Engine misfiring/knocking

[Meoricin]

Hi all,

Not posted before over here, I used to use the MR2oc forums when I had a pair of MK2s, but unfortunately they both passed away for various reasons.

I bought a 2001 Roadster last July, and it's not really seen as much use as it deserved mostly thanks to cycling to work.

Recently I bought a flat and started using the MR2 for my daily commute, and all was going wonderfully; nothing like the roof down in the sun to take your mind off of rush hour traffic!

However, on Thursday while crawling along in traffic the car suddenly turned into a diesel! Chugging along, it was on the verge of stalling at low revs, and making horrible misfiring or knocking sounds as the revs increased, with one small spot at approx 2k-2.5k rpm where it would sit happily and stable, before the knocking came back at higher revs (and it felt like there was no power available).

I initially assumed a misfire, as it sounded like one cylinder wasn't firing properly - so I've bought new plugs, and have been looking into injector failures and what I can do to try and resolve whatever is wrong. The engine light is off - but my OBD2 reader has told me that it's got P0325, which is apparently a knock sensor failure. I'm now terrified that it's terminal (a stretched rod causing a knock is how much first MK2 died). It doesn't use oil that I've noticed, the reading is currently a little under half way on the dipstick, round about where it was when I bought it - coolant is sitting at the 'low' marker, but it's been there for a good while and it's not overheating.

It drives, but I don't really want to be driving it much when it's like this - the last thing I want to do is kill it if it's repairable.

The main issue I have is that the symptoms don't seem consistent. I started it after taking the OBD2 readings, and it sounds normal - no knocking, no misfiring. But when I drive it, a few minutes into the drive it will invariably start, and continue until I stop.

It's still got the pre-cats in (from what I can see), and it's on 110k so they're on my list of things to fix. But I don't really want to spend £££ on a replacement manifold, and then find out that the engine is dead and there's nothing I can do other than replace it.

Any suggestions on things to try for diagnostics which aren't too involved would be much appreciated - I have basic tools (multimeter etc, nothing I can check compression with though), and I can use one of my parents' driveways for a day if I'm disassembling/reassembling, but I can't leave the car there so I'd have to be fitting whatever I try into a day and having the car still running afterwards.

Thanks for reading, and any input anyone can provide - I'm pulling my hair out with this, as I really can't afford to be buying a new car!

[Treboeth]

Take a video and post it up one of the knowledgeable members will help identify the troubles.

[Meoricin]

I'll get a video up tomorrow, good idea!

[ChrisGB]

If it comes and goes intermittently, it's probably electrical. Coilpack failure could cause a misfire, which could cause the power loss and misfire. Earth fault somewhere is another possibility. Crank position sensor earth point can cause random problems. Defective engine temp sensor will sometimes cause lean running if it tells the ECU that the engine is warm when it isn't. MAF failure can cause rough running as you describe. Quite a list to work through!

[Carolyn]

I have not experienced a failing knock sensor but, if your ecu thinks the engine is knocking or that the sensor isn't working it will retard the timing and (possibly?) shut off some sparks.  The failure could also be intermittent or happening when it gets warm.  
As the code for a knock sensor failure is present, perhaps that's the place to start (mind you it is a sod to get to)?
Anyone had knock sensor problems who can assist with info?
This was the best info I could readily find:
 m http://www.freeasestudyguides.com/knock ... ptoms.html m

[jonbill]

The thought I had was that if it's detecting a lot of knock, the ECU may think it implausible and report sensor failure. From OP, it does seem there was a lot of knock.

[beavisrules]

The failure code means it cant detect the sensor , not that its readings are wrong. It can give another error message if the ECU has improbable signals.

[Meoricin]

Well, I'm letting you all down a little here with the videos (I don't have one for you as I couldn't get a good example of the sounds before I tested/checked things further).

The main sound which I had feared was a knock is definitely a misfire - basically every couple seconds while on throttle the exhaust has a deep pop - sounds to me like fuel is burning up in the exhaust. Fuel consumption is up as well.

I bought a compression tester and have tested all the cylinders - I'm a little confused by the results as I understand they should be 180psi~ and all within a few psi of each other. Mine read 110/120/120/120. All read dead on 120 - surely if they're all equal that says something positive, probably with my test procedure or the tester?

The car is now reporting a misfire on cylinder 2 through the OBD, and the spark plug from this cylinder is blackened. I think this is the source of whatever is wrong, and I've got a multimeter so will check the injector and coil for this cylinder tomorrow after work, assuming good weather. New spark plugs haven't changed anything. The misfire is regular once the engine is up to temp, and it feels like the issue revolves around that cylinder.

Still not using oil or coolant that I can detect - though I'm not exactly putting many miles on it like this (just babying it the 10miles~ to work and back).

If it comes to worst case scenario and I need a new engine, does anyone have recommendations for places on the South Coast which could source/fit one, or ideas of what my likely costs would be?

