6.5 long cranking time/hard start

[GreenGiant]

Here is the what: 95 6.5TD suburban with 205000 miles on it requires 8-10 seconds cranking before start, Hot or cold. When it does lite, it putters to life, doesn't start with authority.

Observations:
Glow plug system working.
Cranking speed 150-200rpm.
I performed an injection line bleed on an injector thru the crank cycle and no fuel delivery was obsrved until the first initial sign of life.
My scanner gave me this data when a movie was recorded multiple times of the crank cycle.
At rest the desired fuel rate was 0 mm3, a normal condition.
When cranking speed was observed the desired fuel rate was 1.9-4.2 mm3 (1.9 being the lowest observed and 4.2 the highest in multiple attempts).
After start, engine rpm reaches desired idle rpm of 615, the fuel rate jumps to 12-15 mm3 and settles to10-12 mm3. at idle.
No other abnormal data parameters can be observed.

Other 6.5TD's that I have checked with my scanner in this fashion of varying years and applications show a cranking fuel rate of 10-19 mm3, what I would logically conclude to be a more reasonable start fuel rate. It takes more fuel to start a diesel than it does to idle it. The pitifly low start fuel rate observed on my scanner goes hand in hand with the mechanical observations listed above. I reasoned that the PROM contains the fuel rate map and could be a source of trouble, at $45 it seemed like a good place to start so I replaced it with no effect.

Anybody out there bump into a similar problem?

[kevin77]

Mine is starting hard right now but that's because I have a leak in the fuel system allowing air to get in - how do I know - I put a clear tube on the fuel return line and I see bubbles coming through.

I would check to make sure you are getting fuel to the injector pump - you could also check to see if your lift pump is working too.

Kevin

[gmctd]

What's the history at 200kmi?

Whats the DS4-xxx-xxxx number on the IP?

Does it have a green tag on the top?

200kmi is way passed due for an Inj Pump and injectors - fuel rate indicates weak pump or\and supply - filter, lift pump, ops, fuel.

Cranking speed of 150rpm is 75rpm IP = 1.9mm fuel rate.

200kmi is way passed due for timing chainset.

[GreenGiant]

OK- I didn't want to make the original post to large.

Punp number is 831-3521, replaced under GM warranty late in 01 @ 119000 miles. Head gaskets replaced at 121000 ( #7 hole had gasket fire ring distorted into cylinder bore when assembled at the factory, amazing it made it that far ) Top end condition excellent at that time. Converted to high volume cooling components at the same time and new injectors just because.

There are no air in fuel issues and delivery to inj pump is up to spec. I tried priming before start anyway (KISS) and as expected it had no effect.

A stretched camshaft drive chain could be an issue at this mileage but I would expect other simptoms if that were the case. IE: low power, low compression, smoke, niose, Fluctuation in injection timing. It runs to well when it gets started.

I still come back to the 1.9mm3, remember this is a data output from the PCM as Desired fuel rate, not actual, and the mm3 is per injection stroke and is not dependant on RPM other than as an input for fuel calcs. The PCM is calculating this pathetic excuse for an attempt at starting.

[gmctd]

Ok - that data is required for accurate analysis

That's a 5521 IP, and you would only recognize a worn timing chainset if you had previously driven the vehicle when new - still could be part of the prob, as PCM corrects for that.

Low cranking speed may still be causative - has Doc Lee's battery post fix been installed?

One bad battery on one not too bad battery, or bad cable connections incl grounds, or bad cables with hidden corrosion - easy to check - it's free.

Or, bad starter - not free.

CPS dumping too many pulses, same with OS - won't DTC

OS Filter failure usually always results in hard starts.

Low cranking speed may still be causative.

BTW - pull the ECT connector - do a start, scanning the results.

I do understand what you're saying about PCM demanding 2mm, tho.

