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Hello!
I currently own a 1996 Toyota Corolla with a 1.8L 7A-FE engine. Car is essentially bone stock. I inherited this car from my parents, who left it without service for 8 years (5 of those it was not driven). I’ve taken over and done all the maintenance myself (mostly!). Still runs great, feel wise. I’ve been driving around with a Bluetooth OBD II scanner lately, hooked up to my Android phone running Torque and displaying information. And I’ve noticed some very strange behavior.
At idle, my long term fuel trim reads 7.8%. Hitting the pedal makes the fuel trim go down to 4, and pushing it more and more makes it rise. Flooring it gives about 8.6%. Letting go drops it to 1.6 then it rises to 7.8 immediately. I tested the same scanner and phone on my father’s Miata, and his long term fuel trim is a consistent 0% with slight variations up and down.
Another thing is throttle position. At idle, it says that my throttle body is 10% open. Flooring it makes it go to 77% or so. Tried it on the Miata, 0 to 99.2% so I know my scanner is working. I checked the throttle cable, it’s perfect. Barely loose, just enough as to not pull at the throttle body. Car idles fine at 650-800 RPM at all times, even with AC on. Normal idle without AC is around 700.
My fuel mileage in the city has been pretty bad too. Last fillup netted 19 MPG, but with highway driving, it’s a lot better. Here is a list of maintenance I have performed in the last few months:
- Engine oil and filter (10W-30 as far as I remember, did wonders to stop the car from burning oil. Still full after 1000 miles) plus some Lucas Oil Stabilizer
- PCV valve
- Tires about a year and a half ago (also re-inflated to 32 recently)
- Rotated tires a few months ago
- Air filter (OEM Toyota)
- Distributor cap and rotor
- Spark plug wires (Import Direct, NGK was out of stock)
- Spark plugs (NGK, gapped by me)
- Front oxygen sensor (OEM Denso)
- Fuel filter
- Front brake rotors and pads with full bleeding
- Power steering flush
- Coolant flush
- Transmission flush and filter
I also ran some Seafoam through the gas tank a few times. Doubt that made much of a difference, but it keeps the CEL off on my father’s Miata (bad pre-cat).
Today I’ll go for a good drive and check short term fuel trim, as I’ve read today that it’s more important than long term.
I’m not sure what it is, but I think it’s either clogged fuel injectors or a vacuum leak somewhere. Any advice would be much appreciated!
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[quote=”crypkilla” post=61858]im not gonna re-read this whole thread, but weren’t you still hearing a possible vacuum leak? i dont remember what came of that. I would want to be SURE i didnt have any vac leaks. I havent tried this method, but i would think propane enrichment would be way easier and more effective. a gas would be sucked into a small vac leak easier than a poorly aim stream of liquid.
pick up a propane torch at Home Depot for $13 and fashion some kinda hose onto it to make it easier to poke around. plus the torch will come in handy in the future for all kinds of things. and was it this tread where u were using brake cleaner instead of carb cleaner? is so, im not sure about that.
I thought I was hearing one, yes. Not sure if it’s still there, but if I get bad fuel trim even at high RPM it makes it more unlikely.
Brake cleaner is also combustible, but for the record, I bought a can of carb cleaner and did it with that too. Still nothing. I can try propane enrichment too, I can always try, but isn’t that a major safety hazard?
EDIT: I also think it may not be a vacuum leak because my idle is normal, maybe a little low.
I tested the MAP at idle and various RPM, rock solid. No exhaust blockages. Will take apart the car tomorrow to clean fuel injectors, maybe do the propane trick. I have a can of it lying around.
[quote=”Haloruler64″ post=61862] but if I get bad fuel trim even at high RPM it makes it more unlikely. [/quote]
i guess so huh.
[quote=”Haloruler64″ post=61862] but isn’t that a major safety hazard?[/quote]
idk. take video! lol. ive never done it. seems it could be more dangerous if a bunch of gas accumulates and sparks… idk. in the video doesn Eric say the carb cleaner is more dangerous? seems to me that carb cleaner would be more dangerous to the car (catch the car on fire) and propane more dangerous to you (singe ur eyebrows off) but more effective.
