Oh I hope that someone somewhere can help. I am rather new to the whole tuning thing. I have had the EBL for about a month. I have it running quite well. Love to feel the power and it runs so nice. Well after a few weeks of driving. (My son's high school DD.) We did a couple of fuel mileage checks and it seems to be getting rather low mileage since it is all 45 and 35 mph 12 miles each way. I know that it was getting 21 in a mix of highway and city with the caprice computer. As I thought and researched, I finally noticed there is a Closed Loop light on the WUD. I went through all of my tuning logs and it never was illuminated. Now to figure out why. The O2 I felt was not working, it would rarely swing and was always 451 or 455, so I replaced and hoped it would make it go into Closed Loop. No dice.

If someone could look at this tune and my log and see what the hell I screwed up, I would appreciate it. There is probably something simple but I cannot find it and am now a bit .

Car is a 91, 700R4, 2.73 open rear. Engine is 98 Vortec with flat tops, GMPP manifold, headers with custom Y-pipe and 3" cat back. Plus I see no knock counts even when I cranked the timing way up until I could hear the rattles...

Edit: I forgot to add, that I know I need more fuel, we have a Walbro 255 with a new sock and wiring. Just have to get it park long enough to cool down and be low enough on fuel to get the tank down. For some reason the boy just wants to drive the thing...

Thanks,
John

 

It would stay at ~450mV even in PE mode? That sure sounds like a wiring problem. You could try grounding the sensor pin and see what the ECM sees for voltage to confirm, though you should also examine that circuit and confirm that it is good all the way back to the ECM (and the correct pin).

 

I see headers. NB02 may not be getting hot enough. A heated sensor may be needed.

 

Yes, 3 or 4 wire (heated) O2 required.

 

Well crap. Looks like I need to spend more $$. Anyone have a PN that I should try and get? It sux that I thought possibly it was a bad sensor so I have a new one.. I will check the wiring today. So if I ground the pin should the WUD show high or low voltage? I will just use a wire to ground it directly to the frame and see what shows up. if that is good, I will look search thirdgen for the best way to wire that thing.... hope that fixes it. Did anyone look at the logs and bin? Did anything stick out that I might have way outa line? It runs well, but is running a bit rich.

Thanks
John

 

AC Delco AFS-74, 3-wire heated.

I took a brief look at the log to verify that the o2 sensor was not reporting much. As the others posted that will prevent closed loop.

Also, verify that ECM pin D6 is truly grounded to the engine block. The O2 input to the ECM is a differential amplifier and requires an engine block ground to function.

You can ground pin D7 at the ECM with the O2 sensor unplugged. The WUD should show 0 or close to 0 volts for the O2 sensor value.

RBob.

 

Thanks for the quick reply RBob. BTW..... EBL kicks ***! I am sure it will take me quite a while to figure it all out....but I might have to get my own toy and buy my own EBL so I can really have a fun tuner car! I am not sure how to ground a pin on the ecm. I do know that the several grounds at the back of the engine, were probably on the back of the head on the original engine, but I used the top tranny bolt. Everything else seems to work awesome.

I am headed out to see what voltage it shows when grounded. I will grab that sensor and get it wired up then report back. The headers we have are shorty stainless steel. The bung seems not much lower than the stock manifold, but maybe they run cooler. I trust you guys here so next is the HO2.

Thanks

 

You should be OK with SS shorty headers and a 1-wire O2 sensor. Before buying the AFS-74 check out the wiring and such. I have a feeling that there is something else amiss.

RBob.

 

So RBob, do I unhook the computer and use my fluke to probe the specific pin to see if I have a circuit? This was an original 305 car and the wiring was not hacked except the end going to the fans water temp switch. If I get a bad circuit can I just cut the wire and splice in a new wire in the engine bay and run a new wire over behind the engine to the O2? I have never messed with the wiring at the computer, could that wire have gotten pulled out slightly? Maybe from when we were changing computers? It had a replacement 305 computer when I got it, then the caprice 350 computer and now the EBL. Just wondering, how can I tell if all the wires or pins are in correctly. I hate wiring, learning to enjoy tuning but wiring has never been my thing.

Forgot to add, I disconnected the O2, engine was cold, well cold as it can be on a 100 degree day, and open circuit WUD shows 455mv or 451mv. Using a piece of wire I slipped into the connector and grounded it in several different places and it would always show 460mv. It generally would be either 455 (open) or 460 (grounded). Not sure if this helps.

Thanks,
John

 

What you can do is pull the C/D harness (the bigger one) and run a continuity check between D7 and the O2 sensor plug. Then you can run a continuity check between D6 and ground. Be sure to confirm that resistance is very low (below 1-ohm).

To answer your other question, yes, you can replace wires like that. I've had to do that a few times on my Caprice (including the O2 wire, which was intermittently reading high when wet causing my BLMs to bottom out, and the TPS signal wire, which was also reading intermittently high when wet...hmmm).

 

Thank you Kevm and Rbob! It was in fact a wiring issue... turns out there are grounds that were originally attached to both heads!! The idiots who removed the original yanked the ones from the drivers side head. One of which was the little tan one that grounds the O2. O2 works great now. But now I have horrible surge and hunting while idling. In open loop it runs perfect. Now surging! I am using a modified vortec bin and have now done some VE learns to get the fuel issue back down. Was very pig rich once it went into CL. I have reviewed and reworked the spark tables to be sure it was not changing at idle. Any other areas to look at? Turns out the alternate some how blew out the rear of the bearing and the ***** are falling out... so gotta get a new one tomorrow. All ideas are welcome. Although I wonder what those other 2 wires are that are hanging, maybe they too should be grounded.

 

Look out for exhaust leaks. You may also want to upgrade to the AFS-74 3-wire heated O2 at this point.

What size are your injectors and what was the size of the injectors in the calibration you started with? Could be an O2 prop gain type of issue. Typically attaching a 17 frame/sec log segment of the issue will help identify the issue.

 

Most likely should be connected to the engine block. If the wire colors are black or black/white, they are EFI grounds.

RBob.

 

OK I will get them grounded to the engine in the morning. I guess worst thing is it stays the same. I have attached a data log of the idling issue. It seems to idle pretty good during OL but as soon as it goes into CL it seems to freak out. I tried an old bin and also the factory caprice 5.7 bin and it did the same thing other than it ran super rich on the caprice file. I will also go ahead and pull some plugs and check the wires. This sux that it runs so nice in CL on the road until you stop and it is bucking and jerking. Almost feel like I am Lane Frost!!! Also it idled perfect before I grounded the O2. Maybe those 2 grounds are part of the idling. We will see. I have to say I like that the learn and all has made the actual running better, less fuel and less smelly exhaust. Was tired of it running pig fat and stinking up the entire area and making peoples eyes water!! Much better. This vortec engines VE is way lower than the caprice, I assume that is because of the efficiency? If I can get it to idle I can do some medium and higher speed learning.

 

The idle gets worse in closed loop, but still has issues while in open loop.

The idle speed starts to drop a little and the engine then bounces off the stall saver. This is why the IAC steps and RPM jumps up.

Not sure what is going on, the idle isn't smooth either. It is too jumpy for a stock engine. Double check mechanical conditions such as firing order, plugs, wires, cap, rotor, valve adjustment, and so on.

RBob.