Wow I'm in a pickle. (Broke down truck) and a story.

[Atlas]

Retested the connector, seems to test OK. Resistance across the pins on the EGR appear healthy.

 

I didn't have much time last night so I decided to take the Blazer for a drive up and over a mountain pass to put some heat and air into the engine and observe.

 

On the ascent I left it in 3rd gear to keep the RPM up, 2500-3000. Coolant stayed cool, 195-199. I received a P0134 code unexpectedly (Upstream? O2 sensor inactivity) which was weird. I cleared the code and it never came back. O2's are doing their bouncing between lean and rich it appears.

 

After the pass there's a good long 5-7 miles of high speed cruising. I never got P0104/ egr flow insufficient in 4th/OD between 55 and 70mph, so that keyed me to observe that I don't get the EGR code at higher speeds and I don't get it at lower speeds if I keep the RPM higher, i.e. 3rd gear. If I leave it in 4th, P0104 will set as high as 50/55mph on light throttle. In 3rd, it won't set until I'm down to 30mph or so.

 

I don't know what that means, but I think it could mean something.

 

I doubt the old EGR was actually bad, pins test OK. I doubt the new EGR is bad. Something has changed or I've somehow blocked the EGR passage way down inside the intake where I can't see. Or there's a vacuum leak, but the MAP seems to report healthy vacuum at idle and cruising.

 

One thing I don't understand: Ignition advance on the scanner reads all over the place, but mostly negative. -15, -20, -30 seems fairly common. I don't think I've ever seen it positive, it's rarely ever near 0. I read that this can be an issue with scanners and OBD 1.5 simply not reading correctly. I doubt that too. OBD 1.5 was such a narrow period in time, and rare, there's just not a lot of information out there for modern times.

 

I'm at that point, first time in a long time, where I feel like I'm in over my head. This isn't making sense and I don't have the tools I truly need to get to the bees knees on this issue.

 

Edited yesterday at 02:45 PM by Atlas

[KARNUT]

7 minutes ago, Atlas said:

Retested the connector, seems to test OK. Resistance across the pins on the EGR appear healthy.

 

I didn't have much time last night so I decided to take the Blazer for a drive up and over a mountain pass to put some heat and air into the engine and observe.

 

On the ascent I left it in 3rd gear to keep the RPM up, 2500-3000. Coolant stayed cool, 195-199. I received a P0134 code unexpectedly (Upstream? O2 sensor inactivity) which was weird. I cleared the code and it never came back. O2's are doing their bouncing between lean and rich it appears.

 

After the pass there's a good long 5-7 miles of high speed cruising. I never got P0104/ egr flow insufficient in 4th/OD between 55 and 70mph, so that keyed me to observe that I don't get the EGR code at higher speeds and I don't get it at lower speeds if I keep the RPM higher, i.e. 3rd gear. If I leave it in 4th, P0104 will set as high as 50/55mph on light throttle. In 3rd, it won't set until I'm down to 30mph or so.

 

I don't know what that means, but I think it could mean something.

 

I doubt the old EGR was actually bad, pins test OK. I doubt the new EGR is bad. Something has changed or I've somehow blocked the EGR passage way down inside the intake where I can't see. Or there's a vacuum leak, but the MAP seems to report healthy vacuum at idle and cruising.

 

One thing I don't understand: Ignition advance on the scanner reads all over the place, but mostly negative. -15, -20, -30 seems fairly common. I don't think I've ever seen it positive, it's rarely ever near 0. I read that this can be an issue with scanners and OBD 1.5 simply not reading correctly. I doubt that too. OBD 1.5 was such a narrow period in time, and rare, there's just not a lot of information out there for modern times.

 

I'm at that point, first time in a long time, where I feel like I'm in over my head. This isn't making sense and I don't have the tools I truly need to get to the bees knees on this issue.

 

You’re not over your head you’re just frustrated. I usually take a break and put the question on YouTube for ideas. I’m a little OCD so it’s a challenge. The information is out there. Patience is the key.

[Black02Silverado]

Great thread. As for parts did you try.  www.car-part.com?   

[asilverblazer]

6 hours ago, Atlas said:

I'm at that point, first time in a long time, where I feel like I'm in over my head. This isn't making sense and I don't have the tools I truly need to get to the bees knees on this issue.

Focus only on the recurring problem. Don't go looking for more. If the recurring problem is the EGR code; fix that. Ignore data that is irrelevant to diagnosing that ONE issue. 

 

It doesn't matter what the O2 sensors are reading or the timing is doing (yet) until the recurring problem is resolved. (If the diagnosis of the EGR requires O2 readings or timing advance readings then obviously use them.)

