Felgar

Well the work on my project RX is wrapping up... She's been on stands for 8 months and wants to come down! Anyways the majority of work was asthetic (rust, etc) and also it seems like I fixed about 100 small problems like indicators not working, fender bolts missing, etc.

Anyways, I got the car from my unlce who 8 months previously had the engine rebuilt. At the same time they put in custom headers and exhaust, an oil cooler in front of the radiator, ported intake, and different injectors (I think). It also has cold air intake from in front of the rad; is that stock?

I only drove the car for about 5 days before parking it but it backfires pretty badly - it happens worst when I let off the throttle just after hard acceleration through a gear. As the RPM hits about 2K as it falls back down it will do it almost without fail.

So I figure that at a minimum I want to go through the car and make sure as much of it as possible is tuned and set correctly. I have no idea where to start though. There's the idle control and fuel mixture but after that I pretty much have no clue where to start (or even how to know that the mixture is adjusted properly) and I'm open to suggestions. Do those spark plug tester kits from Victoria British work good?

If more info on the mods is required I'll talk to my uncle and see what I can dig up. I can also post pics if they'll help. Thanks everyone.

Rx-7Doctor

iTrader: (13)

sounds like you need to make sure the tps is working properly and the acv also. is this a gslse 6 port motor? Check for leaks around the intake area If he put different injectors in, what are they, if this is a 6port gslse, the injectors are big enough and without a piggyback
controller or hall tech computer to control fuel flow, you wont be able to correct the problem.
also make sure your vacuum control is working to the fuel pressure regulator. I would like to see pictures of the engine and cold air intake. e-mail them to me at rx7doctor@sbcglobal.yahoo.com.

Felgar

Sure thing rx7doctor. I'll take them tomorrow and post them here as well as email them to you. The car is in my bro's garage accross the city otherwise I'd take them now.

I'll see what info I can big up on the mods - I'll be talking to the original owner later on tonight.

It's funny I've been driving a GSL for 5 years now and until I start tackling some new thing I have the general impression that I know a lot about these cars. Then invariably something comes up and that illusion quickly fades.

Felgar

K I talked to last owner... (this might be a little off cuz he was going by memory)

- The injectors are 800's or 820's.
- It is 6 port. It's ported pretty aggressively (from about 1/2" x 3/4" stock to 3/4" x 1 3/4" from what he told me - could that be right?)
- The intake manifold is also ported.
- The exhaust is custom right from the headers (header, resonator, muffler, etc) - not sure of the exact specs but it's obviously high-flow based on the fact that he melted the bumper with exhaust heat.

Does that info help at all?

LongDuck

He's melting the bumper with exhaust heat because he has a lot of unburned fuel in the exhaust causing the heat. The unburned fuel is there because the injectors are too large for the ECU to control effectively.

Using 800cc injectors is going to throw the ECU coordination of fuel flow off by a lot because the injector mapping is very simple when in open-loop mode - in effect most of the time unless in 5th gear and/or cruising at steady throttle using closed-loop via the O2 sensor. What this means is that the excess fuel is causing backfiring on deceleration, a good indicator of an overly rich mixture, and high exhaust temperatures due to the unburned fuel getting burned in the pipes after being expelled. In this case, the high-flow exhaust system is part of the problem. Installing the standard Cats will likely help with backfiring, but will likely clog up in a very short period of time due to the rich mixture. Obviously, an A/P will be required if a cat is used to give clean O2 rich air to the cat.

I would recommend finding 2 injectors of the correct impedence and flow rate (680's came stock, IIRC) and install these to see if the problems still persist. With the porting that you're talking about, the computer should still be able to operate effectively to get best A/F ratio even without having to step up to larger injectors. I think that the overly large injectors are causing more problems than they're worth at this point.

Also, you'll want to run a quick search on '6-ports' and make sure that yours are working correctly - most likely, a straight pipe exhaust is going to lack the correct backpressure sensing tube which 'powers' the '6'-ports, therefore your ports may not be opening correctly (3800rpm at 2.5-3psi), again contributing to your rich mixture. If the ports don't open, you're not making use of that additional port volume and velocity, effectively choking the engine at high rpm and leading to a rich mixture, decel popping, etc. HTH,

Felgar

Hmm interesting take on it LongDuck. I'll look up how to test the ports.

On a side note the work was done by RX-7 Specialties and they have a very solid reputation. They rebuild large numbers of rotaries and specialize only in these cars. I'd not expect them to create a setup that's fundamentally flawed so maybe there's something I don't know or else a number of factors working together.

Felgar

Here are some pics of the engine, exhaust, and intake. I have 5 mega-pixel versions of the files, so anyone feel free to PM me if you want them emailed to you or I can also resample to a different resolution if you like and send those.

I can also take more (close-ups or whatever) of anything you want. Thanks for the help guys and sorry it took a while to get these up.

