Old Hyundai tuning issues

In reply to bobzilla :

The rear sensor isn't going to change it that much- it should have authority to about 1-2% of the entire trim.  Maybe 3 in that era, but more than likely, it will be less than that.  For what you are trying to debug, just unplug them, deal with the light, and see how the fuel trim changes.

There are NO rear sensors and have not been there since this car was put together in 2019. In the 8k+ Mike's of driving there have been NO rear sensors. 
 

I checked the front injectors by pulling the rail and lifting them out. Pressurized the system and they are bone dry. I've ordered a rear O2 as well. Both are old and crusty. I checked for vacuum leaks and have found none with carb cleaner. 
 

it's got to be something electrical/sensor with the rear bank at this point. Right?

Seems likely.  Didn't you mention you changed the front O2 sensors?

On a bank specific problem, the O2 sensors are the only bank specific problems, unless you have VCT- could be one bank's cams are out.

edit- or an electrical issue with an (or some) injectors.

I have one new OE sensor here and a new one in the way. I'll swap them out next weekend. The injector harness is all one piece and I'm not seeing any issues there. There's no cam trickery going on with this motor. 

So I haven't donw much at all.... depression and motivation have been out of sync. Pulled battery for a couple days, which resets the ecu and its learning etc etc. Still hard to start. The IAC whines.  All the time the key is on. Engine running or not. I think that can't be a good thing. 

Finally did a thing. Pulled the IAC. Not blocked. Not too bad as far as oil/carbon/junk in it. It does rattle like a damn maraca when shaken. Unplug the IAC and it settles down and starts effortlessly. So a new $15 IAC is on its way. I also learned that the rear bank is bank 1 and the front bank is bank2. The more you know.....

Finally got the new IAC, installed it and the front O2 which I now know is bank 2. Fuel trims are much closer now. Starting has gotten better but it's not been driven much. Time will tell. 

Some more research has found a similar issue on a 2.7 Sante Fe. Tried many of the same fixes. Ended up being the inejectors. Resistance was out of whack causing improper fuel delivery. If the starting goes back to the way its been I'll start with the spare rail/injectors and see if that is achange before buying new. Luckily they'r dirt cheap.A complete set of OE are $180. Chinese knockoffs are around the $60 range.

annnnnddddd........ not fixed. Next step try the spare injectors. 

Install one facing up toward an ignition source. Boom! Problem solved. 

Hey Bob,

This is from 17 years ago and most days I can't remember why I walked into the kitchen, but......

Somewhere around the 2003 model year Hyundai had a tsb/recall for swapping the upstream O2's. They switched metals in the sensor (zirconium to something, or something to zirconium). Part of the procedure was to reflash the ecm. If a 2.7 car came in with mismatched sensors and/or reflash it had similar symptoms to what your describing. We would check the ROM i.d. and then verify part #'s on the sensors. Getting everything to match solved a lot of issues for us. 

I have no idea if this is what's going on with your tibby, but reading your post reminded me of that issue. It wouldn't explain why the tibby has run good for 7k miles buy if you go after the upstream o2's might give it a check. 

So I had an epiphany on the way Home. Well more like a random thought. I know sone people have had issues with the fpr in the past. I have a spare rail, fpr and injectors. Checked vacuum on it and it would hold 35psi. Pulled the line on the fpr on the car it come up to 8psi and instantly drop pulling fuel with it. 
 

yay! Found something wrong. 

and that was the return line. Obviously this isn't causing my problems but it's going to cause it's own eventually 

Well, the silver lining is that when you hopefully find the actual problem you'll have baselined the car really well and hopefully have that much more confidence in it. Good luck!

OK, I'm almost calm now....

Got to work, grabbed some 6mm hose. Went out to her truck to find the right rear tire flat. Fine. I got the hose, Tubey will work. Put the hose on the return line. The same hose that comes off the regulator is almost 3/8. F it.... I made it stretch. Go to tighten the clamps and they disintegrate. Fine. I just put a new battery in the C10. It's 2 miles each way I'll take it to work. Fire it up, back it out of the garage, pull hertruck in and yank the tire. Put the tire in her car to go get fixed. Hop back into my truck to go to work it fires right up with a loud SCREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE noise and it's at 10.9V. What the hell? Pull back into the driveway off the side. Turn it off. Noise continues. It's the starter. So I yank the battery cable and the wife took me to work. 

4 cars. 1 usable. I'm not doing this right. At least I now have new clamps and she got the tire fixed (which was brand new 5 weeks ago).

Regulator and return hose may have done the trick. We will see

So no leaks now, less fire hazard. Starts instantly. Had an issue with a hanging idle (idle at 2000, then drop to 1500 then down to 800 at its own slow pace). Got 3 more drive cycles on it and the idle issue is becoming less and less. I'm guessing it's relearning all sorts of bad behaviors.

And a couple more cold starts I call it fixed! The hanging idle is almost gone. I'm guessing the relearn is catching up. Fuel trims on both banks are hovering around 0- -3% from the 6-12% before. 
 

still a

little confused on how a fpr that control rail pressure can cause that type of odd fuel trim issue between banks. 

Definitely fixed. Starts and runs great. I also finally deduced why it was only rich on one bank if it was sucking in fuel from the regulator vacuum line. That vacuum line plug right into the #6 intake tube. So only #6 would be getting that extra shot of fuel, messing everything up. I also wonder if that extra fuel at WOT on track for 15 minutes at a time might not have been an issue as well. Time will tell.

The important issue is it starts and runs great now. 

bobzilla said:

Definitely fixed. Starts and runs great. I also finally deduced why it was only rich on one bank if it was sucking in fuel from the regulator vacuum line. That vacuum line plug right into the #6 intake tube. So only #6 would be getting that extra shot of fuel, messing everything up. I also wonder if that extra fuel at WOT on track for 15 minutes at a time might not have been an issue as well. Time will tell.

The important issue is it starts and runs great now. 

Gonna try to compression test it? You think it could have washed down the cylinder at all?

In reply to kevinatfms :

Not bothering. It runs great. If i start having issues then we'll see.