2nd Gen stalls when accelorator depressed quickly

[Gen2]

New Member. Purchased RX7 2nd gen ITS with no engine or radiator. Car originally built by Rotary Performance. Installed engine from a running donor car with good compression. Replaced fuel filters in fuel cell, injectors, checked oxygen sensor, pressure sensor. Fuel pressure at 45 psi and increases when throttle pressed. Throttle body is modified from original race car. Swapped ECU, MAF and engine wiring harness from donor. Car idles nice and will rev to redline if accelorator depressed slowly. Quick depression of accelorator and car stalls. Dyno showed it to go very lean. Checked grounds. I am stumped and I want to go racing. I would appreciate any advice.

[Gen2]

Oh yeah I did put in a K&N radiator, big oil cooler and fan. Car temp never goes above 190.

[seckerich]

S4 or S5? Either way check the line from the Map sensor to the motor and see if the restrictor is in place. Small pill with .030 - .040 hole in it. If it is S5 it sounds like a bad TPS.

[Gen2]

I have an S5 motor. I could not see a pill but when I blow in the tube there is a significant restriction.

TPS checked out as far as OHM readings withing spec according to the manual. However I did not try to adjust the TPS as described in the manual. Not sure if this would make difference?

Also I should relay that the 5th and 6th ports are open and the VDI is open. Maybe I need to make some adjustments for this.

[Gen2]

I have removed all the emmissions control stuff air pump etc and all the vacuum lines other than the MAP hose and hose to fuel regulator which is an adjustable aftermarket unit for the fuel cell and external fuel pumps.

[Gen2]

ECU is 100% stock. I am thinking it can not handle all the Mods. Opinions?

[C. Ludwig]

The stock ECU will handle the modifications just fine. I would recommend picking up a factory manual (not Haynes or the like) and running through the TPS, MAP, and AFM parameters.

The engine is an S5, are all the electrics S5 as well? You can get a somewhat similar situation with the S5s when they go into OMP limp mode. The secondary injectors will not come online and you won't be able to stab the throttle wide open and rev the motor. You will be able to gently crack the throttle and get it to free rev to the moon. Just won't be able to hold it wide open and get it to do anything.

I do have to say, in situations like this, aftermarket engine management is usually easier to work with.

[Gen2]

Thanks, Another mod I did not mention. I need to make sure I have a list of everything I have done to the motor when I post. I did remove the OMP and am Premixing.

Is there any way to get around the OMP limp mode with the Stock ECU?

[seckerich]

Now we get somewhere. No, it will not run without a working OMP installed on the motor. I think Chris has a relatively inexpensive aftermarket setup that cures this. Otherwise run the pump and premix.

[monsterbronco]

Not to jack the thread, but what is a suggested premix amount?

[Gen2]

Well I hooked up the OMP tonight. Reset the ECU and proceed to lay a nice patch of rubber down my street. :happy204: No where in all my reading and preparing to convert the stock street motor from my donor car was there any mention of OMP limp mode if you remove the OMP. Makes sense to protect the motor you would have a fail safe in the ECU for OMP failure. Street Rotary by Mark Warner goes through the mods but when discussing premixing he does not mention removing the OMP would set the car into limp mode.

I have the OMP bolted to the shock tower which is not ideal. So I would be interested in a solution. Plus it feels like it weighs 2-3 lbs.

Chris thanks for mentioning that my symptoms were OMP limp without me telling anyone that I had removed the OMP.

Well one more 2nd gen RX7 headed back to the track. I saved this one from being taken to the junk yard after sitting in my buddies driveway for 6 years. He blew the motor and radiator after letting it sit over the winter without adding antifreeze.

[Gen2]

Probably best to let someone who is more knowledgeable answer the premix ratio or confirm my answer. I will tell you I am adding 7 oz per 5 gallons. However the Street Rotary book says up to 4 oz per gallon for a 500hp + motor. They also mention for street driven stock car half a quart per 12-14 gallons. That is slightly over 1 oz per gallon. So it seems it depends on how modified your motor is. I am running a S5 N/A no increasing in Hp other than cold air intake, modified throttle body, race beat headers open 5, 6 ports open VDI, ( now with OMP hooked up but not doing anything. I wanted reliability over hp. ITS class

[Eagle7]

I've always run 1 oz per gallon.

[seckerich]

Hope you have the problem solved. I would suggest taking the time to reinstall the omp on the motor so it sees the revolution of the drive pin. I think it will still go into limp mode after a period of time if it is not actually working. I have always run 1 oz/ gal with all my motors so you should be good with something close to that. Try to limit the internet mods and keep it simple if you want a reliable race car. Run good plugs (NGK 10 or cooler), factory mazda filter, and a good free flowing air filter. I guess the modified TB was choke shaft removal? Anything else is a waste of time and illegal. Be aware that the S5 will tend to be rich on the top end. Slower but safe. Have fun and welcome to ITS.

[Gen2]

If I reinstall the OMP won't it be pumping oil? I have removed all the oil injectors and plugged the ports.

Throttle body Mod was removal of the first set of butterfly valves which I assume was the choke since a coolant line ran over to it.