Poor running once getting up to temp

[Rockettvr]

Not posted on here for some time (since I sold up a couple of years back) but I still look in from time to time
Anyway my son still has a 390 recently back kn the road after being laid up since last year
Before being garaged it ran well but since it’s resurrection it’s running bad
Starts well and idles fine when cold but as soon as it starts to warm it starts to misfire/ run v lumpy and cuts out on occasion there’s also a strong smell of fuel - although if you bury the throttle it’ll take off like a scalded cat
Suspected and Tested the CTS which read 300ohms (warm) which should be fine but I’ve ordered a new one anyway
Any other thoughts ???

[spitfire4v8]

My thought is why are you changing something you've tested as being OK?. You must have money to burn.

[Rockettvr]

Thanks for the reply
Positive input is always welcome
No one has money to burn but last Fridays lottery win has certainly helped

1 symptoms point to cts being most likely culprit
2 from bitter experience I know that just that something tests up ok at that point in time , doesn’t necessarily mean it operates correctly throughout its entire operational range
3 A decent CTS costs less than a gallon of premium unleaded - for the cost it makes sense to change it just to eliminate it from the equation
I’ll dig out the multi tester tomorrow and go through and make sure that I’m getting the right resistances and voltages at the right places
In the meantime if anyone has anything they think I should be looking at , that would be very welcome

Edited by Rockettvr on Saturday 14th May 21:13

[105.4]

I don’t mean to be the bearer of bad news, but this is sounding awfully similar to the problems my Chim had when it dropped a liner.

Have you carried out a sniff test?

[Rockettvr]

Hi
Thanks for the reply
Only had a quick look at it this afternoon so not got far into it yet
No sign of oil in water or water in oil but realise that’s not defintive of not having head gasket issues
Checked CTS and coil Various connections ht leads etc
Will spend an hour or two tomorrow going through checking everything with the multi meter
What are the symptoms and How do you diagnose a slipped liner ???

[105.4]

Rockettvr said:

Hi
Thanks for the reply

What are the symptoms and How do you diagnose a slipped liner ???

No emulsification of oil on dipstick or oil filler cap. Slight loss of coolant, but nothing major, more like what you’d get with a slightly cracked expansion tank.

Mine was running fine when cold to cool. It was only when it got up to running temp that it would start missing and running like poo.

A sniff test, (checking for hydrocarbons), returned positive results, (as in bad news).

[KKson]

Just worth checking ignition module, HT leads and coil. All can break down when hot giving you the same symptoms. Top tip is run the engine hot in the dark and inspect the HT system. Any breakdown will be visible.

[wild rover]

Had similar symptoms a few years back, exhaustive test showed nothing. Finally took the afm off, opened it up, cleaned the internals with a spray cleaner and swiped the points with light abrasive paper. Running like a sweetie since. Best of luck.

[wild rover]

Had similar symptoms a few years back, exhaustive test showed nothing. Finally took the afm off, opened it up, cleaned the internals with a spray cleaner and swiped the points with light abrasive paper. Running like a sweetie since. Best of luck.

[blaze_away]

Bad running when hot is sometimes HT breakdown once heated. It was on my Chim 4.6. New genuine bosch coil fixed my problem.

I diagnosed this as follows. Fitted spark testers (they fit between plug and ht lead and flash when spark arrives)
Waited till dark started engine waited for warm up and watched the sparks. They began to look weak and occasionally missed all together. Stopped engine quickly swapped in a cold old coil and problem didappeared. Bought new coil and that fixed it.

[BlueWedgy]

Hi Ron,

When I purchased the TVR from you. I had to reflow the power transistors in the ECU, warm running was not great on tick over, this made things a whole bunch better.
And the earths were loose Passenger head, I assume possible from your previous head work.

Regards

Ray

[SLB]

KKson said:

Just worth checking ignition module

I've had a load of issues with the ignition amp on the side of the dizzy which gave the same symptoms you mention plus reduced revs, but only when warmed-up. Don' bother with anything other than a Lucas replacement as an alternative lasted a year before that gave the same symptoms again. I've gone with the Lucas remote set-up and all has been well for several years now.

[Rockettvr]

Morning gents
Thanks for the replies
Unfortunately a misplaced multi-tester and persistent rain yesterday means I haven’t had a chance to get any diagnostics done as yet


I’m leaning towards it being on the fuelling side as the issue is only on cruising when warm - if you then give it a boot it’ll take off like a scalded cat
I would have thought that ignition issues would be present throughout but I may be mistaken - testing will tell

Hi Ray !!
Glad to hear that the car is running well for you now
I must admit the idle was never great on it but I just put it down to age/wear and tear
My apologies on the loose earth - I’m usually fastidious about such things but guess I must of missed it although I’m surprised it wasn’t causing issues sooner as it’s now 6-7 years since the heads were off
Hope it continues to run well for you
Ron

Edited by Rockettvr on Monday 16th May 07:52

[105.4]

Rockettvr said:

Morning gents
Thanks for the replies
Unfortunately a misplaced multi-tester and persistent rain yesterday means I haven’t had a chance to get any diagnostics done as yet


I’m leaning towards it being on the fuelling side as the issue is only on cruising when warm - if you then give it a boot it’ll take off like a scalded cat
I would have thought that ignition issues would be present throughout but I may be mistaken - testing will tell

Edited by Rockettvr on Monday 16th May 07:52

Despite yesterdays rain, the good news is that now certainly doesn’t sound like a slipped liner.

[Rockettvr]

105.4 said:

Despite yesterdays rain, the good news is that now certainly doesn’t sound like a slipped liner.

[NDA]

Is the fuel pipe getting hot leading to starvation/evaporation?

[Rockettvr]

105.4 said:

Despite yesterdays rain, the good news is that now certainly doesn’t sound like a slipped liner.

[Rockettvr]

Quick update
Finally found my tester - tested everything (cold) all as should be
Took car out for a run - ran well for quite some time ran up to temp and seemed ok for a while then symptoms returned- hesitant /missing etc
Started back home to continue diagnostics and on the way back the fault suddenly cleared and car ran ok again
So drove past my house and a couple of minutes later symptoms returned but then cleared again before I could return home

I guess the only course of action is to take a tool kit and tester out with me and do the diagnosis on the side of the road

So it’s an intermittent fault causing missing/hesitation but clears when you boot it


Coil doesn’t seem hot
All connections seem good

Coil on its way out or failing ignition amplifier???

Frustrating!!!

Edited by Rockettvr on Saturday 21st May 18:18

[blaze_away]

These will help no end, get 8 and put one on each cylinder and look at them when it goes bad vs when its good. I could clearly see mine misfiring when my coil went bad.

https://www.ebay.co.uk/itm/131807893687?mkevt=1&am...

If after testing you want to get a coil go for something you can be sure is genuine, eg this one
https://www.eurocarparts.com/p/bosch-ignition-coil...

With discount applied its about £70

Amp is more difficult to source a good one for which I have ni advice sorry.

Edited by blaze_away on Saturday 21st May 20:21

[Rockettvr]

Solved
Traced to poor/inconsistent spark
Replaced coil amp and leads (tbh I think it was the leads )and now ok
Although another issue has now arisen for which I’ll make another post
Thanks for all the advice