The air intake is taken from below the car through the front grill. Behind the tubs is the rad, and you can see on the other pics where it goes from there. I think it's stock but I'm not sure.

Oh, and the pic of the whole car looks pretty rough - LOL. It's going through some final detailing shortly and it'll look much better with the bumper painted and a good polish. I'm hoping to get it to a 6-8 ft. car but we'll see. Right now it's about 15 ft until it starts looking good.

Felgar

And last is the car (didn't know there's a limit of 5)

84stock

iTrader: (5)

PM me with contact time and neighborhood so we can compare cars. I am in Clagary as well with a 85 GSL SE. You're right about RX7 specialties haviung a good reputation. The previous owner of my car received faithful (and reasonable) quality service for several years. Another faithful customer of theirs bought my 84 gs after his engine dies. Adam suggested he look for another car rather than pouring money into a dead horse when his engine dies, good honest gang there!

Rx-7Doctor

iTrader: (13)

Long duck is correct, the injectors are too large, the stock gslse 680cc are more than sufficient for your engine. The stock computer cannot handle any more, it has one mapping. The air intake you show is stock, recommend dumping the restrictive air-
box and installing a cone filter at the end of the air meter so it can breathe. Also
you would benefit by installing the preslincer made for the se so the 6 ports can
do their job. rx7doctor

Felgar

There is a presilencer on it with a return line, I'm assuming that it's doing the job properly but that's just an assumption. How would I go about testing that?

The curious thing about the air box was that installing a K&N did absolutely nothing, so I was always sort of thinking that it had adequate air flow. If it didn't I'd expect the K&N to have at least helped the situation a little. It's almost like it's not even trying to take in enough air, so the flow capacity of the air box is not even a factor.

Is there no way to change the F/A mixture at all?

Feds

To echo everyone else, those injectors be too fat, and not fat like the kids say.

You can trick the ECU a couple of ways: you can mod the AFM, basically put an offset in the output to make the ecu think less air is coming in. PM 23racer for details.

You can also put a resistor in line with the intake air temp sensor or water temp sensor. This will cause the ecu to think the car is hot and should lean it out (I may be going backwards on this, I don't have an FSM in front of me).

Another option to consider is going to a Megasquirt, or other aftermarket ECU. You can tune the maps, and even convert the 5/6 ports to electric actuation.

Good Luck, whatever you chose!

Felgar

Thanks to everyone for the help so far. Well I'm not very inclined to "detune" the car... I mean yes it's afterburning but I don't want to backtrack if I don't have to. In the end I'm always after more power even if it means spending some cash.

I'm inclined to go the aftermarket ECU to help get the most out of what I have, and the electric actuation is probably a much better way to go than using backpressure anyways. Do you have some links where I could research that more? The ablity to tune the maps would be nice too...

One thing I'm fighting is that I don't even know for sure what mods were done. For all I know the engine was even ported... And maybe the injectors aren't 820's after all. It looks like the air pump is out of the equation (it's the cylinder beneath the air filter box right?)

I should note that it only afterburns when I'm slowing down with restriction on the engine (i.e. letting the engine slow the car while in gear). It always does it between 2K and 2.5K RPM, and if I hit the clutch at 2800 on the way down then it won't do it. Maybe that provides insight for some experts...

Feds

Hey good Point! I don't see an air pump in there at all!

The air pump is belt driven and hangs off the passenger side of the engine. It should be visible in the 3rd picture, but I don't see it. Could be your issue right there...

Getting proper sized injectors is not detuning. If your 820's are only getting pulsed at 50%, then they are only 410's that give you terrible idle. With the stock trap-door afm, you shouldn't need gigantic injectors.

Just google the megasquirt. It's an EFI controller that you put together yourself. Should cost around $300. I am researching the electric actuation, but the 2nd gen section should have some info. There is always the "Lumbar Pump Mod" basically, a seat lumbar pump provides the air pressure.

Felgar

Cool I'll look into the megasquirt. Any chance the AFM isn't stock?

So the air pump works just like on a 12A then eh? I was thinking that it was electric, because I figured the cylinder below the air filter box was the pump. Any idea what it I'm looking at then? It's directly beneath the air filter box, and has an open hose coming off it to the middle of no where. It's 3" in diameter and about 10" long.

Jeff20B

iTrader: (13)

My MegaSquirt so far has costed me $188 or so. I haven't recieved it yet (fingers crossed that it'll arrive today).

You can junk the AFM with MegaSquirt.

Felgar

Seems pretty reasonable... Heck I almost paid that for new door seals.

I'd love to hear about your experiences when you get it.

Jeff20B

iTrader: (13)

If I remember this thread.

Feds

Keep in mind that Jeffer is 'mercan. So canadian figure maybe 250 or so.

