While driving home tonight I noticed that my rpm's were lower.
At 70 mph the rpm's would be easily @ 2500 to 2700 normally.
Now at 70 mph it was at 2300, which is great by itself, just fear it means something bad is about to happen.
Any clues what is or could cause this phenomenon?
I haven't noticed any other performance change or smoke..still have the nailing and vibration, but nothing that it wasn't doing last week.

Thanks

Perhaps that was the TCC locking up.

I was pretty sure it was engaging prior to that. 2300 is what the correct Rpms @ 70 mph with 4:10 gears should have been all along?

2300 is correct, depending on tire size. How long was it running at
2500-2700 ?

Well, I am not sure to be honest. There have been so many things going on with my Suburban, and so many new noises, that I get confused, and forget how it "used to be" before the engine was apart and put back together, I just know that even at 2300 rpm it sounds like 4000 rpm, and there is ALWAYS a vibration. I guess its possible it was the TCC locking up, but I have been driving it for about 5000 miles like that, what would make it all of a sudden start locking in, better yet, what would have made it NOT lock in? It never seemed to slip in any gear and was always responsive with down and up shifts.

The problem with doing LOTS of things at once, and not testing,
is you can not figure out what ( if anything ) is wrong.

If lots of noise, ? Fan clutch always engaged ?

Wrong Water pump for Year engine ( running backwards )?

I think you need to be specific on problems and fix 1 at a time.

If Transmission is not slipping, Shifts normal, and TCC is locking in 3 & 4 gear ( RPM at cruise seems correct ) Than I would accept Transmission is OK and start on other items ( Noise of engine ) whatever.

I am a tad gun shy I know, this is about the only venue I have. Three mechanics ripped me off good, and my luck with the dealer hasn't been so good either. The noise is mostly what I believe to be injector nailing and a "puffing" like sound on the right side. Water pump is the one that was on before engine repair so it should be the correct one. I spoke to a mechanic I found in Ft Worth to rebuild my injectors in an older Mercedes, he works on all diesels, and he seems to think based upon what I told him that its all a timing problem, which would be nice, but never quite so lucky <GRIN>, I plan to see him Tuesday if he can fit me in.

Stock timing is 3.5 deg(-.50 deg tdco). It wil run better if you have him advance it to 8.5 deg (-1.94 deg TDCO)

They way to check it 1st is to see when during time set command goes to 0 and actual is avg 3.5 deg, this will give you confidence egnine is at least capable of meeting factory specs.

Then when rotating toward driver side to attain -1.94 during TDC offset learn sequence & adjustment, timing will follow, to give 8.5 deg at idle. I don't think you want to go to 8.5 deg during time set. At least this is how I did it last go round, also your choice but -1.94 makes a lot of racket on a cold morning, I prefer -1.85 adds git up & go but less rattle when cold.

I have written up in Faqs a time set procedure for for OBD II, worked for me. if you are OBDI it is a similar concept but you need a bi-directional scan tool you can't initiate the learn with APP to the floor.

This is one I received from my scanner company when I asked why their scantool didn't show TDC offset. My scantool is for OBDI only!


Controller Learn Procedures : TDC Offset
-= Page 1 =-

=== TDC Offset Learn Procedure (6.5L Diesel) ===

You must perform a TDC Offset learn procedure if any of the following have

been done or exist:

* Diagnostic Trouble Code (DTC) P1214.

* Engine has been replaced.

* Crankshaft position sensor or engine front cover has been replaced.

* Powertrain Control Module (PCM) and fuel injection pump have been

replaced.

NOTE: DO NOT perform procedure unless sent here from DTC P1214 or one

of the components listed above has been replaced.

1) The PCM has the ability to determine amount of offset required to bring

the engine to TDC when TDC offset is not present or has been cleared.

This procedure must be performed to allow PCM to be updated with the

correct TDC offset for vehicle application.

2) Install the Scan Tool on Data Link Connector (DLC). Start engine and

warm engine until engine coolant temperature is at least 170 Deg F.

Using the scan tool, clear DTCs from PCM. Turn ignition on with

engine off. Fully depress and hold throttle at full throttle for at

least 45 seconds.

3) Turn ignition off for 30 seconds. Start engine. Verify the scan tool

indicates TDC offset has been cleared to zero. If TDC offset has been

cleared to zero, go to next step. If TDC offset has not been cleared to

zero, repeat step 2) until TDC offset has been cleared to zero.