[quote=”Haloruler64″ post=61862]I also think it may not be a vacuum leak because my idle is normal, maybe a little low.[/quote]
brings up another thing i wish i understood: we know vac leaks cause idle issues. but is this only when it’s bad enuf that the computer cant compensate? when the fuel trim maxes out? otherwise isnt the point of the fuel trim to compensate and maintain stoich. so shouldnt a small enuf leak be easily compensated for simply by enriching the fuel and having no other symptoms besides poor fuel economy (or possible symptoms to whatever system has the leak, like PCV not circulating crankcase gases.)
im gonna have to pull out my scan tool and induce some minor vac leaks and see what happens. the more you learn about cars, the less you understand.
as far as injectors go, you could remove the fuel rail, leave the injectors attached, disable the ignition, get some goggles, crank the motor and watch the spray patter! great way to clean the engine bay too! or whatever you point the injectors at.
You’re right, idle would not be affected.
And damn, that’s complicated! Gonna have to do a lot of work to get those injectors clean.
i watched it a few times and it looks pretty easy (i guess i already have all the tools tho, like the tap). that or u could mail your injectors off to a place that will clean them and flow test them and give u a fancy printout and all that for like $16/injector.’
if you need your car every day and u have a local self service junk yard, you could try to pick up an extra set from there to be sent off for cleaning. not sure the cost. i would never advocate stealing but i once found a set of injectors in my socks after visiting my local junk yard. they charge a $1 admission fee. (looks like the Pick-N-Pull in Sacramento wants $6.50 each so in theory if u were closer to that junk yard you could put together a perfectly good set to have on hand, ready to swap in, for $91 + tax. $45 less than the cost of a single brand new injector at O’Reilly Auto Parts)
i looked into sending mine off a while back. there’s an outfit near you that uses the dr. injector equipment or whatever.
http://www.docinjector.com/but i was gonna send mine to these other guys (link below) cuz i really liked the detailed website and felt i would get the most service and also for the cheapest price i could find anywhere. ($16 / inj) check out their description of the procedure. (man i feel like i should get a commission for my excellent referral)
http://www.mrinjector.us/service-procedure.html
but before i blew a hundred bucks on potentially unnecessary injector service, I’d wanna see mine in action. and a couple alligator clips, one AA battery, some wire and tape, a plastic syringe, and some carb cleaner could make that happen. watch a few of those video and mash together ur own set up. i like one where he fills the syringe, then uses the plunger of the syringe to apply pressure instead of the can of carb cleaner. plus it means hooking the syringe to the inj the other way around, thereby avoiding having to cram it over the inj or shave off an o-ring or something stupid.
I read this in a forum and it seems to support your assessment:
Since vacuum is highest at idle, if the trims are higher at idle then it’s most likely a vacuum leak. If the trims are higher when the rpm increses then you may have a fuel delivery problem.
[quote=”Haloruler64″ post=61585]Fuel trim is still erratic, but less so. It’s about -11 to +10[/quote]
is this long term or short term? it’s my understanding that short term will normally be erratic.
PM an email address and i will email u the testing and inspection procedure for the throttle body, throttle opener, and throttle position sensor if you want just for fun. maybe an improperly adjusted TPS makes the computer think there’s more air than there really is so it enriches the mixture? but then i guess it would run rough. nvm. idk. i wanna see video or a report on ur injectors…
just curious to clarify: LTFT is high at idle. then, with car parked, rev to 2,000 – 2,500 RPM for like a minute and watch LTFT. if it comes down, vac leak. stays same or goes up, some other cause. i just wanna be sure the test is done this way, rather than driving under load when the fuel maps might do something different or at way higher RPMS. the only reason to rev to 2k is to reduce the vacuum in the intake manifold.
