Cold Advance on 94 - Info needed

[Splitrimz]

Hello, still struggling with my '94. Replaced all the glow plugs, 3 were bad. I have a lack of cold advance, I can disconnect the ECM water temp sensor and I get good advance. It is not the sensor, I replaced it. This one has got me stumped because disconnecting the sensor tells the ECM to advance, and it does, but that is fooling it with a max reading. I'm thinking that the ECM is not recognizing the gradual signal from the sensor, only the max.

I'm just about set to bite the bullet for a new ECM. Any other suggestions on the cold advance? I have tried several new sensors.

I notice at the place where I priced the ECM that you have to install your old chip. Does the chip have anything to do with cold advance? I would hate to replace the ECM and it is the chip.

I do have my GMTD Scan Tech running but I can't find anything out of order with the readilngs.

Thanks for any suggestions.

Splitrimz

[DmaxMaverick]

You either have the wrong sender, or the right one is wired wrong. Other than that, the PCM is toast.

[Robyn]

Will your scanner give you any info on the advance settings???

The advanced runs along a curve based on the engines temp.
I am not sure of the voltages.

Now I have this question??? How did you come to know you have an advance problem??
Poor cold starts or lot of smoke on start up??

The chip has all the running parameters on it that control most of the engines fueling functions as well as some of the tranny programing.
The advance is basically a function of the sensor and the ecm changes the advance depending on the temp of the coolant.

If you can get advance with the sensor unplugged I am not sure I would spring for an ecm just yet.

The unplugged sensor tells the ECM that its Bloody well damned cold (-30)?? and advances the thing to the nuts to help get it going in sub zero temps.



More info please.

Robyn

[Splitrimz]

First let me thank everyone for trying to help me out. Your comments do help, they make me think it through in more depth.

Hello, I will try to answer questions the best I can in my layman's terms.

The symptom: Note: TDC offset reads -0.18 and never changes.,

On a cold start, with new glow plugs it starts quickly. Idles at 715, measured inj timing is 6.8 deg.,
It doesn't have much of the diesel rattle and when I press the accelerator,
it bogs down and blows smoke, bluish, greyish, the color is subjective. PUMP TIMING=29.57

It gets better, ie. the bog down gets less as the temperature increases until it
reaches about 150 deg or better. It smooths out at this temp and above, no more smoke
and runs like it should. I monitor temperature and inj timing and as temp climbs, see chart below.

If I disconnect the ECM temp sensor, it advances (to 14 degrees) and it idles and runs great
When the temp reaches about 150, I plug the sensor in and it idles back to normal and runs like it should.
. I don't get any codes. PUMP TIMING 36.26

Here is a plot of the warm up sequence, on the last reading it was warm enough and I gave it a little throttle.

ENG coolant RPM INJ TIMING MEAS-DESIRED FUEL TEMP AIR TEMP PUMP TIMING
92.7 ; 750; 7.4 92 70 29.57
100.1 ; 712 ; 6.9 92 69.3 29.13
111.5 ; 675 ; 6.3 92 69.3 28.42
160 ; 600 ; 4.5 92 75.4 26.84
169.8 ; 600 ; 4.5 92.6 80.2 26.66
179.9 ; 919 ; 5.6 93.3 83.5 28.79


Looking at these numbers the pump timing is decreasing during warmup, this seems like it's advancing but
it looks like the injection pump needs a ton of advance. Lift pump is good, 4psi.

See anything in all of this? (Injection Pump?)

Thanks splitrimz

[Splitrimz]

Sorry for the table, it is an eye chart, I discovered these boards would take VB code after I hit the send button.

[Splitrimz]

A better list.


COOLANT TEMP = 92.7
RPM=750
INJ TIMING MEAS = 7.4
FUEL TEMP=92
AIR TEMP=70
PUMP TIMING-29.57



COOLANT TEMP = 100.1
RPM=712
INJ TIMING MEAS = 6.9
FUEL TEMP=92
AIR TEMP=69.3
PUMP TIMING-29.13



COOLANT TEMP = 111.5
RPM=675
INJ TIMING MEAS = 6.3
FUEL TEMP=92
AIR TEMP=69.3
PUMP TIMING-28.42



COOLANT TEMP = 160
RPM=600
INJ TIMING MEAS = 4.5
FUEL TEMP=92
AIR TEMP=75.4
PUMP TIMING-26.84



COOLANT TEMP = 169.8
RPM=600
INJ TIMING MEAS = 4.5
FUEL TEMP=92.6
AIR TEMP=80.2
PUMP TIMING-26.66



COOLANT TEMP = 179.9
RPM=919
INJ TIMING MEAS = 5.6
FUEL TEMP=93.9
AIR TEMP=83.5
PUMP TIMING-28.78

[Robyn]

Your TDC offset should be -1.94 when the engine is warm.

Check the PMD and make sure the resistor is in the plug socket.

If not use a #5 and then do the TDC learn manuever.

Once the offset is correct then see if the cold start improves.

Best

Robyn

[Warren96]

My '94 won't accept TDC offset changes unlless it's over 183F, and there are no codes stored. But like Robyn said, TDC offset should never be that low. Crank it up, and keep us posted.

[Splitrimz]

Thanks for all the input. The solution might be getting closer. Now that I realize that TDC OFFSET is way low, things are starting to come back to me. Over time, I have replaced several FSD modules, some used and some new. I never worried about the resistor because I read incorrectly somewhere that it didn't matter. Well, I got away with that for a long time until about six months ago, I think the ECM "relearned" to 0 resistor, ergo my ongoing problems. That's my story and I'm sticking to it.

When I have the opportunity, I will try to set TDO for the first time with my SCAN TECH, the process seems straight forward. I do have a #4 resistor in the tool box. I'll let you all know how it goes.

SPLITRIMZ

[Splitrimz]

Man, nothing is ever easy! This is the SAGA of trying to set TDCO.

1. Put in #4 resilstor in FSD.

2. Warmed truck up to 180 plus degrees.

3. First step in learn procedure, check DES/ACT/TDCO they are 4.5, 4.5, -.18

4. Next Step click the TDC Time set On button, DES should go to 0, and ACT should read +3.5.
ARGGGGGGGGGGG.....TRUCK STALLS. WHEN I CLICK TDC Time set On button.
5. Clicked TDC Time set BAck On, and started truck.

6. While it was running, I clicked the TDC Learn button. TRUCK STALLS.

Therefore I'm still running at -.18 TDCO. Any suggestions as to why it is stalling?

7. Late update..I tried to give it a little throttle to have a little advance. Tried to set TDCO, it set to 0 and now I'm blessed with Code 88. and it runs like a mis timed truck.

HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks.

[Warren96]

Do you have the ''Driveability,Emissions and Electrical Diagnosis Manual''? On page 3-118 it says the PCM is toast. How about swap in the original "chip"? Maybe the Turbomaster is bad. Maybe one of the members here has an original they will let you borrow or buy. Good luck and keep your fingers crossed.

[Splitrimz]

Hi, the turbomaster in my signature is the manual spring loaded turbo gate control, not a "Chip", It has the original chip. Thanks for your reply.

[JohnC]

I don't have the manuals any more, but I recall that the behavior you are seeing can be caused when the mechanical pump timing is too far outside of the correct window. TDC offset learn runs the timing stepper motor through its range, and if part of that range is outside the range where the engine will run, it stalls. Try advancing the pump about 1/16" and re-run the TDC offset learn.