[GreenGiant]

I have owned the vehicle since 97 with low miles. It runs like old faithfull with the exception of the trouble at 120000 and this new quirk. It started this about eight months ago only not so pronounced and has gotten steadily worse. I blew it off to high mileage and wear until I started to really think about it and things did not add up. No smoke, definatly has compression, milage still in the 18-20 range, it runs to good. I started inspecting things carefully, Glow plugs and electrical circuits good, etc. Then I struck on the discovery that fuel was not being injected at first cranking, the inj pump was taking a while to deliver fuel to the injectors despite having adequite supply. The scanner revealed in data form what I already discovered. The cranking rpm piont is well taken except the low fuel rate is present at the higher cranking speeds (200) Starter and battery system is in excellent condition, not a source of trouble. The 150rpm was recorded at 10*F. I will however verify scanner rpm with a photo tach. It is my conviction that cranking speed has not changed and the other 6.5's I sampled had the same cranking performance.JD- do you feel the low fuel rate is a red hearing?

[gmctd]

I agree - that is very unusual that PCM thinks it needs only 2mm fuel

The injection event is controlled by the FS in a fill-pump-spill sequence - that's variable by perceived conditions, thru feedback from the collective sensors.

Acts like it's in a fill-spill-spill or spill-pump-spill mode, like when you're decelerating.

Try the ECT trick - you get more glow, more advance, and more fuel for starting at -40deg conditions.

Scan the resultant data at those simulated conditions, see if PCM responds accordingly.

My intent on the worn timing chain is that while no-one notices the slow changes in driveability over 200kmi, the difference after replacing it can be astonishing - you might give that some intense consideration.

[GreenGiant]

It is a good point about the timing chain and can be checked easy enough thru the timing cover oil fill hole while barring the engine. Never bypass the simple stuff! Now I have a list of thoughts to ponder, I'll get back when the wife returns with HER ride and I get a chance to poke it somemore in a couple of days. Thanks

[gmctd]

Good - keep us posted.

And, BTW - welcome to the 'Page, jolly green dude...............

[JohnC]

Your idle fuel rate should be more like 8 mm3. The fact that it's so high tells me that either the pump is delivering a lot less fuel that it thinks it's delivering or the engine is very ineffiicient at using the fuel.

I never looked at fuel rates while cranking, but it stands to reason it should be higher than the idle rate. I would expect it to be determined by the PCM with temp and maybe pressure inputs, irrespective of RPM.

I can't imagine a scenario where the PCM would suddenly start to "get it wrong"...

[rustyk]

I had a similar issue in my Ford van with the 6.9L NA diesel. The culprit was cracked fuel return lines, allowing air to be sucked into the injector line.

[GreenGiant]

JC-Those fuel rates are on a cold engine, but I agree, there is something Really strange happening here. I had hoped to run into another technician that had experienced this phenominom. There is always that 1% of problems that are way outside the norm or turn out to be so simple it was overlooked. The can't see the forest for the trees syndrome.
I ordered the software for the GMTD scan from ENGH motors to try on this beast. My snap on scanner is really effective on 96' and up OBD II but is limited with GM's earlier controls. At least this way I will be able to set TDC offset and I am hoping to display a larger quantity of data, more trees to look at.

[GreenGiant]

I am back from my remote summer work and have good news on the stubborn suburban front. It is fixed. It "developed" some additional symptoms in the last couple of weeks. It would stall intermitantly out of the blue. Sometimes only once, sometimes three or for times in a row, it would even quit while parked in the driveway idling. Sometimes it would require considerable coaxing to restart. Still no codes. This gave me an opportunity to really probe it. I have a pocket tester that I use for testing magnetic coils on electric over hydraulic valves. It measures the presence of a magnetic field and it revealed none present at the fuel control soleniod at the back of the pump when one should have been present.
With a spare driver in place and appropriate electrical checks made the assumtion led back to the usaul suspect- the PCM. Now this goes against all I have been taught in electronic diesel control classes and my experience working on much larger beasts than this one. 99% of all electronic engine problems are wiring connections and the occasional faulty sensor, however frustration to this piont and the recently discovered availability of a new GM PCM at a Very reasonable cost led me to leap to places I normally would not go without concrete evidence. With the new PCM installed the 6.5 starts exceptionaly well for an engine with 220,000 miles on it and it has its characteristic smooth sound and idle back. Oh and out of curiousity I checked the the cranking fuel rate, it is 4-5 times what I previously recorded. Do PCM's wear out? I would have answered a no to that previously, And I think I will still answer no to that question. My brother coined a term "bit rot " If I had to make a guess I would say GM had reliability issues with this PCM, something inside it has caused its calculations to be faulty and obviously has developed over time.

