87 rx7 runs good, but when it hits 3.5krpm it feels like its pulling a trailer
 

I have an 87 rx7 5spd. It has 130k miles on it. its very clean and has been well maintained.

It ran great up until about 110k miles or so.

What is happening is when I am accelerating and the rpms get to about 3.5k or so the engine will bog down or all of a sudden feel like I am pulling a trailer.

rpms under 3.5k do not feel this way, it pulls hard.

I have had the car in 2 different shops and they have not been able to find anything.
I have replace the mass air flow sensor, the plugs, the air filter...

I have also replace the idle air control valve and nothing seems to fix it.

This is my 3rd rx7 and I have never experienced this before. My last rx7 had 300,000 miles on it and the apex seal blew. So I bought this one.

If I cannot get any answers on here does anyone know of a reliable rx7 mechanic in the North Houston area?

Thanks,
Chuck

Can you slowly get past the 3.5k rpm threshold w/o any problem?

Does it bog only when you step on it before 3.5k rpm?

Does the car free rev properly when in neutral?

In short, the secondary injectors come online at 3800 rpm. The main reason for there to be a problem at this transition point is usually a poor engine ground used by the ECU. If this were the case then an additional ground at the boost sensor could remedy your problem.

Yes at times I can slowly get past the 3.8k threshold, but if I get on it I cant.
Yes pretty much it bogs only when I get on it, If I ease into it slowly USUALLY it will get past the 3.8k threshold, but then I can feel it at 4.5k or so... its weird...

Yes it free revs properly in neutral.

From what you are saying it sounds like the secondary injectors are not coming online as that is what it exactly feel like.

So can you direct me to where this ground issue may be?
possibly a bad ECU maybe?

Thanks for all your help!

The main ground is found on top of the engine towards the back and driver's side. You won't have free access to it unless you pull the manifold located above it. You could try to add another ground to the boost/pressure sensor located by the passenger strut tower. You tap into that sensor's ground and run the other end to the engine. Takes about 15 minutes or so to do if things fall into place properly. Make sure you identify the ground wire as there are 4 wires to the sensor. Depending on the year of the car dictates the color of the ground wire as the color was changed mid year 87.

If this does not work the problem could still be a grounding issue or it could mean the secondary injectors are clogged or not plugged into the injector plugs properly.

I found the ground behind the intake, its is good and solid and attached to the firewall.

Can you give details on what the booster/pressure sensor is?

Also do you know of any good RX7 mechanics in North Houston?

Wrong ground, the ground satch is talking about you can only access by taking off the upper intake, it screws right into the keg

As previously noted, the sensor is found near the passenger strut tower. It has a vacuum hose connected to it. The plug has 4 wires. B/W reads 12 volts w/key to on. Brown/Red has 2 to 3 volts w/key to on. This leaves two wires left. One of them is Brown/White and has 5 volts w/key to on meaning the remaining wire is the ground wire. Again, depending on whether your car is early 87 or late 87 dictates what color the ground wire is. Late 87 and it's Black, early 87 and it's Brown/Black. And the FSM has all of this info including the exact location of the sensor.