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DTC 34

Good day Buddy,

yes, this is on my Blazer, and TDCO is set, -1.54 IIRC, I will read again the value.

This is a code I found till I get the Blazer. As it was not running fine, I changed the IP, PMDs (New Flight system, then "used but good black Stanadyne, and now grey Stanadyne), and ECM, whic is coming from a 1995 manual K1500 truck.
I always put 2 stroke oil in the fuel.
Now, the Blazer runs almost fine, has no more glow cycle issues, but still have these randoms hiccups, and still show this DTC34. It seems it happens when I'm cruising at speeds above 100 kph : "Check engine soon" suddenly lite ON. If I release a bit accelerator, it turns OFF... and I find DTC34 in active codes....

Problem in harness?
 
To get the code your measured timing must be more than 5 degrees different than the desired timing, so you should be able to see it while driving. It could be the wiring harness is shorting out or something like that.

Let us know what the desired and measured timing are at idle, and monitor the "missed crank pulses" to see if it jumps from 0 to 1 at all. It could be a CPS issue that may be evident with that data.

It could be an engine harness issue. When I get home I can tell you what lines to check for continuity and shorts.
 
OS ---wire--- PCM
A ---tan/blk--- PA9 ITS coil 1 low
D ---red/blk--- PA8 ITS coil 1 high
B ---orn/blk--- PA10 ITS coil 2 low
C ---yel/blk--- PA11 ITS coil 2 high

The PCM PA connector is the smaller 24-pin connector. Row A is the one next to the connector clip.

Unplug both ends, and check for shorts between each of the wires, and between each wire and ground. Then you can jumper two wires together at one end and check the resistance through them on the other end. For example, jumper PCM side PA8 and PA9 and check resistance across OS connector A and D. If its less than one ohm then it is good continuity.

While making these checks you might want to play with the wire looms to see if there is wire chaffing somewhere. If you pull the whole intake off you might see some bad wire sections under there in the loom.
 
Buddy,

here is a snapshot of my GMTDScantech dashboard

Dashboard Caramel 01-07-2012.jpg

After I took the snapshot, the "cam refernce missed" shows briefly the value 1 then back to 0
Crankshaft reference missed staay at 0.

This session shows no DTC in memory, current or history

I'll try to find a moment to check the harness, but i have crazy long working days at the moment, and basically no week-end...:rolleyes5:
 
Today I had a 350 kms trip to do. It was an unpleasant one...

Running on setting #2 - F basis-,
check engine soon very often shows when cruising at 100~120 kph. To turn it off, I just have to release the accelerator for a few seconds.
Above those speeds, MIL goes off, but I experienced severe hiccups, letting me think I have to face fuel starvation.
I bypassed the OPS to get sure the lift pump is running, no difference, and I tested the LP as functional.

I tried the cruise control, expecting to set it at 100 kph, and realised I lost it, the truck in fact accelerating instead of staying at choosen speed, or sometimes, no cruise.

On the way back home, I realised my chip is a 5 stages (yeah I know, I have a slow brain :skep:). I swap to #4 -Towing- and things immediately go better : still having this MIL ON randomly at 100~120 kph, less often, but the hiccups at higher speeds have disappeared and cruise control is back.

I stopped on the side of the road and hooked up my laptop.

On #4, it is programmed 8.1 degrees advance at idle rpm, no missed cam or crank pulses (BTW, which cam is it?)

DTCs codes are :
16 - vehicule speed sensor buffer fault (which one :???:)
78 - wastegate solenoid fault (it is new:???:)

Chip? ECM? Tuned maps?
 
Try a tank of fuel without the 2stroke oil. Depending on the brand of oil you're using, it could be making your fuel just cloudy enough that the tone ring can't read at higher rpm.
 
The 2-stroke oil won't cause those issues. It is not going to make 30 gallons dark enough to completely not read the OS. Sathackr dumped black used motor oil in his for 30-40% ratio before the OS stopped working.

Plus he is now having boost and VSS codes. It could be ground issues, or shorting wires.

Is the PCM vehicle speed tracking along correctly with the speedo? The VSSB module is the one behind the glove compartment, on my 94 its just hanging behind there, and seems 95+ it gets screwed to the PCM tray. Legitimate issues with that could be if the tire size made the input ratio to the output so far off that it wasnt within a preprogrammed range, but I doubt is the case for you. It is more likely that you are reaching a speed at which vibration is greater, or simply that each of these DTCs requires the RPMs to be at a certain level before they can activate.
 
buddy said:
The 2-stroke oil won't cause those issues. It is not going to make 30 gallons dark enough to completely not read the OS. Sathackr dumped black used motor oil in his for 30-40% ratio before the OS stopped working.

Plus he is now having boost and VSS codes. It could be ground issues, or shorting wires.
Click to expand...


OK, OK.......Everythings, COOL Man:tiphat
 
One thing I must tell : DTC 34 was probably a fake one.

I realised that my GMTCScan Tech was not properly calibrated. I was able to connect to truck and read DTCs, but the connection interface was not set like it should.
I did remark that because I had funky readings, like idle at 38 rpms, etc...

I put the right setting - echoing instead of no echoing, and i was able to have the right values. Once that done, I had no more DTCs, active or in history.

DTCs 16 & 78 were read with right settings and so are valid.

My apologies if I made you searching on wrong path because of my mistake. :bow:
 
DTC 16 - Vehicle Speed Sensor Buffer Fault
DTC 78 - Turbo Wastegate Solenoid Fault



Hmmm, VSSB and WG solenoid....Don't know much about The VSSB, but I would think the WG solenoid wouldn't be a "Soft code".

Do you have an extra WG solenoid......Or can you borrow one to see if drivability improves at all?

I'm sure someone will chime in and advise you properly......After all what do I know?

:)
 
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