter lockup is controlled electronically by the PCM. An overlooked broken wire could cause the symptom you describe, amongst other things that can make the PCM unwilling ro unable to control the lockup clutch and the 3-4 shift for that matter.

 

[termnalvee]

Okay, let me calrify: it appears as though the lockup is working because when I shift from overdrive to drive at speed, the RPM's climb by a few 100. It did that even before the tranny was rebuilt. According to the mechanic, AAmco, the engine speed is at 67% of tranny speed once the lockup engages. Apparently, this is what the manual calls for. Nonetheless, engine speed is much higher than it used to be.

Thanks.

 

[Alec]

The torque converter and overdrive are 2 different things:

Overdrive is 4th year, about a 20% reduction in RPMs from 3rd gear.

The TC is the joint between the tranny and motor, and when lockup occurs RPMs lower by a few hundred.

 

[termnalvee]

Ok. so are you saying that the wiring was bad to begin with, and that the tranny and TC did not need replacement? if that's the case, i just blew 1200 large! if it is wiring/electrical won't it show up on a scan? if not, how does one go about testing for it?

thanks

 

[MrShorty]

Depends on what kind of "scan" they performed. No matter what scanner you use, no matter how expensive the scanner was, a '92 likely will not give you anything more than trouble codes, and the absence of trouble codes related to the transmission functions doesn't necessarily mean there isn't a problem. To properly diagnose the two transmission circuits, you need to use a DVOM to measure voltages across the transmission circuits. Let's see if we can walk you through some basic tests of the electrical controls for the A4LD.
First, get a wiring diagram. The wiring diagrams in the vehicle repair guides at www.autozone.com are adequate for this purpose. However, if you can get a hold of a professional edition manual (try the library maybe) it will have more complete wiring diagrams as well as better descriptions of some of the tests that will be mentioned.
Second. Wiring diagram in hand, find the connector at the transmission. It will have three wires, Red (battery voltage), orange/white (3-4 control circuit), and white/purple (tc lockup control circuit). I think those wire colors are right. If not, that's why you have the wiring diagram, so you know which color the wires should be. KOEO, make sure your voltmeter reads battery voltage between each of these leads and ground. (Leave the connector plugged in, so you'll need to backprobe the connector). Make sure you're measuring voltage. Don't want to accidently measure resistance because the PCM is a part of these circuits and you can damage the PCM by measuring resistance. If it fails this test, then there is a bad connection or short somewhere that needs attention.
Third. Connect + lead of DVOM to red wire and - lead of DVOM to tc control circuit wire so that you are measuring the voltage drop across the solenoid. Perform output state test. See www.dalidesign.com/hbook/eectest.html or your favorite professional edition repair manual for instructions. While in output state mode, each time you press the throttle will cause the PCM to switch the solenoids it controls, so, the voltage drop across the solenoid should change states (0V to 12V and 12V to 0V). Also, note any KOEO and continuous memory codes, since you'll have to pass through them on the way to the output state test.
Take it that far and tell us how you make out.

 

[fordkrazy]

isnt it a vaccum modulated TC and shift? a4ld's are completly mechanical right? no electronics except for monitoring? you might want to replace the vaccum hose from the manifold to the tranny or even the modulator itself....sometimes shops miss stuff like that.

 

[MrShorty]

Partially correct. The 1-2 and 2-3 shifts are vacuum modulated. The earliest A4LD's (pre-'88 or so) also vacuum modulated the 3-4 shift. But our A4LD's have electronically controlled 3-4 shift and tc lockup.