I am getting a code 34 stepper motor...I have read that it could be the timing as well. Can I change the stepper motor without removing the IP? How would I check the timing first to determine if the motor is no good? A picture would be appreciated. Thanks Dan.

You can start the truck and watch the foot at the bottom of the stepper move up and down as you move the pump from driver'side to passenger'sside or vice versa. TDG said exactly how to make sure it was right. I think you where sapposed to have the stepper 1/4" shy of all the way in and the foot should stay pretty steady and not search for the right timming. I watch my timing number's on the scanner as I do it.

First thing to do is just look at the pump, it may be difficult to tell, but look at the ESO solenoid on the top/front of the pump and determine if its advanced (towards drivers side) or retarded (pass side) of perpindicular. If its leaned way over to either side, loosen the 3 mounting bolts and put it closer to straight up and down if anything just a hair on the advanced side. Before you move it, scribe a line on the mounting flange of the pump to the timing cover for a reference line, this will let you keep track of how far you move the pump. On the lower passenger side of the pump, looking through the gap between the coolant crossover and the timing cover you can see the 'foot' of the stepper motor. Have some one rev the engine a little and you should see it pull up with RPM, if you see it move 99.9% chance its good, they very rarely fail. After you've verified stepper motor is operational, reset your TDC offset. Warm engine to >170F/70C, with key on engine off, hold accel pedal to floor for 45secs, key off for 30secs and restart engine, listen for brief stumble telling you the TDC offset has been redetermined by the computer and see if the code comes back. It seems you have access to a scanner, which would certainly aid in this process, check TDC offset and get it to withing -.25 to -.75 higher values means the pump is too far retarded and needs to be advanced towards driver's side, while lower numbers mean its too far advanced and needs to be moved towards pass side, just keep in mind were dealing with negative and positive numbers so higher negative numbers would be lower numbers.

Thanks TDG..and QM. No I do not have a scanner but I am going to look into one. Truck is OBD-1 what scanner would you recommend?


I will check stepper "foot" and pump position and advise. It only throws the code when I get on the throttle, while towing machinery or my forklift on my trailer. I assume that if I had a scanner I could plug in and move the pump to the correct offset while running? Dan

Not a good idea to move the pump while idling, you could damage the pump or drive gear. Just mark it, check it move it check it and so on until you get it right, just remember you have to tell the PCM to reset after each adjustment.

I just compared the movement of my 95's stepper motor with the movement of my brother's 95 duallie. The foot of his stepper motor pulls up with engine RPM. Mine does not move. Is it possible that it is jammed? Anyone have a part number for replacement or could it be something else? Electrical connection appears to be good. Should I remove it and see if it's mechanically jammed? Thanks Dan

The criteria for a failed unit was not moving. Call local diesel shops and see if you can run down a local eletronic diesel injection supplier/distributor. I always call the local GM dealership too, for laughs. When I asked for a piston they wanted $189 each. I got it for $35 w/ connecting rod, used but another shop had one for $70 new. It pays(or you don't pay so much) when you look around.

Well called around on Saturday up here. Called my local GM dealer,(waste of time) and BD Power (Valley Fuel Injection) was closed so I decided to try to remove the stepper motor. Yeah it was fun and one of T-25 screws was stripped so that made the job more interesting. Well the plunger would not move at all when I took it out so I did what any good backyard mechanic would do. I soaked it in WD-40 and went in for coffee. When I got back out the plunger moved resonably freely. I figured I had nothing to lose so I re-installed it. Guess what it works! I noticed an immediate increase in power when under load, and no more codes.... I drove in to work this a.m. hammered the throttle more than a few times and still no codes..(about 50 miles) hopefully it's fixed. I think I will look for a spare just to be sure. Dan

Wow, I'm impressed, I've never attempted to repair one once it started hanging.

The low buck approach is king.

The difference in performance is amazing... Truck has way more "snap" and tires seem to break loose if you punch it. Thanks for the info QM and TDG..Dan

The stepper motor is what physically controls the movement of the optical sensor on the data disk. The data disk is spinning at the rpm of the engine. When you step on the APP, the stepper pushes the optical pickup to the driverside (advanced) and the engine speeds up as the data disk catches up to the desired timing event and pulls the optical back to baseline when you let off. Without this advancement in timing the truck will slowly gain speed as the injection event is comming late and nothing advances it from where it just was. The data disk spins a little faster and passes the pickup's desired spot, keeping the engine's speed relatively slow.


