Super rich, ~200 miles to a tank, needing some advice
 

So, backdrop on the car:

1988 SE, with an NA S5 shortblock, S5 manifold. When the S5 manifold was installed, I had the injectors cleaned, and all brand new seals installed. Engine is a new rebuild, around ~2500 miles on it. Currently, the VDI & AUX ports are disabled, as I'm in the process of building a system to actuate them, off a stock smog pump. S4 TB, w/ the throttlebody mod. Rats nest is removed, etc etc etc, the only emissions left on the car really is the intake air temp sensor, the O2 sensor, & the BAC valve.

Using the diagnostic code tester, I get a code for a bad O2 sensor. It's kind of an off & on code. I notice the idle gets really bouncy the instant the ECU detects a flawed O2 sensor.

I'm getting around... 200 or so to a tank, granny driving it. About 50% of this is highway. My questions are:

1) how much "leaner" will fixing the O2 sensor make it?

2) Are their things I could do to lean it out without getting into the ECU? Such as soldering in resistors across the rats nest solenoid plugs, to "trick" the ECU into thinking everything's working right?


As of now I've got a new O2 sensor ready to go in by the end of the weekend, once I get the chance to throw it in. (Not a hard job, but I don't have a jack/jackstands where I'm staying at for the weekend). The point of this thread is to see what kind of improvements I *should* be seeing once the O2 sensors bad, and if there is anything else that can be done. I'm planning to go with the Rtek ECU here after I save up my pennys, haha. But hopefully I can get some help up until then.

Thank you, & sorry for the noob-ish question!

woah u get 200 miles a tank...lucky u

Fix the VDI & 5th/6th Ports. Most city driving/highway driving is around or below the 3500rpm range, when the ports don't need to be open. Having them open full time will hurt fuel economy.

Oh, by not connected, I mean they're shut at the moment.

Replace the O2 sensor and verify that the harness is ok. It's a 1 wire Bosch sensor. You can get it at autozone for like $30

i get more like 300 miles to the tank in mine... stock s4 gxl... the s5 has a bigger gas tank, so it goes further

Ok, just replaced the O2 sensor, and I'm not getting the code anymore. I went with a 2 wire, & ran the white, ground wire, directly to ground, to make sure it's getting a good ground.

However, I've still got a bouncing idle. When I did the S5 manifold swap, I used the air temp sensor that was in the manifold, I pulled that today. It was covered in oil/grease, the sensing end. I put the one in the manifold from my old S4 dynamic chamber, which was alot cleaner. I blasted it with brake cleaner, and installed.

Prior to doing so, and ever since I got the S5 intake on, I had a constant blue-ish smoke on idle. I am running premix, so it's got to be from the excess fuel/2stroke oil being consumed. After changing air temp sensors, that smoke has since gone away.

I guess it's time to drive her, & see what the milage does. I'm going to search and see what I can come up with as to causes for the bouncy idle. TPS is properly set.

Thanks!

how the hell u get that mileage?

A lot of my buddies have Muscle cars and they get better fuel economy than I do. and I probably get about the same as you if not worse. And I have a friend with an RE swap who gets about 250kms on a tank.

i get 240 with city, and 280 highway driving, but i drive at like 80 mph on the highway. if i drove slower, i could def get better mileage.

I think the rtek is going to go in sooner than I originally thought, haha

my car is not broken? no tricks, i did verify that the o2 sensor works, and the emissions stuff works, and i did a tune up, but other than that i haven't touched it.

Alright,, update, I think it's fixed/closer to being resolved.

So I had that bouncing idle, still, after switching out the intake air temp sensor, and the O2 sensor. The TB I had on the car, I got in a batch of free parts I got from a member on here. Well, he did the TB mod on it (removal of the butterflies closest the passenger side). I got to thinking, that there's got to be something related with that TB, as it idled fine/got better MPG w/ the old TB, which I'd taken all the extra stuff off, besides bare necessities, but just wire-tied the 2 butterflies open, so it was always reversible. Anyway, did that, re-checked the TPS with the digital multimeter.... Bouncing idle is now gone.

When I kick on a load, AC + radio + highbeam lights, I get the bouncing idle again, which goes away the INSTANT I disconnect the TPS.

Are there any causes that make a TPS "flutter" like that, besides it being dirty/sticking on the inside?

Did you set the TPS to 1 volt or some other method?

