Misfiring when flooring it from idle - 2l Laser

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Re: Misfiring when flooring it from idle - 2l Laser

Post by SCP440 »

I have heard this before but I know if I use Tesco 99 Octane in my Jensen it will pink but on branded fuel it is silent.
Most modern cars have a knock sensor so most people never notice
One of the car programs did a test using various fuel's and found BP Super Unleaded produced a couple more bhp than other fuel's in the same car .
The other fact is some brand's of E5 contain no Ethanol even though they are are aloud.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by nemo »

My only thoughts on this are that I`m sure Tesco don`t have their own refinery, they must be supplied from a (small number of) `proper` oil companies? I just can`t see them producing a `cheap` petrol for supermarkets. I`d also assumed, like Pbar, that the price was down to bulk buying and loss leading to get people in to their store? But, again, if someone`s personal experience suggests otherwise I wouldn`t say that they`re lying. I remember in the`70s I found my car seemed to pink far less on Texaco fuel than other makes: maybe it`s more that, different suppliers to different supermarkets rather than supermarkets per se ?
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Re: Misfiring when flooring it from idle - 2l Laser

Post by pbar »

There's a lot of snobbery (wrong word really) in the classic car world with fuels, supermarket fuels with it being cheaper gets looked down upon, but it is just the same as far as fuel goes. Excellent point by nemo about supermarkets not having their own refineries, it comes from the same suppliers. Andrew makes a fair point that some petrol companies may use additives and add-ins but any potential benefits may be debatable or subject to marketing myth. Any Tesco petrol station is full to the brim with people and cars of all types filling up but they're not all having problems are they. Also fuel companies are very good at taking people in with marketing, using clever words such as 'power' in their names, I've been involved in marketing in a previous life you won't believe how you get taken in, unknowingly, by some techniques. There's also the placebo factor too of course which causes many to waste their money.
Last edited by pbar on Fri Feb 09, 2024 10:52 am, edited 1 time in total.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by Andrew 2.8i »

nemo wrote: Fri Feb 09, 2024 10:30 am they must be supplied from a (small number of) `proper` oil companies? I just can`t see them producing a `cheap` petrol for supermarkets.
I see what you're saying, but perhaps they produce a base fuel then add extras to their own brands to enhance it?
I'm just guessing.
I would imagine that pbar is, of course, correct in his assertion that bulk buying process and the practice of selling fuel as a loss-leader are contributing factors to them being able to sell fuel at a lower cost.
When I used to work in a petrol station many moons ago, retailers typically made less than 1p per litre. The profit is made with the shop sales.

Andrew.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by nemo »

Andrew 2.8i wrote: Fri Feb 09, 2024 9:57 am
It's true that all fuels will meet a minimum specification, but others may exceed those requirements.
Off topic, but I`m sure the same applies to, for example, rubber fuel hoses. For E10 the requirement is for a hose that meets (IIRC) j30 r9. Which suggests that an earlier spec , say R7 will fail if used with E10. However when that hose was made it met a certain spec which was the only `benchmark` standard AT THAT TIME. But some will have just met it whereas others may have far exceeded it - there will always be differences in quality from different manufacturers but there`s no way of telling which is which. I have some Goodyear hose, R7 I think, so theoretically not suitable for E10, this has been fitted for 16 years now and is absolutely as new. Internally, externally it`s as good as it was when I fitted it. Yet other people have had hoses visibly deteriorating after less than a year. My assumption is that the Goodyear stuff actually meets R9 but couldn`t be labelled as such as the standard didn`t exist then! Just my thoughts.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by nemo »

Andrew 2.8i wrote: Fri Feb 09, 2024 10:50 am
When I used to work in a petrol station many moons ago, retailers typically made less than 1p per litre. The profit is made with the shop sales.

Andrew.
Yes, I know, 20 years ago I could have identified maybe a dozen petrol stations within a 2 mile radius. That is now 3 or 4 .. and a Tesco. Simply because, as you say, the profit on petrol has historically been absolutely minute, the small independants are just no longer viable. Which is sad.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by nemo »

pbar wrote: Fri Feb 09, 2024 10:41 am petrol companies may use additives and add-ins but any potential benefits may be debatable
I don`t know if you remember... (or were even alive?) in the mid `80s, but either Shell or BP, can`t remember, brought out a Super Duper petrol which had special additives which allegedly cleaned your engine while you drove thus giving you extra MPG. Unfortunately it didn`t go down well with Vauxhalls new(ish) OHC engined Astras & Cavaliers. I seem to remember there were huge numbers of engines with burnt out valves, it was a major news story at the time;. The moral: `shoulda gone to Tesco` :D
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Re: Misfiring when flooring it from idle - 2l Laser