When you loosen the three 15mm nuts and rotate the pump you are moving the body of the pump and limiting the movement or desired range of the steeper, and if you tighten it down it will give you a code as soon as it tries to push the steeper into the pump housing. This is where TDC offset comes in. You rotate the pump to the desired TDC offset(-1.5* to -2.0* TDC) and techII it in or do the key on/APP key off/start trick and the "range" is reset and the stepper will not hit the pump and give a stepper out of "range" code. Now to add TDG's optical bump to this.


On the bump you are just slidding the optical to the passide 1mm-1 1/2mm and the optical range remains the same, just 1mm or so advanced of before.


I'm sure that's not a perfect explanation but It's close enough for gov't work.Edited by: quantum mechanic

The stepper motor is what physically moves the optical sensor on the data disk.


Your close QM, but you know I just can't let that go ;)


The stepper motor actually moves a lever, which inturn pushes against a valve at the head of the advance piston tapping into Transfer Pressure inside the pump to move the piston, the piston inturn moves the cam pin which is engaged to the Cam ring, which rotates inside the pump. The optical sensor is bolted to and thus moves with the cam ring. The Data disk is on the Drive shaft of the pump and the optical sensor sends Lo and Hi res signals to the ECM so it can calculate internal pump advance movements relative to the crank sensor and meter fuel delivery quanti****.


On a side note, internal Transfer pressure is set in the fuel inlet of the pump. As a pump wears, internal leakage increases and the blades/liner/blade spring all start to wear, resulting in lower than desired Transfer pressure. This can be partially compensated for by turning the adjusting screw in. To do this, simply remove the inlet hose coming to the pump, using a long 5/32 allen, give the screw inside about a half a turn. This increase in pressure will help move your advance piston more quickly and may make a noticeable difference in overall performance, and, it is COMPLETELY SAFE, so even if you don't notice a difference, you won't damage anything by doing this.

the piston inturn moves the cam pin which is engaged to the Cam ring, which rotates inside the pump


Your close TDG, but you know I just can't let that go ;)


The cam ring does not rotate but does move axially a few degrees, up to ten degrees. The "Rotor" does rotate however.


Now, is that 10 degrees engine or 10 pump degrees or 10 degrees Fahrenheit or 10 degrees Centigrade ?

For it to rotate does not mean it has to make a complete circle and it actually moves about 11 degrees pump.


Also, I said it makes the advance piston move quicker, when actually it makes it respond quicker, not necessarily move faster or further.Edited by: Texas Diesel Guy

I can almost time one now, only my scanner doesn't show tdc offset. Is there any way to determine this from des/act time?


Also, why do you write it quanti****


Edited by: quantum mechanic

Axially means along the plane of the shaft, lengthwise, which would make the sensor move front to rear to front, and not radially side to side.


Talk about yer damaged internals..................


And, long as we're here, may as well note the Inj Pump shaft rotates at 1/2 crank speed, so any degree of pump change is offset by two degrees of crank rotation.


1mm pump movement - or optical sensor - is ~2deg.


To passenger-side is retarding - to driver-side is advancing.


Edited by: gmctd

The only way to judge timing using only DES and ACT, is to see if you are way out of the window, so that your DES will go higher or lower than your ACT can reach.

Would this procedure help with this sick puppy? And can i get at it without removing my top end?

This procedure probably won't help anyone who doesn't have an apparent timing related white smoke problem. But it won't hurt anything, go for it.Edited by: Texas Diesel Guy

CR,


It's the fitting to the right of the cover where the fuel comes in. You remove the brass inlet and the allen screw's inside.


Tex,


-2* tdc what would that look like on des/actual. When I move my pump and then check des/act and the stepper foot, I see it make changes. At one extreme(retarded) it seemed to have to stepper foot in all but a quater and the optical was to the driverside when I pulled the topcover. I was bumping the optical back to baseline and watching the changes to des/act through the range. It stayed atabout 8.8 deg. desired and actual was the one that changed. It would be erratic 8.8 9.0 9.2 8.4 8.6 every fraction of a second with the pump more advanced, stepper going up and down. 6* passenger side it steadied out to 8.5 des 8.5 act and little variation or stepper movement. 10 deg passide actual dropped below desired three degree's.Idle speed had drooped from 675 to 575 RPM that's when I tried to TDC learn,, I know I didn't wait a full 30 sec. before restart. It never stumbled. I let the pump come back to center by loosening the bolts and the pressure of the cam pulled it back toward the driveride 6* then I bumped the optical back to where the pedal requires a feather light touch, it shifts better like that.Edited by: quantum mechanic

Okay, gotta ask this question. . . why did GM in their inventive minds run the timing the way they did if this timing that you are describing is so much better? (with optical bump etc. . .) Is there any adverse wear/stress/ or longevity issues that come into play with this, or did GM just set this thing up too conservative without regard to our power hungry appetites?

