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Discussion Starter · #1 ·
All, My first post though i have been lurking a bit. Just bought my first 6.5. 79k miles. Decent condition. Needed some TLC. Here is what i have done so far.

1) Full front end rebuild
2) Fuel and Oil filters
3) New lift pump... Old one was not pumping well.
4) New Flight Systems PMD and relocated.
5) new alternator (noticed lights flickering @ idle so figured regulator was failing... turned out to be true)

Truck starts in 15F with no block heater. No smoke. Idles smoothly. Same with hot weather. Fires up. no issues. Initially, i had a pile of P1810 codes and a bad converter. Had the trans rebuilt and converter replaced. Since then, i've had some REAL weird issues.

Truck does great until it gets to full temp. 190 - 205F. As soon as it hits 190, the truck develops this hesitation for a second from a dead stop. It feels as though the trans is not in first gear, then it drops down and goes. Reverse is even worse. it will just bog for a second or two then go. Absolutely no other driveability issues. moves well at speed. no smoke. smooth.

I complained to the transmission guy. He said he did a bunch of diagnostics with a Tech 2 and said the PCM was not reading the TFP switch. He tested all the way to PCM and said the harness was good and registering the TFP signals properly up to the PCM.

Have any of you seen this before? Why do i feel like t his transmission is wacked?
 

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Welcome to DieselPlace
(y)
 

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Welcome.
The P1810 codes you were getting before repair are exactly what the mechanic found out after.
If the mechanic is correct then the PCM must be having problems.
Are you getting any codes now? Is the SES light staying on?
The TFP switch uses the PCM's 5v. circuit internally and could be affected by any other device that uses 5v.
FYI - Your 99 has security built in so if you change your PCM the security re-learn will need to be done.
You can DIY, the procedure is in the service manual.
 

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Discussion Starter · #5 ·
Welcome.
The P1810 codes you were getting before repair are exactly what the mechanic found out after.
If the mechanic is correct then the PCM must be having problems.
Are you getting any codes now? Is the SES light staying on?
The TFP switch uses the PCM's 5v. circuit internally and could be affected by any other device that uses 5v.
FYI - Your 99 has security built in so if you change your PCM the security re-learn will need to be done.
You can DIY, the procedure is in the service manual.
I have a new PCM programmed and on its way to me. No SES. No codes at the moment. Just the hesitation in drive from a stop and the same but exaggerated hesitation in reverse from a stop.

I have a haynes manual but don't have any mention of a security relearn procedure.
 

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Discussion Starter · #6 ·
I have a new PCM programmed and on its way to me. No SES. No codes at the moment. Just the hesitation in drive from a stop and the same but exaggerated hesitation in reverse from a stop.

I have a haynes manual but don't have any mention of a security relearn procedure.
Also, i have no security resistor chip in my keys. My 99 z28 has this, but not the burban.
 

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The "chip" is in the lock cyl. on your burb, not the key.
Depending how the PCM is programmed you may or may not need the procedure.
The factory service manuals are in the faqs sticky. Here is a link to the security procedure.
Scroll down to page 8-808. Large file, wait for it.
 

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Discussion Starter · #8 ·
The "chip" is in the lock cyl. on your burb, not the key.
Depending how the PCM is programmed you may or may not need the procedure.
The factory service manuals are in the faqs sticky. Here is a link to the security procedure.
Scroll down to page 8-808. Large file, wait for it.
dude. don't know you. but love you already.
 

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Discussion Starter · #9 ·
How often to the PCMs on these things fail? Is it a relatively common thing?
 

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How often to the PCMs on these things fail? Is it a relatively common thing?
Things like age, heat, humidity, exposure to salty environments (living in the rust belt) can be a factor
 

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Discussion Starter · #11 ·
Holy crap. I installed the pcm. My god. Different truck. Everything works perfectly.
 

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Holy crap. I installed the pcm. My god. Different truck. Everything works perfectly.
Glad you got the issue resolved. Thanks for giving us an update!
(y)
 

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Discussion Starter · #13 ·
WELLL... partially resolved.

threw another P1810 this am. sigh... BUT it drives MUUUUCH better. i was having a lurching issue where at a stop, the truck did not want to stay stopped. now it does't do that. I also no longer have a surge when shifting from R -> N -> D and back. that i think was a TSB. so the updated calibration is much better.

Now i have a P1214. kinda expected since its a new PCM. did the reset procedure but still throwing it so i will need to adjust the IP.


little at a time i guess.
 

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Discussion Starter · #14 ·
Ok so after doing some more diagnostics and performing the reset, it looks like my base offset timing after the PCM replacement is @ -2.5. Truck runs great.

Asking all you guys since i am relatively new, can i drive the truck like this? No check engine lights etc... Not towing or doing any heavy hauling. I have ordered the tools i need to reset this thing properly but will be a week or so until i get them.
 

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If it is still throwing the 1810. Maybe the pressure temp sender is bad. It may test out ok at idle but driving it shows something is wrong. There is a pressure switch for every gear in the TFP plus one for temp. One of the switches could be bad.
 

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Discussion Starter · #16 ·
TFP and harness all replaced. Trans was rebuilt.
 

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How it works -

* These switches are sensors only, they do not control anything.
They verify that the trans. is in the correct gear.
It a fairly simple valve manifold to replace if needed.

The automatic Transmission Fluid Pressure (TFP) manual valve position switch consists of five pressure switches (two normally-closed and three normally-open) and a Transmission Fluid Temperature (TFT) sensor combined into one unit. The combined unit mounts on the valve body. The Powertrain Control Module (PCM) supplies ignition voltage for each range signal. By grounding one or more of the circuits through various combinations of the pressure switches, the PCM detects which manual valve position you select. The PCM compares the actual voltage combination of the switches to a TFP manual valve position switch combination table stored in memory. The TFP manual valve position switch cannot distinguish between PARK and NEUTRAL because the monitored valve body pressures are identical. With the engine OFF and the ignition switch in the RUN position, the TFP manual valve position switch indicates PARK or NEUTRAL. Disconnecting the AT inline 20-way connector removes the ground potential for the three range signals to the PCM. In this case, with the engine OFF, and the ignition switch in the RUN position, D2 will be indicated.

New parts don’t always work.

Has the harness from the 20 pin trans. conn. up to the main harness been opened and inspected, wires separated and checked for damage?

Very common problem.
 

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Discussion Starter · #18 ·
TFP replaced twice.

Rebuilt trans under warranty. Allegedly the guy verified proper function and wiring to the PCM. Pcm wouldnt show gear positon from TFP.

Happy i replaced the PCM. Its much better but now have to deal w timing. This makes me think the old pcm is actually bad since timing moved a lot.

If someone could let me know if its safe to drive w a -2.5deg timing offset that would be awesome.
 
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