1975 Mazda REPU - Build and Repair thread

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Started the truck up for the first time yesterday. It still needs to be tuned but Lui got it to idle. There were a few things to iron out over the last few days but it's all sorted now.

Fuel pump was junk. I diagnosed everything else and had it working at one point but as soon as I upped the fuel pressure it conked out. I picked up an OEM replacement for an '89 Ford F-150 at the parts store that comes with a lifetime warranty.

Alternator wires were reversed so the dash lights weren't coming on. Easy fix.

Throttle position sensor was on backwards. It was symmetrical to mount on either side and the instructions weren't all that clear...but it was another quick fix once we saw the values reversed on the ECU.

Thermostat wasn't opening so I replaced that to be safe.

bbe23d66cc6f931065a42273a9291676.jpg


9a0a7e612c38d1d6e7409fc50482f03d.jpg
 

bazooka joe

No words
Moderator
Contributor
:
2016 Miata Club, 2014 CX5 Touring, Honda 1976 XL 175
Started the truck up for the first time yesterday. It still needs to be tuned but Lui got it to idle. There were a few things to iron out over the last few days but it's all sorted now.

Fuel pump was junk. I diagnosed everything else and had it working at one point but as soon as I upped the fuel pressure it conked out. I picked up an OEM replacement for an '89 Ford F-150 at the parts store that comes with a lifetime warranty.

Alternator wires were reversed so the dash lights weren't coming on. Easy fix.

Throttle position sensor was on backwards. It was symmetrical to mount on either side and the instructions weren't all that clear...but it was another quick fix once we saw the values reversed on the ECU.

Thermostat wasn't opening so I replaced that to be safe.

bbe23d66cc6f931065a42273a9291676.jpg


9a0a7e612c38d1d6e7409fc50482f03d.jpg

Nice work Chris! Looks great too!


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CTt3P5

TAD
Contributor
:
2016 GT ST 47A
I agree on both counts.

Easy fixes are always welcome. What else do you have planned?


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chuyler1

goes to eleven
Moderator
:
2013 CX-9
Well once it's running I plan to just start driving it until next winter. No more projects that will take it off the road. However I do have some things I need to tweak...

The fuel lines and fuel filter under the bed of the truck need to be upgraded. I have a filter, I have lines, I just need various fittings and some help taking the bed off.

I have an extra wire going to the front of the car. Either it's going to power the windshield washer, or serve as a low coolant warning. Can't decide if I want the washer reservoir in the engine bay. The low coolant sensor was never connected so...it's no biggie.

I need to work out an oil catch can of some sort, or hook up a PCV valve to the new intake.

Getting the OMP working again would be nice, but I'll just premix for now.

I want to rebuild the wiper mechanism, it's binding and really slow despite now having a full 14v to operate (old alternator was pretty weak).

The audio system could use some attention. Not a lot of room for kick panel speakers but I've seen others put speakers in the doors. I have the seat thumpers and headrest speakers connected but they are poor quality. You know me, I have standards...and I'll need something that can drown out the new intake sound.

Depending on how much power this makes a future project will be to street port the motor and install a LSD. Then, if it's too much power for the suspension I'll consider putting the coilovers back in so I can maybe autox it a few times.

So anyway, plenty of fun stuff to do...but first is the tune so I can drive it. Lui is coming next week. If it goes well, I'll have it at the Mt Washington meet.
 

bazooka joe

No words
Moderator
Contributor
:
2016 Miata Club, 2014 CX5 Touring, Honda 1976 XL 175
Well once it's running I plan to just start driving it until next winter. No more projects that will take it off the road. However I do have some things I need to tweak...

The fuel lines and fuel filter under the bed of the truck need to be upgraded. I have a filter, I have lines, I just need various fittings and some help taking the bed off.

I have an extra wire going to the front of the car. Either it's going to power the windshield washer, or serve as a low coolant warning. Can't decide if I want the washer reservoir in the engine bay. The low coolant sensor was never connected so...it's no biggie.

