sv51macross

iTrader: (1)

I recently replaced the coolant after 3 years (I know) along with the ECt because I've been getting 11-12 mpg average city driving, grannying a RX-7 as best possible. I haven't verified it yet myself, but my brother has been getting about 10mpg since the flush/ECT replacement.

What the heck is the problem here. I replaced the fuel filter, mpg went down slightly. I replace the ECT, the mileage went down. the warmer weather has no effect on MPG like it should. I am at a loss as to what to do here.

AGreen

iTrader: (11)

You may have broken the wires going to the ECT sensor. You need to check the voltage either at the ecu or backprobe the sensor. Between .5v and 4.5v is what you should get. If it's 0v or 5.0v, you've got a problem.

FirstRotaryExp

iTrader: (3)

this is going to sound strange, but in the 7 years of rx7 ownership, I have never heard of an ECT. The things that are going to affect your MPG's are the o2 sensor (20 bucks for a universal bosch unit from any parts store), fuel filters (tank sock and engine bay filter), injectors (verified not leaking and/or refurbished), WORKING 5th/6th ports on an NA (which it appears you have despite not giving enough information), and 'clean' park plugs. I used to average 20~23 mpg with my old nonturbo with an RB header/presilencer and 2.5" straight pipe into a crap muffler (S4 nonturbo), I also had no emissions (Hard to do with s5's) and never grannied the engine.

It sounds more like you have other issues that are causing an extremely rich condition (possibly a bad AFM or mis adjusted TPS).

arghx

iTrader: (3)

ECT is Engine Coolant Temperature. It's terminology that's more common on other platforms. It's usually called a water thermosensor on this forum. If the sensor has degraded and reads a very low temperature the ECU will dump in fuel.

I agree on o2 sensor and plugs

FirstRotaryExp

iTrader: (3)

Ah see, thats more like it, and yeah...that green plug in the back of the waterpump housing could be broken after all these years or the wires leading into it could be screwed up. But the cheap fixes are O2 and plugs, 40 bucks and 20 minutes....well longer if you still have everything hiding the plugs.

AGreen

iTrader: (11)

No. Actually probe for voltages. Why throw money and parts for a problem they're having rather than spend a little time and actually figure it out. If the O2 sensor is bad, then replace it. If it's working, then don't. You'll know if it's working by checking the only wire coming off it to ground. Check the FSM and see what the voltage spec is, I think it was only up to 1v. The voltage should fluctuate as the ECU corrects the idle enrichment. If it's reading 0v, then it just doesn't work and needs replaced. Pull the spark plugs and check them. If the electrode is rounded off or they're fouled, replace them. If not, then don't.

The original problem was that he changed the "water thermosensor" as Mazda calls it, or as any service technician will call it, the "engine coolant temp sensor". The most likely cause is a broken or ripped out wire from that brittle 20 year old green plug.

And those are definitely not the only factors in fuel mileage. How about condition of engine oil, transmission gear lube, diff lube, viscosity of all the above, tire pressure, condition of catalytic converters, air filter, thermostat (if it's stuck open, the car will take forever to heat up), and about 20+ other things.

sv51macross

iTrader: (1)

Yeah, I guess there are a whole bunch of things to consider.

-First off, the O2 has never worked as long as I've owned the car. There is a tremendous exhuast leak in the manifold area, and the thing is so corroded it will be cheaper and easier to buy a header, and I refuse to buy a ChiCom knockoff for Lucy.
-I never considered that the ECT wiring (I spent 3/4 a semester calling it that and having it ingrained in me. It's an ECT) might be damaged, though when I put the alternator back on the wiring looked intact. I'll try checking it as soon as I remember (it's a family curse) to buy a new battery for me DVOM. Will also check TPS and AFM then. That aside, the car warms up normally. (120-180 seconds before the needle lifts off it's rest in the summer, depending on how much I pay attention)
-I don't think the cats are clogged (though as long as she's been running rich they should!) as she doesn't bog in the slightest when throttle is applied, she's still quite sprightly.
-Plugs and wires (NGK) and fuel filter replaced a couple months back.
-The injectors are a bit of a question mark, as they came with a [used] replacement primary fuel rail when mine started leaking. Fewer miles than my engine, but I should have had them cleaned. (I know, hindsight is 20/20 and all that). I was going to track down a can of BG44K and dump that into the next fill-up, as I flat-out refuse to take the intake manifolds back apart unless something breaks or leaks under there.
-The fuel tank is one area I should go into, especially now that the garage is actually clear enough to put a car into, but after dropping (and reinstalling) the tank on a 95 escort in my auto class last semester, the thought is giving me the heeby-jeebies (especially without a full lift). The fuel level sender is acting weird, so that would be the proverbial two birds with one stone.
-Perhaps I should change the [air]filter, but that would just be one small part of my problem.

