From: Alex Pun (75104.2070@CompuServe.COM) Date: 09 Oct 96 20:55:45 EDT Subject: MR2 AFM Hi, Today I wanted to check my air filter in my MKIIT. I wanted to disconnect the AFM cable so that I could access the air filter. I began by unscrewing the two little screws and after it came out part way, I noticed that was not how the cable should be disconnected. So I put the screws back and saw the wire clip and unplugged it that way. After checking the air filter, I put everything back as it was and now my car won't start. I checked the diagnostic and as expected, it indicated something wrong with the AFM signal. I also noticed that when the key is in the on position, I hear a slight hydraulic sound coming from the front end of the car. Now, I can't even get the diagnostic to work again. Did I damage my AFM? I didn't think that I could because I didn't force anything. Is the AFM that fragile? Why does the diagnostic not work either? Thank you for any help you may provide me with. Alex 1991 MR2 Turbo
From: garye@voodoo.ca.boeing.com (Gary Eng) Date: Wed, 9 Oct 1996 19:08:33 -0700 (PDT) Subject: MR2 Re: AFM Ah Alex, You made the same mistake I did in 1993. Here is my repost of my experience. I repost this one about once a year. =========== cut here ============ I think it is not a problem to do routine maintenance ourselves. My problem was I made a mistake. To recap the mistake: there is a small bundle of wires that plugs into the air-flow meter on the top of the air cleaner. This bundle unplugs from a connector on the meter. Due to brain fade, I did not notice that it unplugs, and I started to remove the entire connector from the meter. DO NOT DO THAT! That action upsets the alignment of internal parts in hte electro-mechanical portion of the meter, which cannot be reset/repaired without knowledge of the internals of the meter. That action also tears the foil that connects the pins to the circuit board. In other words, it's broken. If you just disconnect the plug from the socket, then changing the air filter is not a problem for us home mechanics. Further discussion of the broken air-flow meter Toyota's shop manual does not have any repair procedures for the air-flow meter. The manual does contain some diagnostics tests. If the meter fails any of the tests, then the manual says replace the meter. I called several dealers. None had the meter on the shelf; it's a special order item. Cost? A mere $500.00. Since my meter didn't work and according to the book there was nothing to do except spend $500, I felt I had nothing to lose by disassembling the electro-mechanical portion of the meter. Doing so, I was able properly to reset the connector into the meter, so now the meter passes the diagnostic tests. I reinstalled it, and my car seems to run fine, according to my ear and the seat of my pants. However, I have not yet checked if the engine parameters are still within normal limits. So I am _NOT_ recommending this repair to anyone else. Remember, Toyota says to replace, not repair, this unit. The air-flow meter sends information to the engine's computer, which controls all of the engine's operating parameters. Among those parameters are boost, fuel mix, spark, and spark advance. If these are not to spec, they can cause internal engine damage that is much greater than the $500. [To borrow from Dan Barnes: These are just opinions and only my opinions. They may be wrong, so don't act on them in a way that could cost you lots of money without first getting several other opinions. They aren't the opinions of my employer.] =========== cut here ============ > Alex Pun writes: > > Today I wanted to check my air filter in my MKIIT. I wanted to disconnect > the AFM cable so that I could access the air filter. I began by unscrewing > the two little screws and after it came out part way, I noticed that was > not how the cable should be disconnected. So I put the screws back... > and now my car won't start. > > Alex > 1991 MR2 Turbo > - -- Nothing here should be construed to be the opinion/position of my employer. gary eng garye@voodoo.ca.boeing.com
Date: Thu, 10 Oct 1996 10:33:03 -0700 From: Jeffrey Ho-See (jhosee@orion.davd.com) To: Alex Pun (75104.2070@CompuServe.COM) Subject: Re: AFM > Today I wanted to check my air filter in my MKIIT. I wanted to disconnect the > AFM cable so that I could access the air filter. I began by unscrewing the two > little screws and after it came out part way, I noticed that was not how the > cable should be disconnected. DOH! I didn't wanna do a Homer in front of everyone on the list, so I didn't inform everyone of the same mistake I did. :( I did exactly the same thing 4 days ago. Okay I won't be so ashamed to admit it next time, if it really will save someone of painful learning lessons. > and unplugged it that way. After checking the air filter, I put everything back > as it was and now my car won't start. Yep you screwed up the AFM. You pulled off the other sides connectors to the circuit board like I did. It's very delicate. > end of the car. Now, I can't even get the diagnostic to work again. Did I > damage my AFM? I didn't think that I could because I didn't force anything. Is > the AFM that fragile? Why does the diagnostic not work either? Yes. I am very disappointed in Toyota build quality. Some things they do very shoddily (brake pin switch design). Honda just finds the cheap way around. *sigh* Anyhow, what you need to do is ... with a pick remove the silicon from the top of the AFM housing. Then gently pry up the black cover (there are sensitive things beneath -- so don't screw that up either.) Once you have the cover off, note how everything is BEFORE you touch anything. Certain things are plugged in, and one prong needs to be in the correct position. Unscrew the plug, now you see where you ripped em off the circuit board? Go to Radio Shack and get some solder fluid (you need a flame/lighter to cure it) A solder iron will burn the delicate circuit board (as I found out). Apply the solder fluid, reinstall the harness. Be careful not to apply too much solder as it will spread across the circuit board. Once you're convinced it's not messy... cure it. With a multimeter, verify that the harness pins are indeed connected to the circuit trace (continuity test) Reassemble and use some silicone to seal. I am too scared to even ask Toyota what a AFM costs ... guessing a brake pin switch costs $50, I'd imagine a AFM to cost several hundred. Good luck! Doh! - Jeffrey (if you have further questions) 310-793-0600 x1856 work 310-540-5468 home
Date: Thu, 26 Sep 1996 08:02:19 CDT From: "Terry McLane 312.630.0533" (MCLANE.TERRY@ntrs.com) Subject: Re: richen up fuel mixture To: toyota-mods@cyberspace.cyberauto.com The Nippondenso (Bosch-Style) flow meter is designed to be wide open at peak torque- moving the arm or adjusting the spring tension will not affect wide open throttle richness. Remember that at peak torque, the engine is also at peak efficiency. As rpms increase, the volumetric efficiency falls, causing the mixture to richen. Therefore no extra fuel is needed for each cylinder event. There is compensation made by the computer depending on the MAP sensor in turbo applications, and for the MR2 and All-Trac, they are quite rich at WOT anyway. Modifying the MAF will change the part throttle fuel enrichment. If you add efficiency in the form of headers or high-flow filters, the engine can be slightly lean during part throttle operations. On my All-Trac a three-inch downpipe, an HKS Cat back, and a K&N, I have loosened the spring 8 teeth, this has a marked impact on part throttle response. I played with mine a lot; since it is a log device, it is difficult to get it to be optimal at all part throttle operations. For those familiar with those funny carb things, moving the arm is like changing primary jets, adjusting the spring tension is like adding more accelerator pump! For across the board operations, including WOT, you can modify the mixture in several other ways: Hooking up a (640 ohm I think) resistor across the coolant temperature sensor will defeat closed loop operation and fool the computer into adding more fuel (like adding a choke, without CFM drop) by making the computer think the engine is not warmed up. This should be used carefully, since it will also disable the cooling fans. You can also hook up a potentiometer to the thermistor leads in the MAF, allowing you to trick the computer into thinking the air is colder (richens the mixture), or warmer (leans the mixture) across the board. My recommended approach is to purchase an adjustable fuel pressure regulator- this is probably the easiest approach, and won't affect closed loop operations. Terry Mclane tm8@ntrs.com '90 All-Trac