dan91
Part of things
Posts: 414
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May 29, 2020 19:33:19 GMT
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Its a 1993 1.8 MX5
Essentially whats happening is after 10 or so minutes of driving with the car up to temp I'm getting this odd intermittent issue, its usually under load or at high revs, almost feels like a clutch slip and if you keep your foot in it it picks up again.
Its never done it when the car is warming up, althougha admittedly I'm not revving it out past 5k from cold, but under load from cold its fine.
If I'm pulling from 4'th or 5'th low revs it does it a bit then clears, If I'm pulling hard in third anywhere from 4-6k revs it will do it sometimes, again almost feels like a slipping clutch, loss of power than sort of kicks back in, possibly leaning out? Not sure.
Its not clutch, revs drop rather than rise and ive tried everything to recreate clutch slip to no avail.
I also have a vibration at 60mph+ but wheels are brand new as are tyrtes and all balanced a few days ago, this may be completely unrelated but i feel like it is.
When i changed the spark pluggs out i noticed the old ones were quite yellow, so again possibly leading to leaning out.
Ive changed plugs, leads and MAF so far. I have a fuel filter and fuel pump on the way that id ordered to service anyhow.
I'm thinking fueling, but could it be something like Cam angle sensor or TPS causing this? I'm going to changge fuel filter and pump for good measure aanyhow.
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May 29, 2020 21:00:49 GMT
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Have you tried reading the fault codes?
It does sound like fuel starvation, you could also check fuel pressure.
Also worth checking for air leaks between the maf and throttle body.
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May 29, 2020 21:43:35 GMT
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If it happens when hot I would be suspecting a coil, - that will gradually get worse. Possibly the crank sensor as they in general are known to be heat sensitive - I know the later 1.8 so not sure if they are on the pulley on yours - if so less likley to have heat issues.
Unlikely to be an air leak as that would be much worse at idle and disapear at higher RPM. Fuel filter, pump etc not likely heat affected.
As above though, the flash codes from the diag port will save you throwing parts at it.
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ferny
Club Retro Rides Member
Posts: 981
Club RR Member Number: 13
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May 29, 2020 23:25:20 GMT
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If it's fuel you'll experience it when it is at highest demand - high revs. You'll get similar symptoms with a clogged filter, but it wouldn't clear with revs. I'd also be going for coil. I'll see if I have specs for 1.8 coils but a quick Google will bring up the information you need. Search for "testing mx5 coils" if you have a multimeter. It sounds like spark is breaking down at load. For this reason, check your leads as well. Set the multimeter to resistance and check each lead is similar, but resistance gets slightly higher with length. Any which are faulty will stand out. I say this as I'm on my 3rd set in about four years. Also ensure they have positive clicks when going into the plugs and inside the coil. May sound obvious, but thinking they're on the plugs can cause exactly the fault you describe. Another possible but unlikely reason will be water in the spark plug holes. I used to get this on mine and the spark broke down exactly how you described. 5-10 miles from home it'd splitter, I'd pull over and stick tissue down the hole and then drive on. Unlikely to happen if the engine is still in an mx5 unless you've washed the engine. Start easy and simply first.
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ChasR
RR Helper
motivation
Posts: 10,189
Club RR Member Number: 170
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Fuel IME doesn't tend to cause a misfire ; You tend to get a straight up loss of power. This IMHO will be electrical. I'd be looking at a coil or a crank sensor problem. As someone else has said, get the codes read. I think on these, you can get a 12V LED to get the codes ; Autolink do a decent kit for not alot of money if you can't make your own .
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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We had exactly the same symptoms in our 1.8 NA, in that case a new set of leads solved it. As you've done those I'd be looking at coil pack. I've got a spare I'd offer for testing but it's from a '97 and I don't think they're compatible?
Vibration wise, did it start with the new tyres? Both our mx5's do it to some extent, although having the wheels rebalanaced by someone who knew what they were doing reduced it a fair bit.
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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I thought all 1.8 NA's used the same coil pack - it's the 1.6 that uses a separate ignitor amplifier - or was it 1994 they all changed?
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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There are 3 pin variants and 4 pin variants, both for 1.8s. I think it has to do with whether the tachometer is being fed from the coil packs (early cars) or ECU (late cars) but I'm not sure where the change point was.
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MiataMark
Club Retro Rides Member
Posts: 2,960
Club RR Member Number: 29
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Fault codes are easy to read with a LED, although they don't necessarily tell you much.
I had a similar issue (early 1.6 NA) that was cured with leads and plugs.
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1990 Mazda MX-52012 BMW 118i (170bhp) - white appliance 2011 Land Rover Freelander 2 TD4 2003 Land Rover Discovery II TD52007 Alfa Romeo 159 Sportwagon JTDm
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dan91
Part of things
Posts: 414
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Appologies for the lack of reply, I'm useless!
So basically, the other day it got real bad, throughout all revs, and was cutting out, i was kind of happy in a way because that in my mind confirmed cam angle sensor, right?
So i limped it home, left it a day, tried drivingg again, awful, wouldnt rev in any gear would hesitate and cut out, parked it back up and ordered a cam angle sensor.
New cam angle sensor fitted this afternoon and took it out for a drive, drives so much better.. However.
When warmed up and revving out, Theres a spot at pretty much 5k revs in every gear, almost like its hitting limiter, but if you keep your foot in it, it sorts itself out, feels horrible doing it mind you! Again its hard to describe but its a little loss of pwoer, like a clutch slip in essence but revs drop.
Now this could be timing as i didnt adjust the timing when i put the new CAS in, i lined it up the same as the previous faulty unit. I'm going to borrow a timing gun and set that asap, i don't think thats the issue though as why would timing cause an issue ONLY at 5k revs? Or am i missing something?
Plugs and leads are new, from MX5 parts, so id hazard a guess they are more than adequete and not causing the issue.
Again MAF has been changed with one off of a known good car.
Maybe coil pack but agian i cant see it causing an issue at a specific rev range consistantly, if it was a bit more random in when it did it then maybe?
I have a little LED kit thing to read codes, it read MAF sensor so thats why i changed that, made no difference so i cleared the codes and now none are present even after a drive, so its not throwing a code whatever the issue is.
It now drives pretty much alright 90% of the time its just that hesistant spot at 5k thats throwing me off, its certainly not right but i am miffed as to why.
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dan91
Part of things
Posts: 414
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We had exactly the same symptoms in our 1.8 NA, in that case a new set of leads solved it. As you've done those I'd be looking at coil pack. I've got a spare I'd offer for testing but it's from a '97 and I don't think they're compatible? Vibration wise, did it start with the new tyres? Both our mx5's do it to some extent, although having the wheels rebalanaced by someone who knew what they were doing reduced it a fair bit. Thank you for the offer but yeah mines a 93 so itr wont work unfortunately! Wheels and tyres are brand new, i purchased brand new wheels for it the other week so thats not an issue! As described above its really feeling like a fuel or spark issue to me. When i was a young fool and owned my first ever MK1 i found it it had a cut out at 115mph. When you hit that magical number it cuts out, it almost feels like that? but at 5k revs regardless of gear or speed.
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dan91
Part of things
Posts: 414
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Solved.. shoulda trusted my first hunch. new fuel pump fixed it. mustve just been worn out.
I think the CAS was also playing up so it was a combination of both.
Either way all sorted and running great!
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