Mines RX7

I have been searching and trying to find some info on my air flow meter. I have a 90 GXL and recently replaced the injectors, removed 6th ports, replaced gaskets, and wired open the VDI. I have found a few problems and fixed them. However, now when I have the AFM plugged in, the car will NOT run or idle. But when it is unplugged, it idles great and I get throttle response out of it initially. After it runs for a little bit, whenever I hit the throttle it tries to die. I haven't adjusted the TPS, but I don't know if that's the problem. I have tried resetting my ECU, but still no go. One more thing, last time the ECU was reset, the O2 sensor from the headers was broken. I quickly rigged it together but it still wouldn't start with the damn AFM plugged in! It's really starting to **** me off.

About the BAC, when the key is on, and the car is not running, the BAC valve clicks constantly. Is this how it is supposed to work? Or is it supposed to turn on only when the engine is running?

Mines RX7

bump........

Mines RX7

Okay, here's the long version of the story for those of you who may be able to figure out what is going on.

After I got done boring out the intake manifold and removing the 6th ports, I reset the ECU and started the car. I found that I needed to replace one of the brand new o-rings that I had in my injectors, and I also fixed a gasket leak. So I reset the ECU again and started it. It started, and I was able to rev the engine and it seemed as if all the power was there. After about 20-30 seconds, it wouldn't let me rev it anymore. Whenever I would hit the gas it would try to die, so I just let it idle and warm up because I thought the ECU was just trying to adjust. After it had idled for about a half an hour, the idle was at 750 rpm, right where it should be. But it still would try and die when I gave it gas. I gave the engine a quick look over and noticed that the air flow meter was unplugged. So I plugged it back in, and as soon as I did, it died. Whenever I would start it, it would run for 1-2 seconds and then die. So I pulled the plug out and it started right up and idled just fine. The idle was a little low though, but it's been low since I've had it. So I reset the ECU again and made sure my O2 sensor was securely wired, thinking that maybe the adjustments it made with the AFM and the O2 sensor unplugged wouldn't work with them plugged in, sensible idea, right? No. It still would just start for 1-2 seconds and die right away. So I unplugged the AFM and it started and idled just fine again, but it still would die when I would hit the throttle.

One thing I have not done is messed with the TPS. I don't really know how to adjust it and I don't really know if it's the problem since it does let me rev it when it first starts. Could it be the problem?

Does anyone have any ideas?

Mines RX7

bumpy bump.....

HAILERS

Disconnect the tps and see what happens. The car should be able to run without it. If you have the same thing , then reconnect it. You might have a large air hose off somewhere. Got any bent pins on the afm? Boost/pressue sensor hasn't been messed with, has it? All the plugs back on the ECU, if you took any off? ;You outta gas?

Mines RX7

Okay, I unhooked the TPS, and tried to start it. It did the same thing. Started, ran for 1-2 seconds, and died. That is with the AFM still plugged in. I tried to adjust the TPS, but it didn't seem to make any difference. Then I unplugged the AFM, plugged in the TPS, and started my car. It seemed to have some power loss, but still idled. I did however see a lot of smoke which I am about to research right now because I know that there is tons of stuff on the white smoke symptom. After that I adjusted the dashpot and the cam roller position on the back of the throttle body. It didn't seem to make any difference. As long as that AFM is plugged in, the car does not run.

Oh and one more thing. I tried the ATF trick just to see if it would work. No such luck. I'm stumped. I'm going to go start testing resistances in the AFM and TPS and stuff. If anyone has any ideas I would like to hear them, cause I'm out of 'em

Hailers, I did check out the pins on the AFM plug and they looked fine. I haven't messed with the ECU at all, but I will if I have to.

Mines RX7

Okay, I'm still trying to figure out what's going on. I pulled the plugs, and they were wet, so I went out and bought new plugs, tried to unflood it, but I'm not sure that it worked. I pulled the plugs, pulled the EGI fuse, cranked it with the throttle all the way down and I didn't see any substantial amounts of gas come out of the holes. I put the new plugs in and I'm still having the exact same problem.

I did notice that when the AFM is NOT plugged in, and I try and rev it, it only works while bottom sensor is in contact with the throttle. So maybe it's something wrong with that upper range of the TPS? Or maybe one of my wires is broken that goes to the injectors? I have no idea. I know it's getting gas because the plugs are wet, but I've looked over everything that I can think of and I can't find what's wrong. Maybe I just need to adjust my TPS?

No7Yet

Okay, let me get this straight... you'll start the car, it'll bounce up to the "I've just started" RPM, hold it for a moment, and then when it tries to drop to a "normal" idle level, it dies, correct?

BAC. Plug your AFM back in; I don't think the problem's there.

The BAC compensates for loads on the engine. If it's bad, the car will die as soon as it starts - I just got done diagnosing similar symptoms Saturday. Try replacing it with a known-good unit, or cleaning the one you've got. You mentioned earlier that it's clicking a lot? It shouldn't be. Also try disconnecting it from the engine harness and jumpering a straight 12 volts to it - it should idle at ~1200-1500 RPM, but it'll idle.

