sup guys, stock internally l03 305 tbi engine here in a 92 rs.

Well heres my question i'm getting ****y milage yet i never have a check engine light on and it has a new full tuneup and runs well for 145k miles on it. What i've found out after dynoing it is i'm pushing 152 wheel hp and 237 wheel torque, not bad for stock after 145k miles but, the real thing i was slightly worried about was the afr was 11 to 1 across the board. No wonder it's getting ****ty gas milage at that rate....

So my question is would a faulty 02 sensor cause her to run rich even though it's not setting a code? It's running 11 to 1 across the board at wot and at about 1/2 throttle in drive turning 2500 rpms or so going 70 ish.

Question #2 what is the downside to lowering the fuel pressure a lb or 2 if i built a custom regulater for it to lean it out slightly? Worse atomization possibly or computer freak out problems, any1 know?

Btw i do have acess to a wideband and mustang dyno so i will set it for 13 to 1 afr for the best power making formula,1 way or another. I'm just curious is the adjustable fuel pressure regulator would hurt me more than help me for the most part.

 

Heres the short version i'm running 11 to 1 afr across the board and want to lean it out for optimal power and less fuel consumption.

I want to know why i'm running so rich with a stock tbi?

and if an adjustable fuel pressure regulator would hurt me more than help me.

My initial idea was to pull a lb or 2 of pressure and see how much it leans it out but, being that this is efi i'm not realy sure if pulling some fuel pressure would be a good thing and i'm not sure if the added pressure would be better for atomization or not.

So whats the consesus just do it and find out or what?

 

At WOT your ECM/engine is in PE mode. That in itself is why the 11:1 AFR. At half throttle, the ECM/engine could still be in PE mode. If it is, then same as above.

Normally an engine such as the 305 TBI only requires 10-15% TPS to cruise at 65-70 MPH. With that the ECM/engine will be in closed loop, and, possibly lean cruise mode.

What kind of driving are you doing? Around town? Or hiway? And what is the measured MPG?

RBob.

 

well that explains a little bit but, i'm still curious if it would hurt it any to run it a little leaner up top.

I mostly drive in town and get 14-15 mpg. the only highway driving i've done i got 23.5mpg with a very steady 4 hour drive 55-75 mph max.

In other words i'm not realy very happy with milage and at this time am at a bit of a loss for what would be best to help it out.

 

The reason GM runs it so rich is to cool off the CatCon. They basically put it out with all the fuel. For better performance leaning it out does help.

Your mileage isn't too bad, but should be better. A full tuneup (cap, rotor, plugs, wires) along with an new O2 may do the trick. Bumping the timing up a few degrees may work to an advantage.

RBob.

 

Just another thing to check, when i got my car, it was idling rough, and would throw a rich code on the highway. When i checked my fuel pressure, i had 20psi. My return line was plugged, causing it to run rich.

 

I'm thinking this may very well be my problem..... I'll be checking the fuel pressure on it this week.

I datalogged it at school and i'm going to have to review it a little more tomorow at school again. I think i concluded a few things for sure though. Idle is high at 1000-1025 rpms. 02 sensor voltage tends to run on the rich side .650mv-.850 mv. I also think the tps readings i was getting were crazy but, i'll figure that out tomorow.

O btw it is going in to closed loop and at the correct temperature and in a good state of tune (new pcv, cap rotor wires plugs blah blah).

I pulled 3* off of my base timing after noticing that it was getting knock counts on the scanner as i revved on it hard. It now pretty much runs like **** with 7* base timing. It was at 10-11* and ran real well nice and snappy and more powerful. No idea why my car likes a lot of base but, it does so i suppose i'll be setting it back to 10* later this week and i'll just start running it on premium.

Tomorow i'll be doing component tests on the sensors that i think may be the culprits and replacing a couple a little well worn vaccum lines.

Any more help or pushes in the right direction is much appreciated and thanks for the info given above it helps.

 

Check the fuel pressure. definitly similar symptoms to what i had, O2 showing rich, and a high/rough idle i could not get down. blew out the return line, and it was fine. Hope its something as simple as that.

 

alrighty well i replaced some vaccum components that were showing a little wear but, none were leaks at the time of replacement so that was just prevenative maintnence.

It seems as if all the sensors are working correctly except the knock sensor is picking up fake knock from wornout power steering pump bearings.

Does that mean the everytime the bearings make noise that the sensor is going to retard the timing? If so that kinda sucks........ I suppose this could also be why my car tends to like more base since it's not getting **** for advance from the computer.... Makes sense to me anyways lol.

I also bought a new oem 02 sensor for the hell of it, figured it couldn't hurt after 150k on the stock 1. I'll see what it says tomorow attached to a emissions tester with wideband capabilities for the afr, hopefully it will change for the better.

I'll be checking the ignition primary and secondary waveforms for anything abnormal and then i'll be checking fuel pressure at the rail.

Btw i got a fuel pump relay here not long ago because, mine was worn out and today i checked the codes and got a fuel pump relay code even though it seems to be working fine. So that's a mystery to me as to why it did that..... Anyways i'm going to get that 02 sensor off and the new 1 in. hopefully it won't be as tightly in their as the last 02 sensor i pulled (took a 3 ft braker bar and a torch before that 1 came out.....)

 

alright people new 02 sensor seems to make no noticable difference. I also tested the tps today and it tested out fine. I ran the primary and secondary waveforms on a scope which check out good to my eyes and from the charts i had to compare them too. Everything ignition related and sensor wise seems fine.....

I bought new spark plug wires for it tonight for astetics more than anything else but, it can't hurt......

Basically the car is running rough at an idle and rich throughout the powerband..... Don't know why yet...It feels like a big vaccumm leak but, their isn't 1 that i can find as much as i've looked. Plus if it were it would e running lean i would expect not rich right?

I did a cylinder power balance test and found 2 cylinders doing not much of anything so that's what i'll be looking at for tomorow. I'll do a compression test on the full engine over the weekend and record my findings wet and dry and regap and clean the new plugs and replace them. New wires will be installed and i'll check fuel pressure at the tb tomorow at school. It's gotta be either a fuel problem or compression so it's definetly narrowed down....

My guess is fuel but, we will see.

Anyone know what happens when the knock sensor is picking up fake knock counts? Does it retard timing still and if so how much and how does it do so?