Here we go again.. I thought I had this fixed but this gremlin appeared last night.

Basics: '86 n/a, new ported motor (just out of break in period), all emessions removed. Full exhaust (with RR headers, no cat), Airbox removed and cone filter attached to AFM. Oil Metering System Disabled and pre-mix in fuel.

The car will start up fine (a little rough when cold and gets better when warm). Also when it is first started when cold it will try to die any time the throttle is pressed but that only happens for around 30-45 seconds.

Because I have not re-ajusted the throttle linkage and idle after having the intake manifold off for two nights in a row it idles around 2000 rpm (good sounding and farily steady).

After sitting and running for around 1 minute (maybe 2) the exhaust headers begin to glow. They get very bright and I have not let the car run more than 3 minutes like this.

I tripple checked the CAS to make sure the timing was not way off and checked the pressure at the rails to make sure I did not have a fuel pump/fuel filter problem. Both of them checked out fine. Then Convinced I had a fuel injector problem (110k + miles on injectors) I decided to swap out the stock N/A injectors for some cleaned '87 T2 injectors I happened to have laying around (Yea I know they are bigger and yes they are Low OHM).

After putting everything back together I started it up again and the same thing happened.. After around 1 minute at a very fast idle (~2000prm) the exhaust headers would begin to glow again. Again the fuel pressure checked out.

This morning I pulled the CAS and tried it one tooth in each direction of the set point.. In all cases the exhaust would glow (although runs better when set properly).

I am at a complete loss. I have done everything I know to fix and or diagnose all problems associated with glowing exhaust headers [running lean, extreme timing problem].

Any ideas of something new to try or test?

Is it possible the Air Flow Meter has gone bad and is giving the wrong air reading to the ECU?

What other sensors could of gone bad?



FYI: Time is of the essence. I have to load the car on my trailer tonight because I am supposed to leave EARLY tomorrow morning to attend the Solo I at VIR this weekend (13 hour drive for me).

Thanks.

 

Hey there C! You two be careful going to VIR.

Are you still running the O2 sensor? I can't remember seeing it but I'm assuming you still have it and its mounted after the header goes to a single pipe. Maybe its not working properly. Its a little late but I still have the TII AFM if you want to try it and some extra O2 sensors as well as the ECU from a S4 automatic.

M

 

Yup, sounds familiar. I have a ported 86 GXL, with a RB midpipe and presilencer. When I first put the engine back in, the car wasn't running right. I took it for a test drive, and when I came back from around the block, the exhaust manifold was cherry red. After that, it would only take a minute or two of idling to produce the same glowing results. I spoke to everyone I could get a hold of, but there were no answers. After 4 months of tinkering and swapping CAS, coils/igniters, CPU's, BAC's AMF's, I decided to take it to Mazda. Their rotary guy came in and looked at it. He did tests with all the Mazda computers, and after 13 hours of work- ($783 can in labour) he found the problem: so here it is.

On one of the initial tests, the computer said that the Air Flow Meter was bad. The guy proceeded then to put a new one in out of a working 87. No change- so he kept on looking. When he put that AMF back in the working '87, it suddenly had the same problem as mine. The problem was that there was a short in the harnass going into the AFM, which was blowing every AFM that was put in the car. He fixed the short, I put a new (used) AMF in the car, and havn't looked back.
Your AMF is bad. My advice to you: Go to a scrap yard and get another AFM, and MAKE SURE that he'll give you another one if it is no good. Put it in the car, and if all works well - do a little dance. If it doesn't work, then take the AFM back (because you just blew it - but don't tell the scrap yard that), get another one, and start looking for a short in the wiring. My mechanic told me that when he started doing some tests, it wasn't hard to find the short. Anyway, I hope that my financial raping can benifit you - good luck!
Nick

 

Nick86,
Thank you very much. This probably means that I will not make it to the event this weekend but I am going to try like hell!
During the install of the motor the wiring harness was on and off the car countless times. I either damaged the AFM or the harness. First of all I will try an locate a junk yard that has a AFM. (FPrep2ndGenRX7, thanks for the offer and I might take you up on it but I will try and find one locally today. BTW: I forgot to return your impact wrenches!!)
I will try and contact Mark at KirkRacing to see if he has a spare one sitting around his shop.

As soon as I get home I will start trying to find a short in the wires going to the AFM.

 

Before you go that far... make sure your leading plugs are firing. This sounds to me like the leading coil pack is not working. The car WILL run on just trailing... but it will be a bit hard to start, WAY down on power, and the exhaust will get hot like this.

Brad

 

I forgot about the impact guns. If you can't contact Mark soon enough or if he doesn't have one, you are welcome to come to my house tonight and get my spare one. I know its kinda far to drive but its free. If you do decide to come over can you bring the guns if you go home first? I may need them this weekend with the engine install but its no big deal if you can't. There is other work still to be done.

P.S. - I have a spare ignitor also but I don't know if its the leading or trailing. We can pull one of the skunk car if necessary.

