I have a 1985 rx-7 with an s5 TII motor and the engine has gone into limp mode and I have a couple of questions:

my boost pressure sensor became unplugged at some point, possibly causing the limp mode, but after reconnecting the sensor and disconnecting the battery to reset the ECU i've still been having issues. (I do have a knight sports FCD, and that could've possibly gone bad too, im just trying to narrow down the culprits)

My question first off, is there a way to pull error codes without the green diagnostics connector in the engine bay? (my wiring harness is tucked and its going to take a while to find the connector again) Is there a way to check it at the ecu, even with a test light?

and to give a basic list of other connectors and things i've checked thus far:

the MAF
the MOP
vacuum issues
fuel rail and injectors for leaking or disconnected plugs


Thanks in advance,
Ian

 

Pin 1D and 1F (you select one of these), plus you'll need a voltage source for the lights so you could use either pin 1A or 1B as examples.

Edit: And pin 1I needs to be grounded. This method involves the light checker. W/the checker set up and key to on, the ECU should provide you w/any codes.

 

Thanks, I guess I need to make a light checker. I was just going to use an auto zone circuit tester, but apparently I cut the wires to the diagnostics connector from the ecu anyways. Glad I checked instead of pulling fenders off for nothing.

 

You need to use LED lights that are appropriate for the situation.

http://2ndgenrx7.freeservers.com/error%20codes.html

 

Much appreciated, I was just looking at that article myself. As well as this one, since the codes are apparently different from s4 to s5 as well.

http://www.johnr.com/cpucodes.html

 

Can't you also check via a voltmeter? The FSM for an S5 says that 1D ( the Self-Diagnosis Checker [monitor lamp]) should change from 12v to 6.2v when the CEL would illuminate in the dash of an FC, as long as 1I is grounded, correct?. (Please correct me if i'm wrong) I know there is a difference between the s4 and s5 in connectors as well, and they way it pulls codes- I'm just unsure on the details, I've never had to do this on an Rx-7 before and it's a bit of a crash course.

My local radioshack doesn't have the necessary parts for a self-built LED code checker, and I really don't have the time to order stuff, since this is my daily driver.

 

In your example of the voltage at pin 1D, that just tells you if the diagnosis checker is working within its specified voltage values, but you can't tell what codes there are by measuring this individual voltage value. It doesn't matter that you have an S5 and that there are different codes for an S4. The only thing you are trying to do is replicated the S5 method on a car that has no CEL so you have to make do and incorporate the S4 method. The S5 already has the code checker light prewired and installed in the idiot lights. Since you don't have this feature you need to build your own system that does the same exact thing and this involves applying the S4 method. As far as the S4 is concerned, the S4 doesn't have the CEL light so you need to tap into the ECU and they made a plug in the engine bay in this instance to make it easier for those trying to pull codes rather then forcing them to gain access to the ECU to pull codes. So that there are different connectors between the two systems doesn't mean beans as the basic process is the same.

Source another Radio Shack either locally or online and get the proper lights. I'm sure there are other suppliers for these lights. The process is rather simple. W/the lights in hand the Orange wire at pin 1I is grounded, then connect the two wires to the two respective pins on the ECU. The lights only have two connectors. One needs voltage and the other goes to one of the two pins I pointed out earlier. And then w/key to on the code checker will tell you of any codes. The codes you will get are S5 codes so you look at the S5 chart and get this S4 crap out of your head.

 

I built the code checker, worked like a charm. Apologies for the doubts.

I got code 25, which is the intake manifold sensor that I found unhooked from the FCD.

With the ignition on and the sensor plugged in (with the FCD AND without the FCD) it was reading 4.96v; which is out of the FSM's spec of 3.4-3.6v
Looks like the sensor went bad, perhaps while it came unplugged during driving?

Are these sensors ECU specific? I have a jdm s5 motor

 

I woke up this morning and realized that I was being a dumbass yesterday and was checking the reference signal.

