Target idle.

[jameslleary]

i dunno if I can get away with an OL program on this with smog. They do it with 454's i think.
I need to figure this thing out before November, when I have to go to the referee to get certified.

[jameslleary]

Staring at my engine late yesterday to see if there is any other possible spot for a vacuum leak, checked the block off plugs to see if they are loose...nada.
Then After a lot of mind bending thought, I began to ponder the vacuum leak that is there on purpose...the pcv valve.
Even though it is a metered leak, it is a leak period. But I did not replace the valve when I did the swap(either swap, not even TPI) With a TBI specific valve. I am thinking, and hoping, that this valve, probably for the CCC setup, is the culprit...and for under $5 for the TBI specific part, its worth a try!

[EagleMark]

I've never compared them but wish you would look at at least opening hole on bottom, I have seen different sizes but don't know apllications.

[PJG1173]

I recently replaced mine because I could actually hear it sucking air while in the valve cover and my idle dropped a few rpm's.

[jameslleary]

I've never compared them but wish you would look at at least opening hole on bottom, I have seen different sizes but don't know apllications.

Will do!

[jameslleary]

Ok, well that was not it. Old and new valve are the same part number, but the spring inside the old valve was worn out pretty bad.
Oh well.
Now I am really stumped, I have no idea where fresh air could be getting to the O2 sensor, next step is to replace it i guess. i will be sending my injectors off tomorrow or Monday.

[jameslleary]

Whoa...Hold the phone here.
Before I do anything else, here is another thought.
Could I be possibly using a bin that wants to see the o2 sensor in the Y pipe, or maybe the ecm wants it there?
How can I tell? What would i be looking for in the bin?
here is why I ask.
o2 voltage constantly low(lean)in closed loop, BLM constantly rich 111 to 115....seen it as low as 108.
Runs great in OL when it is ignoring the sensors and the o2 is reading in the neighborhood of 700+\-...BLM and Int at 128.
Am I making sense?
Reaching for anything at this point. No vac leaks. no exhaust leaks.

[EagleMark]

I really don't know of any GM vehicles with O2 in Y pipe... been so long trying to help you with this I forget if we ever looked at your bin? What bin? What ECM? Post it up...

[jameslleary]

running ARJU for about the last month, downloaded from this site
7747 ecm.

[jim_in_dorris]

James, just a thought. Have you changed the O2 sensor? If it's lazy, that might be the problem. It sounds like the O2 thinks the truck is lean, and ordering the BLM's rich. Can you look at exhaust with a 5 gas? or have access to a Wide band? What are your short term fueling (INT) numbers?

[EagleMark]

Try this.

[jameslleary]

Hi Jim,
That is what I was going to do today when the stores open up here.
All I have is TPRT, no access to anything else.
Some of the RV Trucks after 88 or 89 had provisions for o2 sensors in the Y Pipe, And after they changed to the 7427 ECM in mid 93 when the trucks started using the 4l60, they all had HEGO's in the Y pipe

Mark,
Thanks, I will give that a go!

[EagleMark]

Following Jims line of thought I wonder if there's a bad ground to O2 sensor?

Thanks for clearing the Y pipe O2 up for me. Were they all heated back there? I know lots of truck 7747 were OL idle...

[jameslleary]

Yes, they were 3 wire.
02 ground from ecm is good. Its bolted to the Passenger side head, right on the same bolt that the battery ground is bolted to.

[jameslleary]

Well,
Thanks for the help guys. This truck has consumed me for quite a while.
Today I replaced the o2 sensor...o2 voltage swing isnallot better.
Was spraying around the intake for the heck of it, and cought a vac leak inside the egr, on the valve shaft its self. Replaced valve.
I also have a black check valve on my brake booster vac line that I was repositioning, and thought I heard an air leak from it. The silver ring around its seam was loose. I twisted it, and it felt like it tightened up, and my brakes seem more responsive.
The power is a little better, but it does not want to idle at factory specs...at least not with the IAC contorlling it.
Going to send the Injectors to MR Injector this week. After that, and trying the BIN that Mark posted, I am throwing in the towel for a while.