Author Topic: MKIV Engine Problems  (Read 506 times)

MartynG

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MKIV Engine Problems
« on: June 14, 2019, 14:21:37 »
Hi, I'm not sure if anyone will be able to help, but all comments/suggestions gratefully received.
I'm also not particularly mechanically experienced so do bear with the description etc.
I have two concurrent problems with my MK IV (AK1259), whether they are related in any way, I'm not sure.

The car failed its recent MoT on CO output. I've had it to my local engine specialist to have the carb (4 barrel Holley 650 double pumper) cleaned / adjusted which is something it seems to need every couple of years. I understand this is due to the additives in higher octane fuels and the car getting very little use over the winter months. I've noticed over recent runs that the engine note is rather 'woofley' when cruising along in higher gears, in contrast to the previous 'bark' under acceleration.
On the rolling road we found output peaked at about 240bhp some 130/140 bhp less than peak achieved a few years ago and very unresponsive beyond about 3800/4000rpm.
Compression and leak down test of all 8 cylinders was good and within expected parameters.  Plugs were okay. Slight oil leak from the rear of one of the rocker covers noted. The engine runs quietly with nothing giving concern in terms of 'noise'. This is also confirmed by microphone / headphone examination with the engine running at load.  Engine man suggests this means it's unlikely to be a problem with cam lobes. Exhaust manifold downpipes not up to expected temperatures on a laser thermometer. Exhaust tested and no surprises there.

We've also discovered some issues with the wiring. This is causing concern with fuse holders melting and far too much current (17 Amps ?) on ignition circuit. Seems that it's wired through the ignition key and not routed through a relay.

Likely next steps will involve inlet manifold removal to inspect rockers / internals and possible partial re-wire.  All sounding reassuringly expensive ! 

Has anyone experienced similar problems ?
Thanks.

Lolaracer

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Re: MKIV Engine Problems
« Reply #1 on: June 14, 2019, 21:01:17 »
I bet the key gets hot. Is your distributor loose? Maybe the timing is retarded, excuse me, handicapped.

mjf

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Re: MKIV Engine Problems
« Reply #2 on: June 15, 2019, 09:30:23 »
Has your car got fresh fuel in the tank or have you just got the remains of what was left in it before you parked it up over winter ?

MartynG

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Re: MKIV Engine Problems
« Reply #3 on: June 15, 2019, 10:02:10 »
MJF,
Yes, completely fresh 99 octane fuel.

mjf

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Re: MKIV Engine Problems
« Reply #4 on: June 15, 2019, 10:06:44 »
Thats a shame - it would have been an easy fix !!

bbrown

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Re: MKIV Engine Problems
« Reply #5 on: June 15, 2019, 22:41:59 »
I wouldn't start tearing the engine apart for high CO emissions.  The engine is running rich.  Double pumpers are not noted as emissions friendly carbs.  I would really have a good look at that and lean it out.  I would also check out the complete ignition system and timing.

One of my friends had a hell of a time getting his completely stock MkIV (no double pumper) to pass California emissions.  I'll ask him what he had to go through.
Good luck
Bert
Danville, California

B.P.Bird

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Re: MKIV Engine Problems
« Reply #6 on: June 19, 2019, 14:07:25 »
Float bowl levels too high ? Secondaries not opening correctly ? Where is all that current going ? You should not need a relay for the ignition load. Is the cooler fan relay stuck on and running full time ? Could a ballast resistor be missing from an 8 volt coil system ? That level of current is more than capable of setting the poor thing on fire so caution is advised.....
Let us know what you find.
Barrie

AC Ace Bristol

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Re: MKIV Engine Problems
« Reply #7 on: June 19, 2019, 17:19:03 »
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Martyn

Many Cobra Owners experience problem with too high a CO2 reading,  but usually get a pass if they let the Cats get really hot, the CO2 readings reduce and mot pass certificate given.

That is assuming you are running Cats and a stock exhaust system.
worth going throgh Barries suggestions, then if still negative

Alternative is find a different Mot station  who appreciates older cars especially AC's and the like.
Cheers
Keith
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AC Ace Bristol

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Re: MKIV Engine Problems
« Reply #8 on: June 19, 2019, 17:23:46 »
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Martyn
 Definitely worth going through Barrie's suggestions.
 Is this still the same problems experienced a year back ?

