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50 mph at 3000 rmp related to Code 71

Old 08-22-2018, 04:20 PM
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50 mph at 3000 rmp related to Code 71

Appreciate the help folks have given me so far- trying to nail down one (final hopefully issue). I have learned a ton reading the forums- but can't find an answer to this question.

I just replaced the HGs and got the timing and idle set about where it should be 12 degrees BTDC and 800 rpm in P/N.

I get Code 71 after driving about 20 minutes. I have checked all of my vacuum lines and am relatively sure they are connected correctly- although if anyone has a link with good pics I would gladly review it! I am considering using a 10 ohm pin across the temp sensor and calling it good if the Code isn't related to the drive speed...

I can only drive about 50 mph with the 4.56 auto transmission on stock tires 31/10.5/15. It seems to shift up and down fine- but at 40 mph I am in 4th and running 2000 rpms, but almost 3000 at 50 or so. This seems really slow to me even for a 3.slow. If this is normal, then that is fine. I am going to S. America where top speed is probably 45 anyway- but I am worried it means there is something going on that I don't understand. I eliminated the cross over pipe and Cat from the exhaust system, but have not replaced the O2 sensor yet.

The one other issue I notice is that when I left off the gas pedal, the idle very slowly creeps back down and decreases with my speed. Once I stop it sits at 800 rpm pretty comfortably. I am not getting a TPS code and wondered if maybe this was just a sticky cable somewhere?

Am I missing something major or something I need to hunt down tomorrow and fix?
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Old 08-22-2018, 07:34 PM
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Originally Posted by rbNW View Post
Appreciate the help folks have given me so far- trying to nail down one (final hopefully issue). I have learned a ton reading the forums- but can't find an answer to this question.

I just replaced the HGs and got the timing and idle set about where it should be 12 degrees BTDC and 800 rpm in P/N.

I get Code 71 after driving about 20 minutes. I have checked all of my vacuum lines and am relatively sure they are connected correctly- although if anyone has a link with good pics I would gladly review it! I am considering using a 10 ohm pin across the temp sensor and calling it good if the Code isn't related to the drive speed...

I can only drive about 50 mph with the 4.56 auto transmission on stock tires 31/10.5/15. It seems to shift up and down fine- but at 40 mph I am in 4th and running 2000 rpms, but almost 3000 at 50 or so. This seems really slow to me even for a 3.slow. If this is normal, then that is fine. I am going to S. America where top speed is probably 45 anyway- but I am worried it means there is something going on that I don't understand. I eliminated the cross over pipe and Cat from the exhaust system, but have not replaced the O2 sensor yet.

The one other issue I notice is that when I left off the gas pedal, the idle very slowly creeps back down and decreases with my speed. Once I stop it sits at 800 rpm pretty comfortably. I am not getting a TPS code and wondered if maybe this was just a sticky cable somewhere?

Am I missing something major or something I need to hunt down tomorrow and fix?
Pop the hood, spin the throttle plate open let it go, it should SNAP shut if it doesn't disconnect the cable and try again. If there is an issue you now know where to start cable or throttle body.

However incase this is your first auto, this is the normal behavior of the coast brake in an automatic trans, there is no neutral for coasting.

..
No fourth gear in the a340, you mean overdrive. In OD the shaft spins faster than the engine, big load like the tallest gear on a bicycle.

..
With the engine at idle apply vacuum directly to the EGR valves vac port, if the engine doesn't struggle or die the valve needs serviced. (Can usually hear the EGR valve slam shut if you apply and remove vacuum with the engine off, but it's easier to just do it running because it not only verifies the valve opens but that there is flow). Once you've established there is flow you can blame the EGR temp sensor, it's dead or maybe just gunked over and not hitting temp where the ECU expected.

​​​
..
Ok basics covered.. I can babble and ramble..

Rpm is rpm regardless of the engine type/rating. rpm X at the engine gets multiplied by the final drive ratio Y and transferred to the pavement as speed Z. X * Y = Z, there are online calculators for this specific application (grimjeeper's gear calc for example).

There is some variation depending if the torque converter is locked or not. This is possibly what you meant to convey. The engine gets loaded down and the TC unlocks, does its job and multiplies input torque which brings the RPM up by decreasing engine load. (Yeah I'm not Wikipedia, if you want a clearer science answer you have search terms now).

So with my a340f running a vf2a and 265/75r15 in OD.
TC lockup on 2000rpm is 59, 3000 is 89.
No lock up speed is slightly lower at those fixed engine rpm.

What you would notice driving it when the TC unlocks is the speed stays the same (w/ no throttle movement) and the RPM jump up to say 2200 (made up number, maybe over 2500).
...


A340F: left (me) A340H: right (you)


​​​​​​​Maybe time to have your butt-dyno recalibrated to the late 80's... Or one of your gauges could be wrong too.
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Old 08-23-2018, 08:20 AM
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Great info. I can't seem to quote the message in my reply... but that's a totally different tech issue.. .

Thanks for the OD and auto trans issue- makes sense to me.

I will test the EGR this am with a vacuum.

On the TC from what I have read, I am not having any of the symptoms of it going bad- it shifts fine- seems to go into OD around 40mph but I will road test today to make sure the O/D on/off switch is working properly. I took the rig to Les Schwab and they managed to break the brake relay somehow so I had to rig the over-ride button to on all of the time in order to shift out of Park. I tested the relay with a muli-meter and it worked as it should have and I have brake lights- but could not get it to shift out of Park with my foot on the brake.

Based on the chart, it seems that I should be able driving at far lower RPMs at 50 mph....
Thanks,
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Old 08-23-2018, 06:07 PM
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Run the stall test from the transmission section of your FSM. This verifies the torque converter and engine output.

You will also find details on the ECT (electronic control transmission) diagnostic port. You can verify throttle position, indicate gear changes and lockup electronically on a volt meter.
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