GM put timing abot 6* retarded for emissions reasons.

Ok guys, everytime timing is brought up, Im left scratching my head.


How do you determine desired (DES?) and actual (ACT?) timing? I assume that ACT would be determined by a scanner? Does the pump not have any markings relative to its mounting plate to determine DES?

Reason Actual starts hunting is PCM is trying to maintain smooth idle rpm by varying fuel and timing for each cylinder, based on inertial differences from Hi Res counter.


Adjust idle timing too far off, and PCM cannot correct - idle rpm drops, as you saw.


Adj Optical Sensor increases available fuel and timing across the board, including idle - PCM cannot keep up.


Adj OS 1mm to pass-side is retarding - PCM pulls OS and camring back - advance - to previously known position, based on encoder wheel position relative to Crank Position Sensor.


Stepper hunting is also indication of worn timing chain flap.


TDC Offset can be set to various values for each IP timing adjustment, even Positive values.


Mine jumped from -1.80 to +2.0deg just by manipulating the scanner - took series of power cycles, bumping the starter to get it back to -1.94, pump was locked at 8.5 Desired during that sequence of events.


Dunno if it's from using 2004 OBD-II scanner on OBD-I PCM, or what, but it was scary when it happened.


Each TDC Offset adj requires power cycle, restart for the new set to take.


Never saw that procedural oddity described, anywhere........Edited by: gmctd

I gave the adjusting screw a turn as TDG suggested. No noticeable difference going down the road unloaded. Seems to have almost eliminated the rough idle at cold startup though (20F this morning!). We'll see if that difference continues and if any other noticeable changes present themselves.

"yota,


without the scanner, you could only guess at time. Without having a decent understanding of where the relative positions should be, you could throw it off.


http://www.dieselplace.com/forum/uploads/quantummechanic/2004-11-11_084548_scan.jpg


here's my timing readout on my laptop.


I'm writing a letter to the software company "EASE diagnostics" It says that their product falls short of a fully functioning enhanced parameter scantool because without TDC indicated, I can't properlt time this vehicle.





when I made another stab at TDC learn this morning, I took it to the driverside till Des/act was 8.9/7.6 then Attempted TDC learn. It never stumbled but Des/act was 8.6/8.6 and very steady #'s afterwards.Edited by: quantum mechanic

TDG which way should I turn the adjustment screw?

clockwise.

thanks

what does the adjustment screw do?
because my truck has more power after i turned it. It also starts alot better now! :ro)

Hi all

I have been reading this thread. I have a mt2500 scan tool. I can read the timing and the TDC. the timing seems to track inj timing / DES timing 9 - 9, 10.1 - 10.1 and so on, but no matter what I do with the TDC off set never changes. I tried the app reset holding the pedal down 45 sec turn key off 30 sec. TDC always 0.8. 94 chev truck 6.5l no mods. Thanks for the help Joe

That procedure is for the OBDII PCM, as noted - OBDI requires TechX equiv, or 50 starts

??? That procedure works on ALL 6.5s
If you don't move the pump then your TDC offset shouldn't change, if you don't clear the codes and warm the engine up to 170F+ it won't relearn.

I'm not getting any codes. I changed the pump 3 or 4 months ago. I am now selling the truck and wanted to make sure the timing was correct. I need the the computer to relearn the TDC.
I moved the pump 1mm each way, 4* total, Temp 72c. Will it force a relearn if I leave the battery disconnected over night?Is that 50 starts or 50 on offs with the key switch?
Thanks again.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>

need to get up to +77C. Your selling the truck and its way within specs, what are you worried about?

According to the OBDI Diesel EFI Fuel Injection training manual, and the GM Shop manuals, OBDI requires TechI\TechII, or up to 50 full-running starts.

I change the pump (with help from the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:Street w:st="on"><st1:address w:st="on">Diesel Place</st1:address></st1:Street>) without ever checking the timing. I just wanted to make sure everything is what I say. Did I miss something is -0.8 for TDC offset in spec? I have seen different numbers for TDC offset. I was thinking if -0.75 is the upper spec and I advance the time 2* by moving the pump 1mm to diver side everything would be ok.

+8.5deg Des\Act is -1.5deg TDCO, which is a good setting for a little more power than stock.

If you're reading +9deg, you would not want to advance IP.

Set timing to +8.5deg des\act at idle, then PCM will learn TDCO between -.8 and -1.5 over period of time.

What RPM 694?

~600 is ideal at 77*C, iirc

650 to 700, with engine coolant at operating temperature, but above 177deg, min.

