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Weird M35 Throttle Issues

bigkevracer
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bigkevracer Grand Master

bigkevracer

Posted
Posted

I've now got to a point where I think all these bullshit throttle issue deserve their own thread before I set fire to my M35 and watch it burn to the ground.

tl;dr - seems like some kind of electronic thing is causing some kind of vacuum problem.

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Issues started not long after I put the F-con in. As soon as the F-con went in, throttle response wasn't as good.

Had the tune adjusted and fault codes cleared, and it appeared it could have been TPS.

Drove for a while, fault light went on again, left bank lean and throttle fault. Drove fine.

Then it started to randomly disable the throttle. I'd be driving along, and sometimes on throttle, sometimes off, it would disable the throttle. I could coast in to find somewhere nice to park, but no more power.

At the start, I could turn the car off and back on again, and the fault light would stay on but the throttle would be fine again.

Then it got worse, to the point where I'd turn the car off, back on, put my foot flat on the floor, and zero throttle.

I tried disconnecting the throttle harness for the cruise control. Made no difference.

I tried driving with cruise connected, but off, made no difference.

Then I disconnected the F-con. Instantly the fault lights cleared, throttle was back, and I could drive home. Great.

So now I know the fault is in the F-con. So what is it?

I thought I'd worked out it was related to the Conversion Table settings, where it was set to still use the Nissan MAP and IAT sensors. I reflashed it using the HKS MAP and IAT sensors (which are installed and connected) and the throttle worked but the car ran like crap (predictably).

Then on the weekend I put the tuners map back in with their Conversion Table settings (Nissan OEM sensors), and for some reason the throttle worked again.

Great.

I'll go for a drive.

Got 600m before the throttle gave out and lit up with a fault code.

Turned the car off, back on, code cleared, drove home. The only problem was a seeming resistance from the throttle pedal.

Despite how stupid this will sound in a car with an electronic throttle, it was almost as if there was some kind of air resistance in the pedal. Not only that, but when I pressed on the pedal when the resistance would clear I would hear an audible sound that was kind of like an aerosol can. Doesn't sound like the blow off valve, more like an aerosol.

I'm not sure if this is some kind of weird vacuum issue, but if the issue isn't present in several hundred km of driving on stock ECU, but immediate in 500m or so of driving on F-con, my theory is something electronic, or some kind of electronic setting, causing an issue. But I have no idea what it could be.

The current tune was fine on the dyno, uses the stock Nissan OEM sensors, still uses the AFM, and has the stock HKS throttle curve. It just hasn't worked since the car left the dyno.

I'm stumped. Has anyone experienced anything like this, or got any idea what I or the tuners should at least be looking for before I set fire to the stupid thing?

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https://www.sau.com.au/forums/topic/423166-weird-m35-throttle-issues/
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scotty nm35 Grand Master

scotty nm35

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Posted

What was the code?

There is a good chance the fcon is trying to read the throttle position and is pulling the voltage down enough to throw the error code. Mine is probably doing the same thing, but mine works fine once I disconnect the cruise. Perhaps changing the pedal sensor would help us both? Or perhaps we will need to isolate the tps signal before the fcon. (or not use it at all.)

Can you get hold of another Fcon unit to try also?

bigkevracer Grand Master

bigkevracer

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  • Author
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From memory Scotty the code was P0120.

I've been getting it intermittently this week. Sadly there is no one specific condition that causes it. Can be foot flat, can be idling at an intersection, can be on minimal throttle driving down the road.

The other night I discovered that when it goes, it still has power, and was able to drive into a carpark and up a hill.

I could try a new pedal sensor, but I dismissed that as the cause because it doesn't do it without the F-con connected.

I think there are 4 F-cons about, I might try and steal one and try that too.

I was thinking first step should be retune using MAP sensor, which seems to be working for everyone else.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

I'm not even sure the fcon needs the Throttle pedal signal, other than to adjust it. It is actually wanting a TPS signal from the throttle body, which is just as hard to tap off.

I know the Emanage could be tuned without a TPS input, not sure about the Fcon.

Mine has been faultless since I disconnected the cruise.

Commsman Veteran

Commsman

Posted
Posted

Since you don't appear to need it anymore, can I buy the cruise control back off you Scotty? Either that or I can put you in touch with some willing buyers, lol.

bigkevracer Grand Master

bigkevracer

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  • Author
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For me though, I still get the same issue with the cruise disconnected. Well, the pedal harness anyway.

I guess you don't have a spare sensor in one of the wrecks then? Worth trying or swapping over for diagnosis, but I can't help but think if thats all it was then it would fault on the stock ECU.

Commsman Veteran

Commsman

Posted
Posted (edited)

Damn I love having it though. I just wish it would work with the Fcon. Should I give up on it or perhaps blow $250 for a new throttle pedal sensor first?

Don't you have a spare TPS in your wreck or have you tried that with same result? (Edit: D'oh, good thinking Ryan, lol)

I'd be hesitant to spend that much with no guarantee too...

Edited by Commsman
scotty nm35 Grand Master

scotty nm35

Posted
Posted

The pedal sensor was removed and fitted to another car months ago, I wish I had kept it now. Nissan wanted $400 for what is essentially just a trimpot, you can only buy it with the pedal as an assembly.

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