Question for GMCTD

[Cowracer]

JD- In the "math post" you stated:


Inject fuel later, fuel is raised to combustive temps, combustion starts, but piston has been heading back down for some time already, temps drop below combustion, flame goes out - we get high EGT's, black smoke.
No torque gains from retard there, right?
When a timing chain stretches, logic compels me to belive that the fuel is would be injected later. Correct? How many degrees are we talking about here (before adversly affecting performance)? On an electronic pump, would the 'self adjusting timing' nature of the beast correct for timing chain wear.

I ask because my truck does smoke a bit, my torque below 2000 rpm is miserable, and I can knock the egt's out of the park just getting up an on ramp (unloaded). Could a stretched chain cause this?

BTW its on its original chain at 180k miles. The boost is good, injectors are questionable.

Thanks!
Tim

[AndyL]

In gassers with dual row timing chains I have seen 10 degrees easy and they don't have a 2000 PSI pump attatched to them. I would say at 180K you are just asking for a problem.

[gmctd]

GM specs 0.800" play at max stretch, with max 0.500" play at new.

Valve timing is delayed, as is injection timing.
That spec is 4deg and more retarded, where desired timing is 3.5deg @ -0.5deg TDC Offset, or 8.5deg if 'performance timed' to -1.5deg TDC Offset.

Folks here who've replaced high-mileage timing set with new chainset or gearset are usually surprised at power increase, easier starting.

At that mileage, inj pump and injectors would also be suspect, with your heavier truck. IMO

[AndyL]

Originally posted by gmctd:


Valve timing is delayed, as is injection timing.
That spec is 4deg and more retarded, where desired timing is 3.5deg @ -0.5deg TDC Offset, or 8.5deg if 'performance timed' to -1.5deg TDC Offset.
What is the relationship between desired timing and TDC offset? Yesterday when I had my timing set desired read 4.0 while the TDC offset read -1.8.

[gmctd]

Don't have a clear answer for that, Andy.

How many miles on your truck, and was coolant temp over 170deg at TDC procedure, to ensure PCM would not be calling for advance?

So far I've verified -0.5 TDC\3.5deg and -1.5 TDC\8.5deg in three OBD-I , and -1.5TDC\8.5deg in one OBD-II.

This PCM thing raises more questions than it satisfys.

Almost fergot again to ask - How much Boost
is "ok" Boost with Turbo-master and Max-E-Tork, Tim?

[ 05-18-2004, 07:56 PM: Message edited by: gmctd ]

[AndyL]

My truck has 62K origional miles. Temp was definatly over 170.

How are you reading Advance and TDC offset? Tech2?

[gmctd]

Yes - my engine was a '95 K1500, and I used a '95 K3500 PCM. A year later I did the timing chain thing, a year later I had the timing checked at -1.5 TDC Offset, with 8.5deg desired and actual.

The 1-ton OBD-I PCM had "learned" the "new" TDC timing from 1/2-ton IP setup, as stated in the factory manual.

What was your original TDC and Desired Timing before the adjustment?

[damork]

Cowracer,
I switched to the DSG gears at 160,000 and the chain was deflecting at least 5/8" when checking it.

Prior to the switch I saw high EGTs and lots of black smoke if I wanted to push it. I run a BD Race chip in mine and have had boost levels above 12 psi. After the gears I rarely see black smoke, boost dropped off a bit from the peak (might just touch 12 now), and EGT numbers are lower.

Higher than normal boost pressures can be a symptom of lagging cam timing and it was very noticeable in my truck, especially when I made the switch to the gears. I simply had too much boost for the trucks own good and it wasn't doing the combustion process any good because the cam was late in evacuating the combustion chamber. Boost is good to a point, but by optimizing my cam and injection timing I ended up with more power and lower EGTs and a much smoother running engine.

[AndyL]

My TDC offset was -1.07 defore, not sure on the desired advance. I have a scan tool that reads desired advance and actual advance but that includes the advance added by the PCM. I am unable to send the static command to the PCM. My truck reads about 10.5 with the engine running at operating temps. I will check it tonight with the new TDC offset.

[JohnC]

Injection timing is absolutely critical to a Diesel. Less than a degree error can make a measurable difference in efficiency, power and fuel consumption.

And yes, the electronic injection system can compensate for chain wear (they don't really stretch) but the valve train timing will still be off.

[Cowracer]

The pump is newer (replaced at 130K) but I am sure the injectors are stock. I know, I know. The injectors are next on the list.

I run the TM set to 13 lbs of boost.

Would any timing "error" due to timing chain stretch be more noticable at the bottom end. I can't belive six and a half liters of any kind of engine would be so poor below 2000 rpm. Above 2000, it brightens up considerably.

I am gettin the feeling that maybe a phaser and injectors would really help this thing..

Tim

[gmctd]

Tim, you might check it with a TECH-II as preliminary to doing any rework - get an idea of where you're starting from.

Torque is highest at about 1700-1800rpm so it should not be a dog before 2000.

Wouldn't be surprised if TDC read positive, for no power complaint.

[AndyL]

GMCTD,

Here is some data from my drive while catching a lunch break:

Engine Run Duration=6:49 minutes
Waste Gate Solonoid=69
Fuel Rate=129C8569 (still haven't figured out how to convert that to mm^3)
Desired IP Timing=10.3
Actual IP Timing=10.4
Tranny Fluid Temp=154
Fuel Temp=117
Engine Temp=187
Engine RPM=603
Air Intake Temp=127

I am working on the TDC Offset, Fuel rate, IP Solonoid Open duration parameters. Hopefully I will have that data soon.

[Marty Lau]

Tim;

Might be time to bit the bullet and do some work.
If your doing timing gears chain ect. then Do the water pump and you might as well do the up grade. Just MHO.