Code 42 - Fuel Temp Sensor

[Gio]

My knock sensor just got replaced which involves taking the plenum / inlet menifold etc off.

 

I am now getting code 42 fuel temperature sensor warning. My guess is that this is due to the harness being disturbed / brittle.

 

The car appears to start / drive OK so the question is can I carry on driving with a code 42? Will there be any problem with a defunct fuel temp sensor?

 

I read from the manual that this is to pressurise the fuel when the fuel temperature is "higher than specified". What am I risking if this doesn't happen?

 

A cut to safety boost (no problems) or a very large, loud and expensive bang?

As you'd expect from Captain Stock, I will get it fixed but is it a type A or type B job?

 

(Type A = don't touch that ignition, call the tow truck and get it fixed right now.

Type B = nah, it's OK, it can wait til the next paypacket)

 

TIA - Gio

[Guest aaronjb]

IIRC it only raises fuel pressure during hot starting, and only for a few seconds, so it quickly returns to normal - it does that via the PRVR solenoid and pressure vessel. I wouldn't worry too much about it, however in the interests of having a code 55 ;)

 

It's quite likely that they simply forgot to plug the sensor back in, as it's only a single wire and easily missed. It's located as seen below - this is a view from the back of the engine - firewall end - with the upper inlet off, but it's easily visible with everything together once you know what to look for and where to look for it:

 

 

Have a check to see if it's got a single wire connector hooked to it (same kind as on the dashboard temperature sensor)..

[John Dixon]

Car will run rich off max boost when it's faulty as it pulls the PRVR system in all the time I think.

You could bypass the PRVR until you get it sorted.

Worth checking the continuity between the fuel rail and ground, as this can cause the problem if the earth strap is broken / not replaced.

[Gio]

As a non-guru, would I be right to guess running rich is better than running lean (one damages the wallet and the other makes plink-y plink-y plink-y BANG noises in the cylinder)?

 

I checked (thanks for the pic) and think the sensor is plugged back in - but will fiddle with it when it's not quite so hot! Anyhow, it's something that can go on the "it's not yet fixed or it's a new fault when you broke something" list for the mechanic.

 

Thanks for the info - Gio

[Guest Jester]

While you're on the subject on temp sensors, i got a full diagnostics run on the Zed. Everything came back sweet, with the exception of 2 sensors. Collant temp sensor seems to hang around the 70 degree mark and doesn't really fluctuate. Also, my fuel temp sensor is showing 65,500 degrees and doesn't fluctuate much either.

 

Am i right in guessing that the fuel temp sensor is FUBAR'ed? The car seems to be running well now, and just had the cats removed. Any reason to think she will be damaged if i don't replace the sensors right away? I'm driving down to Trax at the weekend and don't want any surprises during the trip down.

 

Thanks

[pete shrimp]

65,500 degrees?? :rofl: Where do you fill up? In the sun? :D

 

Coolant temp sensor is pretty cheap and a doddle to replace, I got one from http://www.courtesyparts.com last year just cos I was buying some other bits and it was cheap. Although it might just need a good clean with a wire brush :)

[Guest Jester]

Yeah, that Optimax is gooooooood sh*t! :o)

 

Great news about the collant sensor. How expensive is the fuel sensor, about the same? Car hasn't exploded yet so hopefully no damage is being caused.

 

By the way, is there any preference on where to put lamba sensors after a decat op? Tie-wrapped mine underneath.

[Guest andyduff]

Gio, as John says check the grounding strap has been connected. Also try resetting the ecu by taking the battery off for 30 mins just in case its simply a stored code...

[Guest andyduff]

Oh, you can just see the grounding strap attached to the lower left corner of the lower intake on the picture ;)

[Gio]

Thanks Andy - the battery was disconnected for a week. I'll get the strap checked.

[Guest aaronjb]

I was thinking about this last night (as you do).. I'm going to stick my neck out and disagree with John about the operation of the PRVR circuit.. I'm convinced (I'll try and find time to check the manual today) that it only operates at start up - or at most on idle.. Two main reasons really:

 

If it pulled the PRVR circuit in during normal driving, the fuel pressure would no longer be affected by boost pressure - so the fuel maps would be instantly wrong.

 

And secondly, I don't think (at the rate fuel is going through the rails) the fuel really has time to heat up - as I understood it, the pressure was raised to try and prevent vapour locks in the fuel lines when you are hot starting the car.

 

Lastly - quite a lot of people (myself included at one point in time) have disabled and removed the PRVR system for one of two reasons - removing all the extra lengths of piping should result in a slightly better response time at the fuel pressure regulator, or the vacuum canister is ruptured which means you introduce an air leak into the intake tract whenever the PRVR system switches on..

 

Still, best to get it sorted.. failing that, I don't think it'll do any harm.

 

Coolant temp sensor on the other hand (in Jester's case) will have an effect in that if it's constantly reading low, you'll be constantly running rich and getting worse fuel economy.. :)

 

JMHO :)

 

Aaron

[Guest Jester]

Thanks Aaron. Might explain why my mileage isn't as good (though that could be me horsing it around a bit more than usual!). Wonder how much it will cost me to get to and from Trax hehe

[AndyP]

I'd like to pretend I'm clever but I'm just quoting from the manual :-

 

Fuel Temperature Sensor

The fuel temperature sensor, built into the fuel tube, senses fuel temperature. When the fuel temperature is higher than specified, the E.C.C.S. control unit turns the P.R.V.R. control solenoid valve ON and raises fuel pressure.

 

Pressure Regulator Vacuum Relief (P.R.V.R.) Control Solenoid Valve

The solenoid valve responds to the ON/OFF signal from the E.C.U. When it is ON, a vacuum signal from the intake manifold is fed into the pressure regulator. When the control unit sends an ON signal, the coil pulls the plunger downward and cuts the vacuum signal.

 

System description

The fuel "pressure-up" control system briefly increases fuel pressure for improved starting performance of a hot engine. Under noirmal operating conditions, manifold vacuum is applied to the fuel pressure regulator. When starting then engine, however, the ECU allows current to flow through the ON/OFF solenoid valve in the control vacuum line, openning this line to the atmosphere. As a result, atmospheric pressure is applied, restricting the fuel return line so as to increase fuel pressure.