LTFT under +10% on a 17 yo car that has experienced some neglect may be totally normal. and you have no other symptoms.
poor fuel econ: who’s to say what effect +10% LTFT has on fuel econ. (i guess maybe a 10% reduction?) not enuf ppl out there with scan tools paying attention to this stuff.
rule one for diagnosing fuel economy is get honest about your driving habits. unless you drive like grandma, you may not see anywhere near the advertised economy. after that look at simple things. abnormal brake drag, tire inflation, etc.
note that your car’s advertised econ in city driving is 23 mpg. on the fuel economy.gov, the average of 3 vehicles only report 20 mpg. anyway, 10% of 23 is 2.3, so if u got 20.7 MPG becuz ur old engine needed to enrich the mixture a bit to run smooth, then i guess that’s not the worst thing. and as some sources have indicated, normal wear and tear in places like the valve train may play a role here.
http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=12789Thanks for all the links! I love the Mr. Injector service, and if I deem that it’s injectors, I’ll send it off. But first, need to do more testing.
I don’t usually watch long term fuel trim, mostly short term because it tells me what the car is doing at that moment. I’ll do a little more testing today after cleaning out the injectors by hand and tell you how LTFT and STFT looks at idle.
Fuel trim under +10% is fine to me, it’s under the norm. I just want to clean everything up for optimal performance without wasting money. Cleaning injectors at home is pretty much free if you have some carb cleaner.
I recently replaced the TPS, it’s reporting the exact same numbers as my old one. Found that one in my underwear.
Fuel economy is somewhere around 20 MPG, which is pretty poor for a Corolla. People on the Toyota Nation forums in the section specifically for 7th gens say they get at least 30. And I drive fairly conservatively 90% of the time, I like getting good mileage. Tire inflation should be fine, recently pumped them though I plan to do it again. Brakes in the front are brand new, no drag. Brakes in the back are drums, which should have a little bit of pressure in default position but are unadjusted and are too weak. Other things that affect mileage: Oil is 10W-30 instead of 5W-30 to prevent burning (7A-FE engines like to burn oil), new distributor rotor and cap, new spark plugs (NGK, OEM brand, gapped according to manual spec), new wires, etc.
That does sound logical. I guess that’s fine. But I’ll try to get things into tip top shape over time (I love this car), and get it running even better. But you are right, my mileage sounds fine. Damn you’re smart.
Well it sounds like your car is in good shape.
Fuel trims, short or long, between -10 and +10 on an older motor are normal.
“A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually they’ll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances. It will fluctuate much slower, possibly appearing static.”
http://www.obd-codes.com/faq/fuel-trims.phpSo keep me posted on what else you learn about the car.
In my personal experience taking care of a ton of my own cars i’ve always wanted to clean some part of the fuel system and see improvements. and ive never seen improvement that way. cuz most fuels systems are perfect. i’ve never personally seen a clogged or even dirty injector. i’ve cut open fuel filters and they always look fine. just dont waste too much money throwing parts at problems that arent there. on the other hand i’ve learned a lot that way.
my final thoughts on other people’s fuel economy: a few forum posts is not a conclusive sample size. it may be only a handful of ppl who reported 30+ mpg. also a situation where ppl may be inclined to embellish a bit or not be very specific. I wouldnt tell u that i get over 16 mpg in my explorer. I would tell u i got 16.5 last fill, 17.2 the one before with pure highway driving and 13.7 before that cuz i did a ton of idling and pulled a small trailer at one point. and finally there’s reporting bias. if a hundred ppl read the thread on “what gas mileage are u getting?” the 5 that are at the way upper end are more inclined to post than the dozens like me in the standard, unremarkable range who may not bother posting. so in my experience forum thread ALWAYS make me feel like im getting atrocious gas mileage. but just look at the published numbers. you should average 24-26 with mixed driving, and 20-23 with all city. so u may or may still be getting slightly poor gas mileage.
Oh man, have i got a present for you…
i’ll email you a better copy as well as the other things i said i’d email[quote=”crypkilla” post=62003]Well it sounds like your car is in good shape.
Fuel trims, short or long, between -10 and +10 on an older motor are normal.
“A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually they’ll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances. It will fluctuate much slower, possibly appearing static.”
http://www.obd-codes.com/faq/fuel-trims.phpSo keep me posted on what else you learn about the car.
