Th0m4s

I guess i nearly fixed everything now. There's only one major problem left: I need half the tank for about 70 miles and the car is bucking under load. The more the engine has to work, the worse the bucking gets. What the hell could that be?

It's a S4 Turbo II with 63000 miles by the way.

An other small problem is that my temperature gauge is too low even for an S4 and my oil pressure gauge is showing too low pressure, too. I tried to ground the sensor wires to check the gauges. They are working correctly so I started changing the sensors. Got a new factory oil pressure gauge. Now the oil pressure value is better but still much too low. What else could be the problem here?

ROTORNEWB

TPS adjustment for the bucking or "spark blowout" due to major fuel consumption. Bad injectors? Fuel leak?

Th0m4s

The tps is adjusted and the injectors were tested by Bosch some weeks ago and all are ok. Got no fuel leaks, too.

By the way I want to change my fuel pump to a Bosch 044 one soon. Will I need a new fuel pressure regulator?

Th0m4s

Today my car remembered me of a hidden fault. Sometimes the tachometer stops working and beeps all the time like I hit the red area. I read the wiring diagram and found out that it's getting the signal from the trailing coil. What if my trailing coil is damaged? Could that cause those high rpm hesitations?

By the way my O2-sensor is broken. That caused the high fuel consumption.

satch

iTrader: (1)

You can disconnect both of the electrical plugs ( two wire and four wire plug) to the trailing coil to see if the problem persists. Trailing coil is used primarily to burn off excess fuel which is not achieved by the leading coil so the engine should run fine w/o it.

mukurosfc3s

iTrader: (10)

one of your secondary injectors isnt working either it got ddisconnected at the injector as they usually do..

Th0m4s

The injectors are 100% working. They were tested and cleaned by Bosch and I checked the connections 3 times allready.

Going to check the trailing coil today. Maybe if it's not firing the engine gets too much gas at high rpms and that causes those hesitations...

mukurosfc3s

iTrader: (10)

do you have a fuel cut defender??? have you done a voltage drop test on the harness to the ecu?

Th0m4s

No FCD, everything is stock. You mean the 12V to 6V thing when the injectors start acting? Did that and everything seemed to be ok.

I recognized today that even after regrounding the ecu grounds there is a slight hesitation at 3800 rpm if I only press down the accelerator a little bit. Might have something to do with the hesitations at higher rpms but why is it still there? I regrounded 3 of the 4 grounds. Just left 2C away because as far as I know it's an outgoing ground from the ecu to the sensors. It should connected to the other grounds inside the ecu allready. Should I ground that, too maybe?

By the way: What else but bad gas mileage could a broken O2 sensor cause?

Oh and shouldn't the boost gauge be showing exactly 0 when I turn the key to ignition? Because mine is showing a slightly lower pressure. Maybe -5.

satch

iTrader: (1)

The cause for the 3800 hesitation, as explained by Mazda, was due to a faulty ground to the AFM. Since 2C feeds this sensor it would make sense to shore up all possibilties and reground it.

The ECU should have a default value in case the Oxygen sensor is not sending a signal to the ECU but for some reason unknown to me it doesn't always result in a smooth running car. Calpatriot, a forum member, has a fair amount of insight into this sensor so an advanced search of the O2 sensor followed by his name (O2 calpatriot) ought to provide you with some relavant source material to read over.

One of his threads: https://www.rx7club.com/showthread.p...sor+calpatriot

Th0m4s

I'm going to ground the last wire tomorrow. Today I disconnected the O2 sensor. There was no error code from that sensor before. I guess it was still sending signals but they were incorrect. Going to watch the fuel mileage now. Theoretically it should be better, right? I'm getting a new O2 seonsor in one week anyways but I was curious if that is really the cause of that creepy fuel mileage.

By the way for some reason there was a problem with the gauge grounding, too I guess. Sometimes It was beeping and the tachometer wasn't moving past 1000rpm. It happened today, too. I connected a new wire to the grounding pin of the gauge cluster and it stopped doing those weird things.

By the way I pulled the spark plugs today. Do they look ok?


I recognized that the rear rotor leading plug looked a bit more used than the front rotor one. could a bad plug wire be the reason?

satch

iTrader: (1)

Could be? Are the plugs the same age?

Th0m4s

Yep. Exactly the same age.