Thanks for all your answers, I'm spending a lot of time thinking about this, and the input helps direct my planning/worrying!

[furbern]

Swap a coilpack, see if the problem moves

[Essex2Visuvesi]

Did you do the compression test on  a cold engine?
120PSI is OK for a cold engine
150PSI is for a hot engine

Also did you try a wet test as well?

[beavisrules]

Also worth a swap round of plugs also.
Recently had my moped go cack on me , nearly new NGK from halfords had gone very high resistance.

but I'd bet on likely being a coil pack or connector.

measuring the wiring a good bet too as they get brittle with age/heat.

[Meoricin]

Did you do the compression test on  a cold engine?
120PSI is OK for a cold engine
150PSI is for a hot engine

Also did you try a wet test as well?

It was on a cold engine, yes!   s:bounce: :bounce: s:bounce:   I'm not quite jumping for joy yet, but that's a bit of good news then.  s:bowdown: :bowdown: s:bowdown:  

I'm going to attack the injector and HT leads/coils with a multimeter this evening and see if I can pin down an immediate cause. If I find something, I'll order an exhaust manifold to replace the pre-cats and replace whatever's broken - and then go from there. If I can stretch the life out a bit longer, great.

I've had a quote for an engine refurb from a place that'll collect the car, refurb the engine and bring it back. £1495+VAT which seems a bit daft when I paid £1300~ for the car in the first place, but I suppose at least then I'd know the engine was good and could focus on other things! Then again, if I'm spending that much I could go and find another one and scrap this one, it's not like it's perfect elsewhere - the gearbox could do with a refresh, the paintwork isn't flawless...  s:flame: :flame: s:flame:  Plus I'd know a bit more about what to look for!

[shnazzle]

I think furbern had the best suggestion yet. Switch the coil packs from the cylinder 2 and see if the code changes to the other cylinder.

Then you've narrowed it down to a coilpack, which could be a hell of a lot cheaper than a rebuild, which I feel is a bit premature at this point! Might be worth doing the compression test again cold and wet to determine the health of the rings, aside from this misfire issue. Just while you're fiddling  s:) s:)  Might do mine actually

[Carolyn]

120 is very very low.  185 is factory spec (so you're right about 180).  I suspect your compression tester isn't accurate (or you didn't give the engine enough spins)  The main thing is the lack of variation, if only one cylinder was bad it would have shown up.  The coil swap is a very good move - a lot less work than testing the harness and a lot less complicated) and it will let you know if it's a coil pack or wiring.
Being picky... (sorry, I'm a pedant), there are no HT leads... I doubt you need an engine refurb to cure a misfire as you've ruled out bores and valves with your compression test.
Another possibility is a dodgy injector (less likely to give your symptoms but possible), but the coil test will help to track that down too.  You can do the same swap trick with a couple of injectors, to narrow that down, but you're not there yet.
Coil swap first, buddy.

[mr mr2]

I had the same fault a few weeks ago was the injector luckily I had a spare in my stash of bits and bobs really easy job if it is that


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[Meoricin]

Well, I was feeling fairly positive today - my injectors arrived, and I was excited to swap the dodgy one out for one of these to see if I noticed a difference. Swapped it out, and it felt good! Not great, but it was relatively smooth, and felt like it would rev happily.

Took it round the block, up to temp and 4krpm (for the first time in weeks), and it decided it didn't like that. Stopped revving, all power disappeared. Limped home (along a thankfully quiet duel carriageway), and it struggled even to propel itself up the short ramp into our car park. I actually had to stop it at the top of the ramp, handbrake on, and pull away again to get it back to its usual parking spot.

It won't go above 2.5krpm at all - no matter how much the throttle is pressed.

New error code showed up to add to the previous Knock sensor and Misfire codes: P1300 which google tells me is igniter circuit 1; Only difference to normal is that I did drive it without the little engine cover on (hassle to re-install it for a short test drive), but I can't see how this would affect it. Too late to keep working (I think the neighbours are probably annoyed enough as it is), so I'm on the train to work tomorrow morning and will have a jiggle of the wiring when I get home tomorrow. I'm pretty sure I didn't knock anything loose though.

[Meoricin]

To answer some of the earlier suggestions as well; prior to the above tests I did some experiments with the coil packs, swapping them round etc and didn't see any change - misfire was stable on cylinder 2 the whole time, so I'd decided it was likely the injector.

[shnazzle]

Maybe the ignition wiring to that coilpack isn't right? With tinkering with the coilpack/injectors you might have jostled it and made it connect, then it came undone again on your drive?
Multimeter time

[shnazzle]

Mind, p1300 is for cyl 1. Sure it's still plugged in properly?

[jonbill]

I would think from the symptoms there's problems with more than 1 cylinder.
What do the plugs look like now?
How old is the fuel?

[Carolyn]

Time to measure the valve clearances, I think. If they are tight (worn valves and seats) they'll get worse as it heats up.