I need to work out an oil catch can of some sort, or hook up a PCV valve to the new intake.

Getting the OMP working again would be nice, but I'll just premix for now.

I want to rebuild the wiper mechanism, it's binding and really slow despite now having a full 14v to operate (old alternator was pretty weak).

The audio system could use some attention. Not a lot of room for kick panel speakers but I've seen others put speakers in the doors. I have the seat thumpers and headrest speakers connected but they are poor quality. You know me, I have standards...and I'll need something that can drown out the new intake sound.

Depending on how much power this makes a future project will be to street port the motor and install a LSD. Then, if it's too much power for the suspension I'll consider putting the coilovers back in so I can maybe autox it a few times.

So anyway, plenty of fun stuff to do...but first is the tune so I can drive it. Lui is coming next week. If it goes well, I'll have it at the Mt Washington meet.

Lmk when you want to lift the bed off and I'll come up


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chuyler1

goes to eleven
Moderator
:
2013 CX-9
Lmk when you want to lift the bed off and I'll come up

Sure thing, maybe a fall meet or something.

Another update. Let's see...
The base tune Lui put on it last week fouled the plugs. Of course we spent several hours scratching our heads as to why it wouldn't start and actually found a few other issues, none of which got the truck running again...until I went to the store and got some RX8 plugs and a timing light to check the timing.

I've been learning quite a bit about tuning and after messing with a basic MAP (manifold air pressure) tune for an RX8 I realized it just wasn't going to work with the ITBs since there is literally no vacuum once the throttles open. Lui hinted at doing a TPS (throttle position sensor) tune instead and after a few hours of searching the internet I finally figured out what he meant and how to set up the ECU.

A few more hours later the truck idles at 14.7 AFR but then stalls as soon as I crack the throttle. It took some more time to figure out I could adjust the step increments on the Y-axis of the fuel map. Instead of throttle positions of 0%, 20%, 40%, etc, I was able to change them to 0%, 1%, 5%, 10%, 20%, 40%, etc so that as soon as I touch the throttle it adds the needed fuel.

So now I've got the truck driving and I made a lap around the block for the first time this afternoon. I turned on the data logged and I have a lot of fine tuning to do. Plenty of backfires and stalls. But once the throttle is opened, it sounds amazing and pulls much harder.

Brakes are another story. With barely any vacuum, the brakes have no boost. I'll have to take care of that later, add it to the list.

Still hoping to get it to the Mt Washington climb a week from today. Anyone else going?
 
:
'86 RX-7 Base, '79 RX-7 GS
Do you think a larger brake vacuum booster would help? Unfortunately it doesn't look like you have a lot of room in there.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
There is more room than the photos may lead to. I'll address the vacuum issue below....

So, the lack of instructions (i.e., no instructions) for the intake, and my relatively beginner status when it comes to these things rears its head again. I took the vacuum barbs that came with the kit and screwed them into the holes they fit into. It turns out those holes are for idle adjustment. Packed away in all the other extra nuts and bolts the kit came with for various throttle linkage options were some idle adjustment needle screws which have the same pitch as the vacuum barbs.

So I took the barbs out, put the idle screws in, messed with adjustments between the screws and cracking the throttle a little and it behaves better now. Ended up with about 2.5 turns of the screws and a slight crack of the throttle. I got it down to an unstable idle at 800Rpm but upped it to 1200 to keep it from stalling.

So that leaves the issue of vacuum. I had side port placed on one of the runners that I was going to use for the brakes (before i found the vacuum manifold) and I grabbed a T to hook both the MAP sensor and brake booster to it. I'm getting a better vacuum signal but since it's only attached to one rotor, the signal isn't reliable. Once I'm driving it's OK, but the ECU is trying to adjust idle and it goes a little bonkers, hence me increasing the idle air for a faster idle. I'm going to tap each of the runners for new vacuum ports but I'm going to proceed with tuning so I can drive it a little. I'm not ready to take the whole thing apart just yet.