I checked the appropriate wire today (G/Y) that goes to the ecu:
both with the FCD AND without the FCD connected

Voltage with ignition on: 2.30v
voltage at 100mmHg: 2.03v

The FSM says that is in spec... So i checked the vacuum line for the sensor to the manifold and there is no dry-rot, the hose looks in good shape. I'm racking my brain about what else would cause the ECU to pull that code.

 

A code 25 is for the Pressure Regulator Control valve.

 

I've obviously been going about this incorrectly and I'm going to go ahead and straight up ask for help.

My setup is:
JDM s5 TII
550cc primary/750cc secondary tuned with SAFCII and wideband
Manual boost controller

If I disconnect the battery and then reconnect it and start the car, it will start fine and then go into limp mode after a couple minutes.


I double checked my error codes and these are what pulled: (I also made sure to pulled codes after the car stalled and died to make sure it was not a non-memorized code)

25 Solenoid, Pressure Regulator Control
31 Solenoid, Relief Valve
32 Solenoid, Switch Valve
34 Solenoid, Bypass Air Control (BAC) Valve
42 Turbo Precontrol Solenoid

All of those are ouput devices, and are firstly being pulled because I deleted emissions. Except for 42, which I believe is the duty solenoid which is removed because I am running a manual boost controller. Since they are output devices, they would not cause limp-mode. So I'm thinking either a sensor has gone bad, or there is short somewhere.


To immediately start the process of elimination, I went ahead and removed the FCD since I am only turning the car on to idle until I can fix the problem anyways. The engine will still continue to go into limp-mode which eliminates the FCD as a possibility.

I went ahead and checked the MAF next. I checked for voltage signal at the ECU and at the MAF with ignition on and at idle; both came back in spec. 4v at ignition on and 2.2-2.4v while at idle; both at the ECU and at the MAF. (This is with SAFC installed however, I do not know how that affects voltage readings, but I assume the voltage would still be correct at the ECU regardless)
However, if the car is idling poorly in limp mode, and then I disconnect the MAF and reconnect it, it will go back to running fine again for a couple of minutes. (I'm not necessarily sure if this means the MAF is the issue...it could just be the ECU going to open loop mode, and then back to closed loop when it goes into limp-mode. Correct?)

To make sure the MAF itself was not bad as well, I went ahead and checked for resistance on the pins on the MAF and the only one that came back (possibly) weird was testing E2<->THA (to the Intake Airtemp Sensor) with a resistance of 1186ohms. However, it was 95* outside today when I checked it. So I assume that is in spec...

The FSM says: @ 68*F 2,000-3,000
@ 104*F 900-1,300

At this point I'm debating putting the stock injectors back in, removing SAFC, and then going through all of the input devices one by one. I was just hoping someone might have some more educated ideas than I would definitely have based off of this information. Any help would be greatly appreciated.

Thanks in advance

 

since they are on the list i would plug solenoids into the PRC connector and the precontrol. i didn't look in the FSM but on the FD both of those will cause a limp home when you hit boost, and the S5 is really similar... anyways, it knocks the two off the list

 

J9, I remember seeing a post while searching where you said there are also perhaps a couple things that will not throw error codes but can also cause limp mode. Do you remember what those might be? Just trying to have all my bases checked. I might have to buy those solenoids from someone on the boards; im not sure I have them anymore- unless you can use another type of solenoid in its place?

 

weird the FC books, don't mention what the ECU does to the output devices. the FD one does. anyways, the check engine light doesn't come on for a most of those, but some of them do have limp home/failsafes!

if you don't have any solenoids, you can use a 15 ohm 12V resistor.

 

Perhaps you could steer me in the right direction here as to what can cause this "phantom" limp-mode? In the mean time, I'll probably be digging through some of the FD fsm tonight and checking my CAS and MOP tomorrow since it seems to be a fuel and ignition cut type of limp mode.