4) With engine running, use the scan tool to verify engine coolant

temperature is greater than 170 Deg F. It may be necessary to drive

vehicle to obtain correct engine coolant temperature if engine coolant

temperature is less than specified.

5) As soon at engine coolant temperature is greater than 170 Deg F (77 Deg

C) and engine speed is less than 1500 RPM, the PCM automatically learns

a NEW TDC offset. The NEW TDC offset will overwrite the previous TDC

offset. Using the scan tool, note NEW TDC offset. TDC offset should be

-.25 to -.75.

6) Shut engine off. If TDC offset is not within specification, go to next

step. If TDC offset is within specification, TDC offset learn procedure

is complete.

7) Using Flange Nut Wrench (J41089), loosen fuel injection pump retaining

nuts. Fuel injection pump must be rotated to change TDC offset. Rotating

fuel injection pump .039" (1.00 mm) will change TDC offset about 2

degrees. Rotating fuel injection pump toward driver's side of vehicle

will produce a positive (+) number and rotating fuel injection pump

toward passenger's side of vehicle will produce a negative (-) number.

8) Using Fuel Injection Pump Wrench (J 29872), slightly rotate fuel

injection pump. Tighten fuel injection pump retaining nuts.

9) Repeat step 2) through 8) until TDC offset is within specification. If

proper TDC offset cannot be obtained, check the following:

* Ensure engine coolant temperature is greater than 170 Deg F (77 Deg

C).

* Electric connectors at PCM are properly installed.

* Electric connectors at injection timing stepper motor on side of

fuel injection pump is correctly installed.

* Ensure latest Techline software was used.

* Check for proper base installation of fuel injection pump. The

electric engine shutoff solenoid on top of fuel injection pump

should be approximately straight up and down.

* Fuel injection pump may be defective, although manufacturer states

this is highly unlikely.

Yup almost says that verbatem in my 98 GMC tech manual, I'm not sure though APP to floor in OBDI does initiate a learn, it does in OBD II once temp is greater than 170F, 76.66 C. Also I have never had my truck self learn as described here, sources how this all works are what have me & GMCTD so baffled no 2 documents agree with what can actually be performed on the truck, in the GM manual no mention is made how to do the learn using a T2, it says you need one to perform it, but still directs you to the APP to the floor method.

If one has a T2 they only need to command the offset learn as for OBD I I'll defer to GMCTD & other since I've never done a learn on one of those.

Well, the IP has finally sent a code to the computer, and the Check engine line came on. I took My Suburban to the dealer yesterday. Got a message today that the new IP will arrive Friday. Guess I will findout if they already know to replace under warranty (hopefully there won't be any problems). 1. Will they replace the FSD? 2. Should I have the injectors replaced at this time as well? 3. What other things should I have them check/replace at this time? THX. Chris

PMD comes on a new pump.

Very good. Should I replace the injectors at this time as well?

Hey, my 3500 auto trans w/OD and size 265 tires and 4.10 gears runs at 2700 to 2800 rpms at 70 mph.

Should i be worried about that?:confused:

Could it be my fuel timing? b/c i almost never blow black smoke...even on really hard runs

Very good. Should I replace the injectors at this time as well?
Please tell us the year and miles on your suburban.

2300 sounds a little low for a 4.10. Mine runs about 2400-2500 at 70 with 285 tires.

Its on a 1998 Suburban with under 100,000 miles. The dealer is replacing the IP, but stated that the injectors will be another $1100 if I want them repalced. Seems a bit high I thought.

My gear calculator shows 2300 rpm to be close with 4.10 and 285/70/16 and a .75 4th gear at 70 MPH. So running higher might well be the TCC issue. The engine noise could be the clutch fan staying engaged as well. RPM problems differences could also be from alternator issues, replacement, pulley size wrong, My RPM were erractic when my alternator was going bad, but I couldn't figure that out till it went totally out and I replaced it then everything worked much better.
Tire size would be helpful also.

Injector can be had in the $300 range I think dealer list is about $76 each so thats about $600 plus labor. Spend $40 for a Snapon injector socket, $25 for JK injector kit your under $400 and DIY, it's a good weekend project.

Yep, thats what I plan to do. Hopefully get some that are balanced while I am at it.

Got the Suburban back with the new IP. All I can say is that it runs like a dog. Hardly any improvement in performance. The work order states the timing was set at 3.5. Is this the reason?