Lighter = Faster (RX-7 Build #2)

magnumP5

Member
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'86 RX-7 Base, '79 RX-7 GS
I hit a snag in the build on Saturday. I finally secured the fan shroud to the radiator so I decided to add the coolant. While I was cleaning up, I noticed coolant dripping from the back of the engine where it meets the transmission. I removed the inspection window covers and used an endoscope to look inside. It looked like coolant was leaking from the engine studs. My first thought was I screwed up a coolant seal when I rebuilt the engine 1.5 years ago. The engine had to come out so I removed all the peripherals and called it a day. I spent the rest of the night reviewing the FSM and engine stud installation instructions to find out where I went wrong. The engine studs run between the inner and outer coolant seals so this likely isn't a seal problem. The engine stud instructions clearly say to use silicone sealant around the threads and I think this is something I overlooked.

By early Sunday afternoon I had the engine out of the car and the clutch and flywheel removed. I removed all 16 of the nuts from the engine studs and there was no sign of sealant on the threads. I think I mixed up the FSM and engine stud instructions because I found sealant under the OEM seal washers but the FSM says to apply engine oil. I pulled and cleaned all the washers and nuts, coated the washers in 10W30, coated the studs with Permatex Black, and reinstalled everything. Hopefully this is was a minor set back but I won't know for sure until I test the seals later today.
 

magnumP5

Member
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'86 RX-7 Base, '79 RX-7 GS
I'm getting very close to firing this thing up. The engine is back in the car and it's holding oil and coolant. I powered up the ECU and display and everything works. I calibrated everything except the fuel level input. I attempted to synchronize the engine and ECU but by then I think I drained the battery too much and wasn't getting any spark. I got one or two flashes from the timing light and then nothing. The steady-state battery voltage was 12.0-12.2V but I failed to note what it was while cranking. The cranking amperage must have been low because my display was resetting every time I hit the starter. I'm getting a good, steady engine speed signal so I don't think it's a trigger problem. I checked the IGN fuse and it was intact as well. I suppose I could have fried the relay but I put the battery back on a trickle charger and I'll try again tonight. If it turns out to be a battery issue I'll pull the larger battery out of the yellow RX-7 and try that next.
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
I got the engine and ECU synchronized and calibrated the fuel level sensor on Saturday. Sunday morning I primed the fuel pump for the first time to make sure there weren't any leaks. Fortunately there were none so everything was looking good for a Sunday afternoon start up. I pushed the car out of the garage, enabled the injectors, primed the fuel pump, hit the starter, and... nothing. Maybe one or two little bumps of ignition but no start.

Time to pull the plugs to look for signs of fuel. I pull the L1 plug and it's bone-dry; not a whiff of gasoline. I pull the L2 plug and immediately there's a strong fuel odor, so the front rotor isn't getting any fuel but the rear is. I've already verified the injectors are good by hooking them up to a 12V power source so I broke out the multimeter and started testing for continuity:

Injector to sub-harness break-out connector: "Beep"
Injector to engine-side bulkhead connector: "Beep"
Injector to ECU: "Silence"

It turns out 3/4 wires in the sub-harness connector were wired incorrectly. After de-pinning and correctly re-pinning that connector there's continuity from the ECU to the injector. Just to be sure I also went back and checked the ignition wires. Fortunately those are all good.
 

mymmeryloss

Member
:
13bT Mazda B2600i
I got the engine and ECU synchronized and calibrated the fuel level sensor on Saturday. Sunday morning I primed the fuel pump for the first time to make sure there weren't any leaks. Fortunately there were none so everything was looking good for a Sunday afternoon start up. I pushed the car out of the garage, enabled the injectors, primed the fuel pump, hit the starter, and... nothing. Maybe one or two little bumps of ignition but no start.

Time to pull the plugs to look for signs of fuel. I pull the L1 plug and it's bone-dry; not a whiff of gasoline. I pull the L2 plug and immediately there's a strong fuel odor, so the front rotor isn't getting any fuel but the rear is. I've already verified the injectors are good by hooking them up to a 12V power source so I broke out the multimeter and started testing for continuity:

Injector to sub-harness break-out connector: "Beep"
Injector to engine-side bulkhead connector: "Beep"
Injector to ECU: "Silence"

It turns out 3/4 wires in the sub-harness connector were wired incorrectly. After de-pinning and correctly re-pinning that connector there's continuity from the ECU to the injector. Just to be sure I also went back and checked the ignition wires. Fortunately those are all good.