Thanks again

 

Sorry to double post, but I do not have much experience with resistors. What wattage do these resistors need to be?

For instance:
http://www.radioshack.com/product/in...uctId=12573351
Radio shack does not even list whether or not these are 12v resistors.

 

http://en.wikipedia.org/wiki/Ohm's_law

if I = V/R , we have 12V, 15ohms, so its 12/15 = .8 amps so you need at least a 1 amp resistor. although bigger is fine.

on an FD it will do limp homes for anything involved with the fuel system, so if you unplug the fuel pump resistor relay, it'll do a cut when it sees boost, so its different than the metering pump limp home, but its still a fail safe. and of course the check engine light stays off, so now you know how i learned about this!

anyways the boost solenoid and the fuel pressure solenoid might do this too, because if there is a problem fuel and or boost is uncertain so it may try to protect itself

 

So, for instance, this:

http://www.madisoundspeakerstore.com...ound-resistor/

Which is a 15 ohm, 25 watt resistor would produce 1.6amps and would be an effective replacement for my solenoids?

 

yep!

 

I attached the duty control solenoid, which removed code 42 (i am going to have to order a proper resistor for the PRC solenoid)

However, I was still having the same issues:

engine falls flat on its face around 2800-3200rpms, or any throttle above 20% shown by the SAFCII

So I checked the MOP today, and the stepping motor was generally in spec (off by + .5 ohms
However the MOP Position Sensor was reading out of spec:
VC<->E2: read 1.38 kohms (which is in spec with FSM's 1-2 kohms)
VO<->E2 + VO<->VC: 2.36kohms (the FSM says it should be 1-2 kohms as well)

(VO<->E2: read .81 kohms + VO<->VC: read 1.55 kohms!)

This sounds like this could be my culprit, however why would it not throw a code for the MOP position sensor if it is out of spec?

 

lol, could it be code 27 and not 25?

 

I suppose it won't hurt to check them again! haha.

Beyond the list of input devices, I guess its good to start narrowing down mechanical issues at this point too. Make sure there is proper air, ignition and fuel; checking the coil packs and fuel pressure.

At this point, I'm hoping its just the MOP, since thats a pretty easy fix.

 

I checked my codes at least another 3 times, the same 4:

25
31
32
34

However, while driving the car today, I noticed something I didn't notice before. Through SAFC my Air-flow reading from the maf was at 40-45% and was fluctuating. So, my first thought was to directly connect the MAF back to the ECU (remove SAFC) and see if it fixed the problem, but it persisted.

So, I rechecked resistance on the MAF, and everything came back well within spec and so I thought I would check voltage instead with just ignition on:

Voltage constant (reference signal) was reading 4.99v

But Voltage signal at the MAF was reading generally between .18-.5v and was fluctuating!
So to be sure the ECU was working correctly, I checked the voltage signal on the ECU side and it was reading the same thing!

I hope my ECU isn't fried.. I'm a little unsure what to do now.

 

Which signal was fluctuating as in which ECU pin/wire color?

EDIT: Pin 2B is an "input" signal so if that voltage was fluctuating well below the 4 volt reading that it should would lead one to believe either the AFM is at fault, or the connection to the AFM specific to that wire is faulty or the wire is grounding out on its way to the ECU or the ECU is pulling down the voltage for some reason.

 

FALSE ALARM, I was checking the MAF wiring while the MAF was unplugged. I double checked everything on the MAF, and its all in spec. (It's been a loooong day)


Still same issues, still no error codes. Just out of curiosity, I did unplug the MOP and check for codes and 20 (and 27 when the position sensor was unplugged) did come up when their respective sensors were unplugged.

But now I'm getting this idle surging? If i hold the throttle at any percentage, the rpm's will fluctuate up and down.. I did reset my TPS, so it was at .84v...I thought that would fix any issues coming from the TPS, not create new issues..