Intermittent misfiring when hot

[gmg31]

I can take my car out for a great drive for hours but once I switch her off if I try to start her again after 30 mins or so she runs terribly. Back firing, shaking very low power and I struggle to get her home. In my view only on 2 cylinders. If I leave her for a couple of hours to cool down she’s fine.

The first time it happened I thought coil pack but surely they either work or they don’t. I’ve read the recent stuff about injectors but again surely that can’t be intermittent.

I can easily re produce this fault so it’s not really intermittent.

Any ideas please.

Thanks.

[Rambo]

Any similarities here....viewtopic.php?f=37&t=27521

Or here.......viewtopic.php?f=38&t=27504

Or here.....viewtopic.php?f=33&t=26644

If you want to inspect or change either or both coil packs check here....http://wikilec.com/view/Ignition_Coil

And don't forget to do the paperclip test. Only a 5 minute job. You may well have some error codes stored on the ECU

PS sounds like you've been having problems since 2015 viewtopic.php?f=33&t=24677&p=310849#p310849

[gmg31]

Hi thanks for your post.

I had read all of those posts prior to my post. The big difference is that my fault is very predictable and easily re produced. If I took my car out today it would run perfectly until I stopped. Then she runs terribly. If I leave her for several hours to cool down completely then she goes back to running perfectly.

I spoke to Steve at SJ today and he couldn't figure it out either. The engine light doesn't come on so presumably there will be no fault code.

So my only option as far as I can see is to change the coil pack and see what happens.

The issue from 2015 was easily fixed with a bottle of redex and better fuel.

Thanks

[GeoffSmith]

SE or S2?

[gmg31]

1992 SE Turbo

[gmg31]

To be honest this has been bugging me for a while and its starting to impact on my summer fun! As I've not spent any money on this car for a while I've decided to go for some electrical upgrades. new coils, new plugs and plug leads and then lets see what happens.

[Rambo]

If things don't get better can I suggest Colin at Revline, Whitley Bay, about an hour up the road from you. Colin has an M100 and is very conversant with the marque

[lotusflasherman]

if no error code I'd be looking at the Temp Coolant Sensor. There is one that drives the Temperature Gauge and another that tells the ECU what fuel to deliver, it's that one to check. Because of the range of resistance it returns for various temperatures it won't throw up an error code but engine can run like a dog when the wrong values are returned. Could be you have corrosion on the spade terminal so readings are higher than they should be... try cleaning it up and check values for hot & cold with a multimeter, they are in the Manual, but not in my head.

The one that drives the Temp Gauge is on the thermostat housing and easy to see, the one you want is below that and not so easy to see - Sod's Law !

(Sometimes just pulling the connecter off and on a couple of times is enough to get a good contact again.)

[Brit-Car-Nut]

Look here for the chart and a picture of what is what...

Coolant Sensor

I fixed it...

[lotusflasherman]

Look here for the chart and a picture of what is what...

Tried your link John and it didn't work for me...

link has gone.. you must be working on it..

Cheers, copied and pasted into New browser but had to add a closing bracket ) after CTS.

[Brit-Car-Nut]

Now Fixed...

[lotusflasherman]

Thanks to John (BCN) can now confirm values should be:

Temp(°C) / Resistance(ohms)
100 / 185
70 / 450
38 / 1800
20 / 3400
4 / 7500
-7 / 13500
-18 / 25000
-40 / 100700
So shows if you have a high resistance contact it will affect the fuelling at high temperature (hot engine), but not so much on a warm engine..

[HJ2]

If the coolant temp sensor turns out to behave nicely: Perhaps one of your injectors does not close completely. After you shut it down, it leaks some fuel in one cilinder and then when you restart it runs like garbage.

The question is: Does the missfire also occurs when you immidiately restart the car after you shut it down? or only after 5...30 minutes?

Injection cleaner might help, but i would swap the injectors for fresh ones if this actually turns out to be the root cause.

[gmg31]

Thank you all for your advice. I shall work my way through these suggestions and fit some new parts and let you know how I get on

[RichardK]

I have had this problem too on my yellow car. I changed coil packs, leads...no change. Was just about to change the injectors, but will do the less fiddly CTS first. Thank you!

Richard

[gmg31]

I changed the CTS today and it’s exactly the same. Running perfectly until I stop for 10 mins and then running really really badly. Leave her to go cold and she’s fine. When I Got home I hooked up a timing light to test the leads and plugs and each one appeared to be fine. So I can only now conclude injectors.

[Simon_P]

decided to go for some electrical upgrades. new coils, new plugs and plug leads and then lets see what happens.

have you done this? And was there any effect?

. So I can only now conclude injectors.

what are you concluding is wrong with them? When was the fuel filter last changed and have you checked the fuel pressure regulator?

Have you done an elanscan?

Is your separate question about the MAT sensor for this issue or a different one?

[gmg31]

decided to go for some electrical upgrades. new coils, new plugs and plug leads and then lets see what happens.

have you done this? And was there any effect?

. So I can only now conclude injectors.

what are you concluding is wrong with them? When was the fuel filter last changed and have you checked the fuel pressure regulator?

Have you done an elanscan?

Is your separate question about the MAT sensor for this issue or a different one?

Following the advice above I opted to change the CTS but didn't change the coil packs. After taking the car and resting for 10 minutes the fault was immediately repeated. I would say this is not a little bit of misfiring btw it is really really bad. loud backfiring shaking and very low power.

When I got home I kept her running and connected up my timing light so I could test each plug lead & all 4 were sparking so I concluded that the coil pack and leads were all Ok. perhaps this is a wrong conclusion.

I don't have a lap top so Elan scan is not an easy option right now.

Wouldn't a hot coil problem be inconsistent?

I spoke to Colin at Revline who suggested the MAT sensor. He wondered if it was failing and telling the car that its a freezing cold day and she's over fueling. I am no further forward.