peejay

(crossposted from GRM)

Last weekend my RX-7 ran progressively worse and worse until it was barely running by the time I got home. I found that at least one of the ignition coils (FC leading coil, one FC trailing coil through distributor, wired in parallel to an MSD 6AL) was arcing to the fenderwell. That would explain... well, all of it. At first it ran great at WOT but barely at part throttle, which usually means the trailing is dead on a bridge port. That coil was definitely bad. The engine was running on one rotor at the end of the trip so the leading is probably shot too. So I ordered some different coils that should work better with the MSD and also allow mounting in a better spot.

A couple days ago, the new coils weren't arrived yet but I wanted the car mobile, so I went to connect a pair of MSD Blaster coils I had lying around and run both coils through the distributor. Problem was, the engine was STILL running on only one rotor when I did that!

Compression is really good by the "pull the leading plugs and crank it" test. Spraying windshield de-icer down the intake (nothing else flammable handy) made the engine run on both rotors and sound pretty happy. So we (probably) have good spark, we (most likely) have good compression, but adding fuel makes it run happier so we must have a bad injector or driver, right?

Tonight I got down to bidness and pulled the carb body off so I could access the injectors. My recollection was that the two injectors were on separate drivers. My recollection was wrong. Both injectors (low impedance) are on Inj1m and share the same power circuit, which goes through a 6-7 ohm resistor block ganked from the FC that donated its coils. So total resistance on that circuit is (2.5 in parallel = 1.25, plus resistor) about 7.5-8ish ohms. Easily dealt with by a single driver and has worked fine since I installed Megasquirt something like 100-120k miles ago. Most of that on a 1.01 board, but now I have a 3.57 that I think has been in there for 10-20k or so. Either way, if one is getting power then they both are, and I tested wire integrity with my Power Probe to be sure.

Then, I pulled the fuel rail, secured the injectors to the rail, connected my laptop and went into test most. My deadtime is .825, arrived at by complete BS methods but it's worked fine for a long time. 2ms pulses gave me tiny little dribbles. 10mm pulses gave me beautiful three-element spray patterns from both injectors. (RC engineering 1000cc/min) And they looked about even. So we are getting equal amounts of fuel from the injectors.

Here is the part where my brain hurts. I started to think, maybe when it was running poorly one of the presilencers collapsed internally and now it has a severe exhaust restriction on one rotor. (Nevermind that the presilencers don't look burnt, and it runs better with additional fuel) So I disconnected the plug wires from the front rotor, gave them suitable ground, and cranked it. No run and barely any kick. A-ha! So I reconnected those and disconnected the wires from the rear rotor. No run and barely any kick. Uh? I reconnected the plug wires. Start and run (barely) on one rotor.

Grasping at anything, I thought, maybe the Inj1 driver is HURT but still sort of functioning. I happen to have a pair of injector connectors powered up and wired to Inj2. After verifying that the computer is running simultaneous, I swapped connectors around so Inj2 is connected to the injectors. No change at all!

One other thing I tried. The MSD gets its trigger from one of the pickup coils in the distributor. The Megasquirt gets its crank signal from the MSD's tach output. The other pickup coil in the distributor has an ignitor that goes to a little junction block with a 1000 ohm (I think) resistor between the two old trailing coil wires. Its only purpose in life is to drive the tach. I removed the junction block, installed an ignition coil in its place, and ran that through the distributor. Still only running on one rotor! So it is (probably) not an MSD box that has stuffed itself.

It's about this point that it was getting to be 9pm and I really needed to stop annoying the neighbors, so I cleaned everything up and went home.

What am I missing??? I don't have a fuel pressure gauge, but I don't see how a failing coil could kill a pump. (It sounds the same as it ever has, really). Fuel composition is probably not an issue. I have a friend with the Mazda factory compression tester, which I'll throw on there for giggles, but it runs better with more fuel. I reloaded my last known-good tune in case somehow all the stray voltage corrupted it, but that made no difference.

I dunno. I dunno at all.

Aaron Cake

iTrader: (1)

Have you swapped injectors and confirmed the bad rotor follows an injector?

peejay

Both injectors are spraying the same in test mode.

I can't identify which rotor is not firing because disabling spark to either rotor makes the engine not run at all.

