Engine Misfire

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Beechy
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Engine Misfire

Post by Beechy »

Hi there, can anybody help?

I bought a Mk3 in October 2020 with 6 months MOT. It ran fine for the first 6 or 7 weeks and quickly became my daily driver.
The car then developed what appeared to be a misfire, so I put some Redex in the tank and filled it up with fresh fuel, but still no improvement.
The following weekend I replaced the plugs but this made no difference.
I then checked the coils and they all seemed fine.
At this point, I thought a good blast down the nearest bypass might help to clear any kind of blockage, but the car quickly got worse and before long, I was doing 20mph with my foot to the floor. Managed to nurse it home.
Over the next few weeks did some reading up, and asked on the MR2 Facebook page if anyone had any ideas of what the problem could be.
Someone suggested I replace the 02 sensors, so I did this next. Still no joy.
Next a mate came around with his code reader and it showed ‘P0303 Cylinder 3 Misfire detected’ so next, I tackled the injectors. I took them out and blasted them with carb cleaner whilst hooked up to 12 volts, and put brand new seals at either end of each injector, put them back into the engine but the issue is still there.
(I gave it a good revving and there appeared to be white smoke coming from the exhaust - don't know if this is important or not?)
I’m aware that the issue could be the Pre-cat disintegrating, but if it is, the car’s probably a write-off anyway, so I want to make sure I’ve done everything else that I can (that doesn’t cost the earth!) before I tackle taking off the exhaust system.
Has anyone got any ideas of what else I can try?


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jimi
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Re: Engine Misfire

Post by jimi »

These threads have similar problems , might give you some clues/idea's
https://www.mr2oc.co.uk/forum/42/145982.html
https://www.mr2oc.co.uk/forum/42/145862.html
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Re: Engine Misfire

Post by MRHAPPY62 »

I had a similar problem with a celica with the 1zz engine , do a compression test mine was a valve .
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Re: Engine Misfire

Post by gavsdavs »

Can you read the OBD data off the car ?
Looking for fuel trims, maf readings, timing advance, sensor voltages/currents/etc

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Re: Engine Misfire

Post by Beechy »

gavsdavs wrote: 13/07/21 22:07 Can you read the OBD data off the car ?
Looking for fuel trims, maf readings, timing advance, sensor voltages/currents/etc
Hi Gavsdavs, I do have some pics of the readings, no idea what they mean apart from the cylinder 3 misfire.
When I took out the injectors, they were quite dirty at the bottom with a sludgey grey liquid.
Before I put the flushed out injectors back in with their new seals on, I managed to get a Covid test swab down there and gave it a twirl, but whatever it was must have dried up by then as it came out fairly clean.
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Beechy
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Re: Engine Misfire

Post by Beechy »

MRHAPPY62 wrote: 10/07/21 21:43 I had a similar problem with a celica with the 1zz engine , do a compression test mine was a valve .


Cheers fella, if I can get it to the garage I'll ask about this :-)

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Beechy
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Re: Engine Misfire

Post by Beechy »

jimi wrote: 10/07/21 18:42 These threads have similar problems , might give you some clues/idea's
https://www.mr2oc.co.uk/forum/42/145982.html
https://www.mr2oc.co.uk/forum/42/145862.html
Thanks Jimi. There's so many things it could be. I'm starting to lean towards dirty fuel as the injectors had a lumpy grey sludge around the seals when I took them out.
Shame I have 3/4 of a tank of petrol!
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Re: Engine Misfire

Post by jimi »

What sensor is related to your second and third pics ?
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Beechy
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Re: Engine Misfire

Post by Beechy »

I'm assuming they're the two 02 sensors. They were bought second hand from eBay, supposed to be from a working car that was being broken. New ones were really expensive!

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Re: Engine Misfire

Post by carolineasb »

Lambda sensors are fragile and don't like being moved :( also OEM Denso seem to be the best to fit and others appear to be false economy. Have you actually checked the condition of the precats? Have you been burning oil? Have you checked the water in the system including the radiator?

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Beechy
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Re: Engine Misfire

Post by Beechy »

Not burning oil that I'm aware of, and the water seems to be stable, no overheating or anything.
I had a bit of trouble when I bought replacement sensors (one of the originals had a resistor bodged on it) as they sent the wrong ones despite having pics of the codes on the ones I took out. I then bought the ones that are currently in and they were off a working engine and had the same codes as the original ones, but they say fail on the reader.
I'm thinking, drain the tank next and remove any sludge so I can eliminate that as an issue.
I looked at Denso sensors, and they're pretty expensive. Definitely on the agenda but whilst I save up for them I'm trying to work through the things that I can do without too much cost.
I had a torch down the holes when the sensors were out, and it looked intact from what I could tell. Again, I'll happily put a non pre-cat exhaust on if if I can get to the bottom of the issue, but seems a waste of money to spend £200 on one to then still have the same issue if you know what I mean?
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