Give that a shot, and report back, soldier!

Brandon

No7Yet

Oh, and the reason your car runs like CRAP over 1/4 throttle (er, whenever the narrow-range TPS pot extends completely) w/o the AFM is because the ECU's in "limp home" mode - it won't "let" you go over 1/4 throttle. That's normal.

Plug that AFM back in!

Brandon

Mines RX7

I pulled off the BAC valve, then I hooked it up to 12V, and it seemed to work great. However, whenever I plug it into it's appropriate plug, it still clicks. I pulled it off with it still plugged in to see if I could see what the hell was wrong. The solenoid oscillates back and forth, almost like it's not getting enough voltage. The resistance of the BAC checked out to be 12 ohms, which is good per the workshop manual. So I tested the voltage output on the BAC plug and it only read about 8.5 volts. I think if this voltage was at 12 or near there, it would probably work. Another thing, it only seems to happen if the key is in the 'on' position for longer than about 30 seconds. During that 30 seconds, the BAC does NOT 'click'. So how do I fix that????

No7Yet

Your BAC is working fine - pull the plug, apply 12V to it, and start the engine like that. It should idle.

My guess is that it's a wiring problem. The oscillation of the plunger shows that it works fine, but whatever's controlling it is going wiggy.

Brandon

Keith

Hey, I know it probably sounds idiotic to you, but I think your problem is a bad AFM. I would check the ECU pin 2B, which is the 12th pin from the right, bottom row on the ECU connector. With the ignition on, engine not running, you should see 4V there. If that is okay, start the engine. As soon as it revs up, the voltage should drop to between 2.5 and 3.5 volts, probably closer to 2.5 volts. If either condition is not satisfied, I would replace the AFM. Just my opinion.

Irv, Keith's dad

HAILERS

Bac's are made to oscillate. Something like 125hz. Thats not your primary problem, and probably not at problem at all. Its reacting to the tps(my assumption), thats why its oscillating. Ignore the bac, do as IRV suggests, and if you set your tps without the engine being hot, reset it after the engine gets running and is fully hot. If it was set at any other condition, then its not set right. Read this article http://www.teamfc3s.org/info/articles/idle.html(I know you don't have a turbo) and in it, it explains the bac's operation. But don't get consumed with the bac being the problem. Its just reacting to an output from the ECU and trying to do its job. BAC is your friend.

Mines RX7

Sorry for the delayed reply, I was out of town for a few days and couldn't work on my car. I got back in town yesterday and decided to check out a few things on my car. First thing I checked was the intake air thermosensor because I remember bending the prongs on it when I was taking the intake manifold out. I checked the resistance while it was still in the engine and it gave me something like 80k ohms. I pulled it out and I noticed that the idiot whoever bored out the intake manifold (me) forgot to clean all the metal shavings out of the thermosensor. I cleaned it out, the resistances seemed normal between 15*C and about 60*C. (I couldn't get it up to 80*C, but it seemed to work fine) I reinstalled it and put the BAC back on and reset the ECU again, then tried to start it. It seems a little better now, however, it still dies.

So I dug out the ECU. I started testing voltages and found a few things. The Narrow range TPS was reading about 1.8 volts at idle position. I adjusted it to read 1.0V, but then the full range TPS read about 0.15V at idle position, instead of 0.8. However, at full throttle, the full range read about 4.2V, which seems to be okay per the manual. Is this part of my problem? To fix this do I need to adjust either of the throttle cables?

I also checked voltage to the injectors, the AFM, main relay, and a couple of other things. Keep in mind my car does not idle so I the only voltages I could verify were the ones where you just had to have the key 'on'. For instance, I couldn't verify the 2.5-3.5V for the AFM at idle. Maybe I need to adjust the dashpot on the back of the throttle body? (I dont really know what it does.)

Today, I'm going to go ahead and buy some connectors to jump that BAC to 12V while starting. I don't think that it's the problem anymore, but if it idles, I'll have a better idea of where to look for the actual problem.

PS I appreciate all the help that you guys are giving me. I refuse to take it to a shop and i'm sure that people understand that.

HAILERS

BAC' ocillate at approx 125hz. Its normal on the whole.

Mines RX7

So if my BAC is fine, then maybe it's the TPS??? I read the manual and it only gave instructions for adjusting the TPS while it's warm. So how do I adjust it while it's cold? I was trying to get the same resistance readings on the TPS by adjusting the screw on the front of the throttle body, and there also seems to be another adjustment screw on the back of the throttle body on the drivers side. I could not get the narrow range and the full range to read 1.0V and .75 volts, respectively. I got it closer, but it's still not within the manual specs. What values should I adjust it to while it's cold???

Henrik

Vacuum leak. When the AFM is unplugged the ECU assumes a 'basic value' (quote from the FSM), I don't know what value it picks. When you plug it back in, it gets a real reading. If that reading is low (due to a vacuum leak) it'll stall out. Do you have a vacuum gauge? If so, what value are you getting at idle?