Post by SCP440 »

Its all about the additives, when the tanker driver arrives at the refinery he adds a container of additives depending on where is supplying before he bulk fills.
Tesco probably just dont add anything.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by EightyFive »

So I took it out for a test drive today, car drove nice when it was driven casually. Tried flooring it close to home just to test it and again after retarding the timing slightly and there was a loud bang as it backfired through the carb. Car struggled to stay running after and completely died shortly after. Wouldn’t even idle and had to push it the last 50m :lol: glad my neighbors were out at work…

Anyway it turned out that when it backfired I guess the carbon and fuel clogged up the primary idle jet. Cleaned it up and got the car running to how it was before. But yeah it’s something that needs to be resolved before I drive it regularly.

I also tested an old coil that was working when removed (not a 2.8 one) and it basically ran the same, so I doubt the coil itself was faulty.

P.S after this conversation on fuel I decided to chance it and fill up with premium fuel from tesco… maybe that’s what did me in haha.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by D366Y »

I had similar symptoms last year.

Valve clearances made a massive difference, definitely check and set them if you haven't already.
Cleaning up the carb was the next thing, the accelerator pump in the carb made a massive difference as well. We replaced quite a few parts on the carb in the field at CRaP last year. Fuel filter in the bottom of the carb, accelerator pump, cleaned the inlets and changed the gasket on the top of the carb - drove like a new car on the way home!
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Re: Misfiring when flooring it from idle - 2l Laser

Post by EightyFive »

D366Y wrote: Fri Feb 09, 2024 6:34 pm I had similar symptoms last year.

Valve clearances made a massive difference, definitely check and set them if you haven't already.
Cleaning up the carb was the next thing, the accelerator pump in the carb made a massive difference as well. We replaced quite a few parts on the carb in the field at CRaP last year. Fuel filter in the bottom of the carb, accelerator pump, cleaned the inlets and changed the gasket on the top of the carb - drove like a new car on the way home!
Okay cheers this'll be my next step then, all seems straight forward enough. Must admit I've never checked the valve clearances on this car as I never knew how, looks straight forward enough to adjust though. I've rebuilt a carb before so pretty confident changing all that stuff. FYI accel pump is def working and shooting a nice squirt of fuel when the throttle is applied so I'm pretty sure that's not the cause. If one jet was gammed up though I wouldn't put it past some of the others being the same.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by pbar »

nemo wrote: Fri Feb 09, 2024 11:35 am
pbar wrote: Fri Feb 09, 2024 10:41 am petrol companies may use additives and add-ins but any potential benefits may be debatable
I don`t know if you remember... (or were even alive?) in the mid `80s, but either Shell or BP, can`t remember, brought out a Super Duper petrol which had special additives which allegedly cleaned your engine while you drove thus giving you extra MPG. Unfortunately it didn`t go down well with Vauxhalls new(ish) OHC engined Astras & Cavaliers. I seem to remember there were huge numbers of engines with burnt out valves, it was a major news story at the time;. The moral: `shoulda gone to Tesco` :D

Shoulda gone to Tesco, yes definitely! Hehe. I was alive then (thank goodness, imagine being a young un now), I don't recall that situation but that's very interesting indeed. Maybe modern day additives are actually causing issues for some classic car owners. Certainly, people come on here with problems and state 'and I always use expensive premium fuel' like it's a good thing, maybe it isn't.

I used to always put expensive fuel in the Capri, but the more I looked into it the more apparently unnecessary it seemed. So I put supermarket fuel in every car now and the only difference I've noticed is my wallet, which is far better off.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by nemo »

EightyFive wrote: Fri Feb 09, 2024 6:54 pm I Must admit I've never checked the valve clearances on this car as I never knew how, looks straight forward enough to adjust though. I've rebuilt a carb before so pretty confident changing all that stuff.
If you`re goingto rebuild the carb, so I`m guessing removing it - adjust the valves before you put it back as one of the valves (No5?) is really very difficult with the carb fitted. Needs a special cranked spanner to get round it.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by D366Y »

nemo wrote: Fri Feb 09, 2024 8:41 pm
EightyFive wrote: Fri Feb 09, 2024 6:54 pm I Must admit I've never checked the valve clearances on this car as I never knew how, looks straight forward enough to adjust though. I've rebuilt a carb before so pretty confident changing all that stuff.
If you`re goingto rebuild the carb, so I`m guessing removing it - adjust the valves before you put it back as one of the valves (No5?) is really very difficult with the carb fitted. Needs a special cranked spanner to get round it.
Can definitely vouch - is a nightmare to get at either valves 5+7 or 6 (cant remember which side it starts on) so would definitely recommend taking the carb off unless you have crows foot socket attachment
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Re: Misfiring when flooring it from idle - 2l Laser

Post by EightyFive »

I find it's also a right pain in the arse to get at the two nuts on the carb closest to the engine without the rocker cover off. So yes I'll definitely be taking the rocker cover and carb off, and reinstalling the carb first after.

