My 4L80E trouble codes

[Retiredwarhorses]

I called the guy that rebuilt the transmission. He agreed the torque converter must not be locking. He said the converter lock is good for about an 800 rpm drop. I asked if he had a scanner that plugged into the transmission directly and he said he did not have one, but they had one at the shop he worked at 20 years ago.

Still need to figure out why limp mode with TPS plugged in and with it disconnected converter won't lock. Frustrating. Mogman is saying I can't just unplug the brakes will need to run a switch. Want to test this next.

I guess you better listen to him…

 

[taskunitbruiser]

Here is the TPS circuit, you simply take a volt meter and pierce the insulation on wire 355 with the positive lead of your meter and ground the negative lead, you should see aprox .5v at idle and 4.5V at WOT (wide open throttle) Run switch on and of course you want to unplug the glow plug temp sensor.
Troubleshooting the TPS is fairly easy.
As you will see if the voltage at wire 355 is below .2v at idle of 4.9v at WOT you will set a code and go into limp mode.
I suspect you will see less than .2v at idle.
View attachment 905752

Thanks. I have that page. I will formally test that middle wire on the TPS with my wife pressing the accelerator. I know you can move it by hand under the hood, but since I was holding the probe and ground I didn't have a free handle. I was working alone.

 

[taskunitbruiser]

Have you read the codes with the TPS plugged in and after confirming it is in limp mode?

Yes. No codes.

Have you checked the signal voltage coming from the TPS?

Yes. After cleaning connection I got 5V reference. Ground is good. For clarity, I have NOT checked the variable voltage since cleaning the sensor connection. When I checked it prior I only did it in the idle position and it was below, about the same low voltage as the ref which I recall being .18

 

[Mogman]

Also on page 75 is a pretty simple test procedure for the brake TCC switch.

 

[taskunitbruiser]

I spoke with a guy at Black Dog Customs and he said the TPS is sensitive and it needs to be .50 V not even .51. Will check [hopefully] tomorrow.

 

[Mogman]

I was going to say if it was too low, set it to .5v, .51 would also work, as long as it does not go below .2v or higher than 4.9v it will "work" just the shift points may be a little off. Setting it to .5v is not the correct procedure but will get you real close.

 

[taskunitbruiser]

Peeled back some insulation on the middle wire. Getting 1.2V instead of .5 (engine off, pedal not depressed). If I loosen the two mounting bolts I should be able to have back and forth play and move it until I get .5 idle and then just verify it smoothly transitions up to 4.5 when pedal depressed?

Zooming out is the high idle voltage at TPS causing the limp mode and with the TPS it can't use TC lockup? This would explain all the problems.

 

[taskunitbruiser]

I loosened the TPS mount bolts and rotated it back (i.e. more upright) and now getting .55V. So "proof of concept". Will need to re-remove air intake to turbo to get better access to those bolts. Fingers crossed it will work!!!??

 

[Mogman]

What were you getting at WOT?

 

[taskunitbruiser]

What were you getting at WOT?

It must have moved a bit and I get slightly different readings but just now I am getting 0.62 V idle and 4.24 WOT. It appears to increase voltage smoothly. It is a new sensor, but I was told there are "new" defective Chinese junk being sold (I won't name the companies mentioned).

The way it is now it shifts very high RPMs in first and second gear way late (2500-3000 range for shift) but once I am in 3d it proceeds to 4th and to TC lockup. RPMs are lower but still see high maybe ~2800 at 55mph. Zero feel of blow-by with oil filler cap removed, by the way.

So, after adjustment I am out of limp mode; but it still shifts much earlier and smoother with TPS unplugged. Haven't ever felt TC lock with TPS unplugged.

I was told by Black Dog Customs owner that the sensor for the tachometer is different from the RPM sensor. Occasionally my tachometer will drop to zero RPMs going down the road, but there is no change in the engine sound so it is bogus. Most of the time it functions correctly and reads 800rpm idle which seems normal to me. He was surprised it shifted at all with the TPS unplugged, much less better.

 

[Mogman]

It must have moved a bit and I get slightly different readings but just now I am getting 0.62 V idle and 4.24 WOT. It appears to increase voltage smoothly. It is a new sensor, but I was told there are "new" defective Chinese junk being sold (I won't name the companies mentioned).

The way it is now it shifts very high RPMs in first and second gear way late (2500-3000 range for shift) but once I am in 3d it proceeds to 4th and to TC lockup. RPMs are lower but still see high maybe ~2800 at 55mph. Zero feel of blow-by with oil filler cap removed, by the way.