I'm not sure what you are thinking about in terms of the air pump. I can't think of anything that would be under there.

Felgar

What? LOL. Ok, I guess I'll take some more pics. Once again the car's parked at my bro's though - this time drying out from a full interior shampoo.

Here's some more unrelated info. The car idles at about 1300 RPM when it's cold, but when the temp needle hits the thick mark on the guage it kicks down to 900 RPM. (Was 800 until I changed the idle speed) It'll stay like that until it gets right to running temperature which is just a hair left of vertical on the temp guage. At that point it will drop 200 RPM (600 before and now 700) without fail, and I can't get it back to 900 RPM when it's fully warm.

And possibly related to that there seems to have been a few times when I was just driving making moderate power at a pretty steady speed where it would accelerate without any extra throttle - like if the ports openned or all of a sudden something else "kicked on." I know I'm getting leading spark (cuz it runs pretty nice, good power, and smooth) but I'm not convinced about the trailing spark. The tach doesn't fail (indicating that my ignitor works) but it almost seems to me like I'm getting no trailing ignition even though I've verfied with a spare plug that the I do get spark while I try turning it over...

Felgar

Ok so here's the pic of what I was talking about. The air box is right at the top left of the frame, and directly below with a little rust bolted to the floor and up-right from the edge of the fan is the thing that seems to be disconnected.

You can see the tube coming out the front but it goes about 6" toward the firewall, turns toward the engine, and then is not connected to anything. There's nothing even close by that it could be connected to.

What is it? Should I just remove it completely - no sense packing around the weight if it's not used...

LongDuck

That air canister that you're describing, in the center/left of the picture above, is actually a muffler for the A/P system during deceleration when the A/P is providing pressure, but not to the exhaust ports and not to the catalysts.

The Air Control Valve mounted to the passenger side of your lower intake manifold is the air pressure mechanism that controls port air direction and volume. This port air is routed from the A/P to one of several locations; 1) the main catalyst (#3, according to Mazda), during idle and cruise conditions, 2) the exhaust ports, from the gap in the lower intake manifold to the exhaust port sleeves during acceleration since the '6'-ports are now being driven by the backpressure (not during cruise), and 3) back through this heavy steel canister 'muffler' during deceleration. The canister is actually pretty heavy, about 10-12lbs if I had to guess, but that's because it's double-walled and pretty stout.

The airpipe that leads to it from the Air Control Valve allows the bypassing AP air to have a place to go that so that your car doesn't sound like a Mack truck with the Jake-Brake running on deceleration - no kidding, it is almost that loud. The front of the canister routes a rubber pipe with a 90 deg bend out to the front of the radiator so that any residual noise gets vented to the front of the car where you're much less likely to hear it on deceleration.

I removed mine back when I did my cold air intake mods, but after 1 run, replaced it quickly - the sounds that the A/P generates on high RPM deceleration is downright nasty, and I never noticed it before with the canister 'muffler' in place. I did leave off the rubber piping leading out the front, however, since I was using that space for my relocated coolant overflow tank. YMMV, but I'd definitely recommend that you leave it there and hooked up. HTH,

Felgar

Awesome info LongDuck - thanks a lot. Same goes for everyone who's been contributing as well.

Driving home today I had the same idle issue. At some point it's like the car gained 15 hp and sure enough when I stopped it was idling at 900-1000, rather than 700 like it usually does. Something seems to be kicking on and off and it's causing some pretty major power losses. I've checked my trailing spark like 5 times including at the slow idle but it still seems like this is the problem - though it musnt be. I'm open to any ideas...

And second, given that the car's ported, has high-flow exhaust, and plenty of fuel supply (too much apparently) I'm thinking that it might really help to get the megasquirt and ditch the afm altogether. What sort of power difference will I see? I'd sure like the ability to change my fuel mapping though, that's for sure.

I'm also adding direct-fire ignition (leading) to my mod list too. I find it hard to believe that the electric fans can really cool as good as the stock fans. I mean, cruising at 100 mph at 5700 RPM (or so) I just don't see how the electric fan could cool as well as the mechanical one. Can it really? Another thread had mentioned that the fans of some old Ford pretty much bolt right on... Nice and easy to do anyways...

Feds

Felgar Felgar Felgar,

At 100 MPH, your fan is useless. In fact, it is likely hurting cooling at that speed. Think about it, if you rev your motor to 5700 rpm, does 100 MPH air come through your rad?

The whole point about the electric fan is that the fan is only usefull when you are going slow/stopped, otherwise, airflow though the rad does the job.

I am making the jump to grasping at straws, but how is your wiring harness? could something be loose, causing the on/off problem?

purple82

It's much smaller and lighter on the 2nd gens. It's basically just a tube with a small resonator on it. Mine pipes back into the intake tube but I'm not sure how it's done stock on 2nd gens. Might be a good upgrade?