Ok, I bought my 86 N/A a few weeks ago, and it's been running very strange for about the past week. Anytime I'm over about 3500 rpm, and I give it more than 1/4 throttle, my engine loses almost all power. It will still accelerate, but just barely. Sometimes the car will also stumble below 3500 rpm when I've been driving for a while.

Here's the weird part.

When I first start the car(whether it is hot or cold), the car will not do this for the first few minutes. If I kill the car for about 30 seconds, and start it back up, it will run fine for a few minutes. It seems to get worse the longer the car is running for. The other day, I got stuck in a traffic jam. It got so bad that I started killing the car about every 5 minutes so it would run better.

Here is what I have already done to the car. Keep in mind that this car is bone stock.

Changed thermostat.
Ran new 2 gauge negative battery terminal.
Ran new ground strap to firewall.
Grounded boost sensor.
Grounded ECU injector wires.
Replaced spark plugs.
(The previous owner had Leading spark plugs where the Trailing plugs go.)
Replaced spark plug wires.
Adjusted TPS.
Previous owner had the secondary injectors replaced with cleaned, used injectors.

I don't know if this is a spark issue or a fuel issue. I would hate to have to take my car into a shop, because I haven't had to take any of my cars to a mechanic in about 4 years. Please help me.

Mike

 

Sounds like a bad TPS.

Edit: Oops, Im signed under my GF's SN. This is mazdaspeed7

 

I thought the TPS might be bad, so I unhooked it to see how the car would run. It seems to run pretty much the same with the TPS unhooked. Only thing it does different is idle a little weird, and backfire a little when I get off the gas.

 

O2 sensor

 

So I hooked the TPS up to a volt meter tonight, and checked the resistance like it sais in the service manual.

Resistance between the upper and lower right wire is about 1 kOhm at idle, and 5kOhm at WOT. That's all within spec.

However, resistance between the upper and lower left wire is 5kOhm at idle, and 0.5kOhm at WOT.

The manual sais it should be 5kOhm at WOT. So, I guess I'll replace the TPS and see what happens.

Anybody have one for sale?

 

If the 02 sensor checks out ok, try the fuel injector resistor.
Check the two pins on each plug for the secondary injectors. With the ignition on, car not running, you should have solid power to one side of each connector and no power to the other side. If you don't you need to replace the resistor which is located on the engine compartment wall in front of the passenger side shock tower.
hanman

 

Looks like it was the O2 sensor after all. I unhooked it just to see if the car would run different. The problem completely went away. I just bought a new one at the auto parts store, and I'm waiting for the car to cool off to install it.

Thank you for your help.

Mike

 

Well, I was wrong. It looks like the 02 sensor didn't fix it. It seemed to run good at first, but after the car had been running for a while, it started acting up again.

I also checked, and the secondary injectors are getting good power. The resistance of the injectors is 2.4 Ohm(which is in spec on an 86). Also, the injector resistor checked out good.

Could it possibly be my fuel pump\fuel regulator\fuel filter?

Any one of those could cause a drop in fuel pressure, and could be starving my engine of fuel, because it only happens when I give it throttle. I guess I'll try those Monday, because I'm off of work.

Any other ideas?

 

injectors, or fuel filter, thats what it sound like to me, cuz when i had a bad secondary injector it wouldnt pull over 3500rpm, its something in the fuel most likely, TPS or O2 wouldnt cause that kind of problem

 

Thats a typo in the manual concerning the tps. Don't waste your money. Its ok.