So, after adjustment I am out of limp mode; but it still shifts much earlier and smoother with TPS unplugged. Haven't ever felt TC lock with TPS unplugged.

I was told by Black Dog Customs owner that the sensor for the tachometer is different from the RPM sensor. Occasionally my tachometer will drop to zero RPMs going down the road, but there is no change in the engine sound so it is bogus. Most of the time it functions correctly and reads 800rpm idle which seems normal to me. He was surprised it shifted at all with the TPS unplugged, much less better.

Most of what you buy that is not from one of the recommended dealers is Chicom junk especially electrical parts.
What model truck do you have?
Do you have the 400A alt? (that's where the tach signal comes from)
The higher the voltage is compared to what it should be tells the trans that the throttle is advanced farther (more load etc) than it is so it will shift late, try to fudge it to around .45-.5v at idle while you wait for a real TPS to arrive.
HPG has them on sale.

Hummer Parts Guy | Search Results

www.hummerpartsguy.com

They only have 2 in stock of the part # 5743243 if that is the one you require.

I have no affiliation with HPG

 

[taskunitbruiser]

Most of what you buy that is not from one of the recommended dealers is Chicom junk especially electrical parts.
What model truck do you have?
Do you have the 400A alt? (that's where the tach signal comes from)
The higher the voltage is compared to what it should be tells the trans that the throttle is advanced farther (more load etc) than it is so it will shift late, try to fudge it to around .45-.5v at idle while you wait for a real TPS to arrive.
HPG has them on sale.

Hummer Parts Guy | Search Results

www.hummerpartsguy.com

They only have 2 in stock of the part # 5743243 if that is the one you require.

I have no affiliation with HPG

Thanks. M1151A1. Yes my alt is the size of a small garbage can, the 400A. So the tach figures out the engine RPMs via the alternator belt speed? Cool.

I ordered the TPS from "globalsourcewd" on eBay.

 

[taskunitbruiser]

They only have 2 in stock of the part # 5743243 if that is the one you require.

My old one was:

GEP18002829 / 01-426-4425 2990-01-426-4425 - SENSOR, THROTTLE POSITION (TPS) {HMMWV SERPENTINE} [GEP] | Hummer Parts Guy (HPG)

www.hummerpartsguy.com

I think the turbo 6.5 and NA 6.5L are different sensors?

 

[Coug]

With the 400 amp alt and the tach getting it's signal from the alt, it also depends on what size pulley is on the alt for what the tach reads. 2800 rpms at 55mph in 4th gear sounds kind of high, at the same level as trucks with the small pulley on the 400 amp generator in other threads.

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[Mogman]

Thanks. M1151A1. Yes my alt is the size of a small garbage can, the 400A. So the tach figures out the engine RPMs via the alternator belt speed? Cool.

I ordered the TPS from "globalsourcewd" on eBay.

Many of the 400A alternators have an undersized pulley so it will charge more at low RPMs, this will make your tach read higher that the RPMs actually are.
It's going to scream like a banshee anyway.
looks like Coug beat me again!!

 

[Coug]

Many of the 400A alternators have an undersized pulley so it will charge more at low RPMs, this will make your tach read higher that the RPMs actually are.
It's going to scream like a banshee anyway.
looks like Coug beat me again!!

Not only scream, but if you try to drive at high speeds, you're likely to destroy the 400 amp alt as well as damage the electrical system in the process.

 

[Mogman]

Your truck is running 3.08 gears its going to run Higher RPMs than the regular A2

 

[Retiredwarhorses]

Many of the 400A alternators have an undersized pulley so it will charge more at low RPMs, this will make your tach read higher that the RPMs actually are.
It's going to scream like a banshee anyway.
looks like Coug beat me again!!

it’s not smaller to make it charge more, it’s smaller so there is a higher output at lower engine rpm’s

 

[taskunitbruiser]

Not only scream, but if you try to drive at high speeds, you're likely to destroy the 400 amp alt as well as damage the electrical system in the process.

What is a safe speed range for the 400A? I read the non load limit of the engine is 4000rpm. Am I correct that there is no rev limiter? Does the pedal contact on the floor board protect against most over-reving?

 

[Retiredwarhorses]

Not only scream, but if you try to drive at high speeds, you're likely to destroy the 400 amp alt as well as damage the electrical system in the process.

the reason for a voltage regulator is to regulate ouput, the regulator is calibrated to prevent any output voltage what the regulator is set for 27.5-28.5 for example….driving at high speeds or rpm’s won’t change the output of the generator