Disconnected it, w/ the car off, & probed it w/ the multimeter. I set it to 1K ohm, w/ closed throttle, & made sure at WOT/ throttle all the way off the TPS, it went up to 6k ohms.

If you never tried the 1 volt method I would suggest you try this and see what happens. There is no point of no return when it comes to setting the TPS so you could always go back to the previous method. The FSM spec indicates the TPS should read 1 volt at the ECU. Since the TPS is very, very, very old the ohm stuff probably doesn't work as well but I might be wrong. Anyways, to set to one volt just thoroughly warm up the car such that you drive it for twenty minutes or so then back probe the Green/Red wire at the TPS plug with the red meter lead and the black meter lead to a ground such as the alternator or negative battery terminal and take a voltage reading with "key to on" and "all accesories off." If it doesn't read 1 volt adjust the screw so that it does read 1 volt.

i like the factory way too, the ECU tells you the TPS is right. the ohm meter isn't bad, but it does ignore the wiring harness, and any difference in ecu's

Thanks, I haven't heard of this method! I'll be doing that tomorrow, once I've got some light under the hood. Thank you man!

LOL your gas mileage is so bad you guys whats wrong with your cars? My na gets like 350+ miles to the tank on the freeway. Its A s5 and streetported. It use to get like 410 or something like that before the streetport and changing the rear end to a T2 unit. You should check all the sensors on the engine for proper operation. 200 miles to the tank? I get better than that with drifting involved.

I drive 2 hrs to drift then drift a half a day then 2 hrs back on the same tank. There's something wrong with your cars. Well besides the guy that created the thread at least he knows there's something wrong with his car.

My stock n/a s4 gets 170-180 miles for 1 tank. Wtf.

Another update, as of 10.19.10:

Getting another O2 sensor code. there must be something else causing it to run rich, which is in turn, VERY pre-maturely killing the O2 sensor. I checked for continuity between the ECU pin & the actual O2 sensor, no problems there. So in my mind, that's got to be an O2 sensor failure, again?

What are some possible other options causing it to run this heavily rich?

Keeping in mind that:
-S5 NA swap, with RB header to presilencer to borla catback
-S5 NA intake manifold
ALL S4 everything else, injectors etc. Injectors were just cleaned and installed with brand new seals and orings.
-emissions removed except for bare essentials (to make less of a head ache having an s5 block in s4 car, plus I'm in FL, so emission testing isn't of a concern here.)
-motor is NOT ported

Are there ways to lean it out without going the rtek route? I do plan on going here eventually, but it would be neat to get some better economy now, haha.

Many thanks for the feedback!

Landon

did you leave the switch in the bottom of the radiator? that thing turns closed loop on and off.

Well mine was rated for 17 street and 23 hwy as you can see lol.... I'm getting like 18 on average though

http://i79.photobucket.com/albums/j1...r/DSC00043.jpg

Does your car still have the Variable resistor? Some will say it only affects the fuel mixture at idle but if the resistor is leaned out and you take the car for a spin at full throttle the car will behave like its starved for fuel. This tells me that it affects the fuel mixture across the whole rpm range but moreso at idle.

stop messing with the stock shit and go stand alone

Trying to "lean out" your car with only a stock ecu is a waste of time and energy.

http://i100.photobucket.com/albums/m...tempswitch.jpg

Is this the radiator switch which *should* be hooked up?

As for the variable resistor (potentiometer), I've got that centered. My idle air mix screw is only backed out about 1/2 turn! Every other car I've looked at it's backed out a good 4 or more turns.

Just put another O2 sensor in tonight, that got my O2 code to go away, but I'm sure this one will be killed from the overdose of fuel here shortly.

Thanks for the help, I think we're starting to head in the right direction

Yep, thats where the rad switch *should be*. Had mine installed and hooked up , but didn't realize that w/ a koyo it sees no coolant flow anyway :facepalm:

Update, soldered the wires leading to the switch together, now the ECU thinks it's always closed. Waiting to see how this & the next/next few tanks of gas go, & we'll see if things have been solved, or if I'm on to the next issue. Thanks!

Next update: as of soldering water temp switch wires together, & driving, I did 238 to a tank, requiring 13.5 or so gallons to fill up-- this was 17.8mpg. Driving style was a mix of city & interstate, w/ AC on over 50% of the time. I filled up again, on thursday, and about 70 miles in, went to a neighborhood garage sale, where I found a timing light for $2.