Unfortunately I won't have access to my capri for about a year now, as I'd love to conclude this thread... Oh well atleast I have a starting point when I get back.

Cheers for the help guys.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by Mc Tool »

Make damn sure you dont drop one of the carb mounting spring washers into the manifold..... it could perhaps find its way into .... oh number one pot and then maybe get jammed down the side of the piston , I mean if that happened it may well munt the top and second rings , and logic would suggest that it would probly also destroy the ring lands on the piston , you might also score the bore too . Damage to the head wouldnt be to bad tho, just a few wee dings ....I would think .
Have a count up of the washers and if there happens to be one missing dont just get another and fit it. you will know pretty much immediately if this does happen .... I strongly suspect that a loud buzzing noise will alert you to this mishap ......should it happen.
Probly the only thing that could make this worse is having inadvertly bought a set of low comp pistons maybe from ebay US ( and having to deck 70 thou off the block to get 10.5:1 comp ) because you would have to buy another whole set of pistons .... again from the states ( probly take 6 weeks to arrive ).
Oh no ! this didnt happen to me :roll: , just saying thats all
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Re: Misfiring when flooring it from idle - 2l Laser

Post by Major_Tom »

EightyFive wrote: Sat Feb 10, 2024 3:38 pm Unfortunately I won't have access to my capri for about a year now, as I'd love to conclude this thread... Oh well atleast I have a starting point when I get back.

Cheers for the help guys.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by pbar »

Major_Tom wrote: Mon Feb 12, 2024 2:21 pm
EightyFive wrote: Sat Feb 10, 2024 3:38 pm Unfortunately I won't have access to my capri for about a year now, as I'd love to conclude this thread... Oh well atleast I have a starting point when I get back.

Cheers for the help guys.
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Re: Misfiring when flooring it from idle - 2l Laser

Post by Bug »

EightyFive wrote: Wed Feb 07, 2024 8:59 pm
SCP440 wrote: Wed Feb 07, 2024 8:49 pm Blow back through the carb is usually an indication of lean running.
As it happens under load is the accelerator pump working ? The other thought is the float height correct? If low the engine might be running out of fuel under high load.
When you set the ignition timing did you have vacuum disconnected ? Is the vacuum canister on the distributor working? Pull the pipe off the carb and suck, with the distributor cap removed as you suck you should see the base plate move and as you release the vacuum it should slam back.
I'll check the accel pump tomorrow, float height I'm not sure tbh and will have to check also. However the carb isn't that old and came off my old 2l and didn't have these issues, however it has not been run in a couple of years so I won't rule it out completely.

Yeah vacuum was disconnected and blocked off, I also tested it by sucking on the pipe, everything seemed okay there.
What was your old 2.0?
Look into the top of ther carb at the Y-shaped acclerator jet. On some models, GL etc, it onlt squirts into the primary barrel.
S models fired into both barrels.
Possibly you are not getting enough fuel in to cover the short gap before the venturi effect can recover from the sudden drop in downstream pressure.

If it is popping back through the carb then it is exactly the same principle as a surge in a jet engine. Flow through the venturi stalls and the airflow reverses momentarily.
When you accelerate slowly good old Bernoulli's Theorem has time to keep up. But suddenly dump all the downstream vacuum effect and the flow stalls in the venturi. It can then actually draw ignited air back from the cylinder. The momentary lack of flow through the carb means the fuel is hanging around in there. Hot gas coming back past the inlet valve ignites this and 'pop'.!
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Re: Misfiring when flooring it from idle - 2l Laser

Post by Mc Tool »

" draw ignited air......."
Yep , there have been a few peeps got their eyebrows singed ( pyrotechnical depilitation :xd: ) . You sorta want to see whats going on down that hole into the engine , so you lean over for a look and get your face BBQ'd, Funny as #uck when you see it happen to someone else :lol:
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