Not arguing, just relaying what the vc says. '93 says 600 rpm low idle and 700 rpm fast idle. '94 says "curb idle speed 560 rpm"

My 94 says 560 too. Thats right where it idles when it's warm.

+8.5deg Des\Act is -1.5deg TDCO, which is a good setting for a little more power than stock.

If you're reading +9deg, you would not want to advance IP.

Set timing to +8.5deg des\act at idle, then PCM will learn TDCO between -.8 and -1.5 over period of time.Des/Act Timing is a totally different thing, and is completely unnaffected by TDC offset. Desired is what the PCM wants pump timing to be, Actual is where the pump actually is, all you want is for the pump to do what the PCM is telling it to do. Setting TDC Offset just ensures that the pump is in position relative to the crank sensor where it can comply with PCM demands.

My '94 drops L.I. speed to 560 also when fully warm.

Ok, folks - you can insult me, you can call me names, you can wink at my wimmin, but it just don't pay to mess with that big stud I rode in on.......

ECT 181deg
EGT 275deg
IAT 85deg
Des tim +8.5deg
Act tim +8.5deg
Fuel rate 8mm3
Inj P.W. 1.91ms
TDCO -1.50deg

DESIRED IDLE SPEED - 694rpm
ENGINE SPEED - 694rpm

TDC Offset is effected by Des\Act timing - add +5deg to Des\Act adds -1deg to TDCO

Who's yer daddy now, boys?:ro)

uh huh! uh huh! uh huh!

I think senility is setting in early ;)

You can set TDC Offset to +0.1 or -1.94 or anywhere in between and your DES timing will be the advance your PCM wants the pump relative to crank, and ACT will follow in suit. TDC Offset value is not a part of that equation. TDC Offset function just validates that the pump is in proper static timing position to operate advance properly.

I have observed the following, OBDI and OBDII, Feb 2004 mfd TechII -

OBDI PCM will learn new TDCO value when Des is changed, as will OBDII - procedures are different.
PCM will learn and retain any of several TDCO values for each timing setting, or changed setting, by simple manipulation of TechII and engine rpm.

For +3.5deg Des, TDCO can be set +1.0 to -0.7
For +8.5deg Des, TDCO can be set 0 to -2.4, sometimes to +2.0 (scary! WTF, over?)

Just by manipulation of RPM and TechII command state.

Scan oem timing at +3.5deg -0.5deg TDCO, move Inj Pump 2.5mm to driver-side, do TDCO trick, gets ya on average -1.5deg TDCO, check timing at +8.5deg Des

Doing TECHII Time Set, then TDCO results in same values.

I needs to do fresh about ten or so of each '95, '96, '98 to really get a feel for what's happening thru various software changes, OBDI, OBDIIa and OBDIIb

OK, now your mixing in a third, also related but very different aspet....the Time Set funtion.
What this does is command the stepper motor to full retard and displays the ACT timing of the pump relative to the crank. Setting this to spec'd 3.5* will put you close to the middle of the window* -0.5 TDC Offset, advancing the pump to achieve 4.0~4.5* will achieve a TDC Offset in the -1.0~-1.5* range, because now your a half to a full degree advanced from the 3.5* spec.

*-Window being the -.25 to -.75 Offset prescribed by GM.

I think I misinterpreted one of my figs. I think the TDC Offset value is actually double the difference between the ACT timing the Time Set Funtion reveals. Thats because we're looking at pump timing, which is double crank timing because the pump rotates at half speed of the crank. So, if you get ~4.0* from the time set, you should get ~1.5 for a TDC Offset....I'll double check on that. I am sure that values higher than 3.5* ACT will yield TDC Offsets >-.5, and the higher the reading the lower the Offset will be, just not 100 percent on the ratio of change between the two.

The valve cover on my 93 states 700rpm at curb idle in nuetral at running temp and states 800 for fast idle. Why are some of the same engines vc's reading different and what is the tq on your 93 QM? Mine reads 200lbs tq @ 3400rpm. My friends 95 with the 6.5 reads 190lbs tq @ 3400 rpm's.

Thats HP you mean, which is still odd, 4911 calibration specs say 210HP.

I'll double check tomorrow but I'm pretty sure that's what I read.
Mark

You should have 300+ ft lbs. Torque, minumun

TDG,
I stand corrected. I was mis-reading. That "was" HP as you stated ... Sorry for the misunderstanding.

QM,
I don't know what the actual torque would be. There is no reading on the VC for torque as I had incorrectly thought in my previous post.

I thank you both for pointing me in the right direction(again).

Mark