Engine Running Rich?

[Tonyman108]

Hi folks. My 2005's fuel economy and engine performance started dropping at about 600 miles. At the time of my 1K service, I just had a mild suspicion that there was a small loss of mid-RPM power, and that my commuting (40-60mph, no stop-n-go) MPG had dropped from the low 30's to 27 or so. I had pretty much expected to see the opposite trend as the engine broke in.

However, at that point, the service guys didn't see anything obvious, and I couldn't swear that these percieved differences weren't due to a combination of my getting used to the rush of driving the thing, and therefore driving it more aggressively more often.

Well, now I'm at 2600 miles or so, and I can't break 25 mpg on my commutes, even when on my best behavior. I've also noticed some more obvious engine glitches. I'm stuck at my in-laws away from my car for several days, fretting, so I thought I 'd post.

Here's what I'm noticing; what does this add up to to you guys?

- It still starts pretty well.

- At high revs (>6k) and full throttle, everything seems just about fine; both by the seat of the pants and by the reading on the speedo in 5th (don't ask where!).

- Applying part throttle (say 20%... enough to get you 3500RPM in neutral) off of idle results in noticable lag at 1000 rpm, then again at about 2500, then the revs rise smoothly to their final destination.

- It sound like fuel is lighting off in the catalyst when backing off even lightly from part throttle, and sometimes just when cruising at light throttle (various uneven, burbly sounds at, say, 3000 RPM in 3rd on a level road). I also recently heard a distinct 'whump' (AKA, a backfire) from the muffler, in a short 1-2 upshift under mild acceleration. I expect to hear this from my buddy's Cooper S under a hard downshift, or just about any time from my old TR-6 with a hot cam and mis-tuned triple Webbers, but it seems odd to hear these noises coming at low revs from a normally aspirated car with EFI and variable valve timing. Is it?

- The engine feels distinctly flat in 4th or higher gear unless I'm up over 5500 or so. I could swear it pulled better before.

- All this stuff is much worse when the engine is cold, but still persists in a warm engine.

- The tailpipe looks a bit sootier (the flat black variety) than I'd expect in a modern car with 2600 miles on it. Of course, this is the only 'modern' car that I have with this sort of performance, so I have nothing to compare it to.


So... if this wasn't a computer-controlled engine with a gazzillion things that can trick me out, I'd think:

1) It can't be spark, or the high-RPM performance would be awful
2) The thing is running rich, on one or all cylinders.

I'd like to get a better handle on this before blowing a day at my (somewhat distant) dealer and being told "they all do that". So I'm thinking I should pull the plugs, and see if one or more of them look odd. I'm hoping that a single sooty plug will tell me something, like that one of the injectors doesn't shut off very cleanly. Failing that, I thought I'd do a compression test, for peace of mind if nothing else.

While I'm getting dirty, what else can I check? Is there any way to test things like throttle or airflow sensor performance without an unreasonably large outlay for diagnostic equipment?

For the record, I love the car anyway.

[aletes]

I would check the MAP and MAF sensors (the Elise has both).

An inexpensive OBDII scanner should be able to read the error codes on your ECU. The ECU codes should tell you if either the MAP or MAF sensors have failed. Although, if your check engine light is not on, I doubt you have a sensor failure.

It is more likely that your MAP or MAF sensors are not providing accurate readings. In order to test the MAP and MAF, you will need a digital multimeter and the factory specifications from the service manual. I don't have the info from the manual, but you could post either here or on EliseTalk and ask someone to scan the pages related to the MAP and MAF sensors.

I doubt you are having a problem with the air flow through the cold air intake, airbox, filter, or manifold. Also, it is unlikely that you have a bad spark plug. If you were having any problems with airflow or ignition, performance would most likely degrade at high RPM.

[Tonyman108]

There is no check engine light on, and there were no codes at the 1K service.

