tmenzz

Recently I've been getting thrown into limp mode. Most of the time a simple cure was to turn the car off/on and it was out of limp mode. It's been progressively getting worse and now i can't get it out of limp mode. I've tried resetting the ECU, but no luck. It also idles rough when warm, but that's been ongoing since the rebuild.

Also, the diagnostics is broken and since it's a JDM Series 7, there's no CEL.

My car is nearly entirely stock with a rebuild less than 3000 miles.

cewrx7r1

iTrader: (2)

Check the FSM for most common causes.

Map sensor bad hose or wiring would be my first to check.

tmenzz

i have done this, but i'll double check. thanks

billyboy

If the diagnostics box is broken somehow, wires should still be accessible?

Pin-outs for the various Japanese versions is on the FdRx7 forum - and you should be able to work from there forward to see what codes are being generated.

tmenzz

Yeah I'm going to have to possibly try that. I'm not sure why it's broken, but maybe it's just some bad connections.

I had past problems with the narrow band TPS signal after I put the engine back in. Maybe that connection isn't as good as I thought it was. Maybe that's throwing it into limp mode.

Anyone know what page discusses limp mode in the FSM or what the Mazda terminology for it is?

billyboy

I think limp mode is the Mazda terminology. You probably need the electrical manual rather than the workshop one.

I have damaged the narrow band sensor wiring in the past doing an install myself and one of the other engine harnesses had the connector broken - probably crushed between the manifold and firewall - so yeah, definitely not an unknown and worth a look-see.

This might help on the diagnostics box, this is a version III S6, non Jap market, so colours will undoubtedly be different, so you'd need to check what comes out of the 16 bit ECU.

tmenzz

Thanks for all of that!

It seems the connections for the TPS were okay. I'm gonna hopefully get it to my garage so I can adjust it. I doubt an out of spec TPS would cause limp mode, but I feel like it's off anyways.

Would a bad ground to the ECU harness cause this?

tmenzz

Duplicate post. Sorry

billyboy

Wouldn't hurt to check the earth.

Mate almost gave himself a brain aneurysm pulling the car apart multiple times over many months, looking for a mysterious problem causing the car to cut out on right hand corners. It was a loose ECU earth.

The two ring terminals under the coils and on the manifold possibly worth checking if the engine has been pulled and overhauled too.

tmenzz

You think a bad ground to the coils would put it in limp mode? I remember one of the ground wires smoked when I first started it up after the rebuild but I thought I fixed it. I don't remember what the ground was for exactly but maybe it's still bad.

danny hahn

TPS not positioned right as well as car not learning its idle will cause limp mode.

billyboy

I've only got ABS codes at hand, engine related ones are playing hide and seek....can't imagine coils come up though, you'll have to wait for someone else to pipe up.

I can tell you, there should be continuity between all three earths on the engine harness, if you've burnt one up. Not an electrician, but sounds like that's fairly serious if it's letting the smoke out and that earth is fairly heavy gauge too. Only time I've heard of things like that happening is with crashed front cuts where damage isn't spotted or front perimeter harnesses worn through by the tyres (lowered cars!).

tmenzz

I was actually uncertain where this ground was suppose to go. It's attached to the ECU harness right by the UIM.

billyboy

Not sure this will reproduce well, the 3 earths are numbered 3, 4 and 5. The one on the uim goes under the rearmost acorn nut ( next to rotor 2 secondary runner) securing upper to lower manifold. There is also the little short braided one from the adjacent engine lift point to the firewall....not displayed on this page at least.




Thought limp codes were in the electrical manual, they're in the wsm. Coils won't display anything, I've had some go out of spec recently as a coincidence.