Oh, I'll also add the brakes feel better. They were originally only getting vacuum from the rear rotor secondary runner so it's no different than stock. I'm hoping to get a little more brake boost when I tap new ports.

Back to the driving and tuning. I'm learning more each time I go out. The truck is behaving better at back road cruising speeds. I haven't ventured onto the highway yet. One thing that was bugging me on my drive last night was what I call an "accelerator pump" issue. On a carb, when you punch the throttle, it squirts some extra fuel. The ECU wasn't doing this for me and the truck would go lean when I pushed the throttle down, backfire, the continue on just fine. I read up last night on "transient throttle" and this is a know issue with ITBs because the MAP sensor won't react fast enough. There is a separate table to map predictive MAP sensor values to throttle positions. If the throttle position changes quickly (how quickly and how much is configurable) then the system will ignore the MAP sensor for a short period and read this predictive table instead. That table was way off based on the logging I've been doing so I updated it late last night and I'm going to try it out this evening.

If that goes well, and I get a few baseline readings for the fuel map, I can turn on the closed loop mode and let it do some "adaptive tuning" for me.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Here's a quick example from the log. Once I'm at about 25% throttle at 2,000 RPMs the car settles into an AFR between 13 and 14, but getting there it leans out and stalls. You can also see here the erratic MAP sensor reading. It goes from 25Kpa straight to almost 100Kpa (no vacuum) with the slightest touch of the throttle. Normally you'd see that value ramp up relative to the throttle position.

2017-08-01_1556.png
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Oh, and there's other stuff I've been messing with this week:

1) The left rear turn signal isn't working. I traced it back to the Hopkins tail light converter I used to combine the signals from marker lights, brake lights, left and right turn signals. It replaces the old set of relays the truck had. I know the converter was working when I installed it because I took video of the flashers and blinkers working. It was a relief to see them work after months of wiring...the only relief I have now is that I installed it with quick release connectors so I can just pull out that section of harness and swap in a new one. I'm going with Curt this time...and I'm going to check it again in a few weeks to make sure it hasn't failed.

2) The tach wasn't working. Turns out I specified the wrong auxilary output so now that works great, including the shift buzzer. In the future, I may hook the shift buzzer to a separate ECU output so I can trigger it at a different RPM. It goes off pretty early.

3) The speedometer makes a ticking sound and flutters. This has been an ongoing issue (other owners report the same). When I rewired the dash I took it apart, cleaned, and oiled it. I'm going to pull the speedometer cable and make sure that is properly lubed as well. It sounds/looks like it is binding or something.

4) I'm not sure I trust the reading from the water temp sensor. I think it reads high because the fan basically turns on and stays on, even after I've been cruising for a while. The factory temp gauge reads fine so I know the truck isn't over heating. I've already adjusted the sensor values based on ones I found online. It only reads maybe 5-10 degrees warmer than my ambient temp when it's been sitting. I may just bump the turn-on temp by 10 degrees and watch the factory gauge to see what happens.
 
:
'86 RX-7 Base, '79 RX-7 GS
There is more room than the photos may lead to. I'll address the vacuum issue below....

So, the lack of instructions (i.e., no instructions) for the intake, and my relatively beginner status when it comes to these things rears its head again. I took the vacuum barbs that came with the kit and screwed them into the holes they fit into. It turns out those holes are for idle adjustment. Packed away in all the other extra nuts and bolts the kit came with for various throttle linkage options were some idle adjustment needle screws which have the same pitch as the vacuum barbs.