U have a lms-efi harness right? Same exact issues im having
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
U have a lms-efi harness right? Same exact issues im having
Were your injector wires mixed up too? I know of at least one other person with the same problem. In the end it's not a big deal. It was easy to fix the issue once I figured it out. If I had paid closer attention to the wire colors I'd have figured it out sooner. As far as I can tell everything else is wired up correctly.

Last night I tried to better set the base fuel pressure on the FPR. The Aeromotive pumps don't hold pressure after they're stopped like the OEM units so it's a two person job. I played with the display as well and got it just about where I want it. The only thing I can't figure out is how to display fuel level in gallons instead of liters. I then proceeded to drain the battery, again, while cranking the engine trying to get some of the excess fuel out of the rear rotor. It's currently pouring down rain outside so it's unlikely I'll get a chance to try to start it today. I'm thinking I may put the spark plugs back in but keep the fuel pump and injectors disabled while cranking tonight. Maybe I'll be able to ignite some of the fuel in the rear rotor.
 

mymmeryloss

Member
:
13bT Mazda B2600i
Were your injector wires mixed up too? I know of at least one other person with the same problem. In the end it's not a big deal. It was easy to fix the issue once I figured it out. If I had paid closer attention to the wire colors I'd have figured it out sooner. As far as I can tell everything else is wired up correctly.

Last night I tried to better set the base fuel pressure on the FPR. The Aeromotive pumps don't hold pressure after they're stopped like the OEM units so it's a two person job. I played with the display as well and got it just about where I want it. The only thing I can't figure out is how to display fuel level in gallons instead of liters. I then proceeded to drain the battery, again, while cranking the engine trying to get some of the excess fuel out of the rear rotor. It's currently pouring down rain outside so it's unlikely I'll get a chance to try to start it today. I'm thinking I may put the spark plugs back in but keep the fuel pump and injectors disabled while cranking tonight. Maybe I'll be able to ignite some of the fuel in the rear rotor.

I don't remember. I pretty much put it in the trailer and haven't touched it in months. Still not running. From what i can remember I'm not getting fuel or spark. Was planning on taking it to my tuner and have him work out all of the kinks and get it 100%.
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
I don't remember. I pretty much put it in the trailer and haven't touched it in months. Still not running. From what i can remember I'm not getting fuel or spark. Was planning on taking it to my tuner and have him work out all of the kinks and get it 100%.
Damn, that sounds worse than my situation. I'm definitely getting spark at all four plugs and I was getting fuel to the rear rotor. I haven't tested the front rotor since fixing the wiring but I'm getting continuity between the ECU and the injector now. You're using an AEM ECU now, right? Does everything else in the truck work? Have you checked for continuity between the pins on the ECU connector(s) and the pins on the coil/injector connectors? My multimeter has a handy setting that audibly beeps when there's continuity. I assume your harness is similar to mine with break-out connectors for the ignition and injection sub-harnesses. My issue was an incorrectly pinned injector sub-harness connector.

Another thing to consider regarding spark. I had a hell of a time getting spark to synchronize the engine and ECU. My tiny battery doesn't output enough power to crank the engine continuously with the plugs installed. I tried pulling the plugs and grounding them to the engine but even though I was getting spark it was too weak to trigger the timing light. I ended up having to jump the battery with one of my other vehicles to get enough cranking amps with the plugs installed to generate a strong enough spark to trigger the timing light. Keep this in mind if your ignition harness is pinned properly and it doesn't look like you're getting spark.
 

mymmeryloss

Member
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13bT Mazda B2600i
That's really good info right there!

Like I said, it has just been sitting. No time to work on it and no motivation. All the money I spent going to SEMA pretty much killed the love I have for that truck for the moment. I will get back on it soon.

Good luck with yours and I look forward to updates!
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
I got it started! I think it was a combination of too much fuel and the throttle being too open. I backed off the throttle stop to around 3% (was 5%) and immediately the engine started to catch more and more with each start attempt. When it finally caught it idled around 700 RPM and was running super rich (<11:1). After adjusting the throttle stop and the fuel settings I got it to idle fairly consistently around 1000 RPM. I played with it for over an hour, varying engine speed from <1000 RPM to just over 3000 RPM. I ultimately stalled the engine with what I think was a lean condition. I tried to restart it but after two failed attempts (too lean again?) I had drained the battery. I'll try again tomorrow but I'm thinking I may have to set up some kind of post start enrichment strategy.

