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RX7 FD wont rev past 3k RPM!!

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Old 03-10-18, 07:59 PM
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Question RX7 FD wont rev past 3k RPM!!

Hey fellow members,

I have been building my FD for some time now, full engine rebuild, body work, paint job, the works. Finally re-installed the engine into the car and the car has an issue. It starts and idles fine, as soon as I rev the engine, it starts back firing like crazy and wont pass 3k RPM. Some history on the car - its a JDM RHD '94 R2. About 95,000 miles on the odometer. Removed the Air pump (blocked off). Stock motor with new apex seals, new housing kit - Water seals etc..., new oil pump, new OEM spark plugs, stock twins, new rotor bearings, new stationary gear bearings. And a bunch of other non engine related mods - clutch master etc...

I have changed/ done the following to address the issue with NO success
1. Tried a different stock ECU - same result
2. Removed the 'rat nest' and changed all vacuum and emission hoses. Used the Mazda vac diagram and traced each line to the correct solenoid etc... pretty confident in the vac lines - same result
3. Changed the injector resistor - same result
4. Changed the igniter - same result
5. Tried a different set of coil packs and spark plug wires - same result
6. Tested the knock sensor, works fine based on Mazda factory check - same result
7. Removed, tested and cleaned injectors, all are flowing correctly - both stock primary and secondary - same result
8. Installed brand new Denso supra pump
9. Installed new OEM fuel filter
10. Checked the fuel pressure regulator, its functioning correctly
11. Tried a MAP sensor from a working RX7 FD - Same result

None of the changes above made the car rev any better. I am all out of ideas and need some help on this. Any info would be greatly appreciated. Completely stock car, minus the fuel pump and a koyo rad. I'm even using the stock airbox and BOV. Thanks for any assistance.

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Old 03-11-18, 12:09 AM
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Trouble shooting this with a stock ECU is completely hopeless unless you are 100% stock, even then it is like using a divining rod... Get a PFC, or Adaptronic so we can see what your computer sees and a complete mod list, or there is not much help to offer IMO.

Can you describe exactly what you meant when you said changed the injector resistor?

Did you check TPS?

Sounds like safe mode.

Last edited by laujesse; 03-11-18 at 12:16 AM.
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Old 03-11-18, 01:35 AM
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I agree 3000 RPM does sound like a possible rev limiter, there are some faults that would cause the ECU to cut fuel or spark to prevent high-RPM damage. I'm not familiar with JDM cars, do you have a check engine light? It's possible to check for fault codes by jumping some of the pins in the diagnostic connector, at least on the US cars. I've heard of some people encountering misfires when the spark plug wires were swapped around wrong. If you have a timing light, use that to double-check that the ignition timing for the front trailing coil is firing near the mark on the crank pulley; the procedure is in the factory service manual. Also look to see that the ignition timing isn't jumping or doing anything odd when the engine is misfiring.
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Old 03-11-18, 07:36 AM
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Could be a bad coil pack harness. Worked on a car a while back that wouldn't rev, the coil pack harness was no good.

Does the car idle properly or is it idling high? Will it hold an idle and fully warm up?

Do you have the grommets around the injectors where the tips of the injectors fit into the housing?

Dale
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Old 03-11-18, 09:41 AM
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Originally Posted by DaleClark View Post
Could be a bad coil pack harness. Worked on a car a while back that wouldn't rev, the coil pack harness was no good.
Another JDM twist to what Dale said, 8 bit and 16 bit coil harness are different, and you won't know unless you are looking for it they are in a different order. Only bring this up because it sounds like you may have multiple cars or engines.
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Old 03-12-18, 07:44 AM
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Originally Posted by laujesse View Post
Trouble shooting this with a stock ECU is completely hopeless unless you are 100% stock, even then it is like using a divining rod... Get a PFC, or Adaptronic so we can see what your computer sees and a complete mod list, or there is not much help to offer IMO.

Can you describe exactly what you meant when you said changed the injector resistor?

Did you check TPS?