Aaron Cake

iTrader: (1)

It does sound like an injector problem. Definitely seen them work on the bench but no in the car. Something to try anyway.

peejay

It's confusing as all heck and I had to walk away from it. I might have a way of checking fuel pressure but I'm not certain of that.

It certainly is acting like a fuel problem because spraying fuel into the inlet makes it run better. Of course it is a bridge port so "better" can be hard to determine if it's not under load, but it seems to rev on both rotors when I give additional fuel and snap the throttle open.

I reiterate that I lifted the rail out and, with my laptop on the cowl, engaged the fuel pump and tested the injector circuit via testmode. Both injectors appear to be spraying identically. I had my hands full doing all this else I would have taken a video And since they are both being driven by the same driver, if one works then they both work. So I feel that I verified that the driver is working and the wiring is good and the resistor block is good and the injectors are good. And switching the injectors from Inj1 to Inj2 made no difference.

I verified that no settings got changed. The firmware in my computer (an MS2/Extra box I bought from DIYAutotune in 2014) has a bug where I have to set it up old-school as a 4 cylinder 2616cc engine. Set up as "rotary", it was doubling the RPM. Made it run a little bit rich One of the thoughts I had was what if it was injecting "1 squirt/cycle" instead of "2 squirts/cycle", then every other revolution would get no fuel and it might sound like it was running on one rotor but actually was running alternate rotors. (Since I'm batch fire, one rotor will always get the fuel injected 180 out so that fuel gets used in the next cycle)

I have had weird things happen with MS tunes getting corrupted before, typically after having the battery disconnected for a long time (which makes little sense to me, either) so my first action was to reload.

I'm wondering if I need to reload the firmware. I have my project pulled up in TS right now and the firmware is "MS2/Extra release 3.3.3 20141112 12:53GMT(c)KC/JSM/JB"

mhr650

It does sound like an injector issue, back when I ran GSL-SE electronics and injectors I had a lot of problems with injectors. Come back from a race and let the car sit for a couple of weeks and when I started prepping for the next race it was running on one rotor. Cleaning the injectors always solved the problem, sometimes he had to work hard to get the offending injector working by running WD-40 through it while pulsing it, but it always came back. You can check which rotor is not firing with a squirt bottle of water to spray on the headers, swap the injectors and see if it follows.

Just curious why if you have a MS on the car you are using a distributor and MSD boxes? Seems like it would be much easier and more cost effective to use GM LS coils, I set my car up that way and it works fantastic. If you are running NA you don't need the expensive IGN-1A coils, just some cheap OEM replacement coils.

peejay

The problem is Megasquirt does not offer any crankwheel read option I can find that doesn't need potentially a full revolution to spark. With a distributor, if there's an ignitable mix in the chamber, you can have the engine running in a maximum of 180 degrees and usually a lot less. This is important when your battery is run down and the car barely can crank, or you stall the engine when cold and need to quickly bump start it. Two situations that I regularly find myself needing. My fans pull more current than the alternator can provide, so I run my battery down over the course of an event and by the end of the event I sometimes need a jump start if it doesn't catch on the first or second rotation.

Besides, any time I think about going to a crank trigger, I read nothing but woes regarding getting good signal at various RPM. The distributor/MSD setup is solid at 200rpm cranking speed and 11000rpm absolute max speed.

If there's a crankwheel option that tells the computer positively when rotor 1 or rotor 2 are coming up, I am all ears. Everything I could find in the literature says the computer won't give spark until after it goes past the missing tooth or "cam" signal.

mhr650

Interesting about starting, I don't use a crank trigger I just have stock FC crank angle sensor. My car starts pretty good but it does take a few cranks, it has never been a problem with endurance racing, but I don't run any fan at all and the only real load on the battery besides the engine is if I am running the cool suit or night racing with lights which are LED and only draw 120 watts.

Any way you could plug in an external battery between sessions for the cool down?

peejay

At the last rallycross, my runs were about 3 minutes apart. Just enough time to get back to grid before I was sent out again for the next low speed dyno pull. So, no.

