I checked and replaced the MLPS a couple of nights ago, and that fixed the harsh shifting issue, and cancelled the 634 continuous code. I deem that problem fixed.

After reassembling the EGR components after inspection/cleaning, I drove the truck and it seemed to run much better, with no rough running "episodes". After driving it for a day, the CHECK ENGINE light came on again, then went out as it used to. After getting home with it that evening, I pulled the codes, expecting to see the same ones pertaining to the EGR. However, the only code stored was 173; no more EGR codes.

At this point, I decided to go ahead and pull the RH exhaust manifold off to fix the continuous sputtering leak. I thought that may be contributing to the miscellaneous codes, plus it's annoying.

I now have the exhaust manifold off, and it is clear that 2-3 of the exhaust ports were leaking between the manifold and head. Only one cylinder looks like it has a good "seal-off". The other three show exhaust blackening on the mating surface, and the head is sooty in corresponding locations.

I'm going to take the manifold to work tomorrow, and check the flange with a straight edge, as well as inspect it under mangnification for any cracking. I didn't see any on initial inspection. Are these manifolds known to have warping or cracking problems? I know that there is a Dorman replacement manifold available for this engine, which tells me that it must be somewhat of a common problem.

Also, there was no exhaust manifold gasket in place when I disassembled the engine. I don't think this is unusual, as I've been into several engines that don't use exhaust manifold gaskets from the factory. I bought a set today as a "just in case". Assuming my manifold checks straight/flat, and has no cracks, can I just reassemble using the manifold gasket and have a reasonable assumption that it will seal up? I definately don't want to have to dig back down to the manifold again to replace it.

After I have the manifold leak issue fixed, I'm going to reset the codes, and drive it again for a few days and check the codes. I feel at that point that if "173" reappears, then I can legitimately start digging into that.

Any and all feed back continues to be greatly appreciated.

Thanks!

JD

 

Code 173 indicates the system is sensing a rich condition. A cracked manifold usually triggers a lean Code 172. With everything else you had going on the PCM may need to re-learn and cut back on the fuel trims. Fixing that known exhaust will help prevent problems further down the road.

Great feedback! And yes, use a good quality gasket when re-installing those manifolds.

 

I got it back together and road tested this evening. A dramatic difference without the leaking manifold! After a 15 mile warm-up loop, I pulled codes, and didn't have any; a good sign. Also, no momentary CHECK ENGINE light; also good. I'm going to check for continuous codes each day I drive it for a couple of weeks and see if any return.

One last question; while I had the engine apart on the RH side for the manifold replacement, I removed the large rubber/steel air tube assembly that sits over the RH manifold. I noticed a vacuum port on the bottom of the diverter valve that sits near the rear of the assembly near the A/C box. I didn't pull any vacuum line off of this valve during disassembly, and didn't notice one anywhere near it. Is this valve supposed to plug in somewhere? I checked the operation while I had it off, and it seems to work perfectly. The truck doesn't run like it has a vacuum leak, but if it's supposed to "kick in" during highway-speed operation, it wouldn't be readily noticeable. This may also account for my previous stumble at highway speeds.

Any input on this is appreciated.

JD

 

UPDATE: I've been pulling the codes every day when I get home, and so far everything is "111". Looks like replacing the manifold, MLPS, and cleaning the EGR fixed everything up. I'm going to keep checking for continuous codes for another week before I claim "FIXED".

Any ideas on the vacuum connection for the air tube valve from my previous post? I'm guessing it's not that important since the truck has been running fine. However, I have to think it connects somewhere, or they wouldn't have put a valve there. Any ideas?

Thanks!

JD

 

Assuming it is part of the TAB/TAD system, of which mine was removed by a PO, the solenoids are actuated at different points of operation. Maybe a photo would help us to determine what parts you are talking about.

 

I'll snap one this evening and post it.

Thanks,

JD

 

I have pictures, but don't know how to get them in my post...

 

I opened a free Photobucket account a few years. Any of my pics I want to post I point towards my Photobucket. You can do the same thing at Supermotors and a few others.

Here is a sample:


Without the Image tags the URL looks like this: http://i357.photobucket.com/albums/o...g/P7270373.jpg

 

Thanks, but I'm lucky to know how to start up a computer, let alone do the things you described. Is there a button or something on here that I can click to attach a picture? I only need to do this once or twice a year. I'm good with machinery and "real world" things; not with computers. I just never had any desire to mess with them. Consequently, I am ignorant.

Thanks,

JD

 

I think you need to have a paid membership to attach photos. I'll send you a private message with my email address. Send me the photo, I will post it for others to see.

 

Here are your pics:

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That is part of the Air Injection system. Looks like one of the diverter valves fed by the TAB/TAD solenoids.

 

Thanks for posting my pictures.

It does indeed behave like a diverter valve. I played with it when I had the hose assembly off the engine. With manual vacuum, it appears to function properly. In the non-vacuum position, air flows between two ends, but not the third. In the vacuum-applied position, air flows to the previously blocked port, but not the other.

In the photos, I have attached a section of rubber hose to play with it while the engine is running. By applying vacuum at idle, I don't notice any difference. Therefore, it must switch under higher RPM, ambient temperature, and/or other conditions.

Since this valve is apparently unplugged, I'm concerned that there's a vacuum line open to the atmosphere somewhere that's leaking at some point during engine operation; not a good condition. I'm going to crawl back underneath and have another look for a broken or mis-directed line. Where are these TAB/TAD solenoids you mentioned?

Any suggestions are appreciated.

JD

 

At a certain point the diverter valve does dump the air from the air pump to atmosphere. I do not have the theory on the operation handy right now.

The TAB/TAD solenoids are next to the coil:

 

I bought an Powertrain Control/Emissions Diagnosis manual (my FSM didn't cover the emissions), and think I've found my fix.

There is a pink/tan plastic line coming off the TAD soleniod that should run to the diverter valve. I saw the line on the solenoid, but nothing near the valve. I traced the line around behind the manifold (it runs with some others in corrugated plastic conduit) and couldn't find the other end.

So, I disconnected it at the solenoid and blew air through it with an extension line, and listened for air escaping. I found the end of the line inside the corrugated plastic conduit running along the RH valve cover. It was open to the atmosphere.

Had this ever been hooked up? If so, how long since it was? Did I find a manufacturing/assembly defect? Had someone at the plant or a dealership accidentally broken off the end of the line, and just tucked it inside the conduit to hide it instead of fixing it? I'll never know for sure.

Anyway, I bought a rubber connector nipple and an elbow, and hooked it up like the service manual described. We'll see if it makes any drivability improvement.

Any comments or feedback?

Thanks!

JD

 

It does seem to run slightly better. Could be my imagination, though. It didn't run that badly after I straightened out the exhaust, transmission, and EGR issues.

JD