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Author: Subject: G27 misfire
AlexXtreme

posted on 8/7/16 at 07:50 AM Reply With Quote
G27 misfire

Hi All,

I have a Ginetta G27 that has developed a misfire (I am assuming / hoping it is electrical at the moment).

It has a silver top with twin 40 webbers... The tickover has dropped with a petrol rich smell coming from the exhaust and it is not pulling as well as it was. The car is not running as hot as it used to as well.
The spark plugs are new. I have replaced the misab plates as the were old and leaking a few months ago. The car passed the MOT a month ago and this has only developed since and I have only drive around 80 miles since due to the crap weather we have had.
One of my first thoughts was to look at the leads (after checking the spark plugs to see which cylinder was the culprit). The leads lead through the engine bulkhead and I cant easily see where they go... how easy is it to access this area to change the plug leads?

Alex

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benchmark51

posted on 8/7/16 at 08:39 AM Reply With Quote
I would do a compression test first then check the ignition over. Then check the carbs.
I assume they were balanced after misabs were changed, but sometimes they need more than one tune.

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AlexXtreme

posted on 8/7/16 at 08:56 AM Reply With Quote
Will check the compression as you suggest... but can not see the ignition as it runs through the b'head
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AlexXtreme

posted on 8/7/16 at 11:43 AM Reply With Quote
Further to this I replaced the misabs after the tune as the leaks were only very minor and appeared when the engine was very hot.

Agreed it could be compression problems however the failure would need to be severe as it seems to be not firing at all on one cylinder from the smell of petrol in the exhaust and this led me to ting it is ignition.

Alex

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benchmark51

posted on 8/7/16 at 03:16 PM Reply With Quote
I went to a friends to balance the webers on his Tiger this week and it was a bit rough. So tinkered with it a bit but decided to check the compressions. All plugs out, started to test number 1 and had a solid jet of water shoot out number 4! Whipped the head off and the gasket was broke between waterway and combustion chamber. Always pays to know the compressions are right first, can save a lot of time.
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AlexXtreme

posted on 8/7/16 at 03:26 PM Reply With Quote
good point and will test this weekend
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AlexXtreme

posted on 16/7/16 at 03:42 PM Reply With Quote
Tested the compression and they are all the same within 5psi anyway.

Also seem to get a good spark from all the leads - or seems like it as I can hear sparks coming from the leads to the plugs on all of them.

The culprit is the most forward piston. I pulled the lead of this spark plug and there is no difference to the misfire.

One thing I did notice is that there is considerable water at lower temps... so possibly the thermostat could need replacing however I do not think it

Any suggestions??

Alex

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benchmark51

posted on 16/7/16 at 04:06 PM Reply With Quote
You took the plugs out to do the compression test, did you notice any difference in colour between the plugs? If you feel the problem is number 1 cylinder, swap that plug for number 4 and see if the problem is still number 1. What were the compression readings?
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AlexXtreme

posted on 16/7/16 at 04:58 PM Reply With Quote
The compression readings were all around 90psi +/- 5 however this was not a "real" number as I do not have a valve on the extension for the compression tester.

No 1 plug was very black... good idea on swapping the plug. They are only a few months ol and the were changed when the car was tunned at on a RR but I guess this plug could be faulty. I was told the engine was in good nick by the guy tuning it and I was seeing 145hp at the wheels (170ish at the engine).

Alex

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benchmark51

posted on 16/7/16 at 05:45 PM Reply With Quote
So if you swap number 1 plug with number 4, is there a difference? does number 4 become the 'weak' cylinder. The compression pressures, I would expect to be significantly higher than 90. Both my ST170 and Pinto are over 150.
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britishtrident

posted on 16/7/16 at 06:47 PM Reply With Quote
First step with a single cylinder misifre on twin DCOE's is always clean the jets for the affected cylinder also check the cold start mechanism (choke) is working and returning fully ***** even if it is not connected to a cable *****.