I don't think I have a bad plug, but I was thinking that a fuel injector problem might show up as a sooty (or wet) plug.

So I guess I haul out my DMM and order the shop notes. Somehow it seems fitting that this might turn out to be an electrical problem. Gee, this is starting earlier than I thought it would ;0)

I've owned an MGA, two B's and a TR6, but then got spoiled by owning a CRX Si and then a Miata; I beat the tar out of both of them for ten years, with nary a hiccup. It is going to be pretty funny if it turns out that the reason the Elise is going to give me that good old British ownership experience is its Toyota engine!

About that OBDII scanner; does anyone have a suggestion as to a good one, preferably one that knows how to read (and possibly erase) the engine history data that the car seems to be accumulating? I find it somewhat disturbing that my mechanic can tell me how many times I've gotten rubber since buying my car!

[aletes]

Originally posted by Tonyman108
About that OBDII scanner; does anyone have a suggestion as to a good one, preferably one that knows how to read (and possibly erase) the engine history data that the car seems to be accumulating? I find it somewhat disturbing that my mechanic can tell me how many times I've gotten rubber since buying my car!

Here is some info on OBD II scanners for the Elise ...

http://www.elisetalk.com/forums/show...&threadid=7330

Here is some info on the Elise ECU ...

http://www.elisetalk.com/forums/show...&threadid=6633

[aletes]

Here is a photo of the MAP and MAF sensors ...

http://www.elisetalk.com/forums/show...MAF#post100768

[erok]

First post here. Coming from a 2000 Celica GTS owner with over 80k miles on it. Try changing gas stations. I've gotten noticeably different performance for a tank at a time. Also weather can play a part. The engine is particularly sensitive to changes in outside air temps, seeming to run best around 40 degrees F in my experience.

Make sure the engine is completely full of motor oil. I swear my can runs better with the oil filled to the max line on the dip stick.

A dirty MAF sensor is often the cause of bogging and rough idle with this engine at higher mileage. Especially if used with an (over) oiled cotton air filter.

Flooring the throttle @ 1000 rpms in anything other than 1st gear can cause the engine to bog. The engine barely makes any torque below 1500 rpms. This is especially the case in cars with the mechanically actuated throttle body engines. In 2003, the Celica got drive by wire throttle however. I assume that's what the Elise has.

In any case, a somewhat lumpy idle and erratic low rpm behavior is widespread in Celicas. It seems to go away with time to a degree as it is rarely a topic of conversation on the celica boards anymore. But it used to be.

I'd top off the oil and change your gas station for a tank or two. If that doesn't work, you can try the MAF sensor, though it shouldn't be dirty yet. Also remember that (at least in the Celica) the ECU has several different fuel maps aimed at getting good milage and low emissions. So try running it through the gears shifting at redline a couple times and you'll know it's running the high performance map.

In my experience, the 2zz has been extremely reliable and trouble free. But keep in mind many Celica owners including me have noticed subtle performance changes with their cars from time to time. Not to worry, after five years my car is running stronger and more smoothly than it ever has. This engine should last well over 100k miles with proper routine maintenance.

[adam]

A couple of things I would try:

1) Check for vacuum leaks. Sometimes this will cause a CEL, but most of the time it doesn't.

2) Also check for carbon fouling. Pull of the intake hose and open the throttle body and stick your finger in the throttle body and see if there is alot of black build up. If so, then get a can of throttle body cleaner. You will have to change the plugs about 5 miles after you finish the procedure.

[Len]

I have found that the majority of engine "fixes" amounted to adding gas cleaner to my fuel tank whenever performance dropped off. Usually, it crisped things up immediately. If the car is set up to run rich, it runs great at high RPMs but can foul plugs quickly if you don't keep your revs up. I don't have an Elise yet but I used to run NGK plugs (great for high Revving engines) in my Ferrari and change them each time I had an oil change, about every 3,000 miles. They're cheap and easy to change. I had a quick one.