Technical Hot restart mystery

[shaun200765]

Hi, been ages since I've been here, apologies, my bad etc ? need your help please peeps.
My beloved Mk2 1.2 8v petrol has developed a really odd fault.
If I start it and don't stop the car then it's great for the entire journey however long. But should I pull over and turn it off then restart and drive again it becomes awful. No power, quite lumpy, crap mpg and just feels horrible.
Done so far...
New ht leads
New coils
(Plugs ok, irridiums)
Replacement battery/gearbox earth cable
Battery recent, alternator good, car serviced religiously and then some.
A big clue is I think it's to do with the power used to crank it cos if you (carefully) kill the ignition whilst still rolling then back on again it's still perfect. It's only after the use of the starter. All clamps and grounds are tip top though.
Any thoughts would be brilliant, thanks as ever ☺ Shaun.

 

[Ziggy122]

Starters not getting stuck engaged?

Weird fault by sounds

 

[shaun200765]

Your not kidding mate. Starter is spot on, just the way it drives after a hot re-start that's the problem. Forgot to say I've also used an electrical contact cleaner in the ecu sockets then clipped back together again. Desperation really lol.
Shaun.

 

[Ziggy122]

Your not kidding mate. Starter is spot on, just the way it drives after a hot re-start that's the problem. Forgot to say I've also used an electrical contact cleaner in the ecu sockets then clipped back together again. Desperation really lol.
Shaun.

What can change from engine start to engine start

Somethings heat soaking and upon restart messing up

I dowt its the ecu.....
As its fine then not - the fine tells me its fine.... and its reacting to a change from cranking whilst hot....

Whats mileage?
Oil or water consumption?
No brakes sticking on once hot?

If left to cool and its great again?

Ziggy

 

[shaun200765]

Thanks Ziggy, you helped me years ago on here and it's good to know your still doing the same for everyone ☺
Zero oil and water consumption, fresh oil change many times a year. 126k miles but sweet as a nut usually.
All brakes new, no binding at all. The car is really looked after and a joy to drive usually.

 

[shaun200765]

Sorry, yes, once cool it's fine until cranked mid journey (stop for milk etc) but will run all day if not turned off. Shaun.

 

[Ziggy122]

2 tests
Compression @ 126k it may be a little low...... but cant assume

Id like to know what oil pressure like

I wonder if - its fine from cold and getting a good oil flow

U stop while its hot - it drains back and is causing a low oil feed - messing up compression??

I dont understand otherwise whats going on....

Ziggy

 

[shaun200765]

Update ☺
Slept on it so to speak and I wondered about the solenoid valve that looks after the evaporation of fuel from the fuel tank/charcoal canister inside the wing. Does this valve only open after hot restart?
What would be the effect on the motor if it was pulling in air due to some issue with the canister etc?
So, armed with this idea I pulled out the nylon pipe from the valve and then plugged it (temporarily) with an 8mm bolt. Jumped in and went for quick road test. Drive great so once warm I pulled over, switched off, waited 5 mins then started up again. Drove perfectly so I repeated this several more times. All good. I don't know if it's a coincidence yet but so far it's good. I'll run like this for a month or so and then report back.
Fingers crossed ☺ Thanks Ziggy.

 

[Ziggy122]

Update ☺
Slept on it so to speak and I wondered about the solenoid valve that looks after the evaporation of fuel from the fuel tank/charcoal canister inside the wing. Does this valve only open after hot restart?
What would be the effect on the motor if it was pulling in air due to some issue with the canister etc?
So, armed with this idea I pulled out the nylon pipe from the valve and then plugged it (temporarily) with an 8mm bolt. Jumped in and went for quick road test. Drive great so once warm I pulled over, switched off, waited 5 mins then started up again. Drove perfectly so I repeated this several more times. All good. I don't know if it's a coincidence yet but so far it's good. I'll run like this for a month or so and then report back.
Fingers crossed ☺ Thanks Ziggy.

Coulda just unplugged the evap electrical connector

Upon startup if the valves sticking itd be pulling fumes and than a vacuum which wont subside.... maybe the canisters disintergrates? But tbh they never fail these days....

May need a smoke test.....

Ziggy

 

[shaun200765]

Thanks again for your thoughts Ziggy, I'll report back asap ☺

 

[Brendan W]

Another thing to consider.
If the temperature sensor is giving incorrect information to the ecu as in telling it's cold when it's actually hot, the ecu will enrich the mixture to cold start levels and the mpg will be bad.

 

[Ziggy122]

Itd be abit weird for it to run fine
If u stalled - and suddenly the sensor aint reading right....

Dont get me wrong anythings possible....

Just sounds odd

Ziggy

 

[shaun200765]

You both bring very reasoned ideas to the table which is exactly what I needed otherwise I'd never have placed this thread ☺
I did consider the temp sender possibility too but I honestly couldn't unclip the sensor plug (to rule it out so the car would run "safe" so to speak, it was red hot out on yet another road test miles from anywhere and everything I touched was boiling ?
It's been 100% again today so I'll leave well alone for now. In a few weeks I'll put it back as it should be and continue to report back. Thanks again for your thoughts and ideas. Shaun.

 

[s and b]

probably a crank sensor fault

 

[Scudmonkey]

probably a crank sensor fault

Could well be, although last time i had a crank sensor issue it caused the exact opposite symptoms, wouldn't start from cold but would start perfectly when warm....

 

[shaun200765]

Final update and I know it sounds unlikely but I've left it a while now just to be sure before coming back on here. I suspect it could be made a sticky as I bet I'm not the only one to do this.
My clever brother suggested I swap the eBay led tail light bulbs for standard I'd fitted just in case it was interfering with part of the car's canbus and I suspect he was right all along. I had noticed strange flickering of the rear lights after I'd locked/un-locked the car on an evening but it doesn't do it any more now with stock bulbs.
So, fingers crossed, it's all done now and been brilliant ever since I changed tail bulbs for stock. Thanks again peeps.

 

[shaun200765]

probably a crank sensor fault

It was