I am helping a friend with his swapped car (S5 motor in S4). We got the car running but it runs rough and when you step on the gas quickly it will die as if its getting flooded out. As far as I know all the proper parts are installed. ALL of the vacuum lines have been removed along with the air pump though. Would putting that back on make it run much smoother? He told me he was driving it and then it lost power and died. Compression is good and is getting spark. Any ideas would be helpful.

 

how do the aux ports activate if you removed the air pump?

 

They don't. The original plan was to go through an rpm switch to activate them before my friend bought it. If we can atleast get it running decently he's planning on going LSx route for a "because racecar" vehicle, which was my friends plan for it. I know he still has the rats nest but I do t remember seeing any solenoids that I remember the engine having unless I overlooked them.

 

Put the BAC valve back on if you removed it. No point in removing the air pump, it only takes a small amount of power to move it.
Check for vacuum leaks. Verify fuel pressure, running and bleed off.

 

Would swapping the injectors have made a difference?

 

Yes. Which injectors and wiring harness does the car have? 86-87.5 have low impedance injectors, if the car has those injectors there will be a injector resistor pack underneath the factory air box. S5 injectors are high impedance.

 

It still has the stock harness, but IIRC the injectors are S5. But what I meant in m previous post is would switching the secondary and primary injectors have made a difference. Or are they the same flow?

 

S5 have high impedance injectors and S4 have low impedance so you can't use high impedance injectors w/a low impedance resistor box. You need to check to see if you have the resistor box as part of the injector circuitry or not. If you do then unplug it and bypass it.

https://www.rx7club.com/attachments/...lackyellow-jpg

 

Alright ill ask him tomorrow. For arguments sake and if they are low impedance S4 injectors, would just putting on the air pump and whatever else there is for the rats nest he has help with the rev problem?

 

Depends. The BAC should never be removed although some remove it during an emissions removal. The air pump is pretty important on an s5 cause it actuates the aux ports. Im not sure but there may be a solenoid on the rack for VDI actuation as well.
Both of those would be easy to rig up with an electric air pump, relay and rpm switches.

 

Been awhile, that's the part on the side of the block under the intake right?

 

need more info, like is this a complete swap with S5 AFM, harness, injectors and ECU?

usually i would start by checking the TPS, then move to codes for oil metering pump, then on to checking fuel pressure and for vacuum leaks. faulty grounds being the main culprit but the most difficult to get to.

 

VDI is part of the extension manifold (middle intake) IIRC the BAC also mounts on that manifold. It has a brown end, square plug and an allen bolt on it.

Do what RotaryEvolution says in that order.

 

The ecu, harness, and AFM I know are S4 components. Not sure about TB or injectors off the top of my head. Is there any physical difference in TBs for NAs between either series? Or is it just the TPS? How would I go about checking fuel pressure? The OMP doesn't work since its got an S4 front cover. Still hooked up but he's been pre mixing it. To what ratio, I'm unsure, but I'd assume he's been using proper ratio.

 

You can rent a fuel pressure gauge from an auto supply store. Measure pressure after the fuel filter or better yet after the return line.

The OMP from an S5 could not work w/an S4 ECU.

The throttlebody is different between series.