Many Cobra Owners experience problem with too high a CO2 reading,  but usually get a pass if they let the Cats get really hot, the CO2 readings reduce and Mot pass certificate given.
That is assuming you are running Cats and a stock exhaust system.

Alternative is find a different Mot station  who appreciates older cars especially AC's and the like.
Cheers
Keith
.

MartynG

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Re: MKIV Engine Problems
« Reply #9 on: June 20, 2019, 16:17:27 »
I wouldn't start tearing the engine apart for high CO emissions.  The engine is running rich.  Double pumpers are not noted as emissions friendly carbs.  I would really have a good look at that and lean it out.  I would also check out the complete ignition system and timing.

One of my friends had a hell of a time getting his completely stock MkIV (no double pumper) to pass California emissions.  I'll ask him what he had to go through.
Good luck
Bert
Danville, California

Thanks Bert,
I think the ignition system needs a good look at.
Engine man has tried some tweaks with the carburettor settings and leaning it out had no particular effect in terms of the performance issues above 4000 rpm and horsepower output.  He tried a different coil but no success there either.
I guess we'll just have to prove the individual elements and tick these things off one by one.
The mystery continues …….


MartynG

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Re: MKIV Engine Problems
« Reply #10 on: June 20, 2019, 16:23:46 »
Float bowl levels too high ? Secondaries not opening correctly ? Where is all that current going ? You should not need a relay for the ignition load. Is the cooler fan relay stuck on and running full time ? Could a ballast resistor be missing from an 8 volt coil system ? That level of current is more than capable of setting the poor thing on fire so caution is advised.....
Let us know what you find.
Barrie

Barrie,
Thanks for the suggestions.
We've looked at the whole carb setup and engine man has had the thing apart a few times, ultrasonically cleaned and properly set up.
The current issue is decidedly a problem and as said one of the fuse carriers was showing signs of overheating / melting.  I've had an issue with a blade fuse melting part of the fusebox in the past so more investigation required wiring wise I suspect.
I will let you all know when we get to the bottom of it.
Many thanks.

MartynG

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Re: MKIV Engine Problems
« Reply #11 on: June 20, 2019, 17:10:27 »
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Martyn

Many Cobra Owners experience problem with too high a CO2 reading,  but usually get a pass if they let the Cats get really hot, the CO2 readings reduce and mot pass certificate given.

That is assuming you are running Cats and a stock exhaust system.
worth going throgh Barries suggestions, then if still negative

Alternative is find a different Mot station  who appreciates older cars especially AC's and the like.
Cheers
Keith

Keith,
Thanks for your post.
No Cats on this baby !
I did get my certificate, they are very Classic friendly.
Best wishes.
Martyn.

AK1181CH

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Re: MKIV Engine Problems
« Reply #12 on: June 22, 2019, 09:06:47 »
Is the cooler fan relay stuck on and running full time ?
Barrie

Also got the ignition key getting hot. 'Til I noticed that it was warming up as soon as the fan started running ! And on my EFI car this problem even created sudden engine shut off !! (bad wire connection and too much Amps pumped at the key). Corrected the fan power source and problem solved.

bbrown

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Re: MKIV Engine Problems
« Reply #13 on: June 30, 2019, 03:37:41 »
Martyn,

Checked with my buddy with the MkIV and he said his engine is fuel injected, so his engine is not like yours. 
I have experience with a specialty firm that managed to get my old Ford to pass the smog test after I had an initial fail at the first smog station.  The main thing they did after they checked fuel pressure and timing was to make sure the catalyst is good and hot before the test, echoing Keith's comments.
Good luck, Bert 

westcott

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Re: MKIV Engine Problems
« Reply #14 on: July 12, 2019, 10:20:16 »
Is the cooler fan relay stuck on and running full time ?
Barrie

Also got the ignition key getting hot. 'Til I noticed that it was warming up as soon as the fan started running ! And on my EFI car this problem even created sudden engine shut off !! (bad wire connection and too much Amps pumped at the key). Corrected the fan power source and problem solved.

Bert,
how did you modify or correct the fan power source, additional high amp relay or complete new wiring ?

Uwe
Everything should be made as simple as possible, but not simpler!