Sounds like safe mode.
Thanks for all the replies guys. I was speaking with a friend over the weekend and he may have access to a diagnostic tool (hooks up to the diagnostic port in the engine bay), I might try it and see if I can see any error codes or get a better idea of whats going on with the computer.
- The injector resistor on the JDM car is located under the brake booster, its a small box similar in appearance to the igniter.
- I haven't checked the TPS as yet, sounds like something to check for sure

Thanks a lot
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Old 03-12-18, 07:45 AM
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Originally Posted by scotty305 View Post
I agree 3000 RPM does sound like a possible rev limiter, there are some faults that would cause the ECU to cut fuel or spark to prevent high-RPM damage. I'm not familiar with JDM cars, do you have a check engine light? It's possible to check for fault codes by jumping some of the pins in the diagnostic connector, at least on the US cars. I've heard of some people encountering misfires when the spark plug wires were swapped around wrong. If you have a timing light, use that to double-check that the ignition timing for the front trailing coil is firing near the mark on the crank pulley; the procedure is in the factory service manual. Also look to see that the ignition timing isn't jumping or doing anything odd when the engine is misfiring.
- No check engine light on the dash.
- Plug wires are correct
- Will try the timing light suggestion

Thanks
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Old 03-12-18, 07:48 AM
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Originally Posted by DaleClark View Post
Could be a bad coil pack harness. Worked on a car a while back that wouldn't rev, the coil pack harness was no good.

Does the car idle properly or is it idling high? Will it hold an idle and fully warm up?

Do you have the grommets around the injectors where the tips of the injectors fit into the housing?

Dale
- Will check on the coil pack harness as well. I think I might be able to swap it out from a working car just to check.
- Car idles normal. Rad fans come in and out like they are suppose to. Will hold solid and warm up to normal operating temps
- Yes grommets are around the injectors, brand new ones in fact, came with a kit I got from Atkins Rotary. Injectors flow properly as well

Thanks
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Old 03-12-18, 07:50 AM
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Originally Posted by laujesse View Post
Another JDM twist to what Dale said, 8 bit and 16 bit coil harness are different, and you won't know unless you are looking for it they are in a different order. Only bring this up because it sounds like you may have multiple cars or engines.
Thanks laujesse, while I dont own the other FDs in the shop I can swap out parts just to test if I might have a bad part. That was the case all of Saturday, swapping MAP sensors etc with no luck. I will look into your suggestion.

Thanks a lot guys, really appreciate it
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Old 03-13-18, 02:02 PM
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Incorrect MAP SENSOR set up if you run an Apexi PFC, bad wiring between the map sensor and ecu, leaking map sensor to manifold hose.
Bad wiring for or bad crank angle sensors.
Poor engine grounds or ecu grounds.
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Old 03-13-18, 04:13 PM
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Originally Posted by cewrx7r1 View Post
Incorrect MAP SENSOR set up if you run an Apexi PFC, bad wiring between the map sensor and ecu, leaking map sensor to manifold hose.
Bad wiring for or bad crank angle sensors.
Poor engine grounds or ecu grounds.
Thanks for the reply. Not running a PFC - stock ECU. I will check all the other recommendations.

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Old 03-14-18, 01:29 AM
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I would also consider checking your pcv valve, if not already vented, and the rest of the check valves.

-groovin
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Old 03-14-18, 07:32 AM
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Thanks groovin. Checked all check valves for correct directional flow, all seem to be fine.

Will be making other checks soon, as recommended by you guys. Thanks for the help

Cheers
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Old 03-15-18, 01:28 AM
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Following.
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Old 03-15-18, 08:25 AM
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I had the same issue when I first bought my FD (back in 2004). It was hitting fuel cut off w/ stock ECU around 3k RPM. I dropped in a PFC and was 'fine'. The real issues were the solenoids and the brittle rubber hoses. Did a full silicone hose swap out, deleted some 'unnecessary' solenoids, and car was good to go.
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Old 03-15-18, 09:33 AM
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Originally Posted by kevinvr6 View Post
I had the same issue when I first bought my FD (back in 2004). It was hitting fuel cut off w/ stock ECU around 3k RPM. I dropped in a PFC and was 'fine'. The real issues were the solenoids and the brittle rubber hoses. Did a full silicone hose swap out, deleted some 'unnecessary' solenoids, and car was good to go.
Thanks for the reply. Changed all vacuum lines in the rat nest and checked solenoids as well. Maybe I missed one, will go back through the solenoids again to verify operation.

Should be using a diagnostic machine over the weekend, so I will post up the results and take it from there

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Old 03-19-18, 01:25 PM
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Hey guys,

Unfortunately I wasn't able to secure the diagnostic machine for this past weekend . I am trying for this week. Will post any updates once I get them.

