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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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Try this. Remove the filter and plug off the intake
with a rag. see if the car stays running. if it conks out
then not a massive vac leak.If still running massive vac leak.
Here is the thing. Your adding fuel for a lean condition. It could
be fuel. Either your injectors could be dirty or your intake valves
could be full of carbon acting as a sponge.causing the o2 to read lean
causing the computer to add more fuel.I’m sure it’s a tiny vac leak, if it’s a leak at all. Because it’s not compensating enough to cause a CEL or cause any problems. Car runs well.
I didn’t really think about the fuel system being an issue. I cleaned out my fuel injectors a bit, but not much. Might do it again. Valves is a more complicated issue… I’ve never messed with that.
Have you tried seafoam in the tank? Seafoam also now
has a spray that you can fog the engine. I would run
seafoam in the tank and fog the intake. see if that helps.Is there a difference between the spray and running the Seafoam through your brake booster lines?
And I have used standard Seafoam in my tank a few times, along with Techron injector cleaner recently.
what I like about the spray is it atomizes instead of that heavy
cylinder dump. If you remove your TB. can you get your hand in
the intake? with that long straw. if you can reach in the intake
and spray the seafoam in each intake runner.wash the walls and soak
it down. don’t start the car.Let it sit for at least a half hour.
reinstall your TB then start the car.Oh, I see. Then I’ll pick up some spray.
Without the TB I cannot fit my hand into the intake. Far too small. But I can take off the intake manifold cover and spray the stuff down the intake runners, though I cleaned around them pretty well with carb cleaner. I’ll try that out though.Any advice on the best way to clean fuel injectors when they are out of the car?
A little googling and I found this:
“For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak”
along with fuel delivery issues, that site also mentions exhaust restrictions
http://www.easterncatalytic.com/education/tech-tips/fuel-trim-can-be-a-valuable-diagnostic-tool/[quote=”Haloruler64″ post=61821]Do you suggest doing it when the car is warm?[/quote]
Im no expert but i suggest doing anything regarding fuel trim when the car is warm (in closed loop). The computer is doing different things with fuel when in open loop.
My car goes into closed loop after 2 minutes, even when the needle is still low. I just ask because the car seemed to run a lot more rich when it’s cold than when it was at operating temp last time I watched it. I’ll do it at operating temp today.
do u have a MAP (manifold absolute pressure) sensor? or a vacuum gauge? i think ETCG has a video on looking for exhaust restrictions that way.
[quote=”Haloruler64″ post=61825]the car seemed to run a lot more rich when it’s cold than when it was at operating temp[/quote]
well here’s what i dont know. Every car runs richer when cold. but is that supposed to be reflected in the short and long term fuel trims? is it a fuel trim? i would think that even if the computer’s fuel maps call for a richer mixture at start up that the fuel trim should still be around 0 cuz the computer isnt enriching an abnormal lean condition, it’s just enriching cuz it’s suppose to.
so im clearly no expert and maybe STFT and LTFT is how the computer accomplishes enriching cold start mixtures in which case the higher LTFT at start up is expected. wish i knew.[quote=”crypkilla” post=61826]do u have a MAP (manifold absolute pressure) sensor? or a vacuum gauge? i think ETCG has a video on looking for exhaust restrictions that way.[/quote]
I’ll check out his videos on exhaust restrictions very soon. I do have a MAP as far as this crappy Chilton manual is concerned, but I’m wary because it’s misinformed me before. Pretty sure I have one though.
My short term fuel trim goes really low when cold, meaning that the computer knows and tries to compensate? I am actually unsure, as logically it’s supposed to recognize that it’s normal. Fuel trim of -19% when cold is normal though, so I guess that answers my question. Test at operating temps.
And yeah, not sure if it affects long term fuel trim, logically it shouldn’t but I don’t know. Cars are weird.
you could use the MAP sensor value on your scan tool to diagnose exhaust resriction instead of a vac gauge like in the video.
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.
http://www.homedepot.com/p/Bernzomatic-UL100-Basic-Propane-Torch-Kit-334458/203665003#.UakTWJyGs7Y
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