So I took the barbs out, put the idle screws in, messed with adjustments between the screws and cracking the throttle a little and it behaves better now. Ended up with about 2.5 turns of the screws and a slight crack of the throttle. I got it down to an unstable idle at 800Rpm but upped it to 1200 to keep it from stalling.
Do you have any pictures of these idle screws? I'm curious since they only method of idle control I have is to crack the butterflies. I'm guessing the screws act like a sort of controlled vacuum leak?

So that leaves the issue of vacuum. I had side port placed on one of the runners that I was going to use for the brakes (before i found the vacuum manifold) and I grabbed a T to hook both the MAP sensor and brake booster to it. I'm getting a better vacuum signal but since it's only attached to one rotor, the signal isn't reliable. Once I'm driving it's OK, but the ECU is trying to adjust idle and it goes a little bonkers, hence me increasing the idle air for a faster idle. I'm going to tap each of the runners for new vacuum ports but I'm going to proceed with tuning so I can drive it a little. I'm not ready to take the whole thing apart just yet.
I was told to avoid MAP tuning and use alpha-n (TPS) only. The internal MAP in my ECU is strictly being used for barometric correction.

Oh, I'll also add the brakes feel better. They were originally only getting vacuum from the rear rotor secondary runner so it's no different than stock. I'm hoping to get a little more brake boost when I tap new ports.
Do you have a check valve on the brake booster vacuum signal? I couldn't see anything in the picture that looked like one. I'd definitely tap each runner for a vacuum signal. On my setup both of my runners are tapped and feed into a vacuum block that supplies the brake booster. I also have two other ports for MAP and the fuel pressure regulator should I decide to use them.

Back to the driving and tuning. I'm learning more each time I go out. The truck is behaving better at back road cruising speeds. I haven't ventured onto the highway yet. One thing that was bugging me on my drive last night was what I call an "accelerator pump" issue. On a carb, when you punch the throttle, it squirts some extra fuel. The ECU wasn't doing this for me and the truck would go lean when I pushed the throttle down, backfire, the continue on just fine. I read up last night on "transient throttle" and this is a know issue with ITBs because the MAP sensor won't react fast enough. There is a separate table to map predictive MAP sensor values to throttle positions. If the throttle position changes quickly (how quickly and how much is configurable) then the system will ignore the MAP sensor for a short period and read this predictive table instead. That table was way off based on the logging I've been doing so I updated it late last night and I'm going to try it out this evening.
It looks like you're on the right track. Haltech has a "Transient Throttle Enhance" feature that does exactly this. It looks for a certain rate of change in throttle position and adds extra injection cycles to compensate.
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
On the diagram, the idle ports are right below the fuel injector port. Inside the throttle body there is a passage that routes past the butterflies. After a cold start last night I adjusted them to 2.5 turns each.

https://www.jenvey.co.uk/images/stories/virtuemart/product/TB45_D.pdf

Adaptronic has a lot of idle control features but I think they all rely upon having an idle air control valve. I'll have to decide whether I need to bother with that. If I can cold start with partial throttle I can probably do without it for now. It's a fair weather vehicle anyway.

No check valve on the brake booster. With the brakes and MAP on the same port I'm getting reliable signal that will work well enough for a TPS tune.

After tweaking the transient throttle table I got the motor to rev much better. I am definitely on the richer side of that setting because there's a slight lurch when I first touch the throttle at cruising speeds. I'll spend more time on that in the future but at least it doesn't lean out and stall every time I try to touch the throttle.

I'm definitely going to tap the runners for a combined vacuum. The vacuum manifold I have is perfect for connecting the MAP sensor, FPR, and brake booster to 4 vacuum ports...I just need the right ports :)

So at this point, I'm going to turn on the rapid learning mode on the ECU. I've got a few different zones dialed in on the map and it runs and drives at every speed. Sounds like a beast at full throttle on the highway and pulls to 8,000 no problem. I didn't push it further. Power doesn't really seem extreme compared to before. More noise, but it's not to the point where it'll brake loose the tires. I think I'll need to street port the motor this winter if I want that.