Loss of power when hot

[azzfox]

I have a strange issue that I cant put my finger on. When the engines cold its really snappy and responsive, but as it warms up it becomes quite gutless. I thought it was engine bay heat getting sucked up the intake, but after installing a CAI it still does it. (but makes more power when cold )

I did a test one night and drove to this lengthy stretch of road while going easy to keep it cool, and once there dropped down a gear and gave the throttle a squeeze and it really snapped back and took off. Then after driving for about 30mins on the way back I did this again but this time it felt "soft" and unresponsive.

Any ideas? First thought fuel pump because when checking for current draw it sounded weak. But then tested with a piece of wire and sounded much better so my multimeter leads must be shot. I now have a new pump on the way anyway lol. Engine temp sits between 1/8 and 1/4 under normal driving conditions. Car has:

CAI
SV3800 tune
new 8mm leads
new plugs
new 91c thermostat and radiator cap
new radiator
new coolant
new oxygen sensor
new fuel filter
new injector seals and filters
all new intake gaskets

Could a sensor of some sort be throwing the ECU off?

[Dum*P*ster]

Prolly a stupid question.. but have you reset your ECU? duno if it will help tho lol

[azzfox]

The battery has been disconnected many many times in the past few months, but I guess once more cant hurt lol

[delcowizzid]

coolant sensor for the ecu is cheap enough to warrent replacing

[delcowizzid]

and if its the series one SV3800 tune it wont be too happy on the series 2 engine

[azzfox]

Reset ECU and cant notice a difference. Coolant temp sensor will be next. Tune is ASBY which Im pretty sure is the newer one.

[levymetal]

my motor is tough as nails when it's cold, absolutely piss-weak when it's hot. mine's a 5lt though. doesn't the computer retard the timing when it's hot? or just gives it more when it's cold. i thought that was my problem anyway.

[stocky]

it pumps more fuel in when its cold. not sure about spark. just remember with the 5 litres the manifolds get real hot real quick

[azzfox]

Maybe you have similar problems lol. Just doesnt seem right. I know during the warm up cycle the ECU runs the A/F a tad rich, which could indicate running lean when hot. I still suspect the fuel pump. Sometimes with the relay shorted out you can hear the fuel passing through the regulator quite loudly, but other times its really quiet but the pump sounds the same. Still going to replace the coolant temp sensor and maybe MAT sensor while Im at it if they arent worth much. Then if still no good then fuel pump.

And if still no good then a decent tune

[greenfoam]

It'll be something with your fuel system cause it to run leaner than it should you can take you pick as to what

[levymetal]

it pumps more fuel in when its cold. not sure about spark. just remember with the 5 litres the manifolds get real hot real quick

yeah that sounds more like it for me anyway

[azzfox]

Replaced coolant temp sensor and it seems to be better, also runs a bit cooler. But, after returning home I checked the fuel pump once again but this time it sounded fine?

Damn cars playing funny buggers with me! My new pump arrived today and now cant decide whether to change it or not lol.

[TIGEN3]

i had a similar problem with a vl calais once turned out it was a faulty coil, check condition of coil packs if you havent already done so, its not the answer but maybe part of the prob.

[dynoryder]

ive herad ppl talk of takeing the temp sencer off the intake so the engine thinks it's cold all the time maby that has something to do with it

srry in cold climates all the time

[azzfox]

Well new pump went in yesterday and I think the old pump was to blame. New pump keeps a constant sound unlike the old one. It also pulls about 7A where as the old one would pull around 6A. From what I can tell the power comes on alot smoother and has much more go when hot. It actually feels like it has more power when hot lol. But that was after one test drive. Will be keeping an eye on things in days to come.

[vpete]

So how has it been performing azzfox??? Problem solved or what???

Cheers................................Pete!

[azzfox]

Yup Im convinced problem solved. The torque is back and no longer have to shift down a gear when hills approach (though tailshaft doesnt like this at low rpm lol), and just really snappy again. Almost temped to now install a fuel pressure gauge to keep an eye on things in the future

[hummhome]

Had problem with our vn calais doing same thing. Fuel pump was to blame. Fuel boils in fuel rail from engine heat when poor fuel pressure. Use genuine pump as have problems with other brands doing same problem. Cheers

[customx89]

Was just wandering azzfox did you have problems with the engine being hard to start when the fuel pump was buggered?

[azzfox]

Hmm nah wasnt hard to start. It wasnt completely buggered, just a bit old and tired I think. Idle doesnt need much fuel pressure plus it still primed on ignition (sounded weak though).

Still so far so good. But occasionally it still feels as if its lacking some kick and its a bit more 'punchy' when cold. The temp gauge sits bit under half under normal driving conditions (hot or cold weather). Our VP sits much lower than this so that could be an indication of something. Has fresh coolant, new radiator and cap and new 91c thermostat. Hmmm...