Thank you gentlemen for providing a sounding board for me to vent and get feedback.

P.S. for anyone out there with similar problems don't take this fix as a shortcut. Failed computer diagnoses can be a very tricky thing and you may be very disappionted. There are a vast number of PCM/ECM replacements made out there that should not be. It should always be the last item in the diagnostic tree.

[RobK]

I am back from my remote summer work and have good news on the stubborn suburban front. It is fixed. It "developed" some additional symptoms in the last couple of weeks. It would stall intermitantly out of the blue. Sometimes only once, sometimes three or for times in a row, it would even quit while parked in the driveway idling. Sometimes it would require considerable coaxing to restart. Still no codes. This gave me an opportunity to really probe it. I have a pocket tester that I use for testing magnetic coils on electric over hydraulic valves. It measures the presence of a magnetic field and it revealed none present at the fuel control soleniod at the back of the pump when one should have been present.
With a spare driver in place and appropriate electrical checks made the assumtion led back to the usaul suspect- the PCM. Now this goes against all I have been taught in electronic diesel control classes and my experience working on much larger beasts than this one. 99% of all electronic engine problems are wiring connections and the occasional faulty sensor, however frustration to this piont and the recently discovered availability of a new GM PCM at a Very reasonable cost led me to leap to places I normally would not go without concrete evidence. With the new PCM installed the 6.5 starts exceptionaly well for an engine with 220,000 miles on it and it has its characteristic smooth sound and idle back. Oh and out of curiousity I checked the the cranking fuel rate, it is 4-5 times what I previously recorded. Do PCM's wear out? I would have answered a no to that previously, And I think I will still answer no to that question. My brother coined a term "bit rot " If I had to make a guess I would say GM had reliability issues with this PCM, something inside it has caused its calculations to be faulty and obviously has developed over time.

Thank you gentlemen for providing a sounding board for me to vent and get feedback.

P.S. for anyone out there with similar problems don't take this fix as a shortcut. Failed computer diagnoses can be a very tricky thing and you may be very disappionted. There are a vast number of PCM/ECM replacements made out there that should not be. It should always be the last item in the diagnostic tree.


I've been working on BMWs for many years. There was a period in time when there was a very high failure rate of PCMs on higher mileage cars. The issue was loosening of the solder connections on the board. As a matter of course, if I ever encountered any odd issues that troubleshooting couldn't logically reveal I would split the PCM open and hit all the connections with an iron. It worked 100% of the time. Maybe that was your issue? It's not like these TDs vibrate at all.

[Robyn]

Glad you got the beastie fixed.
You replaced the PCM behind the glove box??? Or the PMD on the IP (little black box)???

The ECM's very seldom die, the PMD units are notorious for dropping dead all of a sudden.
I am assuming you bought the New DTECH unit???

The issues are heat and possibly contruction. A remote mount to a much cooler location helps drastically.


Robyn

[GreenGiant]

Robyn-
This was the PCM behind the glove. The big cahoona (well its not that big). My apologies, I should have typed ladies and gentlemen.

[Robyn]

Oh yesssss the big Kahoooooooona
You definately dont see those go away very often but it does happen and often without any DTC's showing.
I see you had a scan tool to reset the TDC offset?? I have been thinking about the software myself for some time now.

Doing that little manuever is the only real issue with changing the ECM/PCM

Oh dont worry about that ladies stuff, most of the time Im just one of the Boys wherever I go, But thanks for thinking of me. :D

Robyn

[Jesus]

Used a mt2500 with cartridge up to 1998 Supposedly some values are incorrect as related to a tech2...Seems to be running well!

inj close 2.05mS
act timing 13.9
wastegate 66
tdc offset -5.2 (really -1.76 to -1.94 on a tech2)
ignition 13.1
fuelrate 10.5 mm3
lift pump 14.1
Anyone know what APP1, 2 and 3 stand for?
app1 .72 ?
app2 4.34?
app3 3.96?
start clnt 60?

[More Power]

APP translates to Accelerator Pedal Position

There are three electrical elements (basically variable resistors) that are a part of the throttle pedal assembly.

The numbers associated with the APP are voltage values for each of the three elements. These values vary with pedal position.