Next step is to check the plug leads, plug and coil properly. Ford use extremely wide spark plug gas the result is spark voltages of up to 35kv at full throttle in contrast with the 15kv which was typical back in the day. 35kv puts immense electrical stress on the insulation.
The rule of thumb is in normal air at atmospheric pressure 1mm = 1kv so you need to actually see the spark jump 30+mm at the end of the plug lead, even if the lead and coil pass this test you should do a continuity and ressistance test on the lead with a multimeter -- see official NGK method here https://www.ngk.de/en/technology-in-detail/ignition-cables/diagnosis/testing-of-ignition-cables/


The other spark lead tests are shown on this page http://www.wikihow.com/Test-Spark-Plug-Wires



[Edited on 16/7/16 by britishtrident]





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AlexXtreme

posted on 16/7/16 at 10:29 PM Reply With Quote
Thanks for the suggestion

Will check the choke (it has one fitted) though I do not use it at all.
Any guides on how to clean out the jets? If they were blocked would it run lean rather than what feels like flooding.... I am getting pops from the air intakes and the exhaust smells of petrol.

Just on feel I would say that the around 30mm ish sparks from the leads. It is really hard to check the leads as they run through the engine bulkhead and at the moment I have no idea on how I replace them - I can only just reach the coil when lying in the foot well and I suspect i will need to discontent the dash to get proper access.

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AlexXtreme

posted on 19/7/16 at 09:40 PM Reply With Quote
Right found the solution after the following:

Changed the fuel lines (were perished and leaking fuel) - I know that it might not make any difference but they were perished and leaking like a sieve!

Changed the thermostat - was sticking open and I am sure it was not helping the eng get to temp. Drilled a hole in the new one to help it get to temp with my fuel rail.

Cleaned carbs out with IPA and sucked and deposits out

swapped plugs around and noticed that I was getting a popping sound that followed the movement of the plugs.

One of the plugs was faulty even though it was one a couple of months old and with 300 miles on it :=(

The original were fitted by the tuning company and were std NGK TR5A10... Are these OK plugs? The new one I replaced it with was PTR5A10 (Platinum)

Thanks for the help BTW!

Cheers
Alex

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AlexXtreme

posted on 30/1/17 at 12:53 PM Reply With Quote
Zetec misfire

ok - so I thought I had fixed the misfire but I had not.

Overview of the situation
- Silver Top with twin 40 webers and fast road cams
- manual choke - that does not get used
- all the spark plug gaps aree at 0.7mm - had a dodgy new one that was replaced
- misabs have been replaced
- Has been RR'ed last year at around 145 to 155hp at the engine and at the same time had the webers balanced etc
- I have replaced the leads and plugs
- Cleaned out the carbs and jets with Isopropyl alcohol

The engine starts OK and for the first 10mins or so the tickover is OK at around 900rpm
When driving the car seems to be running fine and does seem to pull well - which it should with this hp.
As the engine gets fully warm it seems to tickover OK at 900rpm but this slowly reduces until it dies.
Odd thing on the compression is that all the cylinders are reading 85 to 90psi...! Thought is was the testing kit was not measuring correctly.
Picture of spark plugs is as below with the upper plug the aft plug and the lower one(blacker) is the front plug
https://photos.google.com/share/AF1QipP3QSKwJVHm4Lp7pReo0e3aKo7_gVbo1UPYuyX-cctKLsc8gs-xKUn7IDrVDtaGCA?key=ZGxmWjZjYlUzVXd1ZEtmUUltcjF1WGtJQkQ4bHNR />
Any ideas?? What is odd to me is that all the pressures are low. If it was worn rings or valves they would be all different - wouldn't they??
Could the timing be out? But is this is the case, how come it is still performing OK on the RR.
Could it still be I am not getting correct pressure reading and it needs tuning again...

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02GF74

posted on 30/1/17 at 09:59 PM Reply With Quote
I am not convinced a new plug can be faulty - they are simple as can be - made from a lump of insulating ceramic with some metal through it - so what can possibly go wrong?. More than likely it is contaminated with soot due to not firing, but that's neither here not there.

Tell us more about the ignition - is it distributor - points or electronic? One coil or multiple e.g. EDIS?

How is timing set?

Your latest post is 6 months after the "fixed it" post so what you see now may be a different problem?

[Edited on 30/1/17 by 02GF74]






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AlexXtreme

posted on 30/1/17 at 10:23 PM Reply With Quote
I think it is the same problem and I was just persuading my self that it was fixed... also only did runs on faster roads and not in traffic / town till the weekend when it was obvious all was not right.