Anyway, I put the header back on the car, noted that attempting to run the engine off of brake cleaner had stuck the apex seals so I poured some 2-cycle oil down the carb throats and cranked it until compression sounded good. Removed sacrificial plugs, pumped out as much oil as practical, put plugs in, cranked it with the fuel injectors fuse in, and...

AND...

Running on one rotor.

Pissed off, I left, bought a can of starting fluid with my last $5, removed the injector fuse, and tried to start it on starting fluid. Which is fun in a left hand drive car. And the ignition switch decided to start to get sticky and re-engage the starter after i let the key off, on the times when the engine would catch.

But on the twelfth or fifteenth attempt, I got it started and I ran over to the carb to work the throttle and keep it running long enough to verify that, yes, the ignition and compression are good, because the engine runs GREAT when fuel is being supplied by a dork holding starting fluid.

All this after I reloaded the firmware and the last known good tune.

Yep, I think I done hurt somethin' in the computer :/

valley

iTrader: (1)

I'm leaning towards some oddity/gremlin in your electronics causing issues when you attempt to put load on the system (as opposed to just "testing". Just going into the injector possibilities (if it runs happily with starter fluid I hesitate to think the coils aren't working enough for startup), although, starter fluid is easier to ignite... :

If one of the injectors is going bad it might work at a lower duty cycle and load but once sped up with a full prime have issues. It could also be that the injector driver is going out... or something as simple as a not-quite-dead connection on an injector (the resistor pack? connector? solder joint?).

The former can be checked with a bucket and and the fuel system off the car. The latter can be checked a few ways but the easiest is probably to swap the injector connectors (you said, batch, right?) and see if the problem follows the connectors (i.e. which rotor is the one running). If it is a wiring problem it's probably pre-resistor pack as one injector appears to be working properly.

peejay

Both injectors are spraying identically at any pulsewidth I cared to try in testmode. The wiring splices (power AND ground) are 2" away from the connectors, and I tested the circuit by blowing the 10 amp circuit breaker on my Power Probe on each wire. If they can pass enough current to pop a 10a breaker, they will have no problem with injector current.

The only thing left is to throw a scope on the injector pulse, but that would be tricky given that there is no way to run the car steady state, or long enough to set up a trigger on the scope. I'm going to send the box in to DIYAutotune and have them repair it.

peejay

The long version is over on the Grassroots Motorsports forum...

The short version is, I figured it out. After upteen dozen compression tests, and pulling the exhaust system apart to look for restrictions like a collapsed exhaust port sleeve, I reverted to a "last known good" setup of MS1/3.0 and GSL-SE injectors, wired to separate resistors and injector drivers, verified that the car actually started and ran okay (which was a relief in itself!!!) and then slowly taking those old parts off one by one, I isolated it to...

The injectors.

Here is what I think happened. I noted that my GSL-SE injectors can rotate when the rail is bolted down, but my RC injectors could not. As the engine ran worse and worse when the trailing ignition was failing/failed, it started occasionally popping back through the intake. I think one of the backfires damaged one or both of the injectors, causing them to expand, and therefore get crushed by the fuel rail.

The injectors sprayed beautifully when pulled out of the engine. I suspect that if I were able to get another intermediate housing into the engine bay, with cut-away injector inserts, and bolt the rail to that and look at the pattern through the intake port, I'd have seen the problem right away.

Very interesting problem, to be sure. And it only took me a month to track it down...

peejay

John Huijben

iTrader: (1)

Wow, that's a tough one to diagnose. Glad you got it sorted.
Seems to run well :-).

peejay

Not really I clearly don't have enough cranking pulsewidth, but the big problem is the day after that meet (a while after sorting the engine out) the engine would run on one rotor on a cold start, after the first time you blip the throttle, and it would clear out and run on both rotors after about 30 seconds.

So, I parked it. I had a feeling I knew what it was...

Today, my Swedish Moose needed to occupy the bay where the RX-7 sits (blown strut, and I chickened out on buying a pair of Evo VIII struts to see if they fit), so I went to back the car out of the garage and it started running on one rotor again. I pushed it back inside and pulled the plugs... both rear plugs were wet with coolant.

Well, it's been five years and a LOT of competition and overheating abuse, that's not terribly bad. Plus the rear rotor is down below 60psi compression, so it's a good time to force me to rebuild it instead of putting it off until there's a catastrophic failure.