By the way I found out those are 4 times SD11A. I heard normally the FC is running with BUR9EQ trailing and BUR7EQ leading plugs and those SD11A plugs might cause bad ignition sometimes. Should i change to BUR9/7EQ? It's strange anyways that the repair shop used SD11A for leading and trailing.

Flomracing

This is because if there is a major fault that is adversely effecting the emissions and the the ECU on some vehicles will go into a "limp mode" which will make it run just good enough to scare the driver and make them take it to a shop, it is really stupid and causes poor emissions and on rx-7s (among other cars) a bad O2 on my car also caused it to rev itself when cold, and that was fixed by replacing the O2 sensor.

Anyway, the hesitation and poor fuel mileage must be caused by running rich, or spark blowing out. Does it backfire much, or blow smoke under acceleration? if not...does it smell like gas anywhere, might have a really bad fuel leak, but thats usually pretty obvious. Those are my 2 cents, let me know what you find or if you have more questions.

Good luck!

Th0m4s

It's running damn rich I guess. It leaks nowhere but at the exhausts the car allways smells like a gas station. I just don't know why.

satch

iTrader: (1)

You might want to check to see if the ECU is running in"open loop" too much.

Th0m4s

How could that happen?

satch

iTrader: (1)

Inaccurate input signals to the ECU with one of those signals being from the Oxygen sensor. It's rather simple to check the state of the ECU relative to being open or closed loop. This info was in the link provided.

Th0m4s

Yep I know. Going to try that tomorrow.

mukurosfc3s

iTrader: (10)

get rid of those pluggs!! what r those acdelco lol get ngk platinum spark pluggs.
have you cheked the grooung cable underneeth the throttle body its off the main harness its two black cables into one (i keep forgeting the name) but its circle and you can run a 12mm bolt. make sure thats connected to to the iron not the housing.
on my s4 im running a wide band and just let the o2 cable loose n it runs fine no hesitations..
maaan hope it works

Th0m4s

Ok some news here. I changed the spark plug wires. Still everything the same. I also asked for new spark plugs but Mazda told me those SD11A plugs I got are the right ones. They didn't want to give me BUR7/9EQ plugs. I ordered them somewhere else now. Stupid Mazda guys...

The O2 sensor is working like it should but it's completely coated with carbon. Should I try to clean it or would I destroy it if I try?

Mazda said the reason for my hesitation could be a damaged leading coil. Could that be?

Th0m4s

Today I took the car for a test drive on the Autobahn and recognized a strange behavior. When I was parking the car again it was definetely hot but it was idling at 850 rpm so I tried to adjust the idle speed. I first tried it without the initial set coupler grounded. It reacted when I tried to set the variable resistor but when I tried to get the idle speed a bit down by screwing the idle adjust screw in it didn't react at all. It was idling at 850 rpm even when the screw was screwed in till mechanical stop.

I then screwed the srew out a bit again and grounded the initial set coupler and the engine immediately went down to 300 rpm. I was able to set the idle speed to 750 rpm without problems but when I disconnected the initial set coupler it went up to 850 again and it was definetely still very hot.

Could it be that my water thermo sensor is the problem and could it also be that that problem is connected to the strange hesitations and to the insane gas mileage? Something like the meintioned spark blowout because the ecu thinks the engine is too cold and injects huge amounts of fuel?

satch

iTrader: (1)

The Initial Set Coupler being jumpered curtails the ability of the BAC to inject unmetered air into the throttle body to a certain extent. If you try to set the idle w/o the coupler jumpered the BAC will fight against the Idle Adjust Screw being tightened as the loss in air entering the throttle body from the tightened screw is offset by the BAC allowing to add more air to compensate for the lost air.

Th0m4s

Ok but why was the BAC opening again after adjusting the idle speed even while the engine was hot? My car was running at 850 rpm again immediately after I removed the bridge from the initial set coupler.

satch

iTrader: (1)

The BAC never turns off completely as its function is always an ongoing process with a running car. Some will set their idle w/the BAC unplugged so as to dial in to the 750 rpm on the nose. Also, if the Variable Resistor is set too rich it will help bump up the idle a bit once the coupler is unplugged. And every possible accessory should be turned off when the idle is set including the interior courtesy lights if the door(s) are open.