ArmenMAxx

iTrader: (21)

A buddy of mine just picked up a FD. Been sitting for years, completely stock 75k miles. Engine seems solid, good vacuum, fast startup even when hot. It does have a constant CEL which puts the car into limp mode. I tried to get the diagnostic CEL code however im getting NO CODE. Its really weird.. I am performing the diagnostic troubleshoot correctly. Attempting to do so (Diagnostic box TEN and GND union) clears the CEL temporarily and the car runs perfect..until the CEL comes back on and SLOWLY the car goes back into limp mode.

We've checked and tested the TPS. Checked all the usual connections, replaced the fuel pump, fuel filter,etc. Its been a while since ive worked on a stock twin FD but im baffled at this point. Mainly, I need to know whats causing the CEL and limp mode. I am in process of swapping in another stock ECU to see if itll change anything..but something is causing the car to go into LIMP MODE after I clear the code and a bad ECU doesnt really fit the bill for me. Its take some driving to trigger the CEL and ultimately LIMP mode.

Question now is why I am not getting a code? We tested the GND port on the diagnostic box and see 12v. Doesnt matter where I ground it, its getting the same NO CODE pattern.

An old thread I used for reference. Seems like on page 2 someone was having a similar issue, however for our case it did not solve anything.

https://www.rx7club.com/3rd-generati...-851414/page2/

Appreciate it gents,

j9fd3s

iTrader: (3)

i would try another ecu and see if you get the same thing, if yes then i have a suggestion.

i was able to confuse the ecu's diagnostic part by wiring a sensor backwards, so if ECU #2 still doesn't spit out codes, start unplugging stuff and see if that matters. obviously start with the easy to race parts, and feel free to pull fuses and ecu connectors. or if you wanna work backwards, i think with just ecu connector #1 plugged in, it should be powered up and then spit out codes (it will be all of them).

there are actually quite a few things that cause a limp home, so just changing parts seems like it would be the most work. although most of the limp homes are for things like the fuel pump relays, so since yours is on a timer i think that would suggest the metering pump

ArmenMAxx

iTrader: (21)

Should gave another stock ecu in by next week. Hoping the issue is just a wacky old ecu.

If it is the oil metering pump, what exactly would be wrong with it? Electical/harness issue,/fuse or mechanical? Want to know before we consider swapping in a new omp, if the ecu doesnt solve the issue.

ArmenMAxx

iTrader: (21)

Installed a known working stock ECU and still having the same issues. Car goes into limp mode with a CEL yet gives no codes.

Really open to any suggestions

j9fd3s

iTrader: (3)

unplug all the ecu connectors except #1, which is the one that goes to the car. if it spits out codes then you have some sort of polarity/wiring issue. if it does not, you may try checking the codes with an LED at the diagnostic box, it could be that the thing that drives the actual check engine light in the e/l box is bad.

just for back ground, i have an REW in my FC, and i have wired it up to use the stock FD ecu. at one point, i checked for codes and none of my stock ecus would spit any out. so i actually went and wired the ecu up out of the car, and with just power, ground and the ten terminal, it spit out codes. it ended up that my map sensor was backwards, and this confused the ecu.

the second bit is that the CEL is an add on, and the ecu does not drive the bulb directly, the signal goes to the diagnostic box, and the e/l unit, and the e/l unit drives the bulb

ArmenMAxx

iTrader: (21)

Thanks,

I had tried using LEDs to get a read however the sequence was still the same... No codes.

Ill try what your recommending and see what happens. If not, im guessing the next best thing is to start replacing common limp mode causing culprits and hope for the best.

j9fd3s

iTrader: (3)

i think its easier to start with most of the ecu unplugged. its unlikely to have 2 bad ecus (i tried 3).

EvanSt

I had my car go into limp mode a few years ago and it didn't throw any codes. It turns out the OMP was bad and as soon as I replaced it it worked fine.

The stepping motor inside the OMP is the thing that will either go bad, or the ECU thinks its bad which then retards the timing and puts it in limp mode. I don't know if that will fix your problem I just thought you could use this info.

kvttrs

iTrader: (1)

I'll be waiting for your solution. I myself am trying to figure it out, with $600 already down the drain for nothing.. new TPS and MAP sensor. I hope you get better luck.

And if you figure out a way to reset the ecu or just turn off limp mode, PLEASE post it on here. I've searched the forums and people keep giving different procedures, even a fellow FD3S owner said something different.