I demand video of it idling very soon. Thank you. :)
I'll get back to you on that...
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
I'm not sure how to embed videos from Google Photos. Does this link work: https://photos.google.com/photo/AF1QipMYj1AWmCbK9VOfteIfcTbSliVo4AskaXp-tGos?

Sorry for the noise. The fan had just kicked on. It's idling around 1000 RPM. Anything less and it gets a little rough/unstable. It's quieter than I expected. Then again, I haven't taken it much over 3500 RPM or about 10% throttle. Tuning this thing is turning out to be difficult. No-load idle it pretty much sorted to 4000 RPM. Tuning under load is the hard part. Going from no load to load is requiring a massive increase in fuel due to the large changes in incoming air volume associated with small throttle movements. Normally this is handled by transient throttle adjustments but I'm told not to mess with that until the base fuel map is sorted. This would be much easier on a dyno...
 
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mymmeryloss

Member
:
13bT Mazda B2600i
Video didnt work for me. This makes me ultra sad that mine still doesn't run haha. Congrats! I bet it feels great!
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
Video didnt work for me. This makes me ultra sad that mine still doesn't run haha. Congrats! I bet it feels great!
I edited the post with a straight hyperlink. Hopefully it'll work now. It's great it runs but I'm having a hell of a time driving it. I need to tune it under load but it's so unstable with anything more than 10% throttle or so. It's also hard to keep track of the AFR's, TPS %, RPM, and drive at the same time. I wonder if I can rent dyno time somewhere nearby. If not, I may try something stupid like jacking the rear of the car up and progressively pulling the parking brake...
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
Still cant see it. Y not just take it to a professional tuner?
I give up with Google Photos. Album is shared and I don't see any reason why people with links can't see it. I've updated the first post of this thread and my signature to include links to the albums themselves instead of pictures. Maybe that works...

Eventually I will take it to a tuner. I'd like to get the car driving first. Otherwise I'd have to find a way to tow it. I don't have a trailer and U-Haul won't let me rent one because my tow vehicle's rating is 4500 lb. There are a couple shops around me that rent dyno time but no one appears to have any rotary experience. That shouldn't be too much of an issue since all I'm doing is trying to hit a certain AFR. I still need to break in the engine after all.
 

magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
Updates:

-Trying to coordinate renting a dyno with a well-known rotary tuning passing through the area in early October.
-Changed the oil and filter. Went with 10W40 this time instead of 20W50. Oil pressure is still 40+ psi at idle. I'll probably try 10W30 at the next change.
-Moved my vacuum manifold to the top of the intake manifold. I was getting condensed fuel pooling in the manifold previously since it was below the ports on the intake manifold.
-Added a 1 bar external MAP sensor to allow for speed-density tuning in the future
-Increased the premix ratio from ~1 oz oil to 1 gal fuel to ~1.5:1. I think this completely screwed up my tune as I had to add a lot of fuel back to get it running right again.
-Fixed a couple leaks although it looks like my water pump is leaking so that'll need replacing in the future. Fun fact: oil/coolant dye is fun to play with.
-Ordered an aftermarket primary fuel rail and slightly smaller injectors (725 cc/min). My current setup has the primary fuel injectors in what is essentially the stock secondary fuel injector location. I think this is leading to fuel-air mixing issues and it part of the reason my idle and part throttle conditions are so unstable. Hopefully adding injectors back to the stock primary location will help although I'll now have to "stage" injectors.

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magnumP5

Member
:
'86 RX-7 Base, '79 RX-7 GS
Love the updates, hate the blocked pictures... :(
Thanks. I've come to the conclusion embedding pictures from Google Photos just isn't a thing anymore. It's annoying you guys can't even access the link in my signature though. The album is shared with anyone who has a link so it should be working.

I'm actually putting miles on the car now. Up to 20-ish total since I did a good 13 mile drive yesterday. Idling (after warmup) and cruising along it does just fine. The biggest issue is transient throttle. I have to be pretty deliberate with the throttle input or it goes really lean. No misfires or anything; just a massive loss of power, and if sustained for too long the car will stall. I'm also fighting an issue where the car stalls when I come to a stop. If I close the throttle and disengage the clutch it dies. I think I need to bump up the fuel or timing below idle speeds or create a zero throttle map.