Also a question - do you have the fuel pump test connector jumpered? The AFM has a switch in it to detect airflow - no airflow and the fuel pump is turned off (safety feature) so it shouldn't run without the AFM plugged in.

Henrik
87TII

Mines RX7

I pulled the code from the ECU, (I don't know why I didn't do this earlier) and it gave me an error code of 8. I guess this means that I have a broken wire or a short somewhere in the AFM circuit. I tested all the harness wires and each of them had continuity to the ECU plugs, so I pulled the AFM out of the car and tested it. The manual says to test for the open and closed values, and my AFM tests 800 ohms closed, and 160 ohms open. They seem fine per the manual. However, the transition from closed to open doesn't linearly decrease with the position of the flow cone. when I try and get values for anywhere in the middle of that, it jumps all over. I've gotten values ranging anywhere from 350 ohms to 1400 ohms.

Does this mean I need another AFM? And if I do, does anyone have one that they could sell me? I don't really want to pay the dealer for one.

Henrik, I went ahead and tested the vacuum. For the one or two seconds that it can run for, it shows about 13psi of vacuum. I think this is at about 2000 rpm, but I'm not quite sure. I'm going to fix this AFM problem first and then check the vacuum again. Just fix one thing, and move on to the next.

No7Yet

I think you're barking up too many trees, here - you need to eliminate some things for sure before you move on to new possibilities.

First, I still stand by my BAC guess. Yes, the BAC oscillates, but it shouldn't be rapidly clicking. Restore the car to "normal", unplug and hard-wire the BAC. If it idles, it's the BAC.

Next, try the AFM. The resistance values you got were correct - it should jump around; that's why the FSM only has you check fully-open and fully-closed values. They're the only predictable ones. If you've got another known-good AFM, swap it in. If not, try starting the car while an assistant holds the AFM door or cone open slightly. That will eliminate any fuel-pump-killing, as well as compensate for any vacuum leaks. Does it work? AFM's good.

Last, get some carb cleaner, and test for vacuum leaks. Hold the car at a constant RPM (say, 1300), and liberally spray it at various hoses; when the quality of the engine's running changes, there's your vacuum leak.

Brandon

No7Yet

Oh, and you got the code 8 because you've been running the car without the AFM, and the ECU in our cars stores codes, goober

Brandon

Mines RX7

Well, I haven't exactly been 'running' the car without the AFM. As soon as you told me to plug it back in, I did. And then I have reset the ECU atleast twice before I checked for that code. I know it's reset right now because it's not even hooked up to my car . I think when I have some free time today, I'll jump that BAC. I'll let you know how it turns out.

Oh yeah, and you're probably right, I'm probalby barking up too many trees.

Monty

Mines RX7

I finally got around to jumping my BAC to 12V today because it's been freezing out these past couple of days. I have a couple of questions about the BAC still. First, when I jump it, do I unplug it? or do I leave the plug on and use probes into the back of the connector? And second, how far is the solenoid supposed to open when at 12V? Mine opened about 1/4 of an inch. Should it actually open up further?

Also, when I first pulled the code from the ECU, it flashed 8 times, then shut off, and then turned on for a few seconds, and then flashed once, like it's another code. Code 1 means a trailing coil problem, so I tested the resistances of the coils and they were 1ohm, which is okay. I pulled the trailing plugs, and the rear one had what looked like oil on it. The front one just looked like build up, but the rear one looked like oil. I tested the plug wires and they were okay too. I think the BAC may be the problem, but I would still like to know why my ECU still throws these codes after being reset so many times.

Mines RX7

bump...

No7Yet

1) Pull the plug to the BAC, and replace the ECU leads with your jumper wire. Cake.

2) That sounds about right. The first few I saw only opened a little bit, but yeah, about 1/4" sounds okay.

3) Now would be a good time to change your plugs and wires. Go ahead, I'll wait

4) How are you resetting the ECU? An easy way is to pull the BTN fuse in the engine bay (BTN = Back To Normal). Just pulling the codes doesn't reset anything...

Good luck,
Brandon

Mines RX7

Today I jumped the BAC and came up with the same result. Car starts right up, and then dies as quick as it started.

As far as resetting the ECU, I have been pulling the battery cable off for various amounts of time. It still doesn't seem to erase the codes though.

After I tried it with the BAC jumped, I tried resetting the ECU again. This time I pulled out the BTN fuse, as you had suggested. I left it out for a couple of minutes and put it back in. I turned my ignition ON, and the check engine light was still there. I pulled the codes again and realized that it wasn't just the air flow meter code that I was getting. I was getting several other ones that were probably caused by me diagnosing my car. There was a code for the Intake Air Thermosensor, both TPS ranges, and the BAC.

So my next thought is that it might be the thermosensor. I tested it a few weeks ago, and it tested fine, but maybe it still sucks. Maybe one of the injectors I bought is defective?

And about the plugs and wires, I have pretty new 8mm wires in there (5 or 6 months old). I replaced the plugs a couple of weeks ago to see if it would help, so they are new too.

What do you think I should try next?

Monty