Hi guys,
I have a 1990 T2 that was rebuilt about 400 miles ago.
Recently it has started running really bad after fully warmed up. After rpms get up to around 4500 its like the engine will not take any more gas. If I give it more gas the engine cuts out badly. The longer the engine has been running the worse the cutting out becomes. After 20-30 minutes it becomes difficult even pulling away from a stop it cuts so bad.
I can't find anything that has changed. I swapped the leading coil pack, reset the TPS, reset the timing, checked for vac leaks .
Any suggestions greatly appreciated.

I searched for a couple of hours for this problem.

 

You might want to check the Water Thermosensor and the IAT sensor within the AFM.

 

Thanks for input. I'll check those thinks first.

 

Another thing to check is the resistance to the fuel pump wiring as a higher resistance could lead to interference of the pump's functionality.

 

What resistance should I expect? And, how should I check for resistance? From the engine bay back to the pump or disconnect the wires at the pump and measure the resistance of the circuit?

 

Go google "rx7 fsm," start with the first result, and start reading. It'll give you the specs.

Check the resistance on the sensor... not the rest of the circuit. (disconnect harness from sensor and probe the sensor, not the harness)

 

[QUOTE=MIDNFauciUSN;11490387]Go google "rx7 fsm," start with the first result, and start reading. It'll give you the specs.

Check the resistance on the sensor... not the rest of the circuit. (disconnect harness from sensor and probe the sensor, not the harness)[/QUOTE

.

 

thanks for the link to the fsm and pointing me in the right direction.

 

I checked the engine thermosensor and the temp sensor in the AFM, both seem to be working properly.
The problem doesn't appear until the car has been driven for 20-30 minutes and it doesn't count if I just warm it up by letting it sit idling in the garage. If I warm the 7 up in the garage and then take a test drive everything seems OK.
I am using a high speed fan from a Mercury Villager for cooling but I'm still using the stock alternator. I read someplace that the stock alternator is not strong enough for the Villager fan but I'm not having any problem with the battery going dead.
But, is it possible that after the fan has been running for awhile, that the alternator just isn't putting out enough current to keep the engine running properly.

 

How about comparing the output of the alternator while idling before you take it for a ride and compare it to the output after the car starts performing unfavorably. What reading did you get from the ECU as it relates to the Water Thermosensor? Should be about .3 volts and it would be best to check after the car has warmed up fully and acting properly and compare it to the reading after the engine operates poorly.

 

Thanks, I'll do as you suggested.

 

may want to check over the ecm ground. with heat comes resistance, and vise versa. just a thought

 

do you still have the stock OMP? check all the wires going to the stock OMP, if one of them develops a resistince problem after warming up the engine will go into limp mode

 

I compared the voltage when cold to when hot. When cold the alt showed 14.2 volts and after warming up the voltage dropped to 13.5. Is that enough drop to cause the engine to run so bad?

 

It's normal for the voltage to drop some as the engine bay heats up. 13.5 volts should be sufficient enough.

 

did you check the AIT at the elbow,throttle body yet?

 

The AIT was one of the fist things that I looked at but since you mentioned it I thought I should check it again. So, I checked it and I got about 180K ohms after warm up. The FSM calls for 3.5 +- 0.4 K ohms.
Hopefully, the AIT is the problem.

 

I finally received the new AIT from Mazdatrix. However, the problem still exists. I read in an old post that sometimes a vacuum leak at the UIM will cause the engine to miss/cutout badly after fully warmed up. So, I'm going to pull the UIM and install a new gasket and re-torque.

 

The UIM gasket looked OK but I replaced it anyway, torqued to specs BUT the poor running condition still exists.
Once the engine is warm the engine it runs really bad.

What would cause the ecu to go into limp mode besides the OMP? I have the RTEK chip with the OMP removed so the OMP should not matter.

 

The poor running doesn't seem to be based on the rpm range as much as it does on how far the pedal is depressed. At any rpm, if the pedal is depressed more than half way, the engine cuts out/back fires almost every time.
I already checked the TPS and no flat spots/dead spots were found.

Any ideas guys.

 

I decided to go back over things that had already been checked. So, I started with fuel pump pressure. Maximum pressure is 22 psi on a WALBRO 255. Definitely something not right.
The pump sounds like it isn't running correctly. The pump probably has about 400 miles on it.
How can I check if the problem is the pump versus the wiring?

 

Just to test the fuel pressure you can run a voltage wire directly from the battery to the pump and see if that changes anything, and while you're at it you could clean up the ground connection for the pump as well.

And see what pressure you get if you dead head the gauge right after the fuel filter and this will give you a heads up as to whether the problem is w/the pump or FPR.

 

Thanks Satch. I started by checking the pressure right after the fuel filter and when it tested low, I pulled the hose before the filter just to be sure the filter wasn't plugged.

 

So you got 22psi w/the gauge inline or did you just not post the dead headed numbers?

 

i would remove the pump and inspect your pump to housing connections.

i just had a customer with a similar issue which had a faulty o-ring installed on the pump without a plastic spacer under it, which allowed the o-ring to push to the bottom of the pump and not seal it to the inlet tube.

all the seals off the old pump have to be switched to the new one: mushroom spacer on the bottom>o-ring>o-ring hat then install with the rubber seat under the pump trimmed to fit the walbro.

alternately you could cut off the o-ring tube and simply use a small length of submersible fuel hose to jumper the connection from the pump to the inlet tube.