Hey everyone,

Trying to diagnose a little quirk I've had w/ my car ever since I got my rebuild finished and getting some miles on her. I have roughly around 3000 miles on a brand new rebuild. Only new mods are: Streetport, Rtek 1.7, 750cc secondaries, FD pump.

Well I finished the break in and started giving her boost almost 1500 miles ago and the problem hasn't always been there. It doesn't do it all the time and doesn't do it @ full boost and when she's revved out. Only time I'm noticing it is when I stab the pedal to the floor or roll into it and it starts building a couple of pounds of boost. I don't think I've ever had it happen above 3500k rpms. It's really weird and I'm not exactly sure it's fuel cut.

Symptoms:

- Car falls on it's face then picks back up where it was before it stumbled.
- Tachometer drops completely to zero then jumps back to where it was before stumbling.
- Sometimes the tachometer wouldn't come back up and read. It would stay @ zero. Turning the ignition off and then on fixed this.

Happens during:

- when in very low rpm's then putting the pedal to the floor to start building boost and revving whatever gear out. Only does it in 1st, 2nd, and 3rd. Never had a problem with it in 4th and 5th.

Never has it been in full boost or tached all the way out or high in rpms when it occurred. It's only when I put the throttle to the floor and in VERY low rpms and still in vacuum to come out of boost. I've never seen it over a few pounds if ANY at all of boost when this happens.

I did paint my engine bay during my rebuild. I'm not sure if the leading or trailing coil pack is getting a good ground to the chassis or if it's going out completely? Only thing that leads me to think it's ignition and I'm no expert. But my meter fuse blew today immediately after it happened. The only time this has happened before was when my reverse switch wires exposed over time and wear shorted out and kept blowing the fuse. Well when trouble shooting that ordeal... I was told that the meter fuse was ran through the leading or trailing coil pack? Is this right? Maybe just the tach had something to do with either coil pack. I'm going to test the resistance in both my coil packs, and sand away the painted areas where the coil packs bolt to the chassis.

I know it's a shitty Rtek chip tune and I'm not sure if it's just the staging of the secondaries but this seems to me like it could be an easy fix and just wondering if anyone might have some input. I've made sure all of my engine and chassis grounds were good to the best of my knowledge but they might need some more looking at.

I haven't posted any recent pictures of my new rebuild or finally getting my RE-Amemiya wing installed. But my car is coming together how I want it a little now! Fresh rebuild, cleaner engine bay, and I'm pretty stoked. Just working out some little kinks! Overall she runs VERY strong and feels amazing compared to before. The pick up is awesome and feels so fresh!











Thanks for whoever reads this and gives input. :P

-Allen G.

 

Good idea about sanding the fender where the coil brackets are bolted to.

The tach is tied to the trailing coil as the trailing coil provides the tach with the signal.

What you really need to do is redo the group of grounds located just below and to the side of the trailing coil. This group of grounds houses the ground to the Main relay and could be causing the Main relay to cut in and out. Maybe not always but when the tach drops all the way to zero is a characteristic of the ECU losing power. The Main relay is responsible for powering your ECU.

Not sure what you mean about the Meter fuse running through the coils. This fuse basically has nothing to do with the coils. The Meter fuse does power the gauges besides the Reverse switch and other components.

Post #7 last reply https://www.rx7club.com/showthread.p...umination+fuse

 

Yeah it was a vague memory of various info and getting it mixed up! lol. I will dig into everything near the brake booster and clutch master cylinder and sand all those grounds down and make sure they are snug. Also the grounds along the frame rail as I think those are still heavily painted. Couldn't hurt.

Thanks for the input man!

 

Main relay ground.

 

Its happens a lot more @ night when its colder too? Was cruising around in another thread and found some similarities... could it be the boost sensor??? I'm going to check it today w/ a multimeter.

 

When checking the Boost sensor also check the vacuum hose for leaks as well. Did you take care of the possible grounding issue.

 

Yes sanded every contact point for a ground and also where the brackets for the coil packs bolt to the chassis as well. That didn't seem to help any.

 

Alright... checked the boost sensor vacuum line and it looked fine. No cracks or splits. But tested the voltage on it w/ the key on and:

Brown / Red wire (calls for 2.3 - 2.7 volts). I got 2.2 volts
Brown / White wire (calls for 3.5 - 4.5). I got 5.9 volts
Black / White = Battery voltage as it should be

Dunno if those are out of spec bad enough to be my problem but who knows. Onto checking the TPS.

Terminals A to B (Calls for 1k @ idle). I got 1.7k ohms. For Wide Open or Full it calls for 4 - 6k ohms and I got 6.9k ohms.

Terminals A to C (Calls for 4-6k ohms all the time). I got 5k ohms @ idle and from idle up *slowly actuating to see if anything changed; it proceeded down to 1.9k ohms during Wide Open or full throttle.

That seems to me to be odd but I've been told and just read in some posts that the TPS on an S4 only reads up to 30% or something like that??? Anywho... that's all I really got around to tonight. I'm still cruising around searching.

-Allen G.

 

You might want to disconnect the vacuum hose, cap it, and then take it for a ride and you could disconnect the TPS as well before taking the car out on the road. Also, the 5.9 volts on the BR/W seems high. The BR/W wire provides voltage to other sensors as well that you can check such as the TPS, Variable resistor and AFM to name a few. When you're driving have you noticed the boost gauge needle not moving when it should? This would be an indicator of an electrical problem with the sensor.

 

What about the readings on the TPS? Do those seem odd or like it could be the problem?

 

Did you set the TPS to 1 volt first then take the ohm readings? The A to C readings are not correct in the FSM as they list the 5k ohm at both idle and full throttle which is incorrect. At idle the range is correct but at full throttle the number should decrease in value.

 

its a busted airflow meter.

 

My thoughts too. That's a sweet looking turbo II man, good job!

 

Thanks for the input guys. I'll try and scoop up an AFM and swap them out and see if that's the issue.