 

Can't you just check the voltage from the AFM at idle?
I haev an S5, so they may be different, so my numbers won't help you, but I'm sure someone can tell you the approx voltage at idle.
It is an oscillating signal too.... sortof strange, but I beleive it can still be diagnosed with a voltmeter.
If you still have the o2 sensor in, you can check the voltage from it- see if it's running to lean. Even take your AFM and reposition the gear out a few teeth, to make it run richer.
I don't know... I havn't tinkered too much with the AFM.

 

I tried everything to the extent of my rotary knowledge and failed. I missed the event this weekend.

Here is what all I tried.

I located 3 spare AFM's. Two of them from running cars and one from an unknown car.
First thing I did was to check for a dead ground on every wire between the AFM and the ECU. I then checked for a cross signal from every wire on the AFM to every other wire that goes to a plug on/near the ECU. None of them turned up any short circuit.

And per the vauge factory service manual I checked all 4 AFM's I had. The one that was on the car was very slighly out of spec so I thought we had it figured out. I put on one of the AFM's that checked in the specified range and started the car up. It seemed to start better and hold a better idle but within 2 minutes at 1500 rpm the headers were glowing again.
I played with the idle a bit and got it down to ~1000 rpm and it took a bit more time but the headers started glowing again.
I then dug out my box of coils that came from a running car and swaped out the leading coil (and did not hook up the MSD ignition). Same result. glowing headers after around 2 minutes.
And somewhere in there I put on new plug wires and new spark plugs. No change.
I then idled the car down a bit more (~800 rpm?) it was a rough idle because of the porting of the motor but it was enough to keep it running. This time the headers did not glow. But if I gave it enough gas for it to rev up to ~3000 rpm the headers would glow in about 30 seconds.
I set the idle back up to around ~1100 (where it is the smoothest idle) and the headers would start to glow again in around 2 minutes just as before.
I also tried manually forcing the AFM trap door open farther than it naturally sits at idle and the glowing headers went away. That tells me it is still a fuel problem. I thought about relaxing the return spring in the AFM to fool it into always reading more air than normal but that is just a hack fix that would mask a serious problem.

And just to recap.. this is ported 13b motor, running 550cc injectors in primarys, fuel pressure is in spec, timing is set, TPS is set, I have confirmed all 4 spark plugs are getting spark, etc. etc.

Anything else to try before I haul it to ATL to Mazcare?

 

Well, that sucks. Did you test the AFM once you took it off the car. If the one that you put on was in spec before, and out of spec after - there's a problem. Have you tried swapping ECU's? Your computer could be leaning the car out for no reason, just a thought. You might want to recheck the O2 sensor connection and voltage as well. At what point in the system did you check the fuel pressure? Right near the injectors, or back by the fuel filter? Also, make sure that when you rev the engine, the timing mark advances.

Nick

 

you said you are running 550's in the primary? is that correct or are you running 550's in the secondary's? if you are running the 550's on the primary's what are your secondary's? this is a n/a right? you can turn the wheel in the afm to righen it up turn it clockwise. but if more fuel is needed you should try an s-afc instead of the afm thing.

 

you said you are running 550's in the primary? is that correct or are you running 550's in the secondary's? if you are running the 550's on the primary's what are your secondary's? this is a n/a right? you can turn the wheel in the afm to richen it up turn it clockwise. but if more fuel is needed you should try an s-afc instead of the afm thing.

 

I have not pulled the AFM now that it has been on the car to check it again. I will do that next time I have a chance to work on the car. I assume that it will check out just as it had before. I am confident there are no shorts going to the AFM that would destroy it. And if it were shorting out I would expect the AFM to be completely fried and not just slightly out of spec like the original one was.

I have not swapped out ECU's. The only other ECU I have access to is out of an automatic (I have been told there is no significant difference). The only problem it I have about 1.5 hour drive each way to get it.

I do not have an o2 sensor hooked up. The RotorSportsRacing headers I have do not have a o2 sensor bung on it. And bescides the car ran great and with out these problems for nearly a year with out an o2 sensor. This has all started since the ported motor install.

When I Checked the fuel pressure it was about 1/2 way between the fuel filter and the primary injector rail.

And I have seen the timing advance when using a timing light as the RPM's rise.

 

I have the 550cc injectors out of an '87 Turbo II in the primary positions just because they were the only other injectors I had. I swapped them trying to rule out faulty injectors. At any rate they should of helped a little bit with the extra fuel that the ECU does not know it is giving. But it did not seem to help at all. FYI: the secondary injectors are stock N/A (480cc?) injectors.

I know I can change the amount of "unmetered" air going into the AFM by the set screw but I think that will just be a hack that masks a more serious problem. There are plenty of people out there running their stock FI with a ported motor that do not have any of the problems I am having. So I know it is possible to get it to run with a proper air/fuel mixture and proper timing with out faking a signal to the computer.