The biggest problem I have is that I am unemployed and relying on parental support for repair costs, so that is the biggest hurdle to the exhaust leak repair I suppose. (Because also I want to get MI Certified in auto mech and apparently deletion of emissions devices gets you banned from that profession in this state, so new cats too) Unless someone has an idea on jury-rigging a way of isolating an O2 from engine bay air. lol I also just checked my front bearings and the vertical play is noticeable, so that has to be done immediately.

[edit] If i sound like a total ***** please call me on it.

Derekcat

iTrader: (8)

So... If I read your posts right... Your O2 sensor is definitely bad, and you're looking at other things affecting fuel economy...?

[Also I had no idea what an "ECT" sensor was until arghx explained... Search of the forums reveals that it means etcetera ^_-]

Also, taking the intake off is actually pretty easy [your job as a mechanic will be much worse than something like that] search the 2nd gen forums for picture guide intake removal and you should find mine. Should only take you 20-30 min to get the TB/Dynamic Chamber/UIM off as a single unit. ^_^

sv51macross

iTrader: (1)

I decided that auto mech wasn't a career I wanted to pursue long-term, and the tool investment is too huge for a short-term job. Taking the Plenum off isn't bad, it's the UIM and especially the LIM I don't want to touch.

Derekcat

iTrader: (8)

Ahh I see. [Probably a good move.. Kinda a painful career]

oops, sorry.. Missed that you have an S5 ^_^' [picture guide does not apply] Tis a bit harder then... Though I still suspect there is a way to remove all 3 as a single unit, I've only taken an S5 NA intake apart once..

Oh, and you wouldn't have to touch the LIM for any of this? Would be a real pain if it were necessary..

[Unrelated: 1,000 posts XD]

blk87Turbo2

iTrader: (23)

Don't bother with the fuel system cleaners, they don't work (I'll try to find the article later, but it was in one of last months import magazines).

Also, if you keep an eye on the classifieds I've seen tubular exhaust manifolds for $40-$140. It would certainly alleviate the exhaust leak issue. And you can replace the downpipe with a catted one from Bonez that should keep you legal. Or you can get OEM replacements from RockAuto.com.

If you know your O2 isn't working properly, there's no point in continuing to troubleshoot the problem.

088

iTrader: (9)

^^ I would be very interested in that article & how they arrived at their conclusions.

blk87Turbo2

iTrader: (23)

They flow checked two different sets of injectors, one was a set from a Honda (250s I believe) the other were a set of factor RX7 injectors. Then they ran the cleaner through them with no improvement in flow.

A side note: In my professional opinion, any temporary effects you may observe after pouring in a cleaner come from the ingredients being burned with the fuel, not from anything being cleaned from the fuel system.

Found the article: http://www.importtuner.com/tech/impp...ers/index.html

RotaryEvolution

iTrader: (30)

in tank injector cleaners don't hardly do anything, and yes, you are.

problem is you need a heavy detergent to clean injectors, dilluting fuel by 1 part to 150 parts of gasoline has almost no effect on them. when injectors sit outside of the fuel system for extended periods of time they actually become more fouled and sticky than if they are in constant use. for example i sent out a bag of injectors to be cleaned, most came back non responsive, a couple came back with low flow and only a small % actually flowed fine.

so installing injectors with unknown shelf time without servicing is a bad idea and in tank cleaner won't help much if any at all.