Stumbles at 2500 rpms
 

I have a 94 mostly stock RX7. When driving it or underload, it will fall on it's face at 2500 rpm. If I keep my foot on the gas it will go dead. I have checked all the vacuum lines that I can see, the secondary turbo is free and the wastegate is working (if I get the rpms high enough unloaded, the wastegate opens and the back intake has suction). I checked the double throttle control actuator, removed the vacuum line so it would open, but it still did the same thing. Does anyone have any ideas, it is not doing something that it should at 2500 rpms.

Any help is appreciated

Thanks

Are you saying that this happens whether you are under load or not? I know the stock ECU sometimes causes hesitation in that area. around 2.5-3k rpm range. My 94 currently has a hesitation in that range only under hard boost.
I have heard many different solutions to the problem. The most common solution i have read is swapping to an apexi FC. Others have said that proper ground wires is enough to eliminate the hesitation.
Im not sure whether or not this helped at all and im not sure why your car has hesitation because it also happens unloaded. Hopefully more experience members can chime in.

It only happens under a load.

Yeah, that just sounds like you're getting the good ol' 3000 RPM hesitation. Adding a ground wire from the negative terminal of the battery to a clean ground on the frame of the car will help, but it will likely always be there with a stock ECU.

The only way to totally eliminate it is with a PowerFC. It's just a bug in the stock ECU.

All FD's with stock ECU's have it to some extent or the other, some are a light change in power as you pass through that part of the powerband, some are violent and jerky when you hit 3k.

Dale

What size wire should I use - I hooked up a 14 gauge wire and it did not help much. Should I use a bigger wire or could it be something else

At more than half throttle the car will competely cut out @ 2500 rpm. If I let off the gas and feather it some, it will keep running but jerk and sputter all over the place. If I give it just a little gas it will drive as long as I keep rpms below 2500

I would suggest the following before you start running grounding wires everywhere:

Start by checking/cleaning your existing grounds (UIM, near the A/C bracket, ignition coil if you have the older harness, and exhaust). Check your TPS to make sure it's not out of spec.



Does the car still have the the double throttle control and coolant line running to the throttle body?

It does still have the double throttle control and not sure about the coolant line - I'm pretty sure it does since it's mostly stock.

You should verify the action of the double throttle control as well.

I vacuum tested the double throttle acutator and it work as it should and with the car running I had vacuum at the DT acuator. I took the vacuum line off so the DTA would stay open and drove it down the road and it did the same thing - So I don't think it is the problem.

There is a good chance that you can improve running by performing Mazda's tech bulletin procedure 005-97, shown in post #42 of this forum thread. I just finished that a couple of days ago, and it cured our 3000 rpm miss. (Maybe a PFC is less sensitive to grounding issues than the stock PCME?)

(Also check out posts #47, #48, and #53 in that thread.)

Thanks, I'll try that tomorrow and let ya'll know if it works

I was also wondering if the #2 catalytic converter could be stopped up. I have a downpipe so no #1 cat. I'm not running hot - does a rotorary engine run hot with a stopped up catalytic converter? I'm also not getting any codes while the car is running - would a stopped up cat throw a code?

A clogged cat will not throw a code. However, usually if the cat is clogged, it will overheat and there is a heat sensor which lights up on the center (shifter) console.

I have same problem but it seems to be happening right at 2000 rpm. I can rev up the engine in neutral fine. When in gear, car will stumble at 2000 rpm and feels like car jerks forward and stumbles. Can't seem to get pass 2k under load. I checked my grounds but may try getting a new gauge wire to the battery negative terminal.

Op, did u find a solution?

Limp mode, search. I'm on my phone ATM so that is as much help as i will be for now.

Old thread. However my car will do that sometimes and it's quite annoying. It will usually do that after it's been sitting for a while and I start to drive it around. No idea what it's about, but it will normally stop doing that after about 10 minutes.

Yea sounds like limp mode. Its not showing any engine codes though. Thought it was a faulty TPS, so swapped that out. No dice.

I think I am having the same problem as you. It's very annoying and I would like some help, also. I think it is a good chance that the problem may be bad grounding.

Resetting my ECU seemed to have fixed the problem. Disconnected the battery, stepped on brake pedal for 30 secs.

I fixed my problem. I added another ground wire from the negative terminal to the bolt that holds down the thing where you put in windshield washer fluid. No hesitation problems anymore.