I may be totally wrong but I don't think it is truly a lack of fuel problem.. I think it is an electrical/mechanical problem that is causing a lack of fuel.

 

i thought it was a rich running condition? not a lean running condition. reason being is if your running 550's in the primaries and you opened the flapper door whic would create more air and that solved your problem then i would think your running to rich.

i'm not sure but i'm pretty sure, that the others that are running stock fi systems on ported motors are doing just that, running stock fi systems. 550 primaries are not stock the n/a secondaries are actually 460 if you could i'd try to swap in those if possible.

just to make sure you did say that when you opened the flaper door more than normal the condition went away right? if so i'd say running rich try an s-afc or something similar and set your idle fuel down.

 

Opening the flapper door did not in any significant amount give any more air to the motor (the throttle plates were closed and car was at idle). What it did do was fool the ECU into thinking it was getting more air than it actually was. And in turn it gave even more fuel, the extra fuel would cool the exhuast temperature.
I know that in some cases that way too much fuel can cause over heated exhaust because it actually burns in the exhaust and not in the motor. But if that were happening on my car fooling the AFM would of made it worse. RIGHT?

I know that it is not normal to run the 550cc injectors on an N/A. The reason they were put in there was because they were the only other injectors I had in the garage and I wanted to eliminate the posibility that I had bad stock injectors. And those remain in the car because it is a 2 hour job to swap out the primary injectors.

 

how much of a glow are we talking about here? on my 91 n/a, the downpipe section on my bonez high-flow cat slightly glows red. you can't see it if there's any light, but at night if you look under there, it has a faint glow to it. i gave them a call and asked if that was normal and they said it was fine.

if your headers are glowing in daylight, you may have a problem. did racing beat say anything about how much the header should glow?

john

 

He has stainless steel headers. They may glow a little at sustained high rpm's under a load but not at idle.

 

I had a cheapshit Pacesetter before and it didn't even glow at idle.

 

I am 99.99999% sure this is not a cheap header problem. The headers I have were made by RotorsportsRacing. They are made of stainless steel and are very heavy. I will pull them from the car when I get a chance and measure the flange and tubing wall thickness just to be sure.

When it was at its worst it was bright red from the motor and down both header tubes around 18". On past RX's I have owned I have seen slighly glowing headers after a very hard run. But this is glowing like the cooking eye on a stove when at idle. And this is VERY visible in the daylight.

I am going to borrow a spare ECU from a buddy of mine and see if that takes care of the problem. If not I will just give up and tow it to Mazcare in Atlanta.

 

Maybe you have something clogging up your exhaust. Did you maybe shove a towel in there when doing the motor swap? Or maybe even a dead animal.

Just a thought!

 

ya that's is what i meant it was seeing more air that is why i was thinking it's a lean condition. do you still have your rich lean screw? what position is it in? and what kind of port did you do again? ya i remember you saying why you used the 550's are you sure they are getting the correct voltage? have you tested them, and your sure they are the low resistance? hmm, and you already tested line preasure at the injectors you might be running to small a fuel line for the 550's did you change the size of the fuel line for the primaries. you said you already tried to change the computer w/no change in condition so i don't think that's your problem. have you tried a fuel pressure regulator or riser? that might provide the extra fuel you need to richen it up. just a few thoughts i'll wait for your responce.

james

 

ok i reread the begining posts so disreguard the questions on tests you have already conducted.

 

Quick question:

Your air box is gone, and you have a cone filter directly on the AFM. Is the AFM held securely in the stock location? You havn't turned it on its side, or left it loose have you? That could effect it's performance too. Just a thought.
Nick

 

TPS? Timing retarded?
Keep at it. Doubt mazda will do much more to the car then you are already doing.

 

I have now tried 2 different ECU's, 4 different AFM's (all check good befor and after), check and adjusted every other sensor known to man.

I know I have good fuel pressure, I know the injectors are firing, I know the spark plugs are getting spark, I know the timing is set. etc. etc. etc.

I must of fixed a vacuum leak the last time the intake manifold was off the car because I can now get it to idle down at 1000. And when idling at 1000 the headers no longer glow. But if I tach the motor up to around 2500 rpm and let it sit the headers start to glow in under 2 minutes. I know that headers will glow after hard runs, but I don't consider 2 minutes at 2500 rpm with no load to be a "hard run". No telling how hot the exhaust would get down long straights at WOT. There has to be something wrong that I just don't know about. But with my luck it will end up being something really silly and simple.

I also checked to make sure the headers were not thinner than they should be. The wall thickness of the tubes are just a hare under 1/8".. so I imagine they are 0.120 tubing. Plenty thick enough stainless to stand up to a normal runing rotary.

So today I am putting it all back together and running it one last time then it is getting loaded on the trailer and we are headed to Mazcare with it. It is not that far of a drive and mabye I can talk the wife into hitting tonights Brave's game too!

Thanks for everyones help. I will keep the board up to date with what they find.