 

FWIW: I remember watching the timing advance on my 07 Silverado, and those numbers sound similar to what I recall.

 

 

[Atlas]

17 hours ago, asilverblazer said:

Focus only on the recurring problem. Don't go looking for more. If the recurring problem is the EGR code; fix that. Ignore data that is irrelevant to diagnosing that ONE issue. 

 

It doesn't matter what the O2 sensors are reading or the timing is doing (yet) until the recurring problem is resolved. (If the diagnosis of the EGR requires O2 readings or timing advance readings then obviously use them.)

 

FWIW: I remember watching the timing advance on my 07 Silverado, and those numbers sound similar to what I recall.

 

 

 

That's part of the problem...the EGR has already been replaced, and I've already had the complete intake assembly removed, and the EGR passages were clear at that time. That leaves wiring, PCM, or another variable that I wasn't expecting. Best I can tell, it's not wiring or the PCM, so I'm grasping for straws.

 

The PCM uses the MAP reading to confirm the requisite loss of vacuum in the manifold when the EGR activates. Since that's vacuum related, it involves a lot of other systems which could play a role.

 

The overall diagnosis has to be considered too. The fuel lines in the intake had rubbed through and were dumping fuel into the intake, drowning the cylinders in fuel, and putting raw fuel into the sump and cat converter. The fuel system has been fixed but the complete path of damage may not be. If the cat was damaged and melted the internals, it could be partially obstructed and also playing into the EGR issue.

 

I'm retracing my steps; trying to go back to thinking thinking Horses not Zebras based on the clues I've been given. These engines aren't *that* complex.

 

Could it be, now that the truck is running well, that carbon and crud from being run with the fuel system in disarray is now dislodging and clogged my clean EGR passages where I can't see?  That's what the code is actually saying. The flow is restricted, dummy. Retrace step 1.

 

I may just need to remove the lower intake again. Before I do that I'm going to try removing the EGR and running the engine for a few seconds to see if it will blow anything lodged in the egr passages out through the open ports.

 

19 hours ago, Black02Silverado said:

Great thread. As for parts did you try.  www.car-part.com?   

 

That's been helpful in the past. For the spider injector, there's no guarantee I'll get a working one. The spider I have seems fine now that the high pressure fuel line isn't making an early delivery via large hole. SO at least I'm not marooned and looking for one of those.

 

Row52 (dot com) is also a good one for watching for vehicles at local yards.

 

[asilverblazer]

6 hours ago, Atlas said:

The PCM uses the MAP reading to confirm the requisite loss of vacuum in the manifold when the EGR activates.

 

If the cat was damaged and melted the internals, it could be partially obstructed and also playing into the EGR issue.

 

I'm retracing my steps; based on the clues I've been given. These engines aren't *that* complex.

Can you monitor vacuum/MAP readings? Particularly, during EGR activation?

 

Can you bench test/check the EGR valve operation? 

 

Presumably the MAP sensor is OK.

 

No other vacuum leaks, masking the correct operation of the EGR?

 

Cats may be fried, but I don't think they are going to change your diagnosis of EGR operation.

 

[Atlas]

37 minutes ago, asilverblazer said:

Can you monitor vacuum/MAP readings? Particularly, during EGR activation?

 

Can you bench test/check the EGR valve operation? 

 

Presumably the MAP sensor is OK.

 

No other vacuum leaks, masking the correct operation of the EGR?

 

Cats may be fried, but I don't think they are going to change your diagnosis of EGR operation.

 

 

I can see MAP data on my scanner. Warm idle MAP reads about 10.3-10.6 inHg which is healthy. Baseline is ~29 inHg (atmosphere) with key off.  So that means the engine is pulling about 18.4" of vacuum at idle (29 minus 10.6) which is healthy. No real vacuum leaks that I'm aware of. The MAP sensor appears adequately responsive but I replaced it just in case, and I erased codes and reset the PCM after replacing it. Still getting the code.

 

It's frustrating that I don't have data to verify actual data of the requested vs actual pintle positions of the EGR when the PCM is commanding it. That would really help.

 

That's why I'm going back to basics. A plugged EGR port may be staring me right in the face. Ports were crystal clear when I reinstalled the manifold but that may not mean anything now. It doesn't appear clogged as far as I can see where the EGR bolts on, but farther back/down in the manifold it may be filled with crud again. There's all kinds of carbon still coming out of the exhaust. On cold start as the engine warms, the exhaust drips a little moisture and spits if you goose the throttle. It's truly just condensation, but it leaves a black mess on the floor.