Terrible idle onset when warm
 

Here it is:
1996 Chev Suburban w/6.5 T.Diesel, injector pump, timing chain replaced 2years (only about 2000 miles) ago... ran great till parked.
Ran great till parked Nov of last year. Though was parked, started / let idle every couple of weeks (yes, I occasionally gave very short mist or either to start);
Engine will run great for about 10 minutes (whether idling or driving)
Like a switch has been flipped, will die (if idleing) or go totally gutless / miss/ blue smoke under 1500 rpm.
If work up to 1500 rpm, when gets past point, runs excellent... untill come to stop sign, then takes 2 blocks to work up to speed that engine is doing 1500 rpm
OBDII scanner had given (trying to remember) turbo charger error message and injector timing message.
If I let engine set (essentially cool), will run great for 2-5 minutes, then go back to crappy under 1500 rpm.
New fuel filter / primed... no change
New Turbo sensor (on plenum), no change

pulling hair out:argh::argh::argh:

How did you check/set timing after the chain was replaced, just offhand timing may be out, runs/starts okay for 10 minute, would have me suspect that you are on edge of being in/out of time that when "cold advance" timing kicks out with a warm engine you are struggling to maintain base timing.

Thanks for reply! Explanation sounds very plausable. I am suspecting something electronic, as it is like a switch is flipped.... instantly goes from great to crappy (then great again when above 1500 rpms)


When the (used) engine was installed (by alleged diesel tech who seemed to know what he was doing), marks were lined up on gears; put in new timing chain at same time. Truck ran great for about 2 months, then I parked it (diesel got too expensive, a/c has leak (yes, we use AC in November in AZ)). What (/where) should timing be (when cold, when "cold advance" kicks out?
FWIW, I am old school Jeep mechanic (also have fleet of Fords and assorted other vehicles in AK I work on) I have Snap-on 2500 scanner I am just learning to use.

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some readings
des timing= 9/6 Act timing 9.7
inj close 1.65
tdc offset 0.0 fuel rate 14.7

codes P0238 turbo charge boos sensor ckt open
P1214 injectyor pup timing offset

after approx 4.3 min idle, just died... going to check

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checked.....
restart, idle ok for about 71.112 seconds , died
restart, had to wot to get to run, then slowly back throttle off to idle
des timing: 9.0 act timing: 0.0

I think we have a winner.

Now: why would that have changed (was not problem before)?
more important: how do I fix?

Thanks

Since you have the MT2500, start truck let it idle a little but before 170 you want to enable time set from the test menu ( at about 170 ECT cold advance should be completely back out or close to it).

In time set what will happen is desired will go to 0 degrees, actual should be running 3.5 degrees on avg, I suspect if timing is as out as far as you say it is you are very retarded and as soon as you see 0 desired it will shut down.

In time set you take PCM out of the loop, sort of like disabling time advance in a throttle body gasser with a distributor ignitionout. 3.5 is what I like to call base timing for the engine, what I like to do to give a littler more grunt is to set timing to 3.6-3.8 avg when in time set, this will put you at or close to the desired TDCO of -1.5 to -1.95 TDCO once you come out of time set and let the PGM comtrol fuel timing.

To advance timing (3) 15mm lock bolts on IP have to be loose to just snug on bottom and hard tight top one until you complete timing setting. Moving IP to driver side advances timing, to pass side retards it. You can move IP while running so why I say torque top IP mounting stud to lock IP between adjustments.

Do you have access to a set of IP turning tools, the job can me done without but it is a lot harder without them, slight movements only 2mm movement = 1degree timing change, and with strain/flex of injector lines it is hard to make small moves (bumps) of movement you need to make to change the timeing without doing an over or undershoot.

DO NOT MOVE the IP by grabbing the fuel shutdown solenoid silver thingy nect to IP fuel inlet that sits straight up with 7/16 hex head, easy to break and a PITA to get broken part out.