Timing is electronic...sorry no idea if multiple or single coil. How can I tell?

I am getting what feels like good sparks from each lead

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ian locostzx9rc2

posted on 30/1/17 at 10:23 PM Reply With Quote
No mention of a coil pack being or new leads
checked if it's a std ford one they fail regularly and carb dirty / balance issue

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02GF74

posted on 30/1/17 at 10:48 PM Reply With Quote
quote:
Originally posted by AlexXtreme
Timing is electronic...sorry no idea if multiple or single coil. How can I tell?



follow lead from the spark plug and see what is at the other end - post photo as I'm sure somebody on here will be able to identify it.

quote:
Originally posted by AlexXtreme
I am getting what feels like good sparks from each lead


That is not a scientific approach - for combustion the engine needs fuel, air and a spark - if it is not firing, then there is issue with one of those.

When the problem occurs does it happen
1. when engine has reached certain temperature? (this would point to engine or carbs)
2. after a fixed length of time? (this would point to coil breaking down after its reached a certain temperature)

Does it always occur? i.e. can you recreate it just by idling?
Does the misfire stay at the same cylinder?
Once it happens, if you turn off engine, and restart, does it misfire immediately? Or how long you have to wait for it to go away?

to summarise, you've replaced spark plug and leads so far?






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AlexXtreme

posted on 30/1/17 at 10:59 PM Reply With Quote
Will post a picture of coil - the coil is under the dash and access is not easy. The leads are new

The problem happens when the car reaches normal temp around 90c
It always occurs and seems to be at the front of the engine - as you can see from the plugs it looks as though the plugs get darker from no 4 to no 1
Once the misfire has started I can restart the engine and it continues to misfire

[Edited on 30/1/17 by AlexXtreme]

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AlexXtreme

posted on 31/1/17 at 12:20 PM Reply With Quote
these are the best pics of what I assume is the coil.... I can not get to it without either taking the steering wheel off or removing the dash

https://goo.gl/photos/xye394GLEojMCWQS7

https://goo.gl/photos/rZUrJitAfW42nei89

Alex

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rusty nuts

posted on 31/1/17 at 01:02 PM Reply With Quote
It looks like a standard Ford coil pack from what I can see , they are sometimes problematic but cheap enough to replace if suspect . When you tested the compressions did you remove all plugs from a hot engine and crank it over with the throttle fully open ? Also after finding low compressions put a teaspoon full of engine oil down the plug hole and repeat the compression test, anything over about a 10% increase indicates worn rings etc . I had problems years ago with a silver top engine that had a rough idle when hot , the compressions had been tested several times all showed up as good . A simple cylinder leakage test showed up a leaking inlet valve. Another problem I've had was the hydraulic tappets pumping up do to excessive oil pressure caused by a pressure relief valve fault. Incorrect oil can cause problems , what oil are you using? It might be worth checking the valve timing?
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AlexXtreme

posted on 31/1/17 at 01:17 PM Reply With Quote
Yes the engine was hot and all plugs remove.... but the throttle was closed! I guess that will be the reason!
I use 3 w 30 oil and will try a drop if the throttle makes the difference.

I thought about the timing however I would not the power I am seeing if the timing was out.

Thanks Rusty!

I suspect it is something to do with the carbs and have provisionally book the car into a tuner I know on the 21st Feb... does anyone have any recommendations for a tuner who knows their carbs around the Southampton area? The guy I know lives in New Milton

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02GF74

posted on 31/1/17 at 05:48 PM Reply With Quote
New plugs new leads so try a replacement coil pack, and check all wiring, remove plugs clean contacts, squirt a drop of wd40 and reconnect. Also check and clean all earths.






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perksy

posted on 31/1/17 at 10:26 PM Reply With Quote
Was going to say leads as they can be a problem on these

If its playing up when the engine is warm/hot, try a new coil first

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AlexXtreme

posted on 1/2/17 at 12:46 PM Reply With Quote
Changing the coil is going to be the last report as it is so much work to do!

Are coils really that un-reliable? I can imagine in the engine bay where it gets warm I can imagine it not lasting long, however mine is under the dash board, only sen 16k miles over 16 years and by the looks of it has been garaged!

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