In my personal experience taking care of a ton of my own cars i’ve always wanted to clean some part of the fuel system and see improvements. and ive never seen improvement that way. cuz most fuels systems are perfect. i’ve never personally seen a clogged or even dirty injector. i’ve cut open fuel filters and they always look fine. just dont waste too much money throwing parts at problems that arent there. on the other hand i’ve learned a lot that way.
my final thoughts on other people’s fuel economy: a few forum posts is not a conclusive sample size. it may be only a handful of ppl who reported 30+ mpg. also a situation where ppl may be inclined to embellish a bit or not be very specific. I wouldnt tell u that i get over 16 mpg in my explorer. I would tell u i got 16.5 last fill, 17.2 the one before with pure highway driving and 13.7 before that cuz i did a ton of idling and pulled a small trailer at one point. and finally there’s reporting bias. if a hundred ppl read the thread on “what gas mileage are u getting?” the 5 that are at the way upper end are more inclined to post than the dozens like me in the standard, unremarkable range who may not bother posting. so in my experience forum thread ALWAYS make me feel like im getting atrocious gas mileage. but just look at the published numbers. you should average 24-26 with mixed driving, and 20-23 with all city. so u may or may still be getting slightly poor gas mileage.[/quote]
I’ll keep an eye on my long term fuel trim, because I’ve reset the ECU so many times it’s all funkeh.
I promised myself not to spend money unnecessarily, and I’m keeping to it!
My city mileage has been around 19, so a bit on the low side anyway. Hopefully it’ll be better now that fuel trim has calmed down, but time will tell.
Also hot damn, thanks for that email! That’s freaking awesome!
take a look at the owner manual in your glove box also. they often recommend a procedure for helping the car relearn idle and shift point after the battery is reset. if nothing else, drive conservatively, lest the computer learn aggressive driving demands. following any procedure offered will help keep fuel economy top notch right from the start, or else it could suffer a bit initially i guess. i think one of my cars just called for the car to idle for a certain number of minutes at first and maybe something else. cant remember.
you’re welcome! everyone should have access to that stuff.
I wish I had the manual. But I know that Toyota offers cut down versions of them, so I’ll look for that info. Either way my next drive will be a two hour drive on the freeway, so that’ll teach it real good. 2,200 RPM constant in overdrive is quite calm and really fuel efficient.
I didn’t get to work on the car today. Needy girlfriend and all 😛 damn priorities. I filled up the gas tank, but it was a partial fill up so I don’t know the mileage.
After the fill up, I drove another 2 hours, or 90 miles, on the freeway. But the city driving was tough, up a tall hill and 5 minutes through a complex at 15 MPH with a LOT of speed bumps. The hill is pretty big. Here is what I got in terms of LTFT and STFT:
Ain’t too bad. Mostly stayed +/- 7 on the freeway, switching between positive and negative like it should, jumped around more in the city, staying more positive. Long term is a little messy, I taught it bad after an ECU reset by testing the car at high RPMs and now it associates high RPM with a higher fuel trim, even when the short term did not go that high.
I’ll test the fuel trim at RPM when stationary tomorrow, and clean the injectors and fuel rail. Then I’ll give the car a good scrubbing, it needs a clean. Here it is at a gas station (warning: crappy cell phone pic at night).
Funny story here. Cleaned the fuel injectors and rail out today. That involved taking apart the intake manifold on my car, so it took a little while. One of the gaskets broke, so I bought new ones. One in the pack was different, so I didn’t use it. I took it for a test drive, and smell gasoline. Also my fuel trim is at 20%. So I stop the car, open the hood, and one of the fuel injectors is spraying fuel EVERYWHERE. Extreme leak. I freak out, yell bad words, and turn off the car. Had my father drive over with tools, we took it apart, checked the gasket, and saw that it was broken in two places. Defective gasket. Put in a new one (I bought double what I needed, and one pack had two defective ones), and put it all back together. Sped run the entire thing, finished before nightfall. I consider this a success. We’ll see how it changes anything, but it’s still a success.
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