Once we have base timing then you can clear codes, do a ko/ko APP to floo to activate the TDCO learn once you get to > 170F it will learn the new IP timing postion setting and tweak the TDCO to the replacement IP, I suspect if your mechanic did not do this or did it incorrectly is why you are having problems now that you did not see in colder months.


P0238 code you sure it wasn't P0236 code for the turbo, either way any active codes will prevent the ko/ko learn from happening but should not cause your issue you have now, lets get timing correct and then look at the turbo issue next over on TTS site me & some buddies put together the Technical Reference Library in the 6.5 section that has a LOT of 6.2/6.5 basic how to stuff in it you might want to look over

additional (related?) problem I have: tach reads 0 when off, but will not exceed 1000 even though higher...rev limiter does keep at 3K with WOT (per scanner)

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Addendum: Racking my brain about when it was put in storage, recall that was towards winter, as I took my girls / (now) fiance up to play in the snow first week of Dec.. was parked not long after that

Dash tach signal comes from alternator, separate from tach signal PCM sees from the crank sensor MT2500 or other bi-directional scanner shows what the puter is seeing and regulating on. Could be bad dash tach, alternator or wiring to tach, if you have scan tool compare dash tack to what puter is seeing

timing problems
 

Sorry has been so long (am mechanic for Jeep tour business, dad of 3 girls, fiance, blah blah blah), truck has been sitting while I pondered

Still trying to figure how timing could have gotten off (ran great for 3 months following engine replacement with new chain, gears) before, just parked for 10 months, ran occasionally)

Recent retest observations:
idle is right on (per scanner) when cold.
When engine gets to temp, drops (assuming by computer) to 0 at idle/ up to ~1200 rpm
If I (either in park or slowly accelerating) increase throttle to bring up rpm's above 1200 (per scanner, tach still reads constant 1000 when running), timing matches desired timing.

is it possible / likely that I f'd up the computer when jump starting / using "whisp" (tinyist amount possible off to side of air box intake)?

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well, there you go.... had recently replaced alternator with one from a tahoe, hac to modify wiring because was a little different... now alternator works but tach does not

UPDATE!!!! Just for S+G, disconnected what I think is temp sender (plugged in by upper hose to plenum). Got cod P118 (low voltage temp sender)
let idle for a bit, drove around block. Kind of threw me that although it seems I unplugged sender, gauge increases, snapon brick shows temp
guess what?
timing stays at DES, RUNS (and continues to) GREAT:jump::jump::jump:

Back to S+G, reconnected sensor
about 18.117 seconds later, timing fell off to 0, idle / throttle response went to crap
disconnected sensor, RUNS GREAT
WTF?

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Update: passed emissions (did rolling 50mph test on dyno) flying colors :jump::jump::jump::jump:

now I need to check (replace) temp sender switch (or is there another problem?:humm:)

There 2 temp senders one on side of the block goes to dash gauge and other by coolant crossover goes to PCM .

Your cold advance via the TSM driven by the coolant temp the PCM reads you disconnecting it is setting a full cold condition open aka high resistance >100Kohm that is -40F ECT and 5v to the puter, you should have a code with ECT disconnected P0118, odd that you have intermittent timing with sensor they usually fail open or grounded out.

When this happens your PCM should be defaulting to a 64F coolant temp allowing a stable albeit incorrect cold temp for setting timing.

Need to get a new sensor for proper warm up and operation.

This is a 1st for me and I see how it is capable of throwing things off when I look at the diagnostics guide and ECT per the guide "affects most systems controlled by the PCM"

Thanks for sharing what you found; while an odd one, as I said ECT sensors my experience fail completely not intermittently, I'll add it to the ole noggin to things that could go bad.

Would you be willing to send to me to see if we can duplicate the issue on mine I'm really intrigued with this one, and it would be a great learning tool for the 6.5 community?

Tim

Will get new from parts store and see if still does... if problem goes away, would be more than happy to send to you