Cheers
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Old 03-23-18, 01:54 PM
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Hey guys,

Diagnostic machine came back with the following codes: 40 and 50
Looked up the codes and it was Solenoid Valve (Purge Control) - code 40 and Solenoid Valve ( Double Throttle Control) - code 50.

Will be checking these over the weekend. May need to order them. I was thinking to change all solenoids but I will see.

Will keep you guys posted with the results.

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Old 03-23-18, 02:16 PM
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If your double throttle solenoid is stuck the it keeps a second set of throttle plates closed. There is a vacuum hose that goes to the back of the throttle body/UIM to the double theottle actuator. If you pull it off and cap it. It will leave the double throttle plates open. This is only used to limit boost and performance when the engine is cold. I’d start there.
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Old 03-23-18, 02:24 PM
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Originally Posted by live2drive15 View Post
If your double throttle solenoid is stuck the it keeps a second set of throttle plates closed. There is a vacuum hose that goes to the back of the throttle body/UIM to the double theottle actuator. If you pull it off and cap it. It will leave the double throttle plates open. This is only used to limit boost and performance when the engine is cold. Id start there.

Thanks a lot, I will also look into that suggestion.

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Old 03-24-18, 09:08 PM
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+1 limp mode. If still the same, try thiese 2 things,.
1. slap in fc leading coils, test it.
2. Do the fuel pump rewire, test it.
i went through the same thing, but i have some other different mods.
good luck.
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Old 03-24-18, 10:35 PM
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Originally Posted by Red94fd View Post
+1 limp mode. If still the same, try thiese 2 things,.
1. slap in fc leading coils, test it.
2. Do the fuel pump rewire, test it.
i went through the same thing, but i have some other different mods.
good luck.
Thanks Red94fd. Don't have a FC coil unfortunately.

Thanks for all the responses. So today I changed both the purge solenoid and double throttle control solenoid with functioning ones (tested the solenoids and worked ok).......... Same problemmmm this is really frustrating. Even tried pulling the vac line for the double throttle and no luck. But I'm trying to stick with it. I hooked up a fuel pressure gauge and was getting less than 15 psi. So I swapped out the fuel pump, same low fuel pressure. That's where I left it for today.

Could it be a FPR issue? I installed a new OEM fuel filter during the rebuild as well.

I am baffled at this point. Open to more suggestions. Oh and I resetted the ECU as well. Negative terminal off for 20 sec and press brake pedal. No luck.

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Old 03-25-18, 06:08 AM
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Tou can get fc coil fro $35 on the 2nd hen for sale section. It took me 2 months testing, i have no much time to mess with it, but i tested the same thing you did. I have 3 sets of fd coil packs, now, Up until i got the fc coil and did the fuel pump rewire. My fuel presure was low too. Brand new walbro 450, new fuel filter, cleaned injectors, vacuum tested, sensors tested, well you know the drill.
do the fuel pump rewire, its easy. The pump will get more voltage and keep presure, specially after 3k rpm. And get fc coil.. lol
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Old 03-25-18, 08:00 AM
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15psi of fuel pressure and the car shouldn't run at all. You may have the gauge on the return side or not getting a good reading or something.

I don't think the ECU will go into limp mode with those 2 codes. May be a wiring issue. The ECU is SUPER dumb when it comes to the codes - it just looks for resistance in the circuit, that's it. if the solenoid is plugged in and resistance is in spec, the ECU is happy.

Have you tested the leading coil per the shop manual? I've found that it's a pretty valid test for spotting coils that are past their prime.

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Old 03-26-18, 11:30 AM
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Originally Posted by DaleClark View Post
15psi of fuel pressure and the car shouldn't run at all. You may have the gauge on the return side or not getting a good reading or something.

I don't think the ECU will go into limp mode with those 2 codes. May be a wiring issue. The ECU is SUPER dumb when it comes to the codes - it just looks for resistance in the circuit, that's it. if the solenoid is plugged in and resistance is in spec, the ECU is happy.

Have you tested the leading coil per the shop manual? I've found that it's a pretty valid test for spotting coils that are past their prime.

Dale
Thanks for the response Dale. Will double check I am using the correct line to check the fuel pressure. Tried working coils, swapped out the ones that came on the car originally and same result. Will check the shop manual to see how to test them.

I am going to try the suggestion from Red94fd, and rewire the pump. Also, I will check the voltage to the pump.

Thanks again for the help guys.

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