I never truely set my timing after the rebuilt-- and it was set a bit 'tarded. I advanced it to 0* TDC, the stock spec. Noticed ALOT more power than I'd had before. While I was working on it, I decided to also *properly* set my idle, so a smooth 750 rpm. At about the 130 mile mark on this tank, I built a green lamp checker, to indicate whether or not I'm sitting in closed loop. I found that my previous driving style kept me in the rich control setting while accelerating, and was able to correct this by going on the closed loop lamp.. a HUGE help! Anyway, I'm now at 235 miles on this tank, and the needle hasn't hit the 2 tick marks on E yet... I'd say I've burned 11 gallons of gas thus far. I really think I can get close to 20mpg on this tank, which was primarily revs up to redline & just all around fun driving. It will be interesting to see what happens next tank, as this car is definitely fixed MPG wise.

Probably the best thing about this tune up, besides the increasement in efficiency & money left in my wallet, is the fact that the car's actually the fastest it's ever been, having the timing properly set.

Good luck, hope this can help someone else enjoy their car more.

If you soldered the two wires to the temp switch located at the bottom of the radiator that should tell the ECU that the coolant temp is always above 62 degrees which should cause the car to rev to 3000 or so each time you cold start the car at least. Since you live in Florida this might not be a problem, but if you lived in a colder climate it would not be a keen idea.

Right, indeed. For whatever reason, my car doesn't do the 3K warm up when I start it. Incase you missed it (this sentance NOT intended to be rude lol) this car has an S5 motor/S5 intake manifold, all else S4. Emissions are removed, including fast idle cam (which is soon to go back on, as it stalls when cold now that timing & idle are properly set). But for whatever reason, this car doesn't do the 3K warm up. I'm assuming part of that system was embedded in the rats nest, and by removing that i now prevent it from happening. I'm curious to know, what enables the engine to rev that high? is it the BAC going wide open?

Thanks!

On an S5, the AWS and the BAC contribute to the 3000 rev upon startup, and the Fast Idle Cam would be independent of the 3000 rev mechanism.

Since your engine is a S5 but are using S4 sensors I guess you are using an S4 ECU. If this were the case then the S4 uses the Air Bypass solenoid in concert with the BAC to create the 3000 startup rpm.

That explains it, then. Thanks bud!

Ill be connecting those sensor wires before I leave town! I get about 270/tank w/ almost exclusively highway driving.

Before I upgraded injectors, got rtek and had those clowns screw up my diff I got 355/ tank on my best run. Hopefully I can get over 300/tank just messing w/the sensor and setting timing. Then I'll see what I can do about creating a "highway tune".

The Water Temp sensor wires being connected together will tell the ECU to initiate the 3000 rpm rev for 17 seconds upon startup. It also affects the Relief solenoid as to whether the air being pumped into the ACV via the air pump is sent to the exhaust ports or dumped into the air silencer which vents the air to the atmosphere. This should have no affect on gas mileage as the system is for emission purposes only.

s4 n/a has a more agressively rich tune under low RPM/high load mapping, the S5 is a little more leanient so a way to adjust fuel will give you better mileage, otherwise dogging the engine is going to get you even worse mileage.

stop listening to people about the O2 sensor, it does little to nothing for 98% of your driving time. but the rich issue will throw a code for the O2 sensor pointing you where you need to look, which is for possible vacuum leaks or too much fuel from the pump/regulator or faulty AFM/variable resistor/pressure sensor/timing out of adjustment/TPS out of adjustment.

hacks.

mine gets about 300ish on a full tank but i have this problem with my tank where i cant get that last 1/4 tank. so i drive around on 3/4 of a tank most of the time. i do a lot of highway driving as well.

you guys have to remember that the S5 has a bigger gas tank, so it goes further on a tank, so you need to quote MPG.

S4 T2 here w/ full emissions removal, so I haven't noticed any of these "symptoms"

355 miles, put in 15.018 gallons = 23.6 mpg

At that point I hadn't done anything to the car, I'm sure a tune up and a tune would help. My "550s"came back as 580s after being cleaned, so I'm sure that's not helping, but I'm not going to tune anything until I get my ic finished and replace this bound up diff which im sure is also hurting mpg.

I get really good highway mileage. Full tank will take me 250 miles at 80-90 mph average highway driving speed.

Now on the street, I average 10mpg. Unfortunately, that is where most of my driving takes place.