Hot Start Problem, where next ?

[J4CKO]

So, have mentioned this before but it is still happening, car starts and runs fine from cold but once warm it starts but wont rev, the rev counter is all over the place, I turn it off and on again and that seems to help, it clears and runs as normal, well as normal as 944s get !

I have changed

Fuel Pressure Regulator - New
DME Relay - New
Air Flow thingy - Second hand
Lambda Probe - New
Battery - New a year ago

So, what should I try next,

My list of possibles, in no particular order

Temp Sensor - Removed and tested it, seemed ok in a pan of water.
Speed Sensor - not sure how this could be related
Crank Sensor - Ok when cold so dont expect it is this
Injectors - Possible but if they are leaking wouldnt it be worse the longer it is left ?
Earths - Again, ok when warm
Fuel damper - Removed vac line, slight whiff of fuel, do these cause this issue
Fuel pump - Ok when cold
Dizzy cap, just went to change it for the spare but it didnt have the pring loaded bit on the top
Rotor Arm ?
Plug Leads ?
Plugs (Removed, checked gaps, seem ok, might change them anyway)
Ignotion Switch - I know they can be a pain in the arse
Coil - Possible I suppose, they do go iffy when hot
DME itself
Fuel filter, cant get it off as stuck to pipe from tank.
Ignition control thing in inner wing on right.


Dont want to put it into a specialist, apart form getting expensive I want to learn from it, but it is so embarassing when it spazzes out in a car park !

 

[Mike_Pollock]

Fuel damper sounds possible, shouldn't smell of petrol I think.

Fuel leaking back to inlet plumbing would help cold starting, but would have thought it would help hot too!

Coil - yes they do break down when hot.

Temp sensor - you are looking at the right one? (Sorry, just checking!)

Fuel Pump - Dizzy - rotor arm - Plugs -Ignition switch - DME - Fuel filter - Injectors - Speed sensor - Crank sensor - Earths - seem unlikley

Would check FPR just in case

 

[J4CKO]

FPR is brand new, the temp sensor is the one at the front with the blue plug which I beleive is the DME one, rather than the 2 pin gauge related one.

Anyone got a known good Coil they want to sell ?

 

[944 man]

My first thought is that its the thingy which maintains the fuel pressure after the engine has been turned off. Without the epressure heatsoak boils the fuel, making hot starting very difficult.

 

[J4CKO]

Is that the fuel pump check valve ?

 

[944 man]

My advice is to start a thread on TIPEC for Jon Mitchells attention. List the complete problem and eveything that you have done to rectify it so far. As an aside Im not convinced that a used cheap AFM off t'eBay certainly rules out your own part (because it isnt known good - although I dont think that it would be an AFM problem anyway).

 

[J4CKO]

No, I dont think its AFM either, it works, seems bit better than the one on it so I am happy, for #12 I think its ruled it out, I will post on Tipec and see what happens.

 

[J4CKO]

Got annoyed with it so cut a 3 inch square hole out of the bottom of the nsf wing, sod it, going to do the bodywork

 

[924nutter]

J4CKO, you may have hit the naill on the head with the coil. The reason I suggest that is because of the dancing rev counter needle. The rev counter possibly derives its signal from one of the coli terminals, terminal one I think. This is 12v feed, as I believe t15 is switched earth. If the coil is breaking down when hot, i.e. going open circuit then the rev counter doesnt "see" the voltage drop across terminal 1 and starts to drop back to zero, then it gets a series of signals and tries to jump to say 950 rpm, then back to zero, a couple of random pulses can give the needle a double kick and make it go round the scale. Just a suggestion, and very easy to check, if for no othereason than to illiminate that.

 

[zcacogp]

ORIGINAL: 924nutter

J4CKO, you may have hit the naill on the head with the coil. The reason I suggest that is because of the dancing rev counter needle. The rev counter possibly derives its signal from one of the coli terminals, terminal one I think. This is 12v feed, as I believe t15 is switched earth. If the coil is breaking down when hot, i.e. going open circuit then the rev counter doesnt "see" the voltage drop across terminal 1 and starts to drop back to zero, then it gets a series of signals and tries to jump to say 950 rpm, then back to zero, a couple of random pulses can give the needle a double kick and make it go round the scale. Just a suggestion, and very easy to check, if for no othereason than to illiminate that.

This is the sort of thinking you need to be doing; some proper diagnostics rather than guessing.

Start simple. Do you have a spark when trying to start from hot? I have one of these:

... and it's just about the more useful diagnostic tool possible. Costs pennies too. If you have a good spark then the problem is fuel, and work on from there.


Oli.

 

[eddieedmo]

hall sensor ?

Nick

 

[944Fripp]

I had a problem about 3 months ago that I was convinced was the fuel damper.

Turned out I had a leak on a vacuum line at the bottom of the engine. Cheap and quick fix!

 

[J4CKO]

ORIGINAL: zcacogp

ORIGINAL: 924nutter

J4CKO, you may have hit the naill on the head with the coil. The reason I suggest that is because of the dancing rev counter needle. The rev counter possibly derives its signal from one of the coli terminals, terminal one I think. This is 12v feed, as I believe t15 is switched earth. If the coil is breaking down when hot, i.e. going open circuit then the rev counter doesnt "see" the voltage drop across terminal 1 and starts to drop back to zero, then it gets a series of signals and tries to jump to say 950 rpm, then back to zero, a couple of random pulses can give the needle a double kick and make it go round the scale. Just a suggestion, and very easy to check, if for no othereason than to illiminate that.

This is the sort of thinking you need to be doing; some proper diagnostics rather than guessing.

Start simple. Do you have a spark when trying to start from hot? I have one of these:

Oil, it run, but like a bag of poo, the rev counter is just showing what the engine is doing, i.e. mentalness.

... and it's just about the more useful diagnostic tool possible. Costs pennies too. If you